Arctic Sea Ice : Forum

Cryosphere => Greenland and Arctic Circle => Topic started by: Espen on March 23, 2013, 09:43:36 PM

Title: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: Espen on March 23, 2013, 09:43:36 PM
Reposted from Arctic Sea Ice Blog;

Jakobshavn Isbræ/Sermeq Kujalleq;

The whole coast north and south of Ilulissat Icefjord, is almost without snowcover and the "ice"fjord is nearly free of ice debris from the glacier, the blue ice color up the "hills" from the coastline, indicating start of melting:

http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2013082.aqua (http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2013082.aqua)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Neven on March 23, 2013, 09:54:58 PM
I've written about a similar event in April 2011 for the ASIB: Flushing out the Fjord (http://neven1.typepad.com/blog/2011/04/flushing-out-the-fjord.html).
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on March 23, 2013, 10:02:16 PM
Neven;

I am aware of that, but this year hardly no snow cover  in the area, and the blue ice indicating melting.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: icebgone on March 23, 2013, 10:05:47 PM
Espen:  SST and air temps have both been way above average.  Has this happened this early before?  I seem to remember a similar melting in April but never March.  If air temps return to long term average beginning late next week I expect a thin film of ice to cover the open water for a short time but glacier melting looks to be large this year irregardless. 
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Neven on March 23, 2013, 10:12:06 PM
Neven;

I am aware of that, but this year hardly no snow cover  in the area, and the blue ice indicating melting.

I didn't mean it as a 'been there, done that', just to link to some extra info. I will possibly blog about this in a week or so. Or two.

Like icebgone says: Temps in Baffin Bay have been anomalously warm almost all winter long, so this part of Greenland will be a thing to watch. I think a repeat of last year is a definite possibility.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on March 23, 2013, 10:31:15 PM
Neven;

I have the feeling this season will be very busy, and there will be a lot of places to watch!? :)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on March 23, 2013, 10:50:12 PM
Espen:   Has this happened this early before?  I seem to remember a similar melting in April but never March. 

IceBgone;

I am not sure about how unusual these March temperatures are, but I went true Modis, and I did not find any images indicating this low level of snow cover in March?
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on March 25, 2013, 05:46:18 PM
Spring cleaning Ilulissat Icefjord;

A big of piece of ice that was resting on the southern shore is on the move:

http://rapidfire.sci.gsfc.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl2_143.A2013084154000-2013084154500.250m.jpg (http://rapidfire.sci.gsfc.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl2_143.A2013084154000-2013084154500.250m.jpg)

Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: CraigsIsland on March 25, 2013, 07:24:27 PM
Google Maps seems to have recent satellite images at: https://maps.google.com/maps?ll=69.166667,-49.833333&spn=0.2,0.2&t=h&q=69.166667,-49.833333 (https://maps.google.com/maps?ll=69.166667,-49.833333&spn=0.2,0.2&t=h&q=69.166667,-49.833333)https://maps.google.com/maps?ll=69.166667,-49.833333&spn=0.2,0.2&t=h&q=69.166667,-49.833333

Bottom left tells me 2013 is when the images were captured. If so- amazing amount of darker densities. I don't know much about this glacier but that looks like a massive outlet into the sea.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: gfwellman on March 25, 2013, 07:32:17 PM
Nah, that looks like last summer.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: ivica on March 25, 2013, 07:54:32 PM
Spring cleaning Ilulissat Icefjord;
A big of piece of ice that was resting on the southern shore is on the move:...

To make that easier for novices I did this image of JIS area using EOSDIS WorldView,
attached:
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: ivica on March 25, 2013, 08:17:43 PM
Map of JIS area, cropped from image given here
https://forum.arctic-sea-ice.net/index.php/topic,143.msg2009.html#msg2009

Map Attached:
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on March 25, 2013, 08:41:59 PM
Thanks ivica!
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on March 25, 2013, 09:06:52 PM
After a few more studies, I found there was some calving activity between day 80 and 84 (today) from the Glacier/Bræ as well.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Laurent on March 25, 2013, 09:28:51 PM
The ice cover is disappearing very fast in front of what remains of the glacier!
Does somebody know if there is some studies about what is going on below the glacier ! How far does the internal sea of Greenland is from the front of Jakobshavn ?
Thanks !
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on March 26, 2013, 12:15:55 PM
A-Team;

May we could ask you to create an animation from Modis, where the calving and cleaning is shown .
It is from day 80 to 84?
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on March 26, 2013, 01:38:27 PM
Thanks to A-Team,

Here is an animation:


http://i1340.photobucket.com/albums/o728/OlTom67/disko4B_zpsd38a386e.gif (http://i1340.photobucket.com/albums/o728/OlTom67/disko4B_zpsd38a386e.gif)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Sigmetnow on March 26, 2013, 03:39:03 PM
Thanks, A-Team!

The animation also shows how quickly the ice is moving down Baffin Bay.

(Hint.)  :D
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: CraigsIsland on March 26, 2013, 05:55:39 PM
Great focal point on one location: disco bay. http://ocean.dmi.dk/arctic/disko.uk.php (http://ocean.dmi.dk/arctic/disko.uk.php)


I haven't had time animate some time periods, but just gazing through the past 1-2 weeks and other years plus other seasons shows a pretty significant change.. Looks like there is a weak shelf too
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: ivica on March 26, 2013, 06:20:13 PM
Could be handy during JIS area melting season,
Weather forecast/statistic for Ilulissat from 2 sources:

     yr.no (http://www.yr.no/place/Greenland/Qaasuitsup/Ilulissat/)   (notice web cam at Hotel Arctic, Ilulissat)

     wunderground.com (http://www.wunderground.com/global/stations/04221.html)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on March 26, 2013, 06:29:05 PM
And we need some animators (gif/png/jpg) because there will be a lot to do, and we cant depend on A-Team alone.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: ivica on March 26, 2013, 06:46:48 PM
Web cam at Hotel Arctic, Ilulissat (http://www.hotelarctic.com/om_hotel_arctic/webcam/),  updates every five minutes:

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.hotelarctic.com%2Ffiles%2Fwebcam%2Fwebcamshot.jpg&hash=531ac17b4db0b493284b2b34cfccb44c)
(click on photo to zoom)

Hotel location can be found on map here (http://www.hotelarctic.com/index.php?pageid=65), search for number 23 (up-middle).
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Sigmetnow on March 26, 2013, 07:57:36 PM
Espen,

I’m willing to make some animations -- but having never done so, I could use some instructions / helpful hints.  I had previously bookmarked the toolson.net/GifAnimation site, so I will try playing with that, and see if things crash miserably....
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on March 26, 2013, 08:51:36 PM
Hi Sigmetnow;

Just try to get used to some of the many gif/png/jpg animators on the net, and of course a nice image editor eg. Photoshop / Gimp etc.
Then you are on the road!
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Laurent on March 26, 2013, 09:14:04 PM
Just watch this video, it may help to make a gif !
How to Create an Animated GIF With GIMP (http://www.youtube.com/watch?v=Qn7ubD-aeeU#ws)
If your are using linux ubuntu/debian it is in the library !
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Sigmetnow on March 27, 2013, 01:05:34 AM
I believe I have GIMP’d successfully!

This should be an animation of the 8 days of Navy Ice Thickness, 3/23 to 3/30/2013, showing their forecast of thinning ice (less black ice, and red is changing to yellow).  I have cropped the images to only show the main ice pack.

Fingers crossed!

Thanks, Laurent!
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Sigmetnow on March 27, 2013, 01:07:13 AM
Happy Dance! ;D ;D ;D
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on March 27, 2013, 08:31:54 AM
Sigmetnow;

Looks good, how about a close up and cropped Modis 250 m of Ilulissat Icefjord from day 79  to 84?
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Laurent on March 27, 2013, 09:14:05 AM
It seems that arctic.io has got something much more powerful !
https://forum.arctic-sea-ice.net/index.php/topic,165.0/topicseen.html
Still in the linux library !
I do not know what does it give ! If you want to try !
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: ivica on March 27, 2013, 09:41:50 AM
More links:
National newspaper Sermitsiaq (http://sermitsiaq.ag/)

One more webcam (http://sermitsiaq.ag/icecam/?lang=EN) at Illulisat Pitoqqeq (http://www.hotelarctic.com/index.php?pageid=65), page contains some videos too.
Unfortunately webcam seems to be down since March, 20.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Sigmetnow on March 27, 2013, 03:37:48 PM
Espen,

Challenge accepted!  Here is March 20 to March 25, 2013.  (Still figuring out how to apply text to an image.)

What’s a good file size/limit for these things?
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on March 27, 2013, 04:24:08 PM
Sigmetnow;

Nice work! If using Photoshop or many other image editors it is pretty easy, use the text tool in each frame, but I dont know what editor you are using?
But I sure we can make use of your talent in "our" documentation department.

Back to the animation, you can easily see a lot ice was moved away in those few days. When we get into the real melting season there will be many more actions both here and other glaciers as well as sea ice movements.

Size is perfect for this event, and the "weight" 5 -600 kb is fine nowadays, but more frames more "weight"!


Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Sigmetnow on March 27, 2013, 05:11:13 PM
Thanks, Espen.
I'm using GIMP for Mac.  I managed to add text -- but now it's saying it won't export as .gif unless I "convert to index color or greyscale first."  I attempted to create an image palette and use one of those values for the text, but still no joy.   Any ideas?

Hmmm... I wonder if "flattening" each text-and-image layer-pair would work?  If so, I need to figure out how to do that for each layer-group.  Will try again later.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on March 27, 2013, 05:17:34 PM
Sigmetnow,

As I recall, the text is in a layer, so you got to flatten the image, I am pretty sure that will work!
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: silkman on March 27, 2013, 06:35:28 PM
Daily animations from Ilulissat isbrae:

http://sermitsiaq.ag/icecam/ (http://sermitsiaq.ag/icecam/)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Phil. on March 27, 2013, 07:06:10 PM
Sigmetnow,

As I recall, the text is in a layer, so you got to flatten the image, I am pretty sure that will work!

Yes you need to flatten with Photoshop.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: TerryM on March 27, 2013, 07:31:44 PM
Daily animations from Ilulissat isbrae:

http://sermitsiaq.ag/icecam/ (http://sermitsiaq.ag/icecam/)


Wonderful link


Thanks
Terry
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Sigmetnow on March 27, 2013, 08:22:59 PM
Espen and Phil,

Found it!  In GIMP, to flatten each text to its image, click on their Group in the Layer window, and in the Layer menu use:  "Merge Layer Group".  The file exported fine after that.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: HeisenIceBerg on March 31, 2013, 07:03:01 AM
There appears to have been a rather large calving event in the past few days.  The piece can first be seen breaking off on Mar 28th; it is roughly triangular with side lengths of approximately 6km each, based on images and the scale from http://earthdata.nasa.gov/labs/worldview/ (http://earthdata.nasa.gov/labs/worldview/).  On Mar 29th and 30th, it can be seen disintegrating, filling much of the bay with the pieces.  Based the way it has disintegrated, I would be surprised if it was just sea ice, but please correct me if it is.

Original images from LANCE-MODIS Terra:
http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2013086.terra.250m (http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2013086.terra.250m)
http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2013087.terra.250m (http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2013087.terra.250m)
http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2013088.terra.250m (http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2013088.terra.250m)
http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2013089.terra.250m (http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2013089.terra.250m)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: gfwellman on March 31, 2013, 08:02:03 AM
You're absolutely right that that was a glacial 'berg, but technically wrong about it being a calving event.  The actual calving front is that double curve just east of the exposed mountains.  All the ice between there and the open water is already calved, but kinda jammed in place.  Probably a lot of grounded bergs anchoring the mass in place.  So the event you gave us such nice pictures of would probably better be described as a large berg getting free of the stuck area.  Probably involved a giant roll-over event that would be almost as exciting as an actual calving anyway.  And then it broke up as you say.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Neven on March 31, 2013, 11:28:47 PM
Nice images, HIB!
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Apocalypse4Real on April 06, 2013, 01:17:10 PM
I noted in another post that Ice Bridge flew the glacier on April 4-5. There are a couple of photos from that day attached.

https://forum.arctic-sea-ice.net/index.php/topic,3.50.html

Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Apocalypse4Real on April 06, 2013, 01:26:07 PM
Here is the IceBridge link to the NASA flight. It includes a video posting.

http://www.nasa.gov/mission_pages/icebridge/index.html (http://www.nasa.gov/mission_pages/icebridge/index.html)

Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Neven on April 06, 2013, 02:35:44 PM
Cool video!  :)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on April 06, 2013, 06:54:33 PM
Only a week or so the Fjord was empty, now it is already full of ice from the Bræ!

http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2013096.terra.250m (http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2013096.terra.250m)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: icebgone on April 07, 2013, 12:48:16 AM
Any plans to measure glacier forward momentum so comparison to prior years is possible?  Also height of melting between years?
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Yuha on April 07, 2013, 09:45:14 AM
The calving front is visibly retreating as seen by comparing terra images from days 94 and 96:

http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2013094.terra.250m (http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2013094.terra.250m)
http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2013096.terra.250m (http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2013096.terra.250m)

It's best to compare even days to even days as there is some strange distortion between odd and even days.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Neven on April 07, 2013, 10:19:38 AM
Wow, well-spotted, Yuha.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on April 07, 2013, 11:02:05 AM
Yaha;

Well spotted, and it must have been a big one, it looks like a 1 km movement!
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: mspelto on April 07, 2013, 01:51:14 PM
 I do not see this 1 km, change, nor do I see the icebergs that should have been generated by such a change.  What am I missing? :-\
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: crandles on April 07, 2013, 02:06:24 PM
http://farm9.staticflickr.com/8249/8627805368_cccb553487_b.jpg (http://farm9.staticflickr.com/8249/8627805368_cccb553487_b.jpg)

Perhaps easier to see loading separate images into two windows and flick between two windows.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on April 07, 2013, 02:07:58 PM
Mauri it is the southern calving front!
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Neven on April 07, 2013, 10:27:04 PM
Arcticio just uploaded this to Youtube:

http://www.youtube.com/watch?v=PYmESTKXOaE# (http://www.youtube.com/watch?v=PYmESTKXOaE#)
A calving event would seem to explain how the fjord is filling up again so fast.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: gfwellman on April 07, 2013, 10:38:52 PM
Flicking between those two images, it looks like the southern calving face is curved a little deeper in the second one.  However, if you watch the film, you see the face seems to pulse a fair bit.  This is presumably either
a) An artifact of the way Modis processes the images or
b) A real measure of the face advancing, then calving, repeat, repeat.

As Jakobshavn is one of the fastest glaciers in Greenland, I would tentatively lean towards (b).  Note that this is not the same thing as permanent retreat of the calving face to a new location.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: OldLeatherneck on April 07, 2013, 11:36:08 PM
A question for the experts: (self-proclaimed or otherwise)

Isn't unusual to have calving events of this magnitude so early in the melt season?
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Sigmetnow on April 08, 2013, 01:38:47 AM
Maybe this will help show the calving.  Here’s April 5 and 7, covering the area in the red box in the still image -- where the glacier meets the Greenland Ice Sheet. The center of the animation shows the semi-circle of the glacier edge has moved downwards -- toward the GIS.

(I’ve omitted April 6 because the land “moves” a little in the image, confusing the issue.)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on April 08, 2013, 06:42:28 AM
Sigmetnow;

Nice thanx!
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Sigmetnow on April 08, 2013, 02:05:53 PM
Two more things....

1) Here’s a scale for the glacier.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Sigmetnow on April 08, 2013, 02:07:35 PM
2)  Notice all the melt happening in this area in just 3 days’ time (April 3 to April 6, 2013).
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Jim Williams on April 08, 2013, 02:38:01 PM
Looks more like a flushing event to me.  Sure would be nice to get some data or recent elevation changes.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: werther on April 08, 2013, 04:08:55 PM
On recent events around Sermeq Kujalleq…
I’ve put 05/07 april MODIS under my CAD file:
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi1036.photobucket.com%2Falbums%2Fa446%2Fhanver1%2FArctic%2520ice%25202013%2FIlulissatday09505042013imagemedium_zpsdc865462.jpg&hash=93492e03f660d8418f2985cde513022d)
It looks like this confirms a recent calving / collapse. It is the small light green area against the blue 2011 calving event line.
The front had returned to this 2011 line during winter, compensating for the June 2012 loss. Now it retreated about  700 m1.

The event could have produced enough debris to fill a large part of the Fjord. The floating ice tongue is several hundreds of meters thick. So 2 km2 could have delivered 1,4 km3, enough for 500 km2 Fjord to get filled again.

I marked a ‘melt zone/bare ice’-line and two remarkable features high up (900 m +SL). One of them is a regular melt lake that usually shows up in May. The melt zone-line nicely shows the thinning basin surrounding the glacier.

There’s enough going on to fear another ravaging summer for the GIS….
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: TerryM on April 08, 2013, 07:21:42 PM
Werther


I'd noticed that in fall of last year the calving front of the more southerly lobe was further south than where it now stands. I'm assuming that over the winter months that portion of the GIS had advanced > 1 km. & it is this advanced tongue that is now calving.


Would this equate to the red line shown on your chart?


Terry
[size=78%] [/size]
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Jim Hunt on April 08, 2013, 07:25:50 PM
A very enlightening picture Werther, thanks.

Is there by any chance a larger version available somewhere? If so would it be OK if I reproduced it on my own blog, or failing that this version?
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: werther on April 08, 2013, 10:50:28 PM
Evening all,

I've taken this detail from the CAD map:

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi1036.photobucket.com%2Falbums%2Fa446%2Fhanver1%2FArctic%2520ice%25202013%2FIlulissatday09508042013detailsmall_zpsb618d18b.jpg&hash=9d5c10511d73c804d6bffb5d00c53817)

It shows the various stages around the calving front during '11, '12 and '13.

This is a very dynamic system, so the continuous retreats and advances are not special in themselves.
The whole picture through the last two years make these movements interesting in their context.
That's why I introduced lots of features in the feeding area higher up on the original map.
Last year the Steffen Research Group reported 5m sinking of the Swiss Camp surface, about 20 km to the NE of the glacier. This process is, IMHO, continuing and accelerating.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi1036.photobucket.com%2Falbums%2Fa446%2Fhanver1%2FArctic%2520ice%25202012%2FSurfacebalanceSwissCamp.jpg&hash=5b2be55d8fc46b203e65e443314791e6)

The calving front is now hovering over the western end of the 1600 m deep trough. As support from the fjord sill is now lacking, velocity and frontal collapses over the trough will become increasingly dynamic.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi1036.photobucket.com%2Falbums%2Fa446%2Fhanver1%2FArctic%2520ice%25202012%2FBedelevationCEJournal23102010.jpg&hash=a0c1cfbbc66cdd55bee1c6598a0f9711)

Terry, does this answer your question?

Jim, I'll try to put a large version on photobucket. All pics on my page are free to use.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: gfwellman on April 09, 2013, 01:00:55 AM
Where did you get that bedrock elevation map?  It's at a much more detailed resolution than
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2F8%2F8b%2FTopographic_map_of_Greenland_bedrock.jpg&hash=5553d5e783013ed3950b0ea81e659268)
If that deep trench connects all the way to the central depression ... well, it's a good thing it's narrow!
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: TerryM on April 09, 2013, 05:13:05 AM
Thanx Werther


My question was answered in far more detail than I'd hoped for!


Terry
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: werther on April 09, 2013, 08:24:56 AM
Hi Jim,
I’ve put a larger version of the map in photobucket:

http://s1036.photobucket.com/user/hanver1/media/Arctic%20ice%202013/Ilulissatday09505042013largemap_zps195977d3.jpg.html (http://s1036.photobucket.com/user/hanver1/media/Arctic%20ice%202013/Ilulissatday09505042013largemap_zps195977d3.jpg.html)

Hope it is useful.

Greg, I took the bedrock map from a Steffen Research Group ppt-presentation, I think 2010. I'll give the link later.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: werther on April 09, 2013, 08:44:38 AM
BTW I don’t think the Sermeq Kujalleq trough pushes through below sea level to the suggested depressions under the ice in central Greenland. The bedrock map suggests a sill about 70 km to the east of the present calving front. That’s more or less where the  summer snow line battle takes place nowadays.

Ocean water can’t get through here, but I imagine the deep trough has free water at it’s bottom. The glacier fills it in almost to the basis in the east, but thins further west. Now that the front has lost contact with the mid-fjord sill and is over the first part of the deep trough, ocean water can mix in. I expect the dynamics to accelerate. One of the aspects could be more pulses of melt water and debris, others continued broad collapses of parts of the floating tongue.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on April 09, 2013, 09:03:25 AM
Werther;

Do we any information about what materials the bedrock/threshold is made of?
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: werther on April 09, 2013, 09:28:42 AM
Morning Espen,
I think I understand what your concern is. If these sills are mainly constituted by boulder clay, they won't be a secure blockade against ocean intrusion.
Maybe we could find geological info on geus.dk?
OTOH, most moraine material has been deposited in Disko Bugt. It shaped up the horseshoe sill at the mouth of the Fjord, where the deep-keeled debris often gets stuck.
The mechanical forces under the glacier being supposedly immense, the inner sills probably consist of very old fold formations. Quite rigid (I hope...).
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on April 09, 2013, 09:33:39 AM
Yes somehow like the glaciers at North East Greenland, were many of them are suffering from starvation, due to rock thresholds.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: CraigsIsland on April 09, 2013, 10:36:05 PM
Comparing MODIS false color composite from a year ago spawns some notable differences:

2012: http://ice-glaces.ec.gc.ca/prods/MODISCOM-F/20120409000000_MODISCOM-F_0006377962.jpg (http://ice-glaces.ec.gc.ca/prods/MODISCOM-F/20120409000000_MODISCOM-F_0006377962.jpg)

2013: http://ice-glaces.ec.gc.ca/prods/MODISCOM-F/20130408000000_MODISCOM-F_0007005320.jpg (http://ice-glaces.ec.gc.ca/prods/MODISCOM-F/20130408000000_MODISCOM-F_0007005320.jpg)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Bernard on April 10, 2013, 12:12:27 AM
The view from the webcam at Hotel Arctic in Ilulissat http://www.hotelarctic.com/files/webcam/webcamshot.jpg (http://www.hotelarctic.com/files/webcam/webcamshot.jpg) is really worth it today.
A week ago the bay was mostly open water except for the impressive bergs run aground in the background. Today it's almost completely covered with a chaos of chunks of all sizes.
Enjoy it now in the calm sunset. Image refreshes every five minutes or so, you can really see all this stuff moving around.
Position of the hotel (and webcam) http://www.geonames.org/8520900 (http://www.geonames.org/8520900)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: anonymous on April 10, 2013, 10:40:44 AM
Hi all, you may enjoy the split zoom at arctic.io to compare day to day and year to year changes. Currently there are 270 full Arctic mosaics (250m per pixel) available and a bot adds the latest every day. The mosaic started some when in April 2008, if you need a date not processed so far let me know, I'll put it into the queue and next day or so you'll have it. If some one is proficient in Google Spreadsheet, I'll give you write access and then it takes only a few hours.

The bold days in the calendar applet indicate available zooms. Sometimes the machinery is dreaming and returns no dates to the interface, just press F5 then to reload and wake it up. Use your mousewheel to zoom and dragging to change the view or the buttons found in lower right corner. F11 to go distraction free and fullscreen.

http://www.arctic.io/split-zoom/2012-04-13;2013-04-09/0.313;0.645;11/Jacobshavn-Glacier (http://www.arctic.io/split-zoom/2012-04-13;2013-04-09/0.313;0.645;11/Jacobshavn-Glacier)

(https://dl.dropbox.com/u/354885/Arctic/asinet/split-zoom-jacobshavn.jpg) (http://www.arctic.io/split-zoom/2012-04-13;2013-04-09/0.313;0.645;11/Jacobshavn-Glacier)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Artful Dodger on April 10, 2013, 11:21:48 AM
The view from the webcam at Hotel Arctic in Ilulissat is really worth it today.
Hi bernard,

Welcome to the Forum! Indeed, the current picture is a keeper, so I've added it as an attachment to preserve it here.

Thanks, and once again welcome!
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Artful Dodger on April 10, 2013, 11:23:03 AM
The view from the webcam at Hotel Arctic in Ilulissat http://www.hotelarctic.com/files/webcam/webcamshot.jpg (http://www.hotelarctic.com/files/webcam/webcamshot.jpg) is really worth it today.
A week ago the bay was mostly open water except for the impressive bergs run aground in the background. Today it's almost completely covered with a chaos of chunks of all sizes.
Enjoy it now in the calm sunset. Image refreshes every five minutes or so, you can really see all this stuff moving around.
Position of the hotel (and webcam) http://www.geonames.org/8520900 (http://www.geonames.org/8520900)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Bernard on April 10, 2013, 01:48:48 PM
@Artful Dodger thanks for the welcome!

The webcam image was already inserted higher in the thread, but better twice than none :)

For the record I'm not related whatsoever with Hotel Arctic, and (unfortunately) never been to Ilulissat (although I keep dreaming of it of course). I observe all this safely and remotely from my France Southern Alps, where ice is also steadily receeding. Last winter was long here with a lot of snow, though, and the spring quite late, wet and fresh ... which might be good news for my "neighbours" such as http://en.wikipedia.org/wiki/Glacier_Blanc. (http://en.wikipedia.org/wiki/Glacier_Blanc.)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Jim Hunt on April 10, 2013, 09:42:35 PM
Hi Werther,

I’ve put a larger version of the map in photobucket. Hope it is useful.

Thanks very much, and it will be very useful. I'd actually started writing an article on the topic, intending to include your image, when the following news broke here in the UK:

http://econnexus.org/met-office-admit-our-climate-is-being-disrupted-by-the-warming-of-the-arctic/ (http://econnexus.org/met-office-admit-our-climate-is-being-disrupted-by-the-warming-of-the-arctic/)

Greenland even got a mention. According to Julia Slingo, chief scientist at the UK's Met Office:

We know there are links, for example, in the ocean temperatures that run down the west coast of Greenland which are very warm at the moment. Exceptionally warm!

Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Apocalypse4Real on April 11, 2013, 04:10:51 AM
Jim, good to see Slingo's change of perspective.

Hunter's team flew Jakobshavn Glacier today. The following photos and Lidar image - all from Ice Bridge.

From April 4  to April 10 2013  - 200 meters were cut from the calving front.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Jim Hunt on April 11, 2013, 10:42:33 AM
After a bit of a delay, here's what I've finally come up with:

http://econnexus.org/nasa-chasing-calving-ice-in-western-greenland/ (http://econnexus.org/nasa-chasing-calving-ice-in-western-greenland/)

I hope that's OK with all concerned. Please let me know ASAP if not!
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Neven on April 11, 2013, 12:18:12 PM
Nice post, Jim. I might do one too in coming days.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Artful Dodger on April 11, 2013, 12:33:41 PM
@Artful Dodger thanks for the welcome!

For the record I'm not related whatsoever with Hotel Arctic, and (unfortunately) never been to Ilulissat

Salut, bernard!

Je suis triste pour la fonte du Groenland et les Hautes-Alpes (https://forum.arctic-sea-ice.net/index.php/topic,216.0.html). Au revoir le climat tempéré.  :'(
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Hunter on April 11, 2013, 05:11:48 PM
Wow, you guys are fast! 

That just shows hows it calved in just a few days.

Crew is over the Geikie peninsula today. 

She does a better job posting pics than I do!
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on April 11, 2013, 05:37:08 PM
Hunter;

Yes it was noticed the same day it happened by "Yuha", the calving though looked mush bigger on the Modis Images, than the 200 meter your measured?
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Hunter on April 11, 2013, 06:24:18 PM
It is possible we did not fly over largest area of calving.  I wouldn't know without digging through all the photos and flightlines. 

Here is the overlay of flightlines from yesterday just fyi.

EDIT: the background image is very old sat imagery from the area
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on April 11, 2013, 06:48:12 PM
Hunter;

I have difficulties placing that image you just supplied, but if you have any images around where the calving line is it would be helpful, I am especially confused by the ice free (open water) areas the image contains.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: ivica on April 11, 2013, 07:15:42 PM
Espen,
Seems that the overlay of flightlines from yesterday, given by Hunter, is put over image present in GoogleEarth.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Hunter on April 11, 2013, 07:18:46 PM
Yes its generic google earth sat view of Jakobshavn. 

Sorry I don't have anything processed that is up to date from yesterday.  Actually running some of it now.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on April 11, 2013, 07:25:53 PM
Hunter and Ivica;

I realized it was a overlay from Google, but even after entering Google maps I could not find the location?

But I and I guess many others around here would love to have some more info/images to study, and it would interesting to know how big the calving actually was?
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: gfwellman on April 11, 2013, 07:28:54 PM
Yes its generic google earth sat view of Jakobshavn.
Which appears to be really old, like 5+ years old based on the position of the calving front.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: ivica on April 11, 2013, 07:38:05 PM
Espen,
Aha, location of Geikie Peninsula is the question?

http://glacierchange.wordpress.com/tag/geikie-peninsula-greenland-glacier-retreat/ (http://glacierchange.wordpress.com/tag/geikie-peninsula-greenland-glacier-retreat/)

or, do I answer wrong 'question', again?  ???
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Laurent on April 11, 2013, 08:03:23 PM
It is easier to understand like that !?
There is around 20 km between the two calving front !
The latest is from today 11th of april 2013.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Bernard on April 11, 2013, 08:38:44 PM
@Lodger
Je suis triste pour la fonte du Groenland et les Hautes-Alpes.
I tried today to figure the size of the last week calving in Jakobshavn Isbræ by comparing its volume to the Hautes-Alpes Glacier Blanc, which we still find here very impressive despite its spectacular recent retreat. According to http://en.wikipedia.org/wiki/Glacier_Blanc (http://en.wikipedia.org/wiki/Glacier_Blanc) the area is a little more than 5 km² for a maximum depth of 250m. Which gives a maximal volume of a little more than 1 km3 of ice.
For the above said calving event, based on a conservative estimation on a 200m retreat on a front of about 5 km, and a thickness of several hundreds of meters, say 500m, we have at least 0.5 km3 gone to the sea. Which means about half the volume of the Glacier Blanc ...
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on April 11, 2013, 08:49:20 PM
Bernard;

Yes there is plenty of ice for a few Gin Fizz!
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Laurent on April 11, 2013, 10:29:14 PM
some news of the white glacier :
http://warpinghistory.blogspot.fr/2012/07/disappearing-acts-life-and-death-of.html (http://warpinghistory.blogspot.fr/2012/07/disappearing-acts-life-and-death-of.html)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: werther on April 12, 2013, 12:27:38 AM
To have a better grasp at what the Icebridge swaths resemble, I rescaled them as good as I could with the coordinates on the pic. Then I introduced it on my CAD frame:

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi1036.photobucket.com%2Falbums%2Fa446%2Fhanver1%2FArctic%2520ice%25202013%2FIlulissatday09511042013Icebridgesmall_zps834e6b9b.jpg&hash=bc83ccaa33007a5deae31514a9a82b11)

The swaths are 250 m wide, so these three cover just a part of the calving front. Depending on the exact location, my opinion is that MODIS indicates a larger distance a bit to the south (left, here).
The most striking part is that with the means we have, we can follow what’s going on at a daily basis when clouds allow…!
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Artful Dodger on April 12, 2013, 10:37:24 AM
Comment for bernard moved to new topic:

3D visualization of Hautes-Alpes / Glacier Blanc with Google Earth and MODIS (https://forum.arctic-sea-ice.net/index.php/topic,216.0.html)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: ivica on April 12, 2013, 10:52:14 AM
Hi, guys.
Do you have a feeling that we are hijacking Espen's thread a bit? ;-)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Artful Dodger on April 12, 2013, 10:59:21 AM
Hi, guys.
Do you have a feeling that we are hijacking Espen's thread a bit? ;-)

Good point, ivica. Will move my Hautes-Alpes comments to an appropriate thread (https://forum.arctic-sea-ice.net/index.php/topic,216.0.html).  ::)

EDIT: Done.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Yuha on April 14, 2013, 11:21:34 PM
The calving continues.
Both calving fronts lose a corner between April 12 and April 14.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: werther on April 15, 2013, 12:05:38 AM
Thanks Yuha!
And confirmed; about 1,2 km2 on the NE side of the main calving front.
Still more than 9 km2 to go to get beyond July '12.
Making exceptional progress this early in spring!
The front is close to losing contact with the sill again. A lot might go in a bang soon (June?).
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: werther on April 15, 2013, 12:07:51 PM
Weather? Sure, but in concert with extreme negative anomaly.
This is daytime max at Kangerlussuaq. The warm event lasted from 1 to 11 April:
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi1036.photobucket.com%2Falbums%2Fa446%2Fhanver1%2FArctic%2520ice%25202013%2FTempKangerlussuaqapril2013_zps92055628.jpg&hash=e27f26b7680247320a077b4a933d3a51)
For this decade nothing alike to be found back to 2006.
MODIS shows snow cover most hit near the icesheet boundary. On the coast the effect was smaller.
It is not of ‘climate-consequence’… a minor, regional event. But if this is capable of producing about 2 km3 calving on Sermeq Kujalleq this early in the season, lets hope June/July doesn’t show comparable circumstances.
BTW weather is in for a decade of freeze over there now. Circulation changed…
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: werther on April 15, 2013, 01:18:26 PM
"...extreme negative anomaly...", confusing.... I meant ...extreme negative AO anomaly... But I guess you would have noticed.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Neven on April 15, 2013, 01:32:38 PM
BTW weather is in for a decade of freeze over there now. Circulation changed…

You mean because of the Cold Pole that shifted over Greenland?
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: werther on April 15, 2013, 02:15:05 PM
You mean because of the Cold Pole that shifted over Greenland?

Well, I hope no Turkey with that adjective...

Neven, since I gather 10-day NCEP/NCAR summaries, I call these decades. I guess that's confusing...I don't mean years.

No, ECMWF shows mostly N/NE winds over Central and West Greenland up to 25/4. No new snow that could help albedo in the coming months. But also a stop to whatever surface melt happened between 1-11 April.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Neven on April 15, 2013, 02:46:22 PM
Neven, since I gather 10-day NCEP/NCAR summaries, I call these decades. I guess that's confusing...I don't mean years.

Right, got it!

BTW, it's because of threads like this one that I'm so happy with the forum!
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Yuha on April 24, 2013, 01:27:54 AM
And confirmed; about 1,2 km2 on the NE side of the main calving front.
Still more than 9 km2 to go to get beyond July '12.

Another 1 or 2 km2 gone, I think.
Compare April 14 and 23.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: CraigsIsland on April 24, 2013, 02:32:00 AM
Money is on calving past July '12
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Anne on April 27, 2013, 11:15:08 AM
A lot of ice in the bay this morning
http://www.hotelarctic.com/om_hotel_arctic/webcam/ (http://www.hotelarctic.com/om_hotel_arctic/webcam/)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on April 30, 2013, 08:19:32 PM
A 1 mm movement today, southern front!
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: CraigsIsland on April 30, 2013, 09:59:30 PM
A 1 mm movement today, southern front!


One millimeter or one kilometer?
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on April 30, 2013, 10:02:50 PM
1 mm represents 1 km at Modis 250M ;)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: CraigsIsland on May 01, 2013, 03:16:44 AM
1 mm represents 1 km at Modis 250M ;)

ah - Thank you!  ;D

that's a large movement. And its about to be May.  :o
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on May 03, 2013, 07:34:41 PM
When the calving is over this will be the result:

Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: sidd on May 04, 2013, 07:49:08 AM
Please, where did you get this old map ? I showed this to a friend, and she immediately began to trace the place names, and wanted to know the source so she could do research. Any leads would be greatly appreciated.

Thanx,

sidd
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on May 04, 2013, 10:52:20 AM
Sidd;

It is from a place names report of Anthony Higgins: Exploration history and place names of northern East Greenland. Bulletin 21 2012.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: sidd on May 05, 2013, 12:17:28 AM
Thanx so much.

sidd
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on May 05, 2013, 12:26:46 AM
sidd;

But be aware some of the names may be be too political Denmark vs Norway, and not be valid now!
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: ivica on May 09, 2013, 12:46:45 PM
What happened to Web cam at Hotel Arctic (http://www.hotelarctic.com/om_hotel_arctic/webcam/)?
A raven with digestive problem?  ;D
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: theoldinsane on May 09, 2013, 06:02:24 PM
What happened to Web cam at Hotel Arctic?
A raven with digestive problem? 

It was a meteroite

http://theoldinsane.blogspot.se/2013/05/fv9-breaking-news-meteroitnedslag-i.html (http://theoldinsane.blogspot.se/2013/05/fv9-breaking-news-meteroitnedslag-i.html)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: birthmark on May 09, 2013, 06:45:51 PM
Maybe, but the doom predicted on that webpage is far-fetched. Frankly,  I think it's a hoax.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: ivica on May 09, 2013, 07:26:24 PM
Folks, I saw those "trails" yesterday, around 6 PM UTC.
The "trails" were on webcam photos this morning too, hence my post.
A raven is still my suspect  ;D

Edit: 6 PM, not 6 AM, eh.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Laurent on May 29, 2013, 11:14:04 AM
At that pace the ice sheet wil join the front of the glacier very soon !
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on June 08, 2013, 08:20:16 PM
The Icefjord  is getting emptied:

http://rapidfire.sci.gsfc.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl2_143.A2013159152000-2013159152500.250m.jpg (http://rapidfire.sci.gsfc.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl2_143.A2013159152000-2013159152500.250m.jpg)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: CraigsIsland on June 10, 2013, 02:16:47 AM
Good eyes out there

should be a remarkable melt season in Greenland this year; already shaping up to be that way.

http://nsidc.org/greenland-today/ (http://nsidc.org/greenland-today/)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: CraigsIsland on June 11, 2013, 09:14:15 PM
I was wondering if I'm seeing this image right - are those melt pond features up and down near the edge of the sheet?

http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2013162.terra.250m (http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2013162.terra.250m)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Laurent on June 11, 2013, 09:45:49 PM
I do think it is !
There was more last year around the Jakobson glacier !
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Yuha on June 13, 2013, 06:57:29 PM
Disko Bay surface waters have warmed up dramatically in the last few days:

http://ocean.dmi.dk/arctic/images/MODIS/Disko/201306050000.MERT.png (http://ocean.dmi.dk/arctic/images/MODIS/Disko/201306050000.MERT.png)
http://ocean.dmi.dk/arctic/images/MODIS/Disko/201306130000.MERT.png (http://ocean.dmi.dk/arctic/images/MODIS/Disko/201306130000.MERT.png)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: CraigsIsland on June 13, 2013, 07:50:29 PM
Forecast temperatures for Ilulisat for 10C+ (50F) for Saturday through Monday:

http://www.dmi.dk/dmi/en/byvejr_gl?by=4221 (http://www.dmi.dk/dmi/en/byvejr_gl?by=4221)

also SST anamolies for Disko Bay
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Focean.dmi.dk%2Farctic%2Fimages%2FMODIS%2FDisko%2F201306130000.MERR.png&hash=ed68fa10e2a168155c0260ef7bdbb4f6)

and SST for Disko Bay (https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Focean.dmi.dk%2Farctic%2Fimages%2FMODIS%2FDisko%2F201306130000.MERT.png&hash=fab761f33b2a81edcec368eb0675bf87)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Laurent on June 16, 2013, 10:53:15 PM
Some move between the day 157 and 167 (juin 16 2013)
More melt ponds appearing very quickly !
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: DaddyBFree on July 13, 2013, 04:20:14 PM
And the calving continues...(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.screencast.com%2Ft%2F8utijiH9J38M&hash=a69ce6084581325578c2f011753e2627)
http://www.screencast.com/t/8utijiH9J38M (http://www.screencast.com/t/8utijiH9J38M)
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: KactionJ on July 15, 2013, 09:28:09 PM
I do not see this 1 km, change, nor do I see the icebergs that should have been generated by such a change.  What am I missing? :-\

Make sure you are looking at the calving front (the butt shape at the start of the fjord).  You won't see the icebergs as the entire fjord is pretty much full of them right now. 

The look at the bottom half circle of the calving front.  It is much more elongated in the later picture.  That retreat is what they are talking about.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on July 16, 2013, 10:10:47 AM
I also noticed the other day, a change in the southern calving front.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Laurent on July 16, 2013, 01:41:25 PM
Between day 161 and yesterday 196
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Yuha on July 19, 2013, 10:39:43 PM
Another big calving (compare days 196 and 200).

The calving front has now retreated beyond last year's position, I think.

Werther, does your CAD agree?
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Espen on July 20, 2013, 09:29:42 AM
Comparing Sep. 2012 and July 19 2013, I believe we are back at square 1?
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: Laurent on July 24, 2013, 11:03:12 AM
Between 196 and 204

Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: ivica on July 24, 2013, 11:24:32 AM
Laurent, thanks, your animation also makes apparent how some melt ponds increases area/volume.
Title: Re: Jakobshavn Isbræ/Sermeq Kujalleq/Ilulissat Icefjord
Post by: werther on July 24, 2013, 01:45:32 PM
Another big calving (compare days 196 and 200).

The calving front has now retreated beyond last year's position, I think.

Werther, does your CAD agree?

Hi Yuha,

Thanks for waking me up, likewise credit to Laurent and Espen et al.
haven't been following this close. Ongoing impression that this year is not an exceptional melt year for Greenland. At least, the SW coast. Might be different in the NE.

But I've given MODIS r02c02 some glances. Think you're right; calving is on it's way to get past 2012. Still, I think it is a regular calving and has little connection with melt patterns in the ablation zone. The landscape around 1100-1200 m seems quiet this period.

Later in the season I'll give it a shot on CAD, when the sea ice chase has passed its yearly hype moment.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Sigmetnow on July 27, 2013, 04:47:20 PM
Rolling Stone has a great article on Jason Box -- will also post this here, since a good chunk of the article concerns his start of the Dark Snow project on Jakobshavn glacier.

http://www.rollingstone.com/greenland-melting#ixzz2aFyKZV2F (http://www.rollingstone.com/greenland-melting#ixzz2aFyKZV2F)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Lennart van der Linde on August 01, 2013, 12:00:48 PM
Upthread the question came up if the glacier trough extends all the way inland into the interior of the ice sheet. This recent paper by Bamber et al gives sort of an answer:
http://www.the-cryosphere.net/7/499/2013/tc-7-499-2013.pdf (http://www.the-cryosphere.net/7/499/2013/tc-7-499-2013.pdf)

On pp.506-507 they say:
“In the Jakobshavn catchment, there is a dendritic channel system extending for about 325 km from the current grounding line into the interior almost as far as the ice divide. It seems likely that this is a palaeo-fluvial feature that predates ice cover in Greenland and may be important for subglacial water routing… The width of the trough is 3–4 km and the region of fastest flow coincides fairly well with the location of the deepest ice. The trough is 1366m below sea level at its deepest point compared to a maximum depth over the entire region of 556m below sea level in the older dataset. The main trough of Jakobshavn Isbrae is not continuous in the new dataset, disappearing around 100 km and reappearing at about 140 km. This does not imply that the trough is discontinuous, but only that there are insufficient data to confirm the trough’s presence or otherwise in this region.”

So maybe warming ocean water could in time eats it way into the interior bottom of the ice sheet?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Laurent on August 03, 2013, 10:01:02 PM
Few changes (apparently, lot of ice going in holyday to the sea) on the front of the Glacier but a lot of move inland. (You have to click on the picture).
Difference between day 204 and 215 !
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 28, 2013, 01:09:24 PM
A prelim of Jakobshavn:

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Laurent on August 30, 2013, 02:41:43 PM
Bedrock map of Jakobshavn :
I did put an arrow where I guess the front of the glacier is, or is it where the sea is viewed !?

You can click on the image to enlarge it !
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 30, 2013, 02:49:26 PM
Laurent where do you get those area bedrock maps from, are they available for all of Greenland Eg North Greenland and North East Greenland?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Laurent on August 30, 2013, 02:54:18 PM
I did put the links here ?
https://forum.arctic-sea-ice.net/index.php/topic,270.msg14150.html#msg14150
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 30, 2013, 02:58:04 PM
I did put the links here ?
https://forum.arctic-sea-ice.net/index.php/topic,270.msg14150.html#msg14150

Yes I know, but I dont see that Jakobshavn part there?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Laurent on August 30, 2013, 04:57:46 PM
This is the link :
http://svs.gsfc.nasa.gov/vis/a000000/a004000/a004097/ (http://svs.gsfc.nasa.gov/vis/a000000/a004000/a004097/)
The image with jakobshavn is after this image, I took the highest resolution and did a crop on it + jpg high compression :
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 30, 2013, 05:00:17 PM
This is the link :
http://svs.gsfc.nasa.gov/vis/a000000/a004000/a004097/ (http://svs.gsfc.nasa.gov/vis/a000000/a004000/a004097/)
The image with jakobshavn is after this image, I took the highest resolution and did a crop on it + jpg high compression :

Laurent, I see, that wont help me though ???
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Laurent on August 30, 2013, 05:04:28 PM
Why don't you ask them !? May be they would gladly give you some other views ? Even better a 3D map of greenland high resolution ?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on October 03, 2013, 02:11:59 PM
An update on retreat, as you can see from this animation spanning from Sept 2011 to Sept 2013, the retreat of Jakobshavn continued this year, an estimated 1 km from 2012 to 2013 alone:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Lennart van der Linde on October 03, 2013, 03:47:04 PM
So that makes the retreat about 19 km over the past 12 years. About 1.5 km/yr on average.

How long can this continue? Do we expect acceleration or slow-down?

I haven't checked IPCC AR5 on this yet, but maybe other people here know?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Lennart van der Linde on October 03, 2013, 04:13:18 PM
A start is this article from 2010:
http://www.cejournal.net/?p=4225 (http://www.cejournal.net/?p=4225)

Because the fjord enters deep into the interior, the glacier is vulnerable to continuing and faster retreat. Maybe the only reason that this will be kept somewhat in check is that the fjord is relatively small, as someone in the comments on the article mentions, referring to the paper by Pfeffer et al 2008.

The map in the article (from a presentation by Konrad Steffen) may be outdated, since Bamber et al published a new map earlier this year (see their figure 3a):
http://www.the-cryosphere.net/7/499/2013/tc-7-499-2013.pdf (http://www.the-cryosphere.net/7/499/2013/tc-7-499-2013.pdf)

The main difference seems to be that the fjord of Humboldt glacier may not extent into the interior as far as is suggested by the earlier map.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on October 03, 2013, 04:33:27 PM
So that makes the retreat about 19 km over the past 12 years. About 1.5 km/yr on average.

How long can this continue? Do we expect acceleration or slow-down?

I haven't checked IPCC AR5 on this yet, but maybe other people here know?

The southern part (the animated) of Jakobshavn seems to be most busy.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on October 23, 2013, 10:25:36 AM
Jacobshavn retreated 3 km in 2013.
Jakobshavn southern calving front retreated ~ 3 km this season, as can be seen in this animation.
And very little action is seen at the northern front.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Neven on October 23, 2013, 11:03:21 AM
Wow, that's quite a bit of retreat, I'd say. Thanks for keeping an eye on this, Espen.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on October 26, 2013, 09:45:07 AM
New updated front map 1851 - 2013:

Please click on image to enlarge for better details!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on October 26, 2013, 03:55:53 PM
Espen....

Is this one of the fastest glaciers in Greenland?

Other than general trends in AGW, what could be contributing to this rapid increase in speed and retreat?

We know that the southern third of Greenland is suffering from unprecedented surface melt with much of that melt flowing via moulins to the bedrock below with some of it reducing friction between the glacier and the bedrock. This could explain it I suppose. I've read things that suggest most of this melt water does not escape to the sea but instead collects under the ice sheet (warming it, softening it etc.) Given the topography of Greenland, (link below) it seems that the Ilulissat Icefjord is very nearly a water path to these inland lakes. Could this be a factor? Could the melt water from surface melt be collecting in these inland lakes? Could they be raising the level of the water? With  the  pressure of the ice above, could this be driving pulses of melt water into this type of fjord?

http://upload.wikimedia.org/wikipedia/commons/8/8b/Topographic_map_of_Greenland_bedrock.jpg (http://upload.wikimedia.org/wikipedia/commons/8/8b/Topographic_map_of_Greenland_bedrock.jpg)

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on October 27, 2013, 08:56:57 PM
We have seen some big movements at Jakobshavn over a number of years now, but what about the future?
Will the calving front move further inland?
My guess is yes, and that prediction is based on what we have already learned / seen.
To prove this I use a Landsat image from October 1972, where there ice-movement lines are clearly seen, it more or less resembles a superhighway system from above, with one highway heading north with little potential for much further extension, but the southern branch got the potential moving much further in both a southern and a south-eastern direction.
It is interesting to see  "Cap Ice" was already "designed" back in 1972, what is behind this resistance may be hidden rocks / island.
What are your thoughts?

Please click on image for enlargement and better details!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on October 28, 2013, 10:59:34 AM
I have have just updated the retreat prediction map, for Jakobshavn.

Please click on image to enlarge and for better details!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: DaddyBFree on October 29, 2013, 06:29:34 PM
Great updates Espen!
The next 40 years have been set up to be quite interesting.  Reminds me of the "Chinese curse" "May you live in interesting times," popularized/modernized by Terry Pratchett and others.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on October 29, 2013, 08:57:38 PM
Thanx DaddyBFree,

Yes it is interesting, that a first generation Landsat image from 1972 (Landsat program was launched in 1972), and almost within few meters tells where Jakobshavn is planning to retreat over the next 41 years (2013), so based on that I have enough confidence to predict where Jakobshavn is heading over the next many years, with a little correction, seen in GREY area around the Green area on the above image, that is where new but not so strong movement lines are found in more recent sat-images.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: ggelsrinc on October 30, 2013, 06:14:14 AM
Bedrock map of Jakobshavn :
I did put an arrow where I guess the front of the glacier is, or is it where the sea is viewed !?

You can click on the image to enlarge it !

Laurent, that image you posted speaks volumes about the past geologic history of that area. The main direction of eventual glacial retreat is written in stone and not surface details, it will eventually follow that easily recognized path of least resistance, it only takes time.

I can see all kinds of past details of other places represented in that image. Will you carefully explain in detail, beyond what you already did, how such exaggerated topographical images can be easily obtained?

In my mind's eye, your image shows me details of past glaciation and retreat; notice the peaks lined up on the right! That carved out image on the left is very typical of multiple coastal glacial feeds, IMO.

I can see major problems for the people living in that area of mining interests around anywhere mother nature was the bulldozer for a season for over millions of years. It's only logical that heavy metals will collect in areas where forces remove lighter materials. This is a tangent that I don't want to discuss on this thread, but I think such areas as Greenland, like the Arctic and Antarctic should be placed under the jurisdiction of all our world's nations and people.

Focusing back on Jakobshavn Isbræ, I don't think there is any doubt the "glacier" (part of the GIS ice sheet flow) will continue it's present path, but will eventually follow that line marked in stone shown on your posted image. The ice has only temporarily met a line of resistance and parted because that is how calving is presently fed with material. I see Jakobshavn Isbræ removing the material from the north and heading east, even before the material from the south is removed.

I don't consider flows from ice sheets, glaciers in the normal sense.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on October 30, 2013, 08:01:56 AM
I'm looking fonrward to Sentinel-1a SAR-satellite that will be launched in 2014 - with it monthly tracking of the calving fronts in Greenland will be possible in all weather conditions + the data will available to anyone.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on October 30, 2013, 10:26:44 AM
Thanks to NASA and Laurent.
Here is a modified bedrock image from Jakobshavn.

Please click on image to enlarge and for better details!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on November 19, 2013, 07:08:27 AM
here is Joughin sounding the alarm,free access


The Cryosphere Discuss., 7, 5461–5473, 2013
www.the-cryosphere-discuss.net/7/5461/2013/ (http://www.the-cryosphere-discuss.net/7/5461/2013/)
doi:10.5194/tcd-7-5461-2013

From the abstract:

" At a point a few kilometres inland from the terminus, the mean annual speed for 2012 is nearly three times as large as that in the mid 1990s, while the peak summer speeds are more than a factor of 4 greater. These speeds were achieved as the glacier terminus retreated to the bottom of an overdeepened basin with a depth of ∼ 1300 m below sea level. "

But scarier, from the paper, suggests that Pffefer's  upper bound estimates from 2008 are already here:

"If, as the glacier recedes up the trough, it is able to maintain the peak speeds year round, then a sustained speedup by a factor of 4 of 5 is conceivable based on recent behavior, which is about half of the ad hoc tenfold upper limit on speed proposed by Pfeffer et al. (2008). Nevertheless, these speeds would occur in a trough roughly twice as deep as prior to the speedup. Hence, a tenfold increase in ice flux may be possible for Jakobshavn Isbræ if the trough does not narrow substantially with distance upstream. Equivalently, while the increase in terminus speed and the glaciers overall maximum speed may remain under a factor of five, as the terminus retreats farther inland where the speeds now are comparatively slow, the relative speedup is much greater (e.g., if the terminus retreated to M26 with a speed of 16 000 m yr−1 , this would represent a twelve-fold speedup). Thinning by hundreds of meters to a terminus near flotation, however, yields something closer to a ten-fold flux increase."

sidd
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Lennart van der Linde on November 19, 2013, 04:18:58 PM
sidd, as I replied on RealClimate:

Thanks for the reference to the draft paper by Joughin & Smith. I'm trying to understand how exactly this compares to Pfeffer et al 2008:
http://www3.geosc.psu.edu/~jfk4/Geosci_500/Discussion%20papers/Last%20week%202/Science%202008%20Pfeffer.pdf (http://www3.geosc.psu.edu/~jfk4/Geosci_500/Discussion%20papers/Last%20week%202/Science%202008%20Pfeffer.pdf)

Pfeffer et al say:
"Average (present day to 2100) outlet glacier speeds required to meet 2- and 5-m SLR targets range from 26.8 km/year to 125 km/year, depending on the scenario considered [table 2 and supporting online material (SOM)]. These velocities must be achieved immediately on all outlets considered and held at that level until 2100."

So about an average speed of 27 km/yr is needed from now until 2100 for all GIS outlet glaciers, in combination with a 10x higher surface melt rate, to get a GIS-contribution to global SLR of 2 meters this century.

It seems Joughin & Smith argue in their last sentence this seems unlikely to be possible. However, Pfeffer et al also show a scenario of 2 meter total SLR by 2100 in which GIS contributes about 54 cm. In this scenario:
"Greenland SMB was accelerated at present-day rates of change, but dynamic discharge was calculated by accelerating outlet glacier velocities by an order of magnitude in the first decade."

This implies that over the 21st century all GIS outlet glaciers should reach an average speed of about 12 km/yr in this scenario, if I understand correctly. Marine outlet glaciers could then reach a higher average speed and land outlet glaciers a lower average, but it's not obvious from Joughin & Smith that such average speeds could be sustained for nine decades, I think.

Jim Hansen for one seems to think Pfeffer et al may under-estimate in particular the potential AIS contribution, so all this is not to say that 2 meter of total SLR by 2100 would be impossible.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Sigmetnow on February 04, 2014, 01:12:18 AM
Glacier that sunk the Titanic speeds toward disaster!   :D

http://www.egu.eu/news/100/greenlands-fastest-glacier-reaches-record-speeds/ (http://www.egu.eu/news/100/greenlands-fastest-glacier-reaches-record-speeds/)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: wili on February 04, 2014, 01:52:39 AM
Good article: "We are now seeing summer speeds more than 4 times what they were in the 1990s on a glacier which at that time was believed to be one of the fastest, if not the fastest, glacier in Greenland..."

"In the summer of 2012 the glacier reached a record speed of more than 17 kilometres per year, or over 46 metres per day. These flow rates are unprecedented: they appear to be the fastest ever recorded for any glacier..."

"We know that from 2000 to 2010 this glacier alone increased sea level by about 1 mm. With the additional speed it likely will contribute a bit more than this over the next decade"

"The researchers believe Jakobshavn Isbræ is in an unstable state, meaning it will continue to retreat further inland in the future."
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on February 04, 2014, 01:57:16 AM
looks like the final version of the Joughin paper i posted above.I have issues with this statement


"While the high spot above the basin may slow flow, the terminus would still be grounded on a bed at least 900 m below sea level, likely yielding speeds well above balance that would maintain strong, although potentially diminished, thinning"

Bassis(2013) DOI: 10.1038/NGEO1887 points out that glacier is unconditionally unstable at approx 1000m against calving

Fig 1b)

htto://membrane.com/sidd/bassis-1b.png
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on February 04, 2014, 07:31:45 AM
Phillips(2013)
doi:10.1002/jgrf.20079

is interesting. Sermeq Avannarleq is close to this region, and the authors tie expansion of melt zone to warming of ice by meltwater that increases leads to flow parameter in Glen's law. In short, once you see surface melt, ice underneath is flowing faster.

"The corresponding increase in the temperature-dependent flow law parameter (A) is a factor of 3.2 and 1.8, respectively. This doubling or tripling of the flow law parameter can have significant thermomechanical consequences on ice velocity."

The quote is in reference to an idealized test case, but they do see that:

(CHW is cryohydrologic warming)

"The base case CHW simulations reproduce the observed increase in inland ice velocity between 2001 and 2007 reasonably well. The no CHW and surface CHW simulations significantly underestimate observed ice surface velocities in both epochs. The higher ice velocities in the base case CHW simulations are attributable to both decreased basal ice viscosities associated with increased basal ice temperatures and an increase in the extent of basal sliding permitted by temperate bed conditions. Only the temperate bed extent predicted by the base case CHW simulation is consistent with independent observations of basal sliding. Based on our sensitivity analysis of CHW, we evaluate alternative explanations for an increase in inland ice velocity and suggest CHW is the most
plausible mechanism."

now consider that equilibrium line altitude and melt zone rose above saddle at 67 N year an a half ago.

sidd
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Lennart van der Linde on February 04, 2014, 01:39:28 PM
Also see the maps and reference to the final Griggs, Bamber et al paper on ASIB (thanks to Tenney Naumer for catching this):
http://neven1.typepad.com/blog/2012/12/looking-for-winter-weirdness-4.html?cid=6a0133f03a1e37970b017c3524438c970b#comment-6a0133f03a1e37970b017c3524438c970b (http://neven1.typepad.com/blog/2012/12/looking-for-winter-weirdness-4.html?cid=6a0133f03a1e37970b017c3524438c970b#comment-6a0133f03a1e37970b017c3524438c970b)

A-team's bedrock map is clearer than the original in the paper.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on February 17, 2014, 08:48:31 PM
Jakobshavn,waiting for your next move:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Yuha on February 17, 2014, 09:11:57 PM
Jakobshavn,waiting for your next move:


The first calving of the season happened already:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on February 17, 2014, 09:27:45 PM
Yuha,

You are right, something definitely moved ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on February 18, 2014, 09:50:40 PM
First 2014 Landsat image from the Ice Cube maker at Jakobshavn, and as Yuha pointed out, the thing is moving:

!!There might be a problem with the February 9 2014 image!!


Please click on image to enlarge and start animation ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: icefest on February 28, 2014, 08:44:58 AM
Thanks for the enimation Espen,

I'm looking forward to this melt season. (with trepidation)



Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Wipneus on February 28, 2014, 01:09:35 PM
Sequence of Landsat 8 images from Feb 9 and 25. More calving has taken place. I estimate the progress of the south branch about 22x21 pixels (left and up). That translates to 456 meters, or about 28 meter per day.
Accuracy should improve when the light gets better (sun elevation is 5.8 and 11.4 degrees ).

(click for that animation)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: AbruptSLR on February 28, 2014, 04:56:43 PM
Wipneus,

If a 1997-1998 like El Nino event happens in 2014-2015 (see the discussion on this probability in the "Consequence" folder), and if such a Super El Nino sufficiently disrupts the Thwaites, and/or Pine Island, Ice Shelf (Shelves); then conditions could be created therefore to set-up calving events for either Thwaites, and/Pine Island, Glacier(s) comparable, or worse, than Jakobshavn is exhibiting.  That is a truly chilling prospect, and if so your Landsat 8 sequences for the Amundsen Sea Embayment glaciers, in the next austral summer, would be greatly appreciated.

Best regards,
ASLR
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on February 28, 2014, 08:21:00 PM
detail of Jacobshawn bedrock, overhead view in attached image

more bedrock images at

http://membrane.com/sidd/greenland-2013/ (http://membrane.com/sidd/greenland-2013/)
i will add more detail and ice surface elevation to those pages this weekend

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on March 03, 2014, 10:48:35 PM
added surface elevation, Jacobshawn,Petermann detail

http://membrane.com/sidd/greenland-2013/ (http://membrane.com/sidd/greenland-2013/)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: werther on March 03, 2014, 10:56:48 PM
Great comparison, Wipneus.
Though I must say the shadow cast by the 100-120 m high calving front plays a delusive role.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on April 09, 2014, 04:41:32 PM
A new calving front seems to be developing in the northern part of the eastern branch, marked with a red circle, 2014 is likely to be a very interesting glacier year!

Please click on image to enlarge!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on April 10, 2014, 07:21:30 PM
As mentioned above the "New Front" development is seen on this NASA image from yesterday
Or is it "only" a ice slide due to the elevation? :
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: mspelto on April 19, 2014, 12:32:58 PM
It is not a new calving front, but it does represent a steepening of the slope, enhanced crevasse and serac activity.  This is close enough to the front to potentially not be stable without retreat to it. We generally do not see such a narrow embayment develop on this glacier, so if it does retreat to that point the lateral extent will be greater.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: mspelto on April 19, 2014, 12:38:31 PM
CHW is not to date an important part of the acceleration puzzle for the GIS, it takes a long time to warm the ice.  This type of acceleration would also tend to impact areas inland more than near the terminus, yet acceleration has been most pronounced at the terminus.  There is limited acceleration away from the large outlet glaciers, yet CHW would impact all locations.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Jim Hunt on April 19, 2014, 01:59:22 PM
As mentioned above the "New Front" development is seen on this NASA image from yesterday

The IceBridge P-3 is heading back to Jakobshavn (https://forum.arctic-sea-ice.net/index.php/topic,779.msg24515.html#msg24515) as we speak.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on April 19, 2014, 03:11:19 PM
It is not a new calving front, but it does represent a steepening of the slope, enhanced crevasse and serac activity.  This is close enough to the front to potentially not be stable without retreat to it. We generally do not see such a narrow embayment develop on this glacier, so if it does retreat to that point the lateral extent will be greater.

Since this enhanced crevasse and serac activity is occurring beyond the existing calving front, should we expect this kind of activity to expand as the calving front retreats?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on April 19, 2014, 03:25:30 PM
It is not a new calving front, but it does represent a steepening of the slope, enhanced crevasse and serac activity.  This is close enough to the front to potentially not be stable without retreat to it. We generally do not see such a narrow embayment develop on this glacier, so if it does retreat to that point the lateral extent will be greater.

Since this enhanced crevasse and serac activity is occurring beyond the existing calving front, should we expect this kind of activity to expand as the calving front retreats?

I would guess it is more likely on the northern "shore" than the southern because of the elevation?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on April 19, 2014, 03:57:23 PM
Just followed the today's flight. It looks like they are following the future retreat route? 
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on April 20, 2014, 11:43:09 PM
Comparison of surface and bedrock. Looks how the surface contours have concave kinks where the cross the bedrock canyons.

For other comparisons and some previous work by Csatho, please see

http://membrane.com/sidd/greenland-2013/walkback.html (http://membrane.com/sidd/greenland-2013/walkback.html)

sidd
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on April 22, 2014, 05:13:12 AM
The ice slide at the northern "shore" is developing, watch the encircled area (red):

Please click on image to start animation!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on April 26, 2014, 04:45:18 AM
And what lies beneath from Hughes(2014) doi:10.5194/tcd-8-2043-2014 (open access)
"Gogineni Gorge"  fig14 attached
I like it

That is a nice paper, but the Byrd comparison is probably better discussed in one of the Antarctica threads.

sidd
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on April 26, 2014, 09:34:05 AM
Sidd,

There seems to be a threshold just behind the present calving front?

And what is the date of the calving front on that image?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on April 26, 2014, 11:34:26 AM
From the same paper : Quantifying the Jakobshavn Effect:
Jakobshavn Isbrae, Greenland, compared
to Byrd Glacier, Antarctica
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on April 26, 2014, 08:08:57 PM
The grounding line seems to be from 2012 as in the other grafs ?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: andy_t_roo on April 27, 2014, 08:31:56 AM
Would you be able to plot the ice thickness at which it would be possible to float at? That could be the limiting factor, as long as the deep area just past the current front remains grounded by the arrival of new ice vs melting then it is fine, but if the Ice thins enough to float, and water manages to infiltrate to the base, then all bets would be off. 
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on May 02, 2014, 08:54:09 PM
Another slice of Jakobshavn since April 23 2014 (Landsat image from May 2 2014 only partial)

Please click on image to start animation:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on May 07, 2014, 09:15:02 PM
Update May 7 2014:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Yuha on May 07, 2014, 11:13:42 PM
Espen's Landsat animation shows that there has been a "spring cleaning" of the fjord recently.

The first image below shows the start of the event on April 21. Most of the fjord was empty but there was a lot of ice dammed behind a blockage. By May 2 (second image) the fjord had been filled and there was a large plume of icebergs in Disko Bay. The event is still not over as can be seen in the images from the last two days.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on May 08, 2014, 12:22:10 AM
Would you be able to plot the ice thickness at which it would be possible to float at?

the number you want is 1.1*bedrock depth
but you might want to look at Volume above Flotation, (VAF)  = total ice thickness - 1.1*bedrock depth

I think someone has done VAF for Jacobshawn, but i can't recall the reference off the top of my head.

sidd
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Bernard on May 14, 2014, 02:50:31 PM
http://www.hotel-arctic.gl/files/webcam/webcamshot.jpg (http://www.hotel-arctic.gl/files/webcam/webcamshot.jpg) has been showing a lot of ice chunks flowing out for a couple of days. Any calving event associated in the past days, or just seasonal flushing?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Anne on May 14, 2014, 04:06:18 PM
Bernard, this webcam is a favourite of mine and I check it out most days. The current flow of ice doesn't seem unusual to me: watching the ice is one of the reasons people stay at the hotel. Sometimes there are icebergs and sometimes just bergy bits and growlers. They shift quite quickly so if you want other people to see what you're looking at it's worth posting the image.

But I'm hardly expert and stand to be corrected.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Anne on May 14, 2014, 05:14:37 PM
Many apologies! You did post the image.
Still doesn't strike me as exceptional.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on May 25, 2014, 09:55:53 PM
Due to a heavy cloud cover above Jakobshavn over a prolonged period, reporting is at a low pace.
But there are indications of a major calving at the southern branch including its northern shore, I base this on a very "cloudy" image from Landsat (May 25) combined with data from ASAR images.
As soon as reasonable images are received, they will be reported.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: jimbenison on May 27, 2014, 08:41:48 PM
I think Espen is right. Either low clouds are creating artifacts here or a huge chunk of ice has fallen into the sea.

https://earthdata.nasa.gov/labs/worldview/?switch=arctic&products=baselayers,!MODIS_Aqua_CorrectedReflectance_TrueColor,MODIS_Terra_CorrectedReflectance_TrueColor~overlays,arctic_coastlines_3413&time=2014-05-27&map=-419200,-2393216,10880,-2168960

It would be great to get a higher resolution pic.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Anne on May 27, 2014, 10:11:15 PM
There's always Hotel Arctic webcam at Ilulissat, which may be north of where you're looking. It's not showing anything exceptional right now.
http://www.hotel-arctic.gl/om_hotel_arctic/webcam/ (http://www.hotel-arctic.gl/om_hotel_arctic/webcam/)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on May 27, 2014, 10:23:05 PM
There's always Hotel Arctic webcam at Ilulissat, which may be north of where you're looking. It's not showing anything exceptional right now.
http://www.hotel-arctic.gl/om_hotel_arctic/webcam/ (http://www.hotel-arctic.gl/om_hotel_arctic/webcam/)

That is way away from where the action is (only about 45 km).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: jimbenison on May 28, 2014, 12:05:41 AM
There's always Hotel Arctic webcam at Ilulissat, which may be north of where you're looking. It's not showing anything exceptional right now.
http://www.hotel-arctic.gl/om_hotel_arctic/webcam/ (http://www.hotel-arctic.gl/om_hotel_arctic/webcam/)

That is way away from where the action is (only about 45 km).

It is far away, but large calving events can push energy all the way out the fiord and move those big bergs. Viewing a time lapse is more informative than a still.

http://www.lookr.com/lookout/1310041325-Ilulissat (http://www.lookr.com/lookout/1310041325-Ilulissat)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 01, 2014, 10:18:38 PM
WOW! This is far more than I expected (May 25), the retreat and calving must have been of record size, not only the southern branch expanded but so did the northern.

Just puzzled to where all that ice went? My estimate is 5 - 6 km2 of glacier ice went down the drain!

Please click on the image to start animation!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Rubikscube on June 01, 2014, 11:08:57 PM
Holy Moly, that's huge. Looks like the entire northern slope on the southern branch just fell into the ocean.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Neven on June 01, 2014, 11:55:37 PM
Pretty big, indeed. Thanks for keeping an eye on this, Espen. I'll put a blog post on the ASIB in a couple of days.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Yuha on June 02, 2014, 02:32:16 AM
Just puzzled to where all that ice went? My estimate is 5 - 6 km2 of glacier ice went down the drain!

5 - 6 km2 seems about right. Furthermore, the glacier is flowing pretty fast. If there had been no calving between May 7 and June 1, the calving front of the southern branch would have moved nearly 1 km forward, now it's about 1 km back. Thus the actual ice lost in the calving(s) is more like 10 km2.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on June 05, 2014, 11:00:28 AM
Jakobshavn is one of the "supersites" for the ESA S-1 satellite which means that it will be imaged with a Synthetic Aperture Radar twice in every 12-day period. As the data will be freely available this will allow continuous monitoring of this key ice stream throughout the year regardless of ambient light or cloud coverage.

Here's an example what will be possible (Kangerdluqssuaq-trakcked with an earlier SAR-satellite):

http://www.esa.int/images/glacier-ERS2-March-May_H.gif (http://www.esa.int/images/glacier-ERS2-March-May_H.gif)

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.esa.int%2Fimages%2Fglacier-ERS2-March-May_H.gif&hash=90bab4f1b559cfa004a6a670fcecd0e6)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Bernard on June 05, 2014, 05:58:09 PM
@nukefix any idea when such Sentinel-1 images will be available?
I did not find any indication at http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-1/Oceans_and_ice (http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-1/Oceans_and_ice)

BTW looking at this Kangerdluqssuaq animation it's amazing how the speed of the ice seems to be the same on each side of the calving front ...
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on June 05, 2014, 08:15:53 PM
@nukefix any idea when such Sentinel-1 images will be available?
The satellite in in commissioning-phase that should take until late September or so. See mission status for updates:

https://sentinel.esa.int/web/sentinel/missions/sentinel-1/mission-status

Some limited imagery is already available at https://senthub.esa.int/ but the search interface is cumbersome to say the least.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 06, 2014, 04:28:21 PM
To answer some questions asked by Steve Bloom at the Sea Ice Blog:

The furthest retreat I have observed was in September / October 2013, after that Jakobshavn expanded into 2014 and started calving again in March / April as can be seen on the animation below:

Please click on image to start animation!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: RaenorShine on June 07, 2014, 11:05:29 AM
RobertScribbler's blog has picked this up from here also (I've cross posted this from the ASIB)

http://robertscribbler.wordpress.com/2014/06/06/ten-cubic-kilometers-of-ice-lost-from-jakobshavn-glacier-in-less-than-one-month/#comments (http://robertscribbler.wordpress.com/2014/06/06/ten-cubic-kilometers-of-ice-lost-from-jakobshavn-glacier-in-less-than-one-month/#comments)

Ten Cubic Kilometers of Ice Lost From Jakobshavn Glacier in Less than One Month
How large is a cubic kilometer? Think of something the size of a mountain. Now multiply that by ten and you end up with a veritable mountain range. Think of it. An entire mountain range of ice. That’s a good rough comparison to the volume of ice lost from just a single Greenland glacier over the course of a mere 26 days from May 7 to June 1 of 2014.

For according to reports from expert sea ice observer Espen over at the scientist and ice researcher camp that is Neven’s Arctic Ice Blog, about 7.5 square kilometers over an ice face about 1,300 meters tall (when including the above and below sea level ice front) shoved off from the great Jakobshavn Ibrae glacier during the past month. It was a period of time well before peak Greenland warming and one that featured a collapse of ice into the heating ocean even larger than the epic event caught on film during the seminal documentary Chasing Ice.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Yuha on June 07, 2014, 06:44:11 PM
(Cross post from ASIB)

Probably the currently most accurate map of the bed topography of Jacobshavn is on page 15 in this paper:

http://www.nature.com/ngeo/journal/v7/n6/extref/ngeo2167-s1.pdf (http://www.nature.com/ngeo/journal/v7/n6/extref/ngeo2167-s1.pdf)

It's a supplement to a recent paper by Morlighem et al in Nature Geoscience (doi:10.1038/ngeo2167). The main paper is behind a paywall but the supplement is free. It covers many other Greenland glaciers too.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: jimbenison on June 08, 2014, 03:06:33 AM
A couple of years ago I stumbled across a paper that showed the bedrock topography of this glacier near the calving front of the south branch in great detail. I have been looking for it for the last week and cannot find it for the life of me. Epsen's image from Sep 27 2013 shows a couple of important features related to it thanks to the lighting angle.

Notice that just upstream of the calving front in the main south ice stream a couple of longitudinal bumps are visible. One is toward the north side and one is almost dead center. These are pinning points with relatively shallow bedrock that pushes the ice higher in these areas. Inland from there the glacier bed gets deeper. The really deep (-1500 meters) portion of the bed is actually a few kilometers upstream of where this branch makes a 45 degree turn due east.

If I can find the paper I will post it. The relationship between surface features on the ice stream and the bedrock topography are pointed out very clearly. It would be extremely handy here.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: icefest on June 08, 2014, 03:54:57 AM
@jimbenison

Was it this image:
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2F9jFUh%2Fa960fd2a26.jpg&hash=f3c9638d9ae02f9f039710c4d3590400)
From here: http://www.igsoc.org/annals/55/67/t67A001.pdf (http://www.igsoc.org/annals/55/67/t67A001.pdf)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on June 08, 2014, 05:59:32 AM
And what lies beneath from Hughes(2014) doi:10.5194/tcd-8-2043-2014 (open access)
"Gogineni Gorge"  fig14 attached
I like it

That is a nice paper, but the Byrd comparison is probably better discussed in one of the Antarctica threads.

sidd

that the best i know
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: jimbenison on June 08, 2014, 01:01:26 PM
@icefest

That's not the one. This is a little better (see figure 1), but it still does not even hold a candle to the level of detail in the one I saw.

http://eprints.lib.hokudai.ac.jp/dspace/bitstream/2115/52825/1/Herzfeld_etal_2012_AnnGlac.pdf (http://eprints.lib.hokudai.ac.jp/dspace/bitstream/2115/52825/1/Herzfeld_etal_2012_AnnGlac.pdf)

I looked through dozens of papers today trying to find it. My best guess is that it's now behind a paywall.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: icefest on June 08, 2014, 01:26:45 PM
Hmm, is this any better?
https://www.cresis.ku.edu/sites/default/files/Research/Sensors/jakobshavn.jpg (https://www.cresis.ku.edu/sites/default/files/Research/Sensors/jakobshavn.jpg)
It looks like some variation of the CReSIS data seems to have the highest resolution.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 08, 2014, 09:56:49 PM
Believe it or not Jakobshavn continues its massive calvings:

Please click on image to start animation!

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Neven on June 08, 2014, 10:08:57 PM
Holy crêpe!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 08, 2014, 10:15:49 PM
Here a triple day animation May 7, June 1 and June 8 2014:

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on June 08, 2014, 10:16:45 PM
If you look at the glacier moving around the bend, it's also moving fast.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on June 08, 2014, 10:23:52 PM
Espen.....I want to confirm what I think I am seeing. You have been watching glaciers for a long time.

On that last animation it looks as if the huge bed of ice (northeast?) of Jakobshavn sped up towards the fjord when the calving removed its pinning or dam effect. Could this part of the ice sheet come into play? Now that Jakobshavn has retreated past this point, has this entire portion of the ice sheet become unstable?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 08, 2014, 10:30:16 PM
Shared Humanity, yes it looks like the whole plateau is on the move, I don't really know what is happening, but there must be a lot of stress and re-stress in area as a whole, and there is more to come over next few days, that can be seen when analyzing the images.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Neven on June 08, 2014, 10:32:40 PM
How much km2 are we talking now? Is this picked up anywhere? NASA?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 08, 2014, 10:37:05 PM
The series of calvings over the last moth are several times bigger than Manhattan NV.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on June 08, 2014, 10:51:12 PM
Espen.....You may want to look at this just published research. I've copied the link from a post by Lynn Shwadchuck on another Greenland thread. They have just completed a detailed topography map using an  entirely different technique. (mass conservation?)

http://www.nature.com/ngeo/journal/v7/n6/extref/ngeo2167-s1.pdf (http://www.nature.com/ngeo/journal/v7/n6/extref/ngeo2167-s1.pdf)

The topography detail on each glacier is amazing. The new topography map suggests that this entire ice sheet that is on the move is grounded below sea level!

Please look at page 15 and tell me I'm seeing this wrong!

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 08, 2014, 10:54:19 PM
How much km2 are we talking now? Is this picked up anywhere? NASA?

My prelim calculation is a total of 10,6 km2 ( May 7  - June 8 ) (excluding expansion)

Or 14,7 times the size of Manhattan NV. ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: LRC1962 on June 08, 2014, 11:30:22 PM
Very sad that Robert Scribbler and here seem to be the only places on the WWW that seem to have caught onto the story. No search engine as of yet can find anything else about this particular calving.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on June 08, 2014, 11:34:59 PM
Very sad that Robert Scribbler and here seem to be the only places on the WWW that seem to have caught onto the story. No search engine as of yet can find anything else about this particular calving.

That's because we have Espen keeping an eye on things. Take a look at the link  that shows detailed topography on 20  separate Greenland glaciers. I think Jakobshavn is going to be a huge story this year!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: mspelto on June 08, 2014, 11:44:10 PM
(https://glacierchange.files.wordpress.com/2009/06/jakobshavn-592014.jpg) May 9th
(https://glacierchange.files.wordpress.com/2009/06/jakobshavn-612014.jpg) June 1

Lack of surficial transverse crevassing is unusual before a large calving event.  Basal crevassing maybe key. Notice the longitudinal feature that marks the main boundary of southern arm.

Jakobshavn overall assessment (http://Jakobshavn overall assessment)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: LRC1962 on June 09, 2014, 12:31:01 AM
Complain to CBC not sure if it will help. Could be melt working through from last year, but also the SSTA around that area has been very high lately, could it not also be a case ocean water working its way underneath and only impacting now? And since it would be traveling either level or even slightly downhill, could get far farther inland then if it had to go uphill.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 09, 2014, 07:41:12 AM
Be aware! We have have not reached the maximum retreat point of September 2013 yet, at some points yes but not depth wise :

Please click on image to start animation!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Neven on June 09, 2014, 08:51:03 AM
Be aware! We have have not reached the maximum retreat point of September 2013 yet, at some points yes but not depth wise :

Please click on image to start animation!

Thanks, Espen. I don't keep an eye on this, and so I didn't know about the retreat point.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 09, 2014, 10:02:35 AM
Be aware! We have have not reached the maximum retreat point of September 2013 yet, at some points yes but not depth wise :

Please click on image to start animation!

Thanks, Espen. I don't keep an eye on this, and so I didn't know about the retreat point.

But I am pretty sure we will pass that point later this season, maybe even within days?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Neven on June 09, 2014, 10:09:51 AM
Well, let us know, and I'll post a follow-up on the ASIB.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Bernard on June 09, 2014, 12:54:48 PM
Espen I suppose in your last animation the date 2013 June 8 has to be read 2014 June 8?  ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 09, 2014, 01:13:26 PM
Bernard, yes that is June 8 2014, very early in the morning :-[

It is now corrected!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 09, 2014, 05:13:13 PM
Although we probably had some of the largest calvings ever seen at Jakobshavn, we did not reach the retreat point Jakobshavn saw in September 2013.
Since September 2013 Jakobshavn grew, but that growth is now almost gone, so if Jakobshavn follow the plan, large calvings usually come in the summer season, we can expect Jakobshavn to retreat beyond the point reached in September 2013.
To illustrate where we are today I have made the graphic below, with the latest Landsat-8 image of Jakobshavn with the retreat line seen in September 2013 (red line).   
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on June 10, 2014, 02:28:51 PM
Shared Humanity, yes it looks like the whole plateau is on the move, I don't really know what is happening, but there must be a lot of stress and re-stress in area as a whole, and there is more to come over next few days, that can be seen when analyzing the images.

If I look at your animation again and compare it to the increasingly accurate topography map from recent completed research published here.......

http://www.nature.com/ngeo/journal/v7/n6/extref/ngeo2167-s1.pdf (http://www.nature.com/ngeo/journal/v7/n6/extref/ngeo2167-s1.pdf)

........the retreating calving face of Jakobshavn is exposing a large section of ice sheet to the north of the Fjord. As can be seen, this portion of the ice is grounded below sea level and is already moving fast. Could we see significant calving from this ice sheet?

Because this ice sheet is grounded below sea level, will it also suffer significant melt by the sea on the bottom of this ice. The grounding is much shallower than the Fjord (perhaps only 200 meters). Would this shallower grounding serve to slow or protect this sheet from bottom melt?

I guess my concern is that, with the retreat of the Jakobshavn, we've essentially doubled the potential calving into the Fjord, perhaps more as this ice sheet calving face is considerably wider.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Rubikscube on June 10, 2014, 07:16:06 PM
Many thanks for all the nice topography maps everyone. I kind of share your concern SH, perhaps first and foremost because of the developments we have seen in the Northern branch during recent years, a branch which also seems to have a quite limited depth. My assumption after seeing the newst maps, is that it wouldn't be a very big surprise to see a third branch slowly emerge.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi58.tinypic.com%2F20as8cj.gif&hash=0edd4e2e3e1cb14af8241e77f617e97e)

However, what really frighten me is this.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi57.tinypic.com%2Ffpcjmo.gif&hash=d73e5654db62594e9252ac3d36d07397)

Hopefully, and probably, it is going take several decades before Jakobshavn splits into multiple branches that each are capable of penetrating several hundred kilometers into the Greenland ice sheet, but the fact that all these canyons exist would suggest pretty strongly that there have been numerous fast moving glacial outlets right in the middle of Greenland during previous meltdowns. It strikes me though, that most of this vast network of canoyns is excluded from more detailed topography maps of Jakobshavn and doesn't seems to be a videly discussed issue. Is it just too far into the future?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 10, 2014, 07:58:04 PM
Thanks guys, for the topography graphics, although I find Jakobshavn interesting, I think it is far more interesting and especially far more serious what is happening at Zachariae Isstrøm.
I know Zachariae Isstrøm is not a media and blogger darling like Jakobshavn, Petermann and to some degree Helheim, very little image/film documentation could be one of the reasons, but the indifference frustrates me?
 
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: jimbenison on June 11, 2014, 08:30:20 AM
Looks like NASA has picked up on the recent calving.

http://earthobservatory.nasa.gov/IOTD/view.php?id=83837&eocn=home&eoci=iotd_readmore (http://earthobservatory.nasa.gov/IOTD/view.php?id=83837&eocn=home&eoci=iotd_readmore)

I tend to agree with Espen on Zachariae. Jakobshavn is relatively narrow and may be already flowing about as fast as it can. It's like a firehose. Zachariae is very wide, it's deep, and it's waking up.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Neven on June 11, 2014, 09:52:01 AM
Looks like NASA has picked up on the recent calving.

http://earthobservatory.nasa.gov/IOTD/view.php?id=83837&eocn=home&eoci=iotd_readmore (http://earthobservatory.nasa.gov/IOTD/view.php?id=83837&eocn=home&eoci=iotd_readmore)

And they link to the ASIB at the end of the article! Well done, Espen!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on June 11, 2014, 03:37:05 PM
Many thanks for all the nice topography maps everyone. I kind of share your concern SH, perhaps first and foremost because of the developments we have seen in the Northern branch during recent years, a branch which also seems to have a quite limited depth. My assumption after seeing the newst maps, is that it wouldn't be a very big surprise to see a third branch slowly emerge.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi58.tinypic.com%2F20as8cj.gif&hash=0edd4e2e3e1cb14af8241e77f617e97e)

However, what really frighten me is this.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi57.tinypic.com%2Ffpcjmo.gif&hash=d73e5654db62594e9252ac3d36d07397)

Hopefully, and probably, it is going take several decades before Jakobshavn splits into multiple branches that each are capable of penetrating several hundred kilometers into the Greenland ice sheet, but the fact that all these canyons exist would suggest pretty strongly that there have been numerous fast moving glacial outlets right in the middle of Greenland during previous meltdowns. It strikes me though, that most of this vast network of canoyns is excluded from more detailed topography maps of Jakobshavn and doesn't seems to be a videly discussed issue. Is it just too far into the future?

I guess my reason for focusing on the ice sheet that is northeast of the Jakobshavn calving face is it is already moving fast, has been unzipped by the retreating Jakobshavn, and, based on the animations by Espen,  is speeding up towards the fjord as I type. The impact of this sheet being exposed to the sea, causing melt and retreat of the grounding line means it will contribute to ice mass loss this year and into the near future. It will be fun to watch. I will be looking at every image Espen posts here.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Laurent on June 11, 2014, 04:48:05 PM
I don't think it is full speed already, there is a few kilometers before it is moving in his deep bed (If I see it correctly).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: LRC1962 on June 11, 2014, 08:28:17 PM
Very interesting talk about studying movement of  Greenland glaciers from an engineers point of veiw.https://www.youtube.com/watch?v=Ftz7XnSZ_mk (https://www.youtube.com/watch?v=Ftz7XnSZ_mk)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 11, 2014, 08:30:04 PM
Cross post from Zachariae Isstrøm thread:

What is all the fuss about?

https://forum.arctic-sea-ice.net/index.php/topic,400.msg28208.html#msg28208
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Laurent on June 11, 2014, 09:14:21 PM
It seems to me that the potential collecting area is higher for Jakobson !? On the geological map of Zachariae it is not clear if it is linked to the inside of Greenland, can you tell us what are the volume potential of each of them ?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Hans on June 11, 2014, 09:41:02 PM
Nasa has a nice "image of the day: http://earthobservatory.nasa.gov/IOTD/view.php?id=83837&src=eoa-iotd (http://earthobservatory.nasa.gov/IOTD/view.php?id=83837&src=eoa-iotd)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 11, 2014, 09:48:29 PM
It seems to me that the potential collecting area is higher for Jakobson !? On the geological map of Zachaeria it is not clear if it is linked to the inside of Greenland, can you tell us what are the volume potential of each of them ?

Laurent,

It seems so, and since Jakobshavn is in the "tropical" and the more accessible part of Greenland, that is where the focus is, but I think there is just as much "raw material" (ice) around Zachariae and not so many "natural outlets" Zachariae is wise to be open for business, when the conditions are fair (climate change).

Just to put it an economical, and not only in an engineering perspective?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: solartim27 on June 12, 2014, 02:00:45 AM
I had posted this on the Greenland melt page:
Any idea what the line to the northand inland of Jacobshavn is?  Melt water channel?  Seemed to form in a week, last clear day there was 6/2.
http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2014162.terra (http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2014162.terra)
 
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: icefest on June 12, 2014, 03:18:48 AM

Any idea what the line to the northand inland of Jacobshavn is?  Melt water channel?  Seemed to form in a week, last clear day there was 6/2.


Clouds.
You can see the shadow in 3-7-6:
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Flance-modis.eosdis.nasa.gov%2Fimagery%2Fsubsets%2F%3Fsubset%3DArctic_r02c02.2014162.terra.367.250m.jpg&hash=d2ec5ee03ad9507ce35581b5994b3c21)

Furthermore if you compare Aqua and Terra true color shots, it visibly moves to the east.
Attachment is animated.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Lennart van der Linde on June 12, 2014, 01:50:34 PM
The NASA-post being picked-up:
http://www.livescience.com/46264-greenland-glacier-loses-ice-photo.html (http://www.livescience.com/46264-greenland-glacier-loses-ice-photo.html)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 14, 2014, 10:39:44 AM
Further calving at Jakobshavn, although the documentation is vague and based on Nasa Modis images, this calving could be beyond September 2013 maximum retreat point:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on June 14, 2014, 05:42:18 PM
With the current condition of the Baffin sea ice, if we get a high established over Greenland with its characteristic flows from the south along the western edge of Greenland, the Jakoshavn may be one of the big stories in this melt season. Not only will the calving face retreat dramatically but I believe we will see significant and unprecedented calving from the ice sheet that is grounded below sea level and is being exposed by the retreat of Jakobshavn.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 14, 2014, 06:35:53 PM
Current conditions are not so important when talking about glaciers, calving and more important retreats are results of what happened years ago, there is time lack. Therefore the current sea ice situation cannot be compared to what is happening with the glaciers.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: LRC1962 on June 14, 2014, 10:54:50 PM
Although I have very little direct knowledge, think of it this way. The glaciers lakes are happening at the top. That is where the ice is originally weakened. Now think how long it will take to get that weakened ice down to the end. Granted, what happens at the bottom end certainly influences the amount of stress farther up, but if the ice has been weakened farther in the first place then the quicker it will break up in the end.
The same as with CO2 and temps. Current temps are results partly of CO2 forces 30-40 years ago. Take CO2 levels then then think of what they are now an project temps 30-40 years down the road.
On the other hand when as in a case of a full glass of water, when things become too much then one thing starts impacting other things that were not impacted before. Are we there yet. I think not, but I also think we are far closer then anyone of us would wish.
The sad thing is all of this could have been avoided because we knew the basics 200 years ago.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 15, 2014, 08:32:43 PM
I am now pretty convinced, on Friday June 13 2014, of all dates? Jakobshavn went into retreat land with another large calving, better documentation will hopefully be available soon, cant figure out Landsat release schedules and priorities? ???

Please click on image to start animation!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on June 23, 2014, 05:43:24 PM
Here is a SAR-image of Jakobshaven taken with Sentinel-1 on 7.6.2014. The images are uncalibrated, polarisation is HH,HH,HV for the RGB-channels, they are both zooms from the same 250-km wide scene. The calving front is very visible in these conditions and in the future we will be getting two images like this in every 12-day period, through weather and clouds!

ps. image-processing done with the open source ESA NEST-toolbox
pps. this is some other ice-stream close to Disko Bay and not Jakobshaven. anyway, the potential of this satellite data is evident for calving-front location detection.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on June 23, 2014, 05:51:54 PM
Oops, wrong ice stream, I'll keep you posted once ESA releases an image that covers Jakobshaven.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 23, 2014, 08:52:32 PM
Really good images for calving and retreat documentation, I thought the intervals (12days) would be shorter when it is a so called Supersite?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Sonia on June 24, 2014, 03:05:04 AM
Don't know the name of the glacier but it's easily seen a bit north of the Jakobshavn.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 24, 2014, 06:41:46 AM
Jakobshavn update:

Due to growth since June 8 the loss since don't look that bad.

Please click on image to start animation!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Yuha on June 24, 2014, 07:15:16 AM
Espen, could you post the June 24 image on its own and without overlapping titles?
It shows the shapes of the ice surface with spectacular clarity.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on June 24, 2014, 09:27:00 AM
Really good images for calving and retreat documentation, I thought the intervals (12days) would be shorter when it is a so called Supersite?
It will be imaged from both ascending and descending orbits every 12 days, it's too early to tell what will be the separation in days between the ascending and descending acquisitions.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 24, 2014, 04:08:44 PM
Espen, could you post the June 24 image on its own and without overlapping titles?
It shows the shapes of the ice surface with spectacular clarity.

NB! This is a cut-out of the original image 4MB.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 24, 2014, 09:18:53 PM
Calving front update:

The image below show where the calving front was on September 27 2013 (red line) and June 24 2014 (yellow line).
At some points Jakobshavn retreated beyond the Sep. 27 2013 calving front, but still behind 2013 at the eastern main gate.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Yuha on June 25, 2014, 04:34:16 PM
Espen, could you post the June 24 image on its own and without overlapping titles?
It shows the shapes of the ice surface with spectacular clarity.

NB! This is a cut-out of the original image 4MB.

Thanks!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 01, 2014, 09:49:55 PM
The 01 Jul 14 Landsat-8 image was released today. Skies were clear over the calving front. Unfortunately LC80842322014182LGN00 being orbital path 84, row 232 just nicks the calving zone, providing the triangular overlap below. Image quality is not the best at the edge of its frame either.

Modis Aqua/Terra on 30 Jun 13 show more of the event but they are a couple of bricks short of a wall in terms of adequate resolution.

The bottom image in the 15 m slide show below has been painted to display different origins of ice arriving at the calving front, based on shear lines. This ice likely has different properties (temperature, thickness, velocity) depending on its origin which presumably correlate with where the calving front calves.

I'm very skeptical of journal displays indicating uniform velocity transects. We have an event here each fall where the students line up on a bridge at 1 m intervals, dropping rubber duckies into the river. As you can imagine, these hardly arrive at the next bridge downstream at the same time. I will put this matter to rest for Jakoshavn Isbrae the day we get our first pair of supersite radar images this fall.

It's very difficult to get a sense of volume lost, which after all is the main interest (increasing contribution to sea level rise). Rather than modeling the glacier, I think it would be better just to make accurate lidar measurements of the downstream fjord (noting tide level). Heights there imply depths since this is mainly ungrounded freshwater ice. Volume is then proportional to the surface integral of the DEM.

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on July 03, 2014, 02:36:45 PM
Calving front update:

The image below show where the calving front was on September 27 2013 (red line) and June 24 2014 (yellow line).
At some points Jakobshavn retreated beyond the Sep. 27 2013 calving front, but still behind 2013 at the eastern main gate.

I believe this image is clearly showing the new calving face is already contributing ice loss into the fjord. The yellow line is retreating northeast. How quickly will the main calving face retreat or will the speed of the glacier prevent this calving face to retreat quickly and allow this new calving  face to march toward the fjord?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 03, 2014, 04:41:38 PM
SH;

That is a very good question, there is bedrock threshold in the near vicinity below where the eastern calving front is at the moment, and I think no one really knows what will happen next, but at one point it will retreat in that direction, if current conditions are not changed.   
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 03, 2014, 08:09:44 PM
Still waiting for Landsat, but here is another calving and potentially a retreat:

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 04, 2014, 12:45:43 AM
Landsat imagery is now available for download at EarthExplorer. The big one is LC80090112014184LGN00_B8. I adjusted all the contrasts within the 16 bit framework of ImageJ as tests show it does make difference.

The most curious thing about this calving event is its edge at the fast-moving main ice stream. The slower ice coming off the hill to the south has not yet participated. The image below is 30m. I upsampled the 15m panchromatic to 7.5 m to see what the details of the calving front looked like ... a work in progress it appears.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 04, 2014, 05:34:05 AM
Here is the Landsat proof of the calving events between June 8 and July 3 2014:

Please click on image to start animation!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 04, 2014, 06:03:21 AM
I would say we are into retreat land already, judge by yourself?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 04, 2014, 07:50:54 AM
This Landsat-8 is a path,row 9,11 which is always followed by a 10,11 the next of which should appear on July 7th, or if not then July 11. It has a few puffies but otherwise is an exceedingly sharp image.

I noticed a peculiar thing about Band 8 panchromatic. It looks a lot better with its grayscale inverted (x --> 255-x). This could have something to do with the lighting. According to the metadata file:

SCENE_CENTER_TIME = 15:00:24.4130118Z
CLOUD_COVER = 1.49
IMAGE_QUALITY_OLI = 9
SUN_AZIMUTH = 173.30855079
SUN_ELEVATION = 43.33909208

It looks like a couple of bergs at the two extremes of the calving front will be calving off sideways. Otherwise, lots of crevices (and even patterns to them) but nothing that indicates a next calving front.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: ablair on July 04, 2014, 11:45:17 AM
I've been watching a developing dark spot above the northern branch and it has suddenly grown into a large hole/ nunatek which indicates how much the level must be lowering. Will be interesting to see this develope into an ice stream divide.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 04, 2014, 04:38:59 PM
Good observation. The north branch is quite interesting in its own right. In the late 1980's, it joined the south fork in an extended down-fjord feature called 'the zipper' (the thicknesses were markedly different). Now that the south fork has retreated up its own channel, there is less back pressure on the north and middle fork calving fronts.

The black streaking on discharged ice below the nunatak probably represents rock on the bottom of calving pieces (as in 'Chasing Ice') rather than moraine streaking from the nunatak.

Note the north fork does not overlie a deep channel nor does it have a large drainage. Thus it does not have potential to be a major contributor to sea level rise.

Below is the panchromatic 7.5m from yesterday of this nunatak. We won't be seeing similar pinning points emerge on the south fork because its channel is thousands of feet below sea level for 125 km inland.

In terms of developing a time series, I looked through the Landsat-8 imagery database posted on the other forum http://forum.arctic-sea-ice.net/index.php/topic,909.0.html (http://forum.arctic-sea-ice.net/index.php/topic,909.0.html), both for other path 9, row 11 cloud-free imagery (which will have the most similar platform geometry if you want a stereo pair or count interometric movement fringes) and also for the most recent regardless of path, row. There is no counterpart to July 3 imagery in the 2013 archive.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 04, 2014, 05:36:22 PM
Nice observation Ablair, yes we will probably see several Nunataks popping up here and there over the years, as we observe at several glaciers around Greenland.
I myself thought it was a melt pond :-[
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Rubikscube on July 04, 2014, 08:26:09 PM
I thought this was just a melt pond as well and that it would rather be caused by an emerging nunatak. Either way it is kind of strange looking.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 05, 2014, 03:20:54 AM
Right, strange flow pattern in the vicinity, topography is a bit of a puzzle. However ordinary google map has a great series of zooms here (once you're sure you're zooming on the right object, the north fork has retreated a lot since this imagery. The melt lake is very black in Landsat today but by clicking on it with the color wand tool, other lakes prove just as black (while most are classic blue). Click if the animation doesn't start.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 05, 2014, 03:33:25 AM
Here we go, perspective DEM from TerraSar. May or may not be some degree of vertical exaggeration. Not sure of the date either. North branch is clear locatable; more extreme topography than i would have guessed from the nadir view of Landsat. It's not so easy to be sure the melt lake is in the pocket though.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: TerryM on July 05, 2014, 08:11:23 AM
Amazing images A-Team !
Terry
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: ablair on July 05, 2014, 01:09:12 PM
Right, strange flow pattern in the vicinity, topography is a bit of a puzzle. However ordinary google map has a great series of zooms here (once you're sure you're zooming on the right object, the north fork has retreated a lot since this imagery. The melt lake is very black in Landsat today but by clicking on it with the color wand tool, other lakes prove just as black (while most are classic blue). Click if the animation doesn't start.
[ Wow - good detective work there, thanks - it's a melt lake then!. that would explain why it grew so quickly. As you say, the topography a bit unusual there/quote]
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on July 05, 2014, 02:15:57 PM
Here we go, perspective DEM from TerraSar. May or may not be some degree of vertical exaggeration. Not sure of the date either. North branch is clear locatable; more extreme topography than i would have guessed from the nadir view of Landsat. It's not so easy to be sure the melt lake is in the pocket though.

I don't think this is vertical exaggeration. I believe what we are seeing is a suggestion of the grounding line and the lowering of the ice surface is evidence of bottom melt. This picture shows this on the North Branch but also shows a similar condition on the new calving face that is emerging due to the retreat of the Jakobshavn up the deep gorge. I think this emerging new calving face has the potential of dumping far more ice into the fjord than we might expect.

As the Jakobshavn calving face continues its retreat, we are going to see the very high ice north of the fjord behave in a very similar fashion as it is also grounded below sea level. The area that should have aggressive bottom melt and calving will be the heavily crevassed regions closest to the fjord.

Oh! I also agree. This is quite simply the most amazing image I have ever seen. Can you secure such images of other glaciers of interest?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on July 05, 2014, 02:44:09 PM
I thought this was just a melt pond as well and that it would rather be caused by an emerging nunatak. Either way it is kind of strange looking.

I absolutely do not believe this is an emerging nunatak. The most accurate topography maps to date (see image below) show no land above sea level in this area of the north branch. On the ice speed image on the left, we also see no pinning effect that should be present if such a nunatak existed. This north branch of the glacier is moving uniformly fast where the shallow basin of water sits beneath it. We do, however, see the effect of the large island that sits just east of the north branch. If you look at the ice speed image on the left, the ice sheet here is moving much slower.

This could be a melt pond but I do not believe this is the case either. I think what we are seeing is open sea, the actual surface water of the shallow basin that sits underneath this portion of the ice sheet. The ice sheet on this particular portion of the north branch has completely melted away. This is why this area is as dark as the water in the open fjord. We are not looking at a shallow melt pond or lake. We are looking at open sea. While it is certainly shallower then the fjord, the topography map suggests this water is perhaps 100 meters deep, maybe deeper.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: crandles on July 05, 2014, 04:17:06 PM
I thought this was just a melt pond as well and that it would rather be caused by an emerging nunatak. Either way it is kind of strange looking.

This could be a melt pond but I do not believe this is the case either. I think what we are seeing is open sea, the actual surface water of the shallow basin that sits underneath this portion of the ice sheet. The ice sheet on this particular portion of the north branch has completely melted away. This is why this area is as dark as the water in the open fjord. We are not looking at a shallow melt pond or lake. We are looking at open sea. While it is certainly shallower then the fjord, the topography map suggests this water is perhaps 100 meters deep, maybe deeper.

Why wouldn't ice be pushed into this below sea level area? Perhaps it is but it keeps melting due to warm water is the only reason I could suggest. This seems unlikely to me without there being known geothermal activity but then I wouldn't really trust my intuition given my lack of knowledge.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on July 05, 2014, 04:24:51 PM
I have been reviewing and comparing these 2 images daily for the past 2 weeks. It is simply remarkable how the ice speed image matches precisely the underlying topography. Every time I review these images (again I do this daily) I begin to understand more about the existing behavior of this glacier but believe I can see how this glacier will behave in the future. Of course, I could be fooling myself. I've had a career in manufacturing management so what makes me an expert?

I have wanted to begin a review of Zacharia Istrom (sic) using the same images because Espen is certain that this glacier has far more sea level rise potential. If Espen feels this way, I am certain I do as well. I simply cannot tear myself away from this monster.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on July 05, 2014, 04:29:20 PM
I thought this was just a melt pond as well and that it would rather be caused by an emerging nunatak. Either way it is kind of strange looking.

This could be a melt pond but I do not believe this is the case either. I think what we are seeing is open sea, the actual surface water of the shallow basin that sits underneath this portion of the ice sheet. The ice sheet on this particular portion of the north branch has completely melted away. This is why this area is as dark as the water in the open fjord. We are not looking at a shallow melt pond or lake. We are looking at open sea. While it is certainly shallower then the fjord, the topography map suggests this water is perhaps 100 meters deep, maybe deeper.

Why wouldn't ice be pushed into this below sea level area? Perhaps it is but it keeps melting due to warm water is the only reason I could suggest. This seems unlikely to me without there being known geothermal activity but then I wouldn't really trust my intuition given my lack of knowledge.

You could be right. I have no more knowledge than you. It could very well be a melt pond or lake. I am fairly certain it is not a nunatak or evidence of an emerging nunatak.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 05, 2014, 05:09:37 PM
I have wanted to begin a review of Zacharia Istrom (sic) using the same images because Espen is certain that this glacier has far more sea level rise potential. If Espen feels this way, I am certain I do as well. I simply cannot tear myself away from this monster.

Compared to Zachariae Isstrøm, Jakobshavn is "just a Mickey Mouse" machine, the image below shows the difference (same scale).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 05, 2014, 06:22:38 PM
I'm going with freshwater melt lake.

The TanDEM-X DEMs provide 5 m/px resolution; DigitalGlobe WorldView 0.5 m/px stereo pairs. Surface rock observation IceBridge ATM/LVIS, ICESat GLAS, and GPS give absolute control on elevation data. A forthcoming paper from the Joughin group has a time series of sub-meter horizontal and vertical absolute accuracy, fully rectified photogrammetry. This feature is well above the error bars for sea level.

Jakobshavn has not been a floating ice shelf situation cf Antarctica since 1998 or so (except ephemerally in winter). The ice here is thousands of feet thick; it goes all the way down to the bedrock (modulo basal meltwater) and retains stratifications formed during the early and mid Holocene down 1500 m below sea level.

On ice-penetrating radar (bedrock), far fewer flight lines exist for the north branch. Here you want to look at adjacent raw radar profiles, look at their spacing and ask yourself how the bedrock surface in between is filled in.

In the late 1980's, there was quite a bit of discussion of a pinning point out in the main south bay of the main fjord. Although way below sea level, it had a very noticeable effect on movement of  ice (which was grounded out there then). It might better be called a seamount than a nunatak.

I don't recall any experimental data on the geothermal gradient for the Jakobshavn region. The expectation is way lower than central Greenland where the weight of the ice has thinned the viscous mantle, thickening it under the island margins and so slowing heat flow upward. There's only been some shallow steam drilling on the icestream and three bore holes (from the 1990's) way up the main branch that did not go to bedrock.

Now the Disko Bugt suture could change the geothermal picture. Although ancient -- archaean micro-continent pushed against paleoproterozoic -- anomalous heat flow could occur along the suture or a re-activated fault. It could also explain why the main Jakobshavn channel is located where it is. However the geology map is showing the suture well to the north, more like Epiq.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on July 05, 2014, 07:57:57 PM
Thanks for the explanation A-Team. Everything you said makes sense. Melt lake it is. I would not call it a pond. It is too large and too deep. Were you able to confirm whether this lake is centered in the depression that you can see in that gorgeous image that you posted above?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 06, 2014, 10:11:06 AM
Here is another reminder animation the first image is almost 42 years old compared to 2014, what a change?

Please click on the image to start the animation!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on July 06, 2014, 03:06:13 PM
Espen....a couple of questions about this retreat.

1) In the next 40 years, should we expect a similar retreat of the glacier up the fjord or might the retreat of the calving face slow down as it moves further into the interior of Greenland.

2) Does it look like the northern calving face has retreated nearly the same distance in this time? Should we expect the retreat of this northern face to continue at this pace?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 06, 2014, 03:37:25 PM
Shared H,

We really don't know, if you ask Anthony Watts it is only temporary, if you ask me it will probably drill its way deep into the interior of Greenland.

The northern branch don't have much further potential in my opinion, it might become an ice fall and a new fascinating tourist attraction? 
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 06, 2014, 04:23:05 PM
The Joughin group has described what they consider the physical limits to acceleration of retreat. It has about 80 km of channel to go; they estimate a few decades for that. In other words, not an abrupt collapse a la Antarctic ice sheets.

Nice imagery, Espen. I found some more recent historic images at the Nasa Visualization Lab, 2001-2006, from an unnamed satellite that has 6x the resolution of Modis Terra in a 28º ccw rotation.

The character of glacier flow on the north branch has really changed. Formerly, a lot of moraine material was coming down. There are also various melt lakes and other features on both channels. The last image in the slide show is a murky Modis from 2014.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 06, 2014, 04:29:05 PM
Hello A-Team the "Calves" also changed characters from before where they were "shipped" away, now they are brutally tumbled around, hopefully no animal activists read this?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 06, 2014, 04:47:06 PM
"The northern branch might become an ice fall and a new fascinating tourist attraction."

Right now, people mostly go to Epiq calving front where there is a hotel with direct views. For that, you would fly to Ilulissat and take a 5 hour boat. (Be careful landing at that airport because I heard the guy who built it took some shortcuts.)

Seattle to Reykjavik is $1783, 12 hours. Reykjavik to Ilulissat $992 but sold out already for August. The Epiq hotel is something like $225 a night.

However we want to go to the calving front at Jakobshavn Isbrae. That is far too dangerous for chartered boat or kayak, though you could go overland to Swiss Camp from Ilulissat with a pack raft for small crossings.

However web cam A shows this is not really not close enough. I suppose there are helicopter or fixed wing charters. Might be better just stay home and just watch 'Chasing Ice' a few more times.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 06, 2014, 04:49:44 PM
Be careful A-Team I was was involved in the construction of the airport in Jakobshavn, although in a minor scale!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 06, 2014, 05:06:16 PM
If you want to watch "Grand Calvings" I suggest Helheim, you can get there from Ammassalik and then cross the fjord and do the "rest" trekking 8)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: VaughnAn on July 07, 2014, 08:17:20 AM
The disintegration of the 5000 feet deep ice from 1794 to roughly 1850 in what is now Glacier Bay, Alaska appears to be a possible example of how some of the Greenland glaciers could disintegrate:

"In 1794, Joseph Whidbey, master of the Discovery during George Vancouver's 1791-95 expedition, reported that his exploration of this part of the coast was blocked by a wall of 2 miles (3.2 km) width and 1,200 metres (3,900 ft)) thick."

[url]http://en.wikipedia.org/wiki/Glacier_Bay_Basin/] (http://[/url)http://en.wikipedia.org/wiki/Glacier_Bay_Basin/

Michael Collier also makes references to Glacier Bay in his book, Sculpted by Ice: Glaciers and the Alaska Landscape.

And from National Geographic:

Scientists call Glacier Bay a living laboratory for the grand processes of glacial retreat.

[url]http://travel.nationalgeographic.com/travel/national-parks/glacier-bay-national-park/] (http://[/url)http://travel.nationalgeographic.com/travel/national-parks/glacier-bay-national-park/

Explorers along the coast of Alaska also described "blocks of ice as large as small cities along the southern coast of what is now Alaska in the early 1800s.

It seems to me that there are enough similarities of a number of Greenland Glaciers to the ice sheet that was once in Glacier Bay that we can compare this mini ice sheet disintegration to the potential demise of many Greenland glaciers and the larger Greenland ice sheet itself.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 07, 2014, 06:04:41 PM
Very interesting post, VaughnAn, one that makes clear the scale at which melting can occur over a historic time frame.

Glacier Bay is an absolutely awesome place -- we went up there last Sept on the Norwegian Princess. Didn't see any calving in a couple of hours parked in front of the glacier but it was making a lot of growling noises. A few glaciers in the western basin are still in balance because of heavy precip being so close to the north Pacific.

I've been pondering whether there is a significant difference between these mountain glaciers and the Greenland ice sheet where there's no underlying mountain.

Jabkoshavn Isbrae is atypical in that it is the only icestream in Greenland that flows over/in a deep gorge, one that averages 1167 m depth below sea level over its last 30 km, not to mention 402 m of ice thickness above for a total of 1569. (I have these numbers handy from calculating total kinetic energy of the icestream today at the Landsat/bedrock forum.)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 07, 2014, 07:34:42 PM
I believe we have some more calvings since July 3 (last Landsat update), this time in the southern branch, but it is unclear whether the northern branchs eastern wall is collapsing?

Please click on image to start animation!

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Rubikscube on July 07, 2014, 07:37:24 PM
I absolutely do not believe this is an emerging nunatak.

I would actually disagree to some extent, and it looks to me as though there is a mountain reaching about 1000 meters above sea level that is the reason, or some of the reason, to why there exists such a melt lake. It also seems that any further development in this part of Jakobshavn will take place in the western areas, which have seen some calvings this year. I have attached my analysis of the northern branch using the same wonderful topography maps as SH at a dangerously high zoom.

Regarding the Zachariae vs Jakobshavn discussion launched by Espen some weeks ago, I would consider Jakobshavn the glacier with the highest volume potential in the very long run. The reasons for that include that the vast network of narrow fjords and overdeepenings that seems to be part of the Jakobshavn system is draining a part of the GIS with significantly thicker ice as well as an apparent lack of fjords connecting Zachariae to the interior of Greenland. That said, Zachariae might have the biggest short term potential, even though I feel pretty confident that volume loss from Jakobshavn will keep increasing.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: VaughnAn on July 07, 2014, 08:52:47 PM
A-Team, I have been to glacier bay too...about 15 years ago...awesome place and did see a couple calvings big enough to rock the ship.

One of the things that came out of all this was that from 1794 and into the early 1800s the ice sheet in glacier bay receded 42 miles even though it was about a mile thick.  It has since receded about another 23 miles to where it is today. I have not been able to find a specific time frame for the recession for the first 42 miles other than it occurred mostly over a period as short as 10 or 20 years.  The tone of anything about this is that one day things were intact and a short time later much of the ice was gone. 


Another important part of this breakup appears to be the size of the icebergs calved.  There are iceberg scrape channels cut through the underwater terminal moraine when large icebergs were pushed out of the bay by the ice disintegrating behind them.

The amount of information about this seems limited but John Muir documented the condition of the flora around the bay in the late 1800s which is consistent with a sudden demise of the lions share of the ice at first then a more protracted demise after that.


[url]http://www.nps.gov/glba/historyculture/john-muir.htm] (http://[/url)http://www.nps.gov/glba/historyculture/john-muir.htm

IMHO, this event is a fairly good predictor of the fortunes of a fair number of Greenland's glaciers.  Sure we have models, data, and evidence for and in Greenland itself but Glacier Bay appears to be the only place humans have witnessed an event on a scale large enough to be a fairly valid example of what is to come in Greenland.

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: VaughnAn on July 07, 2014, 08:55:52 PM
I had problems getting this link into reply #312:

[url]http://www.glacierbay.org/geography.html] (http://[/url)http://www.glacierbay.org/geography.html
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: CraigsIsland on July 07, 2014, 08:56:21 PM
I've been interested in looking at how much acceleration could be caused a number of variables. One of the variables I look at is just reflectivity/albedo in the area. 2014 albedo is currently tracking just above 2012 values for a certain higher elevation dataset- according to Dr. Box at the Dark Snow Project site: http://darksnowproject.org/ (http://darksnowproject.org/).


Here is the Worldview map of the Jakobshavn area: https://earthdata.nasa.gov/labs/worldview/?switch=arctic&products=baselayers,!MODIS_Aqua_CorrectedReflectance_TrueColor,MODIS_Terra_CorrectedReflectance_TrueColor&time=2013-06-05&map=-2048000,,,-1024000 (https://earthdata.nasa.gov/labs/worldview/?switch=arctic&products=baselayers,!MODIS_Aqua_CorrectedReflectance_TrueColor,MODIS_Terra_CorrectedReflectance_TrueColor&time=2013-06-05&map=-2048000,,,-1024000)

Compare 7 July 2014 with 2013 and find a clear view of 2012 around the same day. Of note is the reflectivity around the Calving areas up to 20-50 miles out. Not just the melting ponds, but the amount of darker materials clearly present as a differential and is visible at the 250m resolution on MODIS.

It's amazing to see the changes in a short amount of time. I would be surprised if the GIS as a whole had a blockbuster 2012 like melting percentage that was close to/at 100%. But that's not what I'm concerned about; it's the amount of time that albedo gets exposed to higher temperatures/sunlight for a longer period of time. At the minimum, I see a acceleration of the historical trajectory of calving events.

The following is a lot of amateur presumption and is no way accurate lol:  Since Jacob has that remarkable depth (which could be heated by geothermal properties) beyond the current grounding, I wouldn't be surprised to see a massive event that destabilizes the GIS. Think of it as a sort of canal system where a boat gets lowered into a shallower bit of sea.

thoughts? just say "No" if it's just ridiculous and I'm missing some basic science fundamental. Or inform me. Either way - appreciate it.

The Zach vs. Jacob is  a very interesting dynamic to discuss (and frame for others) on and I'd like to thank those involved in that.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Steve Bloom on July 07, 2014, 09:27:41 PM
VaughnAn, are you aware of any paper(s) on the Glacier Bay collapse of ~200 years ago?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 07, 2014, 11:59:52 PM
Calving looks dramatic, Espen ... the Landsat schedule is shown below, unfortunately the next high resolution image is not due until July 10.

I located the experimental data on temperature profile down the bore holes -- quite interesting. There's been more recent followup on the significance of bottom 'temperate ice' (near melting point) and its effect on creep: surprisingly, not that much.

http://php.scripts.psu.edu/staff/d/j/djl22/GSTREAM/JG2002Luethi.pdf (http://php.scripts.psu.edu/staff/d/j/djl22/GSTREAM/JG2002Luethi.pdf)
http://students.washington.edu/kpoinar/Presentations/AGUposter_kpoinar_2010.pdf (http://students.washington.edu/kpoinar/Presentations/AGUposter_kpoinar_2010.pdf)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: VaughnAn on July 08, 2014, 02:04:18 AM
Steve Bloom,

I have seen no papers.  The information available seems difficult to come by.  I have searched the internet for historical records and have found a few in the past but I have not been able to find them now.  There is a book by John Muir, Travels in Alaska but I do not own a copy.  There seems to be only bits and pieces of information between 1794 and the mid 1800s available.  What is clear is that the ice was there in 1794 when Captain Vancouver visited the area and the it was gone not very many years later.

The Tlingit people who lived in the area had an oral history of the area at the time which is mentioned on the National Park Service website link in my earlier post.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: TerryM on July 08, 2014, 08:35:30 PM
It's been ~45 years since I was on Glacier Bay. I'm sure much has been lost since then though I agree that the big losses took place over a very short period.
If records exist of the crash is it possible that they are hidden away in Russia?
Terry
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 09, 2014, 01:43:49 AM
This is a very fine hand-held from an airplane, maybe IceBridge, on an unknown late summer date. It looks just east upstream on the south branch of the calving front of Jakobshavn Isbrae at the Big Curve. This is some seriously jumbled ice -- we have to applaud the Swiss for venturing out there to drill holes for temperature profiles and bedrock hydraulic connectivity.

The insets in lower left show rendered bedrock DEM under the photo and (logarithmic) ice stream velocities of 2008. The scripts for making these yourself are given over on the Landsat/bedrock forum. The right is a tweaked July 2014 overhead Landsat.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: JayW on July 09, 2014, 01:45:22 AM
Steve Bloom,

I have seen no papers.  The information available seems difficult to come by.  I have searched the internet for historical records and have found a few in the past but I have not been able to find them now.  There is a book by John Muir, Travels in Alaska but I do not own a copy.  There seems to be only bits and pieces of information between 1794 and the mid 1800s available.  What is clear is that the ice was there in 1794 when Captain Vancouver visited the area and the it was gone not very many years later.

The Tlingit people who lived in the area had an oral history of the area at the time which is mentioned on the National Park Service website link in my earlier post.

Here is a paper on glacier bay leading up to 1794, but it doesn't really discuss the retreat following the rapid advance.  Suppose this is going OT, feel free to move my post to the glaciers thread. :)
Link courtesy of Alaska.edu http://uas.alaska.edu/arts_sciences/naturalsciences/envs/faculty_staff/pubs/connor_gbay_holocene_2009.pdf (http://uas.alaska.edu/arts_sciences/naturalsciences/envs/faculty_staff/pubs/connor_gbay_holocene_2009.pdf)
Abstract
The Neoglacial landscape of the Huna Tlingit homeland in Glacier Bay is recreated through new interpretations of the lower Bay's fjordal geomorphology, late Quaternary geology and its ethnographic landscape. Geological interpretation is enhanced by 38 radiocarbon dates compiled from published and unpublished sources, as well as 15 newly dated samples. Neoglacial changes in ice positions, outwash and lake extents are reconstructed for c. 5500―200 cal. yr ago, and portrayed as a set of three landscapes at 1600―1000, 500-300 and 300―200 cal. yr ago. This history reveals episodic ice advance towards the Bay mouth, transforming it from a fjordal seascape into a terrestrial environment dominated by glacier outwash sediments and ice-marginal lake features. This extensive outwash plain was building in lower Glacier Bay by at least 1600 cal. yr ago, and had filled the lower bay by 500 cal. yr ago. The geologic landscape evokes the human-described landscape found in the ethnographic literature. Neoglacial climate and landscape dynamism created difficult but endurable environmental conditions for the Huna Tlingit people living there. Choosing to cope with environmental hardship was perhaps preferable to the more severely deteriorating conditions outside of the Bay as well as conflicts with competing groups. The central portion of the outwash plain persisted until it was overridden by ice moving into Icy Strait between AD 1724―1794. This final ice advance was very abrupt after a prolonged still-stand, evicting the Huna Tlingit from their Glacier Bay homeland.

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 09, 2014, 11:05:31 PM
As we brace for tomorrow's hi-res Landsat (which might not be online until Friday -- and even then might be clouded over), we might set some rules governing 'records'.

It is not enough for the calving line to retreat past the all-time record set on 20 Sep 13. Although mildly remarkable with 70 more days to go in the retreat season, just going slightly beyond last year is not even keeping up with the multi-year trend: an additional km of retreat is the new normal.

Indeed, slightly more would still be business as usual since the rate of retreat may be accelerating. Thus we shouldn't trouble our colleagues on the ASIB with news on this little glacier until the retreat is a second km beyond the first km expected.

Determining the pixel scale on Fig.3 of Joachin 2014 as 23.3 px per km, measuring peak retreats, and finding the increments gives, noting a measurement error of 1 pixel amounts to 35 m:

Since color Landsat is 30m per pixel as it comes (caution: Espen uses a rougher scale), I've moved the goal line to the 1 (yellow) and 2 km (red) distances from the lines of retreat for 03 Jul 14 (image) and 20 Sep 13 (blue).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Neven on July 09, 2014, 11:16:07 PM
As we brace for tomorrow's hi-res Landsat (which might not be online until Friday -- and even then might be clouded over), we might set some rules governing 'records'.

It is not enough for the calving line to retreat past the all-time record set on 20 Sep 13. Although mildly remarkable with 70 more days to go in the retreat season, just going slightly beyond last year is not even keeping up with the multi-year trend: an additional km of retreat is the new normal.

Indeed, slightly more would still be business as usual since the rate of retreat may be accelerating. Thus we shouldn't trouble our colleagues on the ASIB with news on this little glacier until the retreat is a second km beyond the first km expected.

Noted.  :)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 10, 2014, 06:03:49 AM
Yes it is hard to measure a 100 m dash on a moving surface ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 10, 2014, 04:56:05 PM
"hard to measure a 100 m dash on a moving surface"

Right. The relationship between the volume of ice discharged (contribution to sea level rise), position of the calving front, glacier movement and terminus thinning is far from simple. For example, if the velocity of the glacier happened to exactly match the rate of calving, the front would be stationary yet record amounts of ice might calve into the fjord.

The first image below paces off 1 km steps along the main ice stream and shows how the July 2013 velocity spead up towards the terminus. This glacier moves so fast that ice 12 ticks out the blue line will be all calved off within a year.

I sought to find markers on the Landsat time series to see how fast the icestream is moving this year. However it is fairly featureless at 15-30 m resolution so not feasible to measure marker movement. This is a job for Digiglobe imagery -- the zoom from 30 m to google map resolution (24 Jun 12 photo) shows what we are missing.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 11, 2014, 01:46:45 AM
The two expected Landsats came in today, LC80100112014191LGN00, a mostly clear path 10, row 11 and
LC80832332014191LGN00, a path 83, row 233 totally obscured by pretty clouds.

We last had a clear 10,11 on 08 Jun 14 if you are trying to do something along photogrammetric lines. the lat,lon photo centers are 69.60648, -50.86015 and 69.6066,-50.86458 respectively, so very favorable geometrically as those numbers correspond to a nadir displacement of 172 m http://www8.nau.edu/cvm/latlongdist.html (http://www8.nau.edu/cvm/latlongdist.html)

The slides compare the 10 July 14 calving front with 03 Jul 14 (LC80 09 011 2014184LGN00). Both are processed up through cropping and contrast normalization in ImageJ as 16 bit Tiffs, then exported to Gimp for alignment and resolution bumping from 15 m to 7.5 m using Lancsoz3 (sinc).

Note the strong surge of the ice stream -- faster than calving front retreat this week -- moving it 315 m further out in the fjord. Note the sharp shear line in the lower left. The giant iceberg in the upper left is just over a km in width -- this is a good photo pair for measuring berg displacements.

Click on image if it doesn't animate
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 11, 2014, 04:25:09 PM
A-Team, that shows Modis is very unreliable to use as documentation.

It is "What you see, is not what you get" (Wysinwyg).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 11, 2014, 05:32:34 PM
Yes, clouds can look so much like calving front, it takes two very clear days to compare Modis. 250 m vs 15 m resolution means 16.7 pixels in Landsat for the 1 in Modis. Still, it gives a heads-up in most cases. However even with Landsat, it is a struggle to measure ice stream velocities.

It appears that 10 July - 03 July is a pure surge situation, no calving. The same bergs can be seen in both. That provides an opportunity to compare the positional shift of micro-feature pairs.

The largest reliable pixel-pair movement I found was 43 pixels at 7.5 m resolution or 322.5 meters in 7.004 days (subtracting the SCENE_CENTER_TIME time stamps in the metadata files MTL.txt). That works out to 46.1 m per day or
16.8 km per year which is a near-record surge velocity. However, upstream values were less and somewhat variable.

We have an ~ stereo pair of Landsats coming in tomorrow 8,11 and 8,12. Might give us a better sense of the surface, depending on sun heights, azimuths and time differences. The 10 July was SUN_ELEVATION = 42.6, SUN_AZIMUTH = 173.0.

With better imagery, Joachin 2014 did this much more accurately as far as 37 km (M43 in their coords) up the south branch for 2009-13. They see unmistakable acceleration as far as as 20 km from the calving front (M26).

Various explanations have been put forward but I expect the physics here to be resolved by September (which will trickle down to us via a Feb 2015 journal article). That will allow future discharge of Jakobshavn Isbrae to be modeled better than today.

However that model won't be applicable to any other glacier in Greenland as the others lack the overdeepened bed channel. In some ways, GRACE trending (mass balance from gravity) may provide the best overall view of Greenland's total contribution to sea level rise.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 12, 2014, 05:26:38 PM
The two animations below illustrate (imperfectly) certain aspects of surface ice flow on Jakobshavn Isbrae.

The first imagines lines of red and yellow traffic cones laid out in 20 lines perpendicular to main channel by an unpaid intern. These lines progress over a calendar year towards the calving front in proportion to the velocity of their spot.

The velocity increases monotonically closer to the calving front, so from the perspective of a line (lagrangian coords), the faster ones in front are getting farther away whereas the slower ones upstream are falling farther back. The animation does capture that but not very noticeably.

The second animation is similar but also displays the effect of slow-down along the edges. This has the effect of making an initial line of ice more and more convex over time because its center moves more rapidly. The motion illustrated is only heuristic -- not tied quantitatively to the actual data of Joachin et al -- though I did bake in some acceleration using milliseconds of frame delay.

Neither animation captures the seasonality of motion nor the year-to-year acceleration of this motion. While the glacier is fast throughout the year, it moves even faster during the summer months. It would be possible to display the motion accurately but not by the methods I have been using.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 12, 2014, 06:19:40 PM
Great work A-Team and very illustrating.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 13, 2014, 02:39:07 AM
Most unexpectedly, LC80 81 233 2014 192 LGN00_B8 arrived today at EarthExplorer -- and it is a crisp cloud-free beauty. We have not seen anything from satellite path 81 before.

Perhaps the reason is Jakobshavn is usually in the dark at the time of flyover; this photo was taken close to midnight (23:53:59) with the sun only 8.4º above the horizon at an azimuth of -46.8º (ccw from due north).

The illumination gives fantastic shadow relief to an otherwise flat landscape. In fact, with a cosine or two, you could figure out surface heights at the edge of the north channel (which is really an icefall at this point; its depression is more like a tarn than a melt lake).

There has been some calving along the NE edge of the front and it looks like this will continue. I won't belabor the comparison to earlier dates since we just did that yesterday for the 10 July and earlier images. To spare people the gigabyte download and 16 bit processing, I have attached the calving front from the 15 m panchromatic.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 13, 2014, 03:02:24 AM
Here is the shadow situation on the north branch. It sheds light on the melt lake/tarn/nunatak feature we discussed previously.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 14, 2014, 01:17:36 AM
"It doesn't get any better than this" --  the guys are running low at beer camp but just then the swedish bikini team drops by. https://www.youtube.com/watch?v=LtnMtrEB1-I (https://www.youtube.com/watch?v=LtnMtrEB1-I)

Oh yes it does, a lot better. Despite an incomprehensible file navigation system, I eventually stumbled across the Cresis folder containing the P3 radar echoes overflights of Jakobshavn Isbrae for 04 Apr 13. And, make my day, they allowed anonymous guest/password ftp download (201 files).

ftp://data.cresis.ku.edu/data/rds/2013_Greenland_P3/images/20130404_02/ (http://ftp://data.cresis.ku.edu/data/rds/2013_Greenland_P3/images/20130404_02/)

The map in the upper right shows the flight lines: 6-7 transects plus one straight up the channel! These flight lines are also provided as a satellite image overlay.

The flight lines are slightly kattywumpus (not perpendicular to flow lines) so rotation and rescaling of the sat photo is necessary to see what the echogram refers to on the ground (though it also gives coords). The dotted orange rectangle shows this correspondence more or less worked out for the one I tried.

Cresis provides both a raw radar return and an annotated version called echo_picks where someone competent to interpret the data has colored in certain boundary lines. (Actually there is phenomenal software that can do this; I took a pass at this myself with PovRay relief, bottom.)

The example below has two such lines (purple and red) plus an intermediate line that for some unexplained reason is not deemed of interest. I'm guessing that the lines show the ice surface (omitting snow cover), water pockets, a Wisconsonan/Holocene transition, temperate ice, bedrock and side scatter from hills and walls.

The stratifications are rather minimal compared to the deformation drama up at Petermann. However the radar return is measuring dielectric permittivity which can amount to water content which can amount to critical rheological properties of intermediate ice filling the Jabobshavn channel.

So if you came for the bedrock, stay for the stratifications. They provide the natural coordinate system for any serious modeling of this glacier's behavior.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 14, 2014, 05:33:10 AM
A-Team you are really digging into those hidden x-files? Did you stumble over the Swedish Bikini team too? ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 14, 2014, 05:14:45 PM
Not yet, Espen. I'm hoping to get more people engaged in these files now that the football tournament is over (though there is always some other sport to replace it).

I'll post a couple rounds of Cresis profile analysis specific to Jakobshavn Isbrae here but if there's interest, start a separate forum section for ice-penetrating radar, a huge deal in Greenland and Antarctic and critical to Arctic Ocean ice thickness measurement validation (ie volume).

These profiles, in my view, are seriously under-interpreted and in some cases like Petermann Glacier, demonstrably mis-interpreted. The intermediate stratifications and their deformation are exceedingly important to ice sheet history and flow properties; it is not enough simply to read off surface elevations and bedrock depths if the goal is estimating future sea level rise attributable to Greenland by prioritizing to the fastest marine outlet glaciers.

After visiting numerous dead '404' urls, I did eventually find a 'FAQ' among the read-me Cresis files. It did not have any examples of annotated profile features but did explain their rather redundant data storage system and contained some interesting factoids about ice-penetrating radar.

<url>ftp://data.cresis.ku.edu/data/rds/rds_readme.pdf (http://ftp://data.cresis.ku.edu/data/rds/rds_readme.pdf)</url>

The first thing to understand is Cresis uses MatLab formats but you probably do not: $2250 per individual license, $149 for home. The home use license does not include government, academic, commercial, or other organizational use (blog?).

There'd be a learning curve: "MATLAB is a high-level language and interactive environment for numerical computation, visualization, and programming. Using MATLAB, you can analyze data, develop algorithms, and create models and applications." <url>http://www.mathworks.com/products/matlab/ (http://www.mathworks.com/products/matlab/)</url>

However, the data is also available as desktop-readable triples of track location maps (file names ending in _0maps.jpg), radar return profiles (_1echo.jpg), and interpreted tracks (_2echo_picks.jpg). The latter are 'manually driven processes' where a trained individual marks up surface and bottom reflections with purple and red lines respectively. (However bedrock cannot always be located for the Jakobshavn gorge.)

Those depths are captured into excel-readable cvs numerical format. Of the 9 columns, 5 are useful (lat, lon, surface, bottom, elevation), 1 is easily derived (thick = surface - bottom), and 4 can be deleted. Cresis data is carried to excessive precision -- surely the bedrock is not really measured to centimeter accuracy as numbers like 2087.12 suggest. And surely latitude is not usefully measured to 6 decimal points (0.11 m) when profiles show 5 m precision (see below and <url>https://gis.stackexchange.com/questions/8650/how-to-measure-the-accuracy-of-latitude-and-longitude (https://gis.stackexchange.com/questions/8650/how-to-measure-the-accuracy-of-latitude-and-longitude)</url>

The 15 years of flight have generated a lot of files. After drilling down to Greenland, look for the Jakobshavn Isbrae specific folders such as 09_01 (transects) and 09_02 (tracks along the icestream) for the given date, here Apr 14. Each profile covers 50 km, so just two profiles suffice for the Jakobshavn gorge.

The internal dimension of profile jpegs is 931 x 734 pixels (in the example examined). The width is variable but for a 49.91 km transect, the 1 x 734 vertical slices are spaced at 53.6 meters which represents a resolution of 75 points to characterize bedrock topography for a 4 km wide gorge. A buried nunatak or pothole of smaller dimension might still be recognized by combining data from different years as the bedrock doesn't change year to year and the flight lines would be slightly different.

The depth is not measured directly but rather return time of a radar pulse (microseconds of propagation delay). Under the assumption of 3.15 dielectric  for ice -- not applicable to snow, firn, englacial pockets, or wet temperate ice -- the depth is then calculated using the speed of electromagnetic radiation in a medium of refractive index sq rt (3.15), or 168,913,914 m/s instead of the usual 299,792,458 m/s.

The depth scale range has to vary from scene to scene to accommodate top elevation and bedrock depth. In the example I looked at, 2000 vertical meters was represented by 369 pixels for a resolution of 5.4 meters. This scale seems to be consistent, only modified by offsets.

Cresis also offers kml (Google Earth) files for the track segments. I found these convenient for precisely co-registering track profiles via their lat,lon coordinates to Landsat images. Simply mouse along the track to find the exact lat,lon of a radar reflection column. This is otherwise problematic because the icestream channel curves quite a bit. I found a way to lay down a precise grid in Gimp and will post that shortly.

For the two along-gorge, west to east flight lines of April 2014 (which may overlap slightly rather than butt up end-to-front), go to ftp://data.cresis.ku.edu/data/rds/, (http://ftp://data.cresis.ku.edu/data/rds/,) open 2014_Greenland_P3/images_csarp-combined/ and append:

20140409_02/20140409_02_004_0maps.jpg
20140409_02/20140409_02_004_1echo.jpg
20140409_02/20140409_02_004_2echo_picks.jpg

20140409_02/20140409_02_005_0maps.jpg
20140409_02/20140409_02_005_1echo.jpg
20140409_02/20140409_02_005_2echo_picks.jpg

For the seven cross-gorge transects (some require a north/south pair) in west to east order of April 2014, append:

20140409_01/20140409_01_022_0maps.jpg N
20140409_01/20140409_01_021_0maps.jpg S
20140409_01/20140409_01_019_0maps.jpg
20140409_01/20140409_01_017_0maps.jpg N
20140409_01/20140409_01_016_0maps.jpg S
20140409_01/20140409_01_014_0maps.jpg
20140409_01/20140409_01_012_0maps.jpg N
20140409_01/20140409_01_011_0maps.jpg S
20140409_01/20140409_01_009_0maps.jpg
20140409_01/20140409_01_006_0maps.jpg

The data go back quite a few years (to 1993 for Jakobshavn) and involve other aircraft and other radars. It is not trivial to commingle older with newer data but there may be some value to it.

I've attached the 2014 flight line that goes under the calving front -- note the intriguing structure approximately at the first sill.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 14, 2014, 10:31:45 PM
""I'm hoping to get more people engaged in these files now that the football tournament is over (though there is always some other sport to replace it).""


A-Team I understand your frustrations, it would be nice to see you and other capable people work together and get some of the many results I expect are hidden in the those files!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 15, 2014, 06:36:51 PM
Here is the latitude, longitude grid for the area at 30 m resolution in Landsat-8 projection. This is necessary in order to accurately geo-locate ice penetrating radar transects and up-channel flight tracks. I'll post the 15 m channel-only coords over on the Landsat/bedrock forum.

There is plenty of opportunity for error in doing this so the first image outlines how this is done -- pick two fixed rocks whose coordinates can be accurately determined from google earth's very high resolution digiglobe photo. These rocks must also have good vertical and horizontal separation.

Next, choose a grid cell that has easy-to-remember digital lat,lon coordinates and grid spacing favorable to the overall map scale. Note the latitude increments by 0.01 abut the longitude by 0.02. These can be converted into x,y pixel coordinates by considerations of proportionality. The grid itself is drawn in gimp using a deeply buried command, Filters -> Render -> Pattern -> Grid.

Next up: geo-locate some Cresis stratification profiles on our preferred surface imagery and bedrock DEM.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 16, 2014, 04:29:37 AM
Isostatic rebound comes up on the forum from time to time; I came across this recent account specific to the south branch of Jakobshavn Isbrae. The figure shows glacial thinning (Hoehenrate) is on the order of -5 m per year whereas mantle rebound is less than 20 mm per year, centered of course right under the area of mass balance loss. That's a factor of 250.

Upper left shows glacial velocity near the calving front in 2010 was markedly slower towards the sides but pushing 50 m/day towards the center. Upper right shows the region lifted up by tides; at that time, the glacier had a floating tongue.

http://public.beuth-hochschule.de/~korth/GROENLAND/Texte/zfv_2013_1_Dietrich_et-al.pdf (http://public.beuth-hochschule.de/~korth/GROENLAND/Texte/zfv_2013_1_Dietrich_et-al.pdf)

I also found some excellent videos of the fjord and calving front -- take the helicopter tour to save yourself a bucketful of euros:

August, 2012 Jakobshavn calving event (different  from Chasing Ice)
https://www.youtube.com/watch?v=OtBQHF4f6fw (https://www.youtube.com/watch?v=OtBQHF4f6fw)

‪Helikoptertur fra Sermeq Kujalleq til Illulissat‬
https://www.youtube.com/watch?v=PT12yqepn3Q (https://www.youtube.com/watch?v=PT12yqepn3Q)

‪Jakobshavn Glacier POV Helicopter Ride‬
https://www.youtube.com/watch?v=PnDFGSZcDt8 (https://www.youtube.com/watch?v=PnDFGSZcDt8)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on July 16, 2014, 03:03:26 PM
However that model won't be applicable to any other glacier in Greenland as the others lack the overdeepened bed channel. In some ways, GRACE trending (mass balance from gravity) may provide the best overall view of Greenland's total contribution to sea level rise.
Repeat-pass altimetry provides a much higher resolution and reaches pretty close to the margin, so I'd combine the two.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 16, 2014, 07:32:04 PM
The Grace satellite pair is way beyond its design lifetime and had a power outage for a chunk of last summer. Some say they are flying too high for ideal resolution at the scale of Greenland but that Goce can fix that (after a couple more years of data).

Those altimeter measurements are useful for sure. But what exactly are they measuring, surface height of the snow? That would be problematic for mass balance, because the density profile of snow through firn to ice needs to be known. This density could vary significantly depending on depositional and compaction history and water content from melt or rain-on-snow events. Modelling it however might reduce the error to insignificance.

Maps like the one above go beyond determination of overall Greenland mass balance loss -- they seek
to map where that is occurring. That is not needed for sea level rise contribution.

Errors in localization have recently been refined by replacing Grace spherical harmonics expansion to order 60 with Slepian functions. I reviewed this somewhere on the ASIF last year, proposing cylindrical coords for Greenland plus  cylindrical Slepians, the counterpart to Bessel functions, to maybe refine mapping resolution.

That Dec 2012 PNAS paper has free access. I have not had a chance to follow up on the 12 subsequent articles that cite it. In terms of extrapolating mass loss forward in time, that could be done by simple-minded trending or by separately modelling identified main contributors such as Jakobshavn and 3-4 others.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3523835/ (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3523835/)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 17, 2014, 12:27:14 AM
Anyone see any interferometric SAR images on the internet for Jakobshavn? Or for that matter any ESA Sentinel-1 radar images besides the one we have for Epiq?

They have fringes like the one for Petermann glacier below. To some extent on Jakobshavn, the neighboring ice sheet has been entrained by the main high velocity icestream. The crevasse fields (second image, wavelet transform) indicate strain to the extent they depart from gravitational flow (orthogonality to DEM contours). Note SAR velocity fields are projected onto the x,y plane whereas actual movement includes a vertical (z) component.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 17, 2014, 04:37:04 PM
Three new Landsat images were just posted. I'm not sure what caused the five day holdup on the 12 July pair nor for that matter why the 17 July arrived on 17 July. It takes a while to download these giant packages and process them into 8 bit but I have high hopes that something interesting can be done with the near-simultaneous stereo pair. If not, ponder why annual net calving front retreat ~1 km is slightly less than annual glacial advance ~12 km.

Scene   #Day   Day   Mon   Year   Path   Row   Clarity

LC80842322014198LGN00   198   17   Jul   14   84   232   dark + cutoff
LC80080122014193LGN01   193   12   Jul   14   8   12   excellent
LC80080112014193LGN01   193   12   Jul   14   8   11   excellent
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 17, 2014, 07:27:04 PM
A-Team those July 17 images do not include the calving zone?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 17, 2014, 09:59:14 PM
Yes and no. LC80 84 232 2014198LGN00 normally contains an oblique slice of about the SW third of the calving front, not enough really. It's obscured by clouds anyway. It looks to me like the next Landsats are not due until July 24 and July 26th (two). Modis has some clear recent days and is not showing anything dramatic.

It looks like NASA/USGS had some colossal processing pipeline error, possibly involving many terabytes of imagery that had to be re-worked, hence the weeklong snafu.

One of the images today from 11 July had to be rotated 5.6º, probably a sign that it is still in stereographic pj rather than UTM W zone 22. I will write them to get this fixed.

From the metadata files, it appears that path 8, row 11 and path 8, row 12 are taken a mere 24 seconds apart (center of scene time). From the lat,lon distance calculation on the nadirs, the satellite had moved 162 km over the ground. It is 709 km up. A hasty calculation,  2DEGREES(ASIN(82/709)) in the flat earth approximation gives an angular separation of 13.3º for stereo viewing. However there's very little relief on that landscape.

 
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Steve Bloom on July 18, 2014, 12:22:23 AM
A-Team, I'd been wondering about the reconciliation of GRACE and GOCE data as a general matter, but note that GOCE was toast as of last November.  I'll check for any recent pubs and maybe also ask Dumb Scientist about it.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 18, 2014, 01:41:37 AM
Steve,

I got this from an open access article in J. Geod. Sci. 2014; 4:8–18 DOI 10.2478/jogs-2014-0001
M. Herceg, C. C. Tscherning, and J. F. Levinsen
Sensitivity of Goce gradients on Greenland mass variation and changes in ice topography

"...Establishing the presence of an acceleration on the order of magnitude found in the Greenland Ice Sheet requires more than 5 years of data, and we find that the GRACE time series available are now long enough to establish the presence of such an acceleration. Maximally four years of reprocessed GOCE gradient observations will to be available by mid-2014, which may add the supplement GRACE derived solution for mass changes..."

"...The largest accelerations have been observed by the Helheim glacier, Kangerdlugssuaq and Jakobshavn Isbræ"

"...There is hope for future GOCE data acquisitions to be able to further our understanding of mass changes using gravity gradients and gradient anomalies. We expect maximally four years of GOCE gradient observations to be available at the middle of 2014. Furthermore, lowering of the GOCE satellite down to an orbit of 235 km will increase the accuracy and spatial resolution of the measurements. This may then lead to the accuracy needed in order to ob- serve ice mass changes using the GOCE gravity gradients."

"A new GOCE-type mission, with improved accuracy, will undoubtedly provide the possibility to detect areas of mass gain or losses over short time periods."

Sounds like a 'new' mission would indeed be needed if the old one went kaput before mission accomplished.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 18, 2014, 04:06:01 PM
I looked further into the Jakobshavn Isbrae upchannel P3 flight track of 2014. The primary purpose may have been to measure ice surface for purposes of determining thinning relative to previous years; the particular radar configuration did not seem to detect the bedrock layer (or at least that was not 'picked' as it was in other series).

The data comes in the form of an overview map at three levels of resolution, the ice-penetrating radar scan itself with and without a dashed purple surface line, an excel-type file that has elevations for the surface (and mysteriously for bedrock) and so a column for total ice thickness, and a kml file that overlays the track on Google Earth satellite imagery of Nov 2010.

I sought to tile consecutive segments of the flight path. Each segment covers 50 km so only two were needed to get 100 km up the channel (in curved channel coordinates). I soon discovered the radar scans did not use the same vertical scale. Neither did the flight line depictions, which ill-advisedly used a poor quality satellite image from the 1990's at too low a scale.

The image below has rescaled all this to match plus patched in yesterday's Landsat under the flight path and brought way down to 700 px width to fit on this page. The correspondence is not perfect because of the difficulty in stretching the satellite imagery out to linearize the track -- though this can be done in gimp using a piecewise linear cage transform using the 1 km mileposts I marked out in an earlier image.

The alternative is to use the lat,lon scale (which is not flat, as a coord system for the globe) but as noted above Landsat imagery uses mercator UTM zone 22 W meters which conveniently scale to 15 or 30 m Landsat pixels.

The ice-penetrating radar shows some deeper structures just beyond the calving front and stratification layers below the ice surface way upchannel that probably continue to the summit ridge (and probably improve along the way). I have not yet located the flight scenes that would allow tiling to the summit.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 19, 2014, 02:08:53 AM
The red path in the first image follows a glacier flowline. Most published data on Jakobshavn Isbrae uses distances measured along such a path as coordinate system. It takes something to get a glacier to deviate from straight line flow so unsurprisingly this path can be described quite well with a small number (8) straight segments over ~100 km.

The second image 'straightens out' the ice stream. I did this by placing vertical guides at the breakpoints, using the guillotine command in Gimp to get 8 image pieces, sheared each separately in the vertical direction until the red line was horizontal, joined the pieces aligning to the red segments, and then rescaled by the ratio of total segment length to width of a horizontal line in the original. The blue line still carries the original channel contour, just inverted.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 19, 2014, 04:17:34 PM
Land of the midnight sun ... an unexpected but most welcome midnight Landsat image of the calving front in action. It has been 8-9 days since we last got a good look at it.

LC80822332014200LGN00 19 July 14
Path,row = 82,233  Band 8 at 7.5 m
Cloud Cover = 4.9%
Sun Azimuth = -47.3
Sun Elevation = 7.4
Local Time = 00:00:11
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 19, 2014, 04:32:35 PM
Same Landsat image, north branch. These low angle scenes provide good shadows. This is more of a cliff-hanger ice sheet situation than icestream. The tarn we discussed above is not much of a lake at this resolution. I am not seeing any exposed rock in center scene; though something is causing the large dimple just NE of the tarn, it could be at considerable depth. We may find out this season.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 19, 2014, 05:25:16 PM
A-Team, nice shot! I wonder what is the height of that cliff? It must be far above the average around the calving area?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 19, 2014, 10:16:34 PM
Espen, it is hard to pinpoint what exactly is casting the shadows. I did calculate the heights of two peaks and the saddle between them as 261, 205, and 220 meters above sea level. Here I had to triple check that Landsat-8 uses negative azimuths if ccw of true north before tracing shadow peaks back according to sun position.

The sun is above the horizon but the angle is low at 7.415º so the shadows are long. This has conspired with azimuth to shine through the pass while casting long but not too long shadows on sea ice. This method does not provide a height for the white calving front which must have horizontal extent because it would just project as a line if a vertical cliff because the scene is fully nadir.

I don't know what will be left of this by mid-September ... retreat has entered new territory. However the north branch is not currently a large contributor to ice volume discharge in the larger scheme of things (south branch). Its disappearance would perhaps give some general Greenland ice sheet a better route to the sea. The potential drainage basin is small though.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on July 20, 2014, 12:39:58 AM
A-Team....

Beautiful image of the north branch.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 20, 2014, 02:12:48 AM
Yes, these low angle shots on clear days are so photo-realistic that what I labelled the hypotenuses from shadow tip to top of mtn above really should have been the base line pixel measurements that continue at sea level underneath it. So should have used tangent as this is strictly a down-looking satellite (roll angle parameter negligible per metadata).

As luck would have it, sin/cos ~ tan for low angles as cos ~1. So it makes only a tiny difference, ~ another 1-2m in heights, the tallest now being 263 m (more impressive as 863 feet).

The comparison below with 03 Jul 14 (LC80090112014184LGN00_B8) -- which I'm pretty sure are correctly co-registered despite appearances -- shows most of the recession action in the last two weeks has been to the northwest corner of the bay, a more conventional undimpled, simply-crevassed glacier that creeps into the bay without a perceptible cliff.

It would be better here to find an earlier one with a similar sun angle -- I'm updating my Landsat database to include azimuth, sun angle and time of day columns now that I see their utility.

The north branch, after you get past everyone pooh-poohing its significance, is actually quite instructive.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 20, 2014, 02:14:52 AM
Grrrr! Click above to animate. I couldn't clip to 700 pixels without losing natural Landsat scale. The blog software won't animate above this width.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 20, 2014, 03:21:02 AM
This is a totally amazing image for its clarity and relief ... more to come for newly revealed ice wave structures to the east. Below, just the height of Big Berg out in the fjord:

100.5   m: height above sea level by shadow measurement
904.8   m: height below assuming 90% of height is below sea level (ie mass uniformly distributed)
1005.4 m: total height, again assuming first height is representative of mass above sea level
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 20, 2014, 04:51:00 AM
As reported by A-Team above most action is now at the northern branch, the southern branch is in a healing mood:

Please click on the image to start the animation!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: solartim27 on July 20, 2014, 08:02:33 AM
I think the rapid advancement of the calving face just means the bottom of the ice sheet upstream is well lubed by melt water.  I wouldn't call that healing. ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 20, 2014, 10:28:24 AM
And I wonder what happened in that dimple/tarn was it emptied?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 20, 2014, 03:15:47 PM
Looking at the larger picture, there sure are a lot of mid-elevation melt lakes right now. As they fill and overflow to some extent, extensive linear water features are appearing, I suppose ending in draining moulins.

However it's not clear that very many of these drain to the bedrock bottom of Jakobshavn Icebrae, and if they do, whether that ends up as lubricating sheet flow or simply as water coursing down well-established tunnels.

Quite a few other mechanisms have been put forward to explain the moderate seasonality of terminal velocity, among them reduction in back pressure at the calving front from fjord melange (bergs in frozen sea ice).

The speedup is well underway by the first of June, even mid-May in some years, as shown in Fig.2 of Joachin 2014. Moulin meltwater may contribute later on but cannot really be a factor this early in the season.

The calving front position is not a proxy for the rate of ice volume discharge. That is determined solely by ice stream velocity and thickness because sooner or later ice that has surged forward will calve off. Sea level rise -- that is end game here, not JI as a kantian Ding an Sich.

However, as Steve B pointed out a month back, retreat of the calving position  is still significant because it reduces back pressure on the ice stream itself (especially at curves) and side pressure limiting Greenland ice sheet discharge into the ice stream track, the consequences of both being faster volumetric discharge.

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 20, 2014, 03:54:43 PM
I will soon show you a giant melt water lake, that gets emptied now and then, just waiting for August and the right image. The lake is about 4 - 5 km2 and pretty deep, with a rocky bottom.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 20, 2014, 04:08:49 PM
That incredible low angle image yesterday with perfect shadows got me motivated to find the others. It is quite convenient to get Landsat metadata in bulk at http://landsat.usgs.gov/consumer.php (http://landsat.usgs.gov/consumer.php) and then sort through the nuisance xml (that nothing can parse) to find the low sun angle scenes. Discarding the cloudy ones over JI gives the table below for 2014. Snow cover can be an issue with earlier dates.

I've attached a region flanking the upper ice stream where shadowing contrast reveals adjacent ice sheet to the north being seriously distorted by the out-competing ice stream. Note too the subtle ribbing farther up. It looks to me like much older relic features are being over-written but not quite obliterated by the strain rate tensor operative in more recent years.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on July 20, 2014, 04:10:24 PM
It seems that the linear water features around the larger melt lakes are feeding water to the lakes rather than draining them. Is there a way to determine elevation in this area? My guess is the lakes are lower in elevation and  the linear features are melt streams that are feeding them.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 20, 2014, 04:16:28 PM
That incredible low angle image yesterday with perfect shadows got me motivated to find the others. It is quite convenient to get Landsat metadata in bulk at http://landsat.usgs.gov/consumer.php (http://landsat.usgs.gov/consumer.php) and then sort through the nuisance xml (that nothing can parse) to find the low sun angle scenes. Discarding the cloudy ones over JI gives the table below for 2014. Snow cover can be an issue with earlier dates.

I've attached a region flanking the upper ice stream where shadowing contrast reveals adjacent ice sheet to the north being seriously distorted by the out-competing ice stream. Note too the subtle ribbing farther up. It looks to me like much older relic features are being over-written but not quite obliterated by the strain rate tensor operative in more recent years.

Yes A-Team yes you got yourself stocked with a lot of work, be careful with the PCs energy consumption! ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 20, 2014, 07:49:41 PM
"Yes A-Team yes you got yourself stocked with a lot of work, be careful with the PCs energy consumption!"

I wouldn't be surprised if the internet police busted down the door for too many gigabyte Geotiff downloads.

"I will soon show you a giant melt water lake, that gets emptied now and then, just waiting for August and the right image. The lake is about 4 - 5 km2 and pretty deep, with a rocky bottom."

Excellent spotting. The Landsat-8's from last year were so spotty and August so cloudy, I couldn't find a good photo. Google map is showing bottomless pits and strange distributories to the west of JI (did not chase down photo date).

"It seems that the linear water features around the larger melt lakes are feeding water to the lakes rather than draining them. Is there a way to determine elevation in this area?"

Nice suggestion, though the lakes are forming weeks before the linear features. Could be some of both. The Greenland DEM is 'out there' to cm accuracy somewhere on the internet but not necessarily co-registered with our high resolution imagery.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 20, 2014, 08:06:44 PM
Here is another feature from digiglobe hi res, to the east and slightly to the north of the end of the south branch of the JI. The drainage here shows a couple of things going on, including streamlets seemingly confined to linear troughs of ice compression waves. The surface is so flat that the slightest change in elevation can give rise to extended, complex water features.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 20, 2014, 08:16:00 PM
A-Team that melt water lake I mentioned above, is far up north!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 21, 2014, 02:11:35 AM
See down to rocks in a glacial lake? Way up north on coast maybe, not at JI.

Here is transect through Jakobshavn south branch from the Greenland divide ridge down to the sea via the sole experimental channel borehole:1989, Iken B. It depicts bedrock depth (do I believe interior sea level bedrock depiction?), ice thickness, ice temperature profile, and if you look closely the layer of seriously less viscous temperate ice. 2011 ppt from Kristin Poinar, dissertation due out this Sept.

http://students.washington.edu/kpoinar/Presentations/jakobshavn_temperateice_GCC4.pptx (http://students.washington.edu/kpoinar/Presentations/jakobshavn_temperateice_GCC4.pptx)

I also came across the original incredibly sharp image of the N and S calving area acquired by Worldview-2 on 16 Jul 11, apparently mislabeled at google earth as 10 Nov 10. The scale is not provided but may be in feet (1 pixel = 15') rather than meters. In any event, way nicer than anything being kicked out by Landsat. Looks better with grayscale inverted -- north branch calving area shown.

http://eoimages.gsfc.nasa.gov/images/imagerecords/76000/76590/jakobshavn_wv2_2011197_lrg.jpg (http://eoimages.gsfc.nasa.gov/images/imagerecords/76000/76590/jakobshavn_wv2_2011197_lrg.jpg)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 21, 2014, 02:14:52 AM
Grrrr. Forum software took it upon itself to make a crummy compression of the image (why provide scroll bars then not really use?). Click to really see it.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Rubikscube on July 21, 2014, 01:09:34 PM
(do I believe interior sea level bedrock depiction?)

No, you do not, or rather, you should not. The newest topography maps (posted by SH further up the thread) clearly shows that the southern branch continue below sea level for several hundred kilometers inland. Unfortunately all the detailed topography maps for JI that I know of (perhaps I have not looked hard enough) end shortly after the 1000+ overdeepening ends and where the southern branch splits into two (arguably three).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 21, 2014, 03:09:41 PM
Not to worry R, I don't plan to scrape surface and bedrock depths from Bamber 2013 when the whole intermediate ice stratification profile and its transects can be assembled from Cresis. But where did Poinar get the temperature profile? NEEM is way to the north, GISP, GRIP, and NGRIP are old hat and not at the divide on the 69º latitude of JI. Just heuristic I suppose, but what does that say about the modeling that comes off of it.

GISP     65°N 43°W  2037 m
GRIP     72°N 37°W  3028 m
NGRIP   75°N 42°W  2917 m
NEEM    77°N 51°W  2537 m

More not to worry for Espen about "stocking myself with a lot of work". The answer is multi-tasking. Consider 8 small researches @ 4 hours each = 32 hours/week. Fine, not allowed under EU work rules. However with multi-tasking, 8 x 4 still = 4. I think you see the savings?

Recent acceleration of Jakobshavn Isbrae is well-described but not understood. That situation won't last.

The sticking point is not so much the second invariant of a deviatoric strain tensor but rather Newton's first two laws of motion (resp. Euler's deformable rigid bodies, Cauchy's continuum mechanics).

That is, people largely bought into warming of Baffin Bay, turbulent warming at the calving front, loss of ice tongue and melange back pressure and unblocking of north branch fjord side pressure. That caused the south branch to accelerate. However that's a one-off effect yet the acceleration continues, seemingly without a force.

I am reminded of a recent trip getting stuck behind a carload of foreigners on the Grand Canyon south rim, who would repeatedly brake sharply to see a view or photograph a squirrel, then accelerate off abruptly as the driver recalled the midnight flight home from Vegas, with Bryce and Zion yet to do.

As car #2, I had to slow down and speed up the whole while because I could not pass nor reach the AK-47 in the back seat. Car #3 could not see car #1 so had to brake and speed according to car #2. And so on, back to the trading post back on the Navajo res.

Seen from a satellite, this amounts to a wave train moving backwards and dissipating as it goes. The counterpart at JI is then the seasonal cycle at Baffin Bay and fjord slowly propagating up the main ice stream, continuing even as the driving mechanism recedes into irrelevance.

Although dissipating from friction with the ice sheet and its walls, the ensuing heat and softer ice manifest as faster motion of the ice stream under the always-available gravitational force. Under this scenario, the fact that 2013 was actually observed by Joachin 2014 as slower than 2012 is no accident of weather or moulins: it predicts that 2014 etc, while still very fast, will be slower yet as Baffin Bay damps out, rather than be the new normal or a sign of catastrophic accelerations yet to come.

A pity that we cannot determine 2014 surface velocities from Landsat.
https://en.wikipedia.org/wiki/Digital_image_correlation (https://en.wikipedia.org/wiki/Digital_image_correlation)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: SteveMDFP on July 21, 2014, 04:30:52 PM
....
As car #2, I had to slow down and speed up the whole while because I could not pass nor reach the AK-47 in the back seat. 
....

ROFL !!!!  I thoroughly enjoy your posts, as much for the lively language as the technical matters.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Rubikscube on July 23, 2014, 01:43:26 AM
Sweet A-team. I applaud you, Espen and all the other contributing to this section of the forum and I would have loved to help out with the digestion of the massive amounts of data if I had the expertise to do so.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 25, 2014, 03:47:12 PM
Here is one of my better efforts at animation -- for once outdid the Nasa Visualization Lab, a site I mainly study in awe. File size could only be reduced so far (827 kb) without compromising the data so it will likely take a click below to get the animation going.

The data here -- maybe $100k of purchased SAR imagery carefully processed by Rignot 2012 doi:10.1029/2012GL051634 -- is the best we have on overall Greenland ice sheet surface velocities, though higher elevations are still unsatisfactory due to ionospheric disturbances on the same scale as motion and too-long satellite return times.

These velocities range from 1.5 m a year on the summit ridge to 17,000 near the Jakobshavn Isbrae calving front. The animation shows isovelocity contours moving down to the coast. (Technically these are just magnitudes but direction is implied.)

Frame delay is a uniform 100ms; if upper contour movements literally reflected their slow velocities, the animation would take thousands of years to play.

The drainage basins are displayed quite clearly. It looks to me like JI is going to seize catchment from its neighbors over time (for watersheds, called stream piracy). If so, its future contribution to sea level rise has been under-estimated.

If you recall the marching transect animations of lower JI above, those show ~12 km of icestream to be flushed out this  year into the fjord. Ice occupying km 12-20 will be calved off next year. Ice to be flushed in years 3-5 could also be worked out (from a double integral of Joachin's v(x,t) data) but with increasing uncertainty due to coalescence of multiple flows.

The animation here shows the other end of the ice turnover scale. All of Greenland's ice is on the move and always has been, it's just slumping faster now. That's not always apparent when it's replenished by snowfall. The US learned about deformation in a hurry, abandoning Camp Century by Thule in year two; more recently the NEEM drill team came across a doubled-over fold of stratified ice at depth.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: DaddyBFree on July 25, 2014, 04:16:08 PM
Beautiful work A-Team!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on July 25, 2014, 04:23:23 PM
Here is another feature from digiglobe hi res, to the east and slightly to the north of the end of the south branch of the JI. The drainage here shows a couple of things going on, including streamlets seemingly confined to linear troughs of ice compression waves. The surface is so flat that the slightest change in elevation can give rise to extended, complex water features.

It would seem that, once this kind of complex melt driven feature is established on the surface, it would tend to reappear each melt season in this location.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on July 25, 2014, 04:33:32 PM
"The drainage basins are displayed quite clearly. It looks to me like JI is going to seize catchment from its neighbors over time (for watersheds, called stream piracy). If so, its future contribution to sea level rise has been under-estimated."

Stream piracy....I love the image this term creates. It would seem that the underlying topography of Greenland  suggests why this piracy will  take place.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 25, 2014, 06:16:15 PM
Beautiful work A-Team!

Just proud I got him on the the team! ;) ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 25, 2014, 06:18:20 PM
I am studying the melt streams at the moment, but this time the rivers not glaciers!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 26, 2014, 08:19:17 PM
Seems like some serious calving since last Landsat 8 update July 19 2014, but be aware of Modis uncertainty:

 
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 26, 2014, 08:43:24 PM
Below I've tiled eleven consecutive ground-penetrating radar scenes from 2013 that represent an east-west flight line just south of Jakobshavn Isbrae up and slightly over mid-island ridge. These are selected via the kml google earth files Cresis provides.

Quite a few stratifications are easily traceable over the entire 550 km profile. These will have distinct ice fabric and rheological properties and extend as surfaces over huge areas. As isochrons, these surfaces carry a huge amount of information about the deformational and melt history of the Greenland ice sheet.

It is a huge mistake to walk away from these files with just ice-thickness = ice sheet surface - bedrock and toss the stuff in between. The layer surfaces along with z height form the natural modeling coordinate system. Stratification surfaces have the essential physics baked in; coordinates with street smarts can do the heavy lifting. The  x,y,z alternative is just Ptolemy gone polar <url>https://en.wikipedia.org/wiki/Epicycles (https://en.wikipedia.org/wiki/Epicycles)</url>

Tiling takes maybe an hour per 1000 km of flight path because Cresis images do not quite have a uniform width, vertical scale , or overlap even on a single flight. Although it is easily scriptable up to final adjustments, the cross-country files must first be distinguished within a heavy background of grid flights. It is feasible though to work out the whole 3D stratification onion if interpolation works out (left as exercise).

The most useful tracks would start at Jakobshavn and angle right up to a modern bedrock core like NEEM, GRIP, and GISP2. Milcent, Pakitsoq and Crete are lesser known drill sites closer to JI, probably with fewer attributes measured. The steam-drilled holes on JI itself anchor temperature and hydraulics but don't provide ice core stratifications.

The full 550 km profile at original Cresis resolution is rather wide at 10,672 x 656 pixels amd 17.8 Mb for the blog in Gimp xcf format. However as a jpeg at 95% of lossless compression, file size is a more reasonable 2 Mb. However all those pixels still work out to 12.4 feet (3.8 m) of screen width.

If the blog software chokes on this, the original image is online at <url>http://tinyurl.com/na7bxnx (http://tinyurl.com/na7bxnx)</url>. If it works, in-blog scroll bars will provide good panning of the wide image.

I've also attached 700 pixel wide snapshots in decreasing scale. The first is at natural scale but just the first 700 pixels out of the 10,672. The next shows the first 700 of a 2:1 downsampled image; the third 4:1, the fourth is at a 6.5% scale (plus vertical exaggeration) that gets in the whole scene  while maintaining the surface and bottom markups that Cresis annotators put in.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 27, 2014, 01:15:23 AM
Espen, a rather nice Landsat just came in, LC80100112014207LGN00, the path, row 10,11 on day 207 of 26 Jul 14. It's a 3 pm shot with unremarkably azimuths and solar angles, resp 172.9º and 39.7º. (The other one expected for this date, LC80100112014207LGN00 path,row 83,233 is too cloudy.)

I haven't had a chance to really analyze the good one but here it is below. It looks like the south branch is calving so much thick ice that it has completely squeezed out the north branch at its egress, though the discolored streamer (origin unknown) seems to have been entrained in the south branch melange current.

I'm not sure yet what happened to Mr. Big. Seems like it was just the other day that i was measuring his shadow. He may be well down the ford,b over-turned, disintegrated or unrecognizable. However Mr Big II may have taken his place close to the front.

There may be an end-of-season tilt in the balancing act between the glacier coming forward and calving cutting it back. Both are most active in the summer months but their strengths may be differently phased, depending on the year and position relative to the sill.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 27, 2014, 05:25:37 AM
As warned earlier (by Modis https://forum.arctic-sea-ice.net/index.php/topic,154.msg32498.html#msg32498) and indicated by A-Team, Jakobshavn did it again and almost reached the record retreat line set in September 27 2013 in the southern branch, but is now far beyond the prior record retreat line in the northern branch:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 27, 2014, 02:56:23 PM
A dozen Landsats expected between now and the first of September. Half or more will be too cloudy to see the calving front!

LC80 08012 2014 241 LGN00 Aug 29
LC80 08011 2014 241 LGN00 Aug 29
LC80 83233 2014 239 LGN00 Aug 27
LC80 10011 2014 239 LGN00 Aug 27
LC80 09011 2014 232 LGN00 Aug 20
LC80 08012 2014 225 LGN00 Aug 13
LC80 08011 2014 225 LGN00 Aug 13
LC80 83233 2014 223 LGN00 Aug 11
LC80 10011 2014 223 LGN00 Aug 11
LC80 09011 2014 216 LGN00 Aug 04
LC80 08012 2014 209 LGN00 Jul 28
LC80 08011 2014 209 LGN00 Jul 28

Very few clear days for August and September 2013. The animation below compares yesterday with a month later in 2013. Some curious parallels in regards to the north branch.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 27, 2014, 03:03:22 PM
A-Team, that repeating shade in the northern branch could probably be a underground (ice) river outlet?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: mspelto on July 27, 2014, 05:43:26 PM
A Team and Espen excellent work examining the changes in the calving front.  The northern branch cannot be done this summer, the current calving front is too high and the crevassing-rifting behind the front to extreme to be stable.  This area of visible instability does not seem to extend far behind the front at this point.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: DaddyBFree on July 27, 2014, 07:49:39 PM
Is it wildfire smoke that is visible across Greenland from Jakobshavn to Kangerlussuaq today? If so, (the resulting ash/soot) couldn't be good for albedo...
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 27, 2014, 09:48:35 PM
"The northern branch cannot be done this summer, the current calving front is too high and the crevassing-rifting behind the front to extreme to be stable.  This area of visible instability does not seem to extend far behind the front at this point."

Thanks for that analysis. Something like 55 days left yet, relative to last year's maximal retreat of south branch. I've attached a 10 m view from yesterday's panchromatic.

Here are the prospects for animating the north branch for 2014 in terms of cloud-free Landsat. I wonder if a trend is recognizable or the final fall position just remains unpredictable.

1 Jul 26 207 10 11  good 172.9 39.7
1 Jul 19 200 9 11   good 172.8 41.2
1 Jul 19 200 82 233 good -47.3 7.4
1 Jul 12 193 8 11   good 172.9 42.3
1 Jul 11 192 81 233 good -46.8 8.4
1 Jul 10 191 10 11  good 173.0 42.6
1 Jul 03 184 9 11   good 173.3 43.3
1 Jun 24 175 83 233 good -45.7 9.6
1 Jun 10 161 8 12   good 172.6 44.7
1 Jun 10 161 8 11   good 174.8 43.5
1 Jun 08 159 10 11  good 174.9 43.2
0 Jun 01 152 9 11   good 175.3 42.6
0 May 09 129 8 12   good 173.7 39.2
0 May 09 129 8 11   good 175.7 37.9
0 May 07 127 10 11  good 175.7 37.4
0 Apr 21 111 10 11  good 175.4 32.4
0 Apr 14 104 9 11   good 175.0 30.0
0 Apr 07 097 8 12   good 172.8 28.7
0 Apr 07 097 8 11   good 174.6 27.4
0 Mar 22 081 8 12   good 171.9 22.4
0 Mar 22 081 8 11   good 173.7 21.2
1 Feb 25 056 9 11   good 172.6 11.4
1 Feb 09 040 9 11   good 172.6 5.78
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 27, 2014, 10:48:02 PM
It turns out to be quite easy to tile Jakobshavn up to all the bigtime drill core sites, three flight lines do it for 2012. Those sites jump out just from kml flight line intersection mazes. Once tied into the grid, radar isochrons can be assigned actual dates and sometimes interpretations using all the work that has been done on the cores.

Those dark lines on radar represent higher radar dielectric returns and do not literally correspond to optically dark annual rings seen in ice cores. At one time, radar stratification was interpreted as volcanic ash layers, then ionic conductivity, oxygen isotope proxy, then Schmidt ice fabric diagram correlates, Eemian, Wisconsian, hard/soft ice, and more recently as bottom freeze-up deformations.

There's a very helpful ppt online entitled "Deformation and folds of the basal ice under the Greenland ice sheet" by Dahl-Jensen. Antarctica has more advanced analysis in some ways but check out the orientation tensor ellipsoid's eigenvalue profile of NEEM, slide 37.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: CraigsIsland on July 28, 2014, 07:31:33 AM
Is it wildfire smoke that is visible across Greenland from Jakobshavn to Kangerlussuaq today? If so, (the resulting ash/soot) couldn't be good for albedo...

Yeah appears to be from Canada wildfires. At least it's not methane? Looks so bad and I imagine will increase probabilities of more melt. Amazing looking pictures looking down at the area pic pocked with large melting ponds and grayish swatches of ice being transformed by sunlight and gravity.

Nice work lads (and ladies?)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 28, 2014, 05:09:48 PM
Interesting paper (free) entitled "Wintertime storage of water in buried supraglacial lakes across the Greenland Ice Sheet" that discusses features 90 km east of the Jakobshavn calving feature, notably melt lakes that neither drain through a moulin nor freeze solid during the winter.

Some correspond to surface features, others are only detectable by radar (and not all radar configurations at that). We generally have access to less favorable McCORDS so it would be difficult to locate any trend towards new/larger  supraglacial lakes.

http://www.the-cryosphere-discuss.net/8/3999/2014/tcd-8-3999-2014.pdf (http://www.the-cryosphere-discuss.net/8/3999/2014/tcd-8-3999-2014.pdf)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: CraigsIsland on July 28, 2014, 05:31:33 PM
Thanks A-Team for the fascinating read. Great stuff.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 28, 2014, 06:27:40 PM
Whoa ... melting gone wild in the main ice streams feeding the south branch upstream. This is an oblique midnight Landsat with so little contrast that 16 bit processing could barely rescue it: LC80080122014209LGN00 28 July 2014 azimuth -47.9º and sun angle 5.7º.

There is a whole lot more going on than can be displayed in a reasonably sized file. The two images below show more or less the same region with the first at 15 m scale and the second 60 m.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 28, 2014, 06:40:48 PM
Here are the north and south branches from today. Some changes are evident but it may not warrant a full-on comparison with yesterday. The resolution has been slightly upsampled from the original panchromatic 15 m.

There is a new drone paper out from Jason Box and colleagues on the Store Glacier just to the north of JI. It has some interesting new techniques for monitoring calving fronts, among them extracting crevasses by subtracting an original image from its gaussian blur. I will try that for Jakobshavn with one of our better-lit obliques. The crevasses in their zone 4 were mostly filled with water, though that was not determinative of calving.

http://www.the-cryosphere-discuss.net/8/2243/2014/tcd-8-2243-2014.html (http://www.the-cryosphere-discuss.net/8/2243/2014/tcd-8-2243-2014.html)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 28, 2014, 08:25:59 PM
Be aware it is Modis only, but it looks like some more southern branch calving between July 27 and 28:

False alarm Landsat just showed different!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 29, 2014, 12:18:07 AM
Somebody quick, Heimlich manoeuver -- I am choking on the crevasse job those guys did up on Store Glacier.

No, I am not too concerned about the crevasses in Fig.6A either not arriving at the bedrock or continuing well into it (leftmost slice below), though in situ processing won't produce disturbing artifact like this.

Nor am I greatly troubled by the 'difference between image and its gaussian blur' when grain merge would have been better. Subtracting defaults negative numbers to black, differencing takes absolute value to avoid negative grayscales conflating an important distinction; whereas grain merge offsets by 128 thereby centering the resultant histogram losslessly about neutral gray.

However we have to march to a different drummer at Jakobshavn given the large volume of ice discharged. Serious image processing of crevasse fields might start with a fourier transform to determine optimal azimuth for the ideal starting image (which should also be very low sun elevation; LC80822332014200LGN00 does both for JI) and to rationally support subsequent fourier band pass filtering (the high end to clean up speckle). ImageJ and Gimp have the tools, the latter high end donated by David Tschumperlé of CNRS.

After the gaussian blur step pulls out the crevasses from mean field, nothing further can be accomplished dinking with contrast. Instead the best enhancement is probably a bump map (aka height map) lit from the same azimuth (fifth strip below).

That is, we are interested in the orientations, torquing, and widths of crevasse fields relative both to overall and local glacier motions and also in their characteristic spacings (wavelength). Somewhere in there (after due consideration of ice temperature, terrain, velocity, etc etc) lies the explanation of why they are there in the first place.

Imaging processing alone can draw out features not apparent in the original image; at the end of the day, only an experienced glaciologist can read what the crevasse fields are spelling out.

On Jakobshavn Isbrae, the ultimate communicating illustration is perhaps a translucent coloring of each crevasse field with a mouse-over popup providing interpretation; in numerical modeling terms, components of rheology tensors.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 30, 2014, 03:18:46 PM
I looked at one of several approaches to automating internal ice penetrating radar striation finding, that of Patton. This paper  as its example processes an absolutely critical flight line, that between NGRIP and NEEM on 6 May 2011. Those two ice cores have been analyzed for every conceivable parameter, so not only provide precise dates for radar striations (which will not necessarily correspond to visible ice layers) but also clues to why the radar echo is there at all and what the lines mean.

The ice cores thus possess a rather subtle property not initially appreciated, one that forms a coherent hypersurface over a million sq km of Greenland ice sheet in the case of the WHT (Wisconson Holocene Transition). That follows from identification of the WHT down to sea level at FOXX and GULL steam holes (at 515 m and 600 m depths) along a flowline down from Swiss Camp, as well as DUCK right there on the Jakobshavn Isbrae channel.

The key point here is drill holes are points (expensive ones) but radar transects are planar sections whereas Greenland is volume (2.9 million cubic km of ice). We will never have enough drill holes to extrapolate to isochronal hypersurfaces of O18, pH, conductivity, sulfate, methane, beryllium, smoke, ash etc etc. However we do have enough flight lines. Thus correlation of radar striations with ice core dates and properties allows the transects to push out the core properties.

For lower Jakobshavn Isbrae south channel, striations are most evident in the adjacent ice sheet. However seismicity triggered by calving but propagating upstream has been associated with striation overthrusting at the big curve.

The Patton paper begins by clever sharpening of radar striations with a slant gaussian adapted to local slope (discovered by monte carlo sampling of angle to maximal contrast in the fourier transform). That is quite effective (Fig.2-3). The echograms are then processed with contour snakes (ImageJ plugin not used). I found the contiguous color picker in gimp pulls out the same lines with less effort.

Using this, I gave each striation a distinct color in the NGRIP to NEEM product. We'll want this later to color the island-wide hypersurfaces in voxel view and cutaways (plugin --> 3D --> volumeViewer in ImageJ, resp. PovRay). The dark blue line shows an extra just done with the color picker.

The striations on this 423 km track are all continuous so obviously isochrons, but Patton properly verifies this in view of the extreme importance of these two drill sites. Here snowfall and compaction had slightly different histories on NGRIP relative to NEEM so depths and dates had to be cross-correlated (inset below, far right corner), and striations shown to fall on that curve. Which they do, red dots. There is otherwise no interpretation of striation dates in this paper.

Once an overall major striation pattern has been established, its labels can be easily transferred to a new track that doesn't tie in conveniently to NGRIP to NEEM using methods lifted from dendrochronology, tree rings just being annual isochrons wrapped into circles. There, rings on an unknown tree core (~ radar striations on an isolated flight line) are dated by best match to a sliding window (ie convolution) with the fiducial tree ring chronology (itself tiled up like flight lines). That can also be done internally on radar echoes where a striation might be missing for part of the track.

Since only long straight flight lines are really worth processing and unique additions barely run to 10,000 km/yr, I see little point to automation since a given year can be done manually in 20 hours at 500 km/hour. Between the many glitches in data acquisition and bizarre deformations, there has to be a human supervising the process anyway.

I find it exceedingly implausible that glaciologists can add to a field having already undergone 80 years of intensive methodological development (dendrochronology). True,  academics wrote the book on the not-invented-here syndrome so glaciologists can write a new chapter if they choose.

<url>http://www.igsoc.org/annals/55/67/t67A048.pdf (http://www.igsoc.org/annals/55/67/t67A048.pdf)</url>
<url>http://www.igsoc.org/journal/60/222/t13J196.pdf (http://www.igsoc.org/journal/60/222/t13J196.pdf)</url>

The image below is at the original Cresis resolution. It takes 2047 pixels of width to tile up this 423 km flight line as an 877 kb jpeg.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 30, 2014, 04:55:11 PM
You are a tough cookie, A-Team ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 31, 2014, 02:20:28 AM
Espen, there is nothing quite as tasty as a large bowl of low-hanging fruit.

I pulled the raw Cresis radar profiles that go with the recent Swiss Camp drill site article about the Wisconsin-Holocene Transition ice at ~ 600 m into the ice in the vicinity of Jakobshavn north branch. As you can see, that appears associated with a dramatic radar return striation.

https://data.cresis.ku.edu/data/rds/2012_Greenland_P3/images/20120421_01/ (https://data.cresis.ku.edu/data/rds/2012_Greenland_P3/images/20120421_01/)

So not only do we have a definite date for local ice, its hyperplane mesh can be determined from coast to NGRIP-NEEM summit ridge. For that Delauney (~ Voronoi) interpolation can be used, just as they did here for the bedrock grid.

This article "Sustained high basal motion of the Greenland ice sheet revealed by borehole deformation" by C Ryser et al (Journal of Glaciology, Vol. 60, No. 222, 2014 doi: 10.3189/2014JoG13J196) has a lot of interesting detail on the partitioning of surface velocity between deformation and basal sliding. Their study area lies just outside the area of direct dynamic influence of JI.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: AbruptSLR on July 31, 2014, 05:58:50 PM
A-Team,
When you are finished with your bowl of low hanging fruit for the JI, you might be interested in looking at another bowl of low hanging fruit of data for the Thwaites Glacier in the West Antarctic Ice Sheet, WAIS.  In Reply #100 in the "Surge of WAIS Ice Mass Loss" thread (see link below) of the Antarctic folder I posted some of the data from their Antarctic 2012 IceBridge survey for the Thwaites Glacier from two websites that I can no longer access (see following links):

http://forum.arctic-sea-ice.net/index.php/topic,21.100.html (http://forum.arctic-sea-ice.net/index.php/topic,21.100.html)


ftp://n4ftl01u.ecs.nasa.gov/SAN2/ICEBRIDGE_FTP/IRMCR1B_MCORDSxyEcho_v01/2012_AN_NASA/pdf/ (http://ftp://n4ftl01u.ecs.nasa.gov/SAN2/ICEBRIDGE_FTP/IRMCR1B_MCORDSxyEcho_v01/2012_AN_NASA/pdf/)

ftp://n4ftl01u.ecs.nasa.gov/SAN2/ICEBRIDGE/ILATM2.001/ (http://ftp://n4ftl01u.ecs.nasa.gov/SAN2/ICEBRIDGE/ILATM2.001/)

The IceBridge program also provides the following current links to survey data of the Thwaites Glacier:

http://nsidc.org/data/ilatm2 (http://nsidc.org/data/ilatm2)

http://nsidc.org/data/icebridge/index.html (http://nsidc.org/data/icebridge/index.html)

Best,
ASLR
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 01, 2014, 12:46:11 AM
Antarctica makes me sick to the stomach.

Not the WAIS collapse, that had to be coming. However with Abrupt providing a truly superb forum resource, it becomes quite feasible to delve quickly into the details of why and when.

No, it's the graphics. Compare the two below. The first collates all the radar striations that exhibit the Bølling–Allerød transition 14,700 years ago. Fine, a start. But if the Danish government could only give me a krone for every mistake here, I'll not be on a short tourist overflight of the JI calving front -- I'll have enough to buy the helicopter and enjoy a catered ice camp.

Antarctica is totally kicking Greenland's bøtt. Not only did they swipe my idea of bump-mapping the striations a year before I even thought of it, they have miraculously fitted curved vertical radar flight lines onto an elegant bedrock DEM. Which you can rotate, look at upside down or whatever, all with freeware.

Denmark just 5.6 mm people, what can be expected? Well guess what, n.o.b.o.d.y lives in Antarctica.

http://www.antarctica.ac.uk/bas_research/data/access/res/data.php (http://www.antarctica.ac.uk/bas_research/data/access/res/data.php)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: AbruptSLR on August 01, 2014, 02:35:19 AM
A-Team,

Thank you for the link to the British Survey repository.  Your posts on Jakobshavn has inspired me to open a new thread in the Antarctic folder on the internal structure of the Antarctic Ice Sheet (see the link below):

http://forum.arctic-sea-ice.net/index.php/topic,939.0.html (http://forum.arctic-sea-ice.net/index.php/topic,939.0.html)

I will stop intruding on the Greenland folder (which has fascinating discussions, but for which I do not have the time, expertise, or energy to participate appropriately), and I will try expand the information on the new AIS internal structure thread (which I think will become increasingly critical in the Amundsen Sea Embayment marine glaciers in the next few decades).

Best,
ASLR
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 01, 2014, 06:49:21 AM
A-Team yes the Danish involvement in Greenland on all levels, is pathetic! >:(
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on August 01, 2014, 04:33:34 PM
A-Team yes the Danish involvement in Greenland on all levels, is pathetic! >:(

They are focusing on lining up multinationals for exploiting the emerging natural resources.

(I wish this wasn't actually true.)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 01, 2014, 07:46:44 PM
A-Team yes the Danish involvement in Greenland on all levels, is pathetic! >:(

They are focusing on lining up multinationals for exploiting the emerging natural resources.

(I wish this wasn't actually true.)

To be fair, that is a Homerule Authoritys (Greenland "Government") project!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 02, 2014, 02:08:09 PM
Here's a Sentinel-1 SAR-image of Jakobshaven taken on 19.7.2014
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 02, 2014, 02:11:49 PM
Here's a Sentinel-1 SAR-image of Jakobshaven taken on 19.7.2014

Hope they will come up with better resolution?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 02, 2014, 02:55:01 PM
Here's a Sentinel-1 SAR-image of Jakobshaven taken on 19.7.2014
Hope they will come up with better resolution?
Here's a zoom showing individual pixels, the pixel-size is 10m in both range and azimuth. Note that this zoom shows a tiny corner of a 480 megapixel (per polarization) datatake. In other words, S-1 will provide huge area coverage while other SARs should be used when very high resolution is desired.

edit: the cool thing is that starting very soon S-1 will image Jakobshaven twice (ascending and descensing datatakes) every 12 days throughout the year.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 02, 2014, 06:24:35 PM
Nukefix, that is fantastic news. Can you share the link to these Sentinel images ... or does one have to go through a klutzy map search interface?

Here is an awesome image posted by a graduate student ('Spaz') who doesn't even work on Greenland. He used the surf command in MatLab to visualize a 2012 Cresis transect across north central Greenland. The color tinting reflects diminishing return echo power of the radar. The surface is shaded by illumination from above to draw out the layers. The original track data can be found as the file sets 20120507_03, 20120507_04, 20120507_05, and 20120507_06 at the Cresis ftp site.

Greenland is really, really flat. We almost always see it with huge (and unspecified) vertical scale exaggeration. While it does reach a height of  10,551' at Summit (~ GISP2) that takes several hundred km at low gradient to attain. Standing on the surface, it is all but impossible even to see downhill flow lines; other methods had to be used at Foxx/Gull drill sites.

His image has 75x vertical resolution. From it, I made versions with 1x, 5x, and 10x vertical exaggerations. The original  is at <url>http://i.imgur.com/J5oAtH0.jpg (http://i.imgur.com/J5oAtH0.jpg)</url>. The vertical gray pipes are not explained but are possibly NEEM and NEGIS bore holes; I narrowed them and suppressed annoying overlaid text with the cloning tool.

It would make a great deal of sense for Cresis to process every transect flight line in the same manner as Spaz did here and provide the whole collection centrally. And of course the hypersurface story should be updated in real time or at least seasonally with the additional data.

The bottom line here is many isochron striations are easily traced across the entirety of Greenland. This image also refutes published 2014 rubbish to the effect that nothing much has been preserved below the Wisconsin-Holocene Transition at  1.42 kyr.

It's fair to say though, especially in north Greenland, spectacular deformations occur. We know today that many of these are freeze-ups from the bottom at least upstream of Petermann.

Researchers are audibly grumbling about the long-standing obsession with Eemian ice and getting a climate record comparable to the 400 kyr Vostok record in Antarctica. That was never destined to happen because really deep ice is extremely deformed in Greenland -- as we already knew years before NEEM was even drilled. That focus has come at the expense of the mission-critical overall history of the late Pleistocene and Holocene on the Greenland ice sheet.

My question: with hundreds of academic researchers on the Greenland payroll, why do I have to prowl internet blogs for proper workup of the (very expensive) data? These radar overflights began in earnest in 1993.

Click on the image to see full size. It is a beauty.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 02, 2014, 06:38:22 PM
My question: with hundreds of academic researchers on the Greenland payroll, why do I have to prowl internet blogs for proper workup of the (very expensive) data? These radar overflights began in earnest in 1993.

The answer is within your question, I am afraid! ;)

But very nice work again, not sure how many of those mentioned above it is worth, but quite a few!!!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 02, 2014, 07:03:23 PM
Do we know what this is? (red encircled):
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 02, 2014, 08:01:48 PM
Nukefix, that is fantastic news. Can you share the link to these Sentinel images ... or does one have to go through a klutzy map search interface?
It is necessary to go to https://senthub.esa.int/ to do the download. Just draw a rectangle over Greenland and press search. The product in question is:

S1A_IW_GRDH_1SDH_20140719T205102_20140719T205131_001562_001821_F94C

..and the quicklook is here: https://senthub.esa.int/odata/product(239)/Quicklook
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 02, 2014, 10:03:38 PM
Espen, that is a very good question. First thing to do is try to box the features in with nearby tracks to bring their 3D dimensional structure with interpolative range (radar sections being 2D can never fully get to 3D).

That's not impossibly hard with Cresis search though it would be a heck of a lot easier if they replaced what they have with the search code from EarthExplorer. Did I mention that Cresis is totally built around MatLab file format so there is a certain irony to scraping fantastic MatLab scenes off some kid's reddit page.

Second thing to try is look at earlier Bell 2014 posts, see if what you've circled was covered. They verified that at least some of these features are not side-scan radar artifacts (bounces off submerged land forms that confuse the record) but are instead directly nadir, massive freeze-ups of water under the ice sheet. Rocks have much higher density than ice but gravity says they're not there.

A big deal especially for Petermann but I'm recalling these features going all the way south to Epiq. This is a huge interpretive breakthrough if it holds up. They knew to do this from their earlier work in Antarctica!

Abrupt -- thanks for the new for  forum on internal ice structure in Antarctica. I have that open as a browser tab (along with 38 others I can't bear to close).

Nukefix, thanks for those directions. We can do a lot with this Sentinel imagery of JI.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 02, 2014, 10:22:08 PM
Scientists are ever so fond of saying, 'oh yes, my last paper was so incredible but hey I was standing on the shoulders of giants.'  That might even be true, but it doesn't speak to the midgets who kick away the ladder so no one can stand on theirs.

Let's just say that people who publish blurry old unsourced radar scans, rescaled differently in horizontal and vertical dimensions all so it fits on the *print version* of a heavily paywalled 2014 journal page, then flip it horizontally and delete the lat,long data it came with, and mark it up illegibly with off-centered crucial insider knowledge they have on a drill hole (chronological dates correlated to radar horizons) are not furthering climate science research by design.

I did eventually manage to transfer this piece of junk onto a professionally prepared and fully documented image of Pellon discussed earlier. It does seem that a fair proportion of the radar stratifications will have climate-related explanations, rather than rubbish of dielectric echoes arising by haphazard convergences of contributing factors.

The image halves do align over the NGRIP borehole if you slide one over. It is incredibly important to get dates assigned correctly to a high quality recent fiducial stratigraphic track running through the 5 main boreholes before pushing the date lines out to the coasts.

Meanwhile thanks to greatdying2, my time is being well-spent a set of 3 really well done new pdfs on the only deep interior ice stream of Greenland,  NEGIS. People are always trying to blow off the firn but they have very decent results are a bore hole back to 1617. Also an explanation as to why the NEGIS ice stream so high up and located where it is (geothermal heat anomaly and shear margin, resp.) Espen has a NEGIS forum going so better to post on this over there.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 04, 2014, 02:24:30 AM
Phase I, collect all the climate change events that could conceivably have been responsible for radar echo striations in Greenland's glaciers. Here the earlier start-stop dates will be based on GICC05 and later ones (out to the Eemian) on  AICC2012, both in terms of years before 2000 (b2k has supplanted 1950).

And to that, add the depths of these features in the NEEM, NGRIP, GISP, NEGIS, DYE2, and Camp Century drill cores (not forgetting FOXX, GULL nd DUCK for Jakobshavn). And a citation to whatever articles these numbers were lifted from (with the help again of greatdying2).

I'm posting below a simple database of where this project is at. If you see events that have been omitted, dates that are not the best, know of a better published compilation, or have links to articles that can furnish missing drill core depths, please add a comment or PM me.

Phase II, make a catalog of radar striations. That is, the ones that are reproducibly observed with multiple radar setups and traceable over hundreds of km. The trick here is to develop a flexible numbering system that allows for intercalated additions as radar resolution improves. The most representative striation seed area is probably the NGRIP to NEEM ridge line but there is a pressing need to be able to objectively identify the 'same' striation wherever it occurs.

As a second database, a row consists of a name, a depth on one or more of the cores, and an arrow pointing to it in a multi-striation Cresis image.

Phase III is merger ... these are relational databases but (given the holes) lack an overall indexing field. However with enough zigzagging, it will be possible to arrive at a universal date field. Simply sorting on that sandwiches radar striations between the climate events that we know of, and so generates hypotheses as to what might have caused each radar horizon.

There still may be reflections that just do not correspond to any of the couple dozen things they measure on ice cores. So here we are looking for something that was there but didn't get measured.

94 rows, 8 tabbed columns, I hope it retains its pastability into excel in passing through the blogware: I added some new events, filled in the NEEM depth column, and made myriad other small fixes on 04 Aug 14. Will likely move this over to a new forum topic on the interior of the Greenland Ice Sheet to mirror what AbruptASL is doing for Antarctica.

Order   Event   acronym   Start   End   NEEM   NGRIP   GRIP
1   Little Ice Age   LIA   450   150   122   107   ---
2   Medieval Warm Period   MWP   1050   750   245   217   ---
3   Bond   B1   1545   1385   341   304   ---
4   Vesuvius ash layer   ---   1921   ---   410   368   ---
5   Bond   B2   2974   2784   592   539   ---
6   Bond   B3   4329   4155   796   742   ---
7   Bond   B4   5802   5612   981   940   ---
8   Bond   B5   8207   8032   1228   1219   1325
9   ash inside Bond 8.2   ---   8236   8237   1230   1229   1334
10   Holocene Climactic Optimum   HCO   9000   6000   1287   1302   ---
11   Bond   B6   9271   9096   1304   1323   1432
12   Saksunarvatn tholeiitic ash   ---   10347   ---   1364   1410   ---
13   Bond   B7   10413   10253   1367   1414   ---
14   Bond   B8   11180   11020   1399   1463   ---
15   Start of Holocene   end Wisconsin D0   11703   ---   1419   1492   1624
16   Vedde alkali ash   NAAZ I   12171   ---   1429   1506   ---
17   Younger Dryas   GS-1 or H0   12800   11500   1442   1524   ---
18   stadial 1   GS-1   12896   ---   1444   1527   1662
19   interstadial la   GI-la   13099   ---   1450   1535   1672
20   interstadial 1b   GI-1b   13311   ---   1454   1542   1681
21   interstadial lc   GI-lc   13954   ---   1471   1571   1714
22   alkali ash   ---   ---   ---   1472   1573   ---
23   Older Dryas   OD   14000   13500   1472   1572   ---
24   interstadial Id   GI-Id   14075   ---   1473   1575   1719
25   Bølling–Allerød   BA   14100   12900   1474   1576   ---
26   Dansgaard-Oeschger   GI-le DO1   14680   ---   1489   1605   1753
27   Heinrich   H1   18146   15535   1533   1682   ---
28   stadial 2b   GS-2b   20900   ---   1568   1745   1900
29   stadial 2c   GS-2c   22900   ---   1593   1784   1940
30   Dansgaard-Oeschger   GI-2 DO2   23238   ---   1597   1793   1950
31   Last Glacial Maximum   LGM   26500   19500   1627   1844   ---
32   Heinrich   H2   26501   24282   1627   1844   ---
33   Fugloyarbanki tephra   FMAZII   26690   ---   1629   1848   ---
34   stadial 3   GS-3   27540   ---   1638   1862   2018
35   Dansgaard-Oeschger   GI-3 DO3   27780   ---   1641   1869   2025
36   alkali ash   ---   ---   ---   1649   1882   ---
37   stadial 4   GS-4   28600   ---   1650   1883   2038
38   Dansgaard-Oeschger   GI-4 DO4   28900   ---   1654   1892   2046
39   alkali ash   ---   ---   ---   1656   1895   ---
40   tholeiitic ash   ---   ---   ---   1665   1909   ---
41   alkali ash   ---   ---   ---   1669   1915   ---
42   alkali ash   ---   ---   ---   1678   1930   ---
43   stadial 5   GS-5   32000   ---   1683   1939   2087
44   Dansgaard-Oeschger   GI-5 DO5   32500   ---   1690   1952   2099
45   tholeiitic ash   ---   ---   ---   1689   1950   ---
46   Heinrich   H3   32637   31201   1691   1953   ---
47   alkali ash   ---   ---   ---   1690   1952   ---
48   stadial 6   GS-6   33360   ---   1698   1964   2110
49   interstadial 6   GI-6   33716   ---   1703   1975   2119
50   Dansgaard-Oeschger   DO6   33740   ---   1703   1974   ---
51   Mono Lake geomagnetic   Mono   34100   35200   1706   1983   ---
52   stadial 7   GS-7   34740   ---   1712   1990   2132
53   Dansgaard-Oeschger   GI-7 DO7   35480   ---   1722   2009   2149
54   stadial 8   GS-8   36580   ---   1734   2027   2163
55   Dansgaard-Oeschger   GI-8 DO8   38120   ---   1756   2070   2200
56   tholeiitic ash   ---   ---   ---   1756   2064   ---
57   Faroe Marine Ash Zone III   FMAZIII   38070   ---   1757   2067   ---
58   tholeiitic ash   ---   ---   ---   1760   2071   ---
59   tholeiitic ash   ---   ---   ---   1764   2078   ---
60   stadial 9   GS-9   40121   39372   1777   2095   2220
61   Dansgaard-Oeschger   GI-9 DO9   40160   ---   1777   2100   2224
62   Heinrich   H4   40209   38120   1778   2100   ---
63   tholeiitic ash   ---   ---   ---   1780   2104   ---
64   stadial 10   GS-10   40800   ---   1783   2110   2232
65   Laschamp geomagnetic   Las   41520   45600   1792   2119   ---
66   Dansgaard-Oeschger   GI-10 DO10   41460   ---   1791   2124   2243
67   stadial 11   GS-11   42240   ---   1798   2135   2252
68   Dansgaard-Oeschger   GI-11 DO11   43340   ---   1810   2157   2271
69   stadial 12   GS-12   44280   ---   1818   2170   2280
70   Dansgaard-Oeschger   GI-12 DO12   46867   ---   1846   2222   2324
71   Dansgaard-Oeschger   GI-13 DO13   49280   ---   1865   2257   ---
72   Heinrich   H5   49869   46997   1870   2266   ---
73   Dansgaard-Oeschger   GI 14 DO14   54220   ---   1912   2346   ---
74   Heinrich   H5a   55352   54178   1920   2360   ---
75   North Atlantic Ash Zone II   Z2   55400   ---   1920   2359   ---
76   Dansgaard-Oeschger   GI 15 DO15   55800   ---   1923   2366   ---
77   Dansgaard-Oeschger   GI 16 DO16   58280   ---   1942   2403   ---
78   Dansgaard-Oeschger   GI 17 DO17   59440   ---   1951   2420   ---
79   Heinrich   H6   63185   60052   1971   2456   ---
80   Dansgaard-Oeschger   GI 18 DO18   64039   ---   ---   ---   ---
81   Dansgaard-Oeschger   GI 19 DO19   70523   ---   ---   ---   ---
82   Heinrich   H7a   73107   72063   2011   2539   ---
83   Toba ash layer   ---   74000   ---   2015   2547   ---
84   Heinrich   H7b   77023   75849   2031   2583   ---
85   Dansgaard-Oeschger   GI 20 DO20   78286   ---   ---   ---   ---
86   Dansgaard-Oeschger   GI 21 DO21   83692   ---   ---   ---   ---
87   Heinrich   H8   87076   84465   2103   2712   ---
88   Dansgaard-Oeschger   GI 22 DO22   89436   ---   ---   ---   ---
89   Heinrich   H9   93342   89556   2148   2778   ---
90   Dansgaard-Oeschger   GI 23 DO23   102154   ---   ---   ---   ---
91   Heinrich   H10   102872   101958   2184   2879   ---
92   Dansgaard-Oeschger   GI 24 DO24   106769   ---   ---   ---   ---
93   Dansgaard-Oeschger   GI 25 DO25   112615   ---   ---   ---   ---
94   Eemian MIS 5e termination   Eem   125000   ---   ---   ---   ---
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 05, 2014, 02:41:43 AM
Espen may have slept in today, missing a new record. Here is the quickie EarthExplorer for today:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 05, 2014, 04:02:10 AM
Here are separate north and south branch images from today, 10 m resolution derived from the Landsat panchromatic. The database shows the cloud-free Landsats for this year, along with the best case scenario for the rest of August.

LC80080122014241LGN00   Aug   29   241
LC80080112014241LGN00   Aug   29   241
LC80832332014239LGN00   Aug   27   239
LC80100112014239LGN00   Aug   27   239
LC80090112014232LGN00   Aug   20   232
LC80080122014225LGN00   Aug   13   225
LC80080112014225LGN00   Aug   13   225
LC80832332014223LGN00   Aug   11   223
LC80100112014223LGN00   Aug   11   223
LC80090112014216LGN00   Aug   4   216
LC80080122014209LGN00   Jul   28   209
LC80080112014209LGN00   Jul   28   209
LC80812332014208LGN00   Jul   27   208
LC80100112014207LGN00   Jul   26   207
LC80090112014200LGN00   Jul   19   200
LC80822332014200LGN00   Jul   19   200
LC80080122014193LGN01   Jul   12   193
LC80080112014193LGN01   Jul   12   193
 LC80812332014192LGN00   Jul   11   192
LC80100112014191LGN00   Jul   10   191
LC80090112014184LGN00   Jul   3   184
LC80832332014175LGN00   Jun   24   175
LC80080122014161LGN00   Jun   10   161
LC80080112014161LGN00   Jun   10   161
LC80100112014159LGN00   Jun   08   159
LC80090112014152LGN00   Jun   01   152
LC80080122014129LGN00   May   09   129
LC80080112014129LGN00   May   09   129
LC80100112014127LGN00   May   07   127
LC80100112014111LGN00   Apr   21   111
LC80090112014104LGN00   Apr   14   104
LC80080122014097LGN00   Apr   07   097
LC80080112014097LGN00   Apr   07   097
LC80080122014081LGN00   Mar   22   081
LC80080112014081LGN00   Mar   22   081
LC80090112014056LGN01   Feb   25   056
LC80090112014040LGN00   Feb   09   040
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on August 05, 2014, 08:11:40 AM
Do we know what this is? (red encircled):

Let me venture a conjecture: Those are NEGIS and Peterman/Humboldt flows
I am on the road, so i cannot justify this further. Treat as an ansatz, if you will, and consider that deeper ice is warmer and more plastic.

sidd
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 05, 2014, 06:17:33 PM
Sidd, good suggestions -- this is why the whole set of flight transects needs be brought into a single interactive image. The track is a long ways from Petermann glacier per se (see upper right inset on full image) but could represent bottom freeze-up or shear margins of the newly discovered canyon that runs two thirds the length of Greenland, exiting at Petermann.

Some very decent 2014 publications on NEGIS:

Basal conditions and ice dynamics inferred from radar-derived internal stratigraphy of the northeast Greenland ice stream
http://www.igsoc.org/annals/55/67/t67A090.pdf (http://www.igsoc.org/annals/55/67/t67A090.pdf)

Initial results from geophysical surveys and shallow coring of the Northeast Greenland Ice Stream (NEGIS)
http://www.the-cryosphere.net/8/1275/2014/ (http://www.the-cryosphere.net/8/1275/2014/)

Dilatant till facilitates ice-stream flow in northeast Greenland
DOI: 10.1016/j.epsl.2014.05.060 paywalled: $39.95

Here is brief slide show of different combinations of yesterday Landsat Bands 2,4,5 made into color composites. The area shown is the upstream region of Jakobshavn Isbrae, where the ice stream character blurs into generic ice sheet movement. The last one seems quite effective in drawing out melt features of the 'Lake District' that aren't so apparent in grayscale.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 06, 2014, 01:36:47 AM
Espen, sidd: I pulled out the track graphics in the Bamber 2013 Greenland canyon paper in Science. It does look like some of the dipsydoodling in radar horizons is an effect arising in ice sitting over the canyon.

They did not provide track ids nor indicate half of the scales so I could not co-register it with the spectacular colored track above (the new normal). I added a light blue line for sea level -- only the upper right came with a depth scale however. I could not fully remove the gratuitous text that should have been off to the side. I also added arrows from the canyon DEM transects over to the respective radar tracks.

Note all the east-west tracks in light black in upper left; it would not be difficult to krige this feature all the way to where Petermann meets the sea. Three transects is just a start. It is better to extract horizon lines from the radar traces and just display them in see-thru mode (a la Antarctica 2008).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 06, 2014, 04:33:49 PM
Here is a follow-up on the growth of the dynamic influence area of Jakobshavn Isbrae. It is poaching ice sheet input from neighboring ice sheds, as well as implicating more ice sheet east towards the summit. I did not include the color key because the map maker didn't embed it during the map process (considered a class C felony in cartography), causing it to lose all connection with colors in the final map product.

The second map graphs this loss. It is a little confusing because the losses are not shown cumulatively relative to fixed sea level. Note ice losses (thinning + ablation - accumulation) run to about a meter per year even 100 km inland. Joachin 2014 has added 2011-13 but in a different format.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 06, 2014, 11:20:39 PM
Here is a follow-up on the growth of the dynamic influence area of Jakobshavn Isbrae. It is poaching ice sheet input from neighboring ice sheds, as well as implicating more ice sheet east towards the summit.
What altimeter is that based on?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 07, 2014, 03:10:32 AM
So appreciative of google's reverse image search -- I am awash in documents and had tossed this one.

It appears to be a pdf made from a power point presented at a recent but undated NASA conference. The author is Ian Howat of Byrd Polar with five others. This is page 12, details are sketchy but the figure label indicates it comes from an Airborne Topographic Mapper (ATM). Various instruments, not a unique descriptor associated with a particular satellite.

The elevation depletion map series look very similar to velocity map series ... not a coincidence.

http://etienne.berthier.free.fr/SPIRIT/Talk/Howat_Greenland.pdf (http://etienne.berthier.free.fr/SPIRIT/Talk/Howat_Greenland.pdf)

Later (?) Howat reports similar work using "data from ICESat and ATM as well as SPOT 5 DEMs from 2007 and 2008 ... stereoscopic Digital Elevation Models (DEM) from both airborne and satellite..." with article header
Journal of Glaciology, Vol. 00, No. 000, 0000 which does not make a whole lot of sense.

http://bprc.osu.edu/GDG/JFL_JGLAC.pdf (http://bprc.osu.edu/GDG/JFL_JGLAC.pdf)
 
The Joughin 2014 paper added some more recent along-channel surface elevation annual data to this in Fig3 which is cut down to that below.

http://www.the-cryosphere.net/8/209/2014/ (http://www.the-cryosphere.net/8/209/2014/)

There is yet another paper predicting lots of sub-surface lakes in Greenland (a la Antarctica) which claims to reconstruct a time series of drainage patterns since the Last Glacial Maximum, in which in Fig.6 the northern limb of the Jakobshavn drainage network is captured by the Uummannaq system 16,000 yr ago, the opposite of what is trending now.

http://www.the-cryosphere.net/7/1721/2013/ (http://www.the-cryosphere.net/7/1721/2013/)

Two subglacial lakes have been in fact just been discovered just north of Qaanaaq (not confirmed by drilling yet) but they were not among the thousands predicted by the above paper (making me wonder about how much water the above authors were able to squeeze out of a turnip, the Shreve hydraulic potential equation).

http://www.sci-news.com/othersciences/geography/science-subglacial-lakes-greenland-01581.html (http://www.sci-news.com/othersciences/geography/science-subglacial-lakes-greenland-01581.html)
http://onlinelibrary.wiley.com/doi/10.1002/2013GL058383/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2013GL058383/abstract)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 07, 2014, 07:25:18 AM
Update: here are 3 very recent papers on the Greenland ice surface DEM changes (change in height per unit time, dh/dt with dt taken as the year 2012-13. Jacobshavn and NEGIS are given special attention in subsections.

The first paper gives a very thorough technical discussion of what CryoSat-2 actually sees and gets for overall accuracy for anyone here thinking of using this data. For Greenland though, pg 1680, the authors conclude the Greenland Ice Mapping Project (GIMP, second paper) produces a better product.

"Prominent in Greenland is the strong thinning of the entire western ice sheet, as well as the south-east and north-west ice sheet margins, as shown in Fig. 8. The dynamic thinning of Jakobshavn Isbræ in particular has penetrated deep into the ice sheet.... Thinning rates observed in 2011–12 exceeded 4 m per year. This thinning is most pronounced in the
lower part of both tributaries, but extends 250km upstream."

"Thinning of the Zacharias Isstrømen, an outlet glacier of the North East Greenland Ice Stream (NEGIS), show rates of 1.0 m per yr  at the glacier terminus. This thinning extends 250km upstream of the NEGIS, where values of 0.2–0.3 m per yr have been reported... This pattern of pronounced thinning is a new development (third paper).

I've attached their DEM which is well done technically except for the lat,lon line overlay which could have been done as a side thumbnail. The slope map, new for us is, unfortunately provided in postage stamp resolution, ~150 pixels wide or 1/3 that of the DEM. The Greenland dh/dt map is rather pixellated but gives the overall idea; when localized to Jakobshavn, it does a lot better.

Helm 2014 Elevation and elevation change of Greenland and Antarctica derived from CryoSat-2,The Cryosphere Discuss., 8, 1673–1721, 2014 www.the-cryosphere-discuss.net/8/1673/2014/ (http://www.the-cryosphere-discuss.net/8/1673/2014/) doi:10.5194/tcd-8-1673-2014

Howat, I.M., A. Negrete, B.E. Smith, 2014, The Greenland Ice Mapping Project (GIMP) land classification and surface elevation datasets, The Cryosphere, 8, 1509-1518, doi:10.5194/tc-8-1509-2014. Final version 19 Aug 14: http://www.the-cryosphere.net/8/1509/2014/ (http://www.the-cryosphere.net/8/1509/2014/)

Khan 2014: Sustained mass loss of the Northeast Greenland ice sheet triggered by regional warming, Nature Climate Change, doi:10.1038/nclimate2161, 2014.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 07, 2014, 06:46:02 PM
Here is the ultimate Greenland DEM by Howat et al, just clearing open peer review at The Cryosphere. The reviews and responses are well worth reading in their own right for the intricacies involved in processing years of satellite data of diverse origins. While that aspect is far more sophisticated than what we do here (include myself in that), we can still benefit from and perhaps add value to the products.

It's all available for download. While that is fast enough, the file sizes are landsat-huge 16,600 x 30,000 = 489,600,000 pixels on the big guy. So think twice before clicking on a command in ImageJ (even crop) or your desktop will get tied up for 15 minutes. Better to look at the tlle map in the pdf and order only what you need. Conveniently, they provide both plain grayscale DEM and hillside shaded. I've attached an overview plus a couple of zooms into the Jakobshavn calving front.

<url>http://www.the-cryosphere-discuss.net/8/453/2014/tcd-8-453-2014.pdf (http://www.the-cryosphere-discuss.net/8/453/2014/tcd-8-453-2014.pdf)</url>
<url>Index of ftp://ftp-bprc.mps.ohio-state.edu/downloads/gdg/gimpdem/ (http://ftp://ftp-bprc.mps.ohio-state.edu/downloads/gdg/gimpdem/)</url>
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 08, 2014, 06:11:45 PM
The land-terminating glaciers don't get much attention on Greenland but are significant because impacts of overall melting can be disentangled from the effects of warming ocean water (eg Irminger Current) on the bases of marine-terminating glaciers.

The paper below studied an area just to the south of Jakobshavn, hauling radar behind snowmobiles to get a higher resolution sense of bedrock. As a referee noted, the authors did not do a whole lot with interpretation of their data. Indeed, only one radar trace was provided and the rest of the graphics were of 'presentation' quality, ie so-so.

The slides provide the ice stratigraphy, elevation contours, ice thickness and bedrock elevations (all above sea level here). The second graphic, enlarged way beyond resolution provided, fits the radar stratigraphy track to the bedrock surface.

The authors write that the surface topography provides few clues to that of bedrock. Indeed fresh snow and firn form a rather featureless incline. However look how the isochron surfaces drape over bedrock topography while maintaining their spacing. The ice is moving from east to west here.

Here I had to adjust the fit of radar slice hills and valleys to the mounds and drainages of the DEM. The red dots show the literal fit after adjusting the various scales and low res imagery provided. No doubt that closely spaced radar lines would show a fully conformal fit --  a thousand meters of ice with 20 internal reflectors -- to the bottom topography.

http://www.earth-syst-sci-data-discuss.net/7/129/2014/ (http://www.earth-syst-sci-data-discuss.net/7/129/2014/)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 08, 2014, 10:21:43 PM
The land-terminating glaciers don't get much attention on Greenland but are significant because impacts of overall melting can be disentangled from the effects of warming ocean water (eg Irminger Current) on the bases of marine-terminating glaciers.



Yes A-Team, I am aware of the importance of land terminating glaciers, firns and ice caps, at least in my mind they are important, but far less impressive (no calvings), they are are in the same discipline as  "studying paint dry" ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 09, 2014, 12:54:24 AM
Could be completely unreliable (Modis), but still?:

Indications of collapse of side wall (northern) at the southern branch

And that could eventually result in a faster flow?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 09, 2014, 01:34:36 AM
Espen, did you mean 08 Aug above rather than 3rd? Next Landsats arrive Monday -- maybe bringing your spot in the guinness book of records.

Yes, that is jaw-dropping to see so much of the landscape (2nd slide above) moving at merely 8 meters per year, or rather that nearby Jakobshavn ice stream is moving 2,000 times faster. Considering the deepest radar horizons of the ice at the land-terminating site are >10,000 years old, it hasn't come that far down the hill during the Holocene.

There is another new paper out mapping ice "frozen to the bed" across the entire Greenland Ice Sheet; these are 0 meters per year sites, in Antarctica, called 'stagnant'.

I wonder if not moving really corresponds to frozen to the bed, does that also mean a hockey puck is frozen to the ice rink when the players go on break? van der Waal forces are about all that is left between hexagonal ice and rock, not much to talk about. However an ice cube is certainly not frozen to its inert teflon tray yet the tray has to be flexed to get it out, so I suppose there is friction from geometrical constraint.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 09, 2014, 01:50:11 AM
A-Team I prefer the dark Guinness, the one you drink ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: SteveMDFP on August 09, 2014, 04:20:08 AM
Could be completely unreliable (Modis), but still?:

Indications of collapse of side wall (northern) at the southern branch

And that could eventually result in a faster flow?

MODIS false-color suggests cloud effect. 
http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2014220.terra.367.500m (http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2014220.terra.367.500m)

I made a similar error recently, which is how I learned to check the false-color images.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 09, 2014, 09:33:35 AM
Yes Steve, that could be, but ASAR also show some changes:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 09, 2014, 01:24:18 PM
A place in forum history? Still 6 weeks left in the calving season.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 09, 2014, 02:16:20 PM
A place in forum history? Still 6 weeks left in the calving season.

Cheers mate!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: SteveMDFP on August 09, 2014, 03:20:32 PM
Yes Steve, that could be, but ASAR also show some changes:

Wow, that is impressive.  Odd that there should suddenly be a small, dense cloud on the false-color modis at the same spot.  Makes you wonder if a huge calving/collapse could cause its own cloud of snow being thrown up in the air.  We'll know more very soon.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 10, 2014, 05:15:33 PM
I came across this peculiar photo of the late great Willi Dansgaard handling a precious, unprotected DYE3 ice core with ordinary work gloves while smoking a pipe. DYE3 is an old radar station in south central Greenland drilled in 1979. Dansgaard also drilled at Camp Century and on 18 other expeditions.

The odd part is Dansgaard's main lab analytic specialty was mass spectroscopy (16O, 18O, 2H, methane, ammonia, sulfuric acid) and so he would have been acutely aware of the contamination issue. In 1949 this might have been cutting edge knowledge, not 1979.

And he wasn't the only one to contaminate ice cores -- I've seen pictures right up and through NEEM of people not taking even the most elementary precautions (face masks, sterile gloves, clean suits, laminar flow hoods) -- yet later the papers flow on parts per trillion beryllium 10 in 'soil' at the bottom of GISP2, pine needles at the bottom of NGRIP (never pursued) and ancient dna used to date the Greenland Forest and determine whether even the northernmost ice sheet melted out during the Eemian (didn't, putting the onus of sea level rise on Antarctica).

The drilling fluids alone give me the creeps: brown kerosine, n-butyl acetate, lamp oil, halogenated-hydrocarbon densifier, etc. Documented contamination on the outer but not inner surfaces of ice cores includes lead, 1000 times higher bacterial density and 100 times higher dissolved organic carbon.

The cost of deeper cores must run into the tens of millions at these remote expedition sites. Contamination is a very expensive proposition, not just the drilling but for erroneous downstream interpretations that could affect climate policy recommendations.

Steam boring at Jakobshavn raises different issues as a different technology -- a lot of well logging techniques but to date no cores or melt retrieved.

http://meetingorganizer.copernicus.org/EGU2014/EGU2014-10721.pdf (http://meetingorganizer.copernicus.org/EGU2014/EGU2014-10721.pdf)
http://www.ncbi.nlm.nih.gov/pubmed/17615355 (http://www.ncbi.nlm.nih.gov/pubmed/17615355)
 
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on August 10, 2014, 07:31:15 PM
I believe the calving on the north face of the south branch began at least 1  month ago and you captured it on this animation above.

http://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=154.0;attach=8751;image (http://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=154.0;attach=8751;image)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on August 10, 2014, 07:36:51 PM
In fact, the deep crevasing that we see on the north wall of the south branch, I believe is evidence of bottom melt on this portion of the ice sheet due to it be grounded below sea level. (See image below.) As more of this north wall is exposed by the retreat of the glacier up the fjord, it should be the source of some spectacular calving. The ice sheet is very tall at this point.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on August 10, 2014, 07:40:13 PM
This new calving front that is opening up should behave much like the northern calving front, fairly rapid retreat unless the ice sheet begins to move much more rapidly here. I don't think this will happen as the water is shallow, much like the northern calving front. The significant difference from the northern front is the grounding below sea level goes much further into Greenland.

If you look at the speed of the ice sheet, it is clear that the ice is already moving faster over this shallow sea. (See image below.) You can see the faster ice following the outlines of the ice that is grounded below sea level. As the main calving face retreats, unpinning this ice, it should speed up considerably.

I am definitely going to keep watching this area closely. (Or I would if I had a clue how  Espen does his magic.)

It is actually amazing how ice that is grounded below sea level moves so much more rapidly than ice grounded above sea level. If you follow Jacobshavn up the fjord, you see ice on the north of the fjord, well inland from the calving face, that is moving more rapidly towards the fjord. This ice is also grounded below sea level.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 11, 2014, 10:39:49 PM
The Landsats due today have not been posted yet and may not be -- tomorrow is a scheduled server dink day.

The animation below compares the melt lakes, day 214 vs day 200. Some have drained, others have filled. The still image shows the features that have changed.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 12, 2014, 01:24:32 AM
I've been looking to date the oldest ice being flushed out via the Jakobshavn Isbrae. Ice-penetrating radar is by far the easiest way to 'drill' a core -- in fact, a flight track amounts to thousands of virtual cores.

Since radar horizons have been dated with reference to annual ice layer counting at all of the conventional ice cores (NEEM, NGRIP, GRIP and GISP2), simply follow the lowest continuous radar horizon up the hill until it ties in. That gives the age of the ice at JI at that horizon.

Note an annual ice layer at NGRIP is ~13 millimeters thick at a depth of 2500 m which exceeds the resolution of the radar (~ 3.9 meters,  number of vertical pixels representing a 1000 m section of a Cresis jpeg) by a factor of 300. In addition, the striations appear several pixels thick even though they do in fact correspond in some cases to an event wholly confined to one year (eg volcanic ashfall).

But there's more. Deformations to the radar horizons almost always come from below (ignoring firn). If the horizon being followed is not deformed, then neither are the ones above. That implies all the other horizons are present, possibly thinned and not distinctly visible, meaning all the properties logged on the fiducial tie-in core are transferable all along the track, even properties like beryllium-10, temperature, or methane that don't have anything directly to do with bumping dielectric above that of pure ice.

Because the thinning is known from surface to horizon depth, this can actually be verified via radar track synthesis, a 'dry lab' computation that takes properties giving rise to radar reflectors (ie conductance, dust, sulfate) measured along the core and figures out what the radar return from them should look like when thinned.
 
Looking at the Panton and Spuz radar horizon graphics above, the last easily traceable striations are a triple whose top unit hits the NGRIP core at about 2558 meters (resp 2000 m for NEEM). Those depths correspond to calendar dates of ~ 74,000 as determined by annual ice layer counting. There are still older striations but those are intermittant and tracing them soon becomes problematic.

So the issue is, does this get down to where the ice sheet feeds into Jakobshavn Isbrae or even to the coast by Swiss Camp? The lower ice stream itself has undergone a lot of turmoil in conforming to sills and troughs of overdeepenings. There may be one identifiable radar striation but I suspect this is just the Bølling–Allerød at 14100-12900 B2K at a depth of 1576 m up at NGRIP.

I'm interested in the ~ 74,000 triple though because it may correspond to the enormous erruption of Toba, the largest event by far in the Pleistocene. That left its mark all over the world in form of tephra and sulfuric acid depostion. Better yet, that event  was very carefully studied by Svensson and 26 colleagues on multiple Greenland and Antarctic cores.

<url>http://www.clim-past.net/9/749/2013/ (http://www.clim-past.net/9/749/2013/)</url>

The table below describes 9 closely spaced sub-events spanning 1,980 calendar years (25.39 m of NGRIP core) observed isochronically at both poles. (I've added the NEEM dates using the correspondence with NGRIP depths provided by the latest GICC05 timeline.)

Event      Acronym   Year B2K   NEEM   NGRIP  GRIP   GISP2
Toba tephra 1   T1   74057      2015   2547   2565   2591
Toba tephra 2   T2   74156      2016   2548   2565   2592
Toba tephra 3   T3   74358      2016   2550   2567   2593
Toba tephra 4   T4   74484      2017   2551   2567   2594
Toba tephra 5   T5   75039      2020   2558   2572   2599
Toba tephra 6   T6   75064      2020   2559   ---   ---
Toba tephra 7   T7   75479      2023   2564   ---   ---
Toba tephra 8   T8   75505      2023   2565   ---   ---
Toba tephra 9   T9   76037      2026   2573   2581   2608


The accompanying graphic shows annual core values for delta 18O (~temperature), ECM (direct current electrical conductivity measurement of acidity), DEP (dielectric profile), sulfate, and conductivity. There is no mention of radar horizons in the article even though the items that peaked are key players in generating those.

The overall timing corresponds closely to certain Greenland stadials (cold) and Dansgaard-Oeschger interstadials (warm), GS-21, GI-20, GS-20 and GI-19 though Toba is not put forth as an explanation for any of them. For reasons unknown, these AMOC cycles are in a separate graphic on a longer time scale, which I've adjusted below. The radar track running over NGRIP at this depth was enhanced by Panton as discussed above.

Toba was a supervolcano, two orders of magnitude more extreme than Mount Tambora, with a volume of some 2800 cubic km. Its ashfall has a diagnostic horizon called the Youngest Toba Tuff (YTT) that has not yet been identified in polar ice cores. The huge crater is located in Indonesia a couple of degrees north of the equator. There are pros and cons to various theories of nuclear winters and human genetic bottlenecks associated with it.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 12, 2014, 03:20:43 AM
A nice clear ascending orbit Landsat just got posted, LC80100112014223LGN00 path 10, row 11 with the usual azimuths and sun elevations. A very impressive flotilla of icebergs has exited the fjord and is heading north (not shown). The images are made from Bands 3,4,5 composited as CMY which is displayed however as RGB.

Very noticeable calving along much of the north branch though no dramatic change in location.

The south branch is quite curious. The upper two slower feeder streams are developing quite distinct character from the lower two faster feeder streams at the calving front (the ones developing an extensive crevasse network for a km or so upstream. The image looked better to me as flipped north to south.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 12, 2014, 04:40:48 AM
Jakobshavn up date:

No big changes from August 4 2014. Some calving and retreat at the northern branch, gains but changes of direction at the northern side wall in southern branch, it looks like it wants to expand the operation area in southern branch.
It must have been the changes of surface structure in southern branch northern side wall, that made it look like calving in the Modis and ASAR images?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 12, 2014, 11:04:17 AM
Yes Steve, that could be, but ASAR also show some changes:
What is ASAR? Certainly not the Envisat ASAR as that satellite is dead and tumbling..
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: diablobanquisa on August 12, 2014, 02:31:05 PM
Yes Steve, that could be, but ASAR also show some changes:
What is ASAR? Certainly not the Envisat ASAR as that satellite is dead and tumbling..

Now DMI uses RADARSAT instead of ASAR. Both of them are SAR (Synthetic Aperture Radar).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 12, 2014, 03:10:02 PM
I marked up weekly positions of ice that will move to the current position of the calving front under the assumption of a 16 km/yr icestream velocity, which translates to 41 pixels per week on the scale of this 7.5 m image of 11 Aug 14. I slowed this by 1 pixel for each successive week to represent the onset of backpressure from the freezing fjord.

The final position of the calving front amounts to the eastward velocity of calving minus the westward motion of the ice stream. That difference vacillates but was slightly negative for the week of Aug 4-11 (as shown above by Espen): forward motion exceeded backward calving.

This calving proceeds by fits and starts especially at the start of the season so our occasional snapshots in time are not necessarily representative. I suspect the deeply crevassed regions in the center (up to Sep 02 line) will be the next to go.

While retreat of the calving front per se is significant in unleashing future retreat, in terms of sea level rise it is only the volume of ice moving through the flux gate that matters (as it will calve sooner or later). That volume is not so easy to calculate because a faster moving icestream thins which won't show up in nadir-only Landsat view.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 15, 2014, 06:17:38 PM
Espen writes, 'land terminating glaciers, firns and ice caps in the same discipline as "studying paint dry".

Exceptions might include the regions just to the north and south of Jakobshavn; only there are we getting long-term meteorological data on an interior transect (21 years for K-line), direct experimental evidence about hydrological conditions at the bottom of the ice sheet, and convenient access to horizontal ancient ice at ice margins like Pakitsoq.

Mind you, the blogosphere has settled on surface temperature re-analysis from a warm office afar and the melt lake moulin acceleration meme. While rapid draining isn't disputed, what happens at the bedrock is: drainage to the sea via innocuous tunnel or catastrophic sheet. The reality is more nuanced.

Classical summit ridge cores involve multi-year expeditions that cost millions and take a decade to analyze; another one seems not even in the works. Meanwhile steam rigs can drill local clusters to known basal topography and elevation transects at 120 meters/day and get two dozen to bedrock in a summer season. Neither method really yields significant access to older ice.

However studying land-terminating glaciers may be the glaciology equivalent of looking for lost car keys under a street lamp because the light is better there. Results may not be applicable to the Big Three in Greenland, each a special case in its own way: Jakobshavn (fast, narrow, deep ice stream), Petermann (ice shelf, interior connection), and NEGIS (headwall geothermal anomaly, broad discharge).

The images below tell the Pakitsoq story. Ice from the summit below GISP2 has made it way out to the coast above Jakobshavn where, after ablation of ice above, it lies exposed but still nicely layered a few hundred meters east of the rocks. The age of this ice spans the Last Glacial, Bølling–Allerød, Younger Dryas and pre-boreal time frame. I chased down a 2011 ice-penetrating radar overflight a bit further to east as well as what this corresponds to at NGRIP depth scales.

Ice stratigraphy at the Pakitsoq ice margin, West Greenland
V.V. Petrenko et al. Quaternary Science Reviews 25 (2006) 865–875
http://tinyurl.com/q28kxku (http://tinyurl.com/q28kxku)
http://icebubbles.ucsd.edu/Publications/petrenko_pakitsoq_qsr_2006.pdf (http://icebubbles.ucsd.edu/Publications/petrenko_pakitsoq_qsr_2006.pdf)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 17, 2014, 06:28:48 PM
The rocky margin in west-central Greenland is also critical to dating past advances and retreats of both the ice stream per se and position of the overall Greenland ice sheet, in particular responses to previous warming and cooling events. This is done on terminal moraines (10 Be is only formed during surface exposure) and marine sediments (14C in Pluto Lake layers).

At the Last Glacial Maximum, sea level was much lower than today; skid marks on the bottom show the Greenland ice sheet extended way out onto the continental shelf. At Jakobshavn Isfjord, the big ice sheet had not retreated from Disko Bugt and made landfall until well into the early Holocene (~10.2 ka).

The main moraines around the fjord today (map below) are Marrait, Tasiussaq and a historical remnant from the Little Ice Age. These are sometimes lumped as Fjord Stade moraines (stade is french for stage). All three represent glacial advances rather than stillstands. The two older ones extend for hundreds of km, down to land-terminating glaciers inland from Kangerlussuaq, so are not attributable to just a fast-moving ice stream.

Isostatic rebound since deglaciation in the Disko Bugt region is surprisingly high: 15.6 m outboard of the final moraine Marrait, 5.0 m between moraines and 4.6 m inboard of Tasiussaq. These elevation changes have a slight but measurable impact on rate of formation of 10 Be in quartz of moraine boulders. ( 10 Be atoms are counted by mass spectroscopy rather measured from beta decay.)

Melting of the Laurentide Ice Sheet (at its peak, the size of Antarctica) had to have consequences. When moraine ice dams broke, the immense volumes of melt lakes didn't go quietly into the night -- we know that from the flood scours at The Ramparts at Lake Good Hope (which hardly differ from those from Lake Missoula) and erosion in Great Lakes outlets such as the Nadoway drift moraine. Instead, that fresh water was abruptly dumped, variously into the Arctic, Hudson Bay, Mississippi and the North Atlantic.

The larger events had to have had chilling consequences for AMOC thermohaline circulation (Gulf Stream) and indeed sharp cooling is seen in Greenland ice cores and speleotherms. However geologists are still fighting a 19th century war (biblical catastrophism) and can hardly bring themselves to acknowledge the obvious in the scientific literature.

Flood routes matter because they determined the site of freshwater injection; only in recent years have these been definitively identified and dated. (Geographic drainage options changed over time because isostatic rebound altered the topography.)

While temporal correlation supports but does not prove causation, the Younger Dryas event in all likelihood was caused by a massive discharge in late summer of Lake Agassiz out the MacKenzie River into the Arctic Ocean.

In the Late Pleistocene/Early Holocene chronology provided above, the Marrait moraine corresponds to Bond event B6 at 9.3 ka with peak cooling ~3ºC and duration 170 years, attributed to the collapse of an ice dam of the Laurentide Ice Sheet below today's Lake Superior and huge surge of freshwater into the North Atlantic Ocean disrupting the AMOC thermohaline circulation (Gulf Stream).

The Tasiussaq moraine formed around 8.2 ka with peak cooling 3.3ºC, and duration 175 years and corresponded to the larger Bond event B5: Lakes Ojibway and Agassiz suddenly drained into the North Atlantic Ocean via Hudson Bay.

The abrupt coolings at 9.3 and 8.2 ka interrupted a period warmer than today when the western Greenland ice sheet was rapidly retreating. The evidence shows that the region around Jakobshavn can fluctuated more or less in lockstep with temperature variation (ie these changes were not a delayed response to warming at the last glacial termination). However, conditions today have not resulted from a sudden influx of fresh water so the past may not be a wholly reliable guide.

Age of the Fjord Stade moraines in the Disko Bugt region
NE Green et al http://tinyurl.com/pd62eht (http://tinyurl.com/pd62eht)

Freshwater Outburst from Lake Superior as a Trigger for the Cold. Event 9300 Years Ago
Yu et al. http://d.umn.edu/llo/docs/YuetalScience2010.pdf (http://d.umn.edu/llo/docs/YuetalScience2010.pdf)

Identification of Younger Dryas outburst flood path from Lake Agassiz to the Arctic Ocean
JB Murton et al http://www.ualberta.ca/~eec/Murtonetal2010.pdf (http://www.ualberta.ca/~eec/Murtonetal2010.pdf)

Forcing of the cold event 8,200 years ago by catastrophic drainage of Laurentide Lakes
C Morrill et al http://www.clim-past.net/9/423/2013/cp-9-423-2013.pdf (http://www.clim-past.net/9/423/2013/cp-9-423-2013.pdf)
DC Barber et al 1999 http://tinyurl.com/oxc3lfv (http://tinyurl.com/oxc3lfv)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 17, 2014, 07:04:50 PM
A-Team,

Interesting to know there was a separate ice sheet in the Jan Mayen area, I was not aware of that, and all together interesting stuff ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 18, 2014, 01:50:09 AM
As part of the never-ending quest to pull more rabbits out of the Landsat hat by magical adjustment dof imagery bands, I took a look at Dstretch, a fancy but free plugin for ImageJ. (I'm actually running it packaged in a .jar or Java Archive bundle.)

The idea with Dstretch: the satellite might very well offer lots of bands at different wavelengths but due to the bland properties of the ice below, pixel values are exceedingly cross-correlated across channels. That means, up to some conventional contrast rescaling, the bands look very much the same. Know one, predict the others.

If so, image enhancement experiments should begin with channel decorrelation. Dstretch does this by cycling the initial RGB through many other possible color spaces based on certain properties of the initial histograms. This amounts to multiplication by a channel mixing matrix that is further subject to all manner of user fine-tuning.

Dstretch's main claim to fame has been enhancement of all but invisible rock petroglyphs and indeed some astonishing results have been attained there. http://www.dstretch.com/ (http://www.dstretch.com/)

These operations can mostly be done in Gimp though the same level of exploration there would take hours vs minutes here. On Landsat, I found it worked better to have pre-selected an area I was curious about rather than hope to get an entire scene usefully enhanced.

On the Jakobshavn icestream, below, the emphasis is on the wavelike appearance of the region to the north. It's not at all clear to me whether this is within the range of dynamic influence of the ice stream and if so why this particular periodic response results.

The second image shows Zachariae icestream in northeast Greenland. Here I began with one of Wipneus's very sharp images where the 15 m has been stubbed in for the 30 in an HSV decomposition. I'm not familiar enough with the issues there to know is Dstretch is doing anything useful there.

My sense is we should really be working a whole lot more in ImageJ than in Gimp or Photoshop. ImageJ, while it has a learning curve for sure, is much more geared to scientific research, not so much towards graphic arts. The community writing plugins and fixing bugs is very active and almost entirely academic scientists.

In a sense it is mostly a GUI wrapper for whatever operations have been picked up, with some common image manipulations in the core menus. It is very well suited to quantification and 3D representation of Greenland ice-penetrating radar layers. I'll put further thoughts on this in the ImageJ forum someone started a while back as time permits.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: oren on August 18, 2014, 11:41:07 PM
A-Team, thank you for your most enlightening post (#447) I learned a lot, very interesting.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 21, 2014, 06:16:31 AM
Oren, thx!  I've made a lot of other improvements in the annotated post-Eemian timeline for Greenland and will replace the previous version in due course. There is a new interpretive column and the 'best' reference for each line (by which i mean the most recent good journal article that is preferably open source, as anyone can chase down historical credits from that bibliography and push into the present with its cites in google scholar).

Some events left a record in a single annual layer in the ice core (suitable for a single line in the time-ordered database but others extended over thousands of years. Extended events can have very detailed internal substructure (depending on whether anyone has examined them in depth) as well as encompass the timing 'extraneous' single-layer events.

The radar stratigraphy cannot be dated nearly as accurately as an ice core from the echogram itself (see image below). However some of them are in fact single-year depositions of tephra over what was then the entire exposed surface of Greenland. With a good core chronology and knowledge of what gave rise to the reflector, they can in fact be dated.

So there are some display issues here along the lines of relational databases. However I think the 125 kyr timeframe can be cleanly partitioned along the lines of geological charts (eon era period epoch age). Not shooting for an authoritative account here, just a framework and initial outline that the next person with an interest can improve.

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 21, 2014, 04:27:08 PM
Here are a couple more displays that tie radar horizons onto chronologies of ice cores established by ring counting in the main Greenland ice cores, as checked by correlation with Antarctic cores and intermittently by independently dated volcanic eruptions such as Toba.

This is necessary because radar striations only come with depth below surface but not age. This depth is not linearly proportional to age either because the layers get thinner with depth due to compression and thinning. The images below show how to compensate for this to date radar layers.

The first I made from 804 match points between NEEM and NGRIP; note NGRIP annual layers become thicker from 22,250 years b2k on. The second uses the radar flight path between drill sites to make the correlation. It would be straightforward to extend this to NEGIS, GRIP, GISP2, DYE and other cores; alternatively, once a radar layer is dated that date can be extended by simply following the layer out on other flight tracks.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 22, 2014, 03:48:45 PM
Here is a carefully constructed view of the age vs depth for NEEM and NGRIP ice cores by the collaboration team, as well as the relative thickness of annual ice layers. These dates can be transferred across the ice sheet using radar horizons (second image).

http://www.clim-past.net/9/2713/2013/ (http://www.clim-past.net/9/2713/2013/)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 23, 2014, 04:22:13 PM
Some fairly widespread misconceptions arose from one dramatic incident of very rapid drainage of a Greenland melt lake so other researchers were quick to chime in with a more nuanced papers (over a dozen of them). The hydrofracturing moulin mechanism only accounts for a small fraction of observed drainages and even in those, only the most abrupt really overwhelm the subglacial drainage system to the point of buoyant lifting of the ice overcoming its bottom sticking points. 

Overall, short-lived speedups associated with all types of lake drainage amount to only ~ 5% of all summer-specific ice motion, in part because the subglacial drainage system, whether initially distributed sheet or tunnel, is able to increase its capacity in response to inflows, dampening the effect.

To the extent this is true, exacerbating global warming will create more larger and earlier melt lakes; this will increase but not lead to a runaway effect on the overall ice sheet march to the sea. The greater effect may be advection of heat from the glacial surface (from its inefficient contact with the atmosphere) to deeper in the glacier where that energy can drastically reduce ice viscosity.

Here the motion is a few tenths of a km/yr. While that is only a thirtieth that of Jakobshavn, it may pertain to a larger portion of the ice sheet.

The excellent illustration from an excellent article tells the story of two lakes just north of Jakobshavn Isbrae in the variously spelled Paakitsoq region, NE of Swiss Camp and the Luethi study sites. I added the main findings and a few details to make the figure self-contained.

I then chased down three 2014 Landsats to see if the two lakes studied two years earlier were recurrent features with recurrent behavior: sort of, not really, may depend on melt year.

Ice dynamic response to two modes of surface lake drainage
Marco Tedesco et al  2013 Environ. Res. Lett. 8 (2013) 034007
http://iopscience.iop.org/1748-9326/8/3/034007/pdf/1748-9326_8_3_034007.pdf (http://iopscience.iop.org/1748-9326/8/3/034007/pdf/1748-9326_8_3_034007.pdf)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 23, 2014, 07:49:04 PM
Peeking trough the clouds (Radarsat) we may have a calving situation between Aug 18 and Aug 22 2014
It also looks like we are having a depression developing north of the southern branch?:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on August 24, 2014, 03:38:58 AM
I'm not sure that is a depression. It might just be a shadow but that area north of the southern branch is grounded below water just like the north branch. It would not surprise me at all if we saw things change there quickly as the south branch  calving front retreats.

I will also not be surprised when that new island in between these two areas grounded below sea level pokes its head out of the ice.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 25, 2014, 08:13:21 PM
Some impressive calving seen at Jakobshavn between Aug. 19 and Aug. 25 2014:

Fits with what is already observed by Radarsat (see above).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 25, 2014, 08:39:35 PM
With the calving mentioned above, it looks like we are at the same point of retreat as the record set Sep. 27-29 2013, and we still have at least a month left of the traditional calving season for Jakobshavn:

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 28, 2014, 04:57:44 AM
As suggested we had some calvings since last update, Aug. 27 2014 is almost at the maximum retreat set Sep. 27 2013, the northern branch is definitely in the retreat zone. The last frame in the animation below is Sep. 27 2013:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 28, 2014, 02:56:38 PM
Jakobshaven ice-stream calving-front imaged by Sentinel-1 SAR, 17.8.2014. Note in the lower right corner how differentiation between the ice-stream and ice melange with icebergs can be hard.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 28, 2014, 04:26:23 PM
Nukefix, "Note in the lower right corner how differentiation between the ice-stream and ice melange with icebergs can be hard.", is it not more due to the viewing angle?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 28, 2014, 05:37:15 PM
Nukefix, "Note in the lower right corner how differentiation between the ice-stream and ice melange with icebergs can be hard.", is it not more due to the viewing angle?
Even with the same viewing-angle the ease-of-differentiation depends on environmental conditions (season). Higher resolution would make the task easier but this is what we are stuck with. The use of textural measures might make the task a bit easier for a human operator.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 29, 2014, 02:56:32 AM
Landsat LC80100112014239LGN00 just came in at EarthExplorer, it is a beauty. No sign of LC80832332014239LGN00 though, sun angle may be low for ascending orbit and they just are not processing that series (even though it might be fantastic for shadows on nearly flat terrain -- as so provide a very high resolution relative DEM!).

This is a very fine reference shot too for Eqip area glaciers, with icestreams standing out clearly from carried abraded material..

No retreat record ... calving some big ones but not quite keeping up with icestream advance. We have no idea on whether a discharge volume is being set -- I can try once again to see if feature tracking over time is possible from Landsat (to see how seasonal velocity compares to past years).

The north branch has remained very active but its front is not going anywhere.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 29, 2014, 03:16:13 AM
Here are the higher resolution panchromatics from Landsat LC80100112014239LGN00, upsampled to 10m resolution.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 29, 2014, 10:47:08 AM

No retreat record ... calving some big ones but not quite keeping up with icestream advance. We have no idea on whether a discharge volume is being set -- I can try once again to see if feature tracking over time is possible from Landsat (to see how seasonal velocity compares to past years).
Feature-tracking with SAR works, lets hope that the S-1 coverage will cover more of Jakobshaven in the future.

BTW, are you aware of any public-domain feature-tracking code?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 29, 2014, 05:08:27 PM
"BTW, are you aware of any public-domain feature-tracking code?"

Short answer, no. I could look through more 'methods' sections of Greenland and Antarctica journal articles. Wipneus found a trackable hexagon at Zachariae; that gives velocity relative to fixed rock only at that one point. We are looking for the whole velocity vector field (including z height component).

Landsat scenes even with matching path/row don't have quite the same nadir, azimuth nor time-of-day but they seemed well aligned by the time they get to EarthExplorer. Sun elevation though, that changes illumination angle with the season. I posted that data a while back for cloud-free Landsat days of 2013-14.

Jakobshavn Isbrae moves very fast (peaked at 3 pixels/day at 15 m resolution) which is favorable but the icestream virtually featureless for 100 km upstream and small crevasse features may open and close over time. The flow is east to west with crevasses generally orthogonal; the sun is always to the south so shading is unfavorable.

Low sun angles (ascending orbit) later in day would better shadow crevasses and whatever surface relief may be out there. For example LC80822332014200LGN00 on midnight of 19 Jul 14 had an azimuth of -49.7 and sun elevation 7.4. It could be compared with the 27 Jul 14, LC80812332014208LGN00.

It is easy enough to make a very fast blink comparator in gimp with each date, say at 50% translucency. Alternatively, after masking all but the stream channel, one image can be subtracted from the other until the (local) optimal nudging is discovered for the later date (eg three pixels west, one pixel north). I believe some commercial software does nothing more than script this. In the example above, 8 days x 3 px/day focuses the search around 24 pixels to the west.

False color Landsat band mixes have potential but I haven't gotten anywhere with them to date, the interval between Landsats is too long and erratic. SAR doesn't have solar illumination issues. At Petermann, compositing 3 panchromatic B8 bands from different dates as RGB has given spectacular interferometric imagery with a fetching display of the velocity field (as projected on x,y plane).

Rignot et al  doi:10.1029/2012GL051634, 2012 "use Envisat ASAR, ALOS PALSAR and RADARSAT-1 SAR. The SAR data are processed into single look complex images using GAMMA (www.gamma-rs.ch (http://www.gamma-rs.ch)). The data are then combined into radar interferograms after applying a pixel offset correction calculated using a speckle tracking algorithm [Michel and Rignot, 1999]. The 3-D vector of ice velocity is calculated assuming surface parallel flow using only the speckle tracking results, i.e., the interferometric phase is not employed."

Joughin 2014 http://www.the-cryosphere.net/8/209/2014/tc-8-209-2014.html (http://www.the-cryosphere.net/8/209/2014/tc-8-209-2014.html) processes proprietary pairs of DLR TerraSAR-X imagery separated by 11 days with "a set of well-established speckle-tracking techniques" described in an offline 2002 paper http://dx.doi.org/10.3189/172756402781817978 (http://dx.doi.org/10.3189/172756402781817978) that has 181 follow-up cites.

Joughin 2010 http://www.igsoc.org:8080/journal/56/200/j10j204.pdf (http://www.igsoc.org:8080/journal/56/200/j10j204.pdf) has a fine discussion of interferometric InSAR. Earlier in this forum (can't relocate), I posted a fall 2014 abstract that indicates Joaghin's current (advanced) methods for JI.

There are fixed GPS units out on the main ice sheet for slow motion (~50 m/yr) but I'm not aware of public access to real-time data. (SH Doyle Persistent flow acceleration within the interior of the Greenland ice sheet DOI: 10.1002/2013GL058933).

To summarize, the first obstacle (expensive frames) is eliminated with this new satellite though it has missed the summer season and the second obstacle (speckle, interferometric software) is probably surmountable. So I hope you can find a way of doing velocity with Sentinel.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 29, 2014, 05:47:17 PM
Here is a hasty velocity animation at Jakobshavn over 8 days this summer July 11 v July 19 ... next time I would start with images that are better matched for illumination and at 10 m resolution. So it does look like it would be feasible to determine speeds along the centerline of the channel quite a ways up using this time interval though a given feature may not persist over the whole season. We have 21 cloud-free images for the 123 day interval May through August...
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 29, 2014, 06:52:54 PM
That's the benefit of radar, the imaging-geometry and illumination are practically identical from observation to observation.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 29, 2014, 07:15:05 PM
That would be a big plus. How does radar do on snowy scenes though? Seems like surface roughness takes up quite a bit of channel space.

Here is the 09 Feb 14 band 4 Landsat (after a lot of contrast meddling):
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on August 29, 2014, 11:21:26 PM
As suggested we had some calvings since last update, Aug. 27 2014 is almost at the maximum retreat set Sep. 27 2013, the northern branch is definitely in the retreat zone. The last frame in the animation below is Sep. 27 2013:

Looking at the animation, it sure looks like the north wall of the southern branch is calving.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 30, 2014, 08:16:18 PM
Shared Humanity,

Yes, I also expect a new island showing up in the near future.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 31, 2014, 09:21:41 AM
That would be a big plus. How does radar do on snowy scenes though? Seems like surface roughness takes up quite a bit of channel space.
Snow and snow wetness affect the level of backscatter. However, feature-tracking is based on tracking visible features (crevasses), so changing the level of backscatter should not matter that much especially if suitable pre-processing is used to mitigate differences in backscatter-levels.

If anyone would have some feature-tracking code, even in pseudocode, I could try to convert that to a usable open-source feature-tracking module.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 31, 2014, 03:07:40 PM
"... feature-tracking code."

One thing to consider at the outset is measurement error vs available sensor resolution, especially whether final output will allow year on year comparison at say monthly resolution.

For Landset 15 m resolution on the Jakobshavn icestream, suppose a crevasse is moving at 30 m per day. That would be 2 pixels over in a region where the movement is pure east to west (ie compatible with the rectangular pixel grid). However movement confined to the JI channel is varying from that to almost diagonal.

One pixel up, one pixel over amounts to 1.4 pixels of diagonal motion, yet this binning, on top of inevitable Landsat scene to scene registration error, adds up. So here we would not be looking at better than monthly velocities where there are 60 pixels of movement for the 11 km/yr velocity assumed above.

The table below shows how measured km/yr varies with a meter change in meters per day. It follows that Landsat panchromatic might be able to detect a speedup/slowdown relative to 2013 over the melt season but would struggle with month to month comparison.

m/d   px/d   px/m   km/yr
25   1.7   50.7   9.1
26   1.7   52.7   9.5
27   1.8   54.7   9.9
28   1.9   56.7   10.2
29   1.9   58.8   10.6
30   2   60.8   11
31   2.1   62.8   11.3
32   2.1   64.9   11.7
33   2.2   66.9   12
34   2.3   68.9   12.4
35   2.3   70.9   12.8

One thing I've pondered (no doubt definitively addressed by previous ponderous scholarly articles) is whether the two most common methods for upsampling resolution (bicubic and sinc) merely provide delusional eye candy or -- on some terrains at least -- do a decent job of getting at the same result had the instrument resolution actually been better.

I suppose NASA already pursued this when deciding to post Landsat-8 at 15 m, yet that may have been for land whereas the homogeneity and predictability of the Greenland icesheet might make this more favorable (indeed across the board, for all manner of Greenland data). Here the 15 m could be blurred to 30 m (or band 4 30 m used) and then upsamped for subtractive comparison to the original 15 m. The bottom line will be we are better off with Sentinel radar.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on September 01, 2014, 10:16:53 AM
Ideally the image posting should satisfy Nyquist's sampling theorem so a 30m resolution sensor should be sampled/posted at a 15m pixel-size. Feature-tracking is performed over a window and sub-pixel accuracy in the speed-measurements is certainly possible.

Radar-images have a much more stable geometry so it's possible to co-register the scenes to 0.1 pixel (or even 0.001 pixel) accuracy. However, ionospheric disturbances cause some distortion in radar-images when the Sun is very active, these problems show up as banding in the velocity-images and can be largely mitigated with suitable filtering.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on September 18, 2014, 09:21:42 PM
Due to weather conditions, we have not received Landsat images for some time, but we still have Radarsat, and we may have some heavy activities at Jakobshavn during September 11 and September 13 2014, will report more on this later when more reliable data is available:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: AbruptSLR on September 25, 2014, 07:23:05 PM
The attached Sentinel 1-A image of the Jakobshavn Glacier was taken on Sept 23 2014 and shows some more details of the recent calving on the southern branch.

See the following link to get the high or low resolution image yourself:

http://www.esa.int/spaceinimages/Images/2014/09/Jakobshavn_Glacier_Greenland (http://www.esa.int/spaceinimages/Images/2014/09/Jakobshavn_Glacier_Greenland)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on September 25, 2014, 09:39:51 PM
Thanx AbruptSLR for keeping me update! :) ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: AbruptSLR on September 25, 2014, 09:59:14 PM
Espen,

If A-Team was still on-line I sure that he could pull some imagining magic to show all kinds of details that my posted image misses; but it looks like there has not been much (if any) new calving since the event you identified on Sept 13.

Best,
ASLR
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Lennart van der Linde on September 28, 2014, 07:42:35 AM
This was posted by ASLR in the Antarctica-folder, but it may be of interest here too:

The link leads to an open access pdf that provides valuable information about the bed topography of both Jakobshavn (Greenland), and Byrd (Antarctica), Glaciers.

S. GOGINENI, J.-B. YAN, J. PADEN, C. LEUSCHEN, J. LI, F. RODRIGUEZ-MORALES, D. BRAATEN, K. PURDON, Z. WANG, W. LIU, & J. GAUCH, (2014), "Bed topography of Jakobshavn Isbræ, Greenland, and Byrd Glacier, Antarctica", Journal of Glaciology, Vol. 60, No. 223, 2014 doi: 10.3189/2014JoG14J129

http://www.igsoc.org/journal/60/223/j14j129.pdf (http://www.igsoc.org/journal/60/223/j14j129.pdf)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on September 28, 2014, 11:50:51 AM
Hold on AbruptSLR,

I do think we have a new development, according to Modis we passed the previous max. retreat set in September 2013, looking forward to study the next usable landsat image.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: AbruptSLR on September 28, 2014, 03:55:50 PM
Espen,

It looks like you will have a lot of new information to report in your October summary on Greenland Glaciers.

Best,
ASLR
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on September 29, 2014, 04:35:43 AM
Here is the confirmation, we passed the previous retreat record set in September 2013, both the southern branch (slightly) and northern branch (especially) retreated further:

Ps. Notice how the snow/ice retreats on the rocks.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on October 06, 2014, 06:43:22 AM
Prasad Gogineni  and his henchmen have a paper out on subglacial topo under Jacobshawn (and Byrd, in Antarctica), including juicy ice layer data from CRESIS.

doi: 10.3189/2014JoG14J129

Mr. A-Team should be all over this when he reappears.

sidd
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: icefest on October 06, 2014, 12:14:16 PM
Prasad Gogineni  and his henchmen have a paper out on subglacial topo under Jacobshawn (and Byrd, in Antarctica), including juicy ice layer data from CRESIS.

doi: 10.3189/2014JoG14J129

Mr. A-Team should be all over this when he reappears.

sidd

I can't get more than: http://www.igsoc.org/journal/60/223/j14j129.swf (http://www.igsoc.org/journal/60/223/j14j129.swf)
If anyone can find a copy, I'd be appreciative.

-icefest


EDIT: found it!: http://www.igsoc.org/journal/60/223/j14j129.pdf (http://www.igsoc.org/journal/60/223/j14j129.pdf)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on October 22, 2014, 08:36:55 PM
As seen with Sentinel-1 on 19.10
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on October 24, 2014, 10:56:57 AM
Here's a quick-and-dirty 1st guess for the GL location based on the S-1 data above:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on October 24, 2014, 09:12:18 PM
The heavily crevassed north flank of the south branch is all grounded below sea level. I believe the surface condition of this region is evidence of water melting the underside of the glacier.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on November 02, 2014, 04:32:45 PM
"The heavily crevassed north flank of the south branch is all grounded below sea level ...evidence of [sea] water melting the underside of the glacier."

A lot of Greenland is below sea level. However that does not mean that sea water has infiltrated the interior; quite the contrary, fresh water is flowing out. Warming of Baffin Bay primarily affects the calving front of JI and there mostly because of calving induced turbulence which improves heat transfer.

Retreat this year again stopped short of the big sill shown in figure 20b of the Gogineni paper cited above. According to published predictions, this sill will reduce heat exchange with sea water in coming years.

However, you would be correct to say that the bottom of Jakobshavn is not yet well characterized by ice-penetrating radar (despite heroic efforts): the resolution leaves a lot to be desired in terms of resistive knobs; the height distribution of 'temperate' ice is not well known and the composition, height  and hydration state of bottom till have not been determined; and the sole temperature drill profile in the main fork (Iken 1993) never reached bedrock.

While modeling is quite sophisticated these days, at some point it must make contact with experimental observation. Unfortunately the key parameters are precisely those characterizing the lower depths of the channel (softness of ice, resistance to basal slipping). Tight flight patterns of the new radar drone may help in coming seasons, as would new high speed drilling techniques (AGU abstract C53A-0279: ten days for a 3300 m core that includes bedrock).

We might wonder if warmer fjord water in winter will mean later frozen melange and so less resistance to late-season calving. The Landsat season ends this week after two fine low angle shots in late October so we can't monitor open water with that satellite. Sentinel will still work but there we have no public domain imagery from previous years for melange comparison. The fjord web cam might have that data depending on how well it works in dim light.

The images below show the last available Landsat 15 m panchromatic. The extreme western portion of the fjord is still open water.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on November 02, 2014, 06:19:59 PM
Jakobshavn gained some weigth since our latest update, when Jakobshavn reached the maximum retreat (Sep. 28  2014) for the season and overall:

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: oren on November 02, 2014, 07:12:54 PM
Interesting: the south branch advanced quite a lot while the north branch did not advance at all during this period
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Rubikscube on November 03, 2014, 01:15:52 AM
Interesting: the south branch advanced quite a lot while the north branch did not advance at all during this period

The northern branch, especially its eastern part, is virtually stuck on land, so it should not come as a big surprise that it advances very slowly even though it is noteworthy. I would love to see some physical depth measurements taken from the edge of the north branch, but I suspect that anyone taking on such a task might run into some serious problems (such as health and safety requirements).

It is also noteworthy that the "third branch" appears to be advancing fairly rapidly, although the crevasses and apparently low lying ice edge makes it a little difficult to establish exactly how much ice is exiting there.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on November 03, 2014, 01:34:58 PM
Right, the north branch is mostly up against a cliff as can be seen from the bedrock map or from midsummer oblique imagery. From the velocity map, prospects are dim for significant ice volume discharge (relative to the south branch) in coming decades. The middle branch may have better prospects (below).

Much farther to the east, the higher velocity dark blue lobe does not correspond well with the red active tributary of the south branch. So it doesn't really work to assume past glacial gouging of bedrock serves as a proxy to ice volume contributions today or later in the century. The images below are adapted from the latest Gogenini pdf cited above.

The animation below shows a surprising amount of ice movement in the south branch between the Oct 30 and Nov 1 Landsat scenes. Here the scene geometry was not easy to align: the satellite was at the same latitude and azimuth for both but scene-center longitudes (nadirs) were quite different, -47.80º vs -50.89º, or 120 km apart.

The latter has quite remarkable shadows, though the sun elevation at 5.99º is not that much lower than that of the 30th, 6.63. Recall shadow length goes as 1/tan, tan small angles ~ angle itself in radians, and radians convert to degrees by a constant so the ratio of degrees 6.63/5.99 indicates only a 10.7% increase in shadow length in the two day later photo.

A vertical 1.00 meter stick would cast shadows of 8.60 and 9.53 meters at the respective angles (using radians). These scenes thus have considerable value in determining very slight variations in ice surface topography.

The final Jakobshavn Landsat from 2013 was taken on Nov 7 and things did not resume until Feb 9. The lowest acceptable sun elevation was 5.41º for the November scene. I'll post the final database of clear images in a week or so.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on November 03, 2014, 10:14:36 PM
Should you ever wonder exactly what experimental data underlies the pretty bedrock elevation picture at a given location, the first image below shows all the radar flight segments available for the north and south branches of Jakobshavn from 1993-2013. Very few other sites in Greenland have such a high density of flight lines.

There's a whole lot of flight lines but still a whole lot of sq km regions with no coverage whatsoever. What could possibly be a rational basis for interpolation in fairly irregular bedrock terrain? All that's available is the bounding polygon.

We've been wondering what underlies the middle branch so I selected a recent track that sliced through the area (newer radar usually represents better technology), namely a P3 overflight from 2013 that Cresis staff marked up for ice surface (does not include firn) and bedrock, namely 20130404_02_032_2echo_picks, available at https://data.cresis.ku.edu/data/rds/. The 1echo_pick file has raw unannotated data.

After much back-and-forth between Cresis kml, Google Earth pins, Cresis images and Gimp, it's possible to place the desired radar data segment along the track as displayed over the satellite imagery that GooglE uses at this resolution (second image below). Interior Greenland does not have any visible features in satellite imagery (uniform snow).

The dotted green lines show possible troughs gouged out by past ice stream movement. The three minor dips would have to be traced farther east in other flight lines for confirmation.

The P3 flight, being oblique both N-S and to JI main channel, is rotated to horizontal so the precious radar data can be displayed at its native resolution. (It's more complicated but still doable when the track is curved.) The Cresis image here spans 52 km but only provides 4 internal lat,lon coordinates; none of these correspond to internal GPS way points of the Cresis kml file.

I'll skip over other crazy-making details unless there is a public clamor. (Cresis pdfs still have lat,lon way points as text; these can be grepped out site-wide into GooglE path pins, along with internal way points of the kml files themselves, and the whole enchilada distributed as a one-time GooglE import, over an elevation contour base map.)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on November 04, 2014, 05:13:44 PM
Thanks A-Team, that explains a lot! :)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on November 05, 2014, 02:30:21 PM
Lennart, ASLR, sidd, and icefest ask above for comment on the new Gogenini paper at http://www.igsoc.org/journal/60/223/j14j129.pdf (http://www.igsoc.org/journal/60/223/j14j129.pdf) . This is a beautifully written paper that provides significant new information on the Greenland radar program. It would take several posts to cover the ground.

I first puzzled over why the paper used only radar data from 2005-09 for Jakobshavn, whereas a great many overflights with presumably better technology took place over the subsequent years (first image below shows 2010-14 tracks).

It has to do with pretenders to the ice-penetrating radar throne (emphasis added):

'Since 1990, several attempts have been made to sound Jakobshavn and other fast-flowing glaciers, with very limited success. Fully coherent radars operating over the frequency range 1–450 MHz are used for these measurements (Gogineni 2001, 2012; Dall 2012; Morlighem 2014). We first succeeded in sounding Jakobshavn Isbræ ... in 2005.'
Chasing this down, 'Dall 2012 P-band radar sounding in Antarctica' concerns a threat from satellite radar, which could provide more comprehensive coverage of big continents if only the surface clutter issue could be resolved. That radar (ESA Polaris) on airplanes not only reached bedrock in 3300 m ice on the Greenland summit ridge (possibly detecting basal melt as well) in 2008 but also obtained spectacular results (images below) in Antarctica using a remarkably effective enhancement (first derivative of nadir return power) to better get at internal stratifications.

As you might expect, ImageJ is all over gradients, laplacians and hessians of digital imagery, eg http://bigwww.epfl.ch/thevenaz/differentials (http://bigwww.epfl.ch/thevenaz/differentials) . Gimp offers Filters → Artistic → Van Gogh (line integral convolution), various edge detectors, Difference of Gaussians, or roll your own algorithm (bump one pixel up and down, subtract grayscales, take max).

However derivatives would be better taken directly, possibly even in hardware, on incoming 12 bit return data -- in fact the whole Cresis effort should be integrated from antenna design right through digital enhancement product -- too often the latter is an afterthought or salvage effort after the goal post moves (eg from bedrock to radar stratigraphy, internal deformations and water pockets).

Which is exactly what happened here: five years after electrical engineers design the radar instrument and IceBridge conducts the flights, they bring in some poor computer science guy (11th author http://www.csce.uark.edu/~jgauch/ (http://www.csce.uark.edu/~jgauch/)) to recover the latent data via histogram equalization, adaptive median and bas relief edge-detection filtration, all of which are standard menu items in Gimp.

Morlighem 2014 combined sparse radar ice-thickness data with high-resolution ice motion interferometery in a computer-intensive mass conservation optimization model, finding 'deeply incised submarine glacial valleys beneath the Greenland ice sheet' (doi: 10.1038/ngeo2167, paywalled, have copy) to determine ice thickness and bed topography along the entire periphery of the Greenland ice sheet, detecting widespread overdeepenings in the faster moving ice streams that extend 'significantly deeper below sea level and farther inland than previously thought'.

Omg, 'previous thinkers' must mean Gogenini and co-authors of his many papers?!? The response establishes that while Cresis did not invent ice-penetrating radar, they certainly built ever-improving scientific instruments, pioneered their use on a survey-level scale (unlike Polaris) and succeeded in reaching bedrock observationally in very difficult deep ice by 2006 (whereas Morlighem 2014 merely models it).

Note however this modelling does fill in the blanks of bedrock polygons bounded by inevitably sparse radar tracks (see post above), so it's worth a more detailed look as interpolative method.

The 2014 model paper chose to cite a 2001 paper for purposes of invidious comparison (ref 7: Bamber, Gogenini 2001). It is difficult to comprehend how the Rignot group could be unaware of the intervening updates, notably the widely cited replacement (Bamber, Gogenini 2013 doi:10.5194/tc-7-499-2013) given Rignot is listed as co-author. That went online 15 Nov 2012, whereas the Morlighem article was submitted a full year later, 20 Nov 2013.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Lennart van der Linde on November 05, 2014, 10:36:45 PM
Thanks A-Team for your comments on the Gogineni paper.

What I keep wondering about: how important is it that the trough of Jakobshavn Isbrae is at least 100m (?) below sea level all these 200 km inland? How much more vulnerable to melting does this make this glacier compared to glaciers grounded above sea level? Or is this less important due to the relatively small width of this trough, which would cause much tighter kinematic constraints compared to for example Thwaites glacier?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on November 06, 2014, 12:38:05 PM
Lennart, good question.  Indeed what keeps sea water from rushing in and the whole mountain of ice bobbing up, like submerging a ice cube tray in a sink of warm water? So much of north-central Greenland is below sea level that it is seems like one big grounded iceberg.

We should get around to a buoyancy discussion at some point -- for lower JI, it is provided but not discussed much  in the Joughin 2014 paper. It's clearly explained in Martin Lüthi's course "Physics of Glaciers I"  free online at http://people.ee.ethz.ch/~luethim/teaching.html (http://people.ee.ethz.ch/~luethim/teaching.html) and in a 2002 paper "Hydraulic conditions at the base of Jakobshavn Isbrae, West Greenland" (http://people.ee.ethz.ch/~luethim/pdf/40A013.pdf (http://people.ee.ethz.ch/~luethim/pdf/40A013.pdf)). Also relevant: their new paper on boreholes Foxx and Gull on a flow line below Swiss Camp (http://www.the-cryosphere-discuss.net/8/5169/2014/tcd-8-5169-2014.html (http://www.the-cryosphere-discuss.net/8/5169/2014/tcd-8-5169-2014.html)).

It is also key to get a grip on the complex hydraulic connectivity of subglacial water. For that, the 2 Oct 14 Lüthi paper at http://www.nature.com/nature/journal/v514/n7520/full/nature13796.html. (http://www.nature.com/nature/journal/v514/n7520/full/nature13796.html.) Two of the co-authors expand on the paper at http://www.sciencedaily.com/releases/2014/10/141001185934.htm (http://www.sciencedaily.com/releases/2014/10/141001185934.htm)

As far as I can tell, the bottom line on Jakobshavn acceleration is that there is no bottom line, yet. One causal mechanism after another has been ruled out. Only the initial phase of speedup is understood, collapse of its floating ice shelf portion from warming ocean water of Baffin Bay. That was years ago. There's minimal ice shelf today, unless you count the seasonally frozen mixture of fjord and calved products (mélange).

Back-pressure from mélange could account for some portion of calving seasonality. If so, then later freeze-up and earlier melt-out (again, warmer ocean underneath) would increase winter calving episodes of Jakobshavn Isbrae and overall velocity.

It is not feasible to monitor calving in winter at visible wavelengths, though a combination seismometers, web cams, calving seiches, Sentinel radar and Modis SST might be up for the job. I'm seeing a 2010 AGU abstract on this very topic but, four years later, not seeing a published paper. That makes me disinclined to rush into winter monitoring.

Winter MODIS observations of West Greenland fjord ice activity
Abstract C51A-0472 presented at 2010 Fall Meeting, AGU
Cassotto, R. K., M. A. Fahnestock and J. M. Amundson
http://www.science.gov/topicpages/f/fjord+west+greenland.html (http://www.science.gov/topicpages/f/fjord+west+greenland.html)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Lennart van der Linde on November 06, 2014, 01:17:00 PM
That's some nice homework for me, thanks :)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on November 06, 2014, 09:34:13 PM
I am a bit confused about the present (southern) calving area, the images (data) above do not show that, but I suspect there is a "doorstep /threshold" in that area, resulting in a pause of further retreat?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on November 06, 2014, 11:05:26 PM
"...what keeps sea water from rushing in and the whole mountain of ice bobbing up ...?"

A good phrase to look for is Volume Above Flotation (VAF)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on November 07, 2014, 06:13:42 PM
Remember all that rubbish from the '70's about nuclear-powered tugs towing icebergs to Los Angeles, providing water too cheap to meter?

How about some nonsense of our own -- floating the whole of Greenland off its bedrock and towing it to the Arctic Ocean to replace the vanishing sea ice?!?

I believe this would be fully credible to the general public if only we could hoax up a viral visualization. However there a number of technical issues in doing this responsibly. 

For Greenland as iceberg, the newly combined bedrock and surface DEMs in Bamber 2013 provide a 3D ice thickness model, the bottom of the berg appearing as the reverse mold of the bedrock. The absolute thickest spot is 3367 m with NGRIP core only 3085 m in length. The volume of ice has been re-estimated at 2.93 million km3 and the mass as 2.67x 10^18 kg.

If we neglect bubbles, impurities, firn density, temperate ice, ablation, melt lake, moulins and tipping issues, where is the freeboard line on Greenland as it stands? Taking the density of icesheet ice at 911 kg/m3 and that of seawater as 1025 kg kg/m3, it follows that  ~89% of the iceberg's mass is below water.

To find the giant berg's water line, it seems necessary to slice the thickness DEM into say 1 m horizontal sections and determine their area, volume and finally mass contribution. These would have to be summed until the 89% was reached. As byproduct, the center of mass could be located (first moment).

I have no idea where these would be, maybe 1500 m above sea level on present Greenland and midway under the center ridge. It may well be the case that the equilibrium position is upside down yet the initial flotation metastable.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Sleepy on November 07, 2014, 07:08:52 PM
 ;D
Too much information won't sell.
Just tow it up a bit, and let it get stuck between Ellesmere and Svalbard. ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on November 08, 2014, 02:47:08 PM
That's a good start, Sleepy. Perhaps someone could make a paper cut-out of Greenland ice, slide it over a large globe to see if it squeezes through. It docks very nicely to the western shore of Siberia. They have an app for this in plate tectonics (euler angles and all that).

I determined the ocean is far too shallow to permit a full roll-over at half-width. However it is top-heavy so floation collars would be necessary to prevent tilting.

The data (and incoming revisions) to actually make these calculations are not online; it is necessary to email Bamber for the netCDF/GeoTiff file. If it is gridded to 1 km, that would amount to 2.2 million spreadsheet lines with 5 columns (lat,lon, bedrock,surface, ice thickness or 11 million cells.

Set up 300 bins of 10 m height increments and populate them as 1,0 from a spreadsheet logic operation such as IF (if-expression, if-true, if-false) applied to 3rd and 4th columns, sum bin columns, then sum the sum row until 89% is reached.

I would try this first gridded to 25 km for a 625-fold reduction in file size, or better, take one east-west cross section at a time as waterlines of the sections average to the waterline of the whole ice mass.  Easier still, Greenland's surface looks like a small chord of a very large circle in cross section and the bedrock could be similarly approximated. Both waterline and center of gravity then follow from symmetry considerations without any calculation.

So yes, if sea level was 1500 m higher (or following massive, rapid melt-off that outpaced isostatic rebound), nothing  would "... keep sea water from rushing in and the whole mountain of ice bobbing up".

Similar considerations apply to the first 100 km of Jakobshavn Isbrae. Not going to see dynamic thinning at the calving front to the point waves are rolling inland over an underwater  icestream.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on November 08, 2014, 02:53:49 PM
Espen asks if the southern branch has a 'doorstep or threshold' pausing further retreat for the next few years.

The calving front has about reached the main sill below a major overdeepening (latest maps from Gogenini paper in post #492). Being much higher, the bedrock of that sill prevents warm sea water from reaching as much of the underwater part of the calving front. That would favor slow-down. Notice that the resolution of the south channel floor is still not great -- the oblique cross section 20130404_02_032 shown in post #493 has 1 pixel per 56x56 sq m of channel (soccer field resolution).

Perhaps there are some clues from overall history of the fjord. Notice it is a straight deep shot all the way from the bay (confluence of north and south channels) all the way out to the mouth at Disko Bay, where detailed bathymetry is available (fig.1,2). In the past, the glacier has ground a channel into bedrock all the way out to the continental shelf (fig.3). Morraine studies have clarified Holocene glacier advances and retreats though the history is complex having been overwritten so many times.

Upstream of the current calving front, we could ask why the icestream has not gouged out a straight shot as well, despite 2-3 million years of erosion. Instead it resembles a meandering river with tributaries (which indeed may have defined the original course in a balmier era).  I am not recalling anything like this in Norwegian fjords however.

Paleo-drainage reconstruction studies of JI have to undo isostatic depression over time to recover the original topography. Note only the upper of the three main tributaries seems very active today though the lower ones once reamed out a major overdeepening at their confluence.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on November 08, 2014, 04:11:51 PM
A-Team so we will have to wait a few years for the the grinding process of the sill to take place, before we enter into further retreat of the southern branch?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on November 09, 2014, 02:23:48 PM
Espen asks if we will have to wait a few more years before JI becomes unglued.
 
The bedrock is hard unfaulted metamorphic precambrian, the sill has withstood a much larger glacier, one that carved a channel out to Baffin Bay. But we may have *already* waited 'a few more years' --  next year could be a biggie.

The question is what sort of year was 2014, did the acceleration of ice in JI's collection basin fade, continue, or get worse relative to 2010-2013 acceleration years? The position of the calving front, while easy to monitor, does not really address this. The last published data from the Joughin group only cover mid-summer 2013 http://www.the-cryosphere.net/8/209/2014/tc-8-209-2014.html (http://www.the-cryosphere.net/8/209/2014/tc-8-209-2014.html)

With a bit more effort, it turns out (if you believe abstract C24B-02 AGU 2014), we could have measured the 2014 velocity field ourselves from Landsat:

Fahnestock, Scambos, Kinger: The high radiometric resolution [12 bit] of Landsat 8 enables one to track subtle patterns on the surface of the ice sheet, unique at spatial scales of a few hundred meters, between images separated by multiple orbit cycles. In areas with significant dynamic topography generated by ice flow, this requires use of simple spatial filtering techniques first applied by Scambos 1992 [free full http://tinyurl.com/loveunb (http://tinyurl.com/loveunb)].

The result is densely sampled maps of surface motion that begin to rival the coverage available from SAR speckle tracking and interferometry. Displacement accuracy can approach one tenth of a pixel for reasonable chip sizes [small chunk of large image] using conventional normalized cross-correlation; this can exceed the geolocation accuracy of the scenes involved, but coverage is sufficient to allow correction strategies based on very slow moving ice.

I could not find any ppts, posters or publication with actual results. Rather than wait for a paper, we might try the ImageJ-SURF plug-in, http://labun.com/imagej-surf/ (http://labun.com/imagej-surf/) which can provide cross-correlation on matched pairs of cloud-free Landsats (ie same row,path,center). The longer the separation in dates, the better the resolution for the slower moving regions.

Flipping through the 7 articles citing Joughin 2014 at GoogScholar for an update, it turns out T Moon et al just put up a new free/full article that updates JI velocity, detrended velocity, run-off (calving volume), and calving front up to 1 Aug 2013: http://onlinelibrary.wiley.com/doi/10.1002/2014GL061836/full (http://onlinelibrary.wiley.com/doi/10.1002/2014GL061836/full)

Here Jakobshavn is glacier #26 among the 55 studied. Using a pdf extractor on supplemental, the graphical data is provided at a very satisfactory resolution 1800 x 1200 for measuring areas-under-the-curve etc. This shows 2013 continued the remarkable speedup of this glacier despite unremarkable weather (measured as the proxy, runoff), recalling the whole summit melted in 2012, run-off reaching its peak.

Daily ice sheet runoff data comes from KNMI's regional atmospheric climate model RACMO2.3; it is used to identify  subglacial water  and the timing of the seasonal melt cycle. Modeled runoff is defined as unretained melt + rain presumably available for drainage to the bed of the ice sheet, that presumably lubricates it some of the time, facilitating sliding.

If that data is available up through Aug 2014, we might estimate the other lines for 2014 from correlation.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on November 10, 2014, 04:15:10 PM
Here are the 35 cloud-free Landsat-8 scenes of Jakobshavn Isbrae for 2014. They are presented in blocks of matching path,row as this best corresponds to distortion-free geometry (same nadir lat,lon).

The 4th column gives the gap in days between successive cloud-free scenes (a multiple of the 16 day orbit). That gap can be as high as 96 days -- it can be cloudy in west central Greenland.

To measure 2014 velocities with the ImageJ SURF plugin (see post above), the choice of block depends on where you wish to measure it. In late July, the icestream might be moving 50 m/day near the calving front, or ~3 pixels at 15m panchromatic resolution so even the shortest interval (16 days) gives a very generous 48 pixels of feature displacement.

The velocity farther upstream at 5 m/day could still be measured fairly accurately at this temporal gap. However velocity mearurement off to the sides or way upstream would benefit from more time between frames. That might raise other issues: mis-matching of sun angle or azimuth causing different illumination conditions. Note too some path,row combinations do not extend very far to the east.

I've attached a piece of the remarkable scene of 08 Nov 14. Late season to be sure but Landsat with 12 bit sensitivity may be able to continue even later into November. LC80090122014312LGN00 just barely covers the eastern Jakobshavn Fjord but that is enough to show it is not yet frozen into a buttress resisting calving. The shadows are very dramatic and quite useful for the topography of glacial surfaces to the south.

Scene                  Date       Day  Gap Path Row Cent Lat  Cent Lon   sunº  azimu  time
LC80100112014303LGN00  30 Oct 14  303  32  10   11  69.60623  -50.88680  6.63  179.9  15:06:41
LC80100112014271LGN00  28 Sep 14  271  32  10   11  69.60641  -50.87276  18.4  178.1  15:06:55
LC80100112014239LGN00  27 Aug 14  239  16  10   11  69.60655  -50.86838  33.9  174.8  15:07:07
LC80100112014223LGN00  11 Aug 14  223  16  10   11  69.60636  -50.87335  35.6  173.5  15:06:34
LC80100112014207LGN00  26 Jul 14  207  16  10   11  69.60629  -50.85146  39.7  172.9  15:06:41
LC80100112014191LGN00  10 Jul 14  191  32  10   11  69.60648  -50.86015  42.6  173.0  15:06:38
LC80100112014159LGN00  08 Jun 14  159  32  10   11  69.60660  -50.86458  43.2  174.9  15:06:11
LC80100112014127LGN00  07 May 14  127  16  10   11  69.60623  -51.01040  37.4  175.7  15:06:09
LC80100112014111LGN00  21 Apr 14  111  --  10   11  69.60624  -51.00720  32.4  175.4  15:06:25
                   
LC80080112014305LGN00  01 Nov 14  305  96   8   11  69.60646  -47.80095  06.0  179.9  14:54:21
LC80080112014209LGN00  28 Jul 14  209  16   8   11  69.60651  -47.76666  32.3  172.9  14:54:21
LC80080112014193LGN01  12 Jul 14  193  32   8   11  69.60641  -47.76994  42.3  172.9  14:54:17
LC80080112014161LGN00  10 Jun 14  161  32   8   11  69.60660  -47.77320  43.5  174.8  14:53:51
LC80080112014129LGN00  09 May 14  129  32   8   11  69.60666  -47.92350  37.9  175.7  14:53:46
LC80080112014097LGN00  07 Apr 14  097  16   8   11  69.60652  -47.91558  27.4  174.6  14:54:18
LC80080112014081LGN00  22 Mar 14  081  --   8   11  69.60650  -47.90940  21.2  173.7  14:54:32
                   
LC80090112014280LGN00  07 Oct 14  280  64   9   11  69.60638  -49.34008  14.9  178.9  15:00:32
LC80090112014216LGN00  04 Aug 14  216  16   9   11  69.60667  -49.32530  37.5  173.1  15:00:36
LC80090112014200LGN00  19 Jul 14  200  16   9   11  69.60648  -49.31127  41.2  172.8  15:00:29
LC80090112014184LGN00  03 Jul 14  184  32   9   11  69.60638  -49.31424  43.3  173.3  15:00:24
LC80090112014152LGN00  01 Jun 14  152  48   9   11  69.60662  -49.31691  42.6  175.3  14:59:57
LC80090112014104LGN00  14 Apr 14  104  48   9   11  69.60643  -49.45147  30.0  175.0  15:00:20
LC80090112014056LGN01  25 Feb 14  056  16   9   11  69.60626  -49.43474  11.4  172.6  15:01:03
LC80090112014040LGN00  09 Feb 14  040  --   9   11  69.60632  -49.42945  05.8  172.6  15:01:16
                   
LC80080122014305LGN00  01 Nov 14  305  96   8   12  68.27964  -49.49216  07.3  178.4  14:54:45
LC80080122014209LGN00  28 Jul 14  209  16   8   12  68.27976  -49.46022  40.5  170.8  14:54:45
LC80080122014193LGN01  12 Jul 14  193  32   8   12  68.27971  -49.46386  43.6  170.8  14:54:41
LC80080122014161LGN00  10 Jun 14  161  32   8   12  68.27988  -49.46752  44.7  172.6  14:54:15
LC80080122014129LGN00  09 May 14  129  32   8   12  68.27992  -49.60601  39.2  173.7  14:54:10
LC80080122014097LGN00  07 Apr 14  097  16   8   12  68.27955  -49.59887  28.7  172.8  14:54:42
LC80080122014081LGN00  22 Mar 14  081  --   8   12  68.27951  -49.59312  22.4  171.9  14:54:56
                   
LC80812332014208LGN00  27 Jul 14  208  16  81  233  69.60660  -48.19174  05.7  -47.9  23:54:03
LC80812332014192LGN00  11 Jul 14  192  --  81  233  69.60659  -48.20579  08.4  -46.8  23:53:59
                   
LC80822332014200LGN00  19 Jul 14  200  --  82  233  69.60623  -49.73775  07.4  -47.3  00:00:11
                   
LC80832332014175LGN00  24 Jun 14  175  --  83  233  69.60667  -51.29052  09.6  -45.7  00:06:12
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on November 12, 2014, 01:22:22 PM
S-1 image from 4.11.2014 (large jpeg)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on November 12, 2014, 01:50:57 PM
Here's my best guesstimate of the current location of the Calving Front. There's a quite large uncertainty on the CF location on the northern edge of the southern branch as it's difficult to tell whether some areas area still stuck to the ice-stream or are just ice melange. A time-series would make this easier to do..
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on November 13, 2014, 01:58:45 PM
Those are very impressive at full resolution. That area (red tint below) is indeed ambiguous: early start on an ice shelf, melange forming, just passive ice on a relatively quiet zone, or ice cascading down the flattening middle branch terminating in the fjord.

This Sentinel is going to provide an impressive winter time series. Did you not say earlier that the return time between scenes was ~11 days? That will make berg tracking a snap. Those move west only by being pushed out by new calving so are a proxy for that.

The velocity of the icestream will also be easy to get at, either from speckle tracking or interferometry. For the latter, 3 consecutive dates from the same satellite position are needed. (I've tried 2, doubling one to make RGB, with so-so outcome. Here we have data for the past five winters that provide a context for 2014-15.

At some point, we may want to rectify the images from perspective to nadir view for comparison to Landsat. Do you recall the Sentinel viewing angle?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on November 13, 2014, 08:09:13 PM
The area is currently imaged every 12 days and in the future it should be done twice every 12 days from different directions (ascending and descending orbits). Once scihub allows for scripted downloads it would be relatively easy to make a processing-graph in the S-1 Toolbox to add (coregister) the new scene onto the existing stack automatically, making the generation of animations very easy.

Speckle-tracking is the easier and more robust method for getting the ice-stream velocity, IMO, but InSAR (and Multi-Aperture-InSAR) is impressive when it works.

The incidence-angle is between 29 and 46 degrees in IW-mode, next time I'll generate the incidence-angle band too to get exact values at this location. I've been using just ellipsoid-geocoding (as I have no DEM of the area) into WGS84 . Do you know what the projection of the Landsat-imagery is? Using the same projection should help the comparisons..
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on November 14, 2014, 05:33:11 PM
Nice work, Nuke. I am looking forward to how this comes out.

LandSat shut down on 01 Nov for the year at least around the calving front. The metadata file provides endless detail on image geometry. From the table above, it appears that path,row set 9,11 is best centered over the current calving front at lat 69.135, lon -49.570.

GROUP = PROJECTION_PARAMETERS
 MAP_PROJECTION = "UTM"
 DATUM = "WGS84"
 ELLIPSOID = "WGS84"
 UTM_ZONE = 22
 GRID_CELL_SIZE_PANCHROMATIC = 15.00
 GRID_CELL_SIZE_REFLECTIVE = 30.00
 GRID_CELL_SIZE_THERMAL = 30.00
 ORIENTATION = "NORTH_UP"
 RESAMPLING_OPTION = "CUBIC_CONVOLUTION"
END_GROUP = PROJECTION_PARAMETERS

NADIR_OFFNADIR = "NADIR"
SCENE_CENTER_TIME = 14:55:00.8997918Z
ROLL_ANGLE = -0.001
SUN_AZIMUTH = 178.40216329
SUN_ELEVATION = 7.31615968
GROUND_CONTROL_POINTS_MODEL = 291
GEOMETRIC_RMSE_MODEL = 13.438
GEOMETRIC_RMSE_MODEL_Y = 9.108
GEOMETRIC_RMSE_MODEL_X = 9.881


I revisited the "55 Glaciers" paper for Jakobshavn velocity to get some idea of what we could expect for Nov 2014 Sentinel velocities. The paper did not provide the actual data points underlying the graphs nor the method for curve-fitting (which was barely exposed under the fat data triangles).

The authors provided a link to the data repository at NSIDC but this proved to be a wild goose chase. Not only did this not contain the 2013 data used in the graph, instead of storing the Vx,Vy data as plain text csv array (comma separated values, excel friendly), they went for a novel 'binary' format for which Matlab/IDL must be purchased for k$$ (users still have to write code!), the explanation being "data files are in 4-byte big-endian IEEE floating point format with the same byte ordering used by non-Intel Macs, not the standard PC byte order." Non-intel macs are of 2005 vintage, so this page hasn't been updated in 9 years.

Here's what you get in your browser opening on the NSIDC ftp link, dozens of screens like this:

(Îîk(Îîk(Îîk(Îîk(Îîk(Îîk(Îîk(Îîk(Îîk(Îîk(Îîk(Îîk(Îîk(Îîk(Îîk(Îîk(Îîk((Îîk(Îîk(Îîk(?ï­ ?Ø"Á?Îþ»?ÇK?¼ÁP?¸õ­?¸¼?Á4â?âì??öé/@…É@½@fˆ?ýš"@U‘@Nm@JÂ@v¦@}?î?o?Ïãh?¼ Õ?ºxg?Á *?¾:{?­ï?«I%?¨2I? lþ? Ws?£Wþ?¢À#?ŸæY?£´0?¤3˜?¬ÔÆ

Most velocity fields we see simply plot velocity magnitude by color; a simple rectangular png could have been provided here so magnitudes need not be computed by each user from components.

So I just re-processed the graph image. It could not be sub-gridded by month or velocity because the pixel intervals were prime numbers, necessitating rescaling. I extended the trend line into 2015 and replaced the heavy triangles with a smooth hand-drawn curve.

The trend line, probably a least square fit heavily influenced by the big melt year 2012, can't keep going up forever; it shows icestream velocity even in the dead of winter is still quite high. I shadowed in 2013 under 2012 to facilitate comparison. Click on the image to see it at the proper scale.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on November 14, 2014, 10:30:04 PM
Somewhere, long ago, i wrote a FORTRAN program that read IEEE bigendian files. I believe GNU fortran had a specifier like CONVERT that did something like this

sidd
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on December 09, 2014, 04:56:46 PM
S-1 6.12.2014 in UTM22/WGS84, full-resolution jpeg. Looks like the southern side of the southern branch has retreated some more.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on December 09, 2014, 06:09:18 PM
S-1 6.12.2014 in UTM22/WGS84, full-resolution jpeg. Looks like the southern side of the southern branch has retreated some more.

Not really, in the animation below is the 2014 minimum (September 28) compared to December 6 2014:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on December 10, 2014, 02:49:24 PM
Thanks Espen! I can keep producing S-1 in UTM22 as they come in order to make a time-series..
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on December 10, 2014, 05:18:28 PM
Thanks Espen! I can keep producing S-1 in UTM22 as they come in order to make a time-series..

Good idea Nukefix! :)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on December 19, 2014, 04:41:53 PM
I have trouble getting the forum to accept my attachments...perhaps they are too big? Does anyone know what the limits are?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on December 19, 2014, 05:01:33 PM
I have trouble getting the forum to accept my attachments...perhaps they are too big? Does anyone know what the limits are?

It's an enduring mystery. Still, I hope you can continue to post this imagery with degradation of resolution or clarity.

Meanwhile, the 0.5m DigiGlobe panchromatic is now in the public domain and is being processed by Noh and Howat into 2m hillside shaded DEMs, quite spectacular. Hmmm, I wonder how and whether this could be combined with Sentinel. See images at http://forum.arctic-sea-ice.net/index.php/topic,1090.msg41740.html#msg41740 (http://forum.arctic-sea-ice.net/index.php/topic,1090.msg41740.html#msg41740)



Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on December 19, 2014, 05:22:57 PM
S-1 18.12.2014 - practically no calving in the last 12 days
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Neven on December 20, 2014, 10:52:18 PM
I have trouble getting the forum to accept my attachments...perhaps they are too big? Does anyone know what the limits are?

How big are your attachments, nukefix? I don't know what the limits are, but I've asked the ASIF Dungeonmaster. He might know.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on December 22, 2014, 02:40:24 PM
I've had trouble with attachments that are ~4.5MB jpegs, roughly 6000x6000 pixels. They seem to upload fine but then the interface freezes with a blank page and they don't get posted. It would be good to know what the limit is, i.e. is it the number of pixels or the filesize..
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Lennart van der Linde on December 22, 2014, 07:04:27 PM
Wipneus pointed to Messerli et al on GIS-glacier velocities:
http://www.the-cryosphere-discuss.net/8/6235/2014/tcd-8-6235-2014.html (http://www.the-cryosphere-discuss.net/8/6235/2014/tcd-8-6235-2014.html)

So it seems Jakobshavn was over 10% faster this year than the previous record in 2012.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Lennart van der Linde on December 22, 2014, 10:16:52 PM
I checked with co-author Aslak Grinsted, who says the average over 199 days of observations was about 30 m/day, so circa 11 km/yr, if this can be extrapolated like that:
https://twitter.com/AGrinsted/status/547105147567230976 (https://twitter.com/AGrinsted/status/547105147567230976)

I think the record average speed was 11.6 km/yr in 2012, according to Joughin et al 2014:
http://www.the-cryosphere.net/8/209/2014/tc-8-209-2014.pdf (http://www.the-cryosphere.net/8/209/2014/tc-8-209-2014.pdf)

This is almost as fast as the maximum observed temporary speed for Jakobshavn of 12.6 km/yr  in Pfeffer et al 2008:
ftp://soest.hawaii.edu/coastal/Climate%20Articles/Pfeffer%20sea%20level%20calving%202008.pdf (http://ftp://soest.hawaii.edu/coastal/Climate%20Articles/Pfeffer%20sea%20level%20calving%202008.pdf)

So how much faster can this and other GIS-glaciers go? Pfeffer et al assumed an average speed of all GIS marine glacier of 12.6 km/yr between 2020 and 2100 for their extreme 2m by 2100 SLR-scenario. Would that be possible?

And if not, how about WAIS and EAIS glacier contributions this century? Could they lose more ice than the 62cm by 2100 that Pfeffer et al assumed, with over 39cm from WAIS alone? How much of a worst-case was their AIS-scenario?

Rignot recently said he thinks WAIS could lose about one third of its ice in 100-200 years, so that could be almost 1 meter from WAIS alone by 2100, I suppose. So that would add almost 60 cm to Pfeffer et al's worst-case.

So even if GIS would lose less than the 54cm in the worst-case of Pfeffer et al, we could possibly still end up worse than Pfeffer et al assumed, if Rignot is right with his worst-case judgement. Or would he be too pessimistic?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on December 28, 2014, 06:34:00 PM
we could possibly still end up worse than Pfeffer et al assumed, if Rignot is right with his worst-case judgement. Or would he be too pessimistic?
Seems right on-target to me, given the adverse developments lately in Greenland and need to apply the Precautionary Principle in any event.

I located some interesting new papers calculating (yet again) the Greenland mass loss and its allocation to surface and deep interior processes. B Csatho has a most excellent interactive graphic for the PARCA flux gate data around the perimeter of Greenland (http://rsl.geology.buffalo.edu/data/Pages/Greenland_MB_Data.html (http://rsl.geology.buffalo.edu/data/Pages/Greenland_MB_Data.html)). There was a very useful ePoster at AGU 2014 from A Sommers et al as well as our first 2015 paper (from ML Andersen et al.) which compares eight different studies (over different data ranges) in Fig.3.

https://agu.confex.com/data/handout/agu/fm14/Paper_26038_handout_952_0.pdf
Thermo-­mechanically coupled modeling of high elevation regions of the Greenland Ice Sheet
A Sommers et al
http://www.williamcolgan.net/pubs/S0012821X14006360.pdf
Basin-scale partitioning of Greenland ice sheet mass balance components (2007–2011)
M.L. Andersen et al
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on December 28, 2014, 10:25:39 PM
That Andersen paper confirms Enderlin et al,doi:10.5194/tc-7-1007-2013
 in that SMB now domiantes in Greenland.

sidd
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on December 29, 2014, 02:23:16 PM
Andersen paper confirms Enderlin et al, doi:10.5194/tc-7-1007-2013 in that surface mass balance now dominates in Greenland
That doi is an interesting paper in its own right but you may have intended her Feb 2014 doi:10.1002/2013GL059010; note the Nov 2014 B Csatho PNAS paper (free full, reviewed on another forum) has SMB at about half. There's yet more coming per AGU 2014.

Is it time for a worldwide moratorium on Greenland mass loss papers? Perhaps we should lock them all in a room until the various approaches are reconciled. In other disciplines, people do meta-analyses or write expert review articles. Greenland is admittedly a moving target.

I tend to measure progress in terms of observational advances (or not). At this time, there is very little experimental data on the geothermal gradient, roughness of bedrock, properties of till, regions of basal melt and basal stick-slip, churning in the EFZ (radar echo free zone), bedrock deflection of stratigraphy, thermal upheaval and englacial temperature profiles. There's only so far we can go just with surface observations.

The bottom line is indeed sea level rise -- we have a baseline now and the start on the trend; by 2025, maybe a grip on the noise in the trend line and a sense of its change in slope (acceleration). That would amount to descriptive phenomenology supplemented by many a theoretical paper lacking validated initial conditions while pooh-poohing sensitivity to them. However I'm optimistic that the englacial experimental side will improve markedly within the next few years.

Enderlin, E. M., I. M. Howat, S. Jeong, M.-J., Noh, J. H. van Angelen, & M. R. van den
Broeke, 2014. An improved mass budget for the Greenland ice sheet. Geophys. Res. Lett.,
866-872, doi:10.1002/2013GL059010

Annual measurements for 178 outlet glaciers reveal that, despite widespread acceleration, only 15 glaciers accounted for 77% of the 739 ± 29 Gt of ice lost due to acceleration since 2000 and four accounted for ~50%. Among the top sources of loss are several glaciers that have received little scientific attention. The relative contribution of ice discharge to total loss decreased from 58% before 2005 to 32% between 2009 and 2012. As such, 84% of the increase in mass loss after 2009 was due to increased surface runoff. These observations support recent model projections that surface mass balance, rather than ice dynamics, will dominate the ice sheet's contribution to 21st century sea level rise.

Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics
BM Csatho et al www.pnas.org/cgi/doi/10.1073/pnas.1411680112 (http://www.pnas.org/cgi/doi/10.1073/pnas.1411680112)

We estimate a mean annual GrIS mass loss of 243 ± 18 Gt·y−1, equivalent to 0.68 mm·y−1 sea level rise (SLR) for 2003– 2009. Dynamic thinning contributed 48%, with the largest rates occurring in 2004–2006, followed by a gradual decrease balanced by accelerating SMB loss...

High sensitivity of tidewater outlet glacier dynamics to shape
EM Enderlin et al doi:10.5194/tc-7-1007-2013  www.the-cryosphere.net/7/1007/2013/ (http://www.the-cryosphere.net/7/1007/2013/)
http://cci.siteturbine.com/facultystorm/profile/cv.php?profileId=933 (http://cci.siteturbine.com/facultystorm/profile/cv.php?profileId=933)

... for glaciers with similar discharge, the trunks of wider glaciers and those grounded over deeper basal depressions tend to be closer to flotation, so that less dynamically induced thinning results in rapid, unstable retreat following a perturbation.... varying the bed topography within the range of observational uncertainty can result in either stable or unstable retreat due to the same perturbation.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on December 29, 2014, 08:15:47 PM
Hmmm box-plots, I think more research is needed to produce plots with mass-balance each year.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on December 30, 2014, 05:49:26 PM
Argh again I cannot get the attachments through :(
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Laurent on December 30, 2014, 06:46:15 PM
Try to reduce the picture (700x700 pixel is enough)?
Change the extension ?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on January 02, 2015, 04:14:36 PM
Try to reduce the picture (700x700 pixel is enough)?
Change the extension ?
Well, they are already crops of ~20000*20000 pixel images so going to that extent would be really unsatisfactory..
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on January 03, 2015, 11:19:49 PM
already cropped way down from 20000 x 20000 pixels
nuke, could you conveniently post some of those orange quicklooks like Wipneus has been posting? Way lower resolution but still possibly of interest.  http://forum.arctic-sea-ice.net/index.php/topic,176.msg42626.html#msg42626 (http://forum.arctic-sea-ice.net/index.php/topic,176.msg42626.html#msg42626)

It seems like Sentinel is missing the Jakobshavn glacier on about half the days, according to the Danish perimeter series. Better if it went 100 km farther to the east. Is this temporary malfunction, shake-down of routine, or irrevocable orbital consequence? http://ocean.dmi.dk/arctic/morrisjessup.uk.php (http://ocean.dmi.dk/arctic/morrisjessup.uk.php)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Wipneus on January 04, 2015, 08:22:18 AM
Jacobshavn is further south so the orbits are wider apart. Further the preferred acquisition mode (https://sentinel.esa.int/web/sentinel/user-guides/sentinel-1-sar/acquisition-modes) is higher resolution IW (Interferometric Width) rather than the EW (Extra Width) products I use for Nares. Better resolution->narrower swath->longer return times. Perhaps the DMI images can only use EW products?

From the following list we can deduce that at the moment data is missing for 2014-12-30 and perhaps 2015-01-03. The datahub servers seem to be very stressed at the moment, so that may cause the delay.

S1A_IW_GRDH_1SSH_20141019T095957_20141019T100022_002897_003480_C464
S1A_IW_GRDH_1SSH_20141023T204643_20141023T204712_002962_0035DA_DD2A
S1A_IW_GRDH_1SSH_20141031T095957_20141031T100022_003072_003842_4CA7
S1A_IW_GRDH_1SSH_20141104T204643_20141104T204711_003137_0039AD_E786
S1A_IW_GRDH_1SSH_20141112T095957_20141112T100022_003247_003C08_EA1B
S1A_IW_GRDH_1SSH_20141116T204642_20141116T204711_003312_003D5F_79EF
S1A_IW_GRDH_1SSH_20141124T095957_20141124T100022_003422_003FE8_3FAF
S1A_IW_GRDH_1SSH_20141128T204642_20141128T204711_003487_00416D_ABE0
S1A_IW_GRDH_1SSH_20141206T095956_20141206T100021_003597_004401_1CDA
S1A_IW_GRDH_1SSH_20141210T204641_20141210T204710_003662_004568_80DD
S1A_IW_GRDH_1SSH_20141218T095956_20141218T100021_003772_004800_0405
S1A_IW_GRDH_1SSH_20141222T204641_20141222T204710_003837_00496D_02C5

The EW, dual polarization images listed (Nov 29 and later) suggsts a new product today.

S1A_EW_GRDM_1SDH_20141129T100720_20141129T100824_003495_00419D_4E85
S1A_EW_GRDM_1SDH_20141130T203015_20141130T203119_003516_00421B_DCEF
S1A_EW_GRDM_1SDH_20141201T095119_20141201T095223_003524_004252_5179
S1A_EW_GRDM_1SDH_20141203T205450_20141203T205550_003560_004324_4775
S1A_EW_GRDM_1SDH_20141204T101623_20141204T101723_003568_004359_5E8F
S1A_EW_GRDM_1SDH_20141205T203830_20141205T203930_003589_0043CC_E0CA
S1A_EW_GRDM_1SDH_20141211T100719_20141211T100823_003670_004597_FCF3
S1A_EW_GRDM_1SDH_20141212T203014_20141212T203118_003691_004611_338A
S1A_EW_GRDM_1SDH_20141213T095118_20141213T095222_003699_004643_263C
S1A_EW_GRDM_1SDH_20141215T205450_20141215T205550_003735_004724_8AE4
S1A_EW_GRDM_1SDH_20141216T101623_20141216T101723_003743_00475A_6D69
S1A_EW_GRDM_1SDH_20141217T203830_20141217T203930_003764_0047D4_29B4
S1A_EW_GRDM_1SDH_20141223T100719_20141223T100823_003845_004998_2EB3
S1A_EW_GRDM_1SDH_20141224T203013_20141224T203118_003866_004A12_093A
S1A_EW_GRDM_1SDH_20141225T095118_20141225T095222_003874_004A48_6B69
S1A_EW_GRDM_1SDH_20141227T205450_20141227T205550_003910_004B1C_5A9D
S1A_EW_GRDM_1SDH_20141228T101623_20141228T101723_003918_004B4F_F257
S1A_EW_GRDM_1SDH_20141229T203830_20141229T203930_003939_004BBE_D964

I will have a look at the preview images when the servers start responding again.

PS. for the single polarization mode (in the fourth field, SH means "Single HH polarization available") the quick look images are in B&W
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Wipneus on January 04, 2015, 10:00:41 AM
Quick-look image of the last EW product.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Wipneus on January 04, 2015, 10:03:28 AM
Quick-look image of the latest IW product.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Wipneus on January 04, 2015, 10:28:56 AM
Hot from the press, the expected 2015-01-03 IW product just came in.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on January 05, 2015, 11:18:04 AM
Wip, thanks for the Sentinel info, very helpful.

The image below shows the location of the Parca stakes in the vicinity to Jakobshavn. The elevation contours are taken from sidd's site after Bamber 2013. Because the flux gates are about 30 km wide and the velocities were read in 1996, it is less than ideal for Jakobshavn details. None of the 3 stakes shown are among the six for which ePoster data from Sommers AGU2014 is available; the nearest is n32 to the north which is not in the current Jakobshavn drainage basin.

The flux across gates cd64-cd87 sees 7.3 cubic km per year go by at a velocity of 168 m/yer from a 16144 sq km drainage basin; that across cd38-cd64 has 5.8 at 128 m/yr from a 11664 drainage basin, per (per B Csatho web page
http://rsl.geology.buffalo.edu/data/Pages/Greenland_MB_GateJ.html# (http://rsl.geology.buffalo.edu/data/Pages/Greenland_MB_GateJ.html#)

It is getting quite complicated to collect and display all of the relevant data layers, here Landsat-8, Sentinel, elevation, ice thickness, ice surface velocity, flow lines to the summit ridge, ice velocity with depth, ice temperature with depth and isotherm blocks, radar isochronal stratigraphy layers, strain rate, bedrock topography, geothermal flux, temporal variation of all these and so forth.

Greenland 3D representation will tilt software away from gimp towards ImageJ2 which has more advanced features for higher dimensional processing and display.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on January 26, 2015, 11:52:26 PM
It's quite interesting to follow the peer-review comments on the ImGRAFT algorithm paper -- I wish more journals would do this transparently. Recall the paper proposed yet another way of measuring feature movement across pairs of satellite photos, maybe better, maybe not (3 such algorithms come bundled with ImageJ2 alone!).

http://www.the-cryosphere-discuss.net/8/6235/2014/tcd-8-6235-2014-discussion.html (http://www.the-cryosphere-discuss.net/8/6235/2014/tcd-8-6235-2014-discussion.html)

Along the way, the authors asserted a record velocity for Jakobshavn of 52 m/day during July 2014 (suggesting a speedup). However today, Joughin writes that they measure back from the calving terminus itself to avoid crevasse artefacts.

"Nonetheless, we do measure velocities >50 m/day at times in the summer of 2012 (not shown in our paper). We have extended the TSX [TerraSAR-X satellite] record through 2014 and find that, when comparing the speeds at the same point, peaks speeds in July 2014 are considerably slower than the 2012 peak by about 2-3 km/yr [~17% slower] . So any references to faster speeds in 2014 should be removed (this in no way detracts from the quality of the results)."

We're left wondering why this should be the case, what caused the acceleration bubble in the first place, what we can predict for 2015, and what this means long-term for sea level rise from this major contributor. It does seem that runaway acceleration is not a concern for the immediate future.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on February 12, 2015, 09:13:34 PM
Just from the "oven". As can be seen in the animation below, Jakobshavn grew during the winter since the low in September 28 2014. The growth is especially seen at the southern branch:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: icefest on February 12, 2015, 10:02:31 PM
 :o
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on February 13, 2015, 12:42:15 PM
So we have a rather good match year on year on path row, sun elevation and azimuth. That means good co-registration can be obtained; however the colors on the greenish preview pdfs behave quite differently. the 15 m seems to show major ongoing crevassing and calving in the 2015 (or a shot of them frozen in time).

09 Feb 15 LC80090112015043LGN00 9 11 172º 6.67º
    
09 Feb 14 LC80090112014040LGN00 9 11 173º 5.78º
25 Feb 14 LC80090112014056LGN01 9 11 173º 11.4º

As noted on a Feb 15 Sentinel image at another imagery forum, the calving front of Jakobshavn Isbrae recovers somewhat each winter because the ice mélange in the fjord provides buttressing that tamps down calving retreat. I have not looked into the date and position of maximal annual recovery to see if there is a trend.

http://forum.arctic-sea-ice.net/index.php/topic,638.msg45094.html#msg45094 (http://forum.arctic-sea-ice.net/index.php/topic,638.msg45094.html#msg45094)

We know that the Joughin group, which has been providing the best quantitative coverage of Jakobshavn, extended their analysis through 2014. This raises an interesting question as it may not be possible to keep publishing 'Brief Reports' each year -- they may have to bundle it into something bigger (or just put it online).

We also know from AGU 2014 that T Scambos has performed ultra-sensitive velocity measurements using pairs of Landsat-8's in 16-bit mode but that seems not to have come out yet.

Here is something along those lines from U Herzfelt et al in Nov 14: $36 paywalled doi: 10.3189/2014JoG13J129

Our objective is to map dynamic provinces and investigate dynamic changes in Jakobshavn Isbrae. We use an approach that combines structural glaciology and remote-sensing data analysis, facilitated by mathematical characterization of generalized spatial surface roughness that provides parameters related to ice dynamics, deformation and interaction of the ice with bed topography.

The approach is applied to derive time series of elevation and roughness changes and to attribute changes during rapid retreat. Different dynamic types of fast- and slow-moving ice can be mapped from ICESat (2003–09) and ATM data using spatial roughness characterization, validated with ASTER and bed-topographic data.

Results of comparative analysis of elevation changes and roughness changes indicate surface lowering of 10–15 m/yr between 2004 and 2009 but no change in surface roughness and dynamic types. These findings are consistent with a front retreat as part of a fjord-glacier cycle or following warming of fjord water and with climatic warming, but not with an internal dynamic acceleration as a cause of rapid retreat. Relationships to changes in basal water pressure are discussed. All glaciodynamic changes appear to have initiated near the front and propagated up-glacier.
http://www.ingentaconnect.com/content/igsoc/jog/2014/00000060/00000223/art00002 (http://www.ingentaconnect.com/content/igsoc/jog/2014/00000060/00000223/art00002)

This is nice enough Nov 2013 article on melt lakes and water channels specific to Jakobshavn, not sure why it took 6 years to analyze 2007 data but it might serve as a template for an update with today's satellites.

Supraglacial melt channel networks in the Jakobshavn Isbræ region during the 2007 melt season
DJ Lampkin and J VanderBerg
free full: http://onlinelibrary.wiley.com/doi/10.1002/hyp.10085/full (http://onlinelibrary.wiley.com/doi/10.1002/hyp.10085/full)

Supraglacial channels are an important mechanism for surface water transport over the ablation zone of western Greenland. The first assessment of the spatio-temporal distribution of surface melt channels and their relationship to supraglacial lakes over the Jakobshavn Isbræ region of Western Greenland was analysed using Landsat during the 2007 melt season.

A total of 1188 melt channels were delineated and show an increase in the number of melt channels throughout the season, reaching a peak on 9 August. Water-filled melt channels advanced to a maximum elevation of 1647 m on 9 August and attained a minimum average slope of 0.009 on 8 July. The ablation zone demonstrates two hydrologic modes, where crevasse and moulin terminating channels dominate at elevations <800 m and higher-order channel networks >800 m. Development of higher-order networks is interrupted by flow divergence due to partitioning of melt water into vertical infiltration through moulins and crevasse fields prevalent at lower elevations. Tributary and connector networks between 800 and 1200 m in elevation are correlated with fewer lake occurrences, lower surface velocities (~50 m a−1), and ice flow dominated by internal deformation over basal sliding...
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on February 14, 2015, 03:47:31 PM
Amazing images!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on February 14, 2015, 04:07:05 PM
I continue to be fascinated by the calving front on the north side of the main glacier that is right at the main calving front and that is exposed to the fjord that can be seen on the last image. This calving front appears to be draining ice from a portion of the ice sheet that is grounded below sea level and situated north of the main channel. It is actually a fairly large feature.

(See topographical map)

If you look at the ice surface on the red image you have posted, it seems you can see the outline of this shallow bay? Is this visible feature actually surface ice that is lower than the ice adjacent?

Portions of this bedrock are 500 meters below sea level.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on February 19, 2015, 11:39:16 PM
Believe it or not! Massive calving seen at the southern branch of Jakobshavn Isbræ:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: AbruptSLR on February 20, 2015, 12:11:25 AM
A major calving in the middle of Winter!  I can't wait to see what happens this Summer.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on February 20, 2015, 03:58:05 AM
any guesses as to how long b4 JI  southern branch grounding line retreats behind the lip in Gogineni Gorge ?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Jim Hunt on February 20, 2015, 01:24:47 PM
Believe it or not! Massive calving seen at the southern branch of Jakobshavn Isbræ:

Does this Sentinel "PolarView" from the 15th help throw additional light on matters?

The second one, from the 14th, is even less "crystal clear"!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on February 20, 2015, 03:03:44 PM
The image from scihub reveals that a calving-event has apparently taken place.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Jim Hunt on February 20, 2015, 03:18:37 PM
The image from scihub reveals that a calving-event has apparently taken place.

Thanks nukefix. I've incorporated that image into my blog post at:

http://GreatWhiteCon.info/2015/02/shock-news-massive-calving-of-jakobshavn-isbrae/ (http://GreatWhiteCon.info/2015/02/shock-news-massive-calving-of-jakobshavn-isbrae/)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: solartim27 on February 20, 2015, 05:48:05 PM
A major calving in the middle of Winter!  I can't wait to see what happens this Summer.
Could it be that this is routine, and that we are just noticing it, or just now have the ability to see it?  Helheim had a calving event in early January, and has also retreated substantially over the winter in past years.

Be aware, Helheim is fast moving monster (probably why it is named so), the calving line seen late 2013 moved some 2 -  3 km during the winter, we will follow it during the season to see where it ends this season.
 
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Wipneus on February 20, 2015, 05:51:11 PM
Believe it or not! Massive calving seen at the southern branch of Jakobshavn Isbræ:

Does this Sentinel "PolarView" from the 15th help throw additional light on matters?

The second one, from the 14th, is even less "crystal clear"!

These are image made with the sensor in EW (extra wide) mode. Lower resolution and especially worse quality than the IW images that also exist for Jacobshavn. The glare is worsened by the poor image processing that is the fate of these images.

I tried to apply some extra doses of love and care to get some decent images form the raw data.
The result shows beyond doubt that the calving was on February 14/15.

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on February 20, 2015, 08:50:34 PM
Thanks guys for the additional documentation!
From what I can see, Radarsat data, Zachariae is moving big too at the moment, yes this will be an interesting new season. ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on February 20, 2015, 08:55:35 PM
Wow! The massive crevasses were evident earlier but I was thinking they were in a state of suspended animation due to buttressing from frozen mélange in the fjord. I'm going to guess this is an effect of warmer water in Baffin Bay (and so Disko Bay and at the calving front: the mélange is just not strong enough this year to hold back calving.

This was a 2-3 x larger event in terms of cubic km than we were seeing this summer. What effect would consistently less back pressure have on annual discharge? Perhaps lessen the slow-down in winter, thus raising the average monthly discharge and so the annual -- it takes a lot of May and June to re-accelerate Jakobshavn.

Meanwhile, here are the 15 m Landsats.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on February 20, 2015, 09:18:46 PM
Just to keep you informed, this is the retreat situation since 1851, the years mentioned are the minimums (at least 2013 and 2014)!

Please click on image to enlarge!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: werther on February 20, 2015, 09:29:08 PM
Well, what can one add… thought something was moving as I eyeballed Sermeq kujalleq three days ago and saw this MODIS pic, cleared after the sun returned out there last week:

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi1036.photobucket.com%2Falbums%2Fa446%2Fhanver1%2Fr02c02%2520day%2520048%252017022015%2520SK%2520detail%2520small_zps5fnkbzz1.jpg&hash=ec33c3bb1b85732c915e82091d3dc03a)

Next day I saw Espen calling a large calving and he’s right. I haven’t checked the new calving size, but it could actually have been about 7 km2 ( thickness 500-600 m1 so about 3.5-4.2 km3) that has subsided. Still, as spring approaches, the front is about 900 m1 short of the max. June ’12 retreat.
Sermeq Kujalleq is bound in a dynamic struggle to stay in contact with the sill at the entrance of the deep trench. It is just a matter of time until this contact will be lost and we might witness a rapid retreat.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on February 20, 2015, 10:00:42 PM
Wow! The massive crevasses were evident earlier but I was thinking they were in a state of suspended animation due to buttressing from frozen mélange in the fjord. I'm going to guess this is an effect of warmer water in Baffin Bay (and so Disko Bay and at the calving front: the mélange is just not strong enough this year to hold back calving.

A-Team I dont think the fjord and what is in it, have any effect on the forces coming from Jakobshavn, we are in relatively warm water, anyway?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Jim Hunt on February 20, 2015, 10:53:39 PM
A-Team/Werther - Thanks for the additional info, now added to my original article.

I waited till I figured they'd be up and about in Boulder, then I phoned the NSIDC to see if they had any comment. The recorded message said they're all away on what sounds like a team building exercise of some sort. Next I tried DMI, but I guess they'd already all headed off home for the weekend by then :(

Last time I called DMI I discovered that they had a team out in the field in Greenland. I wonder where?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: lanevn on February 20, 2015, 11:06:12 PM
Were that ice  "floating" or it added now to sea level rise?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on February 20, 2015, 11:17:57 PM
Were that ice  "floating" or it added now to sea level rise?

The ice that was above sea level, more or less, will be added to the current sea level eventually, when melted.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on February 21, 2015, 12:38:46 AM
I don't think the fjord and what is in it, have any effect on the forces coming from Jakobshavn

Maybe get permission to take away the flying buttresses from a gothic cathedral to see if it holds up? The speedup started 15 years ago or so when JI lost its floating ice shelf. Now JI is losing its solid mélange which is the temporary winter counterpart to an ice shelf. Many many publications on this for JI, about 1 in 10 we have reviewed here. The blog search tool for 'Baffin" will find the classic Nature paper ... firewalled but I posted the key figures.

Domed ice sheets like Greenland want to sag flat. Frozen mélange on marine terminating glaciers is only one of many sources of resistance (buttressing) to that. The water near the fjord surface is not warm, just ever so slightly above the freezing point. Because the calving wall goes so incredibly deep, when it falls off and turns over sideways, it actually pushes even strongly frozen mélange westward a km or more during an event. Consequent convective mixing at the calving front leading to yet more melt has also been the subject of numerous studies.

Here is a 2015 paper on the Jakobshavn mélange that will cover all the earlier work as well:

Seasonal and interannual variations in ice melange and its impact on terminus stability, Jakobshavn Isbræ, Greenland
R CASSOTTO, M FAHNESTOCK, JM AMUNDSON, M TRUFFER, I JOUGHIN
http://www.igsoc.org:8080/journal/61/225/j13j235.pdf (http://www.igsoc.org:8080/journal/61/225/j13j235.pdf)

We used satellite-derived surface temperatures and time-lapse photography to infer temporal variations in the proglacial ice melange at Jakobshavn Isbræ, a large and rapidly retreating outlet glacier in Greenland.

Freezing of the melange-covered fjord surface during winter is indicated by a decrease in fjord surface temperatures and is associated with a decrease in ice melange mobility and a drastic reduction in iceberg production.

Vigorous calving resumes in spring, typically abruptly, following the steady up-fjord retreat of the sea-ice/ice-melange margin. An analysis of pixel displacement from time-lapse imagery demonstrates that melange motion increases prior to calving and subsequently decreases following several events.

We find that secular changes in ice melange extent, character, and persistence can influence iceberg calving and therefore glacier dynamics over daily-to-monthly timescales which if sustained will influence the mass balance of an ice sheet.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: AbruptSLR on February 21, 2015, 01:14:33 AM
Were that ice  "floating" or it added now to sea level rise?

The ice that was above sea level, more or less, will be added to the current sea level eventually, when melted.

Not to be a nitpicker but as soon as the glacial ice Volume Above Floatation, VAF, joins the mélange it contributes immediately to sea level rise, whether it has melted, or not; because it immediately displaces ocean water.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Pmt111500 on February 21, 2015, 04:27:25 AM
Just to keep you informed, this is the retreat situation since 1851, the years mentioned are the minimums (at least 2013 and 2014)!

Please click on image to enlarge!


tried to combine this image with the bottom topography one on the previous page and got an ugly image that would state the calving front is about 3 km (little under 2miles, if you insist on using obsolete measures) from the last ocean bottom hill before the channel deepens towards the main Ice Sheet. Is this about right? Thus the ocean water should start to get under the GIS in few years.  This would transform parts of it into a very old (130000-year) sea ice, so the deniers might get excited by the sudden increase of old ice. But as I said I'm not too sure the image overlay is in correct position, so not posting it.

This should pretty much ensure, that if there's no top melt on GIS there will be bottom melt, no? Thus GIS might join the WAIS parts in the irreversible melting mode in a few years. the bottom topography map though does not show if there are additional barricades of rock and ice, so not saying +15m ASL is inevitable in 300-1500 years.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on February 21, 2015, 01:19:25 PM
Right, it is not so easy to locate the latest high resolution grayscale DEM of the Jakobshavn sill area in the south branch, even though the garishly colored hill-shaded angled perspective broad area view (like the one that keeps getting posted here) is ultimately bump-mapped up from this flat grayscale.

The short answer is cut to M Morlighem's web page and follow the link to NSIDC data archive for the netCDF files and open with Panoply freeware or the ImageJ2 plugin. That group has refined the 6 main Greenland maps into a self-consistent co-registered GIS dataset using conservation of mass considerations. This will very likely improve on the above Bamber 2013 in these over-deepened marine terminating glaciers (yet how is this to be experimentally validated since radar isn't doing well on these?)

http://sites.uci.edu/morlighem/dataproducts/mass-conservation-dataset/ (http://sites.uci.edu/morlighem/dataproducts/mass-conservation-dataset/)

Otherwise, it is quite difficult to co-register an overhead satellite nadir view with a perspective view with whose angles and viewing location aren't provided when, as here, the elevations have been shaded according to shadows cast by that particular view. That shading was not done sensibly in a HSV (hue saturation value) color space channel.

Since the map-generating software, palette, and command line used are almost never mentioned in glaciology articles (which seldom have substantial 'methods' sections), it would be difficult to monte carlo your way up from a grayscale DEM up to the perspective view, that is, invert the perspective view to the flat gray DEM so you could do a proper overlay.

Nor is it easy to locate the most recent 1D depth profile map of the channel bottom and locate the current calving front relative to nearest sill. Here the experimental error is important as it will be quite high on the deep or steep-walled areas which are especially problematic for ice penetrating radar.

The short answer is cut to Fig.3 of Joughin 2014 (enhanced below). That shows the JI calving front climbing out of a very deep trough and just about at the top of the second highest sill, to be followed by a shallow trough, the main sill, and then a long slide. They ending up tossing all the post-2008 DEM products and all the subsequent grid flights: Free full at http://www.the-cryosphere.net/8/209/2014/tc-8-209-2014.pdf (http://www.the-cryosphere.net/8/209/2014/tc-8-209-2014.pdf)

Bed elevations were interpolated from a gridded map of radar depth soundings produced by the Center for Remote Sensing of Ice Sheets (CReSIS)(Li, 2009; Van der Veen et al., 2011). Multiple versions of the DEM exist, but based on comparison with other data sets our preferred version is the one located at ftp://data.cresis.ku.edu/data/grids/old_format/2008_Jakobshavn.zip. (http://ftp://data.cresis.ku.edu/data/grids/old_format/2008_Jakobshavn.zip.) 
The radar data from middle years is carefully reviewed by Gogenini 2014, http://www.igsoc.org:8080/journal/60/223/j14j129.pdf, (http://www.igsoc.org:8080/journal/60/223/j14j129.pdf,) noting the problems arising from terminal roughness, side reflections, and material at the bottom.

The ice thickness is ~850m at the calving front [which converts calving area to calving volume], increases to~1500m, then decreases to ~1200m between 5 and 7km. Beyond this, the ice thickness varies between 1400 and 1200m. We also observe two distinct echoes separated by 100–200m in the along-flow line echogram caused either by side-wall echoes and bed echoes or multiple interfaces at the bed.
Oddly, this article does not include the great many subsequent grid overflights with what one supposes are improved radar designs nor provide a bottom line map of the depth profile. Ice thickness would have to be subtracted from surface elevation to get at trough and sill.

I've looked at all the later down-channel flights but it is just not possible to read off the trough-and-sill profile at the calving front because the radar is not reaching bedrock (per echo2 image annotations by Cresis themselves).

The data on JI -- even though it is the most intensively flown grid in either Greenland or Antarctica -- is still quite sparse: points at 50 m intervals don't fill lines and lines at 5 km spacing don't fill areas -- Kansas is not flying peano curves. JI is an extreme situation and ice-penetrating radar struggles with flares off the steep walls and noisy crevasses near the terminus.

So who among us has time to compare and contrast the latest trough-and-sill profile from Morlighem with Joughin 2014 and Gogenini 2014?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on February 21, 2015, 03:26:52 PM
Sermeq Kujalleq is bound in a dynamic struggle to stay in contact with the sill at the entrance of the deep trench. It is just a matter of time until this contact will be lost and we might witness a rapid retreat.

To quote Joughin 2014, pg 212, fixes in brackets:

Further summer speedup of Jakobshavn subsequently declined in 2013 as the terminus retreated to higher ground. By contrast, the 2009 mean speed was faster than the 2011, despite a more advanced 2009 terminus position. This difference likely reflects the fact that at these time scales, the other processes and feedbacks have a substantial influence on flow.

If the terminus has reached the bottom of an overdeepened region, then the terminus may be able to find a position of transient stability on the high spot farther upstream [located at positions 12 to 17 km in the inset below] as retreat to shallower depths yields slower speeds (Joughin et al., 2012a).

The relatively high surface slope region upstream of the overdeepened basin [1.5º, image below] where the present heights are [80 to 167 m] metres above flotation, may further slow retreat, since it should take more time to thin to near flotation. By contrast, low surface slopes and heights near flotation likely facilitated the rapid retreat since 2009.

While the high spot above the basin may slow flow, the terminus would still be grounded on a bed at least 900 m below sea level, likely yielding speeds well above balance that would maintain strong though potentially diminished thinning. As a consequence, the terminus likely will continue to retreat, albeit perhaps more slowly in the near term, until it again reaches bed depths similar to summer 2012 (1300 m below sea level) at 15 km farther upstream.

At the current stage, further retreat may largely be driven by ice dynamics with only weak coupling to climate forcing. Thus, a re-advance rather than retreat likely would require a period of several years to decades of cooling. Once past the high spot, the trough extends roughly 50 km farther inland at depths below sea level of 1200 m and more before eventually reaching shallower depths.

Thus, although variation in trough width of 3.5 to 5.5 km could modulate the rate of flow, once into this deepest part of the trough, extreme velocities (12 km/yr) are likely to persist as the terminus rapidly retreats. Furthermore, without the [need] to seasonally advance up a relatively steep bed slope as in the past several winters, such high speeds may be sustained year round.

Because the deep trough of Jakobshavn is extremely difficult to measure with conventional techniques, we cannot rule out that some or all of the high spot might be a gridding artifact, in which case retreat may occur even more rapidly. Similarly, we cannot rule out that some bed highs may not have been resolved that could provide additional points of transient stability.

I re-did the flotation (thinning) graphic below to fix the scaling. The flotation curve looks like the mirror image of the bedrock curve because it is essentially that adjusted for current surface elevation (affine transformation).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Pmt111500 on February 21, 2015, 03:58:10 PM
Thanks, A-Team, this makes it certain my image was falsely located... still not certain by how much, but at least 3 km off to the fjord side... Good to hear there is detailed investigation here.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: werther on February 21, 2015, 04:10:12 PM
Thanks, A-Team,
That quote seems to neatly sum up my own thoughts. I've been writing down and summarizing my views on the process today and will spare everyone the detail as your quote is illustrative enough. Here's a layered insert of the bedrock map I found several years ago on CE-journal, coming from I think a presentation by Konrad Steffen:

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi1036.photobucket.com%2Falbums%2Fa446%2Fhanver1%2FClimate%25202015%2FSermeq%2520Kujalleq%2520bed%2520elevation%2520small_zpsfvas9jaq.jpg&hash=4af0db30c52bce852724b9e57f5e7206)

The black lines on both sides of the gorge represent the sea level on the bedrock. The red line indicates the maximum 2012 retreat. Where yellow fades into green lies -500, and green into blue -1000m. I've been thinking about how 'Baffin Water' could eventually get under the glacier. There's no large intrusion yet. But some specifics in the present situation and the properties of the deep gorge make it likely that this intrusion might become a fact in the next few years.
In that context I just remind the research done by ETH during '03-'04, indicating a layer of free flowing water right under the glacier at the bottom of the deep gorge. The layer was about 120m deep at maximum and extended for 40 km all the way up to the sill.
There's also the present situation, where the dynamic equilibrium during the last few years has created a sort of mixer bassin, about 40 square km, on the Eastern sill-slope, reaching from 300 to 900 m below sea level.
The big question is, will further retreat expose the end of the 40 km stretch of the above mentioned free flowing water layer and its supporting melt water drainage system enough for warmer, saltier ocean water to enter against the pression of the deep-/melt water flow?

If that happens, dig this. It took a century to retreat 30 km up to the head of Ilulissat Fjord. It took only 10 years to retreat another 15 km to where the calving front is oscillating against the backside of the sill. I suppose there are more than enough factors contributing to an even faster retreat as soon as the sill is cleared at last. Within ten years the calving front might be almost halfway into the gorge, leaving a new, deep fjord for ocean water to find a playground.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on February 21, 2015, 04:12:39 PM
A-Team how much of that 628 meter was lost from 2013 to 2014?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on February 21, 2015, 06:43:13 PM
I have been digging into my Landsat Archives, and I cant find evidence of any real calvings this early in the season, is this a new future behavior?
Zachariae is already a year around calving engine. 
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on February 21, 2015, 07:07:14 PM
What is the thickness of the glacier at the pinning point  a few km upstream of the calving front? Is it even close to floating or would it need to thin a lot more, which would require higher flow-speeds?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on February 21, 2015, 08:46:29 PM
What is the thickness of the glacier at the pinning point [sill] a few km upstream of the calving front? Is it even close to floating?
I extracted the flotation graphic from Joughin 2014 and added to #565 above. It is about 150 m too thick, nowhere near floating if we assume the bedrock depth profile is correct. Note the authors themselves are questioning the existence and positions of the sills.

I believe Werther has tracked down the source of an immense amount of journal confusion: the older Steffen paper where the sill is assumed downstream of the current calving front. I have no idea what this could have been based on, very early radar maybe. Cresis did not reach bedrock until 2006-2008.

Thinning of lower JI was discussed in a 2001 Steffen paper:

Abdalati W and Steffen K (2001)
Greenland ice sheet melt extent:1979–1999.
J. Geophys. Res.,106 (D24), 33983–33988
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on February 21, 2015, 11:22:26 PM
I extracted the flotation graphic from Joughin 2014 and added to 564 above. It is about 150 m too thick, nowhere near floating.


The scale on the left for the blue line seems to have been chopped off. Could you indicate the units ?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: werther on February 21, 2015, 11:53:51 PM
Well, I have to admit I'm losing it on A-Team's bedrock length-profile. Maybe I'm relying too much on the clear bedrock map by Steffen I posted earlier. I just don't see any important sill within the next 40 km from the present position of the calving front.
Taking that as fact, there's no 'pinning point' at all a few km upstream. A-Team's profile though presents a buckle out there up from -1300 to about -800. Could be; after all there's no real good data available.
Anyway, I agree with A-Team that glacier thickness is too large for floating out there at this stage. No sill 2100 m, over a sill like in the profile 1400 m. Too much to float, the deep water layer on the bottom of the gorge is under enormous pressure. Nevertheless, dynamic layering, shear and changes in the behaviour/area of the ablation zone could very well change the properties.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on February 22, 2015, 05:26:49 AM
contour map from morlinghem nc file bed layer
upside down, north is down, sorry, don't have time to fix
 
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on February 22, 2015, 10:31:44 AM
Now the numbers are upside down ;):

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on February 22, 2015, 10:44:01 AM
Including the present calving front unless I am completely wrong?

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on February 22, 2015, 11:01:02 AM
How much of that 628 meter was lost from 2013 to 2014?
Not very much, but I wonder if this will be the year that the calving front retreats beyond the sill. Though how would we know if its location and even existence aren't certain? I suppose by a fit to the physics. Yet all is not well there because it seems not to be kicking out any publishable predictions for 2015-20.

You raise an interesting point in that this article pins calving front, surface velocity, and thinning data on a somewhat arbitrary channel centerline coordinates whereas the south channel has ~5-6 km of width. The 2013-14 change line shown above is observed kattywompus to the centerline.

Note the calving front itself is quite heterogeneous in terms of ice origin (the northern third is the ice stream proper, the southern part comes in from the side), so we have a situation where part of the calving front could have already climbed out of the overdeepening. Chasing down the topography of this sill -- rounded knob, asymmetric teardrop, or flat spillway -- with respect to the centerline is really problematic given the data situation.

The scale on the left for the blue line seems to have been chopped off. Could you indicate the units ?
The scale is still there, barely (the m below the 167), it is meters. I do condense the graphic legends to make more room for resolution per the 700 maximal pixel width here. This one had to be radically rescaled vertically in gimp to get its scale readable. The authors did not furnish the underlying numeric data points in journal supplemental (despite utilizing it) so I could not cleanly re-graph it.

The background grid is really needed to subdivide the units which came overly large 500 m chunks in the original, whereas the flotation varies on a scale of meters.

These grids are easy to make in Gimp if you can remember where they have the tool buried: Filters --> Render --> Pattern --> Grid. First count the number of pixels at full range of the scale and decide how that range is best subdivided, eg 165 pixels factors as 3*5*11 so those plus 15, 33, 55 would work for grid spacing pixels (or rescale the 165 to something more decimally like 200).

The trick is not to do the grid within the graph but rather as a separate layer that is otherwise empty (all alpha). That way the color and thickness of the grid can be changed later, but most importantly placed unobtrusively behind the graphic (if the white spaced there can be alpha-ed) and dimmed with the opacity controller.

relying too the clear bedrock map by Steffen
This older map is an important discovery because it explains a lot of confusion in the journals about where the sill is located, before or beyond the current calving front. Presumably later maps based the 2006-08 experimental radar data are better because those years were the first to reach bedrock.

Glaciers almost always have overdeepenings (greater bedrock gouging) and those imply an upstream sill (lesser gouging). I'm wondering about the status of side-looking sonar sounding in the first 100 km of fjord, whether the bathymetry has gotten at all close to the retreating glacier, or whether it could with an autonomous underwater drone. (Radar cannot penetrate sea water so cannot measure depths once the ice is gone.)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on February 22, 2015, 12:15:56 PM
Including the present calving front unless I am completely wrong? Now the numbers are upside down
Nice work, sidd and Espen! Not so easy to place the calving front but it looks about right relative to above sea level exposed rock.

I wonder if Morlighem was limited to 100 m resolution by computational time, model accuracy, or by considerations of input experimental error. In terms of sill peaks, 100 m leaves something to be desired. There seem to be a few bugs such as the -6600 m at the start of the fjord. This bug is a boundary effect that arose elsewhere and is now propagating all over.

This map does not support the classical notion of a shelf or teardrop-shaped knob acting as sill. Instead, it is showing a bottom slanted downward to the north for many tens of km upstream, with maximal depth being a series of -1200 to -1500 m holes adjacent to the northern wall.

In cross-channel profile, the ridge gives a gently slanted structure reaching minimal elevation along the north wall and tapering to shallow on the south. This seems inverted relative to glacial gouging at least in the straightaways. However the high velocity ice stream, as seen clearly in 15 m Landsat8 flowlines, follows very close to the north wall and so differential erosion can be anticipated there. It's not so clear why the tapering extends so evenly to the south wall however.

Note that the surface velocity maps of the lower ice stream that we looked at months ago in great detail have the fastest ice in the middle, tapering symmetrically to the sides. This does not fit the picture of the most glacial excavation taking place on the north side. Most of that action may have taken place earlier when this glacier truly dwarfed what we have today.

If this interjection of physics (requiring mass conservation) to fine-tune initial radar characterization better represents the real situation in the Jakobshavn channel, then it is indeed a breakthrough. It would certainly be cause for deleting many previous modelling papers on this glacier.

However we don't know that -- if the 'inverse' method of Morlighem could be experimentally validated (by improved radar), why would we even need Morlighem's method? (This asks which bottom profile is most consistent with surface observables and basic glaciology.) The marine outlet glaciers have intensive, not sparse, coverage. It's not clear that holding back a subset of flight segments really tests the method.

The asymmetry in the steepness of the channel walls is very striking, indeed puzzling. On river erosion, the inside bend has the steep walls and the outside bend the diffused gradient, as seen here as the glacier rounds the Big Bend and approaches the calving front. Farther upstream there are places where this relation is reversed.

I looked at removing the numbers altogether and coloring between the contours, just the ones below sea level. The trick for that in gimp is color-picking on the blackest black and then growing the selection boundary by a pixel in all directions. However that takes out some of the contour pixels, requiring too much repair work. So I first cut the width down to 700 pixels so the calving front area will display here at its full resolution.

I can improve on the quickie coloring below but just wanted to toss something out for now. The land above sea level is  better done as a grayscale so as not to distract from the channel. This would free up some of the color palette for the channel ... though seems like 15 colors is sufficient.

The palette is made very quickly in gimp choosing first and last colors, doing a gradient across a palette rectangle, softening with the hue slider, overlaying a grid separating colors, and posterizing to discrete colors. Then a central palette color is picked with the eyedropper and used to fill in a color-picked central contour-bounded white space and work out from there. It's hard to tell what contours go with what numbers go but by working out concentrically from the initial choice, the elevation will always jump to the next band available, though at some point that reverses. Takes longer to describe than to do!

If sidd can produce this contour map at slightly higher resolution, the tighter contours will be get better separated and be feasible to infill farther upstream. It's very important not to jpg colors because that eradicates later color-picking.

Notice how the map is cut off on the west side. It can't be extended unless really old radar is around from a time before all this retreat of grounded ice began. If our sill has evaporated, I'm wondering whether the overdeepening west of it is still on solid ground (experimentally speaking).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on February 22, 2015, 12:36:29 PM
And here is one from September 28 2014:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on February 22, 2015, 01:21:02 PM
Let's watch that spelling on Mathieu Morlighem, associated with the Rignot group and now faculty at UC Irvine. The original papers are here:

Deeply incised submarine glacial valleys beneath the Greenland ice sheet
M Morlighem, E Rignot, J Mouginot, H Seroussi, E  Larour
http://www.nature.com/ngeo/journal/v7/n6/full/ngeo2167.html (http://www.nature.com/ngeo/journal/v7/n6/full/ngeo2167.html)

The bed topography beneath the Greenland ice sheet controls the flow of ice and its discharge into the ocean. Outlet glaciers move through a set of narrow valleys whose detailed geometry is poorly known, especially along the southern coasts. As a result, the contribution of the Greenland ice sheet and its glaciers to sea-level change in the coming century is uncertain.

Here, we combine sparse ice-thickness data derived from airborne radar soundings with satellite-derived high-resolution ice motion data through a mass conservation optimization scheme*. We infer ice thickness and bed topography along the entire periphery of the Greenland ice sheet at an unprecedented level of spatial detail and precision. We detect widespread ice-covered valleys that extend significantly deeper below sea level and farther inland than previously thought.

Our findings imply that the outlet glaciers of Greenland, and the ice sheet as a whole, are probably more vulnerable to ocean thermal forcing and peripheral thinning than inferred previously from existing numerical ice-sheet models.

*M Morlighem
A mass conservation approach for mapping glacier ice thickness.
free full http://onlinelibrary.wiley.com/doi/10.1029/2011GL048659/pdf (http://onlinelibrary.wiley.com/doi/10.1029/2011GL048659/pdf)
Geophys. Res. Lett. 38, L19503 (2011).

The traditional method for interpolating ice thickness data from airborne radar sounding surveys onto regular grids is to employ geostatistical techniques such as kriging. While this approach provides continuous maps of ice thickness, it generates products that are not consistent with ice flow dynamics and are impractical for high resolution ice flow simulations.

Here we present a novel approach that combines sparse ice thickness data collected by airborne radar sounding profilers with high resolution swath mapping of ice velocity derived from satellite synthetic-aperture interferometry to obtain a high resolution map of ice thickness that conserves mass and minimizes the departure from observations. We apply this approach to the case of Nioghalvfjerdsfjorden (79North) Glacier.
Let's hope sidd has time to pull out a few more of these contour maps for our favorite glaciers!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on February 22, 2015, 01:30:49 PM
Let's watch that spelling on Mathieu Morlighem, associated with the Rignot group and now faculty at UC Irvine. The original papers are here:

Deeply incised submarine glacial valleys beneath the Greenland ice sheet
M Morlighem, E Rignot, J Mouginot, H Seroussi, E  Larour
http://www.nature.com/ngeo/journal/v7/n6/full/ngeo2167.html (http://www.nature.com/ngeo/journal/v7/n6/full/ngeo2167.html)

The bed topography beneath the Greenland ice sheet controls the flow of ice and its discharge into the ocean. Outlet glaciers move through a set of narrow valleys whose detailed geometry is poorly known, especially along the southern coasts. As a result, the contribution of the Greenland ice sheet and its glaciers to sea-level change in the coming century is uncertain.

Here, we combine sparse ice-thickness data derived from airborne radar soundings with satellite-derived high-resolution ice motion data through a mass conservation optimization scheme*. We infer ice thickness and bed topography along the entire periphery of the Greenland ice sheet at an unprecedented level of spatial detail and precision. We detect widespread ice-covered valleys that extend significantly deeper below sea level and farther inland than previously thought.

Our findings imply that the outlet glaciers of Greenland, and the ice sheet as a whole, are probably more vulnerable to ocean thermal forcing and peripheral thinning than inferred previously from existing numerical ice-sheet models.

*M Morlighem
A mass conservation approach for mapping glacier ice thickness.
free full http://onlinelibrary.wiley.com/doi/10.1029/2011GL048659/pdf (http://onlinelibrary.wiley.com/doi/10.1029/2011GL048659/pdf)
Geophys. Res. Lett. 38, L19503 (2011).

The traditional method for interpolating ice thickness data from airborne radar sounding surveys onto regular grids is to employ geostatistical techniques such as kriging. While this approach provides continuous maps of ice thickness, it generates products that are not consistent with ice flow dynamics and are impractical for high resolution ice flow simulations.

Here we present a novel approach that combines sparse ice thickness data collected by airborne radar sounding profilers with high resolution swath mapping of ice velocity derived from satellite synthetic-aperture interferometry to obtain a high resolution map of ice thickness that conserves mass and minimizes the departure from observations. We apply this approach to the case of Nioghalvfjerdsfjorden (79North) Glacier.
Let's hope sidd has time to pull out a few more of these contour maps for our favorite glaciers!

I will add Zachariae to that list! ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on February 22, 2015, 02:34:45 PM
According to this 2015 paper, we could predict the next calving event just by watching for melange movement on Sentinel, Modis, and Landsat pairs. Counter-intuitively, melange movement precedes calving. Less glamorously, we could look backwards a few weeks and see if the current one could have been anticipated.

Seasonal and interannual variations in ice melange and its impact on terminus stability, Jakobshavn Isbræ, Greenland
R CASSOTTO, M FAHNESTOCK, JM AMUNDSON, M TRUFFER, I JOUGHIN
http://www.igsoc.org:8080/journal/61/225/j13j235.pdf (http://www.igsoc.org:8080/journal/61/225/j13j235.pdf)

We used satellite-derived surface temperatures and time-lapse photography to infer temporal variations in the proglacial ice melange at Jakobshavn Isbræ, a large and rapidly retreating outlet glacier in Greenland.

Freezing of the melange-covered fjord surface during winter is indicated by a decrease in fjord surface temperatures and is associated with a decrease in ice melange mobility and a drastic reduction in iceberg production.

Vigorous calving resumes abruptly in spring following the steady up-fjord retreat of the sea-ice/ice-melange margin. An analysis of pixel displacement from time-lapse imagery demonstrates that melange motion increases prior to calving and subsequently decreases following several events.
 
... In the late 1990s the lower glacier began to thin due to intense submarine melting of a 10km long floating tongue . The resultant loss of buttressing forces caused the glacier to accelerate and stretch, causing the floating tongue to disintegrate and initiating a sustained retreat.

... There is a pattern of seasonal variation in terminus position superimposed on the long-term retreat that can be attributed to variations in the strength of the proglacial ice melange, a dense pack of icebergs that persists year-round, extends >15km down-fjord of the calving front, contains distinct shear bands and is densest near the terminus. Thus the ice melange may act like a weak, granular ice shelf that inhibits calving by transmitting stresses from the fjord walls to the glacier terminus.

... Seasonal variations in calving are important because they  influence a glacier’s long-term rate of retreat through nonlinear processes; longer warm periods that extend the calving season could lead to greater rates of retreat.

... We used MODIS sea surface temperatures (thermal infrared emission) to generate a 12-year proxy record of daily fjord ice conditions in Ilulissat Icefjord

... the 11 April 2009 calving event was the first event of that year; the onset of the break-up of the seasonal floating tongue show an increase in melange mobility in the days leading up to calving. A profile of speed shows the floating
tongue advected into the field of view on 22 March. The tongue progressed steadily down-fjord over the next 20 days. By 8 April, the melange in front of the tongue started to speed up, and on 11 April a large calving event caused the floating tongue to disintegrate and disappear from the profile.

... The speed of the melange increased >40% over mean winter values in the days leading up to calving. Following the event, speeds were much slower as the advancing glacier terminus pushed the post-calving melange down-fjord and compacted it.

... The ability of the melange to prevent ice at the terminus from overturning decreases as the mobility of the melange increases, leading to more frequent calving during periods of enhanced mobility.

... Our record of melange conditions demonstrates that winters with persistently low surface temperatures, taken to indicate rigid and immobile ice melange, had few calving events which permitted the glacier terminus to advance several
kilometers and form a floating tongue.

... Though an ice melange may not have sufficient strength to directly impact the glacier force balance, it can impact glacier velocities indirectly by regulating calving.

...The ability of melange to influence calving seems to have diminished in recent years as conditions warmed and the glacier has retreated into deeper water.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on February 22, 2015, 02:42:19 PM
Let's hope sidd has time to pull out a few more of these contour maps for our favorite glaciers!
I will add Zachariae to that list!
I could sure use Petermann. As with Zach and Niag, there is a real question whether (or how) Morlighem's method takes the upheaval fields into consideration. I would say it doesn't.

That could be good news because then the discrepancy between Morlighem's replacement of bedrock kriging using physics-driven interpolation and what we can see from a rather dense grid then gives some clues as to what modifications the underlying basal sliding model needs to accommodate properties of the upheavals.

This situation is different than Jakobshavn and other deep canyons in that radar doesn't seem to have any problem getting to bedrock even through giant upheavals. However we don't know the composition of these upheavals so not the speed of microwave light through them so consequently not the true depth of bedrock (though it is a good fit to adjacent layer cake without any adjustments). It may be that the ice is moving too slowly lower Petermann for Morlighem's method to have major import.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: mspelto on February 22, 2015, 09:15:51 PM
On Feb. 12th there is some rifting near the calving front, these rifts are structural weaknesses that indicate calving is imminent.  Melange movement ahead of calving generally reflects changes in sub glacial water output.  The amount of calving here is not impressive except for it being February as you have all noted.  Given that the velocity of JI is faster than in the past, that alone makes such an event more likely.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on February 22, 2015, 09:25:39 PM
"I wonder if Morlighem was limited to 100 m resolution ..."

The 100m contour spacing was chosen by me, the nc bed layer can be contoured to arbitrary interval, but the 100m contour already takes hours on the laptop i am travelling with ...

i do have access to heftier hardware, but not the time.

The contours were generated from qgis, but grass or gdal from command line will work also, if someone wants to try.

sidd
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on February 22, 2015, 11:53:58 PM
Including the present calving front unless I am completely wrong?

This map certainly explains the calving that we are seeing along the north wall as the calving face retreats as this portion of the ice sheet is also grounded below sea level. It also explains the broad area of rifting that can be seen as this portion of the ice sheet accelerates to the now open water. It looks like further retreat by the glacier may open up another source of calving along the north wall.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Jim Hunt on February 23, 2015, 11:08:07 AM
It's a while before they wake up in Colorado, but DMI are back at their desks this morning. Their Greenland field trip was to Qaanaaq, as part of the EU ICE-ARC project:

http://www.ice-arc.eu/2015/02/03/twilight-measurements/ (http://www.ice-arc.eu/2015/02/03/twilight-measurements/)

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.ice-arc.eu%2Fwp-content%2Fuploads%2Fsites%2F22%2F2015%2F02%2FTwilight_measurements.png&hash=bcfb2f4a98b4ebf7a35041be93599619)

I'll let you know if anyone there is willing and able to comment on the Jakobshavn calving.

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on February 23, 2015, 01:42:56 PM
can be contoured with Qgis to arbitrary intervals but the 100m contour already takes hours on a laptop
 
Thanks so much for doing this, sidd. Sounds like a high risk operation that has the potential for tying up the computer all day only to wish later different settings had been chosen.

You are apparently the first person to ever do anything with the nc data. Nothing with remotely the detail of this map has ever been published. This is the case with so much of Greenland glaciology -- grievous under-analysis, or no analysis at all, of data. True, it is 'implicit' in the data file but that is like saying dark matter and black holes are 'implicit' in a photograph of an elliptic galaxy. 

I mopped up the color infill with special attention to sills between the potholes (which approach 1600 m below sea level). Having the channel in two dimensions paints a very different picture of the Jakobshavn south channel than what people have been modelling from (a one dimensional centerline that is neither centered nor representative) -- no wonder nothing has been predictable.

Going by this map and Espen's calving front overlay, it would appear that the centerline is currently sitting near the bottom of the overdeepening trough with 200m to climb (1.5 km?) before reaching a minor sill and beginning a 400 m descent into the first pothole. It is not so easy to accurately overlay Joughin 2014's centerline because of their unsatisfactory coordinate system.

I put the map into two tiles (no overlap) so it will display here at resolution.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on February 23, 2015, 07:50:26 PM
Thanks Sidd and A-Team, these new maps explains much more than I already knew about Jakobshavn. ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on February 23, 2015, 07:53:33 PM
"... has the potential for tying up the computer all day only to wish later different settings had been chosen ..."

ah, not so bad, but sometimes i forget that the thing is running in the background, and shut off the machine ... gaaa

"You are apparently the first person to ever do anything with the nc data."

No chance. Everybody knows about nc files, that and PDS (planetary data set) format have been around for a long while, and the tools are opensource (altho some of the data sets have to be run thru a fortran program to unpack, but still not so bad.) I really can't believe that Morlinghem or an associate hasn't done this already. There are error layers in that nc file, but i havent played with them yet.  That will fuzz out the contours.

Hell, i have dumped the nc files to text and then used gnuplot on them sometimes. But don't tell anybody.

sidd
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on February 23, 2015, 07:55:29 PM
 I wanted to ask, does anyone here run a unix ? i can guide em thru a nctools/grass/qgis/gdal setup. Then someone else who has more time can babysit this ?

Anyone ?

sidd
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on February 23, 2015, 09:12:44 PM
sidd, is it a hassle to just output the image as a grayscale DEM, never mind the contours? I can take it from there in terms of re-paletting / 3D / bumpmap / perspective / hillshading / rendering /fly-throughs. I am also set up for cut / display /spling of transects.

It seems to me that a simple 8-bit file would suffice for the ice stream's path: the elevation range is 0 to -1600 m which would be 256 bins of 6 m each after thresholding out above sea level and contrast renormalization. I'll bet though they are carrying it at 16 or 32 bit which are ok for me too and probably better starting points if there have to be manipulations.

If they also have the error map as a grayscale, I can see how that sits relative to the sills and potholes. It can be embedded as a hue color channel over the DEM itself or used as a blur mask. The other thing to do assuming gaussian error is resample the DEM many times per the error distribution and see how robust the sills and troughs are. That could contribute the saturation channel for the HSV.

I recall Morlighem did put out a comparison somewhere with Bamber 2013 in the form of a pixelated postage stamp in a non-quantitative palette, so that's something else we can revisit.

these new maps explains much more than I already knew...
Likewise. This is really the 'missing map' for Jakobshavn. Nothing quite like reading a straightened-channel one-slice one dimensional modelling paper while having this map open.

Below is a mask for the area of interest, its overlay on the 21 Feb 15 Landsat LC80080122015052LGN00 (didn't have good markers for scaling and coregisration), and the B5 channel of that Landsat (note the contributing ice streams, fastest at top).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Jim Hunt on February 23, 2015, 09:13:29 PM
I wanted to ask, does anyone here run a unix ?

Anyone ?

Does Scientific Linux count? If so, then Moi! Should we repair to the Developer's Corner (https://forum.arctic-sea-ice.net/index.php/board,24.0.html)?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Jim Hunt on February 24, 2015, 12:29:35 AM
NSIDC say they have no comment to make on the recent calving, and suggested that I try Jason Box instead. So I did:

https://twitter.com/GreatWhiteCon/status/570001605086588929
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on February 24, 2015, 07:33:13 AM
ok taking the discussion to developers corner

https://forum.arctic-sea-ice.net/index.php/topic,1165.0.html

sidd
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Jim Hunt on February 24, 2015, 09:43:54 AM
I have received a reply from Jason Box, who for those unfamiliar with the name is a Professor at the Geological Survey of Denmark and Greenland, and begetter of the Dark Snow Project (http://forum.arctic-sea-ice.net/index.php/topic,413). Here it is:

It's an interesting finding.

A cautious response: even if this calving were abnormal, we will likely see an advance in the next weeks that will fill the void. Why?

A.) this glacier flows fast and

B.) now with less flow resistance there will likely be an acceleration making the void filling happen even faster.

Here are annual end of melt season area changes measured by PROMICE.org. These are being updated. I will ask Karina Hansen today to update for 2014 and 2015. We could have that result in a few hours.

name ID lat lon region region ID width 1999/00 2000/01 2001/02 2002/03 2003/04 2004/05 2005/06 2006/07 2007/08 2008/09 2009/10 2010/11 2011/12 2012/13
Jakobshavn 14 69.1788 -49.7329 W 105 11.4 -2.75016 -2.4734 -16.357427 -45.617225 -21.235024 -10.015401 -4.155551 -3.829812 -3.202087 -2.174176 -8.725405 -6.69317 -13.742999 -2.825888

In context of the ongoing retreat, I would speculate that this retreat could make further retreat more likely because the acceleration from B.) would cause 'dynamic thinning' that through a positive feedback would reduce glacier bed friction facilitating further thinning and acceleration. This feedback is an amplifier and not runaway but being activated would precondition Jakobshavn glacier for further retreat.

Sorry about the formatting!

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on February 24, 2015, 11:55:59 AM
Sorry about the formatting!
Nice initiative, Jim. Might want to delete on of the duplicate posts. By 'end of melt season area changes", does he mean retreat of the calving front of Jakobshavn, measure not by a line as we have been doing but by the area in km2 between successive retreat lines? Net area works better for last year when the 2013 vs 2014 advance lines crossed.

That could be converted to volume by using the 850 m thickness, but as he points out, this does not give the total volume of annual ice discharge, only the balance between glacier advance and retreat.

The annual volume discharge is tantamount to drawing a line up-glacier that denotes all the ice that will make it to the front that season and figuring the volume using the thinning. (It's not so clear how to treat sub-glacial water discharge as some of that is pass-through meteoric water and some of it is melted ice.)

Nice resource there at PROMICE.org but I am not seeing where the Jakobshavn data is being stored. Have they gotten back to you with the 2014 and 2015 numbers?

Reformatting the areas, some very big years and no discernable trend other than continuing retreat (numbers are consistently negative). Some of the big years are attributable to loss of buttressing from the now-gone floating ice shelf, others may be do to melange being stronger/longer in very cold winter, still others could be impacts from more lubricating water in warm summers (though JI is already modeled as sliding).

name          Jakobshavn
ID                 14
lat                69.179
lon                49.733
region             W
ID               105
width             11.4

1999/00          -2.750
2000/01          -2.473
2001/02         -16.357
2002/03         -45.617
2003/04         -21.235
2004/05         -10.015
2005/06          -4.151
2006/07          -3.830
2007/08          -3.202
2008/09          -2.174
2009/10          -8.725
2010/11          -6.693
2011/12         -13.743
2012/13          -2.826
2013/14          -?.???
2014/15          -?.???
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: andy_t_roo on February 24, 2015, 01:09:27 PM
I recently found http://people.ee.ethz.ch/~luethim/pdf/script/pdg/chapter5.pdf (http://people.ee.ethz.ch/~luethim/pdf/script/pdg/chapter5.pdf) -- on the physical properies of glaciers, and the numerical simulation of velocity and stress fields under various geometries.

Some of the thoughts here might aid discussions on future flow velocities of the various glaciers.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Jim Hunt on February 24, 2015, 01:50:04 PM
Nice initiative, Jim. Might want to delete on of the duplicate posts.

This forum has a mind of its own! Duly deleted. This just in from Karina Hansen via Jason Box, who comments:

In the attached prepared by Karina Hansen you will see a light yellow polygon illustrating the end of melt season 2014 ice Jakobshavn front position retreated from the Feb 2014 (pink line) and Feb 2015 (green line) positions. The Feb 2014 and Feb 2015 positions are roughly the same with 2014 Feb being further retreated than Feb 2015.

The calving appears to be not abnormal at least in terms of where the front position is and therefore is not a shock but rather illustrates my points A. and B. of this morning's message.

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on February 26, 2015, 05:28:59 PM
By popular request, here is the extraordinarily clear, low angle 15 meter B8 band of Landsat 2015-02-21. Hopefully Espen can overlay the calving front over maximal retreat of last year.

PATH = 8 ROW = 12
LC80080122015052LGN00
SUN_AZIMUTH = 170.69201137
SUN_ELEVATION = 11.04439574
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on February 26, 2015, 07:29:00 PM
Here it is:

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on February 26, 2015, 08:27:30 PM
Annual advance advocates anxiously anticipating an apparently arresting accident: could this be the start of next big thing?

The orange arrows possibly point to a widening crevasse that may become the next calving front.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on February 27, 2015, 07:23:33 AM
heres sumpn the right way up ... sorry for the delay
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on February 27, 2015, 11:35:49 AM
Nice, sidd. Below, I colored up at 6x vertical exaggeration the underlying grayscale for that data (big help here from Jim H and sidd over at the developer's corner forum http://forum.arctic-sea-ice.net/index.php/topic,1165.0.html (http://forum.arctic-sea-ice.net/index.php/topic,1165.0.html))

This brings out the troughs and sills in a different way but perhaps most interestingly the old channels and confluences farther back upstream. The second image (taken from Morlighem's home page) shows the broader context of the presumed paleo drainage system -- we don't as yet have this bumped up to native bedrock horizontal resolution (which is 150 m posted, 400 m experimental).

The Jakobshavn fast ice stream today seems to be coming preferentially from northern channel rather than the formerly important easterly two channels, though this is not so evident from surface features, meaning the relative contribution have to be taken from surface velocity maps. I've not seen any explanation for this.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on February 27, 2015, 12:38:03 PM
Here are those upstream velocities from the main source of these, Joughin 2010. I'm recalling that many moons ago an update of these was posted in this forum from a UW disseration. We also know from AG2014 that T Scambos is readying a paper refining the slow velocity map using the newly available pairs 16-bit resolution of Landsat8.

This is easy enough to do ourselves with standard-issue ImageJ2 plugins. With a year separating the 2014-15 images and 15 m resolution, it should be feasible to map the velocity almost to the summit ridge. More ambitiously, Howat has posted 2 m DEMs from worldview 0.6 m pairs but it's not clear that really slow velocities can be pulled from this produce.

The 15 m is more than enough to quantitatively resolve the extent of ice stream confinement to paleo channels. Ice from the sides is also contributing and at elevation will swamp out the channelized flow.

Looks like the 8,11 path rows go the farthest inland for Landshot scenes. The 21 Feb 15 is very clear, about 11º sun angle. There are six cloud-free images with the 'same' geometry from 2014 and one even from 2013, so this should be a snap using bUnwarpJ to get the velocity vector field by image pair feature correlation as at http://forum.arctic-sea-ice.net/index.php/topic,400.msg41367.html#msg41367 (http://forum.arctic-sea-ice.net/index.php/topic,400.msg41367.html#msg41367)

LC8008011 2015 052 LGN00 2015-Feb-21  Sun Elevation = 11.04
LC8008011 2014 305 LGN00 2014-Nov-01  Sun Elevation = 05.99
LC8008011 2014 273 LGN00 2014-Sep-14  Sun Elevation = 17.58
LC8008011 2014 209 LGN00 2014-Jul-28  Sun Elevation = 39.29
LC8008011 2014 193 LGN01 2014-Jul-17  Sun Elevation = 42.31
LC8008011 2014 161 LGN00 2014-Jun-10  Sun Elevation = 43.48
LC8008011 2014 081 LGN00 2014-Mar-22  Sun Elevation = 21.16
LC8008011 2013 270 LGN00 2013-Sep-27  Sun Elevation = 18.66
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on February 27, 2015, 06:44:42 PM
Here's a contour map of the depths of Jakobshavn main channel generated by the incredible French online tool G'MIC (https://gmicol.greyc.fr/) from the bedrock DEM kindly provided by Jim Hunt, followed by a steepness map (norm of gradient) of the side walls.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on February 28, 2015, 03:30:41 PM
The images below take a look at the Jakobshavn paleo confluence with a view towards determining whether upstream fast ice flow today follows the three channels in proportion to their depth.

The first image gives a sense of how intensively Jakobshavn has been sampled by ice penetrating radar (very). The second shows that even slightly past the confluence (67 km from the calving front) that radar is still having great difficulty determining depth bedrock.

The third locates the confluence on 21 Feb 15 Landsat (pink dot) where it is arguably recognizable for some distance on the surface, with the northern fork most prominent, even though it is not the most excavated. The fourth shows bedrock topograpy as refined by Morlighem with the confluence contoured.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on February 28, 2015, 09:03:22 PM
Not reporting another trivial calving this time, but watch the speed of Jakobshavn over 9 days:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on March 01, 2015, 11:31:29 AM
Looking at the distance moved across a transect 5 km upstream of the calving front between 12-28 Feb 15, velocities are moderate by JI summer standards, averaging 23.1 m/day or 8.4 km/yr but with peak speed of 9.3 km/yr which is quite high for February but seeming below the all-time record set in February of 2013.

The error is rather fragile because one pixel off makes a difference at the level of 15 m B8 Landsat channels (which has been bumped up to 10 m here) but the speed is consistently higher in the center of the channel, falling off to the sides as expected from resistance from the wall bedrock.

Since the trough and sill situation is not centered whereas speed is, bedrock topography is not explicitly controlling. However the position of the calving front with respect to this topography does matter, as would timing relative to major calving events.

This transect corresponds, more or less, to the M9 station in Fig.2 of Joughin 2014 www.the-cryosphere.net/8/209/2014 (http://www.the-cryosphere.net/8/209/2014) below. However a real comparison can only be done by replicating their internal system of measurement which is not feasible.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on March 01, 2015, 11:39:30 AM
Looking at the distance moved across a transect 5 km upstream of the calving front between 12-28 Feb 15, velocities are moderate by JI standards, averaging 23.1 m/day or 8.4 km/yr but with peak speed of 9.3 km/yr which is quite high for February but seeming below the all-time record set in February of 2013.

This transect corresponds, more or less, to the M9 station in Fig.2 of Joughin 2014 www.the-cryosphere.net/8/209/2014 (http://www.the-cryosphere.net/8/209/2014) below. However a real comparison can only be done by replicating their internal system of measurement which is not feasible.

A-Team can you the same measurements with the updated images from Wipneus over at the Zachariae section, the thing is really moving at the moment?
https://forum.arctic-sea-ice.net/index.php/topic,400.msg46355.html#msg46355 (https://forum.arctic-sea-ice.net/index.php/topic,400.msg46355.html#msg46355)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on March 01, 2015, 10:49:15 PM
Wipneus is set up to do that for Sentinel. Landsat is not up that far north yet. There is more involved than just determining the velocity vector field ... there is the question of how it compares to earlier years. For that, I would recommend Fig.S13 of the supplemental of Shfaqat Khan 2014 which has a very thorough treatment, free at http://www.nature.com/nclimate/journal/v4/n4/extref/nclimate2161-s1.pdf (http://www.nature.com/nclimate/journal/v4/n4/extref/nclimate2161-s1.pdf)

Zachariae is another case of the tail wagging the dog -- relief of buttressing at the marine terminus is what it takes to get the 600 km long ice stream moving, with melt lakes and lubrication playing less of at role at 79º north (but see attached 2014 melt lake on Petermann) and the relevancy of nearby basal ice upheavals not understood. For now, that acceleration has not propagated very far from the coast.

It's good to remember that the overwhelming bulk of ice volume in Greenland lies above the Parca stake line at 2000 m  so not much will happen to sea level rise until serious ice starts going through the flux gates.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Rubikscube on March 07, 2015, 10:42:02 PM
What is to be made of the very large overdeepening to the south east of JI running in almost opposite direction of the other channels in the JI paleo drainage system? It seems a bit misplaced.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: solartim27 on March 17, 2015, 06:17:48 PM
Not reporting another trivial calving this time, but watch the speed of Jakobshavn over 9 days:

Does not seem to have slowed down any.  Click to animate.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on March 19, 2015, 11:11:54 PM
Lets not forget the facts, see what I read in the newspaper today:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Sleepy on March 20, 2015, 07:01:20 AM
Nice one Espen. Just wondering about the date, when will it be possible to pass between Helheim and Jakobshavn again? I thought I'd add a smiley there but it got stuck...  :-\
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Sleepy on March 21, 2015, 05:58:30 AM
This one's for sale. ;) Only 295€...

(https://www.bergbook.com/images/21105-01.jpg)

"Oerter welche wegen der schwimmenden oder festen Eisberge unbeschifbar sind."
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Carex on March 29, 2015, 03:51:08 PM
That straight is almost completely visible on yesterdays MODIS.  (https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2FArctic_r02c02.2015087.terra.1km.jpg&hash=90868d1e9fc83df812ef5e155d65c428)  I'm a bit illiterate when it comes to posts but I imagine most of you view MODIS regularly.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Carex on March 30, 2015, 12:51:37 PM
Actually, can anyone educate me about the nature of this nearly linear feature that shows up on the 3/28 MODIS image from the mouth of Jakobshavn nearly to the height of land?? And corresponds quite well with the old straight??
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Carex on March 30, 2015, 01:28:14 PM
Let me see if I can actually attach the picture.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Laurent on March 30, 2015, 02:15:09 PM
Do not panic when you see this kind of thing, wait an other set of picture and see if it is still there :
https://earthdata.nasa.gov/labs/worldview/?p=arctic&l=MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Reference_Labels(hidden),Reference_Features(hidden),Coastlines&t=2015-03-29&v=-249655.5089700388,-2354306.117151937,-85815.50897003879,-2238978.117151937

Doesn't seem to be there the 29th...
Probably a cloud !
May be you are talking of something else...be more precise then.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Carex on March 30, 2015, 03:50:21 PM
Details,  Beginning withing a few kilometers of the outlet of Jakobshavn there is a near linear features running very close to SE for 75% to 80% of the distance across the island.  The feature is somewhat irregular in the lower, faster moving sections, from there it becomes quite liner and narrow for a considerable distance. When the feature reaches the upper elevations of the ice cap it becomes less liner and more variable in width.  As it approaches an area of apparent irregular topography influenced by bedrock (or an area of clouds?) it appears to widen slightly into a fan shape, opening toward the high ground. Just east of this, assumed, high ground the feature may be seen again, slightly offset but still bearing SE. The feature fades before bedrock influenced topography is apparent, nearing the east coast. 
Conditions appear to be quite clear as surface details are discernible both SE and NW of the feature.  A vapor trail perhaps?  This should be checkable.  Conditions on the 29th are much cloudier, especially to the east.  I saw this and headed to the forum to ask about it and was greated by those two old maps, very apropo.  The feature is obvious at all pixel sizes from 4K to 250m.  It looks like a giant slump.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on April 02, 2015, 08:56:59 AM
Jakobshavn Isbræ update, as can be watched in animation below, Jakobshavn continuous its "self-destruction":
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on April 02, 2015, 10:34:39 AM
But far away from the max. retreat set September 28 2014:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Iceismylife on April 14, 2015, 11:30:26 PM
A possible explanation for the shallower northern arm of the confluence to be speeding up more than the others is that it is narrower and confines the melt water at its base more.  Also being narrower its base would have experienced more heating when the flow started accelerating, leading it to provide more of the flow to the main channel.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Iceismylife on April 15, 2015, 09:02:33 PM
...
 Is it just too far into the future?
That is the question I've been looking for an answer to.  Assuming the calving face keep retreating at its current rate how long until it gets there?

My read is we are on an exponential growth curve in ice flow. 2X every 5 years.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on May 13, 2015, 05:55:38 AM
Jakobshavn Issbræ the calving-machine is up in gear again:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Yuha on May 13, 2015, 11:37:52 PM
Jakobshavn Issbræ the calving-machine is up in gear again:

The calving was likely triggered by an unplugging of the fjord:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on May 14, 2015, 07:17:48 AM
Updated version:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on May 16, 2015, 04:48:53 PM
Latest High-Resolution Landsat image from May 12 2015:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on May 16, 2015, 11:10:18 PM
The calving front at Jakobshavn is very different to September 28 2014 (record retreat), not only did the glacier expand since then but the front is much narrower?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Jim Hunt on May 16, 2015, 11:51:52 PM
The front is much narrower?

It looks that way to me as well. I've taken the liberty of republishing your animations over at:

http://GreatWhiteCon.info/2015/05/jakobshavn-isbrae-calves-yet-again/ (http://GreatWhiteCon.info/2015/05/jakobshavn-isbrae-calves-yet-again/)

I hope that's OK with you? Please let me know ASAP if not.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on May 17, 2015, 10:30:36 AM
The front is much narrower?

It looks that way to me as well. I've taken the liberty of republishing your animations over at:

http://GreatWhiteCon.info/2015/05/jakobshavn-isbrae-calves-yet-again/ (http://GreatWhiteCon.info/2015/05/jakobshavn-isbrae-calves-yet-again/)

I hope that's OK with you? Please let me know ASAP if not.

Hello Jim, that is ok with me, thanks! :) :)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: tpelte on May 19, 2015, 02:55:51 PM
Huge calving seemed to occur between last sentinel pictures (17 / 18).  Can anyone confirm this with  other satellite pictures ?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on May 19, 2015, 04:32:04 PM
Hello tpelte,

When I compare the images, it looks like the glacier expanded?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: tpelte on May 19, 2015, 05:13:59 PM
I guess I get confused by shadows and brightness of ice at some places.  Sorry for that false alarm.  Thanks for the tremendous work you're doing here.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Lennart van der Linde on May 20, 2015, 10:12:16 PM
Recent lecture by Richard Alley, including remarks on Pollard et al 2015 and Applegate et al 2014 on potentially very fast ice loss from WAIS and GIS, with examples of cliff failure from Jakobshavn:
https://www.youtube.com/watch?v=yCunWFmvUfo (https://www.youtube.com/watch?v=yCunWFmvUfo)

Thanks to Colorado Bob for posting this over at the ASIB.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Bernard on May 26, 2015, 10:52:16 PM
Dear all

Completely puzzled by the aspect of the calving front of Jakobshavn Isbræ in today's view at
http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2015146.terra.250m. (http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2015146.terra.250m.)
Looks completely different, as if some catastrophic calving or surge had happened.
How do you folks read this image?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: solartim27 on May 26, 2015, 11:01:17 PM
I believe it is just a cloud.  The radar images are nice to get below that stuff, though it is cut off so far today:
http://www.polarview.aq/arctic (http://www.polarview.aq/arctic)
http://ocean.dmi.dk/arctic/disko.uk.php (http://ocean.dmi.dk/arctic/disko.uk.php)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Jim Hunt on May 26, 2015, 11:09:32 PM
How do you folks read this image?

Try flipping between Aqua & Terra on Worldview:

http://1.usa.gov/1AskSpn (http://1.usa.gov/1AskSpn)

Looks like a cloud to me.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Bernard on May 27, 2015, 11:06:25 PM
Thanks! Cloud indeed ... back to "normal" today.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on May 29, 2015, 12:20:53 PM
S-1 IW HH-polarization on 27.5.2015
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Yuha on May 29, 2015, 03:21:32 PM
S-1 IW HH-polarization on 27.5.2015

Taken maybe just moments before a significant calving took place.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on May 29, 2015, 05:35:32 PM
A large calving happened between May 26 and May 28 2015:

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on May 30, 2015, 09:13:24 AM
The same calving seen from a Sentinel sensor:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on May 30, 2015, 11:19:59 AM
A new large calving will come soon (red line), can also be observed in the animation above:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on May 30, 2015, 11:48:32 AM
Great Espen! BTW your SAR images have very high contrast, have you experimented with taking a logarithm (or alternatively a square root) of the SAR intensity as it is more pleasing to the human eye?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on May 30, 2015, 11:53:51 AM
Great Espen! BTW your SAR images have very high contrast, have you experimented with taking a logarithm (or alternatively a square root) of the SAR intensity as it is more pleasing to the human eye?

Hello Nukefix,

I am using a filter in Photoshop called Camera Raw Filter and set at auto, I might need some more experience?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on May 30, 2015, 12:13:55 PM
The S-1 SAR-data in the image-files are in amplitude-format, while the "industry-standard" is log_intensity. You can convert amplitude to log-intensity in the following way:

log_intensity = log10(amplitude^2)

This should bring out much more detail for the human eye and you can apply the Photoshop filters afterwards.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on May 30, 2015, 12:28:35 PM
The S-1 SAR-data in the image-files are in amplitude-format, while the "industry-standard" is log_intensity. You can convert amplitude to log-intensity in the following way:

log_intensity = log10(amplitude^2)

This should bring out much more detail for the human eye and you can apply the Photoshop filters afterwards.

Have not a clue what you are writing about, is it possible to code in Photoshop?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on May 31, 2015, 07:10:53 AM
The S-1 SAR-data in the image-files are in amplitude-format, while the "industry-standard" is log_intensity. You can convert amplitude to log-intensity in the following way:

log_intensity = log10(amplitude^2)

This should bring out much more detail for the human eye and you can apply the Photoshop filters afterwards.
Have not a clue what you are writing about, is it possible to code in Photoshop?
I don't know Photoshop but I would imagine there's a plugin that allows for that?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 02, 2015, 06:16:16 AM
I have some difficulties interpreting the Sentinel images from June 1, maybe Wipneus can help?
I know there were some calving activities lately.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: solartim27 on June 02, 2015, 06:52:03 AM
Wind compacted the melange against the calving front??  Looking at Modis, there hasn't been any fresh snow in the area.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Wipneus on June 02, 2015, 08:05:06 AM
I have some difficulties interpreting the Sentinel images from June 1, maybe Wipneus can help?
I know there were some calving activities lately.

I am not sure what I can do. There is for 1 June only a EW med-res image available, just good enough to be not entirely useless. Wait for a IW mode scan, with a higher resolution and much less speckle noise. These are taken much more regularly of JacobsHavn compared to e.g. Zachariae (waiting for months now).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on June 02, 2015, 04:38:56 PM
The thing to remember is that neither Landsat-8 and Sentinel-1 is single purpose. Polar scenes by their nature have very poor intrinsic contrast (off-white on white). Further, some users need the actual instrumental luminance values (eg  band 10 Landsat thermal for ground temperature). Together this means the products provided are not optimally adjusted as downloaded -- a jungle scene has different issues from an ice stream.

The first round of contrast enhancement is usually histogram normalization. That is, the image is not making full use of  dynamic range (eg 20-190 instead of 0-255 on an 8-bit). That's easily fixed by adding a constant and multiplicative rescaling (brightness and contrast knobs).

That is often followed by a second order adjustment of mid-tones (gamma correction). This can greatly improve the image visually but in general loses the original 'scientific' content. Contrarily, functions like log or sq root can have a logical rationale but they seldom produce a favorable visual outcome. (Gimp has a plugin that allows *any* function to be implemented as its power series expansion.)

The next level of contrast enhancement is histogram equalization. This uses the cumulative distribution function (see wikipedia) of pixel intensities to flatten the histogram (ie expand contrast for well-represented pixel values). This is quick and very effective on both Landsat and Sentinel but using the global histogram again means discarding neighborhood information.

Thus neither method is optimal for detecting a developing fracture (Espen's goal in #645) since neighboring pixel correlation is important to that.

It's better here to start with adaptive histogram equalization (CLAHE, see wikipedia). That is provided in Fiji/ImageJ2 at the bottom of the 'Process' menu; see http://fiji.sc/wiki/index.php/Enhance_Local_Contrast_%28CLAHE%29 (http://fiji.sc/wiki/index.php/Enhance_Local_Contrast_%28CLAHE%29)  The image below shows its effect on Landsat's low-budget preview image that Espen likes because of its small file size.

It is imperative to work within the 16-bit world of Landsat and Sentinel for initial contrast adjustments and co-registration rotations. Otherwise you will get unoccupied bars in the histogram.That cannot be currently done within Gimp. However it is easy to do a quick in-and-out within ImageJ and return to your usual image processor with an 8-bit after the benefits of 16-bit have been exhausted..

For a linear feature with predictable orientation (~parallel to the calving front), an edge detector would be the natural follow-on. These are typically directional derivatives or convolutions.

However nothing you can do will make a silk purse out of a sow's ear (Sentinel EW). Ultimately there's no substitute for a really high resolution image, one commensurate with the task at hand.

I'll post a 0.5 m resolution DigiGlobe image of growing fracture tips over at the Petermann forum. Even prior to polar-appropriate contrast enhancement, it's a huge improvement over the 15 m band 8 of Landsat, even if you've applied  CLAHE or retinex in Wipneus's pan-sharpening protocol.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on June 02, 2015, 06:10:18 PM
I took a semi-quantitative look at the big calving event over May 26-28 first reported by Espen in #643. According to the 15 m resolution Landsat band 8, 13317 pixels @ 225 sq m per pixel calved off, so a little under 3 sq km (green tint below), roughly a third of that necessary to reach the 26 Sep 14 maximal retreat (red line).

This has to be slightly corrected for Jakobshavn forward motion of ~26 m per day by the 28th (measured 5 km upstream) which causes the front on the 28th to be too far forward in terms of image overlap, resulting in an under-estimate of area calved. We don’t know if the calving was a single event; if so, that would have been recorded as a westward berg velocity surge on the north side web cam.

Taking the overall thickness of ice at the calving front at 1400 m, this pencils out to 4.5 cu km of non-floating ice. When it melts, that results in 2.78 microns of smoothed-out sea level rise per cubic km, so 0.010 mm. Move along people, nothing to see here (?)

There are lots of good reasons why identification numbers should be provided in forum posts even if they seem too geeky. In this instance, the 2LC80100112015146LGN00 of 26 May 15 is path 10, row 11 just like the 2014 maximal retreat image LC80100112014271LGN00, whereas LC80080112015148LGN00 has a very different viewing geometry, namely path 8, row 11.

This means the images cannot be co-registered without a 5.53º rotation of the 28 May 15. There being no truly fixed features on the ice sheet, the last rock outcrop in the SW corner, together with the tip of the ice-fall separating north and south arms, are the best choices for subsequent registration. A third triangulation point to the east is needed — but not available — to assess residual geometrical distortion.

This particular event mostly tracked pre-existing fractures that can be seen in the 26 May 15 image. It’s not so clear where the next round of calving will occur — that’s a game better played at Petermann. Sentinel EW images (see post #645 and #653) are a few bricks short of a wall in terms of adequate crevasse resolution -- the 2nd image shows various unconvincing enhancements.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 02, 2015, 07:02:08 PM
A-Team

Nice to see you back in in bar ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on June 02, 2015, 07:57:34 PM
Espen, what are you doing still online? I thought your expedition would be camped in front of the Jakobshavn calving front by now enjoying frozen MRE* and fresh kelp. Maybe 2016 for me. That was a great idea ... certainly this last event would have been an unforgettable experience.

Unless the weather got bad:

http://www.theguardian.com/uk-news/2013/aug/19/charity-trekker-froze-death-greenland-storm (http://www.theguardian.com/uk-news/2013/aug/19/charity-trekker-froze-death-greenland-storm)

It seems that the film crew in 'Chasing Ice' spent 3 weeks on the outermost rocks waiting for their big event. If so, it might make more sense to helicopter in (or out) so less time is spent trekking up the fjord with 25 kg packs.

I wonder though if permits can really be obtained -- there is a lot of scientific gear fixed in place and important ongoing research. Those cameras are meant for taking tourist selfies? The best viewing might be from the last rock outcrop ... but not until late July and all the 'view' campsites could already be taken.

*http://www.amazon.com/Meals-Ready-Genuine-Military-Surplus/dp/B005I5ML36
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Rubikscube on June 02, 2015, 11:20:19 PM
Speaking of campsites just got me wondering; how long will it take before the first rock peak through the ice sheet on the opposite side (east/northeast) of the main channel? I guess it has been of greater interest to measure the ice thickness in the main trench rather than the surrounding high ground, but is it possible to get good idea of how thin the ice is there and how long it will take before its gone?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on June 03, 2015, 08:18:11 PM
is it possible to get good idea of how thin the ice is there and how long it will take before its gone?

The thickness ice-to-bedrock for a particular year could be read off a Cresis radar overflight that crossed your area of interest. If there was data for multiple years, that would provide a trend.

However the ice to just north of the main Jakobshavn channel is far from stagnant so it wouldn't be the 'same' ice. The whole ice sheet is sliding downhill so the ice there now will be replaced with ice from the northeast.

Espen ran into that in #630 comparing a late season 28 Sep 2014 to an early season 12 May 14. As the main channel receded past the tongue of the northern icefall, its buttressing was removed and it spilled into the newly opened water.

I looked around for recent ice sheet velocities of this region, finding a Jan 2015 image in a nice Sentinel overview article at  http://tinyurl.com/ps7brk8 (http://tinyurl.com/ps7brk8) and another in a May 25 open source article on accurate balance velocites, http://www.geosci-model-dev.net/8/1275/2015/gmd-8-1275-2015.pdf (http://www.geosci-model-dev.net/8/1275/2015/gmd-8-1275-2015.pdf)

Look for the 'big bend' in Jakobshavn to orient yourself. Then note how much of its surroundings to the north are flowing into the system. I posted some speculation earlier about iceshed capture in the future. It would be fairly tricky to demonstrate this over a limited time interval, even ten years, because of differences in satellite sensors.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Rubikscube on June 04, 2015, 12:57:03 PM
Thanks A-Team. Wonderful as usuall.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on June 04, 2015, 07:41:31 PM
I'd like to re-iterate that log-intensity is often the preferred way of viewing SAR data. This is how I do it in the Sentinel-1 toolbox:

1. Open/import S-1 product
2. Right-click on the Intensity (virtual) band and select "Linear to/from dB" to generate a new virtual band containing log-intensity.
3. Open the new log-intensity-band
4. Play around with histogram in Colour Manipulation toolwindow.

The image-files themselves contain amplitude so if you want to use other tools to manipulate the image you should do the log_intensity = log10(amplitude*amplitude) conversion as a first step.

BTW I hear that there are plans for covering the Greenland margin with S-1 in IW-mode every 12 days - this would be fantastic obviously!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on June 05, 2015, 03:46:41 PM
is it possible to get good idea of how thin the ice is there and how long it will take before its gone?

The thickness ice-to-bedrock for a particular year could be read off a Cresis radar overflight that crossed your area of interest. If there was data for multiple years, that would provide a trend.

However the ice to just north of the main Jakobshavn channel is far from stagnant so it wouldn't be the 'same' ice. The whole ice sheet is sliding downhill so the ice there now will be replaced with ice from the northeast.

Espen ran into that in #630 comparing a late season 28 Sep 2014 to an early season 12 May 14. As the main channel receded past the tongue of the northern icefall, its buttressing was removed and it spilled into the newly opened water.

I looked around for recent ice sheet velocities of this region, finding a Jan 2015 image in a nice Sentinel overview article at  http://tinyurl.com/ps7brk8 (http://tinyurl.com/ps7brk8) and another in a May 25 open source article on accurate balance velocites, http://www.geosci-model-dev.net/8/1275/2015/gmd-8-1275-2015.pdf (http://www.geosci-model-dev.net/8/1275/2015/gmd-8-1275-2015.pdf)

Look for the 'big bend' in Jakobshavn to orient yourself. Then note how much of its surroundings to the north are flowing into the system. I posted some speculation earlier about iceshed capture in the future. It would be fairly tricky to demonstrate this over a limited time interval, even ten years, because of differences in satellite sensors.

If you study the most accurate topography maps of Greenland, a large area of the ice sheet that feeds these two active walls that are flowing into the fjord is grounded below sea level. In fact this area of the sheet is far more vulnerable than the active wall that is to the north.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on June 05, 2015, 03:55:56 PM
Nukefix, useful instructions ... but can you modify the post above to include the best image you can make of the calving front? It takes but seconds to save a screenshot and hit the attachment button below.

At this point, the case has not been made for using Sentinel during between April and October. There is a very clear Landsat for 04 Jun 15 at EarthExplorer, LC80090112015155LGN00.

So we can make side-by-side comparison with your Sentinel image, I am attaching the 15 m Landsat bumped out to 10 m. Note too the 3 new papers out saying Greenland velocity measurements can be not only automated to a few seconds but also made as accurate if not better than with insar.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on June 08, 2015, 12:57:43 AM
I can make an image of the terminus when I'm back at the office. SAR is still weather and and lighting-independent and can be used to monitor speeds during the polar night, which will never work with optical. S-1 IW cannot measure the speeds close to the terminus due to lack of sufficiently high resolution, but it can produce ice-sheet wide maps. If Landsat or Sentinel-2 can be used to patch holes in S-1 - based velocity estimates that would be just great, so both methods are needed!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 11, 2015, 10:00:42 PM
Jakobshavn update:

Both the southern and northern branch of Jakobshavn is now widening and sligthly retreating:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on June 12, 2015, 12:35:49 AM
The whole place is on the move. Looks quite different overall from last year. Yet weather has been colder longer. Maybe less snowpack to begin with?

Very clear 15 m LC80100112015162LGN00_B8 below
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on June 12, 2015, 01:52:44 PM
The  crevassing  and thinning is so  apparent in these detailed images.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on June 12, 2015, 03:41:58 PM
Here are previous clear days with the same Landsat-8 geometry (path,row = 10,11). The animation seems to run without further clicking. It compares day 162 (11 Jun 15) with day 159 (08 Jun 14) of last year. I've added the 21 Jun 13 even though that's ten days forward --  Landsat-8 entered into its 3rd year of availability a while back.

Based on fixed rocks in the lower left and the peninsula separating north and south branches, the three images align correctly -- but have a lot of changes elsewhere.

The 2014 calving front is the one showing greatest retreat for the date. This might be because the ice stream is advancing faster this year relative to rate of calving in the 'new abnormal' of stationary cold weather.

LC80 10011 2015 162 LGN00 most recent
LC80 10011 2015 146 LGN00
LC80 10011 2015 114 LGN00
LC80 10011 2015 050 LGN00

LC80 10011 2014 303 LGN00
LC80 10011 2014 271 LGN00 max retreat
LC80 10011 2014 271 LGN00
LC80 10011 2014 239 LGN00
LC80 10011 2014 223 LGN00
LC80 10011 2014 207 LGN00
LC80 10011 2014 191 LGN00
LC80 10011 2014 159 LGN00 closest to most recent 2015

LC80 10011 2013 172 LGN00 21-JUN-13 clear
LC80 10011 2013 156 LGN00 05-JUN-13 cloudy
LC80 10011 2013 140 LGN01 20-MAY-13 clear
LC80 10011 2013 124 LGN01 04-MAY-13 cloudy
LC80 10011 2013 108 LGN01 18-APR-13 calving front clear
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: oren on June 12, 2015, 03:49:34 PM
So JH actually managed to gain ground in the past 12 months.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on June 12, 2015, 06:44:33 PM
So JH actually managed to gain ground in the past 12 months.

There is quite a bit of variability within a given season, within a given year and from year to year. Although the latter shows a strong multi-decadal trend of calving front retreat, that does not mean that every year sets a new record.

The position of the calving front is a tug-of-war between competing processes -- glacial advance and propensity to calve -- so is not necessarily a good proxy for contribution to sea level rise (volume of grounded ice plus intra-glacial meltwater discharged).

Below is a comparison of the 4th and 11th of June 2015. As an RGB composite, color interference banding shows up as 2-3 areas of rapid motion (bottom center).

Here matching path,row images were not available but no systemic geometric distortion occurred. The 9,11 path,row has the calving front area almost directly below the satellite and would be most favorable for precise velocity measurements. However timing intervals can be problematic if the next orbit encounters clouds. Severely crevassed areas are not favorable either because mere widening can be mistaken for movement.

It would not be easy to determine whether/how much the ice fall on the north shore of the south bank has accelerated. However as the calving front retreats, that does remove buttressing holding back peripheral areas so faster movement there is the expectation. There are limits to any speed-up however, depending on the gravitational driving forces, basal resistance, temperature-dependent internal deformability and so forth.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on June 16, 2015, 05:59:12 PM
Here's a full-res zoom to S-1 IW of the southern trunk of Jakobshaven, from 8.6.2015 (ellipsoid geocoded to Polar Stereographic, 10m pixel-size, ~20m resolution).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on June 16, 2015, 06:24:05 PM
Here's the required operations in the S-1 Toolbox to do this:

1. Open the S-1 image (GRD IW-product downloaded from scihub for example)
2. Click on intensity-band to visualize (converting from linear to dB beforehand (right-click on band and select Linear to/from dB) is advisable)
3. Zoom on the area of interest for subsetting and right-click and select Spatial subset from view
4. Run the attached graph to produce calibrated ellipsoid-geocoded to 10m pixel-size (bicubic) Polar Stereographic projected image that is converted to dB (log-intensity)
5. Click on Sigma-zero in dB band in the generated product to visualize
6. Save the generated product (for example by right-clicking on product and selecting Save Product as
7. Play with the histogram under "colour-management", 100% stretch works quite well already

How to use the attached graph-file:

1. Save the graph-file converting the .txt - ending to .xml (for example in C:\temp)
2. In S1TBX, open graph builder by selecting Graphs/Graph Builder
3. In Graph Builder, click Load and load the graph-file saved in step 1
4. Select your input product (saved in step 6 in the list above) in the tabs in Graph Builder
5. Select the output product name/path as appropriate
6. Run the graph by clicking Process in the Graph Builder
7. Click on Sigma-zero in dB band in the generated product to visualize
8. Play with histogram as in the list above
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on June 17, 2015, 02:21:12 PM
Very helpful. The S-1 toolbox is definitely the way to go. Without the toolkit, I was still able to download and open one of these GDH images for Petermann without it but the outcome was sub-optimal.

http://forum.arctic-sea-ice.net/index.php/topic,53.msg54273.html#msg54273 (http://forum.arctic-sea-ice.net/index.php/topic,53.msg54273.html#msg54273)

Do you have a step-by-step protocol for producing interferometric images? I was under the impression that Sentinel-1B (2016 launch) was necessary for this but they somehow produced the Napa earthquake subsidence fringes just from 1-A. (This is not another Radarsat emulation of Sentinel).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on June 17, 2015, 06:25:43 PM
Do you have a step-by-step protocol for producing interferometric images? I was under the impression that Sentinel-1B (2016 launch) was necessary for this but they somehow produced the Napa earthquake subsidence fringes just from 1-A. (This is not another Radarsat emulation of Sentinel).
For InSAR just a repeated orbit is needed, with S-1A that happens every 12 days and with the 2nd unit there's a chance for InSAR every 6 days (provided that the data is acquired).

S-1 Interferometry with the IW-mode is somewhat involved due to the novel SAR mode but the toolbox is able to do it, tutorials cover the required steps:

http://step.esa.int/main/doc/tutorials/sentinel-1-toolbox-tutorials/ (http://step.esa.int/main/doc/tutorials/sentinel-1-toolbox-tutorials/)

A hindrance with the IW-mode is that movement of the ice (in the along-track direction) generates phase-jumps that make interpretation of the interferogram more difficult. In the worst case the interferogram needs to treated as a mosaic of small (20km * 80km) interferograms.

edit: however InSAR is not needed for velocity mapping, simple feature- or speckle-tracking works well for 12-day repeats already and 6 days promises better coverage of the more difficult areas (snowfall) 
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on June 18, 2015, 03:21:14 PM
movement of the ice (in the along-track direction)

So the case of Jakobshavn which moves east to west (and slightly down) and a satellite moving almost north to south is quite unfavorable (for error term) because there is almost no component of motion in the along-track direction? Whereas Petermann would be more favorable as it moves south to north and NEGIS is intermediate as it moves diagonally though Zachariae again is west-east.

The purpose of Sentinel 1-B for Greenland would then not be velocity but rather simultaneous 'stereo pairs' that allow construction of precise digital elevation maps (and their change over time)?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on June 18, 2015, 03:35:28 PM
movement of the ice (in the along-track direction)
So the case of Jakobshavn which moves east to west (and slightly down) and a satellite moving almost north to south is quite unfavorable (for error term) because there is almost no component of motion in the along-track direction? Whereas Petermann would be more favorable as it moves south to north and NEGIS is intermediate as it moves diagonally though Zachariae again is west-east.
Strictly speaking the phase-jump is not an error-term but real signal related to along-track motion (it is caused by the difference in look-angle between individual radar "bursts"). Let's see in the coming years what the InSAR community can wring out of this data.

The purpose of Sentinel 1-B for Greenland would then not be velocity but rather simultaneous 'stereo pairs' that allow construction of precise digital elevation maps (and their change over time)?
Radargrammery (stereo pairs) will not work for many reasons including resolution and the repeat-period. However, S-1A&B will be great for ice velocity measurements using coherent and incoherent feature-tracking so there's no need to do interferometry as such. InSAR can be used for more precise measurements (in the across-track direction) in the future provided that the experts figure out how to separate phase caused by along-track ice movement from phase coming from the DEM.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on June 18, 2015, 11:29:38 PM
Let's see in the coming years what the InSAR community can wring out of this data....  in the future provided that the experts figure out how to separate phase caused by along-track ice movement from phase coming from the DEM.
Seems like they should have figured this out way back in the grant proposal for the satellite series, rather than later on the fly. Maybe. They already had the RadarSat-2 simulation of Sentinel to work with.

It troubles me that these experts cannot simply record a script as they go along processing images. Then people who are not experts could just change the pointers to the data files and run the script on ESA computers without becoming experts themselves. I'll wager five such scripts would cover 95% of routine client data usage.

For example, that's what I see NASA offering on Landsat-7. You see a preview scene you want on earthexplorer, just put it in your cart and their computer will process it to Level 2 during an idle moment and email you a link to the product in a day or so.

In other words, nobody ever requests Level 2 on 99% of these older scenes, especially the cloudy ones, so it isn't worth the CPU time to go back to process scenes that are never going to be used when they are drowning in incoming scenes of real-time interest.

How likely is it that a highly trained photo analyst will want to also become a highly trained radar instrument designer or highly trained satellite data re-processor? Not very, different skill sets require different aptitudes.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on June 19, 2015, 09:50:05 AM
I think there are several plans in Europe for offering processing capability to scientists and indeed the ability to run scripts is what is offered.

Interpreting and processing SAR images should be in the skill-set of remote sensing specialists, in the end it is not that difficult even if there's a steep learning curve in the beginning. Luckily there are several online courses that explain things from basics to PhD level stuff.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Rubikscube on June 21, 2015, 03:24:07 PM
The 2014 calving front is the one showing greatest retreat for the date. This might be because the ice stream is advancing faster this year relative to rate of calving in the 'new abnormal' of stationary cold weather.

It seems quite logical that a glacier like JH, which behaves so differently from month to month (unlike other glaciers like Zach, which can keep retreating at a steady phase in the midst of winter), is also more likely to respond to 5-6 weeks of abnormal cold by significantly slowing down its rate of calving. Either way it seems the "new abnormal" is finally about to end, ECMWF puts most of Greenland on 10 days of continuous roasting, starting from today.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 27, 2015, 10:35:03 PM
And here is a real big one for the season:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on June 27, 2015, 10:56:41 PM
But still far from the record retreat of September 28 2014:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on June 28, 2015, 02:45:43 AM
It's been quite a while since the last cloud-free day. Odd darker regions are apparent in the central calving front -- possibly an indentation of the calving front will develop?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 01, 2015, 01:05:37 AM
The image below shows, at 7.5 m resolution, net calving front recession and channel widening in the NE that took place at Jakobshavn between 28 May 15 and 30 Jun 15. (Those dates are 32 days apart so have matching Landsat path,row and can be precisely co-registered on fixed rocks.)

This glacier is moving right along now, with quite measurable pixel shifts even over the last two days. However geometric distortion and lack of fixed fiducial points to the east mean too much relative error. I'll look for a pair of clear days at a 16 day interval....
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 01, 2015, 06:02:57 AM
In the latest Modis image, it looks like a big piece took off at the northern shore of the southern branch.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on July 01, 2015, 10:53:29 PM
Grounded below sea level as it is, I still think the northern face of the southern branch is going to surprise us over the next couple of years.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: solartim27 on July 02, 2015, 09:28:38 PM
Just saw this on Climatecrocks.com, original from Vice, dated June 10.

https://news.vice.com/article/watch-a-piece-of-ice-larger-than-two-empire-state-buildings-break-off-a-glacier-in-greenland (https://news.vice.com/article/watch-a-piece-of-ice-larger-than-two-empire-state-buildings-break-off-a-glacier-in-greenland)

http://climatecrocks.com/ (http://climatecrocks.com/)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 05, 2015, 08:41:05 PM
Pretty impressive calving seen between July 2 and July 4 2015 at Jakobshavn:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 06, 2015, 10:04:23 PM
Here we go again, another calving to note, (and very near the maximum retreat):

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 06, 2015, 10:56:47 PM
Just an update:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 07, 2015, 12:23:41 AM
Amazing for this date. In the broader picture, look at all those exposed ribs in the NE corner. Below, a different take on color than EarthExplorer provides in its preview imagery (30 m 731) using adaptively contrast-filtered bands 531 instead on the LC80090112015187LGN00 download package.

Note JI is putting out so much debris that the North Branch material can hardly exit. Indeed the whole fjord is more or less plugged with melange all the way out to the grounding moraine at the mouth ... seems unusual for this late date. However it does not appear solid enough to be furnishing much buttressing to the calving front.

Arrows in the 2nd image, the same Landsat but band 8 bumped to 7.5 m, show possible weaknesses that could go in the next rounds of calving. Note the two troughs bounding an unstable peninsula in the upper left (double arrows).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 09, 2015, 01:52:21 AM
Here is the DMI preview resolution for today's Sentinel -- it does a nice job of capturing the massive plume out in Disco Bay. And it sure looks like major action at the calving front (over-enlarged in 3rd image) -- there's nothing for 8 July 15 on Landsat yet and may never be.

DMI seems to get an early look at Sentinel imagery. While this is a fantastic service, they could improve it by providing image accession numbers -- when I downloaded the latest image of the same date at ESA itself, they don't seem to match the dramatic 3rd image below. I combined horizontal hh and mixed hv polarizations into RGB color using ImageJ2 ... it does not work wonders but at least has the higher native resolution and some feature emphasis.

The key feature in the 3rd image is the dark wedge projecting SE off the dark line of the calving front. The north branch also has an interesting white streak coming down the central crevassed hillside. Hopefully the clear weather will hold until Landsat swings its lazy ass by on July 13th (a path 10, row 11).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 09, 2015, 06:11:53 AM
I am not sure but I do believe we are beyond the September 27 2014 maximum retreat point:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 09, 2015, 08:18:39 PM
Sentinel suspense builds ... I have not been paying attention to its orbital pattern nor to frequency of the useful GRDH saves. Here is Terra from today, terribly over-enlarged to be sure but presenting curious features, presumably associated with new calving. If an ice stream record falls in the glacier but nobody was there to see it, did it make any noise?

Today on June 9th, two new Sentinel images came in. DMI and Polar View offer convenient versions of these, perhaps at the price of resolution loss (third image) as I wait on the Sentinel hub downloads. The IW scene is 3 GB and may not be indexed by the quick look services. Oddly it is dated 16 Feb 15 despite being given the top listing.

S1A_EW_GRDM_1SDH_20150709T203809_20150709T203909_006739_009079_DD28
Date : 2015-07-09T20:38:09.717Z, Instrument : SAR-C, Mode : EW, Satellite : Sentinel-1, Size : 409 MB

S1A_IW_SLC__1SSH_20150216T100008_20150216T100035_004647_005BB8_E22B
Date : 2015-02-16T10:00:08.133Z, Instrument : SAR-C, Mode : IW, Satellite : Sentinel-1, Size : 3 GB
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 10, 2015, 05:45:26 PM
Seems like there are some advantages from using files from the Sentinel hub itself, notably the ability to manipulate within 16-bits (enlargement, rotation and local contrast), and separate HH and HV polarizations which can also be combined into RGB (blue taken as all 0 or black).

The great downside is that north is not up in Sentinel images nor is a rotational angle provided nor is this angle the same between images. This contrasts with DMI and Landsat. For example the 10 June 15 Sentinel needs an 18.9º rotation.

The HV is brighter in this instance. It seems to better distinguish calved from recently calved from freshly calved. I don't know what the physical basis for this is, maybe calved ice becomes less rough over time. Neither polarization combo is proposing about-to-calf.

The Jakobshavn calving front seems to have moved further into record retreat; that can be measured relative to the last fixed point, the rock island in lower left. If this is July 9th and maximal retreat in 2014 occurred in late Sept, this could get interesting. There are three issues: position relative to basal topography sills and troughs, loss of side buttressing if the calving front should retreat past the 'big bend', and greatly reduced obstruction to side tributary inflow.

The comparison to the Sept 27th maximal retreat of last year is somewhat problematic due to geometric effects in two different instruments, plus there has been more melt-out around our favorite reference rock late season adding to the alignment/rescaling uncertainty. Still, after moving Espen's calving front line over to this year's image shows there has been a modest level record retreat.

The June 10th has come in ... this one is rotated CW to better match true north and DMI. This has the effect of rotating the calving line around the reference rock.

S1A_EW_GRDM_1SDH_20150710T095917_20150710T100017_006747_0090B2_65F1
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Anne on July 10, 2015, 10:58:04 PM
Any thoughts on this video of calving from 20 June? Colorado Bob on Robert Scribbler suggests it's not a normal calving but forced by the sweet bluewater from behind.
https://www.youtube.com/watch?v=8sICl7O7NQs (https://www.youtube.com/watch?v=8sICl7O7NQs)
Colorado Bob usually seems to know what he's talking about.

Whatever, it's pretty impressive.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 10, 2015, 11:37:25 PM
Anne, could you please link to the specific page where Robert Scribler quotes Colorado Bob with these words? 
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Anne on July 11, 2015, 02:00:48 AM
Hi, A Team - sorry, my bad. It wasn't a comment of R Scribbler's so he didn't specifically endorse it, but a comment on one of his endless comment streams. I'm trying to find it again. But in any case, I was interested in how an informed person (not me) would interpret the video.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Anne on July 11, 2015, 02:19:06 AM
OK - just shows how false memory can be. The original post in the RS comments wasn't by CB but by Andy in San Diego, and it was CB's comments that struck me:
https://robertscribbler.wordpress.com/2015/07/09/unprecedented-fire-season-has-burned-11-million-acres-so-far-for-alaska-and-canada/#comment-44188
Apologies if I should have posted this in Stupid Questions instead.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on July 11, 2015, 02:44:25 AM
Seems like there are some advantages from using files from the Sentinel hub itself, notably the ability to manipulate within 16-bits (enlargement, rotation and local contrast), and separate HH and HV polarizations which can also be combined into RGB (blue taken as all 0 or black).

The great downside is that north is not up in Sentinel images nor is a rotational angle provided nor is this angle the same between images. This contrasts with DMI and Landsat. For example the 10 June 15 Sentinel needs an 18.9º rotation.

The HV is brighter in this instance. It seems to better distinguish calved from recently calved from freshly calved. I don't know what the physical basis for this is, maybe calved ice becomes less rough over time. Neither polarization combo is proposing about-to-calf.

The Jakobshavn calving front seems to have moved further into record retreat; that can be measured relative to the last fixed point, the rock island in lower left. If this is July 9th and maximal retreat in 2014 occurred in late Sept, this could get interesting. There are three issues: position relative to basal topography sills and troughs, loss of side buttressing if the calving front should retreat past the 'big bend', and greatly reduced obstruction to side tributary inflow.

The comparison to the Sept 27th maximal retreat of last year is somewhat problematic due to geometric effects in two different instruments, plus there has been more melt-out around our favorite reference rock late season adding to the alignment/rescaling uncertainty. Still, after moving Espen's calving front line over to this year's image shows there has been a modest level record retreat.

The June 10th has come in ... this one is rotated CW to better match true north and DMI. This has the effect of rotating the calving line around the reference rock.

S1A_EW_GRDM_1SDH_20150710T095917_20150710T100017_006747_0090B2_65F1

if you watch the video of the calving, particularly the last 4 minutes, I think you are seeing the  formation of that curious feature on the north bank of the main channel. During the video,the camera person shifts away from the massive ice berg and focuses in on what appears to be the north bank sliding into the fjord. I have felt for sometime that the north bank, which is grounded below sea level is seeing significant bottom melt as water from the fjord undercuts it. That initial calving off the main calving front was massive. I believe the force of the water that was displaced wreaked havoc on a portion of the north bank that has already lifted (no longer grounded but more of an ice shelf.)

Of course, I don't know what I am talking about.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 11, 2015, 07:57:20 AM
It's a remarkable video of a major drawn-out calving event. It's worth noting though that at a 40 m per day advance, 1500 m thickness and 5 km width, this glacier is calving a cubic km of ice every 3 days or so.

After some cliff fall, the really large piece broke off to bedrock ~1400 meters below the sea. It rolled back and came out feet first which is a typical but non-intuitive calving mode. (In Chasing Ice, the berg tipped forward). In both clips, we see very dark blue, almost black ice surfacing, some of it perhaps with embedded till.

None of the blue marked in the image below is liquid water -- all of it is immobile ice. You can see a smallish volume of whitish-gray water surging over a divide on the giant calved piece at 5:37. The giant berg is quite a distance from the calving front at this point.

It has not proven possible to get instrumentation on an autonomous submersible or a mooring anywhere near the bedrock/ice interface to measure meltwater discharge. It would be quite dangerous to even bucket-sample surface water from a helicopter in the midst of an event like this.

The lowered water pressure suddenly created by the feet-first rotation to surface and its inrushing replacement have been treated in various modeling papers (and the recent paywalled seismic study), as have relative buoyancy properties of emerging basal fresh meltwater. Most glaciers in Greenland have distributed continuous discharge early in season that matures to more efficient tunnel collection systems later.

As Shared H points out, there is a lot worth looking at in this video depending on your interests. Something massive beyond human experience moving so rapidly will indeed cause all manner of unfamiliar havoc.

Jason Box's drone study was up at Store Glacier. I recall this looked at the role of meltwater in hydrofracturing crevasses and so inducing calving. JC Ryan et al UAV photogrammetry and structure from motion to assess calving dynamics at Store Glacier, a large outlet draining the Greenland ice sheet, The Cryosphere, 9, 1-11, doi:10.5194/tc-9-1-2015, 2015. All of Box's papers, including 3 new ones in review, can be found at https://sites.google.com/site/jboxgreenland/publications. (https://sites.google.com/site/jboxgreenland/publications.)

J Todd and P Christoffersen studied Store in 2014, remarking:

Water pressure is essential for basal crevasse penetration, but it may also be significant in surface crevasses. The process of hydrofracturing by water in surface crevasses is believed to have been a critical factor in the collapse of the Larsen B Ice Shelf. However, while water in surface crevasses may be important, it is extremely difficult to quantify. The relationship between surface melt rate and crevasse water depth depends on the distribution, shape and depth of crevasses, and melting and refreezing on crevasse walls, as well as potential drainage of water from crevasses into englacial, subglacial or proglacial water bodies. As such, it is currently impossible to estimate even an order of magnitude for crevasse water depth at Store in summer. However, outside the 3-month summer melt sea-
son, surface crevasses must be assumed to be dry. http://www.the-cryosphere.net/8/2353/2014/tc-8-2353-2014.pdf (http://www.the-cryosphere.net/8/2353/2014/tc-8-2353-2014.pdf)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Anne on July 11, 2015, 11:31:11 AM
Thank you, A-Team.  :)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on July 11, 2015, 03:15:38 PM
For sure, that is no bergy bit.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Tor Bejnar on July 11, 2015, 04:09:35 PM
Thanks greatly, A-Team.  I wondered what that giant blue 'whale' was doing in the video. (Yes, I knew it wasn't a whale, but I didn't know what the heck I was seeing.)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 11, 2015, 04:59:34 PM
giant blue whale

That one in Chasing Ice even has a mouth and eyes and that same lumbering motion. Spooky. https://www.youtube.com/watch?v=hC3VTgIPoGU (https://www.youtube.com/watch?v=hC3VTgIPoGU)

I have some remaining 'issues' with these big events, notably what happens with air bubbles, especially the squashed out ones, within the ice column upon sudden depressurization as nearly a vertical mile of ice goes horizontal.

Maybe we could get a cheap ice core by scraping a tool along one of these beasts longitudinally after it has shoaled at the far west end of the fjord (Espen?). Till at the very bottom would be especially informative. Its age could not be dated by layer stratigraphy because that is long gone but its thickness, minerals and certain isotopes like beryllium could be informative.

It has not been possible even for a hot water drill to reach bedrock in the south branch of Jakobshavn because of rapid movement, though one hole way upstream got temperatures many hundreds of meters down. Observational data is really needed to anchor models, which do not currently portray JI as a future runaway situation.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 11, 2015, 05:45:47 PM
A-Team you are definitely going to use any drills from my toolbox for that project ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 11, 2015, 11:57:17 PM
... welcome to use any drills from my toolbox for that project

No thx. Maybe you have friend with cordless drill?

I'm seeing two good option on July 6th. The one to the west looks dark in all imagery; the one to the east is ~1 km in lengths. No way they could roll over a second time. It's not so clear though which end is up; for that matter we could end up drilling sideways. It is just a short hop from Illulisat to the history books. You in?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: andy_t_roo on July 12, 2015, 12:10:45 AM

Maybe we could get a cheap ice core by scraping a tool along one of these beasts longitudinally after it has shoaled at the far west end of the fjord (Espen?). Till at the very bottom would be especially informative. Its age could not be dated by layer stratigraphy because that is long gone but its thickness, minerals and certain isotopes like beryllium could be informative.

I would suspect that exposure to seawater would contaminate and parts per million / billion variations what I've cores try to measure...
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 12, 2015, 02:48:56 AM
exposure to seawater would contaminate and parts per million / billion variations what ice cores try to measure..
Surprisingly, small molecules, ions and tephra don't diffuse notably in a cold high pressure ice Ih lattice. If they did, after 100,000 years, there would not be storm-level resolution in a 1 mm annual layer. (See http://onlinelibrary.wiley.com/doi/10.1002/jqs.2684/full (http://onlinelibrary.wiley.com/doi/10.1002/jqs.2684/full))

Anything cored below 100 m on Greenland or Antarctica has to use commercial drilling fluid to compensate for pressure release so the core doesn't shatter. Holes such as NEEM are not abandoned but rather left filled with drilling fluid so they can be revisited.

I was curious too about the contamination issue (recall that posted picture of Dansgaard smoking a pipe as he handled a core with bare hands). At Renland, a 2015 project, they poured in five 200 liter drums of Estisol 140 / Coasol (coconut esters) during drilling.

The cores were later wiped off with paper towels. However it got all over everything including gloves of the  team logging the cores and some ended up back in the freezers in Copenhagen. Egrip will use Estisol 240 -- the days of mxing in greenhouse CFCs are over. See http://www.igsoc.org:8080/annals/55/68/a68a043.pdf (http://www.igsoc.org:8080/annals/55/68/a68a043.pdf)

Estisol is a low-molecular weight mix of fatty acid esters. Let's just say the manufacturer and primary clients (Shell, ExxonMobil...) aren't terribly concerned about contaminants nor, based on personal experience working on a commercial Gulf of Mexico drilling rig, hesitant about tossing used product over the side. So, like furniture fire retardant, it's everywhere.

However, beryllium Be10, where we are talking about counting individual atoms rather than ppb, is implausible as a contaminant in a hydrophobic or even polar fluid. Internal controls are consistent with this.

What I find most appalling is careless DNA contamination of the very bottom core. However a lot of this can be sorted out during computer assembly in a high-throughput metagenomic environment (google-scholar Eske Willerslev or see http://adsabs.harvard.edu/abs/2014EGUGA..1610721F (http://adsabs.harvard.edu/abs/2014EGUGA..1610721F)). Yet this doesn't really fly when you are talking about a common pan-Arctic midge or wind-borne conifer pollen.

After Greenland ice cores arrive in Reno, surface ice is shaved off prior to continuous-flow analytic procedures. The nature of annual resolution wiggles and presence of datable isotopes control for the presence of contaminants, which have in practice not been a significant issue relative to crystal regrowth, folding deformation, boudinage and so forth.

Of course we are only joking (?) about sending Espen off on a floating laboratory, chasing ice samples from calvings.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 13, 2015, 08:46:41 PM
Another big caving seems to going on around Jakobshavn:

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 13, 2015, 11:16:21 PM
Where exactly is this stuff coming from (yellow arrows)? It doesn't show up so well in Band 8; Band 7 may be partly defective. Bands 456 works well, 3rd image. Looks like ice fall accelerating on north side of south branch (white arrows). Another black ice whale seems to have calved?

I sometimes wonder if the calving front is in some sort of equilibrium position (potential well) along the slope to the sill. That is, the glacier moving faster causes it to calf just enough faster, resulting in little net movement of the calving front. During the shoulder seasons, the glacier slows but so does the calving, resulting in little net retreat. It has been a while since we have seen a 'break-out' retreat into wholly new territory.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 14, 2015, 12:11:18 AM
Beyond record retreat at several locations-

Here is some of the answer, we are now into record territory at several locations, especially at the northern branch (far beyond) and southern branch northern shore and some parts of main calving front (southern branch):
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: oren on July 14, 2015, 12:28:08 AM
I wonder if that north face of the south branch could develop further, or if it's a dead end.
btw, the gif shows 2014 by error for the July dates.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 14, 2015, 12:34:36 AM
I wonder if that north face of the south branch could develop further, or if it's a dead end.
btw, the gif shows 2014 by error for the July dates.

Thanx Oren, will be corrected another "big one#"at the Hagen Bræ site.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 14, 2015, 12:49:56 AM
Due to wrong dates here is the updated version, sorry and thanks Oren:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on July 14, 2015, 02:17:07 AM
I wonder if that north face of the south branch could develop further, or if it's a dead end.
btw, the gif shows 2014 by error for the July dates.

Much of the north face is grounded below sea level and the below sea level grounded portion goes fairly far inland.

I absolutely guarantee the north face is going to surprise us.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: plinius on July 14, 2015, 03:07:52 AM
that's a very interesting paradox, when you use "us" instead of "you" ;-)) Better than the classics like "All people from my home town lie."
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 14, 2015, 07:41:25 AM
It has been a while since we have seen a dramatic 'break-out' in calving front -- despite being in 'into record territory at several locations', the last year or two don't show up as noteworthy progression stages on a 1975-2015 chart of maximal retreats, though this season is off to a decent start.

We know, sort of, from ice-penetrating radar that the calving front is currently marching up a ramp to a major sill,  followed by a descent far below sea level into a region of humps, deep troughs and epic potholes.

Actually the experimental situation is murky and the many publications on this topic are careful not to furnish maps in a specified projection at decent scale as a layer stack, making it impossible to accurately overlay say the band 8 Landsat calving front on accurately colored basal topography. 

The animation below shows an illustrative scenario in which the calving front rattles around in a potential well midway up the ramp that it can't climb out of. Every time it tries (calving faster), that releases the glacier to come forward faster, and vice versa. The diagram is strictly heuristic (or if you prefer, speculative rubbish) but not physically unmotivated (early Joughin papers). We're more familiar with received wisdom that glacier retreat accelerates once it is past a sill, this is more of the same.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Greg du Pille on July 14, 2015, 10:26:35 AM
I usually only lurk, as I have no expertise in this subject whatsoever, but I was intrigued by Espen's animation above.  There seem to be 3 largish rocks that appear to the left of the North branch in the 2015 frames which don't show on the 2014 picture.  Is this indicative of rapid thinning of the glacier at this point, or is there a more likely explanation?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 14, 2015, 11:23:53 AM
I usually only lurk, as I have no expertise in this subject whatsoever, but I was intrigued by Espen's animation above.  There seem to be 3 largish rocks that appear to the left of the North branch in the 2015 frames which don't show on the 2014 picture.  Is this indicative of rapid thinning of the glacier at this point, or is there a more likely explanation?

Hello Greg du Pille, it is a combination of thinning and snowfall (late September)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Rubikscube on July 14, 2015, 12:48:22 PM
Much of the north face is grounded below sea level and the below sea level grounded portion goes fairly far inland.

I absolutely guarantee the north face is going to surprise us.

Looking at the north face in the most recent calving video, I'm struck by how tall it is. I can hardly imagine that this 3rd branch will be able to retreat very quickly through such a mountain of ice, after all, despite this area being grounded below sea level, it is quite shallow. There is also a second "cape ice" in the making which probably will result in two separate bulges in the north face, rather than one long calving front which could perhaps be somewhat unpredictable. Then again, I guess my inability to see where a surprise is supposed to come from, is also the reason I will be surprised :D.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: plinius on July 14, 2015, 01:13:39 PM
uhm, I am not sure if I have my maths right, but the taller a glacier cliff is, the more prone it is to cliff failure and cliff+hydrofracturing. So I do not see how one should connect a tall cliff to stability. It is a main driver of dynamic behaviour...

Looking at the north face in the most recent calving video, I'm struck by how tall it is. I can hardly imagine that this 3rd branch will be able to retreat very quickly through such a mountain of ice, after all, despite this area being grounded below sea level, it is quite shallow. There is also a second "cape ice" in the making which probably will result in two separate bulges in the north face, rather than one long calving front which could perhaps be somewhat unpredictable. Then again, I guess my inability to see where a surprise is supposed to come from, is also the reason I will be surprised :D.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 14, 2015, 03:39:16 PM
Please recall that the velocity field and ice discharge volumes are well characterized experimentally and have been posted dozens of time in this forum (admittedly 721 is a goodly number to re-read).

I've also posted a very accurate oblique hillshaded DEM numerous times -- this is even better for hill and rock perspective than ground- or plane-level photography.

The main Jakobshavn ice stream comes down off a 3,000 m ridge hundreds of km to the east. It is the fastest in the world, contributing perhaps 99% of total ice volume discharged at this site. The northern features calving into the bay have insignificant gravity behind them, minor velocities, inconsequential drain fields, no prospects of buttressing the main ice stream, and no real potential to contribute to sea level rise no matter what they do.

In fact, ice to the south of the south branch is contributing far more ice today and will recruit even more in the future -- at the calving front, the fast ice stream only amounts to a quarter of the perimeter arc. The rest is coming from tributary flows from the south. I've colored in these contributing streams in past posts.

The focus here has mostly been calving front position -- very seldom does anyone post imagery even 10 km east (ie include the big bend). It is a good idea to step back once in a while for the big picture of where the ice is coming from -- and this is a great time of year to do so, see  http://earthexplorer.usgs.gov/. (http://earthexplorer.usgs.gov/.)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Rubikscube on July 14, 2015, 08:06:55 PM
uhm, I am not sure if I have my maths right, but the taller a glacier cliff is, the more prone it is to cliff failure and cliff+hydrofracturing. So I do not see how one should connect a tall cliff to stability. It is a main driver of dynamic behaviour...

Well, my thought was that the waters are too shallow, and that ice not really that tall, for cliff failure to be a major concern, and it doesn't seem like the cliff will get much taller than it already is. Thus I intuitively draw the conclusion that more ice takes longer time to export, which implies slower retreat (but not necessarily slower volume discharge). I'm not sure, it may be way too simplistic.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 14, 2015, 09:59:11 PM
Jakobshavn update:

The red line show the retreat September 27 2014 vs. July 13 2015, but overall July 13 2015 is now the date when Jakobshavn retreated the most, less in the southern branch and most in the northern branch.

Red line also show the only (small) area where September 27 2014 is ahead of July 13 2015 retreat wise.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 16, 2015, 06:23:15 AM
Still moving on, very close at record retreat for Jakobshavn:

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on July 16, 2015, 03:41:29 PM
Still moving on, very close at record retreat for Jakobshavn:

It's as if the glacier saw that red line you drew on the previous post.

I also have a question about what the latest animation is showing. It looks as if the water nearest the north face of the southern branch filled with melange over those two days. It whitened considerably. Is that what I'm seeing and is this evidence that the north face of the southern branch is tossing off a lot of bergy bits?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 16, 2015, 05:08:26 PM
It's as if the glacier saw that red line you drew on the previous post.
If it doesn't break out this season, we'll need to seriously revisit the 'stuck on the exit ramp' scenario a few posts back. #717.

what the latest animation is showing. water nearest the north face of the southern branch filled with melange

The enhanced blue is a Landsat band 7 issue. Band 7 (short-wave infrared, 2.11 - 2.29 µ, moisture content of soil and vegetation). Not clouds (cirrus is band 9), though those are encroaching from the west. I would say local temporary surface melt.

The first image below shows the melt status from two consecutive Landsat frames. I've seen it more melted at this time of year -- and less melted too. There is very little meltwater overtly draining into Jakobshavn in any year. I've highlighted one exception, right in the upper channel, that was present last year too.

The second image is a slightly enlarged Band 8, about 10 m. As usual, it is not evident what will calve off in the next 2-3 days. It will be a week before Landsat swings by again, July 22. Today was a very nice stereo pair of path,ro 8,11 and 8,12 -- we have yet to do anything with these.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 16, 2015, 06:24:49 PM
Here is an animation of Jakobshavn retreat over last 16 days ... and the motion of the north side of south branch. These animations are quite useful for distinguishing newly exposed rock from melt -- both can be dark but only surface melt moves. The Landsats have the same geometry but are displaced a dozen pixels in a purely horizontal direction.

The average velocity over the last 16 days is 26.9 meters per day at the site measured. The highest recorded is 52 m/d though where exactly was not documented (too near the front and crevasses may simply be widening, overstating bulk motion.)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Jester Fish on July 16, 2015, 11:48:38 PM
The animation below shows an illustrative scenario in which the calving front rattles around in a potential well midway up the ramp that it can't climb out of. Every time it tries (calving faster), that releases the glacier to come forward faster, and vice versa. The diagram is strictly heuristic (or if you prefer, speculative rubbish) but not physically unmotivated (early Joughin papers). We're more familiar with received wisdom that glacier retreat accelerates once it is past a sill, this is more of the same.

So what would it take to get the little ball up over the hump? (Last I heard Sisyphus was busy  :o). If I understand your description; the caving front would have to increase faster than the downhill movement until a break-even point where there isn't enough mass between the caving front and the sill crest to maintain velocity.

Am I on the right track?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 17, 2015, 02:12:40 AM
So what would it take to get the little ball up over the hump? the calving would have to increase faster than the downhill movement until a break-even point where there isn't enough mass between the calving front and the sill crest to maintain velocity.

Velocity is really due to the gravity acting on ice all the way from calving front to the summit divide of Greenland hundreds of km to the east, as modulated by various restorative forces, seasonal conditions and longer-term trends.

If, and we don't know this yet, when the calving front nears the top of this bedrock ramp, calving starts to slow (for a reason yet to be established, perhaps the one you suggest) and the calving front moves west, until a point lower down on the ramp where calving starts to speed up (for another reason to be established, perhaps the one you suggest).

Picturing stiff ice flowing up to and over a sill, it is easy to imagine post-sill mass in effect cantilevered over the sill pivot point, perhaps supported to some extent by buoyancy from fjord or discharge melt water but not enough as the extending mass goes farther out and breaks off.

Even if the ice is not truly rigid but bends, flows, thins/thickens, somehow managing to conform its basal layer to ramp bedrock, that still might result in stresses above the bend which might manifest first as brittle fractures, crevasses and then as calving, provided the time scale was such that the ice did not have time or fluidity for adaptation.

Note this same ice stream is rounding two fairly pronounced horizontal bends at the same velocity without any visible surface discombobulation, a seeming affront to mass conservation. Even in years when the calving front was 10-20 km out west in the fjord, this same bedrock sill and ramp did not give rise to any surface features (hummock and dip). In other words, it's not feasible to determine bedrock profile from surface topography. Here the ice is ~1500 m thick; flow over bedrock features is damped out.

Still, long-term 'confinement' of the calving front to the ramp region is asking for a goodly number of coincidences in ramp length, sill profile, glacial velocity, ice rheological properties, annual accumulation and so forth, to make it all work out quantitatively. Permanent confinement asks for a whole lot more, given massive parameter changes unavoidable from global warming.

Meanwhile, why did Jakobshavn retreat as much as it has over the last few decades?  Ramps and sills aren't present to play a role. Rapid retreat is generally attributed to warmer ocean water arriving in Baffin Bay and surroundings. That effect depends on circulation not only in the fjord but also on mixing at the underwater part of calving face. As the calving front marches up a ramp, there's less front to be in contact with the ocean water. So calving slows.

There has been a lot of overlap in calving front position summer range the last three years at least, so it's not worth building a sand castle just yet -- September will be here soon enough and maybe it will be over the hump already this year.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: oren on July 17, 2015, 09:27:15 AM
It's interesting to note the big difference in the north side of the south branch between 2013 and 2015. Do you think there is any buttressing effect between the north side and the main glacier? If so, then its receding could help the calving front retreat further.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 17, 2015, 03:55:27 PM
any buttressing effect between the north side and the main glacier? If so, then its receding could help the calving front retreat further.
Yes, depending on the thickness and velocity (~ momentum) of the ice coming roughly orthogonally off the north side, the effect would be to compress the main ice stream to its walls and surface rocks on other side, tending to inhibit motion and calving. The main north branch at one time played this role as did a pinning point mid-fjord. The large bend upstream would have a similar effect. Whether these add up to anything quantitatively is questionable. Really it is the north side that has become uncorked.

Next to nothing is known observationally about the Jakobshavn calving front below the water line (eg, is it vertical to bedrock, inclined, or hollowed out?). Radar has issues in heavily crevassed thick ice by salt water, no one has been able to get close with sonar, seals or submersibles, no disposable probes have been dropped, no drilling is feasible, gravity measurements lack sufficient resolution and unique invertibility, the ice temperature profile cannot be measured, and no helicopter sampling has been done of calved pieces. It's fair to say though that ocean and meltwater are well-mixed by calving turbulence.

Rignot's group tried last August to get a ship into the less active calving fronts of nearby Epiq and Store, pushing small bergs off the half-million dollar sonar with hand-held poles but never got there. http://news.uci.edu/greenland/ (http://news.uci.edu/greenland/)

Jakobshavn may no longer 'trending' in terms of journal articles per year -- perhaps little more can be done, leaving us in predictive limbo. There are far more papers these days on other West Greenland glaciers, mostly on meltwater effects. I could only locate 3 Jakobshavn articles in the last six months:

Seasonal and interannual variations in ice melange and its impact on terminus stability, Jakobshavn Isbræ
R Cassotto et al. http://www.igsoc.org:8080/journal/61/225/j13j235.pdf (http://www.igsoc.org:8080/journal/61/225/j13j235.pdf) free full

"We used satellite-derived surface temperatures and time-lapse photography to infer temporal variations in the proglacial ice melange at Jakobshavn Isbræ. Freezing of the melange-covered fjord surface during winter is indicated by a decrease in fjord surface temperatures and is associated with (1) a decrease in ice melange mobility and (2) a drastic reduction in iceberg production. Vigorous calving resumes in spring, typically abruptly, following the steady up-fjord retreat of the sea-ice/ice-melange margin. An analysis of pixel displacement from time-lapse imagery demonstrates that melange motion increases prior to calving..."

Oceanic Boundary Conditions for Jakobshavn Glacier. Part I: Variability and Renewal of Ilulissat Icefjord Waters, 2001–14
CV Gladish et al  http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-14-0044.1 (http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-14-0044.1) free full
"Jakobshavn Glacier, west Greenland, has responded to temperature changes in Ilulissat Icefjord, into which it terminates. This study collected hydrographic observations inside Ilulissat Icefjord and from adjacent Disko Bay between 2001 and 2014. The warmest deep Disko Bay waters were blocked by the entrance sill and did not reach Jakobshavn Glacier. In the fjord basin, the summer mean temperature was 2.8ºC from 2009 to 2013, excluding 2010, when it was 1ºC cooler." 

Oceanic Boundary Conditions for Jakobshavn Glacier. Part II: Provenance and Sources of Variability of Disko Bay and Ilulissat Icefjord Waters, 1990–2011
CV Gladish et al  free full at ResearchGate

"Jakobshavn Glacier, west Greenland, has responded to temperature changes in Ilulissat Icefjord, into which it terminates. Basin waters in this fjord exchange with neighboring Disko Bay waters of a particular density at least once per year. This study determined the provenance of this isopycnic layer for 1990–2011 using hydrographic data from Cape Farewell to Baffin Bay. The warm Atlantic-origin core of the West Greenland Current never filled deep Disko Bay or entered the fjord basin because of bathymetric impediments on the west Greenland shelf. Instead, equal parts of Atlantic water and less-saline polar water filled the fjord basin and bathed Jakobshavn Glacier...."

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Jester Fish on July 17, 2015, 08:56:06 PM
A-Team- Thanks for the response, fascinating stuff this physics of moving ice.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: oren on July 17, 2015, 09:11:37 PM
Another set of thanks A-Team, your wealth of knowledge (and patience...) is amazing.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 19, 2015, 10:27:48 PM
Here are some pretty clouds and a not-so-pretty smoke plume (from Canada/Alaska) wafting over west Greenland on 19 Jul 15. We don't know that it will get deposited here, further reduce albedo and increase melt though that has happened in recent years.

I added one of the better visualizations of topography around the calving front. The north branch NB is barely noticeable.

The 3rd image shows the calving front relative to ramp and sill according to Joughin et al 2014. As mentioned, researchers have gone around in circles for years in terms of a high resolution bedrock map of the current calving area, despite a very high density of radar overflights, none of which show bedrock out vast amount of additional expert processing (4th image).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: solartim27 on July 20, 2015, 07:26:45 PM
A nice clear series from DMI shows the calving surge exiting 3-4 days later.  July 15 to 19th.  Click to animate.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 20, 2015, 09:07:29 PM
Nice spotting. Might consider cropping, will make the animation a lot smaller and run without a click. Below, I paired the original with a hideous enhancement that however isolates the main south branch calving front.

It appears to me that the surge is coming from the two midway tributaries, not so much from the calving front. Keels of larger bergs can get stuck for months on the Illulisat moraine, so a barrier giving way also merits some consideration.

Today featured both a Radarsat and a Sentinel-1. We don't see Radarsat that often; I don't know where a download is for it nor the ultimate resolution. It looks like a huge plume again to the west.

I've added the 20 Jul 15 full resolution Sentinel, rotated CW by 16.1º to north up and colored by combining hh and hv polarizations. Calving front is maintaining a very respectable level of retreat. Next Landsat is still a couple days away.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 23, 2015, 04:39:05 PM
A new Sentinel paper provides an excellent comparative discussion of determining Greenland-wide and marine-terminating glacial ice velocities with various SAR satellites, and incidentally new winter 2015 maps of Jakobshavn. The short version is Sentinel will provide long-term measurement of change but no improvement in resolution.

The double image below has some interesting features such as a slow island in upper Jakobshavn seen in both Sentinel and TerraSar. The latter does a better job near the calving front and on the north side of the main south channel. The top speed is 30 m/day, more than I would have expected for the dead of winter. (Not shown: the authors' inappropriate and incorrectly made logarithmic key.)

The second graphic shows that while Store Glacier just to the north is moving right along at 16 m/day, that speed has not increased recently whereas Jakobshavn's has, quite a long ways from the calving front.

The Sentinel-1 Mission: New Opportunities for Ice Sheet Observations
T Nagler et al
Remote Sens. 2015, 7(7), 9371-9389; doi:10.3390/rs70709371
http://www.mdpi.com/2072-4292/7/7/9371 (http://www.mdpi.com/2072-4292/7/7/9371)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 27, 2015, 06:07:34 PM
Just received the latest Sentinel Images, and I am sure we are inside the record retreat-zone:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 27, 2015, 07:26:24 PM
Did you verify these have true North up? Sentinel images come with no indication of direction as far as I know. It won't be possible to compare the calving front with Landsat and Modis images, which do have north up, until it is rotated. Even then, it is very difficult to make out the key feature in Sentinel, the last rock island before the calving front begins.

To do this in gimp or ImageJ, use the angle tool line tangent to distant rocks that are recognizable in every image. Subtract angle from Landsat. That's your rotation. To do in 16-bit mode. The image below shows DMI (which is correctly rotated) overlying your Sentinel

With the weather cloudy, Landsat once a week and Modis too small, Sentinel is about it. Note in past years, the record may have been missed in between Landsats.

The second image below compares the 27 Jul 15 Sentinel -- after a 20.75º CW rotation -- to an older unrotated Landsat which we hope represents true North. The Sentinel may have other warping issues. It is a pity that someone hasn't installed a few corner reflectors for radar so that there could be some assurance images are scaled and oriented correctly. Sentinel's orbit is inclined at 98.18º which seems to have no bearing on the rotation needed to get North up.

A new Landsat is due tomorrow the 28th. If the weather is clear, we can toss these Sentinels into the dustbin. Meanwhile I wrote the EOS help desk with some measure of exasperation.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 29, 2015, 11:03:41 PM
Now it is clear. and almost without any academic discussions ( you can never be sure) Jakobshavn Isbræ reached a new low, please note the the growing rocks:

Please click for animation.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 29, 2015, 11:12:59 PM
The Landsat for July 29th just came in. Calving front retreat is respectable but still equally consistent with the "confinement" theory which posits that ocean waters warming the calving face base have less basal surface to affect the farther up the ramp the calving front sits, causing the forward motion of the ice stream to gain ground westward, only to have ocean waters to become more effective again at speeding up calving.

The first image develops a simple frame of reference for image comparison, starting with the 45º line (that gimp draws exactly if you hold down control keys) at the icefall separating n and s branches. The bounding box is flush with the top of the last rock and continues to the diagonal. Then equal buffers are added using bounding box handles in gimp.

If the tongue of the calving front gets entirely out of the SE corner box, reasonable people could agree to declare a significant new record of retreat. Right now it seems a record only here and there.

However the news here seems to be the very active retreat area (yellow tint) in the NE, which is having the effect this year (as first pointed out by Espen quite a ways back) of broadening ice stream width (resp. NE corner and edge of calving front) which as we all know is quite impossible from the terrain map (deal with it). Possibly this just reflects  'pent-up demand' from a minor side component now destabilized by retreat of main channel buttressing.

With two full months to go until the date of last year's date of record retreat, not one person here or in academia has ventured a prediction of where it will end up, which is no different than for any of the marine terminating glaciers of Greenland. How do we get from this ignorance to a confident prediction of future mass balance loss? (I seem not to bring the the right spirit of adventure to climate modeling.)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: solartim27 on July 30, 2015, 03:30:51 AM
Another good view of the calving surge exiting into the bay.  (Ummm, actually..... getting sucked back in?)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Sleepy on July 30, 2015, 05:57:23 AM
Wonderful images above. Are there any recent speed measurements available?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on July 30, 2015, 03:53:55 PM
Optical and SAR can be compared/merged once they are projected to the same map projection.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 30, 2015, 04:32:28 PM
Optical and SAR can be compared/merged once they are projected to the same map projection.

It seems that DMI knows how to do this but does not provide their prescription for it nor do they process the Sentinel images to their native resolution before cropping to the coast. Since everyone agreed long ago on the best standard projection for Greenland, it would make sense to create a cloud-based repository where these Sentinel images of Greenland have been reprocessed. There has been quite a bit of frustration with Landsat bundling and those are now broken out to give more control over downloads.

I never heard back from the 'help desk' on where I might find 'north' in their metadata. Maybe that makes no sense without de-warping. I've also loaded the kml shape files they provide into Google Earth. These are carelessly made and useless for compositing, for example, Petermann fjord sits in the general area of Petermann fjord but does not align to it.

I've found over the years that it makes far more sense for the originating site to do the reprocessing once, optimally. It is very inefficient to repeat that same exercise thousands of times within the non-specialist end user community. What happens in practice is they don't have the time, interest, knowledge, software or computing power.

In my view, 99% of the user community for Sentinel just wants the high repeat, cloud-free, year-round view. They could care less what imaging wavelength was used: where is the calving front, how much of the Amazon did they set on fire last week, where are the big swells. Yes, there is another 1% interested what can be done with the physics of radar reflections and polarizations.

When a data center washes its hands of user-friendly posting, the net result is the data goes unused or misused. To be honest, my sense is they don't give a damn there at Sentinel -- it is all about the 1%.

There's a famous example of this with the human genome project. Voila, we've done our bit, here is your raw fasta file: a 3 billion letter sequence of ATCG which is only the first of thousands. The user community consisted of drs with waiting rooms full of kids having undetermined inherited diseases. How many of these drs have time to write and debug 2 million lines of C to process the file into genes -- isn't this rather inefficient? Solution: do it once, right, centrally: https://genome.ucsc.edu/
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on July 30, 2015, 06:37:27 PM
Here is a September 27 2014 vs. July 29 2015 update as you can see September 27 2014 is only ahead in a tiny spot in the southern branch but overall July 29 2015 is now ahead retreat wise:

Please click on image to enlarge!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on July 30, 2015, 06:57:20 PM
September 28 2014 is still ahead in an important km long region in the southern branch!
Maybe get back to us on this in a week or so? I am recalling 2014 waxing and waning through the summer (not proceeding steadily to Sept climax which it might not have been since it was so cloudy. You can see it was about to shed big chunks.

There are insurmountable obstacles to aligning Landsat images with different path, rows. The 2015 image is LC80100112015210LGN00 so 10, 11 for that. However the 2014 LC80100112014271LGN00 is too, you lucky dog. (There is no 27 Sept 2014 Landsat so I assume you mean the 28th.)

However that doesn't mean the nadirs are the same ... Landsat only repeats up to an enveloping tube ... so they still need very careful alignment on rocks at large scale . Let me see what I get with the higher resolution 15 m band 8's...

29-JUL-15 LC80100112015210LGN00
 Sun Azimuth = 172.84693306
 Sun Elevation = 38.98565902
 Center Latitude 69.60626
 Center Longitude -50.84828

28-SEP-14 LC80100112014271LGN00
 Sun Azimuth    178.10310829
 Sun Elevation    18.35757655
 Center Latitude 69.60641
 Center Longitude -50.87276 

delta latitude 0.00015º (2015 nadir farther south)  166.8 m or 11.12 pixels at 15 m resolution
delta longitude 0.02448º (2015 nadir farther east)  948.6 m or 63.24 pixels at 15 m resolution

Distance between ground points:    0.9487 km
Midpoint:    69°36′23″N, 050°51′38″W
http://www.movable-type.co.uk/scripts/latlong.html (http://www.movable-type.co.uk/scripts/latlong.html)

Pixels between ground points @ 15 m/pxl: 948.7/15 = 63.25 pixels

Landsat is in UTM (universal transverse mercator projection relative to WGS84 geoid) with straight  lines for constant latitude and longitude which means here (because of the deltas) the two images are offset both up 63.24 pixels and over 11.12 pixels (which you could use in ImageJ for 'translocate' in making a co-registered stack. Fractional pixels are not a huge issue but something to keep in mind as unavoidable alignment error, 3.6 m error for the 0.24.

I've added a second animation based on this information. It has pixel-perfect resolution at its 7.5 m resolution on the edges of a 60 x 60 km square. It may be identical to the first alignment, haven't checked. There are no alignment nunataks to the west or northwest, that's just the way it is with marine-terminating glaciers: the interior of Greenland is quite bland and the area is crevassed and moving.

The 2015 has the darker melange.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 01, 2015, 11:45:54 PM
Whoa ... this looks to be the biggest calving ever. Just at DMI resolution though ... need to chase down original Sentinel.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Neven on August 02, 2015, 12:01:53 AM
Wow...

Go, A-Team.  :)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 02, 2015, 12:21:16 AM
Whoa ... this looks to be the biggest calving ever. Just at DMI resolution though ... need to chase down original Sentinel.

Sorry to interrupt here, but there seems to be some heavy calvings line just behind the present calving front:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 02, 2015, 12:53:47 AM
some heavy calvings line just behind the present calving front
Yes, most odd. Landsat from yesterday does not have this yet.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: crandles on August 02, 2015, 12:59:15 AM
some heavy calvings line just behind the present calving front
Yes, most odd

The gif Espen posted above seems to suggest advancement of glacier not retreat. Could 1 Aug image be taken just at start of calving event?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 02, 2015, 01:00:43 AM
some heavy calvings line just behind the present calving front
Yes, most odd

The gif Espen posted above seems to suggest advancement of glacier not retreat. Could 1 Aug image be taken just at start of calving event?

No, the DMI image is from today's Sentinel too.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: crandles on August 02, 2015, 01:06:27 AM
No, the DMI image is from today's Sentinel too.

I am probably being thick, but I don't follow, why does that rule out my suggestion?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 02, 2015, 01:17:06 AM
The Sentinel satellite only pass certain dates, and DMI is using the same data.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 02, 2015, 05:13:22 AM
You bring up a very good question, Crandles. We really need the timestamps on these images to (1) know when they were taken relative to some fixed standard so (2) that it becomes possible to subtract the timestamps to determine how much time elapsed between them (so feature velocity can be determined). Right now, we don't even know the relative order between two on the same Julien calendar date.

DMI does not provide anything but day-month-year (except for NOAA-19, upper right on DMI). They do not even provide the file name that would enable someone to look up the metadata everything is called index.php.gif  In part this may be because they download direct from the satellite (data is not encrypted) and so don't know what file name the satellite center will assign to it.

Now Sentinel file names are themselves metadata, eg S1A_EW_GRDH_1SDH_20150801 T101539_20150801 T101639_etc.tiff, which provides the date (rather than day of year) as well as start-stop times for taking of the image (a bit excessive).

Timestamps in Sentinel is a complex subject but you may be able to subtract two of them to get a time in seconds.. http://publications.jrc.ec.europa.eu/repository/bitstream/JRC92666/lbna27031enn.pdf (http://publications.jrc.ec.europa.eu/repository/bitstream/JRC92666/lbna27031enn.pdf)

Landsat is more easily understood eg  SCENE_CENTER_TIME = "14:54:02.9067400Z" where the 'Z' at the end of that timestamp is interpreted as "zulu time", which means they are in UTC (Universal Time Coordinated) which for our purposes are GMT (Greenwich Mean Time).

All NOAA satellites use zulu timestamping. This would include Terra and Aqua which carry the MODIS instrument. However I don't see timestamps on those at very many sites.

The Z wraps up Alpha Bravo Charlie for fuzzy radio communication ABC's; the Navy, via the U.S. Naval Observatory, is the official US timekeeper.

I have come to prefer conventional dates like 01 Aug 15 to day 213 because of leap year issues and generally want to know the day relative to melt season knowledge. However it is slightly easier to subtract with the latter.

Best practice is to always include the file name somewhere in a post, in the posted image, or in the file name of the posted image. Then the next person can locate the original if need be. However we have a number of rogue individuals posting on these forums.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 02, 2015, 10:22:05 AM
However we have a number of rogue individuals posting on these forums.

I am one of them,and I am not involved in a 100 meter dash or in science for that matter, I will just call it informatism.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: crandles on August 02, 2015, 11:25:09 AM
Looking on Modis between 1/8 and 30/7 I could not detect any differences, so I was tempted to think that whatever happened was after the Modis 1/8 pass but could of course be wrong.

If right, and a calving event takes some time (I think an hour was mentioned on thin ice video), and the latest sentinel image is after the 1/8 Modis pass then catching the calving event in progress doesn't seem impossible, though the image would have to be fairly early in the calving process.

Perhaps too many conditional 'and's in that.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 02, 2015, 11:29:15 AM
Looking on Modis between 1/8 and 30/7 I could not detect any differences, so I was tempted to think that whatever happened was after the Modis 1/8 pass but could of course be wrong.

If right, and a calving event takes some time (I think an hour was mentioned on thin ice video), and the latest sentinel image is after the 1/8 Modis pass then catching the calving event in progress doesn't seem impossible, though the image would have to be fairly early in the calving process.

Perhaps too many conditional 'and's in that.




The Modis images in that part of Greenland is sampled later in the day than the Sentinel images.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 02, 2015, 05:58:39 PM
Right, the order of imaging seems to be NOAA, NOAA, Sentinel, Aqua, Terra. DMI does not do Landsat. That ranges from daily to over a week.

Today the first NOAA came in at 02:24 UTC and the second five hours later at 07:27. These times do form part of the file names used at DMI, eg 201508020727.NOAA.jpg 

The Modis are better than nothing but are marginal for accurate resolution of small features.

It looks like Sentinel missed today up at Petermann. Unless DMI can fill in more of the image with later orbital swaths and Landsat comes through, our ability to measure mean velocities for calved bergs will be minimal. Update: DMI now has a full Sentinel ... I'll post over at the Petermann forum.

Jakobshavn flushes rather fast and even with big distinctive icebergs, tracking is more off than on. (However there is a continuous web cam for this.)

Looking now at the ESA Sentinel site, I am seeing downloadable items for 01 Aug 15 with UTC timestamps explained as T20:00:29.797Z which for us is T20:00 UTC or thirteen hours later than the second NOAA. Nothing showing at this time for August 2nd.
   
S1A_EW_GRDH_1SDH_20150801T200029_20150801T200133_007074_0099FE_94F3
https://scihub.esa.int/dhus/odata/v1/Products('cc78819a-6b96-4d8e-a794-93549686f977')/$value

Date : 2015-08-01T20:00:29.797Z, Instrument : SAR-C, Mode : EW, Satellite : Sentinel-1, Size : 1 GB

I modified this post to include the DMI Radarsat image of Jakobshavn for 03 Aug 15 ... the unusual calving continues.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Iceismylife on August 04, 2015, 07:20:39 PM
some heavy calvings line just behind the present calving front
Yes, most odd. Landsat from yesterday does not have this yet.
OK if it is backing off of the under ice ridge then are we back to tabular calving?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 04, 2015, 10:19:56 PM
if it is backing off of the under ice ridge then are we back to tabular calving?
No, Jakobshavn is done with tabular calving (unless you count breakup of seasonal melange that builds during the winter).

What I expect to see as Jakobshavn retreats farther out of its fjord back into the narrower winding south channel is reduced heat exchange between warm ocean water and ice at the grounding line because the attack surface is less accessible and the water will have been cooled. However the interface is taller to the extend the ice stream is retreating over a reverse grade (ie down from a sill into a trough).

There will still be plenty of convection (heat transfer by mass transport away) via churning induced by frontal calving and upwelling buoyant meltwater, but the resulting ocean water the glacier faces is then colder than open ocean water because circulation and mixing are reduced in the narrow channel and dominated by ice. (Picture the ice stream 10, 20, or 30 km further inland and the long cul de sac of ocean water.)

The icebergs we see streaming away must be balanced by return flow of deeper waters. However surface transport is fairly shallow (tens of meters) whereas the distance through water to bedrock approaches 1500 m. Thus if this were the only consideration, retreat would slow. The narrowness of the channel could offset this somewhat through turbulent interactions with the wlls.

Jason Box just posted an excellent popular piece on the other considerations which almost all favor faster retreatL
http://www.huffingtonpost.com/jason-e-box/ice-melt-fast_b_7927186.html (http://www.huffingtonpost.com/jason-e-box/ice-melt-fast_b_7927186.html)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: plinius on August 04, 2015, 10:54:37 PM
isn't there cliff failure missing in the picture too? Deeper water means higher ice front if the glacier is not to swim up...
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 05, 2015, 02:02:32 AM
Yes, cliff failure. Rignot is saying now the faces of these glaciers are not flat & vertical but in some cases have had cavities hollowed out by circulating warmer water. It is not that this water is so warm but that it is warmer than freezing and that it is circulating against the ice.

If the water were stationary, it might well freeze on since the temperature profile with depth in Greenland gets to 25º and more below zero. But there is no way the glacier front can cool down any substantial part of the fjord or Baffin Bay.

The underwater portion, notably the grounding line, of the calving front of Jakobshavn Isbrae has never been observed. We do not actually know what is actually going on there in terms of meltwater exiting, sill rock or morraine sediment, currents, tides, temperature, ice rheological properties or geometry of the face.

Jakobshavn behind the grounding line is in no danger of popping up like a cork from intruding seawater. The buoyancy shortfall is graphed in Fig.2 of Joughin 2014. These papers about ice sheets rising up briefly under meltwater hydraulics are to the south and concern land-terminating glaciers.

It is all but impossible even to make similar measurements on Jakobshavn because of severe crevassing extending tens of km upstream and its very rapid motion. I personally don't see a whole lot of meltwater systems draining into JI on Landsat; some but not that noticeable, though it is hard to say where meltwater on the sides ends up ultimately exits.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 05, 2015, 12:59:51 PM
With SAR-images the geometry is so well defined that it is quite easily possible to overlay images taken from the same orbit track to the accuracy of 1/1000th of a pixel. So it is not SAR which has problems with geometry, if there are mismatches to optical imagery the problems are at the optical side  :P

That being said, with S-1 the user needs to do some geometric operations in the S-1 Toolbox (for example) in order to transform the images into a suitable map projection. If someone has questions on how to do this I can offer some help during August...once the processing graph is set up it's rather simple to process new acquisitions...
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 05, 2015, 03:12:18 PM
can offer some help during August...once the processing graph is set up it's rather simple to process new acquisitions...
That would be fantastic if you could walk us through an example with a Jakobshavn file. We (me that is) definitely need to move on to the next level of processing using this Toolbox.

Be a pity if a record retreat happened in between cloudy Landsats and we weren't able to document it. In summer 2014 there were hardly any clear days there. 04 Aug 15 Terra compared to 01 below.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Iceismylife on August 05, 2015, 05:57:41 PM
if it is backing off of the under ice ridge then are we back to tabular calving?
No, Jakobshavn is done with tabular calving (unless you count breakup of seasonal melange that builds during the winter).

What I expect to see as Jakobshavn retreats farther out of its fjord back into the narrower winding south channel is reduced heat exchange between warm ocean water and ice at the grounding line because the attack surface is less accessible and the water will have been cooled. However the interface is taller to the extend the ice stream is retreating over a reverse grade (ie down from a sill into a trough).

There will still be plenty of convection (heat transfer by mass transport away) via churning induced by frontal calving and upwelling buoyant meltwater, but the resulting ocean water the glacier faces is then colder than open ocean water because circulation and mixing are reduced in the narrow channel and dominated by ice. (Picture the ice stream 10, 20, or 30 km further inland and the long cul de sac of ocean water.)

The icebergs we see streaming away must be balanced by return flow of deeper waters. However surface transport is fairly shallow (tens of meters) whereas the distance through water to bedrock approaches 1500 m. Thus if this were the only consideration, retreat would slow. The narrowness of the channel could offset this somewhat through turbulent interactions with the wlls.

Jason Box just posted an excellent popular piece on the other considerations which almost all favor faster retreatL
http://www.huffingtonpost.com/jason-e-box/ice-melt-fast_b_7927186.html (http://www.huffingtonpost.com/jason-e-box/ice-melt-fast_b_7927186.html)
What I'm looking at is this.  Sea water is denser than fresh water.  As you cool sea water with ice you also reduce its salinity.  What wins cooler denser sea water or less dense melt diluted sea water?

What I see currently is sea water (warm) flowing along the bottom of the fjord hitting the calving front grounding line. melting ice becoming less dense and flowing out the surface.  The calving face grounding line backing away from the sill will let the sea water flow an additional 20km inland under the ice.  The water along the bottom of the fjord is pulled all the way to the calving face/grounding line.  I'm currently assuming the two to coincide.

I forget where I read that a 1 degree difference between sea water (warmer) and ice will melt about 2.5 cm a day of ice.  Add that to the 20 km of additional area when the glacier backs off of the sill and the sea water circulation in the fjord should go up.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 06, 2015, 12:30:21 AM
can offer some help during August...once the processing graph is set up it's rather simple to process new acquisitions...
That would be fantastic if you could walk us through an example with a Jakobshavn file. We (me that is) definitely need to move on to the next level of processing using this Toolbox.
Happy to help, could you start a topic in the Developers' Corner and I'll jump in? Basically it would be good if you described what are the characteristics of the end product you want (projection etc.).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 08, 2015, 03:45:42 PM
Happy to help, could you start a topic in the Developers' Corner and I'll jump in?
Great, most helpful. Let's just use the Sentinel-2 one already started so as not to spread this out all over. I would say, how do we process a Sentinel image so that it co-registers with Landsat images of Greenland which are in local Mercator projection.

https://scihub.esa.int/dhus/ (https://scihub.esa.int/dhus/)
http://earthexplorer.usgs.gov/ (http://earthexplorer.usgs.gov/)
https://forum.arctic-sea-ice.net/index.php?topic=1348.0 (https://forum.arctic-sea-ice.net/index.php?topic=1348.0)

Which way is up? 

North is not up on Sentinel images as posted, causing us some grief in trying to make a record of the Jakobshavn calving front retreat combining both Landsat and Sentinel views.

In a Landsat mercator download, latitude and longitude lines aren't provided as a mask but they form an ordinary  rectangular grid and north is straight up everywhere on the image. That's not the case in the Earth Explorer viewer which is in Google Earth projection where the lat,lon lines are curved. In Google Earth (and polar stereographic) however, the center-of-image longitude can be rotated to be due north.

Thus there can be no expectation of a single rotation providing a global north on Sentinel images (which are not in mercator) but there should be rotation that provides a local north say midway across the calving front. That would probably suffice for our purposes because residual warping would be second-order error at this scale (though re-projection would be more desirable).

The Sentinel download package does not come with any lat,lon mask that would allow this local rotation to be determined (from a tangent line). However these images do provide quite recognizable traces of coastlines etc so in fact these lat,lon lines would be curved but not pathologically so (ie still smoothly continuous).

I asked the help desk about where in the metadata might I find the precise local anglse of rotation and received this detailed response from eosupport at copernicus.esa.int which I am still digesting:

Sentinel-1 imagery is provided in satellite geometry which is slightly different depending on the type of Level 1 product. For the detected GRD products, the imagery is provided in ground range, x, and azimuth, y, geometry whereas for complex SLC products, the imagery is provided in slant range, x, and azimuth, y, geometry.

This is described at https://sentinel.esa.int/web/sentinel/user-guides/sentinel-1-sar/product-types-processing-levels/level-1. (https://sentinel.esa.int/web/sentinel/user-guides/sentinel-1-sar/product-types-processing-levels/level-1.) As both GRD and SLC imagery are provided in satellite geometry, its orientation with respect to true north will vary with latitude and incidence angle. Thus it is not possible to accurately orientate the imagery with respect to north using a single rotation as this depends on both the x (range) and y (azimuth) position within the image. [[This could be provided by a simple grayscale mask but isn't.]]

Although Sentinel-1 imagery is not provided in a geocoded orientation (like your Landsat image), the product annotation gives a complete description of the transformation from pixel coordinates (x,y) to latitude & longitude via the geo-location data set record.

This data set is described in the Sentinel-1 Product Specification document S1-RS-MDA-52-7441 available from https://sentinel.esa.int/documents/247904/349449/Sentinel-1+Product+Specification+3.0. (https://sentinel.esa.int/documents/247904/349449/Sentinel-1+Product+Specification+3.0.) In particular see Section 6.3.1.7 for a description of the geolocation grid. Below is an example of first point within a grid from a GRD product:

<geolocationGrid>
<geolocationGridPointList count="483">
<geolocationGridPoint>
<azimuthTime>2015-08-04T22:03:55.263139</azimuthTime>
<slantRangeTime>4.976224778237438e-03</slantRangeTime>
<line>0</line>
<pixel>0</pixel>
<latitude>7.768200950286953e+01</latitude>
<longitude>-9.014424336694947e+01</longitude>
<height>-2.077938625589013e-01</height>
<incidenceAngle>1.937838349149362e+01</incidenceAngle>
<elevationAngle>1.737100868906543e+01</elevationAngle>
</geolocationGridPoint>

Note that an approximate orientation of the image with respect to north can be found by extracting the platformHeading parameter within the product annotation (see Table 6-31 of the above product specification document). Note that this is the orientation of the satellite and not the image. An example of this parameter is given for an image at a high latitude:

<generalAnnotation>
<productInformation>
<pass>Ascending</pass>
<timelinessCategory>Fast-24h</timelinessCategory>
<platformHeading>-4.390998067621028e+01</platformHeading>

This seems to say rotate a high latitude (Greenland) ascending orbit image by 43.9º clockwise to get north more or less up. I would need to look up this parameter in a bunch of Jakobshavn, Petermann and Zachariae to see if it varies much. Offhand, it seems too large for the Jakobshavn image we were considering a few posts above.

It is difficult to find pairs of well-separated, consistently identifiable rocks where the angles can be measured on both Sentinel and Landsat, which would sidestep rooting around in Sentinel metadata. That has to do with snow cover and sun angle in Landsat vs blurry resolution and rock shadowing on Sentinel.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 08, 2015, 04:28:34 PM
Here is the DMI Sentinel from August 8th. It is rotate to the north by an undocumented procedure. It may also be re-projected to polar stereographic, it's a great site but details are sketchy, other than Sentinel-1 satellite are processed by DTU (Technical University of Denmark). http://www.seaice.dk/ (http://www.seaice.dk/) has some interesting daily mosaics of the cryosphere.

www.dtu.dk/english (http://www.dtu.dk/english)

Looks like 'something' is happening on the calving front. There is a path,row 9,11 Landsat from today but the EarthExplorer site is barely working again today and the image is hopelessly clouded over. I am chasing down the full resolution Sentinel to see if that helps.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 08, 2015, 05:18:07 PM
It is in a gaining mood
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 08, 2015, 05:50:24 PM
Image rotated by 15º gives quite a good local fit (to Landsat) using that lake in the lower left and the ice fall dividing north and south branches. Looks like a very large piece has calved or is about to.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 08, 2015, 06:16:14 PM
Image rotated by 15º gives quite a good local fit (to Landsat) using that lake in the lower left and the ice fall dividing north and south branches. Looks like a very large piece has calved or is about to.

Yes a very large piece seems to be sent of soon.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 08, 2015, 06:17:53 PM
What is the projection of Landsat exactly? UTM zone something?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 09, 2015, 06:41:37 AM
Yes. Landsat-8 uses Universal Transverse Mercator (UTM) map projection for everything except south of -63º latitude (ie Antarctica) where Polar Stereographic is used, both relative to World Geodetic System 84 datum (WGS84).

Petermann is UTM_ZONE = 20, less commonly 21 as per the metadata file ending in MTL.txt in each package download 
 
Jakobshavn is UTM_ZONE = 22, less commonly 23

Zachariae is UTM_ZONE = 27 for the area Wipneus and Espen have been looking at

Sptizbergen, Jan Mayen, and Iceland we don't look at too often.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 09, 2015, 11:23:25 AM
This is off-topic here, I'll start a new thread in the Developers' Corner.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Iceismylife on August 10, 2015, 12:07:03 AM
if it is backing off of the under ice ridge then are we back to tabular calving?
No, Jakobshavn is done with tabular calving (unless you count breakup of seasonal melange that builds during the winter).

What I expect to see as Jakobshavn retreats farther out of its fjord back into the narrower winding south channel is reduced heat exchange between warm ocean water and ice at the grounding line because the attack surface is less accessible and the water will have been cooled. However the interface is taller to the extend the ice stream is retreating over a reverse grade (ie down from a sill into a trough).

There will still be plenty of convection (heat transfer by mass transport away) via churning induced by frontal calving and upwelling buoyant meltwater, but the resulting ocean water the glacier faces is then colder than open ocean water because circulation and mixing are reduced in the narrow channel and dominated by ice. (Picture the ice stream 10, 20, or 30 km further inland and the long cul de sac of ocean water.)

The icebergs we see streaming away must be balanced by return flow of deeper waters. However surface transport is fairly shallow (tens of meters) whereas the distance through water to bedrock approaches 1500 m. Thus if this were the only consideration, retreat would slow. The narrowness of the channel could offset this somewhat through turbulent interactions with the wlls.

Jason Box just posted an excellent popular piece on the other considerations which almost all favor faster retreatL
http://www.huffingtonpost.com/jason-e-box/ice-melt-fast_b_7927186.html (http://www.huffingtonpost.com/jason-e-box/ice-melt-fast_b_7927186.html)
https://www.google.com/maps/place/Bosphorus,+Turkey/@41.1194435,29.075278,2200m/data= (https://www.google.com/maps/place/Bosphorus,+Turkey/@41.1194435,29.075278,2200m/data=)!3m2!1e3!4b1!4m2!3m1!1s0x14cacaf6a1b454cf:0x7bab8b9dc19261dc

I'm thinking about this place.  Google has it at 16 miles approximately.  The freshwater entering the black sea mixes with the salt water from the Mediterranean this carries the salt water out to sea.  The denser water flows into the black sea at quite a fast speed.  The more fresh water you add the higher the circulation.

Two processes.  One retreat the other thinning.  Both would lead to large scale sea water circulation under the next 20 km of the glacier as the glacier looses contact with the sill. More ice area exposed to sea water gets more melt water, gets more circulation.

Adding heat under the next 20 km of glacier should get it to speed up!

Speeding up gets you thinning and or retreat.

Retreat opens up the sides to attack by sea water.  It also reduces buttressing of the side inflows.  That gets more ice flow.  More ice area exposed to sea water gets you more melt water and more circulation.  (I've driven commercial vehicles.  Go a bit to fast downhill and the brakes over heat.  Smoke, fire and bent metal.  Just a bit too fast is all it takes.)

There are plenty of positive feedback loops.

Are there any negative ones?  Is the system dampened? What keeps the overheated brakes from failing?


Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 10, 2015, 07:39:07 PM
The analogy to a truck is a good one. Where I live, the driver encounters a long 7% grade coming over the pass so the state built two emergency graveled ramps for runaway vehicles. After reaching a small town, the gradient drops to 0.5%, not enough to coast down to the valley, no escape ramps.

Greenland is almost always displayed at extreme vertical scale exaggeration. I used to think wow 10,000 feet from summit to sea level, no wonder Jakobshavn is like a truck barreling over the pass. Later I realized that it is so big and flat that if a truck were set down there, the driver would have no idea how to drive down to the sea.

For a while there, I was posting radar transects at true 1:1 scale but they took up so many horizontal feet of monitor space and got so few views that, like everyone else, I went back to vertical scale exaggeration.

The thing to remember with Jakobshavn is the main ice stream could care less about erosion at the calving front/ocean front that just amounts to bugs hitting the windshield. It is driven by gravitational forces, in proportion to the gradient, and braked by stiff rheology and friction with the sides and bedrock.

However this doesn't explain -- given so many other Greenland glaciers originating off the same summit ridge -- why Jakobshavn so much faster and its trough gouged so much deeper all the way to the interior, with offshore moraines showing it has been exceptional throughout the Pleistocene.

Is Jakobshavn potentially a runaway truck?

The short answer is no one knows because the very fact that it is so deep, fast, and crevassed means it has been impossible to get temperature profiles and basal hydraulics by drilling, see the bedrock very well with radar, measure meltwater inputs, or approach the bathymetry and grounding line with sonar. Nearby glaciers such as Rink, Store and Epiq are much better understood, even though there is some irony in their lesser contribution to sea level rise. See post #215 and #217 on the Hansen article forum.

Somewhere in the many Joughin papers and press commentary on Jakobshavn, I recall him giving good reasons why it is never going to get more than 3x its current velocity. I'll take another look at the assumptions underlying that in view of the Rignot 2015 results to see if those are still valid in the face of future surges in basal meltwater plumes coming out at the calving front.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Iceismylife on August 10, 2015, 10:11:45 PM
The ice flows have been doubling every 5 years for how long?  The main flow doesn't have to go much faster than it currently is to keep up the doubling rate as long as the calving face keep retreating.

The friction of ice in water is approximately zero at zero speed.  The melt water driven surface current is flowing past the calved ice out to sea.  The sea water path inland is very big.   Fast shallow water on top slow deep water going the other direction.  We could see the speed of the calved ice flow measured in km per hour not m per day.

The big question I have is how far inland the calving face will retreat.  It could be stable on the sill for 5 to 10 years before retreating farther inland.  Then make up for lost time very quickly.  As it retreats the grade goes up.  As it thins the grade goes up, and the base friction goes down as it floats off of bed rock.

Up stream a ways it branches into three branches.  The shallowest and narrowest is the fastest flowing.  Why?  My read is steepest grade from summit to main channel and it was the smallest and so experienced the fastest acceleration when the flow went up last at the end of the last ice age.  A lot of the main channel currently has or should have melt water on the bottom and so is floating the ice.

Thank you for going back and looking at the assumptions driving the 3X the current limit.

Lots of positive feed back loops, I don't see a runaway truck lane.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Iceismylife on August 10, 2015, 10:44:15 PM
Thinning slows flow.  Negative feed back. :-\

http://www.the-cryosphere.net/8/209/2014/tc-8-209-2014.pdf (http://www.the-cryosphere.net/8/209/2014/tc-8-209-2014.pdf)

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 10, 2015, 11:15:39 PM
A lot of papers over the years ... the future of Jakobshavn seems to be word salad. It would be better if people would simply lay out their predictions in a format that could be evaluated for prediction skill as time goes by, starting with peak retreat predictions for 2015, 2016, 2017. But that is studiously avoided by everyone in the field.

A Joughin interview online finds him more or less in synch with IPCC on the Hansen matter, with 10' rise this century viewed as exceedingly remote. Yet he has a 2014 paper on the irrevocable collapse potentially underway for Thwaites.

http://www.sciencemag.org/content/344/6185/735 (http://www.sciencemag.org/content/344/6185/735)
https://www.youtube.com/watch?v=X51BLD6LQEA (https://www.youtube.com/watch?v=X51BLD6LQEA)
http://news.nationalgeographic.com/2015/07/150721-james-hansen-sea-level-rise-climate-change-global-warming-science/ (http://news.nationalgeographic.com/2015/07/150721-james-hansen-sea-level-rise-climate-change-global-warming-science/)

Further summer speedup of Jakobshavn Isbræ
I. Joughin and B. E. Smith
http://www.the-cryosphere-discuss.net/7/5461/2013/ (http://www.the-cryosphere-discuss.net/7/5461/2013/)

The transient summer speeds we observe for 2012 (>17000myr−1) appear to represent the fastest observed speed for any outlet glacier or ice stream in Greenland or Antarctica. This yields a speed up by more than a factor of four relative to the 1990s, while the mean annual speedup is by just under a factor of 3. If, as the glacier recedes up the trough, it is able to maintain the peak speeds year round, then a sustained speedup by a factor of 4 of 5 is conceivable based on recent behavior, which is about half of the ad hoc tenfold upper limit on speed proposed by Pfeffer et al. (2008). Nevertheless, these speeds would occur in a trough roughly twice as deep as prior to the speedup.

Hence, a tenfold increase in ice flux may be possible for Jakobshavn Isbræ if the trough does not narrow substantially with distance upstream. Equivalently, while the increase in terminus speed and the glaciers overall maximum speed may remain under a factor of five, as the terminus retreats farther inland where the speeds now are comparatively slow, the relative speedup is much greater (e.g., if the terminus retreated to M26 with a speed of 16000myr−1, this would represent a twelve-fold speedup). Thinning by hundreds of meters to a terminus near flotation, however, yields something closer to a ten-fold flux increase. It is unlikely that such retreat could be sustained for more than a few decades because the terminus would rapidly retreat ∼ 50 km to shallower depths (Joughin et al., 2012).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 11, 2015, 02:18:37 AM
Here is the Radarsat-2 image for today, a curious X at the calving front and seemingly a melting fringe. It is a proprietary Canadian satellite with vaguely similar capabilities to Sentinel 1A. I don't believe there is public access to higher resolution than what is provided below by DMI.

Radarsat swings by Jakobshavn at irregular intervals from a few days to a week. I tried animating the last half-dozen images to make some sense out of today but the geometry varies greatly with no real way of warping them onto fixed rock anchors. There is no Sentinel or Landsat for today ... so what you see is what we get.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: crandles on August 11, 2015, 02:59:59 AM
Looks like a really hard to read draft mark made to be really difficult for a bot to read.

I imagine I can make out

C386Dd3H3CCH
D7723176521515PEC52M
___________________X

The x being on the calving front with the M immediately above. Besides all that on the glacier, there are other areas that seem to have hints of lettering/numbers as well. Quite bizarre.

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 11, 2015, 05:07:14 AM
Quite bizarre.
Attached is a cut-out of the original DMI posting (inset) and a 2x bilinear enlargement. I cannot see the letters myself but your interpretation of an extensive watermark ruining the image makes sense.

Launched in December 2007, Canada's next-generation commercial radar satellite offers powerful technical advancements that will enhance marine surveillance, ice monitoring, disaster management, environmental monitoring, resource management and mapping in Canada and around the world.

This project represents a unique collaboration between government and industry. MacDonald, Dettwiler and Associates Ltd. (MDA) will own and operate the satellite and ground segment. The Canadian Space Agency (CSA) helps fund the construction and launch of the satellite and will recover this investment through the supply of RADARSAT-2 data to the Government of Canada during the lifetime of the mission.

My grasp of higher economic theory is rather minimal but how can the govt of Canada 'recover its investment' by buying and selling to itself? Meanwhile it seems that MDA has totally privatized a public satellite. I've heard that Radarsat just orbits idly (not taking images) until someone pays for a scene order. The Canadian govt may have a standing order -- indeed the only order -- and share these with DMI  for iceberg monitoring and marine safety[?] Again, I will have to defer to someone with more insight into private enterprise to explain how this can make sense to the Canadian taxpayer.

MacDonald, Dettwiler and Associates Ltd. (TSX: MDA) is a Richmond, British Columbia global communications and information company. MDA has locations throughout Canada, and the United States operating under the MDA brand name.MDA provides operational solutions to commercial and government organizations worldwide, including:

    Airborne Surveillance Solutions
    Satellite Ground station
    Maritime Information Systems
    Aviation Information Systems
    Geospatial information services, including Satellite Data Distribution, Value-Added Information Services
    Robotic surgery research via its NeuroArm development program
    Space robotics, satellite information and payload systems
    Radar and optical satellite imagery, and, remote sensing
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Rubikscube on August 11, 2015, 12:32:03 PM
What I still don't get about Jakobshavn is why there is so little interest in the areas east of the currently active main channel. Morlighem shows there are multiple channels hundreds of meters deep stretching for hundreds of kilometers inland, even though those areas appear inactive today there must surely be possible to extract some useful information about the past and future behavior of Jakobshavn by taking a closer look at them. I mean, how can scientist make an even remotely accurate estimate of JHs future contributions to SLR if something like 90% (probably more) of its drainage is ignored? Have they virtually just given up on JH because the main channel more or less inaccessible?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 11, 2015, 01:55:46 PM
S-1 IW on 7.8.2015 in Landsat projection (UTM zone 22 + 15m pixel size)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: ablair on August 11, 2015, 03:30:45 PM
Nice shot, if you zoom into "cap ice" there seems to be a promontory /embayment forming on it's southern shore just past the corner
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 11, 2015, 04:04:20 PM
Nice work, nukefx. I received some additional help from Copernicus this morning and dug into Landsat geocoding a bit,  both described on your new Sentinel forum. The pipe dream here is gesticulating at Landsat and Sentinel urls of the same date and having a script co-register them at 15 m pixels, 16-bit files cropped to specified lat,lon corners for viewing as an ImageJ stack. Interesting concept: pan-sharpening of Sentinel.

http://forum.arctic-sea-ice.net/index.php/topic,1355.msg60306.html#msg60306 (http://forum.arctic-sea-ice.net/index.php/topic,1355.msg60306.html#msg60306)

"To complete our previous message, the user should look at the link below. This even describes how to superimposes a Landsat and S1A image. The blog also describes the ESA tool SNAP (http://step.esa.int/main/toolboxes/snap/ (http://step.esa.int/main/toolboxes/snap/))."

https://scientiaplusconscientia.wordpress.com/2015/08/06/working-with-sentinel-1-data-pre-processing-georeferencing-and-exporting-with-snap/ (https://scientiaplusconscientia.wordpress.com/2015/08/06/working-with-sentinel-1-data-pre-processing-georeferencing-and-exporting-with-snap/)

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 11, 2015, 04:16:48 PM
Nice shot, if you zoom into "cap ice" there seems to be a promontory /embayment forming on it's southern shore just past the corner
I'm thinking you mean the area indicated with the white arrows below. That would be quite interesting to track over the season and indeed the three Landsat-8 years we have now. It may be a new development enabled by buttressing withdrawal of the main ice stream.

http://forum.arctic-sea-ice.net/index.php/topic,154.msg56631.html#msg56631 (http://forum.arctic-sea-ice.net/index.php/topic,154.msg56631.html#msg56631)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: ablair on August 11, 2015, 04:37:23 PM
Very interesting there too but I meant right near the point, further West
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 11, 2015, 04:44:32 PM
What I still don't get about Jakobshavn is why there is so little interest in the areas east of the currently active main channel... how future contributions to SLR if something like 90% (probably more) of its drainage is ignored? Have they given up because the main channel more or less inaccessible?
From watching AGU meeting abstracts and posters from Ph.D dissertations that never seem to emerge as journal articles, I'd guess quite a few approaches haven't panned out.

It is mildly disturbing to see JI research lurch from one trending topic to another. For a while it was all about melange buttressing, then ablation and dynamic thinning, frictional softening on the sides, meltwater moulins and basal lubrication, sills and troughs, and today emergent meltwater plumes entraining warm Atlantic Water that erodes ice at the grounding line.

These mostly fall into 'it's the plug at the bottom' rather than 'it's less resistance to upper driving stress'.

One interesting observational program on upper Jakobshavn has been the PARCA stakes (acronym works in forum search) at about 2000 m. People are also watching the march of melt ponds upslope.

One bit of research that forum folks could do is compare ice volume above and below 2000 m (using the ice thickness DEM). I would guess that melting all of Greenland below 2000 m (leaving, impossibly, a vertical cliff) would not have that much effect on SLR. Nothing much happens without mobilization of higher elevation ice.

The upper velocity field is also regularly measured with SAR for acceleration. However subtracting small numbers in slow-moving regions gives higher uncertainty. Work-in-progress using 16-bit Landsat and Sentinel may improve this situation markedly.

It might be feasible to drill just down from the triple tributary junction. Drill holes never end up truly vertical even on the flats so some motion can be accommodated. The key would be new rapid drilling techniques. They don't need to recover a core necessarily, just get temperature, tilt, basal hydraulics and so forth along the lines of what Luethi has been doing at Swiss Camp.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Tor Bejnar on August 11, 2015, 05:39:13 PM
Melting all ice below 2000 m (and nothing about it) will create (impossible) floating ice mountains, touching the ground only where the bedrock extends above 2000 m (on the east coast). ;D (Sorry about that.)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Iceismylife on August 11, 2015, 06:15:54 PM

Further summer speedup of Jakobshavn Isbræ
I. Joughin and B. E. Smith
http://www.the-cryosphere-discuss.net/7/5461/2013/ (http://www.the-cryosphere-discuss.net/7/5461/2013/)

The transient summer speeds we observe for 2012 (>17000myr−1) appear to represent the fastest observed speed for any outlet glacier or ice stream in Greenland or Antarctica. This yields a speed up by more than a factor of four relative to the 1990s, while the mean annual speedup is by just under a factor of 3. If, as the glacier recedes up the trough, it is able to maintain the peak speeds year round, then a sustained speedup by a factor of 4 of 5 is conceivable based on recent behavior, which is about half of the ad hoc tenfold upper limit on speed proposed by Pfeffer et al. (2008). Nevertheless, these speeds would occur in a trough roughly twice as deep as prior to the speedup.

Hence, a tenfold increase in ice flux may be possible for Jakobshavn Isbræ if the trough does not narrow substantially with distance upstream. Equivalently, while the increase in terminus speed and the glaciers overall maximum speed may remain under a factor of five, as the terminus retreats farther inland where the speeds now are comparatively slow, the relative speedup is much greater (e.g., if the terminus retreated to M26 with a speed of 16000myr−1, this would represent a twelve-fold speedup). Thinning by hundreds of meters to a terminus near flotation, however, yields something closer to a ten-fold flux increase. It is unlikely that such retreat could be sustained for more than a few decades because the terminus would rapidly retreat ∼ 50 km to shallower depths (Joughin et al., 2012).

 "the terminus would rapidly retreat ∼ 50 km to shallower depths"

60 km upstream there is a three way split in the main channel.  Jakobshovn is flowing the shallowest narrowest channel.  Get the other two flowing and then we would have fun.

If it keeps its current retreat average of 1 mile a year up.  Making up lost time for getting off of the sill.  It could be there in 40 years.

It is definitely politically incorrect to predict large sea level rises soon.  But is that what is going to happen?  Joughin said that just looking at doubling times is less than entirely accurate... But what else is there for Jakobshavn?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 12, 2015, 01:20:38 AM
60 km upstream there is a three way split in the main channel.  Jakobshovn is flowing the shallowest narrowest channel.
It's one thing to locate this area on the bed topography, ice thickness, surface elevation maps ... another to co-locate it accurately on surface velocity, Landsat and Sentinel maps. I've posted extensively on the confluence area before ...
http://sites.uci.edu/morlighem/dataproducts/mass-conservation-dataset/ (http://sites.uci.edu/morlighem/dataproducts/mass-conservation-dataset/)

Melting all ice below 2000 m (and nothing about it) will create (impossible) floating ice mountains
Not talking about that. Find the 2000 m contour. Dig a trench straight down to bedrock with your backhoe. Now measure the ice volume downhill. Then measure the ice volume uphill. Divide. Get small number (?)

Or, for a more refined graph of cumulative ice volume vs elevation, select each key color below, count the pixels lit up in the map, get a point for your plot. (Elevation contour: sum thickness of ice for each pixel at that contour = volume of ice at that contour.) Label the other axis for mm of sea level rise if everything at that contour and below melted.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Rubikscube on August 13, 2015, 12:12:01 AM
What could have been a walk in the park becomes a whole lot messier when every thickness map within reach features a myriad of different color contours rather than a nice and tidy little color palette. Or is it just me looking at the wrong places? Well fortunately, when taking a closer look there turned out to be more system in this color anarchy then what seemed at first ("anarchies" often work that way), so it was eventually possible to narrow things down to a handful of specific contours, each representing a thickness.

However, there are problems with this approach, most notably; the pure colors (red, yellow, cyan and blue in this instance) merged with and were eaten by their less pure neighbours so to speak. This effect becomes particularly visible at low elevations where the slope is steeper and the different colors are crammed tighter together. Then, for some reason (I'm tempted to say god knows why, but I'm not sure he does this time) there turns out to be 36 different contours, for one 32 would have fitted perfectly into their color system, as opposed to the current solution which tries to divide 256 on 9, but more importantly it would allow each contour to represent a leap of exactly 100 meters, as opposed to 88,1m which I got from pixel counting their color scale (which by the way measures 241, a prime). Is this because 88 meter fits some margin of error or something like that, or do they just want to mess up the diagrams of excel noobies like me?

Either way I have managed to produce a couple of diagrams that resembles those who were requested, although it is not volume vs elevation, which I agree would be better, but rather volume vs thickness. I'll do the elevation as well, but if someone happens to jump across such a map that doesn't feature every possible RGB combination, that would be helpful and it would enable me to do a bit more than just setting a crude line at approximately 2000m (the same goes for the thickness map of course). Note that I have been treating the individual coutures as ranges which means the volume calculations are based on the medium of these ranges, please let me know if I've gotten that wrong. In this calculation the 2000 meter boundary splits the volume 35/65, give or take a percentage or two.

Click to enlarge.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 13, 2015, 12:54:40 AM
Mighty fine effort, Rcube.

Yes indeed, one of the great unsolved mysteries in glaciology is why so few of them have a clue how to post maps keyed in accord with elementary principles of GIS. Howat seems to be the only one familiar with more useful grayscale.

Here the link I provided above goes to a page linking to an NSIDC datasheet, from there you can bypass optional registration and get to the thickness, bedrock, and elevation data ftp page and download Morlighem's 2.1 GB .nc file (NetCDF) last updated 5/19/15 for which we have found open source viewers. (Although life would be so much easier if they just posted the data in a csv text file for Excel etc. like they do for ice cores.)

ftp://sidads.colorado.edu/DATASETS/IDBMG4_BedMachineGr/MCdataset-2015-04-27.nc (http://ftp://sidads.colorado.edu/DATASETS/IDBMG4_BedMachineGr/MCdataset-2015-04-27.nc)

Much of interior Greenland is below sea level but not by much on average. This means that ice thickness is approximately the same as elevation. I located the 2000 m contour on your graphic as well as Csatho's 2000 m boundary for the PARCA stake flow survey. About 38% of the ice volume lies seaward of an imaginary curtain hanging down from the 2000 m contour.

If this melted, it would produce about 2.8 m of sea level rise, rather respectable. Right now the GrIS is contributing about 0.007 m/yr.

Of course this is not at all how the ice sheet actually melts and flows. Although that massive late-season rain event of 2011 did manage to lift up the whole lower west central ice sheet for a while. There is nothing worse than a rain event at a time when the basal drainage conduits have re-frozen for the year -- and these events are expected to become more common.

Amplified melt and flow of the Greenland ice sheet driven by late-summer cyclonic rainfall
SH Doyle et al
http://www.sciencedaily.com/releases/2015/07/150713113447.htm (http://www.sciencedaily.com/releases/2015/07/150713113447.htm)

Intense rainfall events significantly affect Alpine and Alaskan glaciers through enhanced melting, ice-flow acceleration and subglacial sediment erosion, yet their impact on the Greenland ice sheet has not been assessed. Here we present measurements of ice velocity, subglacial water pressure and meteorological variables from the western margin of the Greenland ice sheet during a week of warm, wet cyclonic weather in late August and early September 2011.

We find that extreme surface runoff from melt and rainfall led to a widespread acceleration in ice flow that extended 140 km into the ice-sheet interior. We suggest that the late-season timing was critical in promoting rapid runoff across an extensive bare ice surface that overwhelmed a subglacial hydrological system in transition to a less-efficient winter mode. Reanalysis data reveal that similar cyclonic weather conditions prevailed across southern and western Greenland during this time, and we observe a corresponding ice-flow response at all land- and marine-terminating glaciers in these regions for which data are available.

Given that the advection of warm, moist air masses and rainfall over Greenland is expected to become more frequent in the coming decades, our findings portend a previously unforeseen vulnerability of the Greenland ice sheet to climate change.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 13, 2015, 03:08:16 PM
Here is the low resolution Sentinel from DMI ... looks interesting, be good to pursue this with Nukefx's protocol for getting it geo-oriented. A Landsat is due tomorrow and then again two days later (16th).

Offhand, I would say the calving front retreat remains stalled. Jakobshavn may have reached 'confinement' status, ie a near steady-state range balancing glacial advance and ocean augmentation of calving, just like its neighbors Store and Rink which have not retreated since the 1940's.

http://forum.arctic-sea-ice.net/index.php/topic,1327.msg60183.html#msg60183 (http://forum.arctic-sea-ice.net/index.php/topic,1327.msg60183.html#msg60183)
http://forum.arctic-sea-ice.net/index.php/topic,1327.msg60197.html#msg60197 (http://forum.arctic-sea-ice.net/index.php/topic,1327.msg60197.html#msg60197)

The fourth image shows that the calving line today is not up to what it was on Day 212, though it has some interesting pre-calving features.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Iceismylife on August 13, 2015, 05:39:25 PM


However, there are problems with this approach, most notably; the pure colors (red, yellow, cyan and blue in this instance) merged with and were eaten by their less pure neighbours so to speak. This effect becomes particularly visible at low elevations where the slope is steeper and the different colors are crammed tighter together. Then, for some reason (I'm tempted to say god knows why, but I'm not sure he does this time) there turns out to be 36 different contours, for one 32 would have fitted perfectly into their color system, as opposed to the current solution which tries to divide 256 on 9, but more importantly it would allow each contour to represent a leap of exactly 100 meters, as opposed to 88,1m which I got from pixel counting their color scale (which by the way measures 241, a prime). Is this because 88 meter fits some margin of error or something like that, or do they just want to mess up the diagrams of excel noobies like me?




Click to enlarge.

Try exactly 100 yards instead of meters.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 13, 2015, 07:38:02 PM
Just adding to what mentioned above:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Iceismylife on August 14, 2015, 07:03:06 PM
Thank you A team for the lovely reference on ice thickness etc.

Looking at ice thickness up Jakoshavn and assuming an average retreat of 1.5 km or 1 mile a year for the next 50 years, it looks like Jakobshavn could raise sea level world wide by 150 to 300 mm.  (6 inches to 1 foot)  That would be by 2065.

What does the IPCC say the sea level rise for the world should be by then?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: oren on August 14, 2015, 08:26:15 PM
Thank you A team for the lovely reference on ice thickness etc.

Looking at ice thickness up Jakoshavn and assuming an average retreat of 1.5 km or 1 mile a year for the next 50 years, it looks like Jakobshavn could raise sea level world wide by 150 to 300 mm.  (6 inches to 1 foot)  That would be by 2065.

What does the IPCC say the sea level rise for the world should be by then?

I believe the main contribution of JH to sea level was through its speed (and acceleration), not through its retreat. 15 km/year and more beats 1.5 km/year.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 14, 2015, 09:14:28 PM
Yes thinning is the real issue to most glaciers in Greenland, not retreat that much!
But that said, retreat is a better explaining tool ;)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 14, 2015, 10:07:18 PM
Here is a gaining report:

It is amazing how much the north eastern part of the southern branch can grow in such a short period?

But there is show retreat seen at the northern branch (western part).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 14, 2015, 11:30:23 PM
Yes, it seems like a lot of things changing this year. For example that brownish basal till in the August image -- we've seen that streaking in the north branch last year but I am not recalling for the channel. Seems like it should be associated with the giant berg but that connection is not evident to me.

There is quite a bit of calving ahead. Again I am not recalling this level of frontal disintegration so far upglacier. The scale here is 7.5 m per pixel, meaning that everything 4 pixels in from the calving front will be gone tomorrow. The yellow boxes are 28x28 pixels or a week worth of glacial advance @ 30 m/day.

The second image shows the extent of ablation. The loss of snow cover over a wide region is exposing the crevasse field for a long ways in the ice stream drainage basin. It seems like nunataks are showing along the channel walls like never before for this date. Have to click to see at 15 m resolution.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on August 15, 2015, 03:03:38 PM
Here is a gaining report:

It is amazing how much the north eastern part of the southern branch can grow in such a short period?

But there is show retreat seen at the northern branch (western part).

Every time you provide a close up animation, I look at what is going on at the northeastern wall of the southern branch. Retreat of the main calving face has unlocked a lot of ice. I think this will be repeated as the calving face continues to retreat. Meanwhile, this newly freed ice which is grounded below sea level is going to continue to dump a lot of ice.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Iceismylife on August 15, 2015, 07:31:14 PM
Thank you A team for the lovely reference on ice thickness etc.

Looking at ice thickness up Jakoshavn and assuming an average retreat of 1.5 km or 1 mile a year for the next 50 years, it looks like Jakobshavn could raise sea level world wide by 150 to 300 mm.  (6 inches to 1 foot)  That would be by 2065.

What does the IPCC say the sea level rise for the world should be by then?
I believe the main contribution of JH to sea level was through its speed (and acceleration), not through its retreat. 15 km/year and more beats 1.5 km/year.
Yep, and advance the calving face 75 km inland and it should thin the drainage by 50%  That gets you 150 mm sea level rise.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 15, 2015, 10:35:17 PM
Although I dont trust Modis Images alot, but we had a new moon and we can see the same behavior elsewhere in Greenland, but it seems Jakobshavn did something very serious:

If so, I bet this one is one of the top 3 within the last 5 years.

And well beyond the previous September 27 2014 max retreat point (southern branch)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 15, 2015, 11:01:20 PM
Here is another version comparing September 27 2014 (previous max retreat) and August 15 2015:

Other calvings seen at least at Hagen Bræ and Upernavik Isstrøm probably a few more.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 15, 2015, 11:21:41 PM
seems Jakobshavn did something very serious, bet this one is one of the top 3 within the last 5 years.
Excellent spotting.

No Sentinel so far for the 14th, DMI is already on the 15th for N Greenland; Landsat due late tonight or tomorrow. The whole area looks unusual as the negative. I added an animated negative with slightly different processing.

To make a quick daily animation comparison, open DMI to the first image, copy image to clipboard, paste as new file in ImageJ. Ditto 2nd. Then make a stack. Crop and enlarge to 700 pxl width as new file (keeping small crop stack in case enhancement has to be discarded). Enhance contrast adaptively and in small stages with CLAHE. Save as animated gif, loop setting 0, 600 ms between frame. The key here is that DMI already has them fairly well aligned if it is the same satellite.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Iceismylife on August 16, 2015, 01:40:17 AM
Is that 1 mile of retreat in one day?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: TenneyNaumer on August 16, 2015, 01:49:39 AM
Hey Espen, aren't the dates backwards on the blue gif (July 29 and Aug 14)?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Laura Derrick on August 16, 2015, 01:54:02 AM
There is some major sliding going on all over. Do you think that's partly tide-related?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: TenneyNaumer on August 16, 2015, 03:54:35 AM
I'm just pulling this out of a hat, but I would say that tides have some effect, but they probably aren't enough to cause such large changes.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Laura Derrick on August 16, 2015, 04:24:04 AM
I'm just pulling this out of a hat, but I would say that tides have some effect, but they probably aren't enough to cause such large changes.

That makes sense. I've noticed that there's more fracturing off of fast ice during high tides, but I hadn't considered before that they might also affect glaciers until seeing a lot of activity this time. It would be interesting to look back and see if there's any correlation.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: solartim27 on August 16, 2015, 07:14:26 AM
I had noticed a weird surge into the bay on the 8/13 Modis, and noticed the front had advanced a good bit, I was wondering if the surge was related to the advance, or some other event I have not noticed.  It seems the surges take 2 - 3 days to exit into the bay, this one will be interesting to watch for.  Here is a gif of the area for 8/5, 8/13, and 8/15.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: TerryM on August 16, 2015, 08:23:32 AM
Very nice catch Espen!


Laura
I've noticed a correlation in the past, but can't come up with an example off the top of my head.


Terry
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Andreas T on August 16, 2015, 08:39:42 AM
have a look at the sequence of 17. 18. 19 July 2015 isn't that a lunar month earlier?
What surprises me, not having looked much at that area before, is how little the shape of the denser region of ice at the mouth of the fjord moves. Are there many stranded icebergs?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 16, 2015, 04:10:35 PM
have a look at the sequence of 17. 18. 19 July 2015 isn't that a lunar month earlier?
What surprises me, not having looked much at that area before, is how little the shape of the denser region of ice at the mouth of the fjord moves. Are there many stranded icebergs?
Yes, there's a shallower zone at the mouth of the fjord where the large icebergs get stuck for awhile.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 16, 2015, 04:27:47 PM
S-1 13.8 EW HH/HV 25m pixel size UTM Zone 22:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 16, 2015, 06:02:51 PM
Yes, there is a much studied terminal moraine from a previous glacial high stand at the mouth of the fjord by Illulisat where icebergs get stuck or scrape keel marks into the bathymetry. We are due for a stereo pair of Landsats today ... will it be cloudy or clear, the suspense builds.

Entity ID: LC80080112015228LGN00
Acquisition Date: 16-Aug-15

Entity ID: LC80080122015228LGN00
Acquisition Date: 16-Aug-15
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 16, 2015, 06:45:25 PM
Not looking great for a cloud-free shot..

http://hotelarctic.com/om_hotel_arctic/webcam/ (http://hotelarctic.com/om_hotel_arctic/webcam/)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 16, 2015, 06:54:55 PM
Yes, there is a much studied terminal moraine from a previous glacial high stand at the mouth of the fjord by Illulisat where icebergs get stuck or scrape keel marks into the bathymetry. We are due for a stereo pair of Landsats today ... will it be cloudy or clear, the suspense builds.

Entity ID: LC80080112015228LGN00
Acquisition Date: 16-Aug-15

Entity ID: LC80080122015228LGN00
Acquisition Date: 16-Aug-15

Relatively clear:

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 16, 2015, 08:47:46 PM
Awright ... a few clouds but not so thick they can't be peeled off. The 2nd image shows band 8 at 7.5 m resolution. While clearly new territory, it is will take a bit (ie lunch time here) to compare to other dates and calculate the area and volume of ice calved. The third image is just the 15 m with a bit of context for folks co-registering different dates using the two fiducial rocks (ground control points).

This is path 8, row 11 if you are looking for near-identical geometry. The 8,12 has just been posted; the overlap miraculously includes the calving front.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Iceismylife on August 16, 2015, 09:32:22 PM
I had noticed a weird surge into the bay on the 8/13 Modis, and noticed the front had advanced a good bit, I was wondering if the surge was related to the advance, or some other event I have not noticed.  It seems the surges take 2 - 3 days to exit into the bay, this one will be interesting to watch for.  Here is a gif of the area for 8/5, 8/13, and 8/15.
Is there a convenient way to check the salinity of the water in those surges?  Are they fresher water from under the glacier?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 16, 2015, 09:36:49 PM
As promised here:
https://forum.arctic-sea-ice.net/index.php/topic,154.msg60840.html#msg60840

we have several records involved:

1. I am pretty sure it is the largest calving seen in many years, if not the largest.

2. And a new record retreat.

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 16, 2015, 09:47:40 PM
And here is the confirmation of the new record retreat:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Laura Derrick on August 16, 2015, 10:04:39 PM
It's amazing also how much more exposed rock there is.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Neven on August 16, 2015, 10:06:53 PM
Thanks for the animations, Espen! I've put up a short blog post on the ASIB: Jakobshavn record retreat (http://neven1.typepad.com/blog/2015/08/jakobshavn-record-retreat.html).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 16, 2015, 10:14:05 PM
Here is the comparison to 14 Aug 15. Some 28036 pink pixels calved off, an area of 28036 * 0.015 * 0.015 = 6.3 km
2
at 15 m resolution pixels. The first and third images show this over the latter and earlier image, respectively. There was a clue to some of this as noted in a post 2-3 days back but no clue as to the full extent observed.

If the ice is 1400 m thick, that works out 8.8 km3, a lot of ice! [These numbers had to be amended from the initially posted values, as Neven and Espen observe below.] 

Note it is imperative to use ground control points in comparing two images with different path,rows. The animation shows the rotation needed in the 14 Aug 15 image, LC80100112015226LGN00_B8 to get it registered with LC80080112015228LGN00_B8
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 16, 2015, 10:27:46 PM
A-Team I think 12,5 km2 is more likely?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Neven on August 16, 2015, 10:28:35 PM
Whoa, 124.6 km2! Is that for real? The last one in February was estimated at 7 km2 by Werther, and a couple of years ago NASA reported (http://www.nasa.gov/topics/earth/features/jakobshavn2010.html#) another 7 km2 calving (North branch).

Edit: thanks, Espen.

Does anyone have any other numbers of calvings in km2 to compare with?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 16, 2015, 10:37:31 PM
The southern calving front is about 5 km wide and the cut is is about ½ the width so 5 x 2,5 = ~ 12,5 km2

And I am sure this is the largest single calving event seen since Jakobshavn went dual (southern/northern branch)?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 17, 2015, 12:47:05 AM
Oops, I used the wrong dimensions, throwing everything off. The revised area should  be 28036 pink pixels * 0.015 * 0.015 sq km per pixel for 15 m resolution band 8 Landsat or 6.3 km2 for the area calved and 28036*0.015*0.015*1.4 = 8.8 km3 for the volume calved, assuming 1400 m average depth of ice. I will fix the original post to avoid later confusion.

I see few prospects for making this any more accurate: it is hard to tell what has calved but hasn't fallen away, is about to calve, and where the white is a vertical face or just a gnarly crevassed area at the front. Similarly for volume, it would be difficult to subtract off air in deep near-calving front crevasses.

None of this ice was floating so it all goes to sea level rise: 8.83 * 2.78 = 24.5 microns (0.0000245 meters, or 0.0245 millimeters, acording to this site:
https://climatesanity.wordpress.com/conversion-factors-for-ice-and-water-mass-and-volume/ (https://climatesanity.wordpress.com/conversion-factors-for-ice-and-water-mass-and-volume/)

How much does one Gigatonne of melted ice (1 km³ of water) raise the oceans?

The oceans occupy 361 million square kilometers ( 361 x 106  km²) of the Earth’s surface.

If one cubic kilometer of water (i.e., one gigatonne of water) is spread evenly over the entire 361 million square kilometers, the thickness of the new layer of water will be given by:

1 km³ / 361 x 106 km²  = 2.78 x 10-6 meters  = 2.78 microns.

That is, one cubic kilometer of water will add less than 3 millionths of a meter to the oceans!

Also, for the 2014 comparison, that date was September 28th. Landsat did not pass over Jakobshavn on the 27th. See earlier screenshot of 2014 dates at http://forum.arctic-sea-ice.net/index.php/topic,154.msg58765.html#msg58765 (http://forum.arctic-sea-ice.net/index.php/topic,154.msg58765.html#msg58765)

The path, row 10,11 back then don't match today's image so a rotation and translation will be needed to finalize the 'record' as needed (which might be gone as soon as tomorrow). These are in effect the first terms of the power series needed to warp one geometry onto another, ie it is the tangent spaces that are being co-registered.

28-SEP-14 LC80 10 011 2014 271 LGN00
 Sun Azimuth    178.10310829
 Sun Elevation    18.35757655
 Center Latitude 69.60641
 Center Longitude -50.87276

16-AUG-15 LC80 08 011 2015 228 LGN00
 Sun Elevation    33.9972875
 Sun Azimuth    173.78957895
 Center Latitude 69.60633
 Center Longitude -47.75851
 Date and time = 2015-08-16 T18:45:44Z
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Rubikscube on August 17, 2015, 01:04:43 AM
It's amazing also how much more exposed rock there is.

The 2014 minimum occured in late September, so notice that the high ground was covered with fresh snow back then. When comparing to summer landsats from June, July 2014 futher up in the thread you have to look really close to find any significant difference at all. During a decade or so it will accumulate into a sizable amount, but from year to year retreat is still painfully slow.

I am under the impression that mega calvings like these usually occurs in June and July, so is it just a coincidence that this one is rather late? The "ramp and sill" image (Joughin et al 2014) posted by A-team previously this summer, indicates to me that we might have jumped over the bump in this latest calving.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 17, 2015, 01:22:46 AM
we might have jumped over the sill in this latest calving.
I like that concept. The idea is the glacier is coming over the sill very fast, over 50 meters/per day according to two accounts. It cannot bend rapidly enough to conform to the downward ramp bedrock and so is slightly cantilevered on the sill fulcrum out into 'space'. According to this notion, the event we have just witnessed amounts to the ice breaking off at the sill peak, no longer being strong enough to hang out like this anymore. (Someone, possibly sidd, suggested something similar at an Antarctic forum long ago.)

What happens next? One option is that the glacier comes forward again to where it was on the 14th, with this large calving pattern then repeated. There are six weeks of action left to the 2014 maximal retreat.

Another option is that Jakobshavn has entered a new regime of rapid repeat. Antarctic glaciers supposedly collapse irreversibly once on a retrograde bed (in part because warm sea water acts on a larger surface area).

We need to be cautious about calving statistics because of strong observational bias -- we simply miss a lot that goes on. As a practical matter, Sentinel hasn't been around very long, DMI Radarsat has limited resolution, Modis has contrast and resolution issues and our favorite, Landsat doesn't come by that often and when it does can encounter weeks of impenetrable clouds.

Since there does not exist a predictive theory of Jakobshavn capable of posting infill for observational gaps, we are discussing quite irregularly averaged-out behavior. The very fact that JI is the world's fastest/deepest ice stream has as a corollary that its essential parameters are the most difficult to observe experimentally.

For a very small investment, it seems feasible to post a monitoring team on site for the entire season.That could consist of heavily instrumented drone cameras as well as 24/7 videography from the last rocks (though that view is increasingly inadequate). It seems like we are missing a lot of easy opportunities to better understand this important glacier -- not to mention not bearing witness to some of the most incredible moments in nature.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 17, 2015, 02:08:18 AM
The image below rotates the 28 Sep 14 by the necessary 5.74º CCW that compensates for the path,row mismatch with the 16 Aug 15. The yellowish-green is the 2014 calving front, the greenish to the east the 2015. The two agree along a line passing by the last exposed rock in the SW (there is never calving below this line; it presumably is a wall of the south branch fjord).
 
The pink line represents 1 km (133.3 pixels =1000 m per km /7.5 pixels per m). The edge of the 2015 is 680 meters beyond that of 2014 as measured along this line.

Because of clouds, we don't know for sure that the 2014 really represents the previous record. However it is the furthest retreat we know of. Note how 2015 is a new record by a substantial margin across the entire calving front.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: AbruptSLR on August 17, 2015, 12:32:48 PM
Here are references for Part I and II of a paper on the oceanic boundary conditions for Jakobshavn Glacier; followed by links to open access pdfs of the references:

Carl V. Gladish, David M. Holland, Aqqalu Rosing-Asvid, Jane W. Behrens, and Jesper Boje, 2015: Oceanic Boundary Conditions for Jakobshavn Glacier. Part I: Variability and Renewal of Ilulissat Icefjord Waters, 2001–14. J. Phys. Oceanogr., 45, 3–32, DOI: 10.1175/JPO-D-14-0044.1
http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-14-0044.1 (http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-14-0044.1)

Abstract: "Jakobshavn Glacier, west Greenland, has responded to temperature changes in Ilulissat Icefjord, into which it terminates. This study collected hydrographic observations inside Ilulissat Icefjord and from adjacent Disko Bay between 2001 and 2014. The warmest deep Disko Bay waters were blocked by the entrance sill and did not reach Jakobshavn Glacier. In the fjord basin, the summer mean temperature was 2.8°C from 2009 to 2013, excluding 2010, when it was 1°C cooler. Despite this variability, summer potential densities in the basin were in the narrow range of 27.20 ≤ σθ ≤ 27.31 kg m−3, and basin water properties matched those of Disko Bay in this layer each summer. This relation has likely held since at least 1980. Basin waters from 2009 and 2011–13 were therefore similar to those in 1998/99, when Jakobshavn Glacier began to retreat, while basin waters in 2010 were as cool as in the 1980s. The 2010 basin temperature anomaly was advected into Disko Bay, not produced by local atmospheric variability.
This anomaly also shows that Ilulissat Icefjord basin waters were renewed annually or faster. Time series fragments inside the fjord did not capture the 2010 anomaly but show that the basin temperatures varied little subannually, outside of summer. Fjord velocity profiles from summer 2013 implied a basin renewal time scale of about 1 month. In model simulations of the fjord circulation, subglacial discharge from Jakobshavn Glacier could drive renewal of the fjord basin over a single summer, while baroclinic forcing from outside the fjord could not, because of the sill at the mouth."


Carl V. Gladish, David M. Holland, and Craig M. Lee, 2015: Oceanic Boundary Conditions for Jakobshavn Glacier. Part II: Provenance and Sources of Variability of Disko Bay and Ilulissat Icefjord Waters, 1990–2011. J. Phys. Oceanogr., 45, 33–63, DOI: 10.1175/JPO-D-14-0045.1

http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-14-0045.1 (http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-14-0045.1)

Abstract: "Jakobshavn Glacier, west Greenland, has responded to temperature changes in Ilulissat Icefjord, into which it terminates. Basin waters in this fjord exchange with neighboring Disko Bay waters of a particular density at least once per year. This study determined the provenance of this isopycnic layer for 1990–2011 using hydrographic data from Cape Farewell to Baffin Bay. The warm Atlantic-origin core of the West Greenland Current never filled deep Disko Bay or entered the fjord basin because of bathymetric impediments on the west Greenland shelf. Instead, equal parts of Atlantic water and less-saline polar water filled the fjord basin and bathed Jakobshavn Glacier. The polar water fraction was often traceable to the East/West Greenland Current but sometimes to the colder Baffin Current. The huge annual temperature cycle on West Greenland Current isopycnals did not propagate into deep Disko Bay or the fjord basin because isopycnals over the west Greenland shelf were depressed during the warm autumn/winter phase of the cycle.
Ilulissat Icefjord basin waters were anomalously cool in summer 2010. This was not because of the record low NAO index winter of 2009/10 or atmospheric anomalies over Baffin Bay but, possibly, because of high freshwater flux through the Canadian Arctic and a weak West Greenland Current in early 2010. Together, this caused cold Baffin Current water to flood the west Greenland shelf. Subpolar gyre warming associated with the NAO anomaly in winter 2009/10 was more likely responsible for the record warm Disko Bay and Ilulissat Icefjord basin waters of 2011/12."

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=4&ved=0CC8QFjADahUKEwiup7XD8K_HAhWD1SwKHTsFCXM&url=http%3A%2F%2Fdspace.mit.edu%2Fopenaccess-disseminate%2F1721.1%2F97579&ei=crPRVa6mPIOrswG7iqSYBw&v6u=https%3A%2F%2Fs-v6exp1-v4.metric.gstatic.com%2Fgen_204%3Fip%3D50.131.126.145%26ts%3D1439806323568686%26auth%3Dwtlmmij4kdsws3qvc22bppnuhp5difnv%26rndm%3D0.029521970489476912&v6s=2&v6t=9186&usg=AFQjCNHhmIz1KvpZu2aw90Mz_k8hGEonTA (http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=4&ved=0CC8QFjADahUKEwiup7XD8K_HAhWD1SwKHTsFCXM&url=http%3A%2F%2Fdspace.mit.edu%2Fopenaccess-disseminate%2F1721.1%2F97579&ei=crPRVa6mPIOrswG7iqSYBw&v6u=https%3A%2F%2Fs-v6exp1-v4.metric.gstatic.com%2Fgen_204%3Fip%3D50.131.126.145%26ts%3D1439806323568686%26auth%3Dwtlmmij4kdsws3qvc22bppnuhp5difnv%26rndm%3D0.029521970489476912&v6s=2&v6t=9186&usg=AFQjCNHhmIz1KvpZu2aw90Mz_k8hGEonTA)

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=5&ved=0CDkQFjAEahUKEwiup7XD8K_HAhWD1SwKHTsFCXM&url=http%3A%2F%2Fdspace.mit.edu%2Fopenaccess-disseminate%2F1721.1%2F97577&ei=crPRVa6mPIOrswG7iqSYBw&v6u=https%3A%2F%2Fs-v6exp1-v4.metric.gstatic.com%2Fgen_204%3Fip%3D50.131.126.145%26ts%3D1439806323568686%26auth%3Dwtlmmij4kdsws3qvc22bppnuhp5difnv%26rndm%3D0.23802496384177957&v6s=2&v6t=8225&usg=AFQjCNFcPC8WD4ocx1c8PVEnVrghxPKjZg (http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=5&ved=0CDkQFjAEahUKEwiup7XD8K_HAhWD1SwKHTsFCXM&url=http%3A%2F%2Fdspace.mit.edu%2Fopenaccess-disseminate%2F1721.1%2F97577&ei=crPRVa6mPIOrswG7iqSYBw&v6u=https%3A%2F%2Fs-v6exp1-v4.metric.gstatic.com%2Fgen_204%3Fip%3D50.131.126.145%26ts%3D1439806323568686%26auth%3Dwtlmmij4kdsws3qvc22bppnuhp5difnv%26rndm%3D0.23802496384177957&v6s=2&v6t=8225&usg=AFQjCNFcPC8WD4ocx1c8PVEnVrghxPKjZg)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Tor Bejnar on August 17, 2015, 02:56:08 PM
...
None of this ice was floating so it all goes to sea level rise: 8.83 * 2.78 = 24.5 microns
...
I don't think this is quite true.  It would be true if the ice had initially been entirely above sea level.  Although none of this ice was floating, it was displacing water: 8-8ths before calving and 7-8ths afterward.  (But we'd have to know the bathymetry to calculate the volume of water displaced before calving.)  The thought experiment is to fully submerge an ice cube in a graduated beaker (and measure the volume), then release the ice cube and measure the apparent volume. (Then add another ice cube!)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 17, 2015, 03:35:05 PM
The calculation assumes full melt-out (which won't take long in Baffin Bay in August). In terms of displacing seawater, assuming quasi steady state, the ice stream will come forward and fully regain its former territory with uphill ice.

The 8.8 cubic km of ice volume converts to 2.1 cubic miles. Note the sill and ramp bathymetry here is not that well known despite a kazillion radar flyovers, making the assumed 1400 m depth a so-so assumption. Probably the best reconstruction is that of Morlighem, the final contours posted several months ago. The portion of the channel now buried in ice does not have a classic U-shaped cross section.

Next Landsat is a full week out:
 Entity ID: LC80090112015233LGN00
 Acquisition Date: 23-AUG-15

Radarsat comes by on a somewhat erratic schedule: 3, 10, 13, 17 so far in August. The images for the latter two dates are below.

Sentinel's schedule is also hard to anticipate: seven appearances so far in August at DMI but three of them [brackets] didn't make it far enough east to pick up Jakobshavn: [16], 13, 12  [09], 08, 06, [01]

However Terra and Aqua come by daily so progress can be followed despite mediocre resolution, provided it is not too cloudy.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: crandles on August 17, 2015, 03:48:04 PM
Does this indicate depth of bedrock below SL
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fforum.arctic-sea-ice.net%2Findex.php%3Faction%3Ddlattach%3Btopic%3D154.0%3Battach%3D18474%3Bimage&hash=d3ec0e8721c8c8aefef1a1bbb9f5c75f)

Estimating ice as 1400m thick grounded on bedrock at least 1000m below SL then volume above floatation is only a fairly small portion - about (1400-1000*8/7)/1400 = 257/1400 = 18.4%? This being a maximum percentage estimate. The average depth below sea level could be as high as 1200m in which case the volume above floatation could be tiny like 28.6m so possibly only 2% of calved volume is above floatation. VAF would cause a rise in sea level of 7/8th of its volume.
2% to 18% is quite a large uncertainty but a fairly small proportion.

Or is ice estimated to be 1400m above SL?

Or should it be calculated in some other way?






Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Yuha on August 17, 2015, 03:52:11 PM
A-Team, your calving area calculation seems to ignore the glacier movement. The glacier advanced a substantial distance over the two days as can be seen by looking at the markings in the ice just upstream of the pink area. My rough eyeball estimate is that the advance was about 75 m adding about 0.3 km2 to the calving area.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: crandles on August 17, 2015, 03:55:47 PM
The calculation assumes full melt-out (which won't take long in Baffin Bay in August).

AFAICS, I don't see any need for this assumption: if it is now floating, it is now displacing its own mass. (OK there is a slight problem re fresh ice in salt water but this is problem is tiny compared to other uncertainties like depth of water.)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 17, 2015, 04:16:11 PM
It has not floated in recent years, it rests on bedrock. Yuha is quite correct: forward motion of the glacier would add to the calved area.

However to do so, we need to pin down event timing relative to the Landsat shot on the 16th -- requiring someone to track down the UTC time stamp for the 2015-08-15 Aqua image Espen posted. On these, it is hard to compare quantitatively with the most recent one not showing the event (though we have a Landsat for August 14th taken at 2015:226:15:06:13.8590580, the August 16th is 2015:228:14:53:53.2749100

That's why I was inquiring over on the sea ice blog whether anyone had chased down the fjord webcam for surges. Ironically that is the same Holland authoring the two fjord water papers cited by AbruptSLR.

I located free full text for both up at ResearchGate -- is anyone able to pull out the vector graphics from Fig.1 of that pdf (and delete all the overlays, posting just a bathymetry jpg, perhaps using Inkscape)?
Oceanic Boundary Conditions for Jakobshavn Glacier. Part I: Variability and Renewal of Ilulissat Icefjord Waters, 2001–14
CV Gladish et al
http://tinyurl.com/qer3sfw (http://tinyurl.com/qer3sfw)

The Joughin bedrock profile should not be used. Despite the fall 2014 publication date of that excellent Brief Note, it only shows a single flowline based on 2008 bathymetry (which they felt was better than later DEMs).

I've re-located some of the Morlighem discussion -- sidd dug into the primary netCDF and I contoured it, some months ago. That is based on mass conservation and has quite a bit better resolution, showing bedrock troughs and hills. Thus to calculate volume, it would be better to sum over each pixel tower (bedrock depth to surface elevation * 225 sq m area) using numerical values in the original netCDF.

I'm not actually seeing the ramps and sills so often alluded to -- those become more complicated given cross-channel dimensionality. There has been a long series of poor practices in scientific articles on JI, not registering model features on contemporary Landsats, not providing kml files for flowlines etc, not specifying map projection, not working in GIS layer mode, not providing anything more than auditorium quality graphics, covering critical data with obscuring text, not utilizing journal supplemental, on and on. Details apparently don't matter when working in sandboxes (models) having no long-term interest. I cannot think of another area of science where this would have been tolerated.
http://forum.arctic-sea-ice.net/index.php/topic,1165.0.html (http://forum.arctic-sea-ice.net/index.php/topic,1165.0.html)

http://forum.arctic-sea-ice.net/index.php/topic,154.msg45799.html#msg45799 (http://forum.arctic-sea-ice.net/index.php/topic,154.msg45799.html#msg45799)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 17, 2015, 07:08:29 PM
I have to make a confession and a correction.
Somehow I archived the September 27 as one from 2014, but the fact is it is from September 27 2013
(A-Team: "Landsat did not pass over Jakobshavn on the 27th" thanks for making me suspicious).
The interesting thing now is when was the previous max. retreat prior to the August 14-15 2015 calving?
Was it September 27 2013 or September 28 2014? Overall I would say 2014, but when only watching the southern branch I am not so sure?
Can you tell the difference?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 17, 2015, 07:50:17 PM
No problem; it is interesting to see them so similar. Does the calving front sequence Neven is showing have the updated calving front for 2013/14? Have you tried reverse image search to try to properly credit the original calving front graphic, tin eye, imageraider, google?

The 2013 is LC80 08 011 2013 270 LGN00 which is a different path,row geometry from the LC80 10 011 2014 271 LGN00 2014 max retreat so a rotation will be necessary to compare the band 8's.

Real-time science is error-prone; we really should finish collecting all the available data first and then re-visit the quantitative analysis. It's helpful though to have input from many perspectives. (Meanwhile our first efforts will be picked up and irrevocably amplified across the web!)

We should also be checking Twitter to see if someone took footage of the event, recalling tourist footage posted in June. I have little doubt that scientific teams, or at least their equipment, is out there on the easternmost rocks.

There is an extensive seismic array set up on Greenland -- glacier calving sets that off (as the ice stream reels from a big calving loss). I haven't used this but believe it is real-time public domain. It could help narrow the time bracket for this event.

Someone needs to measure August 2015 velocities if we want to make a glacier advance correction ... that velocity will be quite uneven along a perpendicular to flow lines. We have posted previously all published velocity maps including ones from approved dissertations back somewhere in this forum but those won't be applicable to a 2015 event.

The other peculiar feature of this event is the off-center lobe of maximal calving. Somewhere I painted on the distinct contributing sources to the calving front. The Jakobshavn Isbrae proper is the ice source only for the northern fifth or so. The ice calved in the lobe originates nearby, angling in from the southern flank perhaps 20 km back. This ice could be warmer at depth -- there are no experimental temperature transects. Alternatively, this region is moving slower so just slower to replenish than the Isbrae proper.

What defines an 'event' anyway? Jakobshavn actually calves 24/7/365, not continuously perhaps but if ice discharge volume were binned into hourly intervals, the plot vs day of year would rarely scrape zero on the graph. This graph (which we don't actually have but might be estimated from the fjord web cam freeboards) is quite seasonal and subject to bin surges that might last for an hour to several days as an initial big calving triggers instability on its flanks and further back.

An event might be objectively defined as the rolling bin average continuously exceeding two std dev of the seasonal norm, with flanking ramp-ups thrown in. We don't know if this event has finished or only paused. We can't determine whether the Modis on the 15th has the same calving front position (modulo glacier advance) as the Landsat on the 16th. The Landsat shows two significant areas 'on the verge' of calving. The 'Chasing Ice' event here lasted 75 minutes.

Terra just came in for the 17th: too cloudy to determine the calving front.

I've collected some more Landsat trivia. EarthExplorer is not posting images in the order taken, who knew? The LC80080122015228LGN00 from yesterday had a stop time of 14:54:48.93 whereas LC80080112015228LGN00 had a stop time of 14:54:25.04 yet is listed second. Landsat is collecting data as nadir line scans, so in theory these two should be identical on the overlap (unless some difference in processing occurs based on image centers).

LC80080122015228LGN00
 Start Time  14:54:17.16
 Stop Time  4:54:48.93

 Center Latitude    68°16'46.70"N
 Center Longitude    49°27'10.01"W

LC80080112015228LGN00
 Start Time 14:53:53.27
 Stop Time  14:54:25.04

 Center Latitude    69°36'22.79"N
 Center Longitude    47°45'30.64"W
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Sourabh on August 17, 2015, 08:13:09 PM
A-Team,

Sorry to ask a stupid (noob) question. Last year also, I was confused on the same image.

I am finding it difficult to visualize carving on the animation you posted (14 vs 16th). 16th Image looks better (solid ice sheet) and it seems lot of slush in 14th. Why is that? Did ice( water) refroze on 16th?

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 17, 2015, 08:35:06 PM
difficult to visualize carving on the animation you posted (14 vs 16th)
The interpretation of Landsat images is seldom clear to me over an entire scene, in part because it is looking straight down and not quite natural color whereas helicopter shots are helpfully oblique. In theory it would help to drape the Landsat over a hill-shaded DEM (if we had a really recent one).

The debris in front of the calving front -- proglacial melange -- provides a clearer boundary to the south than in the northern shore (of the south branch). In fact, it is not at all clear without looking at movement in 5-6 sequential images what is going on in the upper corner. It may help if a Sentinel radar image emerges for a relevant date. It's never a good idea to go with 'it's obvious to me' ... better to find a second line of independent support.

We could retrieve online temperature records -- Holland has/had an automatic weather station on the northwest rocks. Illulisat would also be reporting but that might be moderated by the surrounding bay. I don't believe there is much re-freezing going on (based on youTube events) once the ice hits the water this time of year. The extreme depth of the calving front means extreme turbulent mixing of ocean waters. These have far too much heat content (relative to ice volume) to freeze unless stratified. The ice takes its sweet time to melt in the fjord but drops out quickly once in Disko Bay.

In some instances (like the north shore depression where we went around in circles forever), the matter was ultimately resolved by a huge level zoom luckily provided by a Google Earth base image. Landsat-8 at 15 m is great to have but it's borderline relative to the intrinsic scale of ground features (crevasse width). Worldview 3 is something like 0.5 m but we don't have the budget for access.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: iwantatr8 on August 17, 2015, 08:44:54 PM
A-Team,
Do you have the wider view difference between the 14th and the 16th showing the bend ( you posted a wide view on the 14th #806)?.  I say this as flicking between the Terra images on worldview seems to indicate that something may have happened further upstream. 
There is a hole in the cloud cover for the 17th and a feature starting to appear at the north side of the southern channel on the 15th and 16th may indicate something astonishing for the 17th August.  I might well be wrong but it looks like there may have been a significant further retreat.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 17, 2015, 09:04:18 PM
Can you overlay an arrow or asterisk?

Yes indeed, there is a lot to look at on the 14-16 images beyond the calving front story. If this is the start of an historic unraveling, then we want to documenting as much as we can (before moving to higher ground  ;) )

It is problematic animating very much of these images at 15 m much less 7.5 m because the forum software chokes on large/wide files. Also it might be better to use the 16th vs an earlier image with the same geometry. I have LC80080112015180LGN00 'in stock' but day 180 vs day 228 raises other issues. It looks like LC80080112015212LGN00 might work...
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: iwantatr8 on August 17, 2015, 09:18:53 PM
What I am looking at is attached I'm looking at the 721 terra image.

The first image from the 17 and the second from the 16th.  on the 16th you can locate the feature as being just to the left of the melt lake  beyond the bend, and as a slight lightening that connects the calving face with the top of the bend.

On the 17th the previous calving face is hidden but the melt lake beyond the bend is clearly visible, but the feature has grown to cover most of the glacier and look like a new calving face but this would be some km upstream of the existing face.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 17, 2015, 09:25:22 PM
Backing up here to Espen's collection of maximal calving front retreats, that notion may not be optional for characterizing calving front history since our Landsat snapshot are so sparse and irregular. We could use Radarsat/Sentinel radar for recent years to the extent DMI offers them.

Another idea is to make a weighted average rather than try to identify the absolute maximum. This might give better statistics for trending into the future. The idea graphically is to simply trace the calving front in black in a separate layer over each photo date. These traces are otherwise blank so they can be composited (averaged) in Gimp or ImageJ. This has the effect of making a grayscale of the calving front, with the degree of blackness proportional to the time the calving front spent there. This results in a probabilistic representation that is more useful than a one-off description
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 17, 2015, 09:51:42 PM
The animation compares the region east of the calving front for the 14 and 16th August Landsats. The latter has thin clouds over some of the image. The alignment is anchored in the upper left via a rotation by a rotation of 5.63º and is not globally ideal. It will need a click to get rolling.

The lower three images look at the Radarsat for changes that took place on the 17th. There does seem to have been further calving lobes in the south.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: oren on August 18, 2015, 01:01:28 AM
The animation compares the region east of the calving front for the 14 and 16th August Landsats. The latter has thin clouds over some of the image. The alignment is anchored in the upper left via a rotation by a rotation of 5.63º and is not globally ideal. It will need a click to get rolling.

The lower three images look at the Radarsat for changes that took place on the 17th. There does seem to have been further calving lobes in the south.

From this superb animation it almost seems like there is another northern branch developing on north wall of the south (main) branch. To my untrained eye it suddenly looks more than just random side calvings and general widening of the channel, but rather like a defined inroad deeper into the cliff.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Shared Humanity on August 18, 2015, 01:48:33 AM
The animation compares the region east of the calving front for the 14 and 16th August Landsats. The latter has thin clouds over some of the image. The alignment is anchored in the upper left via a rotation by a rotation of 5.63º and is not globally ideal. It will need a click to get rolling.

The lower three images look at the Radarsat for changes that took place on the 17th. There does seem to have been further calving lobes in the south.

From this superb animation it almost seems like there is another northern branch developing on north wall of the south (main) branch. To my untrained eye it suddenly looks more than just random side calvings and general widening of the channel, but rather like a defined inroad deeper into the cliff.

Most, if not all, of that north wall of the south branch is grounded below sea level. The portion of the ice sheet that is grounded below sea level goes well into the interior. That is a new calving front that will eventually dwarf the north calving front.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 18, 2015, 03:51:39 AM
Ok north branch fans ... here is the day after the big event compared to the previous Landsat of the same orbit 16 days earlier. Again will need a click to start. Things are moving but not nearly as fast as with the south branch or north side of the south branch (which is now unblocked).
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Tor Bejnar on August 18, 2015, 04:05:18 AM
Go, Team, Go! :D
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 18, 2015, 04:27:08 AM
And now, the north side of the south branch which seems to have a large cult following (and rightly so!). Same days of year: 228 and 212. I'll put in additional frame dates at the end of season, maybe 2014 and 2013 too. Click to animate.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on August 18, 2015, 05:57:56 AM
This is what cliff collapse looks like on a 5km wide, 1Km plus deep grounded front, Bassis in action, together with hydro crevassing and fast flow. I shudder to think whats Thwaites will look like over a 55 Km front and no sideways buttress.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Adam Ash on August 18, 2015, 06:04:56 AM
Looking at the terrain models above, the south branch has a few deep pits which the glacier has to climb through - entailing massive dip and rise deflections.

Has there been any finding of ice (with lots of water entrained at depth) fragmenting or stratifying into near horizontal slabs with the upper slabs moving faster than the grounded lower slabs?  I see this as a potential mechanism which would set up the ice to move to some degree independent of the macro-texture of the bedrock, especially where an ice stream has some deep pits to pass over.

The resulting motion of surface slabs running on top of near-horizontal water-lubricated basement ice could allow for significant acceleration of ice movement, especially when supported by large volumes of melt water introduced to the sliding surface via moulins.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Sleepy on August 18, 2015, 06:14:31 AM
This is what cliff collapse looks like on a 5km wide, 1Km plus deep grounded front, Bassis in action, together with hydro crevassing and fast flow. I shudder to think whats Thwaites will look like over a 55 Km front and no sideways buttress.

You're not the only one.
What amazes me the most, is the total lack of interest from my countrymen.

A-team, marvellous images above.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: CraigsIsland on August 18, 2015, 06:25:32 AM
This is what cliff collapse looks like on a 5km wide, 1Km plus deep grounded front, Bassis in action, together with hydro crevassing and fast flow. I shudder to think whats Thwaites will look like over a 55 Km front and no sideways buttress.

You're not the only one.
What amazes me the most, is the total lack of interest from my countrymen.

A-team, marvellous images above.

I'll 2nd exactly what you wrote on both fronts.

Thank you master observers
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 18, 2015, 06:30:22 AM
Good points, all of them. Meanwhile I'm still trying to figure out just what is going on with the north shore of the south branch. It is an interesting area. The animation shows the 5 cloud-free Landsat path,row 8,11 scenes we've had for 2015.

Adam Ash is bringing in some fresh thinking:
The resulting motion of surface slabs running on top of near-horizontal water-lubricated basement ice could allow for significant acceleration of ice movement, especially when supported by large volumes of melt water introduced to the sliding surface via moulins.

Another week of this at JI and there'll be good reason for concern. sidd is likely referring to: http://aoss.engin.umich.edu/people/jbassis (http://aoss.engin.umich.edu/people/jbassis)

Walker C.C., R. Czerwinski, J.N. Bassis and H.A. Fricker, (2013), Structural and environmental controls on Antarctic ice shelf rift propagation inferred from satellite monitoring, Journal of Geophysical Research- Earth Surfaces, in press.

Bassis, J. N., and Jacobs, S., (2013), Diverse calving patterns linked to glacier geometry. Nature Geoscience, 6(10), 833-836.

Duddu, R., J. N. Bassis, and H. Waisman, (2013), A numerical investigation of surface crevasse propagation in glaciers using nonlocal continuum damage mechanics, Geophysical Research Letters., 40, 3064–3068, doi:10.1002/grl.50602.

Bassis, J.N. and C.C. Walker, (2011), Upper and lower limits on the stability of calving glaciers from the yield strength envelope of ice, Proceedings of the Royal Society, doi: 10.1098/rspa.2011.0422, p. 1-19.

Bassis, J.N., (2011), The Statistical Physics of Iceberg Calving and the Emergence of Universal Calving Laws, Journal of Glaciology, (57)201, p. 3-17. 

Bassis, J.N., (2010), Hamilton Type Principles Applied to Ice Sheet Dynamics:  New approximations for the large-scale flow of ice sheets, Journal of Glaciology, (56)197, p. 497-513.

Fricker, H.A., N. W. Young, R. Coleman, J. N. Bassis, J.B. Minster, (2005), Multi-year monitoring of rift propagation on the Amery Ice Shelf, East Antarctica, Geophysical Research Letters, 32, L02502, doi:10.1029/2004GL021036.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Adam Ash on August 18, 2015, 11:10:06 AM
'*massive dip and rise deflections from pits? [not manifested in ice stream surface lidar]'

For the diagrams showing the ground profile please refer to post here by A-Team:-  << Last edited: August 17, 2015, 05:35:04 PM by A-Team>>

AND

'*ice moving independently of bedrock over deep pits [basal meltwater in season, bed may have hydrated till, ice not frozen-on]'

To my eye, from these contour maps of the south branch, reading from bottom (calving face) to top (left to right on the diagrams) we see contours of -1300 (at the calving front), -900, -1200, -1100, -1300, -1500, -1300, -1500, -1400, -1300, -1100, -1500, -1000 at the top of the channel.
So analysing those again from left to right (going uphill) we find the following rises of the bed into the face of the ice flow (falls not noted):+300, +200,+200,+200,+400. 

I don't have decent data on the actual surface level of the glacier, but if I flew down the glacier on its fall line along this channel I would be most surprised to see elevation changes of +200 to +400 in the ice surface rising up in front of me where the ice is climbing out of a low section of the channel.

Hence my suggestion that there could be some sliding of layers (of relatively constant thickness) across these pits which are in-filled by relatively immobile ice, rather than the ice stream proceeding at a constant thickness over the downstream rises.

So, in relation to:
'*ice stratifying into horizontal slabs, upper moving faster than lower? [all layering lost in ice penetrating radar, ice deforming plastically]'
I recall ice penetrating radar and cores of Greenland which have located melt water (as liquid water complete with its heat, as mush and as new ice) in lenses at depth in the firn, and presumably this stratification can occur through the ice sheet in depth, persisting in ice which is discharging via the out fall glaciers.  Such lenses could create sliding surfaces that are quite slippery compared with the basement, and could give rise to significantly higher ice velocities (albeit localised by the extent of the fracture plane) than other calculations (which envisage a homogeneous full-depth ice mass whose progress is determined - in part - by base dynamics) would allow.

Just a thought...
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Iceismylife on August 18, 2015, 06:21:12 PM
The animation compares the region east of the calving front for the 14 and 16th August Landsats. The latter has thin clouds over some of the image. The alignment is anchored in the upper left via a rotation by a rotation of 5.63º and is not globally ideal. It will need a click to get rolling.

The lower three images look at the Radarsat for changes that took place on the 17th. There does seem to have been further calving lobes in the south.

From this superb animation it almost seems like there is another northern branch developing on north wall of the south (main) branch. To my untrained eye it suddenly looks more than just random side calvings and general widening of the channel, but rather like a defined inroad deeper into the cliff.

Most, if not all, of that north wall of the south branch is grounded below sea level. The portion of the ice sheet that is grounded below sea level goes well into the interior. That is a new calving front that will eventually dwarf the north calving front.
(Small potatoes.)

First of thank you for the very nice illustration.

If you follow the main stream upstream a bit you see an off branch on the north side of the main channel that is almost as deep as the main branch headed inland, and not pictured it goes far inland.  When the calving face unplugs that one, by retreating, it will be fun to watch.  (From 4200 ft elevation.)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 18, 2015, 07:33:42 PM
Looks like Jakobshavn continued the project since our last visit there:
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Lennart van der Linde on August 18, 2015, 07:44:37 PM
Look who's tweeting:
https://twitter.com/erignot/status/633572684710866948
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 18, 2015, 10:43:21 PM
The animation below shows the average velocity between day 228 and day 212, the previous Landsat with the same geometry. The center-of-scene times are 5 seconds off from being exactly 16 days apart. The images are modified for contrast and enlarged 2x (to 7.5 m resolution) within their native 16-bit format (actually 12-bit), then matching features are connected at another 2x exaggeration within Gimp.

For example, if the match points have separated by 69.4 pixels, the velocity in meters per day is 32.5=69.4*7.5/16. The sensitivity to a one pixel error gives a range of 32.1-33.0. Note the velocity seems slower towards the sides. Features seem to be holding up quite well over this time span, ie crevasse widening is not a source of artifact even though the points are quite near the front.

There are better automated ways of doing this over thousands of 'chips' so I'll just leave it as giving some idea of how fast the ice stream was advancing. The all-time reported record is something like 52 m/d. However a velocity in the 'upper 30's' fits well within the Joughin seasonal scheme above, as posted by Crandles at http://forum.arctic-sea-ice.net/index.php/topic,154.msg60965.html#msg60965 (http://forum.arctic-sea-ice.net/index.php/topic,154.msg60965.html#msg60965)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 18, 2015, 11:31:44 PM
Great to see folks doing some independent thinking on the ice physics behind this event -- and where it might lead. After that, might take a look at what seasoned glaciologists consider the core issues for Jakobshavn. The two best recent papers are open source:

Brief Communication: Further summer speedup of Jakobshavn Isbræ
I Joughin et al 03 Feb 2014
http://www.the-cryosphere.net/8/209/2014/tc-8-209-2014.html (http://www.the-cryosphere.net/8/209/2014/tc-8-209-2014.html)

Seasonal to decadal scale variations in the surface velocity of Jakobshavn Isbrae, Greenland: Observation and model-based analysis
I Joughin et al 25 May 2012
http://onlinelibrary.wiley.com/doi/10.1002/2014GL062248/full (http://onlinelibrary.wiley.com/doi/10.1002/2014GL062248/full)

Eric Rignot, like Joughin originally a Ph.D in electrical engineering, is very familiar with interferometric measurement of ice sheet velocities (having been observing glaciers with SAR since 1989), so it's interesting to see his Twitter take on this Jakobshavn event ("galloping retreat"). We've covered his most recent field work on Greenland glaciers (notably Rink and Store calving front sonar) over at another forum:

http://forum.arctic-sea-ice.net/index.php/topic,1327.msg60183.html#msg60183 (http://forum.arctic-sea-ice.net/index.php/topic,1327.msg60183.html#msg60183)
http://forum.arctic-sea-ice.net/index.php/topic,1327.msg60197.html#msg60197 (http://forum.arctic-sea-ice.net/index.php/topic,1327.msg60197.html#msg60197)

I wonder if he has access to other types of satellite imagery that he could share through that site. We have maxed out on our time coverage of the event itself and can hardly follow the aftermath with just Modis. Here are Rignot's presentations coming at AGU2015 this December.

Ocean Melting Greenland (OMG) bathymetric survey of northwest Greenland:implications for recent evolution of its glaciers
Eric J Rignot and MW Wood [http://tinyurl.com/paxfb5f]
A bathymetry survey of northwest Greenland  took place July 22-August 19 and Sept 2-Sept 14 from Ilulissat to Thule. We deployed a multibeam Reson 7160 with 512 beams installed on the hull of the Cape Race vessel, with enhanced capabilities for fjord wall and ice face mapping. The survey tracks were optimized with airborne gravity data collected by NASA Operation IceBridge which indicated the presence of troughs, bed topography mapped inland using a mass conservation approach, and the spatial distribution of ice discharge.

The goal was to identify all troughs that are major pathways for subsurface ocean heat and constrain glacier ice front thickness. The data reveal many deep, U-shaped, submarine valleys connected to the glaciers, intercut with sills and over deepened in narrower passages where former glaciers and ice streams merged into larger units; as well as fjords ending in shallow plateaus with glaciers in retreated positions.

The presence of warm, salty water of Atlantic origin (AW) in the fjords is documented using CTD. Some glaciers sit on shallow plateaus in cold, fresh polar waters at the end of deep fjords, while others are deeper and standing in AW. Satellite imagery from 1962 to 2015 illustrate how the evolution of the glaciers under ocean thermal forcing has been modulated by the presence and/or absence of natural pathways for AW.

Observing and Understanding Changes in Polar Ice Sheets and Glaciers Using Airborne and Satellite Remote Sensing
EJ Rignot [session 8074 convener]  https://agu.confex.com/agu/fm15/preliminaryview.cgi/Session8077 (https://agu.confex.com/agu/fm15/preliminaryview.cgi/Session8077)

Ice-ocean interactions in Greenland and Antarctica
EJ Rignot [session 8074 convener] https://agu.confex.com/agu/fm15/preliminaryview.cgi/Session8074 (https://agu.confex.com/agu/fm15/preliminaryview.cgi/Session8074)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on August 19, 2015, 12:07:05 AM
Yes, i should have said that the Bassis paper i had in mind was the one on Bassis, J. N., and Jacobs, S., (2013), Diverse calving patterns linked to glacier geometry. Nature Geoscience, 6(10), 833-836

I repost Fig 1 b which shows the instability at 1km total height.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 19, 2015, 12:28:11 AM
Do we have some people here who already have a clue on how to access and interpret seismic data?

It seems to me the Ilulisat station of the Greenland Ice Sheet Monitoring Network (GLISN) should have recorded portions of the Jakobshavn event, helping us with timing and substructure. Not sure the best way of going about this, but so far have drilled in a ways eventually getting daily Iluli seismographs for our date range:

Greenland Ice Sheet Monitoring Network
http://ds.iris.edu/ds/nodes/dmc/services/seedlink/ (http://ds.iris.edu/ds/nodes/dmc/services/seedlink/)
http://ds.iris.edu/ds/nodes/dmc/data/#requests (http://ds.iris.edu/ds/nodes/dmc/data/#requests)
http://ds.iris.edu/mda/DK/ILULI (http://ds.iris.edu/mda/DK/ILULI)
http://ds.iris.edu/ds/nodes/dmc/tools/stationmonitor/DK/ILULI/ (http://ds.iris.edu/ds/nodes/dmc/tools/stationmonitor/DK/ILULI/)

IRIS established the Greenland Ice Sheet Monitoring Network (GLISN) of seismic and geodetic sensors to observe the dynamic behavior of the Greenland Ice Sheet as it interacts with the atmosphere, oceans, and solid Earth. GLISN offers the unique ability to record, understand, and respond to changes in the size and scope of the Greenland Ice Sheet’s behavior as it reacts to climate change. Glacial-earthquakes are increasing in occurrence, and their spatiotemporal patterns continue to evolve. Rates of crustal seismicity are also expected to grow as ice melts and withdraws, but the background rates are poorly known.

Models of the Greenland Ice Sheet are hampered by limited knowledge of its basal conditions including the geothermal heat flux, and characterization and interpretation of mass-loss signals observed using GRACE and GPS data are complicated by limited knowledge of the viscoelastic properties of the crust and mantle underlying Greenland.

Seismic imaging techniques using observations of the propagating seismic wavefield can characterize the subsurface structure, permitting inference of heat flux and the space- and time-varying response to surface loading and unloading. Similarly, analyses of seismic source signals due to ice and water motion, rock fracturing, and ocean loading provide constraints on processes including iceberg calving, deformation within the ice mass and at the bed, changes in the bedrock stress state, and variability in sea state and sea-ice cover. Such observations provide key input for the effort to understand the effects of surface melt and ice-ocean interactions on ice-sheet and glacier dynamics.

All data and metadata are freely and openly available through the IRIS Data Management Center. GLISN allows the Arctic science community full access to year-round recordings of seismic and geodetic signals produced by the Greenland Ice Sheet.
Here is what we are looking for (legend for first image):
Spectrogram (bottom) and waveforms (top) of of 14 s of seismic data showing one intermediate depth (marked with red box) and three shallow icequakes (Röösli et al., 2012). Spectrum of the intermediate depth icequake is characterized by high frequency content in the 20-80 Hz range; shallow icequakes are characterized by much lower frequency content in the 10-20 Hz range. Waveforms at the top are bandpass filtered in the 1-80 Hz range.
Here is one of a dozen or so seismic studies in West Greenland:
Glacier, fjord, and seismic response to recent large calving events, Jakobshavn Isbræ, Greenland
JM Amundson et al
http://onlinelibrary.wiley.com/doi/10.1029/2008GL035281/full (http://onlinelibrary.wiley.com/doi/10.1029/2008GL035281/full)
The recent loss of Jakobshavn Isbræ's extensive floating ice tongue has been accompanied by a change in near terminus behavior. Calving currently occurs primarily in summer from a grounded terminus, involves the detachment and overturning of several icebergs within 30–60 min, and produces long-lasting and far-reaching ocean waves and seismic signals, including “glacial earthquakes”. Calving also increases near-terminus glacier velocities by ∼3% but does not cause episodic rapid glacier slip, thereby contradicting the originally proposed glacial earthquake mechanism. We propose that the earthquakes are instead caused by icebergs scraping the fjord bottom during calving. The recent loss of Jakobshavn Isbræ's extensive floating ice tongue produces long-lasting and far-reaching ocean waves and seismic signals
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: plinius on August 19, 2015, 02:23:15 AM
naive suggestion by my side - get the data plus at least one reference station about 1000km or so away (and _NOT_ in Iceland...). Then look for the following: Low Hz waveforms (iceberg singing, should be lower frequency than the normal noise), strong and _short_ bursts, because the longer ones are usually far away earthquakes, and avoid notable s-->p structure (that selects close events in addition, if you do not have directional information you recognize those with a lower amplitude precursor that quite suddenly jumps into a far larger amplitude that then decays, s waves travel faster/more direct than the transversal p-waves in the crust). Once you have those, you check with your reference station that the event is far weaker there. No fun, getting through that forest...

P.S.: Can also cross-check with that:
http://www.emsc-csem.org/Earthquake/ (http://www.emsc-csem.org/Earthquake/)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: AbruptSLR on August 19, 2015, 03:38:27 AM
The first figure is from Holland et al. (2008) and shows how when the atmospheric/oceanic conditions are correct the Irminger Current (the pink curve in panel a) conveys relatively warm water to Disko Bay and from there into Ilulissat Icefjord.

David M. Holland, Robert H. Thomas, Brad de Young, Mads H. Ribergaard & Bjarne Lyberth (2008), "Acceleration of Jakobshavn Isbræ triggered by warm subsurface ocean waters", Nature Geoscience 1, 659 – 664, doi:10.1038/ngeo316

The second figure is from Gladish et al. (2015, Part I), and shows how the modified Irminger Current water reaches the calving front of the Jakobshavn Glacier and accelerates cliff failure calving events.

Carl V. Gladish, David M. Holland, Aqqalu Rosing-Asvid, Jane W. Behrens, and Jesper Boje, 2015: Oceanic Boundary Conditions for Jakobshavn Glacier. Part I: Variability and Renewal of Ilulissat Icefjord Waters, 2001–14. J. Phys. Oceanogr., 45, 3–32, DOI: 10.1175/JPO-D-14-0044.1
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: TenneyNaumer on August 19, 2015, 04:08:32 AM
What great animations!  Thanks so much for all that hard work!

Things really are hoppin' 'n poppin' at the Jakobshavn Isbrae (what is plural for Isbrae?  or should we get a translation of "forked tongue"?)

I also saw that the Loch Ness Monster is alive and well and having a fine time up in the north branch.

It is interesting that since at least 2009, the first two weeks in August have been a time when a lot of the moulins up and disappear en masse. 
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 19, 2015, 05:51:53 AM
That is Isbræer! ;) (not easier)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Carex on August 19, 2015, 03:07:58 PM
All this excitement and no one is lamenting that Espen's proposed camp-out on the rocks, to watch the calving, never materialized!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 19, 2015, 03:59:11 PM
Lamenting
It looks to me from that June 2015 phone-filming of a large calving event that much of the front is no longer visible from the last rocks on the SE side of the south channel. That would be ever so much more the case so today -- the calving lobe is around the corner. It would be very dangerous to go out on the adjacent crevasse fields, even slow moving ones. Still, the noise and bergs floating by would be impressive even if the primary calving was not visible or several km away.

I re-located DM Holland's web cams and weather station. It has a better view from the north shore and is a whole lot easier to get to from town. They seem stuck on 29 Jul 15; so far I have not obtained any information about the mid-August calving event. Their photo is awesome at 2842 x 1602 resolution (shown reduced below).
http://efdl_ems.cims.nyu.edu/aws_jig/overview.html (http://efdl_ems.cims.nyu.edu/aws_jig/overview.html)

The best vantage point really is the divider between north and south branches. While this looks like a crazy unstable icefall, several years of Landsat show that it is very stable. It would take a helicopter to get there and, if Greenland is anything like going out to Baja islands, you would not want to pay the return fare in advance.

I've attached the Radarsat from yesterday whose orbit, like the Sentinel's, missed the calving front itself. Those semi-circular waves of debris spreading out may or may not be artifactual. There is no way of enhancing these images further.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 19, 2015, 04:29:46 PM
Abstracts are closed already for the next AGU meeting, Dec 2015 San Francisco. Hopefully we will have a few live bloggers this year. A few keyword searches turns up the Greenland talks. However the 'abstract' links are dead; AGU search requires a password but oddly googling the titles often recovers the abstract (ie the AGU site is still broken but differently from last year). https://agu.confex.com/agu/fm15/preliminaryview.cgi/start.html (https://agu.confex.com/agu/fm15/preliminaryview.cgi/start.html)

Abstracts can be found by putting 'http://fallmeeting.agu.org/2015/abstract/' (http://fallmeeting.agu.org/2015/abstract/') in front of the title (spaces replaced by dashes). The alphabetic author search is quite effective: https://agu.confex.com/agu/fm15/preliminaryview.cgi/peopleindex_y (https://agu.confex.com/agu/fm15/preliminaryview.cgi/peopleindex_y)

Calving and velocity variations observed by Terrestrial Radar Interferometry at Jakobshavn Isbræ in 2015
S Xie http://tinyurl.com/q889dmr (http://tinyurl.com/q889dmr)

The Autumn of break-ups: When Jakobshavn Isbrae lost its floating tongue
A Aschwanden http://tinyurl.com/phr23cr (http://tinyurl.com/phr23cr)

Bed topography of Jakobshavn Isbræ, Greenland from high-resolution gravity data
Lu An http://tinyurl.com/ou3qm35 (http://tinyurl.com/ou3qm35)

Seismic Imaging of Sub-Glacial Sediments at Jakobshavn Isbræ and NEEM Greenland
GP Tsoflias http://tinyurl.com/nwbkzoh (http://tinyurl.com/nwbkzoh)

Quantifying Sub-Glacial Abrasion at Jakobshavn Isbræ: A Novel Approach Using In Situ 10Be Measurements
NE Young [abstract not found]

Basin-Wide Mass Balance of Jakobshavn Isbræ during 1880-2100
IS Muresan http://tinyurl.com/psckmkz (http://tinyurl.com/psckmkz)

Seasonal and interannual evolution of Jakobshavn Isbrae, Greenland from a 2008-2015 high-res DEM and velocity time series
DE Shean http://tinyurl.com/qjnuyrj (http://tinyurl.com/qjnuyrj)

Paleo-reconstruction of the Jakobshavn Glacier during the late Holocene using ISSM and Paleo-data of Margin Migration
http://tinyurl.com/oqjlrry (http://tinyurl.com/oqjlrry)

Spatial Elevation Changes Observed at Helheim Glacier and Comparison with Jakobshavn Isbræ
C Roberts http://tinyurl.com/np27or5 (http://tinyurl.com/np27or5)

Subaqueous melting in Zachariae Isstrom, Northeast Greenland combining observations and an ocean general circulation model
C Cai http://tinyurl.com/oq62mje (http://tinyurl.com/oq62mje)

Deformation Studies of NEEM, Greenland Basal Folded Ice
K Keegan http://tinyurl.com/pwgdbrl (http://tinyurl.com/pwgdbrl)

Ocean observations from below Petermann Gletscher
Andreas Muenchow [no abstract, work ongoing]

Reverse glacier motion during iceberg calving and the cause of glacial earthquakes
Tavi Murray http://tinyurl.com/opduxky (http://tinyurl.com/opduxky)
Glacier seismicity update to 2015 Science article free full http://tinyurl.com/ozrkfub (http://tinyurl.com/ozrkfub)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Rubikscube on August 19, 2015, 05:26:32 PM
The best vantage point really is the divider between north and south branches. While this looks like a crazy unstable icefall, several years of Landsat show that it is very stable. It would take a helicopter to get there and, if Greenland is anything like Mexico, you would not want to pay the return fare in advance.

Whoa, hold your horses... you mean like camping on Cape Ice? Those crevasses aren't harmless just because they aren't moving. I presume you will have to scout a location in advance at least (that would be some additional expenses on worldview imagery i suppose). Fortunately, I imagine every country in the world to be more like Mexico than Greenland :D.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 19, 2015, 05:46:14 PM
those crevasses aren't harmless... to scout a location in advance
Fine, stay home then and read the adventure blog. WorldView for 25 Aug 2012 below.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 19, 2015, 05:48:15 PM
Some of these AGU talks will shed experimental light on perennially speculative discussions on our forums, such as the true bedrock topography, sediments on top of that, responses to tide and timing of south branch collapse. NEEM, good grief, they could have kept drilling and obtained a 50 m sediment core

Bed topography of Jakobshavn Isbræ, Greenland from high-resolution gravity data
Lu An, UC Irvine [Rignot group?]

Jakobshavn is one of the largest marine terminating outlet glaciers in Greenland, feeding a fjord about 800 m deep in the west coast. It sped up more than twofold since 2002 and contributed nearly 1 mm of global sea level rise during the period from 2000 to 2011. Holland 2008 posit that these changes coincided with a change in ocean conditions beneath the former ice tongue, yet little is known about the depth of the glacier at its grounding line and upstream of the grounding line and the sea floor depth of the fjord is not well known either.

Here, we present a new approach to infer the glacier bed topography, ice thickness and sea floor bathymetry near the grounding line using high-resolution airborne gravity data from AirGRAV collected in August 2012 from a helicopter platform. The data combined with radio echo sounding data, discrete point soundings in the fjord and the mass conservation approach on land ice.

AirGRAV acquired a 500m spacing grid of free-air gravity data at 50 knots with sub-milligal accuracy, i.e. much higher than NASA Operation IceBridge’s 5.2km resolution at 290 knots. We use a 3D inversion of the gravity data combining our observations and a forward modeling of the surrounding gravity field, and constrained at the boundary by radar echo soundings and point bathymetry. We reconstruct seamless bed topography at the grounding line that matches interior data and the sea floor bathymetry.

The results reveal the true depth at the elbow of the terminal valley and the bed reversal in the proximity of the current grounding line. The analysis provides guidelines for future gravity survey of narrow fjords in terms of spatial resolution and gravity precision. The results also demonstrate the practicality of using high resolution gravity survey to resolve bed topography near glacier snouts in places where radar sounding has been significantly challenged in the past. The inversion results are critical to re-interpret the recent evolution of Jakobshavn and reduce uncertainties in projecting its future contribution to sea level.


Calving and velocity variations observed by Terrestrial Radar Interferometry at Jakobshavn Isbræ, Greenland, in 2015
Surui Xie, U South Florida Tampa

We observed the highly dynamic terminus of Jakobshavn Isbræ in Greenland by using a Terrestrial Radar Interferometer (TRI) during a 5 days’ period in early June, 2015. Calving and ice surface velocity variations were captured by our continuous measurements with a sampling rate of 90 seconds. Our terrestrial-derived time series show that calving events are characterized by suddenly fluctuations in surface velocities, which is very distinct in the mélange and less distinct on the glacier. Except for the relatively fast and steady motion, the glacier also moves in response to the semidiurnal ocean tides, and the impact of tides decreases rapidly upstream from the terminus.

Seismic Imaging of Sub-Glacial Sediments at Jakobshavn Isbræ and NEEM Greenland
Georgios Tsoflias,  UKansas [Cresis?]

Sub-glacial sediment conditions can have a major control on glacier flow yet these are difficult to measure directly. We present active source seismic reflection experiments that imaged sub-glacial sections at Jakobshavn Isbræ and at the NEEM drill site.

At Jakobshavn Isbræ we re-processed an existing 9.8 km-long high-resolution seismic line using an iterative approach to determine seismic velocities for enhancing sub-glacial imaging. The seismic profile imaged sediments ranging in thickness between 35 and 200 meters over underlying bedrock.

Based on the geometry of the reflections we interpret three distinct seismic facies: a basal till layer, accreted sediments and re-worked till. The basal till and accreted sediments vary in thickness from less than 5 m to nearly 100 m thick and are interpreted as the zone of most recent deposition.

A reflection polarity reversal observed at a low topographic region along the ice-sediment interface suggests the presence of liquid water spanning approximately 200 m along the profile.

At NEEM we acquired a 5.8 km long-offset shot gather. Seismic imaging revealed two prominent reflections at the base of the ice. The upper reflection is interpreted at the base of ice – top of till interface whereas the lower reflection is interpreted as the base of till – top of bedrock. The thickness of the subglacial sediment section at NEEM is estimated to approximately 50 m using seismic imaging. The NEEM ice core drilled through the upper part of this section and ceased drilling before reaching bedrock.


Basin-Wide Mass Balance of Jakobshavn Isbræ (West Greenland) during 1880-2100
Ioana Muresan, DTU Space Denmark

Here we use a 3-D PISM modeling approach... thinning and retreat is mostly controlled by a loss of resistive stresses at the terminus through glacier dynamics induced calving rather than by changes in oceanic temperatures.

We find that under atmospheric/no ocean RCP 4.5 and RCP 8.5 forcing an increase in ocean temperatures of just 0.7 °C (relative to 1880-2012) is enough to trigger a collapse of the JI’s southern tributary by 2050 which further destabilizes JI and unleashes a major glacial collapse of ~25 km.

JI’s contribution to SLR is 2.8 mm for the period 1880 to 2014, from which the contribution between 1997 to 2014 represents 27%. By the end of the century contributions to SLR as high as 11 mm under RCP 8.5 can be expected from Jakobshavn Isbræ alone.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: AbruptSLR on August 19, 2015, 06:06:46 PM
The linked reference by Hughes et al (2015) presents state-of-the-art analysis about the Jakobshavn Effect (Hughes, 1986), focused on progressive ice-bed uncoupling due to such factors as: basal meltwater, buoyancy friction (particularly with changing surface elevation indicated in the attached image for Jakobshavn), boundary constraints of the fjord.  This work has relevance to multiple marine-terminating, and marine, glaciers in both Greenland and Antarctica:

Hughes, T., Sargent, A., Fastook, J., Purdon, K., Li, J., Yan, J.-B., and Gogineni, S.: Sheet, stream, and shelf flow as progressive ice-bed uncoupling: Byrd Glacier, Antarctica, and Jakobshavn Isbrae, Greenland, The Cryosphere Discuss., 9, 4271-4354, doi:10.5194/tcd-9-4271-2015, 2015.

http://www.the-cryosphere-discuss.net/9/4271/2015/tcd-9-4271-2015.pdf (http://www.the-cryosphere-discuss.net/9/4271/2015/tcd-9-4271-2015.pdf)

Abstract. The first-order control of ice thickness and height above sea level is linked to the decreasing strength of ice-bed coupling alone flowlines from an interior ice divide to the calving front of an ice shelf. Uncoupling progresses as a frozen bed progressively thaws for sheet flow, as a thawed bed is progressively drowned for stream flow, and as lateral and/or local grounding vanish for shelf flow. This can reduce ice thicknesses by 90 % and ice elevations by 99 % along flowlines. Original work presented here includes (1) replacing flow and sliding laws for sheet flow with upper and lower yield stresses for creep in cold overlying ice and basal ice sliding over deforming till, respectively, (2) replacing integrating the Navier–Stokes equations for stream flow with geometrical solutions to the force balance, and (3) including resistance to shelf flow caused by lateral confinement in a fjord and local grounding at ice rumples and ice rises. A comparison is made between our approach and two approaches based on continuum mechanics. Applications are made to Byrd Glacier in Antarctica and Jakobshavn Isbrae in Greenland.


Extract: "Warming in high polar latitudes can, in principle, trigger a succession of positive feedback mechanisms called the Jakobshavn Effect (Hughes, 1986). Buoyancy fraction phiB combines the two dominant mechanisms, reduced ice-bed coupling when surface meltwater floods the bed under an ice stream and reduced ice-shelf buttressing when an ice shelf disintegrates beyond the ice stream. For Greenland, the Jakobshavn Effect would move northward along the east and west coasts, affecting all calving ice streams."
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 19, 2015, 06:26:49 PM
Here is what can be done with better access to imagery than what we have:

Seasonal and interannual evolution of Jakobshavn Isbrae, Greenland from a 2008-2015 high-res DEM and velocity time series
David Shean, UWashington [Joughin group?]

Greenland’s large marine-terminating outlet glaciers have displayed marked retreat, speedup, and thinning in recent decades. Jakobshavn Isbrae, one of Greenland’s largest outlet glaciers, has retreated ~15 km, accelerated ~150%, and thinned ~200 m since the early 1990s.

Here we present a comprehensive analysis of high-resolution elevation (2-5 m/px) and velocity (100 m/px) time series with daily and monthly temporal coverage.

The Jakobshavn DEM time series consists of over 70 WorldView 1-3 stereo DEMs and 11 TanDEM-X spanning 2008-2015. Complementary point elevation data from Operation IceBridge and ICESat-1 GLAS extend the surface elevation record to 1999 and provide essential absolute control data, enabling sub-meter horizontal/vertical accuracy for gridded DEMs.

Velocity data are primarily derived from TerraSAR-X/TanDEM-X image pairs with 11-day interval from 2009-2015.
These elevation and velocity data capture outlet glacier evolution with unprecedented detail during the post-ICESat era.

The lower trunk of Jakobshavn displays significant seasonal velocity variations, with recent rates of ~8 km/yr during winter and >17 km/yr during summer. DEM data show corresponding seasonal elevation changes of -30 to -45 m in summer and +15 to +20 m in winter, with decreasing magnitude upstream.

Seasonal discharge varies from ~30-35 Gt/yr in winter to ~45-55 Gt/yr in summer, and we integrate these measurements for improved long-term mass-balance estimates. Recent interannual trends show increased discharge, velocity, and thinning of 15-20 m/yr which is consistent with long-term altimetry records.

The DEM time series also reveal new details about calving front and mélange evolution during the seasonal cycle.
Similar time series are available for Kangerdlugssuaq and Helheim Glaciers. These observations are improving our understanding of outlet glacier dynamics, while complementing ongoing efforts to constrain estimates for ice-sheet mass balance and present/future sea level rise contributions.


Spatial Elevation Changes Observed at Helheim Glacier, Southeast Greenland, and Comparison with Kangerlussuaq Glacier and Jakobshavn Isbræ
Carolyn Roberts [Csatho group?]

Mass loss from Southeast Greenland is about 50% of total ice loss from the entire Greenland Ice Sheet with Helheim and Kangerlussuaq the main contributors...

Helheim experienced a dramatic thinning event of 50 m in 2004 with an abrupt cessation in 2006, followed by a sequence of thickening/thinning events of lesser magnitude from 2006 – 2012. This complex behavior is further investigated using multi-sensor surface elevation data over a broad region of the glacier trunk during the period of 1981 – 2012. The onset of the rapid thinning event occurred over most of the glacier trunk rather than at the calving front.

 At the commencement of the rapid thinning event, Helheim Glacier’s calving front appeared to be grounded. This is in contrast to Jakobshavn Isbræ which was approaching flotation prior to its rapid thinning events in 1999.

Additionally, the new dataset reveals curvilinear bands (1 km long, 100 m wide) of 10 m elevation change corresponding to lateral shear zones and tributary confluence junctions.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 19, 2015, 08:57:43 PM
Uh-oh. How many hundreds of ice sheet model articles used a seriously wrong form of Glens Law? Almost all of them. How many will be fixed, withdrawn or retracted in the next year: zero.

While these experiments are not easy (compared to hitting 'return' at a model command line), it just goes to show (once more) that theory decoupled from experiment is a colossal waste of time.

Dislocation Creep of Ice At Glaciological Pressures and Temperatures
Chao Qi, U Pennsylvania
https://fallmeeting.agu.org/2015/abstract/dislocation-creep-of-ice-at-glaciological-pressures-and-temperatures/ (https://fallmeeting.agu.org/2015/abstract/dislocation-creep-of-ice-at-glaciological-pressures-and-temperatures/)
https://en.wikipedia.org/wiki/Ice-sheet_dynamics#Flow_dynamics (https://en.wikipedia.org/wiki/Ice-sheet_dynamics#Flow_dynamics)
http://tinyurl.com/q6u5nnw (http://tinyurl.com/q6u5nnw) and http://tinyurl.com/pobf6kc (http://tinyurl.com/pobf6kc) free full to original 1952 and 1958 articles

The Glen law, a power law between effective strain rate and effective stress of the form Ataun, where A is a [[poorly known]] temperature-dependent parameter and n is the stress exponent of value 3, attributed to dislocation creep, has underpinned models and calculations of glacier flow for over six decades.

Compilations of ice creep data from tests at ambient and elevated confining pressures, however, suggest that dislocation creep of ice is characterized by a value of n=4, not 3. While high-pressure experiments on ice provide the best constraints on the dislocation creep regime and have consistently yielded a stress exponent of ~4, most of these tests have been conducted at much-lower-than-glaciological temperatures.

To investigate dislocation creep of ice at glaciological conditions, we deformed samples at temperatures  264 K and elevated confining pressures up to ~30 MPa, the maximum cryostatic pressure in the ice sheets...Plots of strain rate vs. both peak stress and flow stress yield a value of n=4, consistent with previous data from higher-pressure, lower-temperature tests, from some ambient pressure experiments, and with models of climb-limited dislocation creep (Weertman, 1968).

At stresses <3 MPa, tests on the finer-grained samples show a slight decrease in n to a value below 4, while data for the coarser-grained samples show no such transition, consistent with the onset of dislocation-accommodated grain boundary sliding (GBS) in the finer-grained samples at low stresses.

Our data demonstrate that Glen's law is an average of two creep regimes – dislocation creep proper, with n=4, and dislocation-accommodated GBS, with n about 2 – and fails to accurately describe the rheological behavior of ice over the broad range of strain rates in natural ice bodies.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Neven on August 19, 2015, 09:55:16 PM
There's a great article (http://www.washingtonpost.com/news/energy-environment/wp/2015/08/19/one-of-the-worlds-fastest-melting-glaciers-may-have-just-lost-its-biggest-chunk-of-ice-ever/) up on the Washington Post website linking to the ASIB blog post on this, with reactions from Alley, Box and Rignot.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Lennart van der Linde on August 19, 2015, 10:03:49 PM
Neven, did you change your name from Akropolis to Curlin (as the WP-article calls you)?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Neven on August 19, 2015, 10:13:42 PM
Neven, did you change your name from Akropolis to Curlin (as the WP-article calls you)?

No, Acropolis is/was my pseudonym. Don't tell anyone.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Lennart van der Linde on August 19, 2015, 10:21:20 PM
Ah, i see...
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 19, 2015, 10:22:03 PM
There's a great article (http://www.washingtonpost.com/news/energy-environment/wp/2015/08/19/one-of-the-worlds-fastest-melting-glaciers-may-have-just-lost-its-biggest-chunk-of-ice-ever/) up on the Washington Post website linking to the ASIB blog post on this, with reactions from Alley, Box and Rignot.

Thanks Neven,

1. Typical scientist reaction from one corner.

2. How big is a calving, and how long a break before a new calving is starting?

3. Why on earth dont they pool part of their respective budgets to fund some serious surveillance equipment up there?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Neven on August 19, 2015, 10:29:23 PM
2. How big is a calving, and how long a break before a new calving is starting?

3. Why on earth dont they pool part of their respective budgets to fund some serious surveillance equipment up there?

I left a comment echoing your sentiment, Espen:

"Thanks for the link, and thanks for asking the experts about this, great article. If people want to know what a calving looks like in 3D, here's an excerpt from the Chasing Ice documentary: https://youtu.be/hC3VTgIPoGU
 
We obviously need to develop rules and definition for what constitutes a calving. In what timespan? 24 hrs? 48 hrs? Oh, and a dedicated satellite that just hovers over Jakobshavn Isbrae and a couple of drones, just in case.  ;)
 
All kidding aside, this was yet another big calving (it's difficult to compare as there isn't as much info on individual calving events as there is on the glacier and its retreat in general), the retreat line has moved to a new position, and might move some more in the next couple of weeks."
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 20, 2015, 12:35:56 AM
I dunno, the article was lame, creating controversy when there is none. The right question to ask: "does this huge event herald a new stage in the world's fastest glacier?" All these open source animations and the reporter just pastes up irrelevant stock photos.

Curlin could be just another round of aliasing ... suspiciously close to Canadian shuffleboard played on an ice sheet.

Holland's site, as I noted above in #877, could settle the time structure if the web cams had been working which they currently are not. No one has ever tracked volume calved vs time as far as I know. The easiest way to do that is integrate velocity over time just up from the calving front as distance moved is a proxy for volume (as D Shean does at Dec 15 AGU post #867 above).

But there the problem is the sketchy monitoring. As Espen says, they have not invested diddly into decent surveilance equipment. They come up to get a paper's worth, turn around and go home mid-season. This is going to look really really stupid if this turns out to be a historic moment when it all began to unravel.

The Aqua, followed by Terra 5 hours later (?), may show the lobe deepening but that is uncertain.

Holland's site, as I noted above, could settle the time structure if the web cams had been working which they currently are not. No one has ever tracked volume calved vs time as far as I know. The easiest way to do that is integrate velocity over time just up from the calving front as distance moved is a proxy for volume (as D Shean does at Dec 15 AGU post #867 above).

But there the problem is the sketchy monitoring. As Espen says, they have not invested diddly into decent surveilance equipment. They come up to get a paper's worth, turn around and leave mid-season. This is going to look really really stupid if this turns out to be a historic moment when it all began to unravel.

The Aqua, followed by Terra 5 hours later (?), may show the lobe deepening but that is uncertain.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Rubikscube on August 20, 2015, 02:42:14 AM
Fine, stay home then and read the adventure blog. WorldView for 25 Aug 2012 below.

Hehe, I certainly won't be dragging my sorry ass into that minefield, not sure your helicopter guy will agree to ditch you down there either, even if you pay him ever so much (like I said this is not Mexico).

Say whatever you want about Google, but they do actually got  street view (https://www.google.no/maps/@69.1184243,-49.6434799,3a,75y,101h,90t/data=!3m7!1e1!3m5!1su1uMkRYFZEaHiPhIMKKUdg!2e0!6s%2F%2Fgeo1.ggpht.com%2Fcbk%3Fpanoid%3Du1uMkRYFZEaHiPhIMKKUdg%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D101.06%26pitch%3D-2.68!7i13312!8i6656) from the outer island towards the south branch, they have even bothered to walk up several "streets" as well, and from what I can see, the main ice stream remains pretty much visible all the way up to the bend (the light makes it a bit difficult to judge). A camera there should be able to monitor the calving front for many years from now given that JI doesn't start retreating at absurd speeds.

Back to the volume vs elevation plot, I promised an estimate, but I'm not able to draw even a crude 2000 m line in their elevation plot. I will see what I can do with the cdf, but most likely I'm too much of a programming noob to make any sense of it.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 20, 2015, 03:01:17 AM
1. Typical scientist reaction from one corner.
Really. Staking out the middle ground, not go a micron beyond the data?  Box, Rignot, Hansen have a better idea -- it's past time to get the message out and stop the equivocating blather.

The fact is, this event was wholly without precedent in terms of volume of grounded glacier calved at the key geometric sill that is so influential a driver of future retreat. I've looked at every Landat-8 ever taken of Jakobshavn -- nothing else comes close. The burden of disproof thus falls on those who haven't looked at the data. In terms of time-stamps, consecutive Modis shots define a 24 hour window, shorter than the 48 hour Landsats.

Why would I want to compare this event to tabular calving volumes of a long-gone floating ice shelf 20 years ago that don't contribute to sea level rise? It's all about where this event occurred and what happens next (if anything).

There are three ways of looking at the Dec 2015 AGU abstracts I collected above: 

-1- Safe to ignore, it's not published yet, wait for eventual IPCC consensus, more studies are needed;

-2- Isn't it great how science just marches on, smoothly progressing to ever greater understanding!

-3- Wtf is with these clowns, how did they get it so dead wrong for so long?!%*?

I am in the third camp, being very familiar with meeting abstracts/posters and what they mean and do not mean. Here  the specificity (level of detail) is very alarming. We had no idea whether Jakobshavn sat on bedrock, till, sediment, or  meltwater. We spent 22 years on radar flyover without ever really getting down to the bottom of the elbow. We dinked around not observing the interface of glacier front and ocean as if sonar imaging had not been invented in WWII. Seasonal volume discharge integration, who knew? Model after model deforming the glacier with the wrong Glen-Nye flow exponents and temperature profile.

All that's changed now -- see posts #881, #883, #884. And it could have been done years and years ago.

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: sidd on August 20, 2015, 05:29:03 AM
Didnt Schoof have a glen's law exponent of 4 way back in 2007 ? or someone else had evidence that it was closer to 4.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Neven on August 20, 2015, 07:01:04 AM
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fforum.arctic-sea-ice.net%2Findex.php%3Faction%3Ddlattach%3Btopic%3D154.0%3Battach%3D20226%3Bimage&hash=ee77e6f388cad6458063981e7f809c30)

I want those pants! Brush, baby, brush!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: TenneyNaumer on August 20, 2015, 08:55:53 AM
Hey Espen, at least it is not going to be  Jakobshavn Isbræeren -- LOL!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: TenneyNaumer on August 20, 2015, 08:58:43 AM
A-Team, I noticed that white line sticking out of the latest image of the south branch -- it's just a contrail, isn't it?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 20, 2015, 10:05:28 AM
The southern side of the fjord has a good view of the calving front as Google street-view shows and it would be a good place for more instrumentation for understanding calving processes. However I'd monitor the calving front from space, now that S-1 IW every 12 days is virtually guaranteed this can be done year round and perhaps in the future we'll get images even more often once the 2nd satellite in the constellation is up. Good times!

Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: skanky on August 20, 2015, 10:16:38 AM
EOB - http://earthobservatory.nasa.gov/IOTD/view.php?id=86436&eocn=home&eoci=iotd_readmore (http://earthobservatory.nasa.gov/IOTD/view.php?id=86436&eocn=home&eoci=iotd_readmore)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Neven on August 20, 2015, 10:33:10 AM
Thanks, Skanky! Wow, that image comparison tool is so beautiful.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 20, 2015, 11:16:46 AM
monitor the calving front year round from space, now that S-1 IW every 12 days is virtually guaranteed.., even more often with the 2nd satellite
Yes, the Sentinel program is a huge step forward in terms of really systematic year round monitoring of Jakobshavn. At Petermann, 81ºN, there can be 3-4x daily coverage by Landsat, Sentinel, Modis and NOAA. However available daylight limits non-radar satellites to day 33-268 and in summer clouds can be present for weeks on end. Oddly coverage at Zachariae/Niog at 79ºN is far less frequent.

Didn't Schoof or someone have a Glen's law exponent of 4 way back in 2007?
sidd, I edited cites and verbiage from all the AGU abstracts; these provide more Glen flow history. It takes a very specialized type of laboratory to make physically relevant experimental measurements. The 'n' is discussed fairly frequently, the poorly characterized 'A' and its temperature dependence are usually passed over. The sensitivity of model outcomes to their variation is occasionally explored.

The interesting part for me is where Chao Qi concludes Glen flow is a superpositioning of two creep regimes: dislocation creep proper with n=4 and dislocation-accommodated grain boundary sliding with n about 2. Otherwise "it fails to accurately describe the rheological behavior of ice over the broad range of strain rates in natural ice bodies."

that white line sticking out of the latest image of the south branch -- it's just a contrail, isn't it?
Good suggestion. The white line can also be seen in the second image though it's less noticeable (dissipated?). It seems out of kilter with other cloud forms in the image. We've also seen elongated smoke plumes at this latitude. Given the low resolution of these images, further analysis seems infeasible.

image comparison slider tool is so effective.
Most be stock code, I see it on other sites so wonder if WordPress could support it. In fact one of the bloggers here had it going on a personal site, am recalling artische penguin. I'm skeptical though that it is as transportable as an animated gif. It may just be an active alpha transparency channel over a two image stack.

Actually, what's even more effective is to load the images (as many as you want) into an ImageJ "stack". This has a very very rapid slider action over the entire image.

This is great to see a NASA science writer digging into the forum rather than just news page. They seem to have some secret sauce that produces far more realistic color than anything served over at Earth Explorer. Something more than just pan-sharpening with band 8 or 731 color; we do that already.

These NASA Earth Observatory images were made by Joshua Stevens from the USGS Landsats but it doesn't say how. The originals are 17481 × 17581, meaning only 1/34th was processed. I've written him to see if the method is something we could do ourselves.

Their processing is really fantastic at distinguishing clear water, till water, muddy water, algal lakes, berg-filled meltwater and wet areas from nunataks and similar. The third image highlights melt within the south branch elbow via color inversion.

For convenient reference, those 3000x3000 pixel 15 m images without the caption overlays are stored at:

http://eoimages.gsfc.nasa.gov/images/imagerecords/86000/86436/jakobshavn_oli_2015228_lrg.jpg (http://eoimages.gsfc.nasa.gov/images/imagerecords/86000/86436/jakobshavn_oli_2015228_lrg.jpg)
http://eoimages.gsfc.nasa.gov/images/imagerecords/86000/86436/jakobshavn_oli_2015212_lrg.jpg (http://eoimages.gsfc.nasa.gov/images/imagerecords/86000/86436/jakobshavn_oli_2015212_lrg.jpg)
http://earthobservatory.nasa.gov/IOTD/view.php?id=86436&eocn=home&eoci=iotd_readmore (http://earthobservatory.nasa.gov/IOTD/view.php?id=86436&eocn=home&eoci=iotd_readmore) (story)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Adam Ash on August 20, 2015, 03:34:44 PM
Further to my ramblings about alternate sliding possibilities... (Don't fret I will drop it soon!)

While (as I understand it) the generic ice flow model looks at plastic flow of the entire depth of the glacier, I see a couple of bits of evidence from recent posts which leads me to wonder about the full-depth plastic flow model.

1.  Having re-watched that Chasing Ice video, I see that many of the icebergs which ended up floating at the calving face had dimensions of tens to (it seemed) hundred of metres above water level, and many of the bits which ended up lying on their sides were potentially of the 1000 metre class.  Some of the bits which calved clearly had a huge underwater draft.  So a lot of that calving event seemed to be from an ice face with a full 1000 metre draft.   

But when I look at the images in current posts of this recent calving the melange does not seem to contain those big pieces.  This could suggest that the calving was from a tongue of just moderate draft (200 to 500 metres perhaps).

This thinner slab could result from either a top-slab sliding out into the calving area and breaking off, or a rapid undercutting of a full face by warmer water, or a combination of all three (there is always an alternative explanation).

2. Second bit of 'evidence' is the nice base profile in post #882. This shows a significant high point about 10 km up from the calving face.  The ice thickness here reduces to about 60% of the depth either side of it.  There is a corresponding reduction in the thickness of the ice there, but only a very slight increase in ice surface level immediately downstream.

If the plastic flow model is true, then (assuming a similar channel width through and either side of this high point) the velocity of the ice over this shallow section must increase (by ~150%?) in order to sustain the mass-flow rate past the point.

Looking at the available imagery I do not see any 'concertina-ing' of the ice mass as it passes that point, or any other evidence that the velocity over the shallows is somehow ~150% of the velocity either side of it.  With a peak observed velocity of around 50 metres per day (about 3.4 furlongs per fortnight, for the more scientifically-minded among us) I doubt that V^2/2g surface level suppression of the flow makes much difference to the surface level or cross section in this case.  So somehow a constant mass-flow (which for almost-solid relatively incompressible ice would mean: for constant volume per unit time past a point) is occurring along the glacier channel in spite of the cross section varying considerably and the surface velocity (seemingly) remaining largely unchanged over the choke point.

A way to resolve this difficulty could be to adopt my suggestion - that the glacier ice (at times) moves as a comparatively shallow sheet which maintain fairly uniform depth (hence cross section) - with the base of the moving sheet clipping the tops of the 'high spots' of the basement of the channel.

I acknowledge that I have not seen any evidence of slab-flow above water level at the calving face in any of the many videos I have seen of calving glaciers, but I do see many layers of clearer ice lenses and horizontal mid-depth tunnels where clearly there are / have been bodies of free flowing water at various depths in the glacier.

To support data acquisition from satellite  imagery, sending a helicopter over the glacier with a fire bucket full of red paint (or sea water+ a kg bag of Rhodamine-B) and regularly dumping big red spots along  selected cross sections would facilitate easier calculation of surface velocity, and any leaks of R-B at the calving face would give info on in-glacier hydraulics.  (Besides, there would be a certain macabre pathos to be found in the sight of a glacier bleeding as it dies!)

Just a thought...
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 20, 2015, 09:09:42 PM
rapid undercutting of a full face by warmer water
That's surely what's trending today in West Greenland glaciology: seasonally peak meltwater gushing out at respectable velocity at the bottom of the calving face, rising to the surface because as fresh water it is less dense (more buoyant) than fjord saltwater, entraining a flow of replacement ocean water that caverns out the face around the meltwater exits.

The coupling of up-glacier moulin meltwater to ocean circulation comes about from turbulent mixing at the face. Without this effect, stagnant ocean water at the face would melt ice quite slowly and not undermine the upper face.

Notice that the true color NASA imagery shows only a hint of till turbidity in immediate melange on day 228 whereas in the very NE corner of the image turbidity is quite pronounced (showing it is displayed when present). At this point in time, we couldn't even begin to plot the volume and sites of meltwater exit over the season.

Even as we await actual observational sonar imaging (AGU 2015 abstracts) of the bottom of the calving face, not to mention a factually revised elbow DEM from air gravity inversion, it's good to read and re-read the abstract describing what is at the bottom of this glacier: it's not in contact with bedrock but rather gliding on 100 m of sediment and till layers. What fraction of that is hydrated (and what fraction of that water is liquid at what temperature) remains unknown, as is the erosional effect of moulin meltwater drainage.

The abstract by G Tsoflias (post #881) uses a seismic track to image sub-glacial sediments along the southern branch, concluding that the sediments between 35 and 200 meters thick overlie bedrock as three distinct facies: a basal till layer, accreted sediments and re-worked till. The basal till and accreted sediments vary in thickness from less than 5 m to nearly 100 m thick, with liquid water occupying 200 m along a trough at the ice-sediment interface.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 20, 2015, 09:38:46 PM
I asked Joshua Steven, the senior imagery specialist at NASA Earth Observatory if he could disclose some of their image processing tricks, notably how the two Landsats were processed so nicely to natural color. He got back to me right away with a very helpful response.

Much to my surprise, this did not involve pages of command line in expensive proprietary software we had no prospects of ever duplicating, nor did it involve rational scientific algorithms based on deep physical principles from electromagnetic theory. Instead, he just uses Photoshop on an iMac. In other words, each image is different and color correction remains a bit of an art form to get them looking attractive without loss of scientific attributes.

He starts with bands 432 for RGB, then:

use curve adjustments to brighten the image and bring their color more inline with what a high-altitude observer would see. Landsat scenes often come out looking a bit blue due to Rayleigh scattering and atmospheric haze. So toning down the blues does a great deal in making the overall color more realistic."

The method we use at the Earth Observatory is described in an excellent tutorial written by my predecessor, Rob Simmon. It can be found here: http://earthobservatory.nasa.gov/blogs/elegantfigures/2013/10/22/how-to-make-a-true-color-landsat-8-image/ (http://earthobservatory.nasa.gov/blogs/elegantfigures/2013/10/22/how-to-make-a-true-color-landsat-8-image/)

Tom Patterson at the National Parks Service has written a similar tutorial, that also includes pansharpening: http://www.shadedrelief.com/landsat8/introduction.html (http://www.shadedrelief.com/landsat8/introduction.html)

Other readers have asked about doing the color correction in ArcGIS, so I am currently working on a tutorial for that. It should be posted in the next couple of days.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 20, 2015, 10:11:56 PM
More action at Jakobshavn (Sorry I dont have any Sentinel data from Aug. 16 2015)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 20, 2015, 10:52:29 PM
Right, Sentinel has not been by this way since the 13th. Not likely they will goose the orbit just because some internet forum wants more coverage of a particular glacier.

Hopefully nukefix can work some magic on the Landsat-compatible georeferencing of the 13th and 20th. (It's explained well over at Developers Corner but I've not had time to dig into that yet.)

I will lighten up the animation and rotate it a bit shortly
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: wili on August 20, 2015, 11:17:36 PM
How much further back is that thing likely to go this melt season?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 20, 2015, 11:55:23 PM
How much further back is that thing likely to go this melt season?
The animation below aligns the 20 Aug 15 Sentinel of Espen's post above with the 16 Aug 15 Landsat day 228. There was a rotation of 21.8, a rescaling of 80%, and translations of ground control points, all done more accurately had nukefx's protocol been used. I dropped the 13th because it confused the comparison. Basically there seems to be little change since the post-event Landsat.

Since the glacier front has advanced 35 m each day, this means calving has kept up but not gained ground. The calving front retreats only when calving exceeds advance.

Last two years, the maximal retreat seems to have been in late September, so five weeks to go other things being equal (which they never are).

There are five distinct issues here:

-- what caused the record event, anything special going on?

-- what will happen next, is this the beginning of a new regime?

-- where will the calving front end up, how does relief of buttressing affect main and marginal inflow?

-- what is going on with ice stream velocity, acceleration relative to previous years, and volume discharge (SLR)?

-- what will happen over the winter in terms of net advance of the calving front?

It's great to see four leading scientists with extensive experience with Jakobshavn commenting in the Nasa feature. Will they make predictions? (My prediction is no, none of them will get into specifics.)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: wili on August 21, 2015, 05:25:48 AM
Thanks for a more detailed answer (with supplemental questions!) than my simple-minded question deserved.

I am in no position to do so myself, but it does seem to me that it would be a valuable, if perhaps humbling, learning experience for those who know most about the ice up there and its dynamics to try to come up with hypotheses about what exactly will happen next and why. Then we could see how things actually panned out and figure out where the assumptions were wrong.

Kind of the closest thing we get to testable hypotheses in real world large scales situations like this. Of course, they're not exactly repeatable, but unfortunately we are bound to see more sea-bound glaciers passing these tipping points in the future to apply knowledge from this one to. I suppose it's all academic, but that's what academics (and various and sundry ice nerds) do, isn't it?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 21, 2015, 11:46:25 AM
S-1 views the carnage 19.8.2015 (IW in UTM Zone 22 15m pixel size).

edit: S-1 product filename is erroneous in the jpg, the image has been processed from product S1A_IW_GRDH_1SSH_20150819T204653_20150819T204718_007337_00A135_2D70
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 21, 2015, 12:16:43 PM
The animation below aligns the 20 Aug 15 Sentinel of Espen's post above with the 16 Aug 15 Landsat day 228.
Try with the S-1 IW I just posted above..should look great (I hope)!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: oren on August 21, 2015, 01:55:30 PM
I wonder if anyone is counting the total JH flux. It's might be still negligible, but now JH is not only width x depth x annual velocity of main branch + retreat, instead there's all sorts of ice crumbling into the much-longer fjord from newly-exposed cliff faces especially from the north side. The hi-res animations show it quite well.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Wipneus on August 21, 2015, 04:32:18 PM
Also ESA has released an image about the Jakobshavn calving:

Chasing Ice (http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-1/Chasing_ice)

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.esa.int%2Fvar%2Fesa%2Fstorage%2Fimages%2Fesa_multimedia%2Fimages%2F2015%2F08%2Fchasing_glacier_retreat%2F15562607-1-eng-GB%2FChasing_glacier_retreat_node_full_image_2.jpg&hash=04135ad15799270c0fd1f4ae8463b7ea)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 21, 2015, 04:48:52 PM
anyone measuring total JH flux....all sorts of ice crumbling into the much-longer fjord from newly-exposed cliff
Briefly, I am headed out on a camping trip and will be offline for a few weeks.

Probably not. The velocity is so much greater in the main south channel that it dominates the discharge volume. However it would be picked up in total mass balance loss of Greenland as measured by GRACE (though it would slip through the cracks of overall measurement error).

The animation below shows the post-calving NASA Landsat aligned with nukefix's mercatorized Sentinel at the divider between north and south branches. They are off by a rotation of 5.53º by the lake, the other useful ground control point. Not clear where this discrepancy arises but I will try again to see if ESA got the same re-projection.

The second animation shows a region of ambiguous calving whose interpretation affects overall interpretation of area calved by the time of the 16 Aug 2015 Landsat. Note it is reproduced quite well in the Sentinel images of the 19th and 20th. It looks to me like the area with the yellowish tint has slumped into the fjord but is still 'leaning' against the main calving front (or pinned on a rock wall protrusion). The reddish area shows one of the component sub-streams seemingly pushing into this area.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: AbruptSLR on August 21, 2015, 05:04:30 PM

There are five distinct issues here:

-- what caused the record event, anything special going on?

-- what will happen next, is this the beginning of a new regime?

-- where will the calving front end up, how does relief of buttressing affect main and marginal inflow?

-- what is going on with ice stream velocity, acceleration relative to previous years, and volume discharge (SLR)?

-- what will happen over the winter in terms of net advance of the calving front?

To re-state (from other threads) the obvious:
(a) The linked reference indicates that GFDL CM2.1 finds that the AMOC is changing to increase warming of the subpolar gyre (SPG, see the attached image), while cooling the adjoining Gulf Stream region, as projected by Hansen et al 2015.  Warming the SPG allows the Irminger Current to carry warmer water to Disko Bay:

Zhang, J, and Rong Zhang, July 2015: On the Evolution of Atlantic Meridional Overturning Circulation (AMOC) Fingerprint and Implications for Decadal Predictability in the North Atlantic. Geophysical Research Letters, 42(13), DOI:10.1002/2015GL064596.

http://onlinelibrary.wiley.com/doi/10.1002/2015GL064596/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2015GL064596/abstract)

Abstract: "It has been suggested previously that the Atlantic Meridional Overturning Circulation (AMOC) anomaly associated with changes in the North Atlantic Deep Water formation propagates southward with an advection speed north of 34°N. In this study, using Geophysical Fluid Dynamics Laboratory Coupled Model version 2.1 (GFDL CM2.1), we show that this slow southward propagation of the AMOC anomaly is crucial for the evolution and the enhanced decadal predictability of the AMOC fingerprint—the leading mode of upper ocean heat content (UOHC) in the extratropical North Atlantic. A positive AMOC anomaly in northern high latitudes leads to a convergence/divergence of the Atlantic meridional heat transport (MHT) anomaly in the subpolar/Gulf Stream region, thus warming in the subpolar gyre (SPG) and cooling in the Gulf Stream region after several years. Recent decadal prediction studies successfully predicted the observed warm shift in the SPG in the mid-1990s. Our results here provide the physical mechanism for the enhanced decadal prediction skills in the SPG UOHC."

(b) Due to the high flow rate of Jakobshavn, the surface elevation near the calving front keeps decreasing (due to ice thinning); which destabilizes the ice-face as buoyance forces exceed gravitational forces (on the chunk of ice downstream of the last crevasse parallel to the calving front).

(c) The crevasse pattern in the ice can facilitate early calving (as we saw for the Pine Island Ice Shelf this July), and looking at the fracture pattern upstream of the middle of the Jakobshavn calving face, I believe that this ice can calve more readily than that on the adjoining ice face. 

(d) Obviously, if the calving front has moved upstream of any local sill or side-wall buttressing, then this could move Jakobshavn into a new calving regime.

(e) Fluctuation in the buttressing from the mélange are of fundamental importance and can be influenced by the flushing action of the floating ice out of the fjord.

With several weeks to go in the summer season, it will be quite the show to watch.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 21, 2015, 05:15:18 PM
The account at ESA, written by an unknown person following this issue in some detail, needs to be read closely for its area (12.5 km2) and volume measurements (17.5 km3 assuming 1400 m depth) because the Sentinel bracketing dates (27 July, 13  19 August) are wider than our Landsats.

http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-1/Chasing_ice (http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-1/Chasing_ice)

"The new face of the glacier has been pushed inland by several kilometres to what appears to be its furthest easterly location since monitoring began in the mid-1880s. The volume calved could cover the whole of Manhattan Island by a layer of ice about 300 m thick. [[Yes but how deep would it cover the ESA headquarters in Paris?]]

Jakobshavn glacier drains 6.5% of the Greenland ice sheet, producing around 10% its icebergs. This amounts to some 35 billion tonnes of ice that calve every year.

Other similar events have been documented where the glacier parted with 7 sq km of ice, both earlier this year and back in 2010." [[In other words, a record calving relative to contemporary ramp and sill position]]

The high resolution image 7756 x 5003 143 MB is geocoded and possibly re-projected to Landsat mercator; it is located at :
http://www.esa.int/var/esa/storage/images/esa_multimedia/images/2015/08/chasing_glacier_retreat/15562607-1-eng-GB/Chasing_glacier_retreat.jpg (http://www.esa.int/var/esa/storage/images/esa_multimedia/images/2015/08/chasing_glacier_retreat/15562607-1-eng-GB/Chasing_glacier_retreat.jpg)

The image uses Sentinel-1A images from 27 July, and 13 and 19 August as the red, green and blue channels, showing the position of the calving front and "other dynamic features" on each respective date. In second image, I split the ESA RGB into its channels, fixed contrast a bit and animated. It is still a stretch to see the westernmost extension of the calving front (they placed a huge white arrow to close to the data) and I would say we have it better characterized here.

The angle between the ground control points is identical to that provided by nukefix, again it does not match that of Nasa's Landsat. This raises the question whether something is wrong in SNAP toolbox procedures as 5.53º is way too far off.

One thing's for sure: this event will get hijacked if we don't continue to do better follow-up work than the paid professionals.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Iceismylife on August 21, 2015, 06:02:24 PM

The coupling of up-glacier moulin meltwater to ocean circulation comes about from turbulent mixing at the face. Without this effect, stagnant ocean water at the face would melt ice quite slowly and not undermine the upper face.

I read a paper that quoted 10 meters per year for ice lose per degree above melting.  That works out to 2.7 cm per day.  I think the assumption was un-pumped by a current.  With the current surface sea temps of around 45~50 deg F. That gets you about five inches of fresh water added to the fjord for every square inch of wetted ice area a day.

The fresh water emanating from under the glacier entraining more sea water would be on top of that.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 21, 2015, 06:10:15 PM
One thing's for sure: this event will get hijacked if we don't continue to do better follow-up work than the paid professionals.


Hello A-Team! that is what they are getting paid for? And that is what the whole circus is all about, but "the amateurs" are normally quicker though!
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Iceismylife on August 21, 2015, 06:47:28 PM
...

One thing's for sure: this event will get hijacked if we don't continue to do better follow-up work than the paid professionals.
That is the quote of the year.

OK my $0.25 worth.

It looks like we've had two large pieces come off at 2/3 of a km thickness in resent calvings.  So take that as the ice thickness.  This would have been a free floating tong of ice.  That was cantilevered over the sill and grounding line.  Someone has observed that there have been surges in the fjord. One happened just prior to the big calving event.  The first depression prior to the sill would be a logical reservoir to fill and drain to cause the surges.  So a surge just before the new moon would load the top of the glacier after the sill in tension.  The high tide with the new moon or the low tide with it would have put higher stresses into the system.  And we are now on the other side of the sill.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: Espen on August 21, 2015, 08:28:57 PM
Neven our questions are responded somehow:

"Recently we learned that the Jakobshavn Glacier, one of Greenland’s fastest sliding, may  have just lost the biggest piece of ice that scientists have yet seen — on the order of 5 square miles in area on its surface. "Perhaps the most troubling thing is that scientists don’t even know if that’s a record: Greenland is incompletely monitored, so they can’t really say for sure."

To add my humble opinion ( not a so called expert) I am pretty sure this calving session (to be more precise) is the largest since the tabular age of Jakobshavn (period)!!!!!!!


http://www.washingtonpost.com/news/energy-environment/wp/2015/08/20/greenlands-stunning-melting-in-24-unforgettable-images/ (http://www.washingtonpost.com/news/energy-environment/wp/2015/08/20/greenlands-stunning-melting-in-24-unforgettable-images/)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 21, 2015, 10:57:27 PM
-- this event will get hijacked if we don't continue to do better follow-up work than the paid professionals.
-- that is what they are getting paid for? And that is what the whole circus is all about, but we're normally quicker!
They need to get their facts straight or go home. I propose docking their next paycheck for "48 hours" and putting it in the tip jar. Let's start with my post #805 of August 14 (420 views):

"There is quite a bit of calving ahead. Again I am not recalling this level of frontal disintegration so far upglacier. The scale here is 7.5 m per pixel [[image from Landsat B8 band]], meaning that everything 4 pixels in from the calving front will be gone tomorrow."
Do the math. 'Tomorrow' in the context of an August 14th post means August 15th. If I had intended August 16th, well the "day after tomorrow' was available for that. What part of g.o.n.e don't you understand?

Sure enough, Espen catches the 14/15th overnight event on a Modis pair so helpfully provided by DMI, puts up co-registered animations twice (posts #808 and #809, 362 views) at 10:35:17 PM and 11:01 PM followed by confirmation ruling out cloud artifacts via advanced image enhancement and a third 14-on-15 reverse animation 11:21 in my post #808, 353 views. We're still around noon on August 15 and this event has largely been consummated within a 24 hour time frame as predicted the day before.

Remember the scientific community's shabby treatment of Patrick Lockerby and the calving of Petermann (with the important exception of Andreas Muenchow)? I do. And Lockerby did it with physics, not just looking at satellite photos.

Espen you can run from the term 'scientist' but you cannot hide from 'Expert Observer' status, having looked at maybe 5x the number of satellite images of Greenland as the nearest scientist. And I'll go mano-a-mano with any of these clowns for who's who overall in science. Sure I explain stuff here but I can make it incomprehensibly complex (is there an audience for that?).

Meanwhile, the ESA has misinformed 2,083 visitors so far to which we could add more millions of WaPo and general internet readers. We try to arrive at the facts here and get the word out -- but so far that's only been to 420 visitors (going by count maximum under images).

So a new twist on an old saying: the bullsh*t got half way around the world even though the truth did already have its pants on. And six months from now, you'll see a journal article re-creating (plagiarizing) the animations and analysis above (Not-Invented-Here-By-One-Of-Us).

Too bad the gear's all gone, nobody monitoring anything that we know of:

Glacier, fjord, and seismic response to recent large calving events, Jakobshavn Isbræ, Greenland
JM Amundson, M Truffer, MP Lüthi, M Fahnestock, M West, and RJ Motyka
http://onlinelibrary.wiley.com/doi/10.1029/2008GL035281/full (http://onlinelibrary.wiley.com/doi/10.1029/2008GL035281/full)

During summer 2007 we deployed several instruments, all synchronized to UTC time, to study Jakobshavn Isbræ and its proglacial fjord before, during, and after large calving events. Three cameras took photos of the terminus and fjord every 10 minutes from 13 May to 8 June 2007, every hour from 8 June to 17 August 2007, every six hours from 23 August 2007 to 7 May 2008, and every 10 minutes from 7 May to 14 May 2008.

Ocean and seismic waves from calving events were recorded with a tide gauge and a seismometer. A Keller DC-22 pressure sensor, which has a resolution of 0.002 m, was placed in Ilulissat Harbor, 50 km west of the glacier terminus; it logged data every 10 minutes from 11 May to 22 August 2007.

A Mark Products L22 3-component velocity seismometer was placed on bedrock 1 km south of the glacier terminus and ran with a sampling frequency of 200 Hz from 17 May to 17 August 2007 and 100 Hz from 22 August to 22 November 2007 and from 9 April to 9 May 2008. The data gap in winter was due to a loss of battery power. The instrument has a natural frequency of 2 Hz and a sensitivity of 88 V s m−1.

Optical and GPS surveys were conducted to monitor iceberg and glacier motion. Six survey reflectors were placed on the lower 4 km of the glacier and surveyed every 15 minutes with a Leica automatic theodolite from 15 May to 9 June 2007. Nine dual-frequency GPS receivers were deployed higher on the glacier, five on the main flow line and four on a perpendicular transect. These units were installed between 22 May and 1 June 2007 and, except for three that failed in July, ran until 23 August 2007.

Additionally, two telemetered GPS units were placed on large icebergs; data from these were retrieved from 29 May to 8 June 2007. All GPS units logged position data every 15 seconds. The data were differentially corrected against one of two base stations located on opposite sides of the fjord. The measurement uncertainties of the optical and GPS surveys were estimated by de-trending several days of data at a time, removing extreme outliers that clearly indicate bad surveys, and calculating the root mean square errors. The errors for the optical and GPS surveys were ±0.15 m and ±0.02 m, respectively.
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: A-Team on August 21, 2015, 11:55:13 PM
Hello WaPo ... just looking at the 24 old photos in your 20 August 15 listicle on Jakobshavn's recent record event.

Did you know that all the images and animations on these forums are FREE FOR THE TAKING? Yes that's right, brand new, not previously published, open source, public domain, no IP rights retained, no copyright, no watermarks, no permissions, no secondary infringements, no credits (site link appreciated), nothing to do, good to go.

Yes it's true -- when we upload our work to the open internet here, we do so knowing it's in the wild, beyond recall, out of our control, gone, anybody can use it however they want and guess what we don't lose any sleep over it.

Tabular iceberg in Uummannaaq in 2010 -- are you sure that's where and when this photo was taken?
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: nukefix on August 22, 2015, 08:59:13 AM

The angle between the ground control points is identical to that provided by nukefix, again it does not match that of Nasa's Landsat. This raises the question whether something is wrong in SNAP toolbox procedures as 5.53º is way too far off.
According to this it's the Landsat that is "off" since it's not in UTM but in Polar Stereographic at the latitude of Jakobshavn.

http://landsat.usgs.gov/landsat8.php (http://landsat.usgs.gov/landsat8.php)
Title: Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
Post by: skanky on August 23, 2015, 12:33:33 AM
ESA:

https://flic.kr/p/xkXGvY
https://flic.kr/p/wFHtWt
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: Espen on August 23, 2015, 10:09:46 PM
Jakobshavn gained a little since the big calving event last week:

Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: solartim27 on August 23, 2015, 11:58:54 PM
Had a nice clear Terra image today, with no sign of a surge into the bay after the big collapse.  I can't imagine that it happened and dissipated during the cloudy days.  Could there have been a big meltwater drainage before the collapse that undermined the front, causing the collapse?  And how many licks does it take to get to the center of a tootsie roll lollipop?
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: nukefix on September 01, 2015, 11:32:08 AM
S-1 IW 31.8.2015 in UTM22 15m pixel size. No new big calvings.
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: nukefix on September 01, 2015, 12:12:02 PM
Animation between S-1 IW 19.8.2015 & 31.8.2015. Click to animate.
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: georged on September 02, 2015, 12:05:07 AM
Can Jakobshavn credibly be called one glacier anymore? The northern front and and the eastern front appear to be operating quite independently.

The designation as a single glacier with two feeds made sense until about 2005-2006, but a decade later there is absolutely no sign that the two fronts will ever unify again.
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: Seumas on September 02, 2015, 12:38:43 AM
That's a good question. Is it like ice shelves, where we'll end up with Jakobshavn-A and Jakobshavn-B ? Or maybe Jakobshavn North and Jakobshavn East.

Is there a set naming scheme for when this happens?
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: oren on September 02, 2015, 07:23:44 AM
I believe that at this point there is just one glacier or ice stream - the south branch. The north branch and the new north-wall-of-the-south-branch are areas where the ice sheet is calving or flowing directly into the sea. More like "ice falls".
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: plinius on September 02, 2015, 05:01:30 PM
I am not sure I understood your distinction. Isn't the main branch also just calving directly?
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: AbruptSLR on September 02, 2015, 05:50:20 PM
I believe that at this point there is just one glacier or ice stream - the south branch. The north branch and the new north-wall-of-the-south-branch are areas where the ice sheet is calving or flowing directly into the sea. More like "ice falls".

Per the linked Wikipedia article, an icefall is a much different thing than what is occurring at the north branch:

https://en.wikipedia.org/wiki/Icefall

Extract: "An icefall is a portion of some glaciers characterized by rapid flow and a chaotic crevassed surface. Perhaps the most conspicuous consequence of glacier flow, icefalls occur where the glacier bed steepens and/or narrows. The term icefall is formed by analogy with the word waterfall, a similar, but much higher speed, flow phenomenon.

Most glacier ice flows at speeds of a few hundred metres per year or less. However, the flow of ice in an icefall may be measured in kilometres per year. Such rapid flow cannot be accommodated by plastic deformation of the ice."
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: Lennart van der Linde on September 02, 2015, 09:41:39 PM
Some nice airial footage of Jakobshavn calving in May 2014:
http://jasonbox.net/what-massive-greenland-iceberg-calving-looks-like-from-the-air/ (http://jasonbox.net/what-massive-greenland-iceberg-calving-looks-like-from-the-air/)
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: oren on September 03, 2015, 07:30:23 AM
I apologize for the use of layman terms. I mean that when looking at satellite images, you can easily see the main ice stream of the south branch coming from the interior. Visually I see a big difference between that and whatever the north branch should be called.
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: Espen on September 03, 2015, 07:48:43 PM
From Washington Post:

"According to Box, the iceberg calving observed last month might have been one of the largest breaks for this glacier — though it wasn’t the largest. That distinction might go to a break that occurred between 2002 and 2004 and was about 1.5 times the size of Manhattan."

So now we are talking about a record calving lasting 2 years from 2002 to 2004, that is a new standard!?

And by the way in 2002 - 2004 the glacier calved tabular calves.
That is a completely different ball game!

http://www.washingtonpost.com/news/energy-environment/wp/2015/09/02/watch-as-a-massive-chunk-of-ice-breaks-off-of-the-worlds-fastest-melting-glacier/ (http://www.washingtonpost.com/news/energy-environment/wp/2015/09/02/watch-as-a-massive-chunk-of-ice-breaks-off-of-the-worlds-fastest-melting-glacier/)
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: sidd on September 04, 2015, 02:21:38 AM
Yes, this is a new ballgame. we are at the 1Km cliff instability there even without surface melt and crevassing. In this context, I have been reading the appendices and supplementaries to the Pollard(2015)  open access paper http://dx.doi.org/10.1016/j.epsl.2014.12.035 (http://dx.doi.org/10.1016/j.epsl.2014.12.035) and what i find is not encouraging. I will try to post some thoughts somewhere.
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: TenneyNaumer on September 12, 2015, 04:55:07 AM
A few days ago, temps were very high along the edge of the ice sheet near Jakobshavn, and it may even have rained.  Unfortunately, clouds have obscured the region ever since, so there are no good views, but it still seems to me that something has been going on there, and this satellite photo has a very odd spot that looks like water:

http://rapidfire.sci.gsfc.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl1_143.A2015253155500-2015253160000.250m.jpg (http://rapidfire.sci.gsfc.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl1_143.A2015253155500-2015253160000.250m.jpg)
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: solartim27 on September 12, 2015, 07:17:02 AM
The calving front is cut off, but something (wind?) pushes this berg a good ways down the channel.  Starts right past the blue edge on Sept 6th,  second shot from the 11th.
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: solartim27 on September 12, 2015, 07:23:15 AM
Here's a wider look for Sept 1, 6, and 11 from DMI
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: TenneyNaumer on September 12, 2015, 07:21:57 PM
I may be confused by effects caused by clouds, but I am "speculating" that things are going on with the edge of the ice sheet near Jakobshavn and also perhaps there may have been further ice falls.  I have to wonder what this is (see image) -- it's to the south of Jakobshavn (from the link posted above). Also, there are still some very large supraglacial lakes that seem to be unusual for this time of year:

Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: crandles on September 12, 2015, 09:43:54 PM
I may be confused by effects caused by clouds, but I am "speculating" that things are going on with the edge of the ice sheet near Jakobshavn and also perhaps there may have been further ice falls.  I have to wonder what this is (see image) -- it's to the south of Jakobshavn (from the link posted above). Also, there are still some very large supraglacial lakes that seem to be unusual for this time of year:

Is the location where indicated in red circle or somewhere else?

(https://farm6.staticflickr.com/5808/21336067726_4ede88fbb4_z.jpg) (https://flic.kr/p/yvoVAE)featurelocation (https://flic.kr/p/yvoVAE) by crandles57 (https://www.flickr.com/photos/37346653@N05/), on Flickr

Does seem a little odd. 367 and 721 bands also seem to indicate water rather than clouds or ice or land. Snow won't create a dam and it would be pretty unlikely for hail/ice pellets to freeze together sufficiently to be able to create any significant dam.
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: TenneyNaumer on September 13, 2015, 07:22:40 AM
That's a very good comparison photo -- thanks!

I have been watching -- for years -- what looks like "steam" clouds near the sites of supraglacial lakes when they drain.  But this time it does appear that this hole is over land or near the sea, not ice.
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: TenneyNaumer on September 13, 2015, 07:26:05 AM
There is another phenomenon that relates to that side of the ice sheet.  Generally, several supraglacial lakes appear to drain at nearly the same time (or over a day or two).  I have to wonder if there is a connection.  But what could that connection be?   It was only recently discovered that there were vast amounts of water under the surface of the ice sheet.  Could it be that this water drains in places, which might then cause the lakes on the surface above to also drain?
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: solartim27 on September 13, 2015, 08:27:40 AM
There is a possible view of a lake draining from up in the northeast on this message from
L. Bistrup Bræ / Storstrømmen / Dove Bugt / North East Greenland

Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: TenneyNaumer on September 13, 2015, 08:58:15 AM
That's a good example of water continuing to flow out from under the calving fronts. 

In 2010, that sort of thing continued well into December.  I imagine it will again this year.
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: solartim27 on September 13, 2015, 10:02:13 PM
Here is a gif between Sep 6 and 12.  I don't see any major changes in the calving front, but note the difference in motion of the bergs labeled A, B, and C.  I believe berg A does not move, but appears to because of the different resolutions, sattelite position, and my matching errors.
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: nukefix on September 14, 2015, 12:00:19 PM
S-1 IW 19.8.2015/31.8.2015/12.9.2015. Processed with ESA SNAP and Easy GIF Animator. Click to animate.
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: nukefix on September 14, 2015, 12:44:40 PM
Some observation based on the animation above:

- freezing of the ice melange seems to be setting in in the last frame
- northern side of the southern branch seems to be flowing faster than the southern side
- there a new "calving" in the northern wall of the south branch in the last frame
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: AbruptSLR on September 14, 2015, 10:46:36 PM
The linked article provides a nice summary of both observed and modeled ice mass loss from Jakobshavn from 1990 through 2014 (see attached plot):

Muresan, I. S., Khan, S. A., Aschwanden, A., Khroulev, C., Van Dam, T., Bamber, J., van den Broeke, M. R., Wouters, B., Kuipers Munneke, P., and Kjær, K. H.: Glacier dynamics over the last quarter of a century at Jakobshavn Isbræ, The Cryosphere Discuss., 9, 4865-4892, doi:10.5194/tcd-9-4865-2015, 2015

http://www.the-cryosphere-discuss.net/9/4865/2015/tcd-9-4865-2015.html (http://www.the-cryosphere-discuss.net/9/4865/2015/tcd-9-4865-2015.html)
http://www.the-cryosphere-discuss.net/9/4865/2015/tcd-9-4865-2015.pdf (http://www.the-cryosphere-discuss.net/9/4865/2015/tcd-9-4865-2015.pdf)


Abstract: "Observations over the past two decades show substantial ice loss associated with the speedup of marine terminating glaciers in Greenland. Here we use a regional 3-D outlet glacier model to simulate the behaviour of Jakobshavn Isbræ (JI) located in west Greenland. Using atmospheric and oceanic forcing we tune our model to reproduce the observed frontal changes of JI during 1990–2014. We identify two major accelerations. The first occurs in 1998, and is triggered by moderate thinning prior to 1998. The second acceleration, which starts in 2003 and peaks in summer 2004, is triggered by the final breakup of the floating tongue, which generates a reduction in buttressing at the JI terminus. This results in further thinning, and as the slope steepens inland, sustained high velocities have been observed at JI over the last decade. As opposed to other regions on the Greenland Ice Sheet (GrIS), where dynamically induced mass loss has slowed down over recent years, both modelled and observed results for JI suggest a continuation of the acceleration in mass loss. Further, we find that our model is not able to capture the 2012 peak in the observed velocities. Our analysis suggests that the 2012 acceleration of JI is likely the result of an exceptionally long melt season dominated by extreme melt events. Considering that such extreme surface melt events are expected to intensify in the future, our findings suggest that the 21st century projections of the GrIS mass loss and the future sea level rise may be larger than predicted by existing modelling results."
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: sidd on September 17, 2015, 05:20:31 AM
At the same journal, there is an earlier paper bu Hughes and some of the usual suspects comparing Byrd and Jacobshawn in the context of flow under ice-bed uncoupling, using a nice geometical approach outlined by Hughes in earlier papers

http://www.the-cryosphere-discuss.net/9/4271/2015/tcd-9-4271-2015.html (http://www.the-cryosphere-discuss.net/9/4271/2015/tcd-9-4271-2015.html)
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: nukefix on September 17, 2015, 11:44:56 AM
Here is a gif between Sep 6 and 12.  I don't see any major changes in the calving front, but note the difference in motion of the bergs labeled A, B, and C.  I believe berg A does not move, but appears to because of the different resolutions, sattelite position, and my matching errors.
I find it amazing that the iceberg C moved 18.5km in 12 days, which is some 1.5km per day. There must be a strong current that side of the fjord pushing the iceberg outward so quickly.
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: A-Team on September 23, 2015, 10:46:43 AM
The significance of the record-breaking calving event of 15 Aug 2015 — by far the largest ever documented at Jakobshavn — depends on earlier preconditioning of the crevasse system and later response of the glacier to the loss of nearly a kilometer of calving front depth.

We're in fairly good shape in terms of preconditioning imagery; the main issue is correlating ice-to-be-calved condition to flow bands. Recall surface flow lines can be followed tens of km upstream at Jakobshavn. Flow bands are bounding pairs of flow lines, at Jakobshavn most usefully marking out ice origination sources. Less than a third of the calving front tracks back to the deep interior, the rest comes in from a few sources on the south side.

One explanatory scenario posits that calving was delayed for a week or two prior to the event (maybe having to do with still/trough/elbow position/late melt season) while preconditioning continued all the while. Calving then suddenly caught up with preconditioning on the 15th, giving rise to the extraordinary event.

This would leave very little preconditioned ice available for calving post-event and so predicts the calving front will simply march forward at the ~ 40 m/day rate of glacial advance with little new debris in the water. That's in fact what is observed in the first 3 post-event Landsats (1st animation). A cyclic repetition of this scenario in future summers is then predictable.

A more drastic scenario interprets the event as the initial marker of Jakobshavn entering a collapse phase (2nd animation). Here we have zero guidance from glacial modelling because these ignore the elbow, narrowing and have the ocean interface, temperature and bedrock profiles and till depth completely off.

'All models are wrong and frequently none of them are useful.'

Longer term, the data situation is very unfortunate: we’ve had weeks of clouds this September (just like 2014) when the glacier’s response can only be monitored with less satisfactory Sentinel, Radarsat, Aqua and Terra. These don't have sufficient resolution to map preconditioning features.

In addition, it appears to me there has been a rare screw-up with Landsat targeting resulting in the loss of critical data -- the 17 Sep 15 Landsats LC80080122015260LGN00 and LC80080112015260LGN00.

Although those two have been in the orbital pattern for almost three years now, the help desk is claiming Jakobshavn was never on the acquisition list for that date, pointing to http://landsat.usgs.gov//L8_Pend_Acq/y2015/Sep/Sep-17-2015.txt (http://landsat.usgs.gov//L8_Pend_Acq/y2015/Sep/Sep-17-2015.txt) (vary the 17 to see path,row for other dates).

It’s a pity that the scientific community didn’t bestir itself enough to put a daily plane in the air from Illulisat ($200 an hour?) and monitor the glacier from under the clouds at photographic resolution. Maybe someone did via a south shore drone but is not disclosing prior to later publication. Fields like astronomy have a well developed hot line and response plan for transient events, not glaciology though.

It's possible that proprietary high resolution imagery like WorldView3 exists; hopefully someone has the budget for that. Otherwise we are in a race with time, clouds and shortening daylight with Landsat8 for any further post-event details. It's quite possible we will never be any real understanding of this event.

I'll attach all this imagery in a bit.

2015 276 08 11 LC80080112015258LGN00 08-OCT-15 Landsat8 coming?
2015 274 10 11 LC80100112015274LGN00 01-OCT-15 Landsat8 coming?
2015 267 09 11 LC80090112015267LGN00 24-SEP-15 Landsat8 coming tomorrow?
                                     20-SEP-15 Sentinel-1 coverage
                                     18-SEP-15 Sentinel-1 coverage
2015 260 08 12 LC80080122015260LGN00 17-SEP-15 Landsat8 data lost or never acquired
2015 260 08 11 LC80080112015260LGN00 17-SEP-15 Landsat8 data lost or never acquired
2015 258 10 11 LC80100112015258LGN00 15-SEP-15 cloudy
                                     21-SEP-15 AQUA clear
                                     14-SEP-15 AQUA clear
                                     13-SEP-15 AQUA clear
                                     13-SEP-15 Sentinel-1 coverage
                                     10-SEP-15 Radarsat-2 coverage
2015 251 09 11 LC80090112015251LGN00 08-SEP-15 Landsat8 clear
                                     08-SEP-15 AQUA clear
                                     07-SEP-15 AQUA clear
                                     06-SEP-15 AQUA clear
                                     06-SEP-15 Sentinel-1 coverage
                                     03-SEP-15 AQUA clear
                                     03-SEP-15 Radarsat-2 coverage                                   
                                     01-SEP-15 Sentinel-1 coverage
2015 244 08 11 LC80080112015244LGN00 01-SEP-15 Landsat8 cloudy
                                     31-AUG-15 Radarsat-2 coverage
2015 242 10 11 LC80100112015242LGN00 30-AUG-15 Landsat8 cloudy
                                     27-AUG-15 AQUA clear
                                     27-AUG-15 Sentinel-1 coverage
                                     26-AUG-15 AQUA clear
                                     25-AUG-15 AQUA clear
                                     25-AUG-15 Sentinel-1 coverage
                                     24-AUG-15 Radarsat-2 coverage
                                     24-AUG-15 AQUA clear
                                     23-AUG-15 AQUA clear
2015 235 09 11 LC80090112015235LGN00 23-AUG-15 Landsat8 clear
                                     22-AUG-15 AQUA clear
                                     20-AUG-15 Sentinel-1 coverage
                                     18-AUG-15 AQUA clear
                                     19-AUG-15 AQUA clear
                                     17-AUG-15 Radarsat-2 coverage
                                     17-AUG-15 AQUA clear
2015 228 08 11 LC80080112015228LGN00 16-AUG-15 Landsat8 clear
                                     16-AUG-15 AQUA clear
                                     15-AUG-15 AQUA clear
2015 226 10 11 LC80100112015226LGN00 14-AUG-15 Landsat8 clear
                                     14-AUG-15 AQUA clear
                                     13-AUG-15 AQUA clear
                                     13-AUG-15 Sentinel-1 coverage
                                     12-AUG-15 Sentinel-1 coverage
                                     10-AUG-15 Radarsat-2 coverage
                                     08-AUG-15 Sentinel-1 coverage
2015 219 09 11 LC80090112015219LGN00 07-AUG-15 Landsat8 cloudy
                                     06-AUG-15 AQUA clear
                                     05-AUG-15 AQUA clear
                                     04-AUG-15 AQUA clouds
                                     03-AUG-15 Radarsat-2 coverage
                                     01-AUG-15 Sentinel-1 coverage
                                     02-AUG-15 AQUA clear
                                     01-AUG-15 AQUA clear
                                     31-JUL-15 AQUA clear
2015 212 08 11 LC80080112015212LGN00 31-JUL-15 Landsat8 clear
2015 210 10 11 LC80100112015210LGN00 29-JUL-15 Landsat8 clear
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: A-Team on September 25, 2015, 12:37:05 AM
The next Landsat8 just came in, 16 days after the last cloud-free image of. 08 Sep 15. The new image LC80090112015267LGN00 is too cloudy to provide details but the outline of the calving front can be discerned.

I looked into the timing a bit. There is a 7 hour time difference between Landsat's Greenwich Mean Time and my location in Tucson, AZ which mercifully does not observe daylight savings time. Looking at their posted capture schedule, the Jakobshavn scene was to be acquired at 15:00 GMT by the Svalbard (SGS) ground station. So that would be 8:00 am here. It took 7 hours to get the image processed and accessible at Earth Explorer, which is decent enough.

I have to do the big download in the wee hours because of bandwidth limitations on the Excede satellite and will process band 8 at that time.

However you can see already that the odd angular shape of the calving has not changed much but has simply moved downstream, still in line with the first scenario above. At better resolution, it would be worthwhile to take a closer look for calved bergs since August 16th.
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: A-Team on September 25, 2015, 01:30:55 PM
On the high resolution Landsat8 LC80090112015267LGN00_B8 of Sept 24th, which has the same path,row geometry as Sep 8th but low angled solar illumination, the clouds are not too bad in the vicinity of the calving front. I've doubled down on the ground resolution to 7.5 m and added a faint yellow grid scale of 30 pixels which amounts to 225 m x 225 m boxes.

The grid is tilted at 42º so that it follows glacial flow lines after the elbow, ie four of these boxes in from the calving front is 900 m back, or a month of motion at 30 m/day, representing the ice that will be calved off were calving front to remain stationary (more likely, it will move westward).

Note calving is not at all perpendicular the flow but penetrates much deeper near the south wall. I've never seen the calving front cleaved strictly perpendicular to the flow but more typically has been arched deeper in the center (where the velocity is highest).

The current calving front line does not correlate either with flow bands (defined by upstream ice origins) or transverse velocity profile. The area 1-2 km upstream seems unusually cross-crevassedsuggesting it is preconditioned to calving. With the melt season ending, it's not clear whether we'll see that or not.

The alligator skin region is tinted reddish in the second image below, its eastern boundary partly obscured by clouds. The yellow over-tint indicates an odd region already present in the Aug 16th post-event Landsat that appears to have broken off from the calving front but not made its way into the fjord, perhaps because it is supported by a bedrock ledge below or is leaning back against the calving front in a quasi-stable manner.

If this cross-crevassed region represents a new and ongoing development, it would favor the second scenario (two posts back) in which Jakobshavn has crossed the Rubicon into an altogether new and unstable phase. However it is not so easy to compare images because of clouds, different sun angles, different melt extent, and possibly snowfall (or rain).

2015 290 10 11 LC80100112015290LGN00 17-OCT-15 Landsat8 next scene
2015 283 09 11 LC80090112015283LGN00 10-OCT-15 Landsat8 clear                         sun 13.7º
2015 274 10 11 LC80100112015274LGN00 01-OCT-15 Landsat8 cloudy                       sun 17º
2015 267 09 11 LC80090112015267LGN00 24-SEP-15 Landsat8 partly cloudy              sun 20º
2015 251 09 11 LC80090112015251LGN00 08-SEP-15 Landsat8 clear                           sun 26º
2015 235 09 11 LC80090112015235LGN00 23-AUG-15 Landsat8 clear                           sun 32º
2015 228 08 11 LC80080112015228LGN00 16-AUG-15 Landsat8 clear first post-event   sun 34º
2015 226 10 11 LC80100112015226LGN00 14-AUG-15 Landsat8 clear last pre-event
2015 212 08 11 LC80080112015212LGN00 31-JUL-15 Landsat8 clear
2015 210 10 11 LC80100112015210LGN00 29-JUL-15 Landsat8 clear


With Sentinel, we can follow the position of the calving front even in the dead of winter, though glacial velocity (which drops somewhat in winter) is not so easily measured.  Landsat scenes are still taken ± 43 days about Jan 1st, so there is about a three month hiatus there.
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: A-Team on September 26, 2015, 01:21:07 PM
Below is a sequence of Sentinel-1 and Radarsat-2 covering before and after of the record calving event. These are simply taken from the low resolution snapshots available from DMI and expanded 3x in resolution. It would have been better to download the higher resolution images but these don't seem to be in the public domain for Radarsat.

The images are fairly well aligned on rock control points but do not make for a good time series animation because it turns out DMI too has not fully resolved geo-coding issues with radar data. In other words, the images are rotated correctly to match Aqua etc but their geometry otherwise does not quite match. This makes for a jerky animation.

The other issue is that some days the fjord melange and calving area are quite bright but some days they are dark. This may have to do with the ice surface being rougher/smoother depending on daytime temperature melt affecting its radar reflectance.

The first image needs a click to display at its full 700 pixel width. I will add some full resolution Sentinels in a bit; there is an IW image for Sept 24th. Note the confluence area is more distinct in Sentinel than Landsat (2nd image, far right). The third image (which is rotated CW 22º) shows the calving region on Sept 25th.
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: A-Team on September 27, 2015, 12:18:14 PM
Once upon a time, Jakobshavn Isbrae was not grounded at the calving front but instead had a freely floating ice shelf. Later, like all but 7 of Greenland's many glaciers, it lost its ice shelf. Today Jakobshavn is grounded on till over bedrock in its entirety (with only frozen-on melange and related extensions in winter for temporary ice shelf).

It's easy to tell from aerial photos -- which go back 65 years -- when Jakobshavn lost its ice shelf. That's because ice shelves rift off large stable tabular pieces that remain top-side up whereas calving at a grounded terminus yields unstable  irregular blocks of ice that roll over on their sides.

The Landsat7 image below was taken in 26 May 2003, some months after a large section of the ice shelf disintegrated into dozens of tabular blocks, each retaining the surface pattern of the remaining ice shelf. Not one of these blocks subsequently turned over.

Thus prior to this event, Jakobshavn was not grounded at the bottom of the fjord but instead had a free floating ice shelf whose thickness could have been readily determined from the freeboard of the tabular cleavage products.

Jakobshavn no longer calves tabular pieces. Instead, the lower terminus is highly crevassed (unlike an ice shelf) and large blocks of ice fall from the front of calving front (rather than drift away from interior rifts in an ice shelf).

Since calving of a glacier at a grounded terminus is a wholly different process than rifting of an ice shelf, it makes no sense whatsoever to compare them. The former is gravitationally driven physics whereas the latter, at hydrostatic equilibrium, is driven by horizontal shearing (tides, currents, wind, pinning points, bottom melt). Because of this, calved ice contributes to sea level rise but ice rifted from an ice shelf does not.

Comparing like to like, the event of 15 Aug 2015 was indeed unprecedented by a wide margin. It's fair to say though that the relevant period of comparison is fairly short, perhaps only five years.

The significance lies not so much in setting a volume record but rather in what happens next: has upstream Jakobshavn become unstabilized? We may or may not see an effect this year before winter sets in.

Jakobshavn is currently an immense mass of rapidly moving ice forced to alter course to make the sharp bends of the elbow region. Having the ice stream front retreat above the elbow removes a prodigious amount of resistance, which will only be partially offset by new buttressing as sides flow in and compete for channel. This will cause the ice stream to speed up and draw in an ever-widening area of ice sheet beyond its current 6%.
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: AbruptSLR on September 27, 2015, 07:09:35 PM
The linked NASA article discusses how an extreme "Spring Tide" could have contributed to an iceberg from the Jakobshavn Glacier (see image) to sink the Titanic.  While this article focuses on the likelihood that the spring tide refloated deep draft icebergs, we should all remember that such extreme spring tides can also promote iceberg calving events (both in Greenland and in Antarctica):

http://sservi.nasa.gov/articles/did-the-moon-contribute-to-the-sinking-of-the-titanic/ (http://sservi.nasa.gov/articles/did-the-moon-contribute-to-the-sinking-of-the-titanic/)

Extract: "As Greenland icebergs travel southward, many become stuck in the shallow waters off the coasts of Labrador and Newfoundland. Normally, icebergs remain in place and cannot resume moving southward until they’ve melted enough to refloat or a high enough tide frees them. A single iceberg can become stuck multiple times on its journey southward, a process that can take several years. But the unusually high tide in January 1912 could have been enough to dislodge many of those icebergs and move them back into the southbound ocean currents, where they would have just enough time to reach the shipping lanes for that fateful encounter with the Titanic."
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: Espen on September 27, 2015, 07:28:54 PM
The linked NASA article discusses how an extreme "Spring Tide" could have contributed to an iceberg from the Jakobshavn Glacier (see image) to sink the Titanic.  While this article focuses on the likelihood that the spring tide refloated deep draft icebergs, we should all remember that such extreme spring tides can also promote iceberg calving events (both in Greenland and in Antarctica):

http://sservi.nasa.gov/articles/did-the-moon-contribute-to-the-sinking-of-the-titanic/ (http://sservi.nasa.gov/articles/did-the-moon-contribute-to-the-sinking-of-the-titanic/)

Extract: "As Greenland icebergs travel southward, many become stuck in the shallow waters off the coasts of Labrador and Newfoundland. Normally, icebergs remain in place and cannot resume moving southward until they’ve melted enough to refloat or a high enough tide frees them. A single iceberg can become stuck multiple times on its journey southward, a process that can take several years. But the unusually high tide in January 1912 could have been enough to dislodge many of those icebergs and move them back into the southbound ocean currents, where they would have just enough time to reach the shipping lanes for that fateful encounter with the Titanic."

I really doubt this theory, mainly because sea ice conditions was way different back then (1912) and since the accident happened in the month of April, months (3) before the melt season.
If it was an iceberg it could be one from many glaciers not only Jakobshavn, it was either a freak accident (a late iceberg) or maybe even a drunk crew!     
Title: Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
Post by: A-Team on September 28, 2015, 01:19:21 PM
really doubt this theory.. sea ice conditions very different in 1912 ... accident happened on April 15th ... before the melt season
Likewise. If Jakobshavn had a floating ice shelf back then (which follows from the known position of the calving front in that year, historic acc