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Author Topic: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland  (Read 575001 times)

Shared Humanity

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #700 on: July 11, 2015, 03:15:38 PM »
For sure, that is no bergy bit.

Tor Bejnar

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #701 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.)
Arctic ice is healthy for children and other living things.

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #702 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.

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.
« Last Edit: July 11, 2015, 05:08:09 PM by A-Team »

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #703 on: July 11, 2015, 05:45:47 PM »
A-Team you are definitely going to use any drills from my toolbox for that project ;)
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A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #704 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?

andy_t_roo

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #705 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...

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #706 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)

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

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). 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.
« Last Edit: July 12, 2015, 03:05:33 AM by A-Team »

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #707 on: July 13, 2015, 08:46:41 PM »
Another big caving seems to going on around Jakobshavn:

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A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #708 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.
« Last Edit: July 14, 2015, 07:02:57 AM by A-Team »

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #709 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):
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oren

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #710 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.

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #711 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.
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Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #712 on: July 14, 2015, 12:49:56 AM »
Due to wrong dates here is the updated version, sorry and thanks Oren:
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Shared Humanity

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #713 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.

plinius

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #714 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."

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #715 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.

Greg du Pille

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #716 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?

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #717 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)
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Rubikscube

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #718 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.

plinius

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #719 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.

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #720 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/.

Rubikscube

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #721 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.

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #722 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.
« Last Edit: July 14, 2015, 10:25:03 PM by Espen »
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Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #723 on: July 16, 2015, 06:23:15 AM »
Still moving on, very close at record retreat for Jakobshavn:

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Shared Humanity

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #724 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?

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #725 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.
« Last Edit: July 16, 2015, 05:15:36 PM by A-Team »

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #726 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.)
« Last Edit: July 16, 2015, 07:07:50 PM by A-Team »

Jester Fish

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #727 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?

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #728 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.
« Last Edit: July 17, 2015, 06:07:56 AM by A-Team »

oren

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #729 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.

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #730 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/

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 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 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...."


Jester Fish

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #731 on: July 17, 2015, 08:56:06 PM »
A-Team- Thanks for the response, fascinating stuff this physics of moving ice.

oren

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #732 on: July 17, 2015, 09:11:37 PM »
Another set of thanks A-Team, your wealth of knowledge (and patience...) is amazing.

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #733 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).

solartim27

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #734 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.
FNORD

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #735 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.
« Last Edit: July 20, 2015, 11:09:40 PM by A-Team »

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #736 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
« Last Edit: July 23, 2015, 06:37:20 PM by A-Team »

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #737 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:
Have a ice day!

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #738 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.
« Last Edit: July 28, 2015, 05:37:50 PM by A-Team »

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #739 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.
Have a ice day!

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #740 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.)
« Last Edit: July 30, 2015, 06:22:54 AM by A-Team »

solartim27

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #741 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?)
FNORD

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #742 on: July 30, 2015, 05:57:23 AM »
Wonderful images above. Are there any recent speed measurements available?

nukefix

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #743 on: July 30, 2015, 03:53:55 PM »
Optical and SAR can be compared/merged once they are projected to the same map projection.

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #744 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/
« Last Edit: July 30, 2015, 06:45:41 PM by A-Team »

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #745 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!
Have a ice day!

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #746 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

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.
« Last Edit: July 30, 2015, 10:45:59 PM by A-Team »

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #747 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.

Neven

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #748 on: August 02, 2015, 12:01:53 AM »
Wow...

Go, A-Team.  :)
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Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #749 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:
Have a ice day!