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Author Topic: The Nares Strait thread  (Read 328234 times)

Clenchie

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Re: The Nares Strait thread
« Reply #1200 on: June 30, 2017, 08:59:05 PM »
(There are a few quite small floes (bergs?) near the lower right corner of this animation that don't move, including a "" shaped one.) [Bell Floe is about 15 km wide.]

Those look to be either land masses or glitches on the image because they don't move one iota despite all the movement around them.  I have tried to enlarge the image but all I get is large pixels, without definition enough to discern their true nature.  They are very small.  I wonder if there is someone with more detailed knowledge of the waters in that area, or maybe access to images with better resolution.

Update:  if you go to 24th September 2015 you will see something in the exact same spot that doesn't move in the days either side.  There is more ice but the same spot is there.
« Last Edit: June 30, 2017, 10:07:18 PM by Clenchie »
Ice flows make nice floes but icebergs don't make nice burgers.

bairgon

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Re: The Nares Strait thread
« Reply #1201 on: July 01, 2017, 01:04:19 AM »
(There are a few quite small floes (bergs?) near the lower right corner of this animation that don't move, including a "" shaped one.) [Bell Floe is about 15 km wide.]


Those look to be either land masses or glitches on the image because they don't move one iota despite all the movement around them.  I have tried to enlarge the image but all I get is large pixels, without definition enough to discern their true nature.  They are very small.  I wonder if there is someone with more detailed knowledge of the waters in that area, or maybe access to images with better resolution.

Update:  if you go to 24th September 2015 you will see something in the exact same spot that doesn't move in the days either side.  There is more ice but the same spot is there.


As I stated a little while ago, with a link to Sentinel which shows much better resolution:

Finally found the answer. They are grounded calved icebergs from the nearby glacier. The Sentinel playground shows them clearly here.


I found a reference to the Humboldt Glacier calving front being up to 50m high. That would give a considerable depth below water. As the icebergs are in lines I expect there are some old sills at that end of Kane basin.

bairgon

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Re: The Nares Strait thread
« Reply #1202 on: July 01, 2017, 08:21:37 AM »
Finally found the answer. They are grounded calved icebergs from the nearby glacier. The Sentinel playground shows them clearly here.


I found a sequence near the bell floe on Sentinel - at this link - that shows this very clearly.

The GIF below starts at 16th June and skips cloudy days. The last image is the last available, from 29th June.

Points to note: watch the triangular-shaped iceberg at top right. It moves a little, seems to get stuck, and then gets knocked out of position by some sea ice and appears at bottom left. You can also see another square-ish iceberg which moves out of the original line but ends up stuck despite the sea ice coming through.

Also note the difference in the colouring. The sea ice is clearly covered in melt ponds, but the icebergs stay gray presumably because they are not flat. I've put in a nice shot at full resolution illustrating this from 27th June.

Edit: corrected left/right; and note that the triangular iceberg is around 300m long.
« Last Edit: July 01, 2017, 08:50:27 AM by bairgon »

oren

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Re: The Nares Strait thread
« Reply #1203 on: July 01, 2017, 08:50:50 AM »
Thanks bairgon, great animation and explanation.

Clenchie

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Re: The Nares Strait thread
« Reply #1204 on: July 01, 2017, 06:36:21 PM »
Thanks bairgon, great animation and explanation.

Yes Bairgs, your theory has great merit.  The underwater obstructions must wreak havoc with the ice and cause chaotic flow patterns.
Ice flows make nice floes but icebergs don't make nice burgers.

bairgon

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Re: The Nares Strait thread
« Reply #1205 on: July 01, 2017, 11:05:01 PM »
the shadow of the main branch looks like it will allow the estimation of the calving front height via using incidence angle & sun elevation angle at the time of imaging...


Looking at the calving front of Humboldt Glacier, shadows can be seen in the lee of the icebergs.

Using the scale and a mm rule my best guess is that the shadows are around 40m. Using the excellent suncalc website for that date and changing the time to match the shadows shows that the height of the iceberg is around 25m.

Assuming that the iceberg has a linear profile (i.e. it doesn't get fat underwater) then the draft of the iceberg would be around 175m.

The bathymetry map attached shows a ridge about 100m deep running parallel to Humboldt, explaining why these icebergs get stuck.


Clenchie

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Re: The Nares Strait thread
« Reply #1206 on: July 02, 2017, 04:37:25 PM »
Nice works Bairgs. 8)
Ice flows make nice floes but icebergs don't make nice burgers.

oren

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Re: The Nares Strait thread
« Reply #1207 on: July 02, 2017, 04:39:14 PM »
Nice works Bairgs. 8)
+1
Armchair science at its finest

Shared Humanity

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Re: The Nares Strait thread
« Reply #1208 on: July 02, 2017, 05:31:28 PM »
Nice works Bairgs. 8)
+1
Armchair science at its finest

Agreed.

Phil.

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Re: The Nares Strait thread
« Reply #1209 on: July 04, 2017, 01:39:45 PM »
"Balanced"?  Viewing successive EOSDIS Worldview images (from June 21), the Bell Floe has moved at least 15 km each day until yesterday (between June 28 and 29 [video below]) when one corner of it moved only a few km (northward).  With wind out of the north (per Windytv's now-cast, at least), this northward movement of the floe would be due to the gyre.  Smaller floes in the area aren't moving much.  (There are a few quite small floes (bergs?) near the lower right corner of this animation that don't move, including a "" shaped one.) [Bell Floe is about 15 km wide.]

Judging by the latest Sentinel image the Bell Floe has broken up somewhat.

http://ocean.dmi.dk/arctic/images/MODIS/Kane/20170703s01b.ASAR.jpg

Tor Bejnar

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Re: The Nares Strait thread
« Reply #1210 on: July 04, 2017, 02:33:00 PM »
Maybe it should have been called the Liberty Bell  :'(  (although its breakage occurred on the 2nd of July, as best I can tell [edit: the Continental Congress resolved to leave GB on July 2nd; Jefferson showed the 'Declaration' to journalists on the 4th - the original 'fake news' story!])
« Last Edit: July 05, 2017, 02:05:24 PM by Tor Bejnar »
Arctic ice is healthy for children and other living things.

Tor Bejnar

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Re: The Nares Strait thread
« Reply #1211 on: July 05, 2017, 02:08:33 PM »
Half the ice in Lincoln Sea has become fast ice while half is mobile, per DMI Sentinel images (movie: July 2 & 4; still: July 4)
Arctic ice is healthy for children and other living things.

Phil.

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Re: The Nares Strait thread
« Reply #1212 on: July 07, 2017, 09:32:17 PM »
The North end of the Nares strait is now crammed with mobile ice it'll be interesting to see how fast it moves through.

numerobis

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Re: The Nares Strait thread
« Reply #1213 on: July 13, 2017, 03:09:28 PM »
From the pictures, it looks like nothing much is going through Fram. Is it melting at the top end, or is there just no pressure through the pipe?

johnm33

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Re: The Nares Strait thread
« Reply #1214 on: July 13, 2017, 06:06:17 PM »
There was a full moon on sunday, the flow usually builds for 3-4 days so I suspect it's flowing well, below the clouds. Open links and click images to expand https://seaice.uni-bremen.de/data/amsr2/asi_daygrid_swath/n6250/2017/jul/Arctic/asi-AMSR2-n6250-20170709-v5_nic.png [9th]
https://seaice.uni-bremen.de/data/amsr2/asi_daygrid_swath/n6250/2017/jul/Arctic/asi-AMSR2-n6250-20170712-v5_nic.png [12th]

Andreas T

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Re: The Nares Strait thread
« Reply #1215 on: July 13, 2017, 08:00:38 PM »
the wind was blowing from the southern end of the strait until recently, strongly at times. See nullschool or these on the spot measurements from Hans island https://dataservices.sams.ac.uk/aws/

Tor Bejnar

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Re: The Nares Strait thread
« Reply #1216 on: July 17, 2017, 05:46:42 PM »
The older ice in the Lincoln Sea near Greenland has not moved much in weeks (it seems), but it is now on the move, again.  This July 15-16 gif (DMI Sentinel images) shows the westward movement.  Some of this feeds Nares Strait.  (The >5km floes are still some distance from Nares.)
« Last Edit: July 17, 2017, 05:58:34 PM by Tor Bejnar »
Arctic ice is healthy for children and other living things.

oren

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Re: The Nares Strait thread
« Reply #1217 on: July 18, 2017, 01:21:45 AM »
Temps have been spiking recently, reaching 10oc. I find it surprising that any fast ice still remains in the fjords around the strait.