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FredBear

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Antarctic Icebergs
« on: February 06, 2018, 02:49:42 PM »
Have been looking at the icebergs, particularly around the Weddell Sea recently.

a68a (82*25nm) hit the headlines when it calved in 2017 but there is also a23a (44*40nm) which has been grounded to the SE for many years, although it does seem to have moved slightly NW since January 2017. (Also I wonder if a23a is accumulating snow faster than it is melting - the Brunt ice shelf to the NE accumulates about 1.5 m per year?).

Some other 'bergs are heading off from the Weddell Sea in the direction of South Georgia - b15z (15*7nm), b15t (25*6nm), c28b (21*14nm) and b09f (20*8nm) are fairly clear.

A new recruit has been b15aa (11*6nm) which came round the bend from the east above the Brunt ice shelf (about October 24 2017) and has been drifting round in small circles all this summer season, rather than going south towards Brunt.


Don't know if this is of interest to other readers or if there is anything to add?

Tealight

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Re: Antarctic Icebergs
« Reply #1 on: February 07, 2018, 09:20:57 PM »
I keep a look on icebergs as well because they are the main mechanism for ice loss of the continent apart from subsurface melting. Typically ice-shelfs are getting thinner towards the edge and icebergs are the thinnest parts so i assume A23a is losing mass as well. Once it floats freely in the Weddell Sea it doesn't matter anyway, because it can leave Antarctic waters in a few month and melt in the South Atlantic.

The icebergs B15z, B15t,C28b and B09f you mentioned have drifted from the center of the Weddell Sea to the current position in just 12 month ( see image and NASA link). A23a might follow the same path.

Same icebergs 12 month ago:
https://go.nasa.gov/2EP1APk

My focus is more on West-Antarctica particularly B22a (44X24 nm) which blocks Thwaites Glacier from the open sea. If this beast becomes loose all the icebergs behind can drift out as well.


AbruptSLR

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Re: Antarctic Icebergs
« Reply #2 on: February 07, 2018, 10:39:12 PM »
Linked is a regularly updated list of the locations of large Antarctic icebergs:

http://www.scp.byu.edu/current_icebergs.html
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gerontocrat

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Re: Antarctic Icebergs
« Reply #3 on: February 24, 2018, 02:23:43 PM »
The quote is from Johnm33 - he was answering

Quote
In order to move north bergs have to be accelerated eastward by about 5kph for every 20k travelled [needs checking], or their inertia will press them against the peninsular. So they need to get caught up in a powerful current or tidal movement to 'escape' antarctica. If you look at the 600 s lat. you'll see that for practical purposes a berg, going n, is moving directly away from the axis of rotation, and that the 600lat. is approx half the distance the equator is from that axis, thus the surface speed is approx half that at the equator. We know there's a powerful clockwise tidal flow through Weddel. 
https://earth.nullschool.net/#current/ocean/surface/currents/overlay=sea_surface_temp/azimuthal_equidistant
The icebergs escaping but not from Weddel look more like rare events, but worth looking into, given their similarities, as/when time permits.

"We know there's a powerful clockwise tidal flow through Weddell" - you knew,  I did not.  During Antarctica's brief summer, drift seemed to slow down a lot. Does that tidal current diminish in summer?

Tor Bejnar also posted this link on the Larsen C thread. I have copied it so I can remember where it is.
Quote
The Antarctic Iceberg Tracking Database (http://www.scp.byu.edu/data/iceberg/)shows where icebergs have traveled.

What a super image
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johnm33

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Re: Antarctic Icebergs
« Reply #4 on: February 24, 2018, 03:08:55 PM »
gerontocrat
Here's a link to polar tidal animations. You'll see that there's some limited action where the other bergs get energised to escape. Tides are seasonal to the extent that they're generally more extreme, high/low, when the Sun's over the equator rather than the tropics cancer/capricorn, but the extremes are really driven by the the moons position relative to the sun and also by mslp, so a lower pressure means higher tides. Then there's winds, currents and resonances ... 

FredBear

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Re: Antarctic Icebergs
« Reply #5 on: June 07, 2018, 11:56:23 AM »
I see that Susan Anderson has found the latest EO pictures of B-15Z breaking up:-

https://earthobservatory.nasa.gov/IOTD/view.php?id=92238&src=eoa-iotd

A link to a 27 October 2017 from EO:-

https://earthobservatory.nasa.gov/IOTD/view.php?id=91181

FredBear

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Re: Antarctic Icebergs
« Reply #6 on: December 13, 2018, 02:13:58 AM »
Iceberg B15AA (12/12/2018 Lng -39.49, Lat -65.06 approx) is still moving NW, but more slowly than the thinner sea ice floes that have been passing it. However, recently the surrounding sea ice floes have been breaking up rapidly and the iceberg is now approaching the inner edge of the 'goodbye waves'. It could soon be floating free in the southern ocean?

A23A is still grounded (top NE corner has only moved from Lng -40.52 Lat -76.06 [2000 Mar 05] to Lng -39.86 Lat -75.66 [2018 Dec 05] over 18.75 years!). It has had a tendency block ice flow to the south and east of the Weddell Sea over this time. The Brunt ice shelf to the NE accumulates 1.5m snow/year (which has been burying the BAS Halley stations), so it might be possible that A23A is growing in thickness rather than melting? This iceberg could affect any break-up of the Brunt ice shelf & where the resulting icebergs move, as the natural flow is to the south and west.

FredBear

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Re: Antarctic Icebergs
« Reply #7 on: December 13, 2018, 02:25:36 AM »
I notice that BYU have not updated iceberg positions for some time, more up-to-date positions can be found at:-   

https://www.natice.noaa.gov/pub/icebergs/Iceberg_Tabular.pdf

Tealight

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Re: Antarctic Icebergs
« Reply #8 on: January 08, 2019, 02:00:38 PM »
Over the last year Iceberg B22A has moved a few kilometer north-west opening up more space for Thwaites Glacier and soon the Crosson Ice Shelf to clear out all icebergs and thick multi-year sea ice that has been stuck behind it for years. Perhaps some of the larger icebergs can finally begin their journey around Antarctica this year.

Link to current conditions:
https://go.nasa.gov/2FdzdNV

FredBear

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Re: Antarctic Icebergs
« Reply #9 on: January 09, 2019, 02:50:30 AM »
B22A and many surrounding icebergs in this area seem to have a raft-type structure composed of smaller "logs" of ice which move as together as units. Eventually many of the "logs" break away forming the smaller bergs littering this part of the sea.
To me this seems to be quite different behaviour from most calvings, for example the Pine Island Icebergs which start off large and planar (with their designation) and then break up into smaller pieces, or calvings from other ice shelves.
Is this an example of ice-cliff failure in the Thwaites Glacier, just a feature of the speed of calving, or because any outward flow from the coast is not constrained by fjord walls?

(In the northern hemisphere I suspect that Jakobshaven has a high surface flow which washes it's icebergs downstream rapidly so that they do not build up in the fjord.)

FredBear

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Re: Antarctic Icebergs
« Reply #10 on: January 16, 2019, 02:35:51 AM »
Looking at    http://www.arctic.io/explorer/   top right drop down  Antarctica-true color

B22 broke clear from Thwaites between 2002.02.13 and 2002.03.13 and joined the ice peninsular (which often formed) by about 2012.03.20.
Another major calving from the Thwaites tongue occurred in the dark before 2012.09.01 and headed north east of B22 towards the open sea. It drifted westwards, then back towards the coast, onwards towards the northern Ross Sea, where it was breaking up on 2018.03.14 (long153.9, lat 67.8 )
This shows that Thwaites is fairly free to calve even if B22A does not move (and the ice tongue that B22A joined at the base is more often present than not.) but some of the other 'bergs are trapped to the west of Thwaites.

There was more sea ice around Pine Island/Thwaites last year than usual but it is breaking up a bit more this year   .   .   .   watching with interest to see what will transpire.

Tealight

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Re: Antarctic Icebergs
« Reply #11 on: January 17, 2019, 11:46:51 AM »
Looking at    http://www.arctic.io/explorer/   top right drop down  Antarctica-true color

B22 broke clear from Thwaites between 2002.02.13 and 2002.03.13 and joined the ice peninsular (which often formed) by about 2012.03.20.
Another major calving from the Thwaites tongue occurred in the dark before 2012.09.01 and headed north east of B22 towards the open sea. It drifted westwards, then back towards the coast, onwards towards the northern Ross Sea, where it was breaking up on 2018.03.14 (long153.9, lat 67.8 )
This shows that Thwaites is fairly free to calve even if B22A does not move (and the ice tongue that B22A joined at the base is more often present than not.) but some of the other 'bergs are trapped to the west of Thwaites.

If you only look at ice edge glacier definitions it is true that Thwaites could calve freely the last few years. Especially the sub-region of Thwaites Ice Tongue where several other icebergs came from. I meant more the whole Thwaites area. Haynes Glacier is really just a sub glacier of Thwaites. Even the Crosson ice shelf is connected to Thwaites over Pope/Smith glacier.

steve s

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Re: Antarctic Icebergs
« Reply #12 on: January 17, 2019, 06:37:29 PM »
The Thwaites' bergs seem to require time -- years -- losing depth in warm water before they are free to drift out to sea. I wish I had a better picture of the undersea topography relative to the existing sea ice and bergs. 

Tealight

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Re: Antarctic Icebergs
« Reply #13 on: February 20, 2019, 10:45:37 PM »
A small part of A68A completly disintegrated instead of breaking off in one piece. Previous images are in the "Rift in Larsen C" topic which really isn't fitting anymore.

https://forum.arctic-sea-ice.net/index.php/topic,1175.msg186956.html#msg186956

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Re: Antarctic Icebergs
« Reply #14 on: February 21, 2019, 02:58:45 PM »
https://www.polarview.aq/

In under 16 hours another chunk came off iceberg A68a

b_lumenkraft

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Re: Antarctic Icebergs
« Reply #15 on: February 21, 2019, 04:34:14 PM »
Isn't this where it is suspected to be grounded due to the pivoting around this place?

Maybe it's the ocean current pulling so hard, it has to give somewhere.

Tor Bejnar

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Re: Antarctic Icebergs
« Reply #16 on: February 21, 2019, 04:37:07 PM »
That's my guess. [Edit:  lots of historical images of A68-A in the Rift in the Larsen C thread.  First reported as 'detached' in linked post.]
« Last Edit: February 25, 2019, 05:13:31 PM by Tor Bejnar »
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FredBear

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Re: Antarctic Icebergs
« Reply #17 on: February 26, 2019, 12:50:55 PM »
Re:- Reply 14.
All the bits of A68A seem to be moving - just not very much?

Shared Humanity

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Re: Antarctic Icebergs
« Reply #18 on: February 26, 2019, 08:46:17 PM »
If you look at the first image, fractures in A68 propagate from the calving area across the berg. Wouldn't surprise me to see this calving to continue and eventually cause the berg to separate into two large pieces.

Tor Bejnar

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Re: Antarctic Icebergs
« Reply #19 on: February 26, 2019, 09:33:16 PM »
Today's PolarView shows no (significant) breakage since the 20th (unlike before then!).

[It sure looks like a bite: teeth marks and all!]
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b_lumenkraft

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Re: Antarctic Icebergs
« Reply #20 on: March 03, 2019, 06:16:53 PM »
The 180 is completed!

Andreas T

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Re: Antarctic Icebergs
« Reply #21 on: March 03, 2019, 09:52:26 PM »
on the other side of the Wedell sea there is an ice berg drifting towards the Brunt ice shelf. Maybe another "Pooh stick" (as in the Milne books) to watch.