Support the Arctic Sea Ice Forum and Blog

Author Topic: Antarctic Icebergs  (Read 6885 times)

FredBear

  • Frazil ice
  • Posts: 121
    • View Profile
  • Liked: 13
  • Likes Given: 30
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

  • Frazil ice
  • Posts: 427
    • View Profile
    • CryosphereComputing
  • Liked: 128
  • Likes Given: 14
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

  • Multi-year ice
  • Posts: 17172
    • View Profile
  • Liked: 353
  • Likes Given: 209
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
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

gerontocrat

  • First-year ice
  • Posts: 5818
    • View Profile
  • Liked: 971
  • Likes Given: 18
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
"Para a Causa do Povo a Luta Continua!"
"And that's all I'm going to say about that". Forrest Gump
"Damn, I wanted to see what happened next" (Epitaph)

johnm33

  • Nilas ice
  • Posts: 1257
    • View Profile
  • Liked: 62
  • Likes Given: 34
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

  • Frazil ice
  • Posts: 121
    • View Profile
  • Liked: 13
  • Likes Given: 30
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

  • Frazil ice
  • Posts: 121
    • View Profile
  • Liked: 13
  • Likes Given: 30
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

  • Frazil ice
  • Posts: 121
    • View Profile
  • Liked: 13
  • Likes Given: 30
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

  • Frazil ice
  • Posts: 427
    • View Profile
    • CryosphereComputing
  • Liked: 128
  • Likes Given: 14
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

  • Frazil ice
  • Posts: 121
    • View Profile
  • Liked: 13
  • Likes Given: 30
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

  • Frazil ice
  • Posts: 121
    • View Profile
  • Liked: 13
  • Likes Given: 30
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

  • Frazil ice
  • Posts: 427
    • View Profile
    • CryosphereComputing
  • Liked: 128
  • Likes Given: 14
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

  • New ice
  • Posts: 72
    • View Profile
  • Liked: 4
  • Likes Given: 5
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

  • Frazil ice
  • Posts: 427
    • View Profile
    • CryosphereComputing
  • Liked: 128
  • Likes Given: 14
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

interstitial

  • Frazil ice
  • Posts: 146
    • View Profile
  • Liked: 25
  • Likes Given: 56
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

  • Guest
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

  • Young ice
  • Posts: 2915
    • View Profile
  • Liked: 258
  • Likes Given: 146
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 »
Arctic ice is healthy for children and other living things.

FredBear

  • Frazil ice
  • Posts: 121
    • View Profile
  • Liked: 13
  • Likes Given: 30
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

  • Young ice
  • Posts: 3818
    • View Profile
  • Liked: 320
  • Likes Given: 37
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

  • Young ice
  • Posts: 2915
    • View Profile
  • Liked: 258
  • Likes Given: 146
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!]
Arctic ice is healthy for children and other living things.

b_lumenkraft

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

Andreas T

  • Nilas ice
  • Posts: 1125
    • View Profile
  • Liked: 11
  • Likes Given: 2
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.

Tor Bejnar

  • Young ice
  • Posts: 2915
    • View Profile
  • Liked: 258
  • Likes Given: 146
Re: Antarctic Icebergs
« Reply #22 on: March 20, 2019, 08:43:26 PM »
Ice Island A68-A appears to have not moved 'much at all' since March 3rd.  (PolarView image from today.  WorldView image [insert] from gif recently posted [above].) [two images are not quite to same scale.]
Arctic ice is healthy for children and other living things.

Tor Bejnar

  • Young ice
  • Posts: 2915
    • View Profile
  • Liked: 258
  • Likes Given: 146
Re: Antarctic Icebergs
« Reply #23 on: April 03, 2019, 07:15:28 PM »
A68-A has moved since the previous post.  As of April 2, it has moved northward (NNW) (parallel to the local coast) about 30 km. It's got to go due east, then northeastwards to stay away from land.  I think the 'bluish tinged' coast due north (upper left corner) is Robertson Island.  PolarView image from 2019-04-02 [map credit]
« Last Edit: April 08, 2019, 09:12:40 PM by Tor Bejnar »
Arctic ice is healthy for children and other living things.

Tor Bejnar

  • Young ice
  • Posts: 2915
    • View Profile
  • Liked: 258
  • Likes Given: 146
Re: Antarctic Icebergs
« Reply #24 on: April 08, 2019, 09:10:32 PM »
A68-A have move north about 12 km in 6 days, per today's PolarView (and the image above).

[Note: as 1º latitude = 110 km, the 'waist' of A68-A is about 27 km wide.]
Arctic ice is healthy for children and other living things.

Tor Bejnar

  • Young ice
  • Posts: 2915
    • View Profile
  • Liked: 258
  • Likes Given: 146
Re: Antarctic Icebergs
« Reply #25 on: April 16, 2019, 04:40:06 PM »
During this week (as of March 15), A68-A has moved 6 km northwards (measuring at the side of the ice island closest to the point just north of Larsen C Ice Shelf, and the south end has moved (rotated) about 7 km eastward (away from Larsen C).  (Image is stitched from two Polar View images [north and south].)  I'm guessing the ice island will continue its slow counterclockwise spin and will thus not get stuck south of Robertson Island, although I expect the ice to bump into the island (in 3 weeks, at the current rate).
Arctic ice is healthy for children and other living things.

b_lumenkraft

  • Guest
Re: Antarctic Icebergs
« Reply #26 on: April 16, 2019, 05:07:23 PM »
Will it make a 360?  ;D

Tealight

  • Frazil ice
  • Posts: 427
    • View Profile
    • CryosphereComputing
  • Liked: 128
  • Likes Given: 14
Re: Antarctic Icebergs
« Reply #27 on: May 03, 2019, 08:18:24 PM »
Now A68-A is just 5.5km away from the islands. I wonder if it's actually going to collide with the island itself. According to the Bedrock map the area is quite shallow, but it might be wrong. The small part that broke off early (A68-B) is currently in 40-50m deep waters.

interstitial

  • Frazil ice
  • Posts: 146
    • View Profile
  • Liked: 25
  • Likes Given: 56
Re: Antarctic Icebergs
« Reply #28 on: May 03, 2019, 08:51:17 PM »
I was looking at that yesterday and thinking the front end was grounded or nearly so. It looks to me like the back end has started to roll around towards the front because of this. On the other hand that could just be the way the currents are pushing the iceberg around.

Tor Bejnar

  • Young ice
  • Posts: 2915
    • View Profile
  • Liked: 258
  • Likes Given: 146
Re: Antarctic Icebergs
« Reply #29 on: May 14, 2019, 09:39:50 PM »
A68A is mostly rotating between April 15 and May 14: today's PolarView compared with last month's composite.
Arctic ice is healthy for children and other living things.

Tealight

  • Frazil ice
  • Posts: 427
    • View Profile
    • CryosphereComputing
  • Liked: 128
  • Likes Given: 14
Re: Antarctic Icebergs
« Reply #30 on: May 28, 2019, 10:11:01 PM »
A68A rotation continues in the same spot. Animation beween 3rd May and 28th May.

Adam Ash

  • Frazil ice
  • Posts: 301
    • View Profile
    • The 100 metre line
  • Liked: 5
  • Likes Given: 19
Re: Antarctic Icebergs
« Reply #31 on: May 29, 2019, 02:17:18 PM »
...tho its rotation is around a point away from the berg.  Thus it is floating free of restraining points beneath it, IMHO.

IceConcerned

  • New ice
  • Posts: 16
    • View Profile
  • Liked: 9
  • Likes Given: 0
Re: Antarctic Icebergs
« Reply #32 on: June 10, 2019, 03:10:07 PM »
As seen on Polarview SAR imagery : https://www.polarview.aq/images/105_S1jpgfull/S1A_IW_GRDH_1SSH_20190608T080144_5C66_S_1.final.jpg,
it appears the rotation of the iceberg is going on.

I am wondering besides, with such a big bloc at the outlet of the gulf, will there be no effect (through tides, diverged currents...) on the remains of Larsen B ? I have the impression that the cracks around the islets in particular are growing wider and longer ? (maybe just an illusion). To be noted, there was a minor calving at the norther junction with the meninsula a few days ago (with the resulting iceberg still visible in the gulf, oriented more or less N-S)

Tor Bejnar

  • Young ice
  • Posts: 2915
    • View Profile
  • Liked: 258
  • Likes Given: 146
Re: Antarctic Icebergs
« Reply #33 on: June 10, 2019, 05:55:58 PM »
A68-A is rotating around a different center now.  I thought it would be closer to the island/peninsula, but it is also 'moving out'.  New PolarView image ('added' to the previous GIF) is from June 8.
Arctic ice is healthy for children and other living things.

b_lumenkraft

  • Guest
Re: Antarctic Icebergs
« Reply #34 on: June 10, 2019, 06:33:07 PM »
Something is there beneath the surface. I'd guess it'll lose it's nose.

Tor Bejnar

  • Young ice
  • Posts: 2915
    • View Profile
  • Liked: 258
  • Likes Given: 146
Re: Antarctic Icebergs
« Reply #35 on: June 26, 2019, 09:36:06 PM »
A68-A is amazingly close to Robertson Island.  From the last published image just above, the ice island has rotated a little (counterclockwise as always) and snuggled up close to the island.  At the surface, the ice island is about 300 meters from the thin white line that approximates the edge of the island.  (yellow lines approximate the gap) PolarView image from today
Arctic ice is healthy for children and other living things.

magnamentis

  • Guest
Re: Antarctic Icebergs
« Reply #36 on: June 26, 2019, 11:23:45 PM »
A68-A is amazingly close to Robertson Island.  From the last published image just above, the ice island has rotated a little (counterclockwise as always) and snuggled up close to the island.  At the surface, the ice island is about 300 meters from the thin white line that approximates the edge of the island.  (yellow lines approximate the gap) PolarView image from today

i suspect that there is contact under water ?

Tor Bejnar

  • Young ice
  • Posts: 2915
    • View Profile
  • Liked: 258
  • Likes Given: 146
Re: Antarctic Icebergs
« Reply #37 on: July 05, 2019, 05:06:15 PM »
Ice Island A68-A continues to move back and forth (tides? wind?) as it approaches the end of its 2nd year as a free agent - no pesky fast ice will hold it in place.  It has actually slid back, or to the 'left' or westward, a spot from the June 26 image (above), but has rotated a hair counterclockwise (as always).
Arctic ice is healthy for children and other living things.

gerontocrat

  • First-year ice
  • Posts: 5818
    • View Profile
  • Liked: 971
  • Likes Given: 18
Re: Antarctic Icebergs
« Reply #38 on: July 12, 2019, 08:55:06 PM »
The BBC have got a movie on A68-A's progress over the last 2 years.

https://www.bbc.co.uk/news/science-environment-48920168

I suppose if I was clever I could filch it from the web-page, but I am not (sigh)
"Para a Causa do Povo a Luta Continua!"
"And that's all I'm going to say about that". Forrest Gump
"Damn, I wanted to see what happened next" (Epitaph)

Tor Bejnar

  • Young ice
  • Posts: 2915
    • View Profile
  • Liked: 258
  • Likes Given: 146
Re: Antarctic Icebergs
« Reply #39 on: July 19, 2019, 06:55:33 PM »
A68-A is (slowly) escaping from the clutches of Robertson Island [blue-highlighted blob on the left in new image] in the dark of night.  July 3 image from above; July 16 image from PolarView.  Rotation during these two weeks is about 10º - pretty fast! Near Robertson Island, A68-A slid southwestwards a bit.
Arctic ice is healthy for children and other living things.

Tor Bejnar

  • Young ice
  • Posts: 2915
    • View Profile
  • Liked: 258
  • Likes Given: 146
Re: Antarctic Icebergs
« Reply #40 on: August 09, 2019, 07:05:20 PM »
A68-A has rotated another 15 or so degrees, plus a piece broke off on the 'left' side …  PolarView image from 2019-08-08

Interesting icy feature at the 'top' end of the ice island.   [my guess: ] Caused by the sea ice moving 'north' faster than the ice island?
Arctic ice is healthy for children and other living things.

blumenkraft

  • Frazil ice
  • Posts: 293
  • Fans of Hans Club - circa 2018
    • View Profile
  • Liked: 131
  • Likes Given: 150
Re: Antarctic Icebergs
« Reply #41 on: August 09, 2019, 07:22:26 PM »
Interesting icy feature at the 'top' end of the ice island.

I see them all the time. I think it's caused by wind.

For example at the Brunt shelf (Pic1) or PIG (Pic2).
“You are not entitled to your opinion. You are entitled to your informed opinion. No one is entitled to be ignorant.”

Stephan

  • Grease ice
  • Posts: 606
    • View Profile
  • Liked: 127
  • Likes Given: 89
Re: Antarctic Icebergs
« Reply #42 on: August 09, 2019, 10:19:25 PM »
I just realized a new little crack on the very W tip of the PIG, where (behind it) a minor calving occurred in June (https://forum.arctic-sea-ice.net/index.php/topic,429.msg205693.html#msg205693).

DrTskoul

  • Nilas ice
  • Posts: 1411
    • View Profile
  • Liked: 183
  • Likes Given: 59
Re: Antarctic Icebergs
« Reply #43 on: August 09, 2019, 11:27:43 PM »
A68-A has rotated another 15 or so degrees, plus a piece broke off on the 'left' side …  PolarView image from 2019-08-08

Interesting icy feature at the 'top' end of the ice island.   [my guess: ] Caused by the sea ice moving 'north' faster than the ice island?

Looks the sea is rushing away....