Sea Ice in Amundsen Sea / Pine Island Bay

[Stephan]

I start this topic to discuss the different patterns of sea ice and its melting during austral summer which should be separated from Thwaites Glacier / Pine Island Glacier calving events (see the individual threads).
I compared the last for years (see attached pictures from EOSDIS Worldview), which differ widely in extent and structure of the sea ice. I chose clear days, so all pictures are from around end September, but not at the same date. In this time of the year the changes from day to day can be relevant.
2016 saw in general a low sea ice cover in that area, 2017 had the closest ice cover. All pictures show the SE→NW flow of the ice.

[blumenkraft]

My bet is on Circumpolar Deep Water upwellings.

Glaciological and oceanographic observations coupled with numerical models show that warm Circumpolar Deep Water (CDW) upwelling onto the West Antarctic continental shelf causes melting of the undersides of floating ice shelves. Because these ice shelves buttress glaciers feeding into them, their ocean-induced thinning is driving Antarctic ice-sheet loss today.

Link >> https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5510715/

One day, near the southern edge of Pine Island Glacier Ice Shelf, the researchers directly observed the strength of the melting process as they watched frigid,  seawater appear to boil on the surface like a kettle on the stove. To Jacobs, it suggested that deep water, buoyed by added fresh glacial melt, was rising to the surface in a process called upwelling. Jacobs had never witnessed upwelling first hand, but colleagues had described something similar in the fjords of Greenland, where summer runoff and melting glacier fronts can also drive buoyant plumes to the sea surface

Link >> https://www.earth.columbia.edu/articles/view/2815

The ice, the ocean and the atmosphere are all intrinsically linked, and in Antarctica we now see how complex changes in atmospheric circulation, driven by climate change and the ozone hole, are changing ocean circulation. Increased upwelling of warm, salty Circumpolar Deep Water is melting away the base of the ice shelves and the grounding lines of some of the largest, most vulnerable glaciers and ice streams in Antarctica, resulting in rapid, far-reaching and irreversible changes.

Link >> http://www.antarcticglaciers.org/glaciers-and-climate/ice-ocean-interactions/changes-circumpolar-deep-water/

[Stephan]

I will add some pictures from time to time to compare 2019 with earlier years.
This year the sea ice seems to be much more fragile than last year. I attach the photos from EOSDIS Oct 30, 2019 (upper) and Oct 30, 2018 (lower). Unfortunately there was no day without clouds, but I think you can get an idea of the difference of this year compared with last year.

PS: The orange circled iceberg is one of the remainders of last year's calving.

[Stephan]

To bring some more input into this thread I present a picture of the Pine Island Bay (N is to the left) from EOSDIS on Jan 11, 2020. To the lower right you can see the sea ice in front of Thwaites Eastern Ice Shelf, and in the upper right corner you can see the tip of the SW Tributary with its grounded icebergs.
It shows the decomposition of the sea ice NW of Velasco Glacier (circled in green).
I compared the situation with Jan 11 in the last years.
2019 the whole Pine Island Bay was filled with sea ice, so was 2018. 2017, after the big El Niño year the whole Pine Island Bay was free of sea ice, so was 2015. 2016 and 2014 had a mixed appearance. Most part of Pine Island Bay were ice-free, but that NE part of it (the area circled in green and N of it) had an almost complete sea ice cover.

See attached picture.

[paolo]

Stephan,
what you call "Velasco Glacier" is the NIS. The "Velasco Glacier" bounds the NIS to the north, see picture below.

added zoom

[Stephan]

Liberation of some sea ice between Thwaites and B-22 iceberg.
In the last month NW of Thwaites Ice Tongue the sea ice opened and fractured into hundreds of floes. They were kept prisoner between the fast ice in the south and the (slowly NW moving) iceberg B-22. With SW winds in the past week some of the ice could escape. Now the wind blows again from the SE. On the western end of that open sea there are a lot of grounded icebergs sitting on an underwater ridge. In addition a bigger iceberg has flown there and got stuck and blocked the flow-out of the sea ice. I have called it "Cork". Now a bigger part of it has calved and after that it turned counterclockwise (40°) to give way to the sea ice which is now slowly flowing out.

The first image shows the area I am writing about. Green circled is the open water with the sea ice on it. The orange square is the region of the "Cork" and the area of the second image.
The second image gives the details. All grounded icebergs are circled in yellow. So it is not easy for an ordinary sea ice floe to move around these obstacles...

[Stephan]

The freezing season has started in Southern Amundsen Sea.
As a follow-up to my last posting in this thread I must consider that most of the icebergs in the green circled area could not leave the open seas south of B-22. The cork has further turned counterclockwise and closed the gap almost completely. This movement was partly made possible by the further NW movement of B-22 (ca. 2 km in the last five weeks).
Three weeks ago the whole green circled area contained open waters with some icebergs. Now it has rapidly frozen. So I do not expect any further erosion of the fast ice south of it (as was observed massively last year). This will also support the ice west of the Thwaites Ice Tongue and Crosson Ice Shelf for the next months.

See attached picture.

[Stephan]

I had a look at the situation of sea ice along Pine Island Bay and came across to make a picture of each year since 2016 for a qualitative comparison.
All pictures come from around Dec 15-Dec 23, trying to find a real clear day isn't too easy.
What I find: 2016 had extraordinary low sea ice in that area, followed by 2018, 2019 and 2020. 2021 is among the years with the highest sea ice concentration, together with 2017. The distribution changes from year to year. Sometimes B-22 is surrounded by open waters and Pine Island Bay is full of ice, in other years it is the other way round.
I guess that sea ice stabilizes PIG, Thwaites and B-22 - so let's hope 2021 (soon 2022) will be on the "higher ice side" in this Austral summer.

See attached picture. I added some features and names for a better orientation. North is almost left.