Introduction | Topography | Oceanography | Ice streams and ice shelves | References | Comments |
Introduction
The West Antarctic Ice Sheet (the WAIS) is capable of rapid change as it is a marine ice sheet and therefore could be unstable. It has the potential to raise global sea level by 3.3 m[1] over a matter of centuries. The Transantarctic Mountains divide the West Antarctic Ice Sheet from the East Antarctic Ice Sheet[2]. West Antarctica is approximately 97% ice-covered, and is 1.97 x 106 km2 in area. The West Antarctic Ice Sheet flows into the Bellingshausen, Weddell, Amundsen and Ross seas.
There are principally three sectors of the ice sheet, which flow northeast-ward into the Weddell Sea, westward into the Ross Ice Shelf and northward into the Amundsen/Bellingshausen seas. The highest elevations reached are 3000 m above sea level[2], occurring at the divides between these sectors. The size of the West Antarctic Ice Sheet is limited, despite its high average snow falls, by the faster speeds of its ice streams.
Topography
The West Antarctic Ice Sheet is, in places, over 2000 m thick, with the geological floor well below sea level. The marine basins are variable, with both rough mountainous terrain and flat, deep oceanic basins[2], with a maximum depth of 2555 m below present sea level.
During past interglacials, the West Antarctic Ice Sheet has been completely removed[3], which is one of the arguments supporting a Marine Ice Sheet Instability hypothesis. During past glacials, the West Antarctic Ice Sheet extended to the continental shelf edge[4-6], drained by numerous ice streams[7, 8], such as the Pine Island and Thwaites ice streams, which flow out into the Amundsen Sea. In the four-panel figure opposite, you can see these two ice streams clearly. They are grounded below sea level and drain a large proportion of the West Antarctic Ice Sheet.
In the map below, showing ice thicknesses across the Antarctic continent, you can see that the West Antarctic Ice Sheet has ice thicknesses of up to 2000 m, but that it is largely grounded below sea level. The maximum altitude of the ice surface is less than 2000 m above sea level. The West Antarctic Ice Sheet is divided from the East Antarctic Ice Sheet by the large Transantarctic Mountains.
Oceanography
West Antarctica is surrounded by a strong clockwise circumpolar circulation. These currents play a significant role in the global thermohaline circulation, and are one of the reasons why Antarctica is so cold.
At shallower depths, Circumpolar Deep Water can move across the continental shelf and reach the underside of ice shelves[2], which it can rapidly melt due to its relatively warm temperatures.
Ice streams and ice shelves
The West Antarctic Ice Sheet is drained by several large ice streams. The basal sediments of West Antarctica comprise soft marine sediments. Combined with geothermal heating at the base, this is sufficient to allow glaciers to slide rapidly: see Glacial Processes. This ice flow is partly constrained by buttressing ice shelves. The ice streams flow from an inland reservoir of ice towards the ocean, passing over a grounding line and, in places, into an ice shelf. Nearly all the precipitation received in West Antarctica eventually passes through these ice streams[2].
Further reading
To learn more about the West Antarctic Ice Sheet, you can read:
- Ice Shelves
- Ice Streams
- Marine Ice Sheet Instability
- Antarctica’s contribution to global sea level rise
- Van den Broeke et al., 2011
Go to top or jump to Antarctic Peninsula Ice Sheet.
Go to top or jump to Antarctic Peninsula Ice Sheet.
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It seems to me from what you’re say here is that very big chunks will slide of & float away in a matter of months or years someday. Not decades or centuries that you state here as sudden. It doesn’t even have to float away just become ungrounded. Sliding just a few feet before lifting up for miles & miles at a time with little indication before hand, is really possible I’m sure, if the undermining ocean gets hot enough.
I agree with you. One day I defrosted my fridge while staying all the time in the kitchen. At first, nothing happened. Then it started to melt and to drip gently, then heavier and faster. And all of a sudden a big chunk of ice separated and fell off. I think we know very little about large ice mass dynamics because so far we never witnessed a large scale (or “big fridge”) defrosting. When one knows that huge cavities already exist underneath, the threat of this scenario is real.
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There should be a “water lift” at play. As the underside of the ice melts, it freshens the water in contact with it which should send a current flowing upward under the ice to flow out on the surface. This should suck in more of the slightly warm ocean water to further the melt. Instead of simple thermodynamics, you have a mass transfer situation (convection). As the grounding line gets deeper as the ice retreats on the retrograde slope, the water lift effect should increase.
This is very interesting.
What is the possibility of the entire east antarctic ice sheet “breaking” at the south pole & at Willis all the way around the coast to Mertz start a slow slide to the ocean. What are the conjunctions for something on this scale? Could a comet enter the atmosphere & break apart over where the ice shelves along the coast are? If enough heating along this entire coast inland and rapid melting along this area,could the buttressing of the shelf could be compromised?. Say this were to happen, at what speed would the entire east antarctic ice sheet start to slide or drift? What is the age of the ice within this?
Where did the BEDMAP2 image come from?
Because I didn’t find it in the Fretwell’s paper.
Thank you.
Hi, Thank you for your question. Information on the BEDMAP2 dataset can be found here Bedmap2: improved ice bed, surface and thickness datasets for Antarctica hope this helps.
Hi, I also want to know the reference of the BEDMAP2 image. But there is no same image in Fretwell’s paper and even in the paper, you replied.
Merry Christmas!
Thank you
Hi, the figure has been created using the data from Fretwell et al. The figure used on this webpage has been created by us for the purpose of this page.
How this helps.
Laura
Hi, I also want to know the reference to the BEDMAP2 image. But there is no same image in Fretwell’s paper; even in the paper, you replied ahead. Where can I find the reference? Thank you!
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