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West Antarctic Ice Sheet
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The West Antarctic Ice Sheet (WAIS) is the segment of the continental ice sheet that covers West (or Lesser) Antarctica, the portion of Antarctica west of the Transantarctic Mountains. The WAIS is classified as a marine-based ice sheet, meaning that its bed lies well below sea level and its edges flow into floating ice shelves. The WAIS is bounded by the Ross Ice Shelf, the Ronne Ice Shelf, and outlet glaciers that drain into the Amundsen Sea.
Contents [hide]
1 Description
2 Potential collapse of the WAIS
3 Impact of Greenland ice sheet melting
4 References
5 See also
6 External links
[edit] Description
A satellite composite image of AntarcticaIt is estimated that the volume of the Antarctic ice sheet is about 25.4 million km3, and the WAIS contains just under 10% of this, or 2.2 million km3.[1] This enormous weight has caused the underlying rock to sink by between 0.5 and 1 kilometres[2] in a process known as isostatic depression.
Under the massive forces of their own weight, the ice sheets deform and drag themselves outward. The interior ice flows slowly over rough bedrock. Away from the interior, the ice is channelled into ice streams, transporting ice from the center of the continent to the sea. These streams are separated by slow-flowing ice ridges. The inter-stream ridges are frozen to the bed while the bed beneath the ice streams consists of water-saturated clay. The clay was deposited before the ice sheet occupied the region, when much of West Antarctica was a marine seaway. The rapid ice-stream flow is due to the water-saturated clay.
When ice streams finally reach the coast and push out across the ocean, they pass over rocky terrain, anchoring themselves to the irregular rocks to form a hinge. The ice will continue to grow outward onto the water. The result is a large, floating shelf of ice affixed to the continent. [3]
[edit] Potential collapse of the WAIS
In January 2006, in a UK government-commissioned report, the head of the British Antarctic Survey, Chris Rapley, warned that this huge west Antarctic ice sheet may be starting to disintegrate, an event that could raise sea levels by at least 5 metres (16 ft). Estimates by others have ranged from 6 to 15 m (20–50 ft). Rapley said a previous Intergovernmental Panel on Climate Change report playing down worries about the ice sheet's stability should be revised. "The last IPCC report characterized Antarctica as a slumbering giant in terms of climate change," he wrote. "I would say it is now an awakened giant. There is real concern." [4]
Rapley said, "Parts of the Antarctic ice sheet that rest on bedrock below sea level have begun to discharge ice fast enough to make a significant contribution to sea level rise. Understanding the reason for this change is urgent in order to be able to predict how much ice may ultimately be discharged and over what timescale. Current computer models do not include the effect of liquid water on ice sheet sliding and flow, and so provide only conservative estimates of future behaviour." [5]
Jim Hansen, a senior NASA scientist who is a leading climate adviser to the US government, said the results were deeply worrying. "Once a sheet starts to disintegrate, it can reach a tipping point beyond which break-up is explosively rapid," he said. [6]
Indications that climate change may be affecting the west Antarctic ice sheet comes from three glaciers, including Pine Island and Thwaites. Data reveal they are losing more ice - mainly through the calving of icebergs - than is being replaced by snowfall. According to a preliminary analysis, the difference between the mass lost and mass replaced is about 60%. The melting of these three glaciers alone is contributing an estimated 0.24 millimetres per year to the rise in the worldwide sea level.[4]
[edit] Impact of Greenland ice sheet melting
While models predict significant melting of the Greenland ice sheet as summer temperatures in the Arctic rise by between 3 and 5 ºC (5.4–9 ºF), most models suggest that the ice sheets of Antarctica will remain more stable. However, historical data shows that the last time that Greenland became this warm, the sea level rise generated by meltwater destabilised the Antarctic ice. That means that the models of sea-level rise used to predict an increase of up to 1 m (3 ft) by 2100 may have significantly underestimated its ultimate extent, which could be as great as 6 m (20 ft). [7] [8]
This conclusion emerged from a study that used data from ancient coral reefs, ice cores and other natural records to reconstruct the climate during the last gap between Ice Ages, between 129,000 and 116,000 years ago. Scientists used computer models to show that meltwater from Greenland raised the sea level by up to 3.4 m (11 ft), but coral records showed that the total global rise was between 4 and 6 m (13–20 ft). The most likely explanation is the melting of Antarctic ice sheets: as sea levels rose, the floating ice shelves off the coast of the continent would have become more likely to break up. That in turn would have allowed glaciers to dump more ice from the continent itself into the sea. The base of the West Antarctic ice sheet lies below sea level, which allows ice to escape to the sea easily.[7] [8]
[edit] References
^ Lythe, Matthew B. & Vaughan, David G. (Jun 2001), "BEDMAP: A new ice thickness and subglacial topographic model of Antarctica", Journal of Geophysical Research 106 (B6): 11335–11352, DOI dx.doi.org
^ Anderson, John B. (1999), Antarctic marine geology, Cambridge University Press, p. 59, ISBN 0521593174, <http://books.google.com/books?id=f9YqF73oe4IC>
^ Ice Shelves, Antarctic and Southern Ocean Coalition,
^ a b Jenny Hogan, "Antarctic ice sheet is an 'awakened giant'", New Scientist, February 2, 2005
^ "West Antarctic ice sheet: Waking the sleeping giant?", Symposium, February 19, 2006
^ Jonathan Leake and Jonathan Milne, "Focus: The climate of fear", The Sunday Times - Britain, February 19, 2006
^ a b "London 'under water by 2100' as Antarctica crumbles into the sea", The Times (UK), March 24, 2006
^ a b Otto-Bliesner, Bette L.; Marshall, Shawn J. & Overpeck, Jonathan T. et al. (24 March 2006), "Simulating Arctic climate warmth and icefield retreat in the last interglaciation", Science 311 (5768): 1751–1753, DOI dx.doi.org
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