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The West Antarctic Ice Sheet (WAIS) blankets the continent of Antarctica west of the Transantarctic Mountains, covering the area called "Lesser Antarctica". 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. It is estimated that it contains seven million cubic miles of ice.
Description
The weight of Antarctica's ice is so enormous that it has literally pressed the continent two thirds of a mile into the earth. 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 anomalously fast-flowing 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. http://www.asoc.org/general/iceshelve.htm
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 16 feet. by others have ranged from 20 to 50 feet. 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." http://www.newscientist.com/article.ns?id=dn6962
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." http://www.innovations-report.com/html/reports/earth_sciences/report-55525.html
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. http://www.timesonline.co.uk/article/0,,2087-2047195_3,00.html
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 one-tenth of an inch per year to the rise in the worldwide sea level. http://www.newscientist.com/article.ns?id=dn6962
Impact of Greenland ice sheet melting
While the Greenland ice sheet is expected to start melting as summer temperatures in the Arctic rise by 3C degrees to 5C (5.4F-9F), most models suggest that the ice sheets of Antarctica will remain more stable.
The historical data, however, show that the last time that Greenland became this warm, the sea level rise generated by meltwater destabilised the Antarctic ice, leading to a much higher increase than can be explained by Arctic ice alone.
That means that the models of sea-level rise used to predict an increase of up to 3 feet by 2100 may have significantly underestimated its ultimate extent, which could be as great as 20 feet. *
References
External links
"West Antarctic Ice Sheet"