West Antarctic Ice Sheet

West Antarctic Ice Sheet

Discussion
Ask a question about 'West Antarctic Ice Sheet'
Start a new discussion about 'West Antarctic Ice Sheet'
Answer questions from other users
Full Discussion Forum
 
Encyclopedia
The '''West Antarctic Ice Sheet''' ('''WAIS''') is the segment of the [[Antarctic ice sheet|continental ice sheet]] that covers [[West Antarctica|West (or Lesser) Antarctica]], the portion of [[Antarctica]] on the side of the [[Transantarctic Mountains]] which lies in the [[Western Hemisphere]]. 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]]. ==Description== [[File:West-antarctica.png|thumb|200px|A map of West Antarctica]] It 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. The weight of the ice has caused the underlying rock to sink by between 0.5 and 1 kilometres in a process known as [[Isostasy|isostatic depression]]. Under the force of its own weight, the ice sheet deforms and flows. The interior ice flows slowly over rough [[bedrock]]. In some circumstances, ice can flow faster in [[ice stream]]s, 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 [[sediment]]s. Many of these sediments were deposited before the ice sheet occupied the region, when much of West Antarctica was covered by the ocean. The rapid ice-stream flow is a non-linear process still not fully understood; streams can start and stop for unclear reasons. When ice reaches the coast, it will continue to flow outward onto the water. The result is a large, floating shelf of ice affixed to the continent. ==Potential collapse== [[File:AntarcticBedrock.jpg|thumb|250px|A topographic and [[bathymetry|bathymetric]] map of Antarctica without its ice sheets, assuming constant sea levels and no [[post-glacial rebound]].]] Large parts of the WAIS sit on a bed which is below sea level and slopes downward inland. This slope, and the low isostatic head, mean that the ice sheet is theoretically unstable: a small retreat could in theory destabilize the entire WAIS leading to rapid disintegration. Current [[ice sheet model|computer models]] do not include the physics necessary to simulate this process, and observations do not provide guidance, so predictions as to its rate of retreat remain uncertain. This has been known for decades.{{citation needed|date=March 2011}} 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. It has been hypothesised that this disintegration could raise sea levels by approximately 3.3 metres (10 ft). (If the entire West Antarctic Ice Sheet were to melt, this would contribute 4.8 m to global sea level.) Rapley said a previous [[Intergovernmental Panel on Climate Change]] (IPCC) report that played down the worries of 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." Note that the IPCC report did not use the words "slumbering giant". 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." [[James E. Hansen]], a senior NASA scientist and leading climate expert, 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. Indications that the West Antarctic Ice Sheet is losing mass at an increasing rate come from the [[Amundsen Sea]] sector, and three glaciers in particular: the [[Pine Island Glacier|Pine Island]], [[Thwaites Glacier|Thwaites]] and [[Smith Glacier]]s. Data reveal they are losing more ice 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. There is growing evidence that this trend is accelerating: there has been a 75% increase in Antarctic ice mass loss in the ten years 1996–2006, with glacier acceleration a primary cause. Polar ice experts from the U.S. and U.K. met at the [[University of Texas at Austin]] in March, 2007 for the [http://www.jsg.utexas.edu/walse/ West Antarctic Links to Sea-Level Estimation (WALSE) Workshop]. The experts discussed a new hypothesis that explains the observed increased melting of the West Antarctic Ice Sheet. They proposed that changes in air circulation patterns have led to increased upwelling of warm, deep ocean water along the coast of Antarctica and that this warm water has increased melting of floating [[Ice shelf|ice shelves]] at the edge of the ice sheet. An ocean model has shown how changes in winds can help channel the water along deep troughs on the sea floor, toward the ice shelves of outlet glaciers. The exact cause of the changes in circulation patterns is not known and they may be due to natural variability. However, this connection between the atmosphere and upwelling of deep ocean water provides a mechanism by which human induced climate changes could cause an accelerated loss of ice from WAIS. Recently published data collected from satellites support this hypothesis, suggesting that the west Antarctic ice sheet is beginning to show signs of instability. ==Warming== The West Antarctic ice sheet has warmed by more than 0.1 °C/decade in the last 50 years, and is strongest in winter and spring. Although this is partly offset by fall cooling in East Antarctica, this effect is restricted to the 1980s and 1990s. The continent-wide average surface temperature trend of Antarctica is positive and [[Statistical significance|significant]] at >0.05°C/decade since 1957. This warming of WAIS is strongest in the Antarctic Peninsula. ==See also== * [[East Antarctic Ice Sheet]] * [[List of glaciers in the Antarctic]] * [[WAIS Divide]] Ice Core Drilling Project ==External links== * [http://www.jsg.utexas.edu/news/feats/2007/crystal_ball.html Crystal Ball: Scientists Race to Foretell West Antarctica's Unclear Future] * [http://neptune.gsfc.nasa.gov/wais/ WAIS – West Antarctic Ice Sheet Initiative] – A multidisciplinary study of rapid climate change and [[future sea level]]. Sponsored by [[National Science Foundation]] Office of Polar Programs and [[NASA]] Earth Science. * [http://nsidc.org/data/waiscores/index.html U.S. National Snow and Ice Data Center Antarctic Data] * [http://www.commondreams.org/headlines05/0202-04.htm Dramatic change in West Antarctic ice could produce 16ft rise in sea levels] * [http://www.jsg.utexas.edu/walse/statement.html U.K. and U.S. Polar Ice Experts Urge Improved Monitoring to Reduce Uncertainty over Potential Sea-Level Rise] * [http://www.sciencedaily.com/releases/2004/09/040927082256.htm Structure Found Deep Within West Antarctic Ice Sheet], September 2004 {{coord missing|Antarctica}}