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October 10, 2008

Wind-induced circulation changes in the ocean are the dominant cause of the recent ice losses through the glaciers draining both the Greenland and West Antarctic ice sheets, not "global warming," according to two new studies.

The first study, published in Nature Geoscience, found that there has been a rapid acceleration of several outlet glaciers in Greenland and Antarctica; most notably, Jakobshavn Isbræ, a large outlet glacier feeding a deep-ocean fjord on Greenland's west coast, which went from a slow thickening to a rapid thinning in 1997:

  • Researchers found a sudden increase in subsurface ocean temperature in 1997 along the entire west coast of Greenland, suggesting that the changes in Jakobshavn Isbræ were triggered by the arrival of relatively warm water originating from the Irminger Sea near Iceland.
  • They traced these oceanic changes back to changes in the atmospheric circulation in the North Atlantic region.
  • In conclusion, they predict that future rapid dynamic responses of other outlet glaciers to climate change will require an improved understanding of the effect of changes in region ocean and atmosphere circulation on the delivery of warm subsurface waters to the periphery of the ice sheets.

The second study, published in Geophysical Research Letters, focused on the delivery of Circumpolar Deep Water (CDW) to the inner continental shelf around Pine Island Bay (Antarctica).  The most significant result was that temperature changes in CDW related to regional wind forcing:

  • Easterly winds over the shelf edge change to westerlies when the Amundsen Sea Low migrates west and south in winter/spring.
  • This drives seasonal on-shelf flow, while inter-annual changes in the wind forcing lead to inflow variability on a decadal timescale.
  • A modeled period of warming following low CDW influx in the late 1980's and early 1990's coincides with a period of observed thinning and acceleration of Pine Island Glacier.

Source: Paul Biggs, "Winds are Dominant Cause of Greenland and West Antarctic Ice Sheet Losses," Climate Research News, October 3, 2008; based upon: David M. Holland, et al., "Acceleration of Jakobshavn Isbræ triggered by warm subsurface ocean waters," Nature Geoscience, September 2008, and Malte Thoma, "Modelling Circumpolar Deep Water intrusions on the Amundsen Sea continental shelf, Antarctica," Geophysical Research Letters, Vol. 35, 2008.

For Nature Geoscience study: 

For Geophysical Research Letters study: 


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