Enhanced Propagation of Atmospheric Waves Over the Last 30 Years: the Teleconnection Between Increased Tropical Sea Surface Temperatures and West Antarctic Warming.

A new study just published (April 10, 2011) in Nature Geoscience by UW scientists Quinghua Ding, Eric Steig and Marcel Kuttel, Quaternary Research Center and Earth & Space Sciences, and David Battisti, Atmospheric Sciences, argues that recent warming in West Antarctica, which is strongest in winter and spring, has been caused by the increase in tropical sea surface temperatures which increases the occurrence of Rossby wave trains. This teleconnection was previously shown to be important in West Antarctica only during some El Nino events.

Observational data was used in the present study to show a strong statistical link between temperatures in West Antarctica, atmospheric circulation over the Amundsen Sea, and sea surface temperatures (SST’s) in the central equatorial Pacific. The observed changes in tropical SST’s can account for between half and all of the observed change in West Antarctic winter temperatures in the last 30 years.

In an independent paper published in January in the journal Climate Dynamics, researchers at the NSF-sponsored National Center for Atmospheric Research made a similar argument to that of Ding and co-authors, but focused on changes in austral spring. David Schneider, lead author of the Climate Dynamics paper, notes that spring, rather than winter, is the season with the greatest observed warming across West Antarctica, and that temperatures there are highly correlated with sea ice loss in the adjacent Amundsen and Bellingshausen Seas. The sea ice loss and the West Antarctic warming have both been influenced by warming in the tropics, Schneider and his co-authors argued. Schneider was a student of Eric Steig's in ESS, and completed his PhD in 2005. Steig notes that both papers were written entirely independently and he was surprised and delighted by the confluence of ideas.

Steig says that all these results have implications for the dynamics of the West Antarctic ice sheet. The atmospheric circulation changes discussed in their paper are associated with increased westerlies in the Amundsen Sea Embayment, where the fast moving Pine Island and Thwaites Glaciers have accelerated in recent decades. The most commonly hypothesized cause of that acceleration is melting from below, due to the heat supplied by upwelling circumpolar deep water (CDW) under the floating margins of these glaciers. Increased upwelling of CDW, in turn, is likely a response to increased westerlies. The timing, notes Steig, is intriguing: the biggest shift in tropical Pacific SSTs, and also in Amundsen Sea Embayment winds occurred between the 1980s and 1990s. It was in the early 1990s that the most recent accelerations of Pine Island and Thwaites Glaciers began. A similar timing was first recognized during a chance meeting between David Battisti and the British Antarctic Survey’s Adrian Jenkins, a glaciologist who has published some of the important work demonstrating the link between ocean circulation and glacier melting under Pine Island Glacier. The group is now teaming up with Jenkins on another paper, currently in preparation.

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