Warm Ocean Waters are Speeding Greenland Glacier Melt

According to newly published letter from NASA and university researchers in Nature Geoscience (Rapid submarine melting of the calving faces of West Greenland glaciers, 14 Feb. 2010),  at the lower reaches of west Greenland glaciers -- where the glaciers terminate in ocean waters--  the submerged portions of the glaciers are melting 100 times faster than the above water areas of the glaciers where warm air temperatures drive the melting. 

In the same issue of Nature Geoscience, a separate group of researchers report (Rapid circulation of warm subtropical waters in a major glacial fjord in East Greenland) that warming subtropical waters are circulating under the ice, causing "enhanced submarine melting at the glacier terminus."

Greenland glacier ice melt

Though not one of the glaciers studied by the researchers who reported their findings in Nature Geoscience, the Ilulissat Glacier is in the same region -- and is rapidly receding. Source: Extreme Ice Survey

The findings are consistent with those of a third group of researchers who reported in 2008 (Acceleration of Jakobshavn Isbræ triggered by warm subsurface ocean waters, Nature Geoscience) that a rapid acceleration of the Greenland's Jakobshavn Isbræ glacier during the previous decade was linked to "a sudden increase in subsurface ocean temperature in 1997 along the entire west coast of Greenland."  That in turn resulted from "the arrival of relatively warm water originating from the Irminger Sea near Iceland" related to "changes in the atmospheric circulation in the North Atlantic region."

The magnitude and significance of the underwater melting has not until now been fully appreciated. The only earlier measurements of undersea glacier melt occurred in Alaska; and due to lack of data, only sparse understanding exists about the rates of melting and its affects on glaciers.

Eric Rignot, co-author of last week's Nature Geoscience letter on submarine melting, is a researcher at the University of California, Irvine and at NASA’s Jet Propulsion Laboratory (JPL). In a press release issued by JPL ( NASA Finds Warmer Ocean Speeding Greenland Glacier Melt), he said:

"All major Greenland glaciers end up in the ocean, and tidewater glaciers control 90 percent of the ice discharged by Greenland into the sea. Submarine melting may therefore have a large indirect impact on the ice mass budget of the entire Greenland Ice Sheet. If we are to determine the future of the Greenland Ice Sheet more reliably in a changing climate, more complete and detailed studies of the interactions between ice and ocean at the ice sheet's margins are essential." [emphasis added]

The melting of the Greenland Ice Sheet is important because of its impact on sea level rise, particularly on the U.S. East Coast (see Sea Level Rise May Pose Greatest Threat to Northeast U.S., Canada, press release, 27 May 2009, from the National Science Foundation). According to the JPL press release, Greenland’s loss of ice mass tripled between 1996 and 2007.

Research shows melting is occurring faster than previously anticipated. Findings reported in the journal Hydrological Processes (Greenland Ice Sheet surface mass-balance modelling and freshwater flux for 2007, and in a 1995-2007 perspective, published online June 2009) revealed that in the 13 years from 1995-2007, the Greenland Ice Sheet may have been responsible for nearly 25 percent of the global sea rise. The study also showed that sea level rise is now occurring 50 percent faster than the average for the 20th century.

The implications of last week's Nature Geoscience findings are ominous.  In its report, Abrupt Climate Change, the U.S. Global Change Research Program (USGCRP) in December 2008 concluded that "The interaction of warm waters with the periphery of the large ice sheets represents one of the most significant possibilities for abrupt change in the climate system."

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