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Warm Ocean Currents Main Cause of Antarctic Ice Loss

Bottom melting of ice shelves from a changing climate allows increased glacier discharge into the ocean Michael Van Woert, NOAA NESDIS, ORA

Warm ocean waters are melting the base of numerous ice shelves around Antarctica which increases the discharge of ice into the ocean from inland glaciers flowing down to the coast, according to a study recently published in Nature. The study, which was headed by Dr. Hamish Pritchard of the British Antarctic Survey, establishes this process as the main factor in the recent mass loss of the Antarctic ice sheet and as a contributory factor to rising sea levels.

There are two known ways in which ice shelves can melt: from above, by warm air, or from below, by warm ocean waters. Accurately differentiating between the two has proven to be extremely difficult. In this study, however, Pritchard and team used approximately 4.5 million measurements made by a laser instrument mounted on NASA's ICESat satellite to deduce the source of any changing thickness. Fifty-four ice shelves were mapped of which 20 were found to be melting from below with the most rapid and widespread losses – up to 6.8 meters (22.3 feet) per year – occurring on Antarctica’s western coast. These results were compared with previous monitoring studies of the glaciers feeding into them. In each case where there was ice shelf melting from ocean waters, the tributary glaciers had accelerated and were thus draining more ice into the ocean. The research team attributed the increase in glacier velocity to reduced buttressing by the thinning ice shelves.

But why is this happening now? “We think that it's linked to changes in wind patterns,” Pritchard said in a statement. “Studies have shown that Antarctic winds have changed because of changes in climate, and that this has affected the strength and direction of ocean currents. As a result warm water is funneled beneath the floating ice. These studies and our new results therefore suggest that Antarctica's glaciers are responding rapidly to a changing climate."

Source:  Pritchard, H.D. et al.  2012.  Antarctic ice-sheet loss driven by basal melting of ice shelves.  Nature 484(7395): 502-505.

Contact: Hamish Pritchard, British Antarctic Survey, Cambridge, UK.  E-mail: h.pritchard@bas.ac.uk

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