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Under-ice floods speed glaciers towards the sea

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Scientists have reported the first direct evidence of a link between flooding underneath the Antarctic ice sheet and the rate at which glaciers are discharged into the sea. The study, which was published online on Nature Geoscience yesterday [subscription], has important implications for understanding how ice released into the ocean from the Greenland and Antarctic land masses could raise sea level.

Led by Leigh Stearns of the Climate Change Institute at the University of Maine, the trio of researchers found that ice on the Byrd Glacier in East Antarctica accelerated just as there was a massive release of water from lakes beneath the ice.

Over the past 20 years, researchers have discovered more than 150 lakes beneath the Antarctic ice pack, the largest of which (Lake Vostok) is equal in size to Lake Ontario in Canada.

And more than a year ago, researchers reported that these subglacial lakes could actually lubricate the flow of ice off the continent and into the ocean, as I reported over on Nature News at the time.

But up until now, scientists have been missing the crucial observations to verify that discrete flooding events beneath the ice can speed up the rate of ice movement downstream. Writing in a News and Views article also on Nature Geoscience, Helen Amanda Fricker of Scripps Institution of Oceanography in La Jolla, California points out that it’s been difficult to do this because ‘the subglacial environment is one of the least accessible places on Earth for data collection’. Also, often different scientists are working on ice flow and subglacial flooding independent of each other. Fricker explains that in fact two of the scientists involved in the study were working independently until they discovered the exciting connection between their data during a coffee break at last year’s AGU Fall Meeting.

So, they combined a 48-year record of ice velocity measurements from the Byrd Glacier in East Antarctica with ice-penetrating data from the Ice, Cloud and Land Elevation Satellite (ICESat), which was launched in 2003. The ice velocity data showed that the glacier picked up speed by about 10% between December 2005 and February 2007, while the satellite data showed that there was a simultaneous release of 1.7km3 of water from lakes under the ice.

The subglacial flooding isn’t thought to be related to climate change, but the study should help scientists to better understand the movement of ice masses, and provide more accurate data on glacier dynamics for climate models.

Olive Heffernan

IMAGE: Byrd Glacier, Antarctica in April 2007. NASA


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