Geophysics
Massive Antarctic lakes discovered

Ice flow dynamics in Antarctica is a key understanding that is lacking in effective modeling of the impact of climate change. The recent discovery of a massive “plumbing” system of linked reservoirs 1,000 meters beneath two major ice streams of the West Antarctic Ice Sheet, however, may help fill out those models.

Ice streams are the principal conveyor of ice from the interior of a continental ice sheet to the ocean. The ice streams, which typically reach a width of 100 kilometers and move at a non-glacial pace of up to 1.5 meters per day, lubricate the ice sheet to allow it to slide piecemeal into the ocean. In recent years, researchers have discovered lakes beneath the giant ice sheets, but until now they had not realized how interconnected they are, says Helen Amanda Fricker of Scripps Institution of Oceanography (see Geotimes, March 2006). Understanding the relationships between the ice streams, lakes and ocean discharge, she says, “would help tremendously our understanding of how much sea levels will rise” with global climate change.

Using NASA’s ICESat weather satellite, Fricker and her team analyzed changes in ice stream thickness and topographic changes between 2003 and 2006. Those ice stream surface changes are due to the movement of water deep beneath the ice, the team reported Feb. 15 in Science Express.

The under-ice lake system works like a series of cascading pools at varying heights, Fricker says, with copious amounts of water flowing beneath the ice streams toward the ocean. “Previously, we thought the water under the ice flowed as a thin sheet, a millimeter thick or less,” says Robert Bindschadler of NASA Goddard Space Flight Center, a co-author on the study.

The team was also surprised to find a series of large subglacial lakes beneath the ice streams, with one lake alone holding water volumes equal to that of Lake Ontario, Fricker says. Additionally, the researchers were shocked at the volume of discharge: One subglacial lake discharged about 2 cubic kilometers of water in just three years. “We didn’t realize that the water under these ice streams was moving in such large quantities, and on such short timescales,” she says. “We thought these changes took place over years and decades, but we are seeing large changes over months.”

Indeed, Bindschadler says, “every time we think we have a handle on the timescales we’re dealing with, they end up changing faster than we think.”

Although this study will allow researchers to improve their physical models of the water’s movement, researchers are still not clear on how the lakes affect the rates of glacial melting and whether they cause ice streams to move faster or slow down. Antarctic ice streams require subglacial water to activate their fast flows, says Garry Clarke, a glaciologist at the University of British Columbia. Thus, “anything that affects the distribution of water [under] ice streams should affect” the flow.

This study “is drawing a lot of attention,” Clarke says. “It is truly splendid to discover that we can learn a lot about subglacial [water] processes without actually drilling through the ice.” The new research provides glaciologists with new tools that make possible measurements that used to require dangerous and expensive drilling.

Sally Adee
Geotimes contributing writer

Links:
"Great lakes of Antarctica," Geotimes, March 2006

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