Glacial lubrication.
This is the first view of a channel cut out of the Antarctic continental shelf by high pressure "ice streams" that flow beneath the ice sheet.

Polar Science from the Deep--Part III

John is a Science contributing correspondent.

The research vessel JCR has now dropped anchor at the Rothera research station on the Antarctic Peninsula, and the scientists are flying back home today via Punta Arenas, Chile. As they were pulling in, the researchers emailed ScienceNOW one last dispatch. Their first report which included images from the remote-controlled vehicle Isis under 3500 meters of water, the deepest dive ever in the Southern Ocean--focused on the Antarctica's geologic past. The second dispatch found evidence of a biological invasion in the making. The final word from the JCR concerns the future.

One of the most fearsome possible consequences of climate change is a major rise in sea levels. How high--and how fast--the seas will rise depends mostly on how much ice will slide off its perch on continental bedrock into the oceans. Scientists have had major difficulties figuring out what causes glaciers to break away from land because they don't have access to the bottom where the action is, says Rob Larter, a marine geophysicist with the British Antarctic Survey in Cambridge, U.K. "All proposed mechanisms for fast glacier flow require an ample supply of water at the ice bed," he wrote from the ship yesterday. Sonar imaging has revealed what look like meltwater channels beneath the Antarctic ice sheet. And last year, researchers spotted signs of water moving beneath the Antarctic ice sheet in satellite data (ScienceNOW, 19 April 2006).

Why is it so hard to study the base of ice sheets? The ice sheet is up to 4 kilometers thick, which hampers the use of seismic and other geophysical probes. Only a handful of very expensive holes have ever been drilled into the bed. There is a good view, however: 10,000 years ago, glaciers retreated rapidly from some parts of the continental shelf around Antarctica, leaving the former ice sheet bed "perfectly preserved," Larter says, albeit under 500 meters of water. So Isis visited the bottom of the ice sheet's leading edge last week for a first-hand look.

The images sent up provide the first views of "ice streams" flowing beneath the Antarctic glaciers into the ocean. The meltwater has flowed long and fast enough to cut channels into the bedrock, says Larter. "What we have found is one piece of the machinery that operates in large ice sheets, which puts us one step nearer being able to reliably model how they behave." With a single image, all models of ice flow that do not include subglacial water can now be ruled out. (Most models do, however). The implications for predicting sea level changes will take some time to sort out, Larter says.

Expect to hear more from the JCR cruise later this year as the scientists piece together their cache of data. But for now, it's time to get used to life on land once again.

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