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Antarctic glacier melt explained

Antarctic glacier melt is a major cause of rising sea levels. With the help of a robotic underwater vehicle, scientists have now determined why one big glacier is disappearing.

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Connection to climate change?

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What caused the initial separation of the glacier from the ridge is uncertain.

"We do not know what kick-started the initial retreat from the ridge, but we do know that it started some time prior to 1970," said study leader Adrian Jenkins of the British Antarctic Survey.

Researchers only began to closely study Pine Island Glacier in the 1990s, so there are no direct observations of the glacier before and during its separation from the ridge. To learn more about that process, scientists will need to use ice cores (long cylinders of ice drilled from glaciers that show the successive layers of ice that formed over the years) and computer modeling to figure exactly what happened, Jenkins said.

Learning more about that process "is vital for evaluating the risk of the potential widespread collapse of West Antarctic glaciers," he said.

The case of Pine Island Glacier does present cause for concern, the scientists say.

"Since our first measurements in the Amundsen Sea, estimates of Antarctica's recent contributions to sea level rise have changed from near-zero to significant and increasing," said study team member Stan Jacobs of Columbia University's Lamont-Doherty Earth Observatory in New York. "Now finding that the [Pine Island Glacier]'s grounding line has recently retreated more than 30 km [19 miles] from a shallow ridge into deeper water, where it is pursued by a warming ocean, only adds to our concern that this region is indeed the 'weak underbelly' of the West Antarctic Ice Sheet."

The study of Pine Island Glacier was detailed in the June 20 early issue of the journal Nature Geoscience.

IN PICTURES: Antarctica