Ice shelves in west Antarctica's Amundsen Sea Embayment are fraying at the edges, a new study suggests.
Ice shelves are the frozen, floating platforms of ice that mark where land ice -- a glacier or an ice sheet -- meets the ocean. They lose ice by calving or breaking off icebergs from their leading edge, where ice meets water.
Photograph of an ice shelf by Damerau
But new research shows that, at least in one region of Antarctica, ice shelves are also losing ice from their sides, or margins.
"You essentially have a seam," where either two different ice shelves meet or an ice shelf meets rocky bay walls, said lead author Joseph MacGregor, a glaciologist at the University of Texas, Austin.
"Where that is is often cracked. When the ice floats, it cracks further," he said. "And that margin is vulnerable to retreat. The places where two glaciers meet is often where retreat has been the largest."
While ice shelves normally calve icebergs from their front faces -- causing the front edge of the ice to retreat closer to shore -- the ice normally recovers by readvancing steadily over time.
Where glaciers can lose their grip
But in the Amundsen Sea Embayment, home to the Thwaites, Pine Island, Smith and Haynes glaciers, "that's not what we saw at the margins," MacGregor said.
Instead, along those margins, ice cracked and pieces broke off -- and in response, the ice sheet retreated, rather than slowly advancing.
"The only way you can tease this apart is looking at the long-term record," said MacGregor. He and his colleagues examined images of the study region collected between 1972 and 2011 by the federal government's Landsat satellites.
The researchers believe the phenomenon could further accelerate the rapid thinning of the region's glaciers.
"It's decreasing the resistance of the ice shelf to flow," MacGregor said. "Eventually, what you could end up with is losing all grip from the sides."
The researchers believe the ice shelves will continue to shrink at their margins as the glaciers to which they are connected keeping thinning and accelerating.
The study was published in the latest issue of the Journal of Glaciology.
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