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.

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...