Breakup of the shelves can accelerate the flow of continental ice to the sea, contributing to sea-level rise, and the Antarctic shelves 'are melting too fast,' the study's lead author says.
Emperor penguins walk across sea ice near Ross Island, Antarctica. New research finds the frozen continent's ice shelves melting at an alarming rate.
Courtesy Thomas Beer/AP/File
EnlargeSeveral small ice shelves along the East Antarctic coast appear to be melting at surprisingly high rates, some at rates comparable to those of shelves in West Antarctica, long a center of concern over the impact of climate change on the region's vast ice sheet and sea-level rise.
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This is an unexpected result of a new study that documents the current status of ice shelves around Antarctica's coastline and the relative influence of the factors melting them.
It's unclear if the unexpected melt rates represent a trend. Conditions off the East Antarctic coast have been less-well studied than those off of West Antarctica, notes Stanley Jacobs, a researcher at Columbia University's Lamont-Doherty Earth Observatory in Palisades, N.Y., and a member of the team reporting its results in the current issue of the journal Science.
The cause also is unclear. But a lead suspect is relatively warm water that deep currents drive up onto the continental shelf. This water melts the ice shelves from underneath.
Still, "the numbers were a little bit larger than we were expecting ? about the same as for shelves on the West Antarctic Ice Sheet," Dr. Jacobs says.
Ice shelves are the leading edges of glaciers that flow from the continental interior into bays and fjords. Friction with a bay's sides or with raised features on the sea floor turn the buoyant ice shelves into brakes that slow the pace at which the glacial ice upstream moves toward the sea. The last area where the ice touches sea floor is known as the grounding line.
Relatively warm water, driven by deep-ocean currents up onto the continental shelf, can melt the shelves from underneath. The water-induced melting also can cause the grounding line to retreat. Both are thought to contribute to the break-up, or calving, of the ice shelves into icebergs. On the shelf surface, meltwater can work its way into crevasses, freeze, and act as a wedge to help cleave the ice.
"Ice shelf melt doesn't necessarily mean an ice shelf is decaying; it can be compensated by the ice flow from the continent," notes Eric Rignot, a professor of earth science at UC Irvine and the study's lead author. "But in a number of places around Antarctica, ice shelves are melting too fast."
Excessive breakup of the shelves can accelerate the flow of continental ice to the sea, contributing to sea-level rise.
Some of the most dramatic break-ups have occurred along the Antarctic Peninsula, a region of the continent that has seen some of the most pronounced warming on the planet ? warming most climate scientists attribute to the build-up of greenhouse gases in the atmosphere from burning fossil fuel and from land-use changes.
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