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Thaw at Antarctica’s Fringes Speeds Melting Far Inland

The thinning of even small portions of floating ice along Antarctica’s coast can accelerate the loss of ice grounded on rocks hundreds of miles away, a new study finds.

(CN) – The thinning of even small portions of floating ice along Antarctica’s coast can accelerate the loss of ice grounded on rocks hundreds of miles away, a new study finds.

Though researchers know that ice shelves surrounding the continent control the flow of ice from land into the ocean, it had been assumed this ice flow is most susceptible to melting at the base near the grounding line, where ice enters the sea and becomes afloat.

However, melting within and along the fringes of ice shelves can directly affect ice very far inland which in turn stimulates sea-level rise, a team of scientists reports Monday in the journal Nature Climate Change.

“Destabilizing the floating ice in some areas sends a signal as far as 900 kilometers (559 miles) across the largest ice shelf in Antarctica, which is in itself larger than Germany,” said lead author Ronja Reese, a doctoral student at the Potsdam Institute for Climate Impact Research (PIK). “It does so with an amazing speed, similar to the speed with which shocks from an earthquake travel.”

Observations show Antarctic ice shelves are thinning, which makes it important to calculate the resulting impact on large ice masses on land.

The team simulated the ice flows to examine this possible side effect of global warming.

“While the air above most of Antarctica is constantly below the freezing point, the main risk for ice stability comes from the depths of the surrounding sea,” said co-author Ricarda Winkelmann, Reese’s advisor at PIK. “Warmer water offshore that accesses cavities beneath the ice shelves can thin the floating ice.”

This melting does not add to sea-level rise as the ice is already in the ocean.

“However, the ice shelves are of huge importance because they buttress the ice flow from the grounded ice into the ocean,” Winkelmann said. “Changes in the ice shelves can have a huge impact on the stress balance at the grounding line of the continental ice masses.

“This process is actually the main reason for the currently observed sea level contribution of Antarctica.”

The study is the first to systematically quantify the impact of the thinning of ice shelves around Antarctica, according to co-author Hilmar Gudmundsson, a researcher with the British Antarctic Survey.

“We had thought that the impact might be significant, now we know that it is,” Gudmundsson said.

The team identified the areas of floating ice that can produce the strongest response and found these regions are located at the fringes of some ice shelves, in addition to the grounding lines of ice streams and ice rises. Particularly sensitive fringes are typically near Antarctica's surrounding waters, which are warmer.

Some of the lower layers of Earth’s southernmost seas can be warmer than upper layers, which are closer to the cold air above the ocean.

“While our approach is purely diagnostic and cannot be directly translated into a forecast of ice-mass loss, it shows the risks we run in Antarctica if we do not limit heating up our planet,” said co-author Anders Levermann, a climate scientist from PIK. “We mapped the most critical regions of the floating ice which can induce a strong response of the grounded ice to even slight changes in ice thickness.”

The team’s findings demonstrate the need for more targeted monitoring of changes in ice thickness or in ocean temperatures below these regions, according to Levermann.

“And it can serve as a warning to all of us that what has been called eternal ice might not be so eternal after all,” Levermann said.

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