ice shelf

Meltwater may fracture Antarctic ice shelves and speed sea level rise

The Ross ice shelf in Antarctica

Shutterstock / Dale Lorna Jacobsen

Almost two-thirds of the ice shelves crucial to stopping the collapse of Antarctica’s ice sheets are at risk of fracturing by water, according to an analysis that warns of “major consequences” for sea level rise from the vulnerability.

Most of the continent’s ice is held back from the ocean by buttressing, floating tongues, known as ice shelves. These are melting from below due to warming oceans, but scientists are also striving to better understand how meltwater on top of the shelves affects them.

It has been suggested that the collapse of the Larsen B ice shelf in 2002 was partly due to ponds of meltwater inundating and expanding surface fractures in the ice, in a process known as hydrofracturing. Climate change is expected to increase such meltwater.

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Now a US and European team has pinpointed where meltwater can weaken shelves, potentially speeding up the collapse of the ice sheets and sea level rise. Ching-Yao Lai at Columbia University in New York and her colleagues found that 60 per cent of the buttressing ice shelves are vulnerable to hydrofracture if filled with water.

They arrived at the figure by training a neural network to identify fractures from satellite images of the continent, a task too time-consuming for people. The results closely tallied with a model predicting where fractures would be. Calculations of ice stresses and forces were then run to estimate which fractures would become unstable if filled with water.

“Not all parts of ice shelves are created equal: some are buttressing, some are not. It’s not only that there is meltwater, but does it turn up in those vulnerable places,” says Jonathan Kingslake at Columbia University, who worked on the study.

Before this research, we couldn’t say what effect extra melting in Antarctica would have on ice shelves, says Alex Brisbourne at the British Antarctic Survey. He says: “60 per cent is a significant proportion which is threatened by a warmer climate.”

Brisbourne notes that the study makes some assumptions that may not reflect reality – such as water flowing rapidly into fractures even though some may flow slowly, refreeze and stabilise fractures – but he says that such limitations are unlikely to change the overall findings.

Journal reference: Nature, DOI: 10.1038/s41586-020-2627-8

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