Cold ice shelves Antarctica more vulnerable than previously thought

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Satellite image meltwater ponds
Satellite image meltwater ponds
Some cold ice shelves in Antarctica, which researchers initially thought would remain stable over the coming centuries, turn out to be vulnerable in the event of further global warming. This conclusion results from a study led by Utrecht climate researcher Melchior van Wessem. When ice shelves break up, they do not contribute to sea level rise, because they are already floating in the ocean. However, they buttress land ice that will flow faster into the ocean as a result of their breaking up, which does cause faster sea level rise. The results of the study will appear today in Nature Climate Change.

The Ross ice shelf in Antarctica is about the size of Spain, making it the largest ice shelf in the world. It is a floating sheet of ice, which is hundreds of meters thick and fed by the ice on land. Although all of Antarctica’s ice shelves are naturally cold, the average temperature on this ice shelf is even lower. Because of these cold conditions, climate scientists initially thought the Ross ice shelf and other similar ice shelves were safe from global warming over the next century.

Sea level rise

Van Wessem’s research shows that even these cold ice shelves need to be carefully monitored. Due to relatively little snowfall on cold ice shelves like Ross, the threshold for the formation of ponds of meltwater on these ice shelves appears to be much lower: up to ten degrees lower than on ice shelves where there is a relatively large amount of snowfall.

The creation of ponds of meltwater on an ice shelf is bad news. When an ice shelf has cracks, water from the ponds can flow into the cracks. This can cause the ice shelf to break up in a short period of time. More than sixty percent of Antarctica’s ice shelves, including Ross, have such cracks and thus could potentially disintegrate when meltwater ponds form. If that happens, the adjacent land ice could flow more rapidly into the ocean and raise sea levels.

Meltwater ponds on cold ice shelves like Ross begin to form at an average annual temperature of -15 degrees Celsius. According to the latest climate models, with average global warming those temperatures could be reached on the Ross ice shelf by the end of this century.

What surprised me most is that the amount of snowfall strongly determines the threshold for the formation of meltwater ponds

Melchior van Wessem

Simulating snowfall

There is enough land ice in Antarctica to raise global mean sea level by tens of meters. Ice shelf breakup is widely seen as a crucial but poorly understood process that largely determines how fast Antarctic ice will melt in the future. "What surprised me most is that the amount of snowfall strongly determines the threshold for the formation of meltwater ponds," says Van Wessem. "With my research, I was trying to improve predictions of melt, but now it turns out that snowfall plays a much bigger role than previously thought. As far as I am concerned, it is therefore just as important to improve the simulation of snowfall in Antarctica, so that the models we use to make predictions about the melting of the ice sheet and the sea level rise it produces become more accurate."

Publication

’Variable temperature thresholds of melt pond formation on Antarctic ice shelves’ Nature Climate Change, 26 januari 2023 J. Melchior van Wessem*, Michiel R. van den Broeke*, Bert Wouters*, Stef Lhermitte from TU Delft
*Utrecht University
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