New tipping point discovered beneath the Antarctic ice sheet

Warm water seeping beneath ice sheets can melt them in a way that scientists have not accounted for in models of sea level rise, says new research from the British Antarctic Survey (BAS).

“We have identified the possibility of a new tipping-point in Antarctic ice sheet melting,” says Alex Bradley, an ice dynamics researcher at the British Antarctic Survey (BAS) and lead author of the new paper in the journal Nature Geoscience.

“This means our projections of sea level rise might be significant underestimates.”

The research focuses on a region of ice sheets called the grounding zone, where ground-based ice meets the sea. Over time, land-based ice moves into the ocean where it eventually melts, contributing to sea level rise.

The researchers modelled how seawater can seep between this land and the ice sheet on top of it. They also looked at how this process affects the localised melting of the ice, which lubricates the ice bed and influences the speed at which it slides towards the sea. 

They found this process accelerates with warming water.

“Ice sheets are very sensitive to melting in their grounding zones,” says Bradley.

“We find that grounding zone melting displays a ‘tipping point like’ behaviour, where a very small change in ocean temperature can cause a very big increase in grounding zone melting, which would lead to a very big change in flow of the ice above it.”

Warm water in the grounding zone melts new cavities in the ice sheet that allows access for more water to enter, which causes further melting. The tipping point is that only a small increase in water temperature can have a very large impact on the extent of ice melt.

This could explain why ice sheets in Antarctica and Greenland seem to be shrinking faster than expected, given that this kind of ice melt is currently not accounted for in models used by the Intergovernmental Panel on Climate Change (IPCC).

“This is missing physics, which isn’t in our ice sheet models. They don’t have the ability to simulate melting beneath grounded ice, which we think is happening,” says Bradley.

“We’re working on putting that into our models now.”

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