Antarctic ice shelves have twice as much meltwater as previously thought

Using artificial intelligence techniques, A team of scientists has discovered that at the height of the Antarctic summer, in January, more than half (57%) of all meltwater from the Antarctic ice shelves remains in the form of slush (water-soaked snow).

This melting, which until now had not been quantified and is not taken into account in climate models, can profoundly affect the stability of ice shelves and accelerate the rise in sea level, warns the study, led by the University of Cambridge (United Kingdom) and published this Thursday in ‘Nature Geoscience’.

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Each summer, as the climate warms, water accumulates on the surface of Antarctica’s floating ice shelves..

Previous research has shown that surface lakes of meltwater can contribute to the fracturing and collapse of ice shelves, because the weight of the water can cause the ice to break up but the role of slush in the stability of ice shelves ice is more difficult to determine.

“We can use satellite images to map meltwater lakes in much of Antarctica, but sleet is difficult to map because it looks like other things, such as cloud shadows, when viewed from a satellite,” explains lead author Rebecca Dell of the Scott Polar Research Institute (SPRI) in Cambridge.

However, using machine learning techniques, “we can go beyond what the human eye can see and get a clearer picture of how sleet could be affecting the ice in Antarctica,” Dell says.

Satellite data

Using optical data from NASA’s Landsat 8 satellite, the team, along with researchers from the University of Colorado Boulder in the United States and the University of Delft in the Netherlands, trained a machine learning model to obtain monthly records of meltwater and meltwater lakes across 57 Antarctic ice shelves between 2013 and 2021.

Thus, they discovered that at the height of the Antarctic summer, more than half (57%) of the meltwater on the Antarctic ice shelves remains in the form of slush, and that the remaining 43% is meltwater.

“This slush has never been mapped on a large scale across all of Antarctica’s large ice shelves, so more than half of all surface meltwater has been ignored until now,” Dell says.

Platform stability

Meltwater affects the stability of the floating ice shelves that line the Antarctic coast.

As the climate warms and melt rates increase in Antarctica, meltwater – whether in the form of lakes or slush – can enter and fracture ice cracks, which could lead to ice shelves collapsing. more vulnerable, which in turn would cause ice from inland glaciers to spill into the ocean and contribute to sea level rise.

“Because sleet is more solid than meltwater, it won’t cause hydrofracturing in the same way as lake water, but it’s something we need to take into account when predicting whether ice shelves will collapse or not. “says Ian Willis, co-author of the study at the University of Cambridge.

Furthermore, it also has a great effect on melting rates. Because sleet and lakes are less white than snow or ice, they absorb more heat from the sun, causing more snowmelt.

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This additional melt is not accounted for in climate models, which can lead to underestimation of ice sheet melt projections and ice shelf stability.

“In the future, places in Antarctica that are currently free of water or meltwater are likely to begin to change. As the climate continues to warm, more melting will occur, which could have implications for ice stability and sea level rise,” Willis concludes.