Published in Nature Geoscience, the study, led by the University of Adelaide and University of Melbourne, found long periods of sea ice loss surrounding the ice shelves occurred in the six to 18 months prior to calving, as well as the collapse of the ‘landfast’ sea ice attached to the ice shelves only weeks prior to the calving events.
“Sea ice is retreating at an unprecedented rate all around Antarctica and our work suggests this will put further pressure on already thinned and weakened ice shelves,” said Professor Luke Bennetts, from the University of Melbourne.
“This could lead to more large-scale calving events, with profound implications for the future of global sea levels.”
The Antarctic Ice Sheet is the thick layer of ice that sits on top of Antarctica. It holds enough fresh water to raise current sea levels by more than 50 metres.
Ice shelves are floating platforms that form as glaciers flow off the Antarctic continent onto the ocean, whereas sea ice forms when the surface of the ocean freezes.
“Except for a relatively short period around summer, sea ice creates a protective barrier between the ice shelves and the potentially damaging swells of the Southern Ocean. Without this barrier, the swells can bend and flex pre-weakened ice shelves until they break,” Professor Bennetts said.
Previous research has shown that warming temperatures are causing more rapid melting and more frequent ‘calving’ of icebergs from some ice shelves.
“Increased melting and calving does not directly increase sea levels, as the ice shelves are already floating on the ocean, but it reduces the ability of the ice shelves to push back against the glacial flow into the ocean, which does raise sea levels,” Professor Bennetts said.
Nathan Teder, a PhD candidate at the University of Adelaide who led the study, said his team also developed a novel mathematical model to quantify the ice shelf flexing caused by the huge Southern Ocean swells.
“There is currently no observation system that allows for long-term recording of swell waves that pass through Antarctic sea ice to reach ice shelves, so mathematical modelling is an essential link in quantifying the connection between ice shelf stability and changes in local sea ice and ocean conditions,” said Mr Teder.
The research was funded by the Australian Antarctic Science Program and the Australian Research Council and collaborators included the University of Melbourne, the University of Adelaide, the Australian Bureau of Meteorology, the University of Tasmania, and the Australian Antarctic Division.