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Professor Julian Dowdeswell, College Fellow and Brian Buckley Fellow in Polar Sciences, and Dr Frazer Christie, College Postdoctoral Associate, are co-authors on a paper that finds that ice sheets can retreat up to 600 metres a day during periods of climate warming, 20 times faster than the highest rate of retreat previously measured.

They were part of an international team of researchers who used high-resolution imagery of the seafloor to reveal just how quickly a former ice sheet that extended from Norway retreated at the end of the last Ice Age, about 20,000 years ago. 

The team mapped more than 7,600 small-scale landforms called corrugation ridges across the seafloor. The ridges are less than 2.5 metres high and are spaced between about 25 and 300 metres apart.

These landforms are understood to have formed when the ice sheet’s retreating margin moved up and down with the tides, pushing seafloor sediments into a ridge every low tide. Given that two ridges would have been produced each day, the researchers were able to calculate how quickly the ice sheet retreated.

, reported in the journal Nature, show the former ice sheet underwent pulses of rapid retreat at a speed of 50 to 600 metres per day. This is much faster than any ice sheet retreat rate that has been observed from satellites or inferred from similar landforms in Antarctica.

“Our research provides a warning from the past about the speeds that ice sheets are physically capable of retreating at,” said Dr Christine Batchelor from Newcastle University, who led the research. “Our results show that pulses of rapid retreat can be far quicker than anything we’ve seen so far.”

Information about how ice sheets behaved during past periods of climate warming is important to inform computer simulations that predict future ice sheet and sea-level change. 

The new research suggests that periods of such rapid ice-sheet retreat may only last for short periods of time: from days to months.

“This shows how rates of ice-sheet retreat averaged over several years or longer can conceal shorter episodes of more rapid retreat,” said Professor Julian Dowdeswell, who is also the former Director of Cambridge’s Scott Polar Research Institute. “It is important that computer simulations are able to reproduce this ‘pulsed’ ice-sheet behaviour.”

The seafloor landforms also shed light into the mechanism by which such rapid retreat can occur. The researchers found that the former ice sheet had retreated fastest across the flattest parts of its bed.

“An ice margin can unground from the seafloor and retreat near-instantly when it becomes buoyant,” said Dr Frazer Christie, also from the Scott Polar Research Institute. “This style of retreat only occurs across relatively flat beds, where less melting is required to thin the overlying ice to the point where it starts to float.”

The researchers conclude that pulses of similarly rapid retreat could soon be observed in parts of Antarctica. This includes at West Antarctica’s vast Thwaites Glacier, which is the subject of considerable international research due to its potential susceptibility to unstable retreat. The authors of this new study suggest that Thwaites Glacier could undergo a pulse of rapid retreat because it has recently retreated close to a flat area of its bed.

“Our findings suggest that present-day rates of melting are sufficient to cause short pulses of rapid retreat across flat-bedded areas of the Antarctic Ice Sheet, including at Thwaites,” said Dr Christine Batchelor. “Satellites may well detect this style of ice-sheet retreat in the near future, especially if we continue our current trend of climate warming.”

Reference:

Christine L Batchelor et al. Nature (2023), DOI: 10.1038/s41586-023-05876-1

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