Ice sheets retreating up to 20 times faster than previously thought

Ice sheets have been shown to retreat up to 600 metres a day during periods of climate warming – 20 times faster than the highest rate of retreat previously measured.

Researchers from Newcastle, Cambridge and Loughborough universities used high-resolution imagery of the seafloor to reveal the speed at which 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 which are understood to have formed when the ice sheet’s retreating margin moved up and down with the tides.

Given that two ridges would have been produced each day under two tidal cycles, the researchers were able to calculate how quickly the ice sheet retreated.

Their results show the former ice sheet underwent pulses of rapid retreat at a speed of 50 to 600 metres per day – 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. “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 rapid ice-sheet retreat may only last for short periods of time.

“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 from University of Cambridge. “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, with the ice sheet retreating fastest across the flattest parts of its bed.

Co-author Dr Frazer Christie said: “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 concluded 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.

It is thought 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”, Batchelor added. “Satellites may well detect this style of ice-sheet retreat in the near-future, especially if we continue our current trend of climate warming.”

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