Ice sheet retreat of up to 600m a day happened at end of last Ice Age - and could be seen soon in Antarctica, say Cambridge researchers

A “warning from the past” has been uncovered, after researchers found 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.

An international research team used high-resolution imagery of the seafloor to reveal how quickly a former ice sheet that extended from Norway retreated at the end of the last Ice Age, about 20,000 years ago. And the researchers say something similar could soon be observed in Antarctica.

More than 7,600 small-scale landforms called corrugation ridges across the seafloor were mapped by the team, which included University of Cambridge researchers.

The ridges - less than 2.5 metres high and spaced between about 25 and 300 metres apart - 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.

With two ridges produced each day, researchers were able to calculate how quickly the ice sheet retreated.

Reporting their findings in the journal Nature, they explain how 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 seen from satellites or previously 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.”

Such information is key to informing computer simulations that predict future ice sheet and sea-level change.

The findings suggest the rapid ice-sheet retreat may only last for 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 co-author Professor Julian Dowdeswell from Cambridge’s Scott Polar Research Institute. “It is important that computer simulations are able to reproduce this ‘pulsed’ ice-sheet behaviour.”

And they found 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 co-author 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.”

Pulses of similarly rapid retreat could soon be seen in parts of Antarctica, they predict, including at West Antarctica’s vast Thwaites Glacier.

This is the subject of much international research due to its potential susceptibility to unstable retreat.

The new study suggests 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 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.”