Polar ice sheets may retreat much faster than previously thought

Norway’s historic ice sheet might have retreated by greater than 600 metres per day on the finish of the final glaciation.

This is 10 occasions sooner than earlier estimates, suggesting that fashionable ice sheets may soften on the sea ground at far larger speeds than scientists had beforehand suspected, says Christine Batchelor at Newcastle University within the UK.

“Potentially, it shows us that ice sheets are physically capable of retreating at speeds that are an order of magnitude higher than anything we’ve seen [before],” she says. “It kind of provides a warning for what could happen if we continue our trajectory – or particularly if we end up on an upwards trajectory – of warming over the coming decades.”

Ice sheets connect to the bedrock of the ocean ground till rising sea temperatures break down that bond by inflicting the ice-ocean junction to soften on the sea ground, leaving that part of ice floating as an ice shelf. The boundary of the ice hooked up to bedrock known as the grounding line.

Over the previous 50 years, scientists have used satellite tv for pc knowledge to trace the place of the grounding traces in ice sheets in Antarctica and Greenland. Retreating grounding traces have to this point raised world sea ranges by an estimated 0.7 millimetres every year for the reason that Nineteen Nineties.

But Batchelor and her colleagues suspected that satellite tv for pc knowledge won’t be telling the entire story. They determined to take a more in-depth take a look at the historical past of grounding-line modifications on the finish of the final glacial interval, between 15,000 and 19,000 years in the past. At the time, the Scandinavian ice sheet started retreating because the local weather began to heat as a part of a pure heating and cooling cycle, says Batchelor.

She and her colleagues realised that retreating ice sheets left long-lasting traces known as corrugation ridges within the sediment on the ocean ground. These options type properly beneath the ocean’s waves and thus can stay undisturbed for tens of millennia, offering a document of the historical past of glacial melting, she says.

Batchelor and her group used ship-based units to map the topography of the ocean ground throughout 30,000 sq. kilometres of the mid-Norwegian continental shelf, together with 7678 corrugation ridges.

They discovered proof of historic grounding-line retreat of as much as 610 metres per day, with 70 per cent of the areas exhibiting retreats of greater than 100 metres per day – no less than throughout “pulse” intervals that may final days to months. The values far exceed all beforehand reported charges of grounding-line retreat from satellite tv for pc and marine geological data, says Batchelor.

The charge of this retreat was notably excessive alongside flatter areas of the ocean ground, she provides.

Applied to the current day, the findings counsel that an estimated soften charge of a number of tens of centimetres per day in West Antarctica might trigger grounded ice retreat of as much as a number of a whole bunch of metres per day, particularly throughout low-gradient areas.

That may very well be a selected downside with Antarctica’s Thwaites glacier, which has a central trunk grounded on a really flat mattress.

“This has widespread implications for key regions of Antarctica currently undergoing retreat that are of concern for future sea level rise,” says Adam Sproson on the Japan Agency for Marine-Earth Science and Technology.

“Although such extreme rates of grounding-line retreat have not been observed in the modern [period], these results from the geological record, along with numerical models of ice sheet behaviour, suggest rapid and extensive grounding-line retreat is possible under current climate conditions in Antarctica,” says Sproson.

“This could potentially have a significant impact on future global sea level rise if key regions of Antarctica that are currently observing an increase in retreat rates, such as in the Amundsen Sea region, speed up to the levels recorded by Batchelor [and her team].”