University of Adelaide research reveals chilling cause of Antarctic ice shelf collapse

ANTARCTIC ice shelves are usually protected by floating sea ice, but global warming is melting the ice floes, exposing the huge shelves to destructive waves. Now there’s warnings of extreme sea level rises.

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WHEN the Larsen B Ice Shelf collapsed in the late summer of 2002, a huge expanse of compacted snow, built up over 11,500 years, tore away from the Antarctic Peninsula into the sea.

That exposed glaciers and increased the flow from these rivers of ice up to eightfold the following year.

It’s disturbing because this “grounded ice” on land contributes to sea level rise. And the Antarctic Ice Sheet contains more than 90 per cent of the world’s ice, enough to potentially raise global sea level by about 57m.

What’s worse is that the Larsen B collapse was not an isolated event.

The sheared area of the northeast side of Scar Inelet Ice Shelf - the largest remnant of the Larsen B Ice Shelf which disintegrated in 2002. Picture: Ted Scambos/NSIDC/AAD

Several disintegrations have happened when floating sea ice was significantly reduced or absent, and when ocean waves were large. Without the protective ice to dampen the force of the waves, they caused further collapses.

Scientists fear forecasts for sea level rises caused by global warming fail to take into account the critical factors contributing to these major ice shelf disintegrations.

Writing in the journalNature, researchers say “the recent abrupt, rapid and catastrophic large-scale disintegrations of ice shelves along the Antarctic Peninsula is of major concern because this process indirectly contributes to sea level rise from the Antarctic Ice Sheet”.

Using satellite imagery and wave data, the international research team developed a conceptual model of the sequence of events and factors common to recent ice shelf disintegrations including:

Larsen A Ice Shelf (1995) with an area about 860 km2 lost in just two days and a total loss of 1600 km2 in 39 days;

Satellite images show the shattering of Larsen B Ice Shelf, from January 31 2002 (top left) to March 5 2002 (bottom right).

Larsen B Ice Shelf (2002) with an area of 3320km2 lost from January 31 to March 17, 2002;

Wilkins Ice Shelf (2008 and 2009) with an area about 800km2 lost in 2008 and 1450km2 in 2009.

University of Adelaide senior lecturer Dr Luke Bennetts has evidence to show that stormy seas are compounding the problem.

Stormy seas are compounding the disintegration of the ice sheets.

“Our work has provided evidence that these large scale disintegrations of Antarctic ice shelves are triggered by impacts by ocean swells, which have been able to reach the ice shelf fronts due to loss of regional sea ice,” he said.

“Waves are carrying huge stores of energy and when they reach the coastline, which in the Antarctic means reaching the ice shelves, these waves have destructive impacts.”

Sea ice bobbing around on the ocean surface acts as a protective buffer that dampens down waves. But warmer seas have less sea ice, especially during the summer months.

Waves also tend to be larger or more extreme, due to stronger winds.

Dr Bennetts said climate change research was not taking into account the effects of waves on the ice shelves. Picture: Jessica Fitzpatrick/Australian Antarctic Division

“People who are looking at the way the ice shelves are responding to climate change are not incorporating the effects of the surrounding sea ice and definitely not the effects of ocean waves,” Dr Bennetts said. “So we’re hoping now they will take notice of our work and incorporate those elements.” Dr Bennetts used applied maths to show waves doing damage, reaching exposed ice shelf and causing the first few kilometres of its outer margin to flex. Over time this enlarges fractures and triggers runaway collapse.