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Large waves cause Antarctic ice shelves to collapse

Large waves cause Antarctic ice shelves to collapse

Large waves cause Antarctic ice shelves to collapse

Storm-driven ocean swells have triggered the catastrophic disintegration of Antarctic ice shelves in recent decades, according to new research published in Nature.

Lead author Dr Rob Massom, of the Australian Antarctic Division and the Antarctic Climate and Ecosystems Cooperative Research Centre, says that reduced sea ice coverage since the late 1980s has led to increased exposure of ice shelves on the Antarctic Peninsula to ocean swells, causing them to flex and break.

“Sea ice acts as a protective buffer to ice shelves, by dampening destructive ocean swells before they reach the ice shelf edge,” Dr Massom says.

“But where there is loss of sea ice, storm-generated ocean swells can easily reach the exposed ice shelf, causing the first few kilometres of its outer margin to flex.”

“Over time, this flexing enlarges pre-existing fractures until long thin ‘sliver’ icebergs break away or ‘calve’ from the shelf front.”

“This is like the ‘straw that broke the camel’s back’, triggering the runaway collapse of large areas of ice shelves weakened by pre-existing fracturing and decades of surface flooding.”

Study co-author Dr Luke Bennetts, from the University of Adelaide’s School of Mathematical Sciences, says that the finding highlights the need for sea ice and ocean waves to be included in ice sheet modelling.

This will allow scientists to more accurately forecast the fate of the remaining ice shelves and better predict the contribution of Antarctica’s ice sheet to sea level rise, as climate changes.

“The contribution of the Antarctic Ice Sheet is currently the greatest source of uncertainty in projections of global mean sea level rise,” Dr Bennetts says.

The discovery comes after the international research team, from Australia, the United States and New Zealand, combined satellite images and surface and ocean wave data with modelling, to analyse five major ice shelf disintegrations, between 1995 and 2009.

These included the abrupt and rapid losses of 1,600 square kilometres of ice from the Larsen A Ice Shelf in 1995, 3,320 square kilometres from the Larsen B Ice Shelf in 2002, and 1450 square kilometres from the Wilkins Ice Shelf in 2009.

Each disintegration event occurred during periods when sea ice was significantly reduced or absent, and when ocean waves were large.

In only a matter of days, the collapse of the Larsen B Ice Shelf in 2002 removed an area of ice shelf that had been in place for the previous 11,500 years. Removal of the ice shelf buttressing effect also caused a 3- to 8-fold increase in the discharge of glacial ice, behind the shelf, into the ocean, in the year following disintegration.

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