How much ice can Antarctica afford to lose?


The belt holding in Antarctica's ice stocks is slowly loosening, but a new study has identified weak spots. Belinda Smith reports.


The ice front of Fleming Glacier, which fed the former Wordie Ice Shelf, and broke up towards the end of the 1990s. Picture taken on November 17, 2011.
MATTHIAS BRAUN, UNIVERSITY OF ERLANGEN-NUREMBERG, GERMANY
The massive ice sheets that drape Antarctica – including the East Antarctic ice sheet, the world’s thickest and biggest – are generally kept from flowing into the ocean by ice shelves, floating chunks of ice that fringe the continent.

But some of these ice shelves have disintegrated over the past decades. Larsen A and Larsen B disappeared from the Antarctic Peninsula in 1995 and 2002 respectively. So how many more can disappear before ice sheets tumble freely into the sea?

A study led by Johannes Fürst from the Laboratory of Glaciology and Environmental Geophysics in Paris mapped out ice shelves holding the most ice back.

In doing so, they identified areas which, should they crumble, will have disastrous consequences – including raising sea levels.

The ice front of Fleming Glacier, which fed the former Wordie Ice Shelf, and broke up towards the end of the 1990s. Picture taken on November 17, 2011. – Matthias Braun, University of Erlangen-Nuremberg, Germany

Not all ice shelves are created equal. Some simply float on the ocean, and don't hold back any ice.

Others, though, are the only barrier keeping ice behind slipping away.

So for each Antarctic ice shelf, the researchers calculated and mapped the area which didn't hold back the ice sheet at all, or reined it in only a little. They called these areas "passive ice shelf".

Overall, only around 13% of the ice shelf area was classed as passive. The Larsen C ice shelf, in the Weddell Sea is almost entirely passive ice shelf, the researchers found.

But the ice shelves on the Amundsen and Bellingshausen seas contained the least amount of passive ice shelf, with 7% and 5% respectively.

Highly crevassed ice front of the Ferrigno Ice Stream in the Bellingshausen Sea. Picture taken on November 16, 2011.
MATTHIAS BRAUN, UNIVERSITY OF ERLANGEN-NUREMBERG, GERMANY

And not only are those ice shelves already thinning, the ice sitting behind them is on bedrock sloping towards the coast.

The authors say monitoring these shelves for any fractures is urgently needed.

The work was published in Nature Climate Change.

Related reading:
Ice shelves are disappearing

Belinda smith 2016 2.jpg?ixlib=rails 2.1
Belinda Smith is a science and technology journalist in Melbourne, Australia.
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