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Antarctic ice shelf 'hanging by a thread'

18:08 25 March 2008

NewScientist.com news service

Catherine Brahic

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A thin strip of ice, just 6 kilometres
wide, may be all that is holding back the collapse of a huge ice shelf in
Antarctica

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A narrow strip of ice is now bracing the remainder of the Wilkins ice
sheet (Image: NSIDC)Enlarge

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A thin strip of ice, just 6 kilometres wide, is all that is holding back the
collapse of a huge ice shelf in Antarctica, according to glaciologists.

The Wilkins ice shelf – previously some 16,000 square kilometres in area –
has been disintegrating fast. On 28 February, an iceberg 41 km long and 2.5 km
wide broke off the ice shelf. This triggered the runaway disintegration of a
further 570 square kilometres of ice.

"I would be very surprised if it survives more than a couple more melt
seasons," says Ted Scambos of the University of Colorado, US.

Other researchers, including David Vaughan of the British Antarctic Survey,
believe it could be gone within weeks. "The ice shelf is hanging by a thread –
we'll know in the next few days or weeks what its fate will be," he says.

'Narrow brace'

Although researchers agree the disintegration of the Wilkins ice shelf will
not contribute to rising sea levels, they say it may help them understand what
triggers such events in order to predict when they are likely to happen
again.

"There now remains just a narrow beam of ice, roughly 6 km wide, which is
bracing the rest of the shelf," says Scambos. "If that beam breaks up, about
half of the ice shelf will probably very quickly break apart."

However Scambos says this is not likely to happen this year, as the southern
winter is settling in.

The break up is already helping researchers understand what triggers the
disintegration of ice sheets. They now know that waves generated by storms over
the open ocean are just as important as air and water temperature.

No sea-level rise

"The waves travel thousands of kilometres and are long and gentle. They are
able to flex and break an ice shelf," says Scambos.

Normally, a slurry of sea ice floating in front of the ice shelf would act as
a wave breaker, keeping the surrounding waters still. But this year – as in 2002
when the Larsen B shelf dramatically
disappeared in just 30 days – warm temperatures melted away much of the sea
ice. The glaciologists believe this is what has caused the break up of the
Wilkins ice shelf in recent weeks.

The Wilkins ice sheet is not connected to inland glaciers in the same way as
Larsen B was. As a result, its collapse will not accelerate the flow of glaciers
into the ocean, and so will not immediately cause a sea-level rise.

Climate Change – Want to know more about global warming – the
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report.

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Video Related To The Antarctic Ice Shelf Collapse Story

By Jdhamilton

Tue Mar 25 19:17:58 GMT 2008
This story just appeared
recently, but the video associated with the story "is no longer available". What
Gives????

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Sea Level Rise

By Pete Cahill

Tue Mar 25 19:44:55 GMT 2008
Presumably the difference, in
terms of sea level rise, between glacier-connected and non-glacier-connected ice
shelves is the volume of ice eventually tipped into the sea. So what are the
relative volumes? How much ice is in the Wilkins Shelf and much much does it
need to cause a measurable rise in sea level?

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Sea Level Rise

By William Smith

Tue Mar 25 20:16:58 GMT 2008
The Wilkins Shelf will not
cause any rise in sea level if it melts because it is floating in the sea and
therefore already displacing its own weight of sea water. Only ice which is on
land i.e in glaciers will cause an increase in sea level as it melts. The
Wilkins Shelf separating will not accelarate the melting of any glaciers on the
land behind it. However it is a dramatic demonstration of increasing
temperatures in the Antarctic

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Sea Level Rise

By Ray Wills

Wed Mar 26 12:19:28 GMT 2008
This is true in terms of
direct volume addition, but not the whole story as the meltwater is then
available to warm and therefore contribute to thermal expansion of the ocean -
which it would not do if frozen...

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Climate Change

By David Orr

Wed Mar 26 02:02:14 GMT 2008
Does it not seem that although
the antarctic ice is melting rather fast, the resolve of "concerned nations" to
at least attempt remedial action is melting faster.

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