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Antarctic ice shelf collapses
19/03/2002 11:23 - (SA)
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A photograph taken in early March 2002, from an Otter aircraft showing how part of the Larsen B Antarctic ice shelf has collapsed with staggering rapidity. (P Skvarca and S Tojeiro, AP)
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Auckland - In what is being touted as the biggest event of its kind in 30 years, an Antarctic ice shelf has collapsed and broken up into thousands of icebergs, the US based National Snow and Ice Data Centre (NSIDC) said on Tuesday.
On its website the University of Colorado-based
centre said a major part of the Larsen B ice shelf, believed to
have been there for up to 12 000 years, collapsed over a 35-day period.
On the eastern side of the Antarctic Peninsula, due south of
South Americas Cape Horn, Larsen has been a centre of concern for
several years and is believed to be suffering the effects of global warming.
The area that collapsed totalled 3.250 square kilometres (1.300
square miles).
It contained 720 billion tons of ice. Over the last five years
the shelf has lost a total of 5.700 square kilometres (2.280 square miles), and is now about 40 percent the size of its previous minimum stable extent.
The centre said the latest collapse of the 220-metre (733-foot)
thick shelf began on January 31.
"The shattered ice formed a plume of thousands of icebergs
adrift in the Weddell Sea," it said.
Climate warming
"This is the largest single event in a series of retreats by ice
shelves in the Peninsula over the last 30 years. The retreats are
attributed to a strong climate warming in the region."
It said the rate of warming was around 0.5 degrees Celsius (32.9
Fahrenheit) per decade, and the trend has been on since at least
the late 1940s.
Around the Peninsula since 1974, NSIDC said, the seven ice
shelves declined by a total of about 13.500 square kilometres
(5.212 square miles).
It said the break up of the Peninsula ice shelves had little
consequence for the global sea level but could affect the rate of
ice flow off the continent.
"Ice shelves act as a buttress, or braking system, for
glaciers," the centre said. "Further, the shelves keep warmer
marine air at a distance from the glaciers. Therefore, they
moderate the amount of melting that occurs on the glaciers'
surfaces.
"Once their ice shelves are removed, the glaciers increase in
speed due to meltwater percolation and/or a reduction of braking
forces, and they may begin to dump more ice into the ocean than
they gather as snow in their catchments.."
Last November the head of the Glaciological Division of the
Instituto Antartico Argentino, Pedro Skvarca, warned of a possible break-up of Larsen, due to warm spring temperatures and a dramatic 20 percent rise in the rate of flow of the ice shelf.
Researcher Ted Scambos said the ice disintegrates
because of the presence of ponded melt water on the surface in late summer as the climate has warmed in the area.
Meltwater acts to enhance fracturing of the shelf by filling
smaller cracks and forcing them through the thickness of the ice
due to the weight of the water. - Sapa-AFP
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