Ice Bridge Holding Antarctic Ice Shelf Cracks Up
Date: 06-Apr-09
Country: NORWAY
Author: Alister Doyle, Environment Correspondent
Ice Bridge Holding Antarctic Ice Shelf Cracks Up Photo: Alister Doyle
A 20 metre-high ice cliff forming the edge of the Wilkins Ice
shelf on the Antarctic Peninsula is seen from a plane January 18, 2009.
Photo: Alister Doyle
OSLO - An ice bridge which had apparently held a vast Antarctic ice shelf in
place during recorded history shattered on Saturday and could herald a wider
collapse linked to global warming, a leading scientist said.
"It's amazing how the ice has ruptured. Two days ago it was intact," David
Vaughan, a glaciologist with the British Antarctic Survey, told Reuters of a
satellite image of the Wilkins Ice Shelf on the Antarctic Peninsula.
The satellite picture, from the European Space Agency (ESA), showed that a
40 km (25 mile) long strip of ice believed to pin the Wilkins Ice Shelf in
place had splintered at its narrowest point, about 500 metres wide.
"We've waited a long time to see this," he said.
The Wilkins, now the size of Jamaica or the US state of Connecticut, is one
of 10 shelves to have shrunk or collapsed in recent years on the Antarctic
Peninsula, where temperatures have risen in recent decades apparently
because of global warming.
The ESA picture showed a jumble of huge flat-topped icebergs in the sea
where the ice bridge had been on Friday, pinning the Wilkins to the coast
and running northwest to Charcot Islandt.
"Charcot Island will be a real island for the first time in history,"
Vaughan said.
Vaughan, who landed on the flat-topped ice bridge on the Wilkins in January
in a ski-equipped plane with other scientists and two Reuters reporters,
said change in Antarctica was rarely so dramatic. It was the first -- and
last -- visit to the area.
The loss of the ice bridge, jutting about 20 metres out of the water and
which was almost 100 km wide in 1950, may now allow ocean currents to wash
away far more of the Wilkins shelf.
"My feeling is that we will lose more of the ice, but there will be a
remnant to the south," said Vaughan. Ice shelves float on the water, formed
by ice spilling off Antarctica, and can be hundreds of metres thick.
Nine other shelves have receded or collapsed around the Antarctic Peninsula
in the past 50 years, often abruptly like the Larsen A in 1995 or the Larsen
B in 2002 further north.
DISAPPEAR FROM MAP
Cores of sediments on the seabed indicate that some of these ice shelves had
been in place for at least 10,000 years. Vaughan said an ice shelf would
take many hundreds of years to form.
In January, the remaining ice bridge had been surrounded by icebergs the
size of shopping malls, many of them trapped in sea ice. A few seals were
visible lolling on sea ice in the low Antarctic sunshine.
On that visit, Vaughan put up a GPS satellite monitoring device and
predicted the ice bridge would break within weeks. The plane left quickly,
in case the ice was unstable on a part of the world about to disappear from
the map.
Temperatures on the Antarctic Peninsula have risen by up to about 3 Celsius
(5.4 Fahrenheit) in the past 50 years, the fastest rate of warming in the
Southern Hemisphere.
"We believe the warming on the Antarctic Peninsla is related to global
climate change, though the links are not entirely clear," Vaughan said.
Antarctica's response to warming will go a long way to deciding the pace of
global sea level rise.
About 175 nations have been meeting in Bonn, Germany, since March 29 as part
of a push to agree by the end of 2009 a new UN treaty to combat climate
change. The talks end on April 8.
The loss of ice shelves does not affect sea levels -- floating ice contracts
as it melts and so does not raise ocean levels. But their loss can allow
glaciers on land to slide more rapidly towards the sea, adding water to the
oceans.
The Wilkins does not have much ice pent up behind it. But bigger ice shelves
to the south on the frozen continent, where no major warming has been
detected, hold back far more ice.
© Thomson Reuters 2009 All rights reserved
|