Antarctic
Glaciers Melting Faster This Year
Antarctic
glaciers are melting and moving more quickly toward the sea in the wake of the
collapse of a 1,200 square mile ice shelf in March 2002, scientists said
Wednesday.
The
recent events are a predicted consequence of climate change and underscore the
potential for sea level rise as a result of climate warming over the Earth's
polar caps.
The
new study, led by the University of Colorado at Boulder (CU-Boulder) and a
related study by NASA's Jet Propulsion Laboratory, was published online
Wednesday - it will be published in the September 28 issue of "Geophysical
Research Letters."
University
of Colorado at Boulder researcher Ted Scambos said Landsat
7 satellite images taken before, during and after the breakup of the Larsen B
ice shelf in March 2002 show that several of the glaciers are now moving at up
to five times their previous speed.
Other
satellite data show that the glaciers also have thinned since the disintegration
of the Larsen B, he said.
"The
Larsen area can be looked at as a miniature experiment, showing how warming can
dramatically change the ice sheets, and how fast it can happen," he said.
"At every step in the process, things have occurred more rapidly than we
expected."
The
study also included elevation measurements from NASA's Ice Cloud and Land
Elevation Satellite, or ICESat.
A
similar study is being simultaneously published in "Geophysical Research
Letters." by researchers at NASA's Jet Propulsion Laboratory.
That
study used radar images and airborne measurements to profile ice thickness in
the same region of the Antarctic and showed further glacier acceleration in late
2003 and early 2004, with some glaciers reaching eight times their original
speeds.
Glaciers
showed an almost immediate response after the ice shelf collapse, with some
nearly tripling in speed within a matter of months, according to the CU-Boulder
study.
The
Hektoria and Green glaciers, which sped up the most,
are currently moving about a mile per year - most glaciers move much more
slowly, from a few inches to several hundred yards annually.
The
satellite images used in the CU-Boulder study also showed the lower parts of the
glaciers fracturing and disintegrating in response to the loss of the ice shelf.
Glaciers where the Larsen B ice shelf remains intact have shown little change, Scambos
said.
The
area, located at the far northern tip of the Antarctic just south of
"This
study shows very clearly that glaciers which flow into ice shelves are partially
controlled by the presence of the shelf, which acts as a kind of braking
system," Scambos said. "Removing the shelf
makes them speed up."
The
CU study highlights the sensitivity of the poles to climate change, Scambos
added.
"As
temperatures crossed the threshold of melting in the summer months, ice shelves
in the area rapidly disintegrated," he said. "Not only do the ice
shelves collapse rapidly, but the subsequent effects on the glaciers are
immediate."
In
three cases since 1995, large areas in the Antarctic have collapsed suddenly.
They include the 618 square mile Larsen A Ice Shelf in 1995, the 425 square mile
Wilkins Ice Shelf in 1998 and the 1,235 square mile Larsen B Ice Shelf in 2002.
According
to Scambos, the recent warming trend in the area has
led to greater amounts of melt "ponding"
on the ice shelves, weakening and then destroying them.
"Meltwater
at the surface acts to increase the extent of fracturing in the ice," he
said. The weight of the water essentially forces the cracks open, so a
relatively small amount of climate warming can destroy large, centuries-old ice
shelves.
"While
the consequences of this area are small compared to other parts of the
Antarctic, it is a harbinger of what will happen when the large ice sheets begin
to warm," Scambos said. "The much larger
ice shelves in other parts of
The
While
researchers once thought summertime temperatures in the Ross ice-shelf area were
far below freezing and therefore stable, they appear to be just a few degrees
below the threshold for surface ponding, Scambos
said.
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