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Alan Buis (818) 354-0474
Jet Propulsion Laboratory, Pasadena, Calif.

Gretchen Cook-Anderson (202) 358-0836
NASA Headquarters, Washington,
D.C.

NEWS RELEASE: 2004-233 September 21, 2004

Glaciers Surge When Ice Shelf Breaks up

Since 2002, when the Larsen B ice shelf broke away from the coast of
the Antarctic Peninsula, scientists have witnessed profound increases
in the flow of nearby glaciers into the Weddell Sea. These
observations were made possible through NASA, Canadian and European
satellite data.

Two NASA-funded reports, appearing in the Geophysical Research Letters
journal, used different techniques to arrive at similar results.
Researchers from NASA's Jet Propulsion Laboratory, Pasadena, Calif.,
NASA's Goddard Space Flight Center, Greenbelt, Md., and the National
Snow and Ice Data Center, Boulder, Colo., said the findings prove ice
shelves act as "brakes" on the glaciers that flow into them. The
results also suggest climate warming can rapidly lead to rises in sea
level.

Large ice shelves in the Antarctic Peninsula disintegrated in 1995 and
2002, as a result of climate warming. Almost immediately after the
2002 Larsen B ice shelf collapse, researchers observed nearby glaciers
flowing up to eight times faster than prior to the breakup. The
speed-up also caused glacier elevations to drop, lowering them by as
much as 38 meters (124 feet) in six months.

"Glaciers in the Antarctic Peninsula accelerated in response to the
removal of the Larsen B ice shelf," said Dr. Eric Rignot, a JPL
researcher and lead author of one of the studies. "These two papers
clearly illustrate, for the first time, the relationship between ice
shelf collapses caused by climate warming, and accelerated glacier
flow."

Rignot's study used data from European Space Agency Remote Sensing
Satellites and the Canadian Space Agency Radarsat satellite. The
United States and Canada share a joint agreement on Radarsat, which
NASA launched.

"If anyone was waiting to find out whether Antarctica would respond
quickly to climate warming, I think the answer is yes," said Dr. Ted
Scambos, a National Snow and Ice Data Center glaciologist and lead
author of the second study. "We've seen 150 miles of coastline change
drastically in just 15 years." He used data from IceSat, a NASA laser
altimetry mission launched in 2003, and Landsat 7, jointly run by NASA
and the U. S. Geological Survey.

The papers illustrate relationships between climate change, ice shelf
breakup, and increased flow of ice from glaciers into oceans.
Increased flow of land ice into oceans contributes to sea level rise.
While the Larsen area glaciers are too small to significantly affect
sea level, they offer insight into what will happen when climate
change spreads to regions farther south, where glaciers are much
larger.

Scambos and colleagues used five Landsat 7 images of the Antarctic
Peninsula from before and after the Larsen B breakup. The images
revealed crevasses on the surfaces of glaciers. By tracking the
movement of crevasses in sequence from one image to the next, the
researchers were able to calculate velocities of the glaciers.

The surfaces of glaciers dropped rapidly as the flow sped up,
according to IceSat measurements. "The thinning of these glaciers was
so dramatic that it was easily detected with IceSat, which can measure
elevation changes to within an inch or two," said Dr. Christopher
Shuman, a Goddard Space Flight Center researcher and a co-author on
the Scambos paper.

The Scambos study examined the period right after the Larsen B ice
shelf collapse to try to isolate the immediate effects of ice shelf
loss on the glaciers. Rignot's study used Radarsat to take monthly
measurements that are continuing. Clouds do not limit Radarsat
measurements, so it can provide continuous, broad velocity
information.

According to Rignot's study, the Hektoria, Green and Evans glaciers
flowed eight times faster in 2003 than in 2000. They slowed moderately
in late 2003. The Jorum and Crane glaciers accelerated two-fold in
early 2003 and three-fold by the end of 2003. Adjacent glaciers, where
the shelves remained intact, showed no significant changes according
to both studies. The studies provide clear evidence ice shelves
restrain glaciers, and indicate present climate is more closely linked
to sea level rise than once thought, Scambos added.

For information and images of this research on the Internet, visit
http://www.gsfc.nasa.gov/topstory/2004/0913larsen.html
. For
information about NASA programs, visit http://www.nasa.gov/