Sept. 21, 2004

Gretchen Cook-Anderson 
Headquarters, Washington
(Phone: 202/358-0836)

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

RELEASE: 04-302

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 (JPL), Pasadena, 
Calif., NASA's Goddard Space Flight Center (GSFC), Greenbelt, Md., 
and the National Snow and Ice Data Center (NSIDC), 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 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 added.

Rignot's study used data from European Space Agency Remote Sensing 
Satellites (ERS) and 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 Ted 
Scambos, an NSIDC glaciologist and lead author of the second study. 
"We've seen 150 miles of coastline change drastically in just 15 
years," he added. 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 Christopher 
Shuman, a GSFC 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 on the Internet, visit: 

http://www.nasa.gov 

	
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