Ambiente: Glaciers Surge When Ice Shelf Breaks up

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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/ .

JPL is managed for NASA by the California Institute of Technology in Pasadena.

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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.

Keith Koehler (757) 824-1579
Wallops Flight Facility, Wallops Island, Va.

News Release: 2004-237 September 23, 2004

Scientists Report Increased Thinning of West Antarctic Glaciers

Glaciers in West Antarctica are shrinking at a rate substantially higher than was observed in the 1990s. They are losing 60 percent more ice into the Amundsen Sea than they accumulate from inland snowfall.

The study was conducted by a science team from NASA, U.S. universities and from the Centro de Estudios Científicos in Chile. It is based on satellite data and comprehensive measurements made in 2002 by a science team aboard a Chilean P-3 aircraft equipped with NASA sensors. The journal Science published the findings today online.

The ice loss from the measured glaciers corresponds to an annual sea-level rise of .2 millimeters (.008 inches), or more than 10 percent of the total global increase of about 1.8 millimeters (.07 inches) per year.

For a balanced glacial system, the amount of glacier ice melting or flowing into the sea roughly equals the ice formed from snow accumulations farther inland. The scientists report the Amundsen Sea glaciers are not in balance.

Dr. Bob Thomas, a science team member with EG&G Services at the NASA Goddard Space Flight Center's Wallops Flight Facility, Wallops Island, Va., commented that as the glaciers flow to the ocean, they become afloat to form ice shelves. "The ice shelves act like a cork and slow down the flow of the glacier," Thomas said.

"Ice shelves in the Amundsen Sea appear to be thinning, offering less resistance to their tributary glaciers. Our measurements show an increase in glacier thinning rates that affects not only the mouth of the glacier, but also 100 kilometers (60 miles) to 300 kilometers (190 miles) inland," Thomas said.

The scientists noted that the Earth underneath the ice is farther below sea level than had been assumed, so the ice is thicker than once thought. This increases the amount of ice each glacier can discharge into the ocean as its speed increases. It makes it easier for the thinning glacier to float free from its bed, and thus further 'loosen the cork'," Thomas said.

Thomas pointed out that the observed increases in velocities and thinning rates apply to only a short time period, so it is too early to tell if the accelerated thinning is part of a natural cycle or is a sign of a longer-term change. "Continued observation is important," he said.

"The rates of glacier change remain relatively small at present," said Dr. Eric Rignot, a study participant from NASA's Jet Propulsion Laboratory, Pasadena, Calif. "But the potential exists for these glaciers to increase global sea level by more than one meter. The time scale over which this will take place depends on how much faster the glaciers can flow, which we do not know at present."

Thomas said that in the last 10 years the ability to accurately measure glaciers worldwide has greatly improved. Measurements from aircraft and satellites like NASA's Ice, Cloud and Land Elevation Satellite (ICESat), launched in 2003, have greatly improved accuracy.

To access the study on Science Express, the Web site of the journal Science, visit http://www.sciencexpress.org/ .

JPL is managed for NASA by the California Institute of Technology in Pasadena.

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