Glaciers Surge When Ice Shelf Breaks Up

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.