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Antarctica: Ice Shelf Collapse May Have Implications for Global Sea Level, Studies Say |
| September 24, 2004 |
 | The recent warming trend in the Antarctic has led to greater amounts of meltwater ponding on ice shelves, gradually weakening and destroying them.
Photo: NOAA |
Glaciers in Antarctica's most rapidly warming region have quickened their pace following the collapse of an enormous ice shelf the size of the state of Delaware, according to several new studies on the incident.
Similar findings from two NASA-funded reports, both appearing in the journal Geophysical Research Letters, show that ice shelves act as "brakes" on the glaciers that flow into them.
Satellite images taken before, during and after the break-up 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, said researcher Ted Scambos, author of a University of Colorado at Boulder (CU-Boulder) study. Other satellite data show that the glaciers also have thinned significantly since the disintegration of the Larsen B, he said.
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 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 speed-up also caused glacier elevations to drop, lowering them by as much as 38 meters (124 feet) in six months. The recent events show that one of the effects of climate warning over the Earth’s poles could be a rise in sea level.
"If anyone was waiting to find out whether Antarctica would respond quickly to climate warming, I think the answer is yes," said Scambos. "We've seen 150 miles of coastline change drastically in just 15 years.”
"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 added. "At every step in the process, things have occurred more rapidly than we expected."
Scambos and colleagues used five Landsat 7 satellite 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 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.
Separate Studies, Similar Findings
A similar study by researchers at NASA's Jet Propulsion Laboratory (JPL) is being simultaneously published in Geophysical Research Letters. Headed by Eric Rignot, the JPL study used radar images and airborne measurements to construct ice thickness profiles in the same region of the Antarctic and showed further glacier acceleration in late 2003 and early 2004.
"These two papers clearly illustrate, for the first time, the relationship between ice shelf collapses caused by climate warming, and accelerated glacier flow," Rignot said.
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.
The study area, located at the far northern tip of the Antarctic just south of Chile and Argentina, has seen a rise in mean annual temperatures of up to 2.5 degrees Celsius (4.5 degrees Fahrenheit) in the past 60 years - faster than almost any region in the world. In the past 30 years, ice shelves in the region have decreased by more than 13,000 square kilometres (5,200 square miles).
According to Scambos, the recent warming trend in the area has led to greater amounts of meltwater ponding on the ice shelves, weakening and 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 warned. "The [collapse of] much larger ice shelves in other parts of Antarctica could have much greater effects on the rate of sea-level rise."
Since 1995, three large areas of the Antarctic have collapsed suddenly. They include the Larsen A Ice Shelf in 1995 (1600 square kilometres, or 618 square miles), the Wilkins Ice Shelf in 1998 (1100 square kilometers, or 425 square miles) and the Larsen B Ice Shelf in 2002 (3200 square kilometres, or 1,235 square miles).
Source: Vancouver Aquarium Marine Science Centre
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