| 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 (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. 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. ###
Contacts: Gretchen Cook-Anderson
NASA Headquarters, Washington DC
202-358-0836 Krishna Ramanujan
Goddard Space Flight Center, Greenbelt, MD
607-273-2561 | |
Map of the Study Area
This satellite image from NASA’s MODIS sensor aboard the Terra spacecraft shows the Larsen B Ice Shelf region on 1 November 2003. Red dots indicate sites where ice flow speed was measured using more detailed Landsat 7 images. The colored lines track the retreat of the Larsen B Ice Shelf during the past 6 years, and the black line shows the coastline, or “grounding line,” where the thick ice begins to float off the sea floor. Blue lines on the glaciers show the location of laser elevation profiles from ICESat. A weather station location marked in the upper right of the image map (”Matienzo AWS”) has tracked atmospheric warming in summers over the past 30+ years in the region. Credit: National Snow And Ice Data Center (NSIDC) 
Larsen Ice Shelf Break-Up
This animation zooms into the Larsen Ice Shelf on August 8, 2000, melt ponds on its surface. The visualization was created using RADARSAT data of Antarctica, Landsat 7 data of Larsen Ice Shelf area, and finally Landsat panchromatic band (15m) data. Credit: NASA/USGS
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RADARSAT Peers Through The Clouds
This series of radar images shows change in the ice shelf configuration between 1996 and 2003. The first image was derived from the European Space Agency’s (ESA) ERS-1 satellite and the last four from the Canadian Space Agency’s (CSA) Radarsat-1 satellite. Credit: ESA (for the 1996 image) and CSA (for the other four images)
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Ice Environments 101
This image graphically illustrates the Earth’s dynamic ice and snow cover from continental ice sheets to the ocean’s sea ice. For a detailed description of these and other ice features, visit: http://icesat.gsfc.nasa.gov/ docs/IceBasics.htm
Credit: NASA 
ICESat criss-crosses Antarctica
ICESat’s orbit was designed to maximize coverage over the polar ice sheets, where ground tracks intersect to create an intricate mesh of elevation data points. The accumulation of these data points across Antarctica results in a new three-dimensional elevation model. ICESat repeats its orbital pattern thus allowing the GLAS instrument to measure changes over time in the same location. ICESat’s primary mission requires the satellite’s advanced technology to provide data on the critically important third dimension, elevation necessary to assess ice sheet mass balance Credit: NASA |
