Magazine article Science News

Greenland's Ice Is Thinner at the Margins

Magazine article Science News

Greenland's Ice Is Thinner at the Margins

Article excerpt

Two new NASA studies show that the central portion of Greenland's ice sheet isn't, on the whole, getting any thinner. However, one of the investigations finds substantial thinning along most margins of the ice sheet--changes that are contributing to rising sea levels.

Scientists at NASA's Wallops Flight Facility in Wallops Island, Va., led both studies, which they report in the July 21 SCIENCE.

One group used the Global Positioning System to measure the downhill flow of ice at elevations of about 2,000 meters above sea level from 1993 to 1997. Survey points were typically about 30 kilometers apart. Together, these roughly 150 points bordered the approximately 1 million square kilometers of Greenland's central ice sheet.

On average, the high-altitude portion of the ice sheet is neither gaining nor losing thickness, glaciologist Robert H. Thomas and his colleagues report. Ice flowing down past the 2,000-m contour is almost balanced by the accumulation of snow above that level. Particular areas, however, show significant net gains and losses.

For example, the extreme southwestern portion of the central ice sheet thickens by some 210 millimeters each year. Although increased snowfall accounts for some of this growth, the scientists suggest that this area also accumulates ice flowing from higher elevations, a result of warming temperatures.

During the same period, the far southeastern portion of the ice sheet has been thinning by almost 300 mm annually, primarily due to increased melting. …

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