Cold discomfort. The Larsen Ice Shelf is imperiled from above and below.

Ice Shelf Feels the Heat

Warming waters may doom the Antarctic Peninsula's Larsen Ice Shelf, and other Antarctic ice shelves could be more endangered than had been thought, according to a paper published in the 31 October issue of Science.

When two chunks of ice roughly the size of Luxembourg broke off the Larsen Ice Shelf in 1995 and 2002 (ScienceNOW, 19 March 2002), experts scrambled to figure out how it had happened. Suspicion for the Larsen's breakup initially fell on air temperatures on the peninsula, which rose by 2.5ºC over the past half-century, 10 times faster than the global trend. The warm summer air creates pools of meltwater that eventually force crevasses apart, leading to catastrophic breakups.

But the new study suggests that air temperatures can't be the whole story. Andrew Shepherd, a glaciologist at the University of Cambridge, U.K., and co-workers quantified the ice shelf's thinning using satellite radar measurements of the shelf's height. They found that the shelf thinned by up to 18 meters between 1992 and 2001. One possible explanation, that the summer meltwater includes snow that refreezes into denser ice, fell through when the team calculated that the shelf doesn't receive enough solar energy to drive that process.

The only other possibility is that the ice shelf is melting from below. Although there are no long-term ocean temperature data from the Larsen shelf, deep waters farther out in the Weddell Sea have been warming over the past 3 decades, Shepherd's team notes. Also, a British Antarctic Survey ship sailing near the Larsen shelf in 2002 detected temperatures warm enough to melt ice at 300 meters. At the current melting rate, the Larsen will reach the breaking point within this century, Shepherd's team predicts.

Others caution that the findings are not rock solid. Satellite data are imprecise, notes glaciologist Ted Scambos of the National Snow and Ice Data Center in Boulder, Colorado. But if the results hold up, the study will serve as a wake-up call that larger ice shelves on mainland Antarctica may also be vulnerable to ocean warming, says oceanographer Stan Jacobs of the Lamont-Doherty Earth Observatory in Palisades, New York. These larger shelves hold back massive aboveground ice sheets that would dramatically raise global sea level if they melted. "It's a good model for what could happen," Jacobs says.

Related site
Antarctic Ice Shelves site from National Snow and Ice Data Center