Melting Southern Ice Sheets Surprise Scientists

While NASA satellite data clearly shows the Arctic is thinning, researchers from the British Antarctic Survey and the University of Bristol say the "dynamic thinning" of glaciers now reaches all latitudes in Greenland and has intensified on key Antarctic coastlines. Working with millions of NASA satellite measurements, the researchers claim the ice sheets are shrinking faster than scientists previously thought.

The research shows the most profound loss of ice sheets in Greenland and western Antarctica is a result of glaciers speeding up where they flow into the sea. The ice melt is penetrating far into the ice sheets' interior and is spreading as ice shelves thin by ocean-driven melt. Ice shelf collapse has triggered particularly strong thinning that has endured for decades.

"We were surprised to see such a strong pattern of thinning glaciers across such large areas of coastline—it's widespread and in some cases thinning extends hundreds of kilometres inland," Dr. Hamish Pritchard from British Antarctic Survey, said in this week's journal Nature. "We think that warm ocean currents reaching the coast and melting the glacier front is the most likely cause of faster glacier flow. This kind of ice loss is so poorly understood that it remains the most unpredictable part of future sea level rise."

Comparing the rates of change in elevation of both fast-flowing and slow-flowing ice, the researchers found that 81 out 111 fast-moving glaciers found ice thinning at rates twice that of slow-flowing ice at the same altitude. The ice loss from many glaciers in both Antarctica and Greenland is greater than the rate of snowfall further inland.

NASA plans to continue to study the ice melt this fall when a team of explorers will fly over Earth's southern ice-covered regions to study changes to its sea ice, ice sheets and glaciers as part of NASA's Operation Ice Bridge. NASA's DC-8—the largest aircraft in NASA's airborne science fleet—is scheduled to leave NASA's Dryden Flight Research Center in Edwards, Calif., on Oct. 12 and fly to Punta Arenas, Chile, where the plane, crew and researchers will be based through mid-November.

For six weeks, the Ice Bridge team will traverse the Southern Ocean for up to 17 flights over West Antarctica, the Antarctic Peninsula and coastal areas where sea ice is prevalent.

This fall's Antarctic campaign will begin the first sustained airborne research effort of its kind over the continent. Data collected by researchers will help scientists bridge the gap between NASA's ICESat (Ice, Cloud and Land Elevation Satellite), which is operating the last of its three lasers, and ICESat-II, scheduled to launch in 2014.

The Ice Bridge flights will help scientists maintain the record of changes to sea ice and ice sheets that have been collected since 2003 by ICESat. The flights will lack the continentwide coverage that can be achieved by satellite, but the flights will turn up new information not possible from orbit, such as the shape of the terrain below the ice.

"Space-based instruments like the ICESat lasers are the only way to find out where change is occurring in remote, continent-sized ice sheets like Antarctica," Tom Wagner, cryosphere program scientist at NASA headquarters in Washington, D.C., said in a statement. "But aircraft missions like Ice Bridge allow us to follow up with more detailed studies and make other measurements critical to modeling sea level rise."