Warm ocean currents cause ice loss from Antarctica

Washington, April 26 (IANS) Warm ocean currents attacking the underside of ice shelves may help explain recent ice loss from Antarctica, says a new study.

A team of scientists used measurements from NASA's Ice, Cloud, and land Elevation Satellite (ICESat) and models to differentiate between the two known causes of melting ice shelves: warm ocean currents thawing the underbelly of the floating extensions of ice sheets and warm air melting them from above.

The finding brings scientists a step closer to providing reliable projections of future sea level rise. The researchers concluded that 20 of the 54 ice shelves are being melted by warm ocean currents.

Most of these are in West Antarctica, where inland glaciers flowing down to the coast and feeding into these thinning ice shelves have accelerated, draining more ice into the sea and contributing to sea-level rise, according to a statement of the British Antarctic Survey.

This ocean-driven thinning is responsible for the most widespread and rapid ice losses in West Antarctica, and for the majority of Antarctic ice sheet loss during the study period.

"We can lose an awful lot of ice to the sea without ever having summers warm enough to make the snow on top of the glaciers melt," said Hamish Pritchard of the British Antarctic Survey in Cambridge, UK, who led the study. "The oceans can do all the work from below."

To map the changing thickness of almost all the floating ice shelves around Antarctica, the team used a time series of 4.5 million surface height measurements taken by a laser instrument mounted on ICESat from October 2003 to October 2008.

"This study demonstrates the power of space-based, laser altimetry for understanding Earth processes," said Tom Wagner, cryosphere programme scientist at NASA Headquarters in Washington.

ICESat was the first satellite specifically designed to use laser altimetry (measuring the altitude of an object above a fixed level) to study the Earth's polar regions. It operated from 2003 to 2009. Its successor, ICESat-2, is scheduled for launch in 2016.