London, November 23 An analysis of data from a gravity-measuring satellite mission has determined that the East Antarctic ice sheet has been losing mass for the last three years.

According to a report by BBC News, the data comes from NASA's Gravity Recovery and Climate Experiment (Grace) mission.

The scientists involved say they are "surprised" by the finding, because the giant East Antarctic sheet, unlike the west, has been thought to be stable.

Other scientists say that ice loss could not yet be pinned on climate change, and uncertainties in the data are large.

Grace has previously shown that the smaller West Antarctic and Greenland ice sheets are losing mass.

These two bodies of ice contain enough water to raise sea levels by about six to seven metres (20ft) each if they melted completely.

Melting the East Antarctic sheet would raise sea levels by much more - about 50-60 m.

But, scientists have generally discounted the possibility of it happening because the region is so cold.

The Grace measurements suggest there was no net ice loss between 2002 and 2006. But since then, East Antarctica has been losing 57 billion tonnes (Gt) per year.

"We felt surprised to see this change in East Antarctica," study leader Jianli Chen from the Centre for Space Research at the University of Texas in Austin told BBC News.

The Grace data gives a picture of where ice is being lost across the continent; and these areas are mainly on the coast.

It is not clear what physical processes could be driving any loss of mass here, although it is not simply melting due to high air temperatures, because temperatures are well below zero.

One clue could lie in research published last year by Leigh Stearns and colleagues, showing that lakes under the ice sheet can periodically overflow, with the liquid water then acting as a lubricant to speed glaciers on their way towards the sea.

Commenting on the new research, Dr Stearns told BBC News, "In these coastal regions, the ice loss could be driven by some interaction with the oceans or some weather patterns, or it could be a sub-glacial lake that drained and caused some thinning - so it might not be climate-related."

"It awakens us to the fact that the East Antarctic sheet is more dynamic than we thought, and we do need to pay attention to it because its potential for sea level rise is so much greater than in West Antarctica or Greenland," she said. (ANI)