Lasers beamed from space have detected what researchers have long suspected: big sloshing lakes of water underneath Antarctic ice.

These lakes, some stretching across hundreds of square miles (km), fill and drain so dramatically that the movement can be seen by a satellite looking at the icy surface of the southern continent, glaciologists reported in Thursday's editions of the journal Science.

Global warming did not create these big pockets of water -- they lie beneath some 2,300 feet of compressed snow and ice, too deep to be affected by temperature changes on the surface -- but knowing how they behave is important to understanding the impact of climate change on the Antarctic ice sheet, study author Helen Fricker said by telephone.

About 90 percent of the world's fresh water is locked in the thick ice cap that covers Antarctica; if it all melts, scientists estimate it could cause a 23-foot (7-meter) rise in world sea levels. Even a 39-inch (1-meter) sea level rise could cause havoc in coastal and low-lying areas around the globe, according to a World Bank study released this week.

"Because climate is changing, we need to be able to predict what's going to happen to the Antarctic ice sheet," said Fricker, of the Scripps Institute of Oceanography and the University of California, San Diego.


"We need computer models to be faithful to the processes that are actually going on on the ice sheet," she said. At this point, computer models do not show how the subglacial water is moving around.

To detect the subglacial lakes, Fricker and her colleagues used data from NASA's ICESat, which sends laser pulses down from space to the Antarctic surface and back, much as sonar uses sound pulses to determine underwater features.

The satellite detected dips in the surface that moved around as the hidden lakes drained and filled beneath the surface glaciers, which are moving rivers of ice.

"The parts that are changing are changing so rapidly that they can't be anything else but (sub-surface) water," she said. "It's such a quick thing."

"Quick" can be a relative term when talking about the movement around glaciers, which tend to move very slowly. But one lake that measured around 19 miles by 6 miles (30 km by 10 km) caused a 30 foot (9 meter) change in elevation at the surface when it drained over a period of about 30 months, Fricker said.

The project took observations from 2003 through 2006 of the Whillans and Mercer Ice Streams, two of the fast-moving glaciers that carry ice from the Antarctic interior to the floating ice sheet that covers parts of the Ross Sea.