POSTED: 10:49 a.m. EST, February 16, 2007

WASHINGTON (Reuters) -- 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, 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 rise in world sea levels. Even a 39-inch sea level rise could cause havoc in coastal and low-lying areas around the globe, according to a World Bank study released this week.