Plumbing Antarctica for climate clues.

Climate scientists have been struggling for years to figure out whether global warming will awaken a sleeping southern giant: the vast glacial blanket covering the western portion of Antarctica. A trio of new studies in the Oct. 8 SCIENCE provides clues to how much of a threat this ice poses.

Unlike the more stable ice in East Antarctica, the West Antarctic Ice Sheet (WAIS) has melted and regrown in recent geologic times, raising the possibility that global warming could cause it to break up. This disaster would flood many coastal cities around the world.

In one new study, Howard B. Conway of the University of Washington in Seattle and his colleagues report on one piece of West Antarctica, the floating apron of ice covering part of the Ross Sea. During the peak of the last ice age 18,000 years ago, that entire ice layer reached all the way to the seafloor. Since then, the line where ice meets seafloor has retreated southward, by more than 1,000 kilometers in places.

By dating the positions of this so-called grounding line, Conway's group demonstrated that the retreat has been steady since the beginning of the warm period 10,000 years ago known as an interglacial episode. Any recent human-caused warming of the climate is simply adding to a process triggered by the end of the last ice age. "Continued recession and perhaps even complete disintegration of the WAIS within the present interglacial period could well be inevitable," concludes Conway's team.

Another group, led by Ian Joughin of the Jet Propulsion Laboratory in Pasadena, Calif., used satellite data to study rivers of ice flowing toward the Ross Sea. These broad currents, called ice streams, course at speeds hundreds of times faster than the movement of surrounding ice. Researchers are concerned about these currents because they would play a pivotal role if the West Antarctic ice sheet started to collapse.

Joughin and his colleagues analyzed data collected during a 30-day period in 1997, when a Canadian radar satellite was pointing south instead of in its normal northerly orientation. By comparing images taken weeks apart, the researchers mapped the speed of the Antarctic ice. They discovered tributaries extending hundreds of kilometers upstream of the ice streams. The researchers were surprised to find some tributaries feeding two different ice streams, says Joughin.

"What they've demonstrated is that with appropriate satellites, they can tell us what is going on. We're going to learn so much. It's phenomenal," says Richard B. Alley, a glaciologist at Pennsylvania State University in State College.

A third study showed that during the end of the last ice age, the thickness of the inner part of the West Antarctic ice sheet didn't change as much as previously thought.