Spy satellite plumbs secrets of Antarctica.

In the frostiest campaign of the Cold War, the Central Intelligence Agency pointed covert satellite cameras toward Antarctica to map the frozen continent. Thirty-five years later, scientists are using declassified photographs from that mission to gain unparalleled insight into the behavior of Antarctica's icy cover.

A comparison of the CIA photographs with more recent data reveals that a giant river of Antarctic ice has slowed 50 percent in 3 decades, a much bigger change than scientists had expected. The discovery, reported in the Jan. 30 Science, complicates attempts to predict whether melting Antarctic ice will contribute to rising sea levels in the next century, say scientists.

"It makes our life harder," says study author Robert Bindschadler, a glaciologist at NASA's Goddard Space Flight Center in Greenbelt, Md.

The Antarctic analysis is the first scientific study to mine information from the formerly secret pictures, says Bindschadler. In 1995, President Clinton signed an order declassifying all intelligence satellite photography taken before 1972.

The CIA's Corona satellites carried large spools of film into space. After photographs were taken, the satellites jettisoned the exposed film, which was then snared in midfall by military planes. During 1963, the CIA photographed giant rivers of ice, called ice streams, which drain into the Ross Ice Shelf.

Up to 80 kilometers across and hundreds of kilometers long, ice streams flow 10 to 100 times faster than the ice along their banks. Scientists consider the streams critical to the stability of the ice sheet covering West Antarctica. If the streams were to speed up, they would drain ice from the interior of the continent and deposit it on the floating ice shelves, thus raising global sea levels (SN: 2/13/93, p. 104).

Bindschadler and Patricia Vornberger of General Science Corp. in Laurel, Md., compared satellite images to measure how far key features had moved over the decades. They calculate that Ice Stream B--one of the five leading into the Ross Ice Shelf--was traveling at about 970 meters per year in 1963. Researchers on the ice in 1984 and 1985 observed that the ice was then moving at only 471 in per year, less than half as fast. Over this same period, the ice stream widened by 4 km, much more than researchers had anticipated.

The combination of changes surprised Antarctic specialists--theory predicts that ice streams should behave in the opposite way. The relatively slowmoving banks of the ice stream are thought to restrict its flow. As the stream widens, the banks move away from the center of the stream and the ice there should flow faster, says Charles F. Raymond of the University of Washington in Seattle. "It's clear that it's not that simple," he says.