Buried under Antarctica's miles-thick ice sheet, more than a hundred lakes are dotted around the continent. Now, for the first time, scientists are connecting the dots.
A new study found that natural "plumbing" can form under the ice, linking under-ice lakes that are hundreds of miles apart. These channels may allow water to gush suddenly from one lake to another.
Although the surface of East Antarctica is the coldest place on Earth, a combination of effects keeps the subglacial lakes from freezing.
Cold as it is, the ice cover forms a sort of insulating blanket that traps heat radiated by the Earth. In addition, the ice that traps the water in place exerts enormous pressure, which has the effect of lowering the freezing point of water.
The discovery, to be published in tomorrow's issue of the journal Nature, comes at a crucial moment.
A Russian team is poised to tap into Lake Vostok, the largest of the subglacial lakes, in search of microbes that may live inside.
But other researchers are concerned that the Russian team is being cavalier. Their untested drilling method risks contaminating the lake with foreign microbes, critics say.
If sudden and massive flows between the lakes are possible, this raises the stakes for such drilling projects. Contamination in one lake could spread to many neighboring lakes in the same watershed.
"Now you have to accept that there will be communication between the lakes," said Martin Siegert, a member of the research team and a glaciologist at the University of Bristol in the United Kingdom.
Go With the Flow
Climate physicist Duncan Wingham of University College London in the U.K. uses radar surveys to measure the elevation of the Antarctic ice sheet.
Recently he and colleagues spotted a strange event at Dome C, a peak on the ice sheet that covers a cluster of subglacial lakes.
In one area directly above a subglacial lake, the ice fell by more than ten feet (three meters) over the course of 16 months, from late 1996 to early 1998, Wingham's team found.
The ice elevation normally changes less than a tenth of that amount each year.
Over the same period in two neighboring areas 180 miles (290 kilometers) away, also above lakes, the ice rose by three feet (one meter) or more.
The only explanation, the researchers say, is that, in a process not yet completely understood, water suddenly rushed out of one lake, ran beneath the ice sheet, then pooled in other lakes.
The lake that lost water is about 230 square miles (600 square kilometers) in area, a bit larger than California's Lake Tahoe.
Thus, the researchers estimate, the water must have flowed out of the lake at a rate that was, on average, about equal to that of a major river, such as London's Thames.
Raising the Stakes
"The chances are that what we've seen is a very common process," Siegert said. "We just haven't seen it before."
Other researchers agree that the new findings increase the risk of contamination spreading between lakes.
"We have to assume in every case that this risk exists and work to address it," said microbial ecologist Cynan Ellis-Evans of the British Antarctic Survey.
Many scientists suggest probing one of the smaller subglacial lakes before hitting Lake Vostok and have urged the Russian team to hold off.
The critics recommend waiting until scientists have developed better equipment and gained a better understanding of the subglacial systems.
"This is why we are taking so much time to get into a subglacial lake," Ellis-Evans said.
Microbiologist John Priscu of Montana State University in Bozeman agrees that plans to drill into the lakes have to take account of connections between the lakes.
The new findings also indicate that "subglacial lakes play a larger role in polar regions than previously thought," Priscu said.
Some areas in Antarctica show evidence of catastrophic floods in the past. One such spot is the Labyrinth, where deep trenches are carved into Wright Valley, a relatively ice-free area of the continent.
Trenches like those in the Labyrinth would require far bigger flows than those that Wingham and colleagues found in their study. But it is possible that huge subglacial lakes dumped their waters in the past, Siegert and Priscu say.
"To cause some of these features, a large amount of meltwater must have been released," Siegert said. "The only candidates are subglacial lakes."