Microbes turn up deep in Antarctic lake ice. (Life at the Frigid Edge).

A pocket of cold, concentrated saltwater at the bottom of Antarctica's Lake Vida has been sealed off from the world for at least 2,800 years. Yet it could still harbor life, say researchers who found microbes in the ice fight above the briny layer.

Peter T. Doran of the University of Illinois in Chicago and his team started studying the frozen 5-kilometer-long lake after learning that it contains liquid.

Previously, researchers thought that Lake Vida--one of the largest lakes in the McMurdo Dry Valleys desert--was just a "big chunk of ice," says Doran. However, in 1995 ice-penetrating radar revealed saltwater 19 meters down. "This brine pocket in the center of the lake popped up like a sore thumb," says Doran.

The next year, Doran and his colleagues returned to Lake Vida to obtain cores as deep as 15.8 m. However, fearing that they might contaminate the buffed pocket of liquid with contemporary microbes, they stopped their drilling short of it.

Instead, the researchers sampled the top of an overlying 3-m-thick layer of slushy saltwater. They also left probes at the bottom of the boreholes to monitor the temperature there for 4 years. The water is so salty--seven times the salt concentration of seawater--that it can remain liquid even at-10[degrees]C.

Lake Vida differs from other nearby, perennially ice-covered lakes. In those bodies, meltwater enters by flowing under a 3-to-6-m ice cover. In contrast, meltwater and sediments carrying microorganisms don't enter Lake Vida but instead freeze on top of it in a bubble-pocked layer thick enough to block sunlight from reaching the bottom. The resulting 19-m cover--the thickest lake ice ever recorded--is an "ice museum" recording biological history, says John C. Priscu of Montana State University-Bozeman.

The researchers were surprised to discover that 12-m-deep ice samples dated to 2,800 years ago contained viable microbial life. Some icebound microbes, such as cyanobacteria, became active and grew when the researchers, thawed them.

The scientists, who report their findings in an upcoming Proceedings of the National Academy of Sciences, plan to sample Lake Vida's brine in a few years. A similar challenge also faces scientists pining to sample Antarctica's Lake Vostok, which receives meltwater from the 4-km-thick glacier that covers it (SN: 10/2/99, p. 216).

Charles R. Bentley of the University of Wisconsin-Madison is eager to learn more about life in such an extreme environment. "The idea that the lake water has been isolated for at least 2,800 years is fascinating," he says.

Lake Vida is unique, agrees Diane M. McKnight of the University of Colorado in Boulder. It's the first example of an ice-sealed lake that has no contact with overlying glacial ice, new meltwater, or the atmosphere.

Priscu says that finding viable life in seemingly inhospitable places, such as deep in Lake Vida's ice, supports his view that Earth's biosphere is much larger than previously imagined. "The microbial world has few limits on our planet," he says.