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Buried lake could test life's limits

Scientists find some of Earth's coldest, saltiest water beneath metres of Antarctic ice.
17 December 2002

PHILIP BALL

Lake Vida is covered with 19 meters of ice.
© Portland State Uni.

As salty as the Dead Sea and ten degrees below zero, Lake Vida, is one of the strangest, most inhospitable environments on Earth. Found under nineteen metres of ice in the parched and barren wastes of Antarctica, the polar lake might help researchers weigh the odds of life having existed on other worlds.

It could be an analogue of the last vestiges of liquid water on Mars, say discoverers Peter Doran of the University of Illinois in Chicago and coworkers who surveyed Lake Vida using drilling and radar1. It might also ape the salty global ocean thought to persist today beneath 4 kilometres of ice on Jupiter's moon Europa.

Extreme saltiness is one of the key differences between Lake Vida and Lake Vostok, a much bigger, freshwater lake in eastern Antarctica with an ice cap nearly four kilometers thick. NASA is considering sending a robotic water vehicle under the ice to probe Lake Vostok for life. Frozen bacteria have been found close to the bottom of its cap.

Very salty water is poisonous to many life forms. A few single-celled organisms thrive in places like the Dead Sea and the Great Salt Lake in Utah, which are of similar salinity to Lake Vida.

But Vida is also extremely cold. Salt puts its freezing point lower than that of pure water. Low temperatures tend to make protein molecules fall apart and lose their function, and organisms need special anti-freeze mechanisms to survive.

Doran's team drilled out columns of ice from the cap, reaching down to within about 3 meters of the water below. They didn't penetrate into the water to avoid contaminating the buried lake with organisms from the surface.

The ice core contains several layers of microbes clustered into mats, they report. These came to life when thawed. This suggests that the microbes might survive if the water level of the lake was to rise upwards by ice melting.

Microbes in the ice 12 meters below the surface are around 2800 years old. This implies that the remote little pocket of brine hasn't seen open air since the time of Homer.

Lake Vida is one of several lake basins in the McMurdo Dry Valleys near the coast of Antarctica, where less than 10 centimeters of snow fall all year and the temperature can drop to minus 30 ºC. With a surface area of 6.8 square kilometers, the lake was believed to be frozen solid.

Then a survey conducted in late 1995 found that radar waves were absorbed 19 meters below the ice surface, implying the presence of liquid water. The researchers estimate that the water is about 5 m deep. More of it might freeze - increasing the saltiness of the rest still further - if the valley has an even colder snap.

References
  1. Doran, P. T., Fritsen, C. H, McKay, C. P., Priscu, J. C. & Adams, E. E. Formation and character of an ancient 19-m ice cover and underlying trapped brine in an 'ice-sealed' east Antarctica lake. Proceedings of the National Academy of Sciences USA, published online, doi:10.1073/pnas.222680999 (2002). |Article|


© Nature News Service / Macmillan Magazines Ltd 2002

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