06 September 2010

A Lake in Antarctica

In a radar image, Lake Vostok appears as a smooth patch. (NASA)

One of the largest lakes in the world is located in Antarctica. If you are familiar with Antarctica, this should sound strange, because the entire continent is covered with ice. It should be too cold for lakes to exist there, and that is true…on the surface. But some unique conditions exist that allow lakes of liquid water to form under kilometers of ice. They are called subglacial lakes, and about 150 have been found in Antarctica. Geothermal heat rises from the bedrock below the glacier, and the glacier itself traps the heat at the base, keeping it insulated from the surface, where the temperature can be -60C (-75F). The heat melts the bottom of the glacier, and depressions in the bedrock trap the liquid water as the glacier slides overtop, sealing it off. At high pressure water freezes at lower temperatures, so the millions of tons of ice pressing on the lake makes its temperature hover around -3C (27F), despite the lake being fresh water.

The largest of the subglacial lakes is called lake Vostok, after the Russian research station that sits on the ice 4000 meters (13,000 ft) above the lake. The lake is approximately the same size and shape as lake Ontario (250km by 50km). With an average depth of over 300m (1000 ft), Vostok is the 7th largest lake on Earth by volume.

Most interesting about lake Vostok is its potential as an ecosystem. The lake has been sealed off from the surface for at least one million years. It is possible that bacteria or other microorganisms have adapted to the unique environment of the lake, and a unique set of species may live in it. Space scientists are especially interested, because lake Vostok is incredibly similar to liquid oceans that are probably below the icy surfaces of Jupiter's moon Europa and Saturn's Enceladus. Sealed from the surface and with no sunlight, if life continues to exist in lake Vostok after millions of years, it would be the best evidence yet that those moons may be hosting primitive life right now. The lake can also be used to test robots that we might send to investigate the ocean below Europa. We might know more about life in the lake very shortly. The Russian research team has been drilling down to the lake for about 15 years, stopping and starting many times, partially for concerns about contaminating the sterile lake. In March of this year, they announced that they are only 100 meters from the surface of the lake, and expect to break through some time this winter.

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