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Lake Vostok

Lake Vostok is a subglacial lake in Antarctica . It is located at 77S 105E, beneath Russia's Vostok Station, 4000 meters under the surface of the central Antarctic ice sheet. It is 250 kilometers long by 40 kilometers wide at its widest point and is 500 meters deep. Lake Vostok is immense in size, covering an area of 14,000 square kilometers approximately the size of Lake Ontario. It has an estimated volume of 1800 cubic km and consists of freshwater.

Russian and British scientists discovered the lake existence in 1996 by integrating a variety of data, including airborne ice-penetrating radar observations and spaceborne radar altimetry. It has been confirmed that the lake contains plenty of liquid water under the kilometers deep ice-cap , promising to be the most pristine lake on Earth. Its water is very old, with a mean residence time in the order of 1 million years (as compared with 6 years for Lake Ontario which is typical for lakes of that size)

The average water temperature is around -3 C, below normal freezing point. As to why it remains liquid in the coldest place on Earth, it has been suggested that heat from the earth's interior (from radioactive decay) has kept it from freezing in the form of geothermal heat, radiating up from below warms rocks on the bottom of the lake. The ice sheet itself may be acting as a blanket, protecting the lake from cold temperatures on the surface.

Another possibility is that the lake has not yet had time enough to freeze after a temperate period that ended about 5,000 years ago. A third hypothesis has the lake remaining liquid due to the pressure of the ice bearing down on it.

Researchers working at Vostok Station produced one of the world's longest ice cores in 1998. A joint Russian, French, and U.S, team drilled and analyzed the core, which is 3623 meters (11,886 feet) long. Ice samples from cores drilled close to the top of the lake have been analysed to be as old as 420,000 years, suggesting that the lake has been sealed under the icecap for between 500,000 and more than a million years. Drilling of the core was deliberately halted roughly 150 meters (492 feet) above the suspected boundary where the ice sheet and the liquid waters of the lake are thought to meet to prevent contamination of the lake.

From this core, specifically from ice that is thought to have formed from lake water freezing onto the base of the ice sheet, evidence has been found, in form of some microbes, to suggest that the lake water supports life. Scientists suggested that the lake could possess a unique habitat for ancient bacteria with an isolated microbial gene pool containing characteristics developed perhaps 500,000 years ago.

Lake Vostok is an extreme environment, one that is supersaturated with oxygen, typically 50 times higher than the oxygen levels in ordinary freshwater lakes on Earth. This high pressure is due to the sheer weight of the continental ice-cap sitting on top of Lake Vostok. Besides dissolving in the water, oxygen and other gases also is trapped in a type of structure called a 'clathrate' (see Clathrate hydrate). In clathrate structures, gases are enclosed in an icy cage and look like packed snow. These structures form at the high pressure depths of Lake Vostok and would be unstable if brought to the surface.

Due to this fact, if water is released from Lake Vostok due to drilling, it could gush like a popped can of soda and if not contained, opening the lake to possible contamination and posing a potential health hazard to scientists.

No other natural lake environment on Earth has this much oxygen. Organisms in Lake Vostok are believed to be capable of overcoming very high oxygen stress. Organisms living in Lake Vostok may have had to evolve special adaptations, such as high concentrations of protective enzymes, in order to survive the lake's oxygen-rich environment.

Due to the lake's similiarity to Europa, a moon of Jupiter, confirming that life can survive in Lake Vostok might strengthen the argument for the presence of life on Europa.