Subglacial radar image of Lake Vostok. Source: NASAimages.org, http://mm04.nasaimages.org/MediaManager/srvr?mediafile=/Size4/NSVS-3-NA/4601/vostok.jpg.
Any decent world atlas or reference book worth its beans will display a list of various global superlatives, and always included is a list of the world’s largest lakes. It’s rather stunning though that most publications usually omit the 15th largest lake by area and 7th largest by volume on the entire planet. Of course, it’s easy to forget a body of water that no human has ever laid eyes upon, because this particular lake sits four kilometres below the surface of the East Antarctic ice sheet.
At 15 690 km2, Lake Vostok is the largest lake in Antarctica, and it is entirely subglacial. The only reason it remains liquid is due to the extreme pressure of the overlying ice; the actual lake water is below freezing at around -3°C. Named for the Russian research station it lies four kilometres beneath (the coldest place on Earth), the lake was discovered via radar by researchers from the Scott Polar Research Institute via radio-echo sounding in 1973. The actual dimensions of the lake were not delineated until 1996 by a Russian/British research team, however (perhaps this somewhat recent date is why Lake Vostok doesn’t get the credit it deserves). The lake consists of a northern (900 m below sea level) and southern basin (800-1700 m below sea level), with 22 subglacial water cavities around the lake.
The lake itself is quite old, perhaps more than 35 million years in age. Just because the lake has been completely sealed by ice for that period of time does not mean that the water remains static, however. As water at the top of the lake freezes to the bottom of the ice sheet, it is carried away by the ice sheet’s slow-but-steady march to the ocean. New water then enters the lake, most likely via subglacial meltwater. It takes 13 000 years for the equivalent of the volume lake to completely change over, but it does change over (the water itself is much older, perhaps 400 000 years in age but spending most of its time as ice before entering the lake). Lake Vostok isn’t the only subglacial lake underneath Antarctic ice sheets; NASA’s ICESat satellite has helped identify 145 such lakes beneath the ice. The lakes may even be connected by a network of subglacial rivers.
Because of the extreme isolation of the lake, it is believed that Lake Vostok’s waters could contain various undiscovered lifeforms and unique geochemical processes. Previous ice cores drilled into the accreted lake ice beneath the ice sheet have demonstrated a population of microorganisms. This has made it quite tantalising for scientists looking to drill through the ice sheet into the lake. NASA, for example, are interested in the lake for its conditions that are analogous to those on Jupiter’s moon Europa or subglacial polar regions of Mars; if life can be found in Lake Vostok, then it could potentially exist on extraterrestrial bodies with similar subglacial lakes. The issue, of course, is that once you’ve drilled even a slight hole into the lake, you’ve compromised the isolation of the lake and have potentially contaminated it.
Russia has been pushing for a long time to drill into the lake (a previous ice core drilling project was stopped 200 m above the lake surface to prevent contamination from the Freon and airplane fuel used to keep the drill cooled- this project may have discovered a thermophilic bacterium that would indicate the presence of heat vents on the lake floor and further the evidence that the deep lake was formed in a rift valley); there is only so much information about subglacial conditions you can glean from remote sensing. An observatory proposed by the Earth Institute at Columbia University would attempt to mitigate contamination concerns as much as possible. Meanwhile, a new Russian probe has drilled to within 100 m of the lake surface using new equipment designed to prevent contamination; it is scheduled to hit water in the next few months. It should be interesting to see what kind of microorganisms have evolved in the extremely oligotrophic, high-pressure environment where oxygen levels are 50 times greater than that in regular fresh water and pressure is 360 times greater than that at sea level above the surface.
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