Drilling into the past

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Details of a huge and unusual freshwater lake have recently been revealed for the first time. The lake is situated in the driest place on Earth Antarctica and has never been seen by human eye, because it is buried under some four kilometres of ice. It extends over an area of 14,000 square kilo­metres comparable in size to Lake Ontario, and 21 times larger than Lake Taupo and in places may be more than 500 metres deep.

Given that the mean temperature on the surface of the ice above the lake is no higher than -50°C, one might wonder at liquid water deeper down. The reason is that heat is constantly escaping from ‘ the Earth’s core, and the thick ice actually acts as an insu­lating blanket to keep out the cold. Even so, at one end of the lake the temperature is a chilly -3.15°C, and at the other, downstream, end, 200 kilometres away, it is -2.46°C.

First evidence for the existence of the lake came in the mid 1970s from a radio-echo sounding survey of ice depths over east Antarctica. Then satellite altimetry in 1993 provided very accurate altitudes over a broad swathe of Antarctica, revealing areas of level ice that corresponded to the lake of the radio-echo survey. Seismic data has since revealed that the ice is 3700 m thick, the water is 510 m deep, and the lake floor is 700 m below sea level. The ice in that part of Antarctica is actually floating on the lake.

Calculations of precipita­tion, ice thickness and heat flow suggest that 1 mm of ice melts from the bottom of the ice sheet into the lake each year, and that it takes a million years for snow precipitated at the surface to reach the lake. Once melted, water is thought to remain in the lake for 50,000 years.

As the ice melts into the lake, microorganisms and dust (presumably blown to Antarctica from surrounding land, and carried down with the ice) are released into its botttom of the lake, and this may be up to 100 m thick.

Despite the extreme conditions huge pressures, low nutrient status of the lake waters, complete darkness life is likely to exist in the lake’s depths. Scientists believe that the lake waters may contain organisms from a million or more years ago organisms that have been completely sealed off from all contact with the modern world, including its life forms and its atmosphere.

For the past three years, a deep drilling project has been taking cores from the ice above the lake, which has been named Lake Vostok. Microbes are being found in the cores. The oldest viable organisms so far recovered are spore-forming bacteria from 2395 metres down, corresponding to an age of 200,000 years.

At a workshop held earlier this year at the Scott Polar Research Institute in Cambridge to discuss the biological implications of the lake and its possible inhabit­ants, it was de­cided that drilling should not ap­proach the lake for fear of contaminating it with drilling mud and organisms from world .

Accordingly, drilling has halted 250 metres above the lake surface.Sampling the water without contaminating it is beyond the present capabili­ties of drilling technology, but the prospect of finding million-year-old organisms will no doubt ensure that efforts to do the impossible will be made in the not too distant future.

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