Deep in the Antarctic interior, buried under thousands of meters (more than two miles) of ice, lies Lake Vostok, the world's largest subglacial lake. Scientists believe that the waters of Lake Vostok have not been disturbed for hundreds of thousands of years, and there are tantalizing clues that microbes, isolated for at least as long, may exist.
Now, the most comprehensive measurements of the lake — roughly the size of Lake Ontario in North America — indicate that it is divided into two distinct basins that may have different water chemistry and biological characteristics. The findings have important implications for the diversity of any microbial life in Lake Vostok and for how scientists should study the lake's various ecosystems, if an international scientific consensus is ever reached to explore the lake.
Lake Vostok is thought to be a very good terrestrial analogue to the conditions on Europa, a moon of Jupiter thought to hold a large liquid ocean far beneath its frozen surface. Scientists have argued that if microbial life can exist in Vostok, then it also might thrive on Europa.
In a paper published June 19, 2004 in Geophysical Research Letters, a journal of the American Geophysical Union, scientists from the Lamont-Doherty Earth Observatory of Columbia University and the University of Tokyo describe the first-ever map of water-depth in Lake Vostok.
Russia has long maintained a research station at Lake Vostok, and Russian scientists have previously probed the lake with seismic waves. But these soundings produced measurements of the water depth only at isolated points. The new measurements are significant because they provide a comprehensive picture of the entire lakebed and indicate that, contrary to what scientists had assumed, the bottom of the lake is not one continuous feature but contains a previously unknown northern sub-basin that is divided from the southern lakebed by a prominent ridge.
Michael Studinger of Lamont-Doherty, a principal author of the paper, said that the existence of two distinct regions within the lake would have significant implications for the kinds of ecosystems scientists could expect to find in the lake and how they should go about exploring them. "The ridge between the two basins will limit water exchange between the two systems," he said. "Consequently, the chemical and biological composition of these two ecosystems is likely to be different."
Using laser altimeter, ice-penetrating radar, and gravity measurements collected by aircraft flying over the lake, Studinger and Robin Bell of Lamont-Doherty and Anahita Tikku, then at the University of Tokyo, estimate that Lake Vostok contains roughly 5,400 cubic kilometers (1,300 cubic miles) of water.
Their measurements also indicate that the lake is divided into two distinct sub-basins separated by a narrow ridge. The water over that ridge is relatively shallow (200 meters or 650 feet deep), as compared to the rest of the lake, where the water ranges from roughly 400 meters (1,300 feet) deep in the northern basin to 800 meters (2,600 feet) deep in the southern. The National Science Foundation (NSF) supported the research.
The scientists conclude that the arrangement of the two basins, their separation, and the characteristics of the meltwater may all have implications for the circulation of water within the lake. For example, it is possible that if the water in the lake were fresh, the meltwater in the northern basin would sink to the bottom of that basin, limiting the exchange of waters between the two basins. The meltwater in the adjacent basin would likely be different. The two lake basins could therefore have very different bottoms and very different biological and chemical compositions.
Scientists involved in deciding whether and how to proceed with an exploration of Lake Vostok have stressed that a great deal of technological development would have to take place before a device could be deployed to conduct contamination-free sampling. Currently, there is no scientific sampling of the lake being carried out. The new measurements also indicate that different strategies would probably have to be developed depending on the types of lake sediments targeted. The ultimate goal of any sampling strategy would be to obtain water and sediment samples from the lake bottom.
The lake mapping would help to guide this scientific work. From the observed melting and freezing patterns of ice moving over Lake Vostok, it is evident that the northern basin would contain sediments of rock debris carried from land and deposited into the lake. The southern basin, where water is frozen back to the base of the ice sheet, would not have these same land deposits, but would more likely contain sediment deposits that recorded the environmental conditions before the ice sheet sealed off the lake.
For a NSF fact sheet on Lake Vostok, see: http://www.nsf.gov/od/lpa/news/02/fslakevostok.htm