Lake Vostok is the largest of more than 140 subglacial lakes found under the surface of Antarctica. The overlying ice provides a continuous paleoclimatic record of 400,000 years, although the lake water itself may have been isolated for 15 to 25 million years. The lake is named after the Vostok, the 900-ton corvette of Russian Antarctic pioneer Fabian von Bellingshausen.
Lake Vostok is located beneath Russia’s Vostok Station under the surface of the central East Antarctic Ice Sheet, which is at 3488 metres (11,443.6 ft) above mean sea level. The surface of this fresh water lake is 4000 metres (13,123.4 ft) under the surface of the ice, which places it at 512 metres (1,679.8 ft) below sea level. Measuring 250 kilometres (155.3 mi) long by 50 kilometres (31.1 mi) wide at its widest point, Lake Vostok is similar in size to Lake Ontario. Lake Vostok covers an area of 15690 square kilometre. The average depth is 344 metres (1,128.6 ft). It has an estimated volume of 5400 cubic kilometres (1,295.5 cu mi). The lake is divided into two deep basins by a ridge. The liquid water over the ridge is about 200 metres (656.2 ft), compared to roughly 400 metres (1,312.3 ft) deep in the northern basin and 800 metres (2,624.7 ft) deep in the southern.
No water sample has been obtained yet.
Russian scientist P.A. Kropotkin first proposed the idea of fresh water under Antarctic ice sheets at the end of the 19th century. He theorized that the tremendous pressure exerted by the cumulative mass of thousands of vertical meters of ice could increase the temperature at the lowest portions of the ice sheet to the point where the ice would melt. Kropotkin’s theory was further developed by Russian glaciologist I.A Zotikov, who wrote his Ph.D. thesis on this subject in 1967. Russian scientist A.P. Kapitsa used seismic soundings in the region of Vostok Station in 1959 and 1964 to measure the thickness of the ice sheet.
When British scientists in Antarctica performed airborne ice-penetrating radar surveys in the early 1970s, they detected unusual radar readings at the site which suggested the presence of a liquid, freshwater lake below the ice. In 1991, Jeff Ridley, a remote sensing specialist with the Mullard Space Science Laboratory at University College London, directed theERS-1 satellite to turn its high-frequency array toward the center of the Antarctic ice cap. The data from ERS-1 confirmed the findings from the 1973 British surveys, but this new data was not published in the Journal of Glaciology until 1993. Space-based radar revealed that this subglacial body of fresh water was one of the largest lakes in the world—and one of some 140 subglacial lakes in Antarctica. Russian and British scientists delineated the lake in 1996 by integrating a variety of data, including airborne ice-penetrating radar imaging observations and space-based radar altimetry. It has been confirmed that the lake contains large amounts of liquid water under the more than 3 kilometres (1.9 mi) thick ice cap, promising to be the most unspoiled lake on Earth. The lake has at least 22 cavities of liquid water, averaging 10 kilometres (6.2 mi) each.
In 2005 an island was found in the central part of the lake. Then, in January 2006, the discovery of two nearby smaller lakes under the ice cap was published; they are named 90 Degrees East and Sovetskaya. It is suspected that these Antarctic subglacial lakes may be connected by a network of subterranean rivers. Centre for Polar Observation & Modelling glaciologists Duncan Wingham and Martin Siegert published in Nature in 2006 that many of the subglacial lakes of Antarctica are at least temporarily interconnected. Because of varying water pressure in individual lakes, large subsurface rivers may suddenly form and then force large amounts of water through the solid ice.
Geological History and Research
Africa separated from Antarctica around 160 million years ago, followed by the Indian subcontinent, in the earlyCretaceous (about 125 million years ago). About 65 million years ago, Antarctica (then connected to Australia) still had atropical to subtropical climate, complete with marsupial fauna and an extensive temperate rainforest.
The Lake Vostok basin is a small (50 km wide) tectonic feature within the overall setting of a several hundred kilometer widecontinental collision zone between the Gamburtsev Mountain Range, a subglacial mountain range and the Dome C region. The lake water is cradled on a bed of sediments 70 metres (229.7 ft) thick, offering the possibility that they contain a unique record of the climate and life in Antarctica before the ice cap formed.
The lake water is believed to have been sealed off under the thick ice sheet about 15 million years ago. Initially, it was thought that the same water had made up the lake since the time of its formation, giving a residence time in the order of one million years. Later research by Robin Bell and Michael Studinger from the Lamont–Doherty Earth Observatory of Columbia University suggested that the water of the lake is continually freezing and being carried away by the motion of the Antarctic ice sheet, while being replaced by water melting from other parts of the ice sheet in these high pressure conditions. This resulted in an estimate that the entire volume of the lake is frozen and removed every 13,300 years—its effective mean residence time.
Drilling for sample cores was halted in 1998 at roughly 100 metres (328.1 ft). In November 2010, when the team came up with new, ecologically-safe methods of probing the lake without contamination; the scientists submitted a final environmental evaluation of the project to the Antarctic Treaty System‘s environmental protection committee and were given the go-ahead to sample the ancient waters. In January 2011 the head of the Russian Antarctic Expedition, Valery Lukin, announced that his team had only 50 meters of ice left to drill in order to reach the water. The researchers then switched to a new thermal drill head with a “clean” silicone oil fluid to drill the rest of the way. Instead of drilling all the way into the water, they would stop just above it, when a sensor on the thermal drill detects free water. At that point, the drill will be stopped and extracted from the bore hole, thereby lowering the pressure beneath it and drawing water into the hole and left for quite some time to freeze, creating a plug of frozen ice in the bottom of the hole. Finally, next summer, the team would drill down again to take a sample of that ice and analyze it.
Drilling stopped on 5 February 2011 at a depth of 3720 metres (12,204.7 ft) so that the research team could make it off the ice and onto the last flight before the beginning of the Antarctic winter season. The drilling team left by aircraft on February 6 and will have to wait until the next austral summer begins in December 2011 to try again.
In the Antarctic summer of 2012–13, the Russian team also plans to send an underwater robot into the lake to collect water samples and sediments from the bottom. An environmental assessment of the plan will be submitted at the Antarctic Treaty’s consultative meeting in May 2012.
It was at Vostok Station that the coldest temperature ever observed on Earth was recorded on 21 July 1983. The average water temperature is calculated to be around -3 °C; it remains liquid below the normal freezing point because of high pressure from the weight of the ice above it. Geothermal heat from the Earth’s interior warms the bottom of the lake. The ice sheet itself insulates the lake from cold temperatures on the surface.
Researchers working at Vostok Station produced one of the world’s longest ice cores in 1998. A joint Russian, French, and United States team drilled and analyzed the core, which is 3623 metres (11,886.5 ft) long. Ice samples from cores drilled close to the top of the lake have been assessed to be as old as 420,000 years, suggesting that the lake was sealed under the ice cap 15 million years ago. Drilling of the core was deliberately halted roughly 100 metres (328.1 ft) above the suspected boundary where the ice sheet and the liquid waters of the lake are thought to meet. This was to prevent contamination of the lake from the 60 ton column of freon and kerosene Russian scientists filled it with to prevent the borehole from collapsing and freezing over.
From this core, specifically from ice that is thought to have formed from lake water freezing onto the base of the ice sheet,extremophile microbes were found, suggesting 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 oligotrophic extreme environment, one that is expected to be supersaturated with nitrogen and oxygen, measuring 2.5 liters of nitrogen and oxygen per 1 kilograms (2.2 lb) of water, that is 50 times higher than those typically found in ordinary freshwater lakes on Earth. The sheer weight and pressure (350 atmospheres) of the continental ice cap on top of Lake Vostok is believed to contribute to the high gas concentration.
Besides dissolving in the water, oxygen and other gases are trapped in a type of structure called a clathrate. 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 become unstable if brought to the surface.
In April 2005, German, Russian, and Japanese researchers found that the lake has tides. Depending on the position of the Sun and the Moon, the surface of the lake rises about 12 millimeters.
The lake is under complete darkness and expected to be rich in oxygen, so there is speculation that any organisms inhabiting the lake could have evolved in a manner unique to this environment. These adaptations to an oxygen-rich environment might include high concentrations of protective oxidative enzymes.
Living Hydrogenophilus thermoluteolus microorganisms have been found in Lake Vostok’s deep ice core drillings; they are an extant surface dwelling species. This suggests the presence of a deep biosphere utilizing a geothermal system of the bedrock encircling the subglacial lake. There is optimism that microbial life in the lake may be possible despite high pressure, constant cold, low nutrient input, potentially high oxygen concentration and an absence of sunlight.
Due to the lake’s similarity to Jupiter‘s moon Europa and Saturn‘s moon Enceladus, any confirmation of life living in Lake Vostok would strengthen the prospect for the possible presence of life on Europa or Enceladus.
The drilling project was opposed by some environmental groups and scientists who argued that hot-water drilling would do less environmental damage. The Russians however complained that hot-water drilling required more power than they could generate at their remote camp. Scientists of the United States National Research Council have taken the position that it should be assumed that microbial life exists in Lake Vostok and that after such a long isolation, any life forms in the lake require strict protection from contamination. Sediments on its floor should give clues to its long-term climate, and isotopes in its water are expected to help geologists determine how and when subglacial lakes such as Lake Vostok form. However, meticulously documented decontamination procedures will be required to establish the credibility of the scientific data obtained.
The drilling technique employed thus far by the Russians has involved the use of freon and kerosene to lubricate the borehole and prevent it from collapsing and freezing over; 60 tons of these chemicals have been used thus far on the ice above Lake Vostok. Other countries, particularly the United States and Britain, have failed to persuade the Russians not to pierce to the lake until cleaner technologies such as hot-water drilling are available. Though the Russians claims to have improved their operations, they continue to use the same borehole, which has already been filled with kerosene. According to the head of Russian Antarctic Expeditions, Valery Lukin, the new equipment had been developed by researchers at the St. Petersburg Nuclear Physics Institute that would ensure the lake remains uncontaminated upon intrusion. Lukin has repeatedly reassured other signatory nations to the Antarctic Treaty System that the drilling will not affect the lake. He argues that on breakthrough, water will rush up the borehole, freeze, and seal the chemical fluids out.
The international scientific community however remains unconvinced by these arguments. The Antarctic and Southern Ocean Coalition argues that this is a profoundly misguided step, which endangers not only Lake Vostok itself, but could harm other subglacial lakes in Antarctica, which some scientists are convinced are inter-linked with Lake Vostok. This coalition asserts that “it would be far preferable to join with other countries to penetrate a smaller and more isolated lake, before re-examining whether penetration of Lake Vostok is environmentally defensible. If we are wise, the Lake
will be allowed to reveal its secrets in due course.”