Подлёдное озеро Восток: крупнейшее в Антарктиде

Antarctica's largest known subglacial lake

Lake Vostok is located at the southern Pole of Cold, beneath Russia's Vostok Station under the surface of the central East Antarctic Ice Sheet, which is at above mean sea level. The surface of this fresh water lake is approximately under the surface of the ice, which places it at approximately below sea level. Measuring long by wide at its widest point, making it the 6th largest lake by volume. The lake is divided into two deep basins by a ridge. The liquid water depth over the ridge is about , compared to roughly deep in the northern basin and deep in the southern. The lake is named after Vostok Station, which in turn is named after the Vostok (Восток), a sloop of war, which means "East" in Russian. The existence of a subglacial lake in the Vostok region was first suggested by Russian geographer Andrey Kapitsa based on seismic soundings made during the Soviet Antarctic Expeditions in 1959 and 1964 to measure the thickness of the ice sheet. led to the final confirmation of the existence of the lake in 1993 by J. P. Ridley using ERS 1 laser altimetry. to 25 million years. On 5 February 2012, a team of Russian scientists completed the longest ever ice core of and pierced the ice shield to the surface of the lake. The first core of freshly frozen lake ice was obtained on 10 January 2013 at a depth of However, as soon as the ice was pierced, water from the underlying lake gushed up the borehole, mixing it with the Freon and kerosene used to keep the borehole from freezing. and Saturn's moon Enceladus.

Russian scientist Peter 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 decrease the melting point at the lowest portions of the ice sheet to the point where the ice would become liquid water. Kropotkin's theory was further developed by Russian glaciologist I. A. Zotikov, who wrote his PhD thesis on this subject in 1967. Kapitsa was the first to suggest the existence of a subglacial lake in the region, and the subsequent research confirmed his hypothesis. 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 the ERS 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 these new data were not published in the Journal of Glaciology until 1993. Space based radar revealed that this subglacial body of fresh water is 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 by integrating a variety of data, including airborne ice penetrating radar imaging observations and space based radar altimetry, and the discovery of the lake was published in the science journal Nature on 20 June 1996. It has been confirmed that the lake contains large amounts of liquid water under the more than ice cap. The lake has at least 22 cavities of liquid water, averaging each. The station after which the lake is named commemorates the Vostok (Восток), the 900 ton sloop of war ship sailed by one of the discoverers of Antarctica, Russian explorer Admiral Fabian von Bellingshausen. 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 subglacial rivers. Centre for Polar Observation & Modelling glaciologists propose that many of the subglacial lakes of Antarctica are at least temporarily interconnected. The Lake Vostok basin is a small tectonic feature within the overall setting of a several hundred kilometer wide continental 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 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 estimated to have been sealed off under the thick ice sheet about 15 million years ago. The coldest naturally occurring temperature ever observed on Earth, , was recorded at Vostok Station on 21 July 1983. Geothermal heat from the Earth's interior may warm the bottom of the lake, while the ice sheet itself insulates the lake from cold temperatures on the surface. Lake Vostok is an oligotrophic extreme environment, one that is expected to be supersaturated with nitrogen and oxygen, measuring of nitrogen and oxygen per of water, that is 50 times higher than those typically found in ordinary freshwater lakes on Earth's surface. The sheer weight and pressure around of the continental ice cap on top of Lake Vostok is estimated 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. Depending on the position of the Sun and the Moon, the surface of the lake rises about The lake is under complete darkness, under of pressure, 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. Living Hydrogenophilus thermoluteolus micro organisms 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. Jupiter's moon Europa and Saturn's moon Enceladus may also harbor lakes or oceans below a thick crust of ice. Any confirmation of life in Lake Vostok could strengthen the prospect for the presence of life on icy moons.

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 long. Ice samples from cores drilled close to the top of the lake have been assessed to be as old as 420,000 years. The assumption is that the lake has been sealed from the surface since the ice sheet was formed 15 million years ago. Drilling of the core was deliberately halted roughly above the suspected boundary between the ice sheet and the liquid waters of the lake. This was to prevent contamination of the lake with the 60 ton column of Freon and kerosene used to prevent the borehole from collapsing and freezing over. In January 2011, the head of the Russian Antarctic Expedition, Valery Lukin, announced that his team had only of ice left to drill in order to reach the water. Instead of drilling all the way into the water, they said they would stop just above it when a sensor on the thermal drill detected free water. At that point, the drill was to be stopped and extracted from the bore hole. Removal of the drill would lower the pressure beneath it, drawing water into the hole to be left to freeze, creating a plug of ice in the bottom of the hole. Drilling stopped on 5 February 2011 at a depth of so that the research team could make it off the ice before the beginning of the Antarctic winter season. The drilling team left by aircraft on 6 February 2011. By plan, the following summer, the team was to drill down again to take a sample of that ice and analyze it. The Russians resumed drilling into the lake in January 2012 and reached the upper surface of the water on 6 February 2012. The researchers allowed the rushing lake water to freeze within the bore hole and months later, they collected ice core samples of this newly formed ice and sent to the Laboratory for Glaciology and Environmental Geophysics in Grenoble, France, for analysis.

Scientists first reported evidence of microbes in the accretion ice in 1999. Since then, a different team led by Scott O. Rogers has been identifying a variety of bacteria and fungi from accretion ice (not from the subglacial water layer) collected during U. S. drilling projects in the 1990s. According to him, this indicates that the lake below the ice is not sterile but contains a unique ecosystem. Then Scott Rogers published in July 2013 that his team performed nucleic acid (DNA and RNA) sequencing and the results allowed deduction of the metabolic pathways represented in the accretion ice and, by extension, in the lake. The team found 3,507 unique gene sequences, and approximately 94% of the sequences were from bacteria and 6% were from Eukarya. Taxonomic classifications (to genus and/or species) or identification were possible for 1,623 of the sequences. In general, the taxa were similar to organisms previously described from lakes, brackish water, marine environments, soil, glaciers, ice, lake sediments, deep sea sediments, deep sea thermal vents, animals and plants. Sequences from aerobic, anaerobic, psychrophilic, thermophilic, halophilic, alkaliphilic, acidophilic, desiccation resistant, autotrophic, and heterotrophic organisms were present, including a number from multicellular eukaryotes. They found that the basal ice contained an almost completely different community of organisms compared to those found in the lake accretion ice, indicating that they signified two completely different ecosystems. Additional bacteria and eukaryotes were reported. The highest diversity of organisms in the lake ice was significantly associated (p<0.05) with higher concentrations of ions and amino acids. While their previous work indicated the presence of bacteria that inhabit fish intestines, no sequences from fish were found. However, in the 2020 study, they found an rRNA sequence that was >97% similar to that from a rock cod common along the coast of Antarctica (Notothenia coriiceps). This is the first report of a fish species possibly residing in Lake Vostok. The fish is known to produce antifreeze proteins. Microbiologist David Pearce of the University of Northumbria in Newcastle, UK, stated that the DNA could simply be contamination from the drilling process, and not representative of Lake Vostok itself. The old ice cores were drilled in the 1990s to look for evidence of past climates buried in the ice, rather than for life, so the drilling equipment was not sterilized. Also Sergey Bulat, a Lake Vostok expert at the Petersburg Nuclear Physics Institute in Gatchina, Russia, doubts that any of the cells or DNA fragments in the samples would belong to organisms that might actually exist in the lake. He says that it is very probable that the samples are heavily contaminated with tissue and microbes from the outside world. The contamination possibility has been refuted by Scott Rogers, because the control measures were rigorous, and the combinations of organisms found in each of the ice samples were consistent with organisms living in a cold lake and ice (including a sequence from an Antarctic rock cod), and were inconsistent with contamination introduced while sampling or from the lab procedures. Also, all of the lab procedures were performed in parallel with ice samples from Lake Erie, and the two resulting data sets were completely different. The Lake Erie sample exhibited many signals of human habitation, while the Lake Vostok ice samples exhibited no signals of human habitation. The Lake Erie sample also had an almost completely different profile of bacterial and eukaryotic phyla.

Russian and French scientists have been carrying out molecular DNA studies of the water from Lake Vostok that was frozen in the borehole, by constructing numerous DNA libraries, which are collections of fragments of DNA that allow scientists to identify which species of bacteria they may belong to. Samples taken from the lake so far contain about one part of kerosene per 1000 of water, and they are contaminated with bacteria previously present in the drill bit and the kerosene drilling fluid. So far, the scientists have been able to identify 255 contaminant species, but also have found an unknown bacterium when they initially drilled down to the lake's surface in 2012, with no matches in any international databases, and they hope it may be a unique inhabitant of Lake Vostok. However, Vladimar Korolev, the laboratory head of the study at the same institution, said that the bacteria could in principle be a contaminant that uses kerosene—the antifreeze used during drilling—as an energy source. Critics from the scientific community state that no valuable information can be obtained until they can test clean samples of lake water, uncontaminated by drilling fluid. Regardless of the contamination issues, in May 2013 the drilling facility at the Russian Vostok Antarctic station was declared a historic monument as "the result of the recognition of the achievements of the Russian research of Antarctica by the international scientific community, and of the unique operations on opening the subglacial Lake Vostok performed by Russian scientists on February 5, 2012." In January 2015, the Russian press stated that Russian scientists have made a new "clean" borehole into Lake Vostok using a special 50 kilogram probe that collected about 1 liter of water not adulterated by the antifreezing fluid. The drilling technology used proved to be inappropriate to collect liquid water in general and clean samples in particular and results were unreported. It was predicted that the water would rise 30–40 m in the bottom part of the borehole, but in fact the water rose from the lake to a height of more than 500 m. In October of that same year, the work was suspended for that southern summer because of insufficient funding by the federal Russian government. In 2019 the Russian government ordered that a new wintering complex be installed at the Lake Vostok research station, funded in part by Russian billionaire Leonid Mikhelson. This complex will be capable of supporting 35 people in the summer, 15 in the winter and will have 4 diesel generators with a capacity of 200 kilowatts each. The new complex, consisting of 133 modules, was delivered to Progress Station in December 2021 and will be transported to the Lake Vostok research station and installed over the next four years.

The drilling project has been opposed by some environmental groups and scientists who have argued that hot water drilling would have a more limited environmental impact. The main concern is that the lake could become contaminated with the antifreeze that the Russians used to keep the bore hole from refreezing. 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. The original drilling technique employed by the Russians involved the use of Freon and kerosene to lubricate the borehole and prevent it from collapsing and freezing over; of these chemicals have been used thus far on the ice above Lake Vostok. Though the Russians claim to have improved their operations, they continue to use the same borehole, which has already been contaminated with kerosene. According to the head of Russian Antarctic Expeditions, Valery Lukin, new equipment was developed by researchers at the Petersburg Nuclear Physics Institute that would ensure the lake remains uncontaminated upon intrusion. Some environmentalist groups remain unconvinced by these arguments. The Antarctic and Southern Ocean Coalition has argued that this manner of drilling is a profoundly misguided step which endangers Lake Vostok and other subglacial lakes in Antarctica (which some scientists are convinced are inter linked with Lake Vostok). Additionally, hot water drilling would have required more power than the Russian expedition could have generated at their remote camp.