| Lake Untersee | |
|---|---|
| Untersee (German) | |
.jpg) Lake Untersee in 1996 | |
  Lake Untersee Location of Lake Untersee inAntarctica | |
| Location | Queen Maud Land,Antarctica |
| Coordinates | 71°20′S13°27′E / 71.333°S 13.450°E /-71.333; 13.450 |
| Type | glacial |
| Etymology | "Lower Lake" (from German "unter" [lower] + "see" [lake]) |
| Basin countries | (Antarctica) |
| Max. length | 6.5 kilometres (4.0 mi) |
| Max. width | 2.5 kilometres (1.6 mi) |
| Surface area | 11.4 square kilometres (4.4 sq mi) |
| Max. depth | 169 metres (554 ft) |
| Surface elevation | 563 metres (1,847 ft) |
| Frozen | Permanently |
| References | Wand et al.[1] |
Lake Untersee (German:Untersee, "Lower Lake") is the largest surface freshwater lake in the interior of theGruber Mountains of centralQueen Maud Land inEast Antarctica. It is situated 90 kilometres (56 mi) to the southeast of theSchirmacher Oasis. The lake is approximately 6.5 kilometres (4.0 mi) long and 2.5 kilometres (1.6 mi) wide, with a surface area of 11.4 square kilometres (4.4 sq mi), and a maximum depth of 169 metres (554 ft). The lake is permanently covered with ice and is partly bounded byglacier ice.[2][3]
Lake Untersee is an unusual lake, withpH between 9.8 and 12.1,[1][4] dissolved oxygen at 150 per centsupersaturation, and very lowprimary production in the water column. Despite the high oxygen supersaturation in most of the lake, there is a small sub-basin at the southern end that is anoxic, and itssediments may have a highermethane concentration than those of any other known lake on Earth.[4][5] Much of the primary production is in microbial communities that grow on the floor of the lake asstromatolites.[6] The water temperature varies between 0.5 °C (32.9 °F) and 5 °C (41 °F) and the ice cover on the lake is 2–6 metres (6.6–19.7 ft) thick.[1][4] The ice cover may have persisted for over 100,000 years, and some scientists studying climate change fear significant environmental changes associated withglobal warming in the coming decades.[3] In the past, the water chemistry of the lake has been compared toClorox.[7] However, the chemical activity of bleach is due to Cl− in addition to a pH that is higher than that measures in Lake Untersee, and Lake Untersee does not have high chlorine or chlorite concentrations.[1][4]
Lake Untersee lies in the interior of the Gruber Mountains of centralQueen Maud Land in East Antarctica, which is roughly on the same longitude asHuab, in theSkeleton Coast National Park on the northern coast ofNamibia. It is situated 90 kilometres (56 mi) to the southeast of theSchirmacher Oasis.[8]Aurkjosen Cirque lies at the east side of the lake.[9]
The lake is approximately 6.5 kilometres (4.0 mi) long and 2.5 kilometres (1.6 mi) wide and has a surface area of 11.4 square kilometres (4.4 sq mi) (10 square kilometres (3.9 sq mi) is also reported). Its maximum depth is 169 metres (554 ft). It is permanently covered with ice, which has an average thickness of 3 metres (9.8 ft) in summer.[1] The lake is dammed by theAnuchin Glacier, and meltwater from the Anuchin Glacier is the main source of water.[1] The lake has no outlet. Water is lost throughsublimation andablation of the ice cover. The lake is categorized as an ultra-oligotrophic lake.[1]
Lake Ober-See, a smaller (3.4 square kilometres (1.3 sq mi) glacial lake, is located a few kilometres to the northeast and is similar in most respects.[10]
Isotope studies have established that the lake has long had a permanent ice cover. Further, studies carried out during theaustral summer confirm the lake's homogeneous characteristics, with thermal convection as the reason given for its hydro-geochemical and isotropical nature. It is replenished perennially by a process of underwater melting of the adjacent glacier ice. It is also stated that the lake existed during theHolocene period when it emerged from a melt-water pond.[2]
Studies of Lake Untersee have revealed that there are several large boulders which dam the lake.Geodetic studies carried out during two summer seasons indicated that the boulders move at an annual rate of 1.1–3.9 metres (3.6–12.8 ft). Residence time of the boulders has been estimated as 500 years. The floating boulders, which are several metres in diameter, have evolved as result of debris deposits from pro-glacial interaction, mass wasting from hills surrounding the lake and the displacement of glacial ice by lake ice.[11]
The lake was first discovered bythe German Antarctic Expedition of 1938–39. After that, several expeditions have studied the lake's characteristics. The first reconnaissance study of the lake was carried out by N. G. Kosenko and D. D. Kolobov in early 1969, followed by more studies by Russian and German scientists, namely by W. D. Hermichenet al. (1985), E. Kaupet al. (1988) and A. Loopmannet al. (1988).[1]
In studies carried out prior to 1991–92 on physical and chemical parameters of the lake water, Lake Untersee was stated to be well-mixed andunstratified. However, studies performed in the summer of 1991–92 found significant stratification in a 500-metre (1,600 ft) wide trough in the southeastern part of the lake, where it is up to 105 metres (344 ft) deep.[1] There were sharp vertical gradients of temperature, pH,dissolved oxygen andelectrical conductivity. While athermocline was recorded at a depth between 40 metres (130 ft) and 50 metres (160 ft), an oxycline followed at 70–80 metres (230–260 ft), with achemocline extending from 80 metres (260 ft) to bottom of the lake. Below 80 metres (260 ft), the water column wasanoxic and smelled ofhydrogen sulfide. The presence of hydrogen sulfide was associated with decreasedsulfate concentrations, indicating that it probably arose frombacterial reduction of sulfate.[1]
The salt content of the upper levels of the lake is about 50 times that of glacial melt water.[2]Salinity increased below 80 metres (260 ft), withsodium ion concentration andelectrolytic conductivity more than doubling.[1] The lake is highly alkaline (pH 10.4) down to a depth of 70 metres (230 ft); below this depth, pH drops, reaching the slightly acidic value of 6.1 at maximum depth. The proportion ofmethane in the sediment at the lake bottom is the highest recorded for any lake in the world, according toNASA scientists.[12]
In 2008, as part of the Tawani Foundation 2008 Antarctic International Expedition (see below), Dale Andersen and Ian Hawes discovered conical stromatolites growing in Lake Untersee, the largest living ones known to date.[6] Small microbial pinnacles are also present, and it appears that the large conical stromatolites and the small pinnacles are made by different microbial communities. These communities provide an important analog to some of the oldest fossil stromatolites found to date.
In November and December 2008, the "Tawani Foundation 2008 Antarctic International Expedition" headed by Richard Hoover of NASA'sMarshall Space Flight Center used the lake as a test bed in its hunt for extreme life. Conditions in the lake are similar in some respects to those thought to exist on othermoons andplanets that contain water ice and methane; thus, this lake might provide an analog to environments that exist elsewhere in space. The expedition did find several new strains ofextremophile microorganisms in the lake's waters, including achemolithotroph that metabolises hydrogen.[13]
This expedition involved an interdisciplinary international team of ten scientists and two teachers who explored not only Lake Untersee but also the Schirmacher Oasis. The geomicrobiological aspects of this expedition had three objectives: "to test laser induced fluorescence emission (L.I.F.E.) to be used for the exploration of theMarsregolith and poles; monitor global climate change; and to evaluate methods for detecting hydrocarbon contamination and subsequent bio-remediation in a fragile, endangered ecosystem."[3] The results indicate that Lake Untersee, as a permanently ice-covered region, has very little usable soil and could be likened to the polar regions of Mars.[3]
Experiments conducted have examined themetagenomes ofeukaryotes; identifiedProkaryotes and viruses inhabiting the lake; provided evidence of virus-mediatedhorizontal gene transfer and adaptive metabolic or cold protectivephenotype alterations, identified microbial nanowire connections between multiple species at the ice-water interface, in the water column, and in the sediment; and established biomass estimates of life in the lake ice during the early spring growing season usinglaser-inducedfluorescence emission (L.I.F.E.) imaging techniques.[3]
Two scientific divers were also part of this team. Dale Andersen, with theSETI Institute's Carl Sagan Center for the Study of Life in the Universe, and Ian Hawes of Aquatic Research Solutions dived in Lake Untersee to study its unique microbial communities.
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