Lake Untersee
Encyclopedia
Lake Untersee is the largest surface freshwater lake in the interior of the Gruber Mountains
Gruber Mountains
Gruber Mountains is a small group of mountains consisting of a main massif and several rocky outliers, forming the northeast portion of the Wohlthat Mountains in Queen Maud Land. Discovered and plotted from air photos by the German Antarctic Expedition, 1938–39, under Alfred Ritscher...

 of central Queen Maud Land
Queen Maud Land
Queen Maud Land is a c. 2.7 million-square-kilometre region of Antarctica claimed as a dependent territory by Norway. The territory lies between 20° west and 45° east, between the British Antarctic Territory to the west and the Australian Antarctic Territory to the east. The latitudinal...

 in East Antarctica
East Antarctica
East Antarctica, also called Greater Antarctica, constitutes the majority of the Antarctic continent, lying on the Indian Ocean side of the Transantarctic Mountains...

. It is situated 90 kilometres (55.9 mi) to the southwest of the Schirmacher Oasis
Schirmacher Oasis
The Schirmacher Oasis is a 25 km long and up to 3 km wide ice-free plateau with more than 100 fresh water lakes. It is situated in the Schirmacher Hills on the Princess Astrid Coast in Queen Maud Land in East Antarctica, and is on average 100 metres above sea level...

. The lake is approximately 6.5 kilometres (4 mi) long and 2.5 kilometres (1.6 mi) wide, with a surface area of 11.4 square kilometre, and a maximum depth of 169 metres (554.5 ft). The lake is permanently covered with ice and is partly bounded by glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...

 ice.

Lake Untersee is an unusual lake, with pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 between 9.8 and 12.1, dissolved oxygen at 150 percent supersaturation
Supersaturation
The term supersaturation refers to a solution that contains more of the dissolved material than could be dissolved by the solvent under normal circumstances...

 and very low primary production
Primary production
400px|thumb|Global oceanic and terrestrial photoautotroph abundance, from September [[1997]] to August 2000. As an estimate of autotroph biomass, it is only a rough indicator of primary production potential, and not an actual estimate of it...

 in the water column. In spite of the high O2 supersaturation in most of the lake, there is a small sub-basin at the southern end that is anoxic and its sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

s may have a higher methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

 concentration than those of any other known lake on Earth. Much of the primary production is in microbial communities that grow on the floor of the lake as stromatolite
Stromatolite
Stromatolites or stromatoliths are layered accretionary structures formed in shallow water by the trapping, binding and cementation of sedimentary grains by biofilms of microorganisms, especially cyanobacteria ....

s. 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 m (6.6–19.7 ft) thick. The ice cover may have persisted for over 100,000 years, and some scientists studying climate change fear significant environmental changes associated with global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

 in the coming decades. (In the past, the water chemistry of the lake has been compared to Clorox
Bleach
Bleach refers to a number of chemicals that remove color, whiten, or disinfect, often via oxidation. Common chemical bleaches include household chlorine bleach , lye, oxygen bleach , and bleaching powder...

. 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 concentrations, let alone high chlorite concentrations.)

Geography

Lake Untersee lies in the interior of the Gruber Mountains of central Queen Maud Land
Queen Maud Land
Queen Maud Land is a c. 2.7 million-square-kilometre region of Antarctica claimed as a dependent territory by Norway. The territory lies between 20° west and 45° east, between the British Antarctic Territory to the west and the Australian Antarctic Territory to the east. The latitudinal...

 in East Antarctica, which is roughly on the same longitude as Huab, in the Skeleton Coast National Park
Skeleton Coast National Park
Skeleton Coast National Park is a national park located in northwest Namibia, and has the most inaccessible shores, dotted with shipwrecks. The park is , and possibly the least visited park in the world...

 on the northern coast of Namibia
Namibia
Namibia, officially the Republic of Namibia , is a country in southern Africa whose western border is the Atlantic Ocean. It shares land borders with Angola and Zambia to the north, Botswana to the east and South Africa to the south and east. It gained independence from South Africa on 21 March...

. It is situated 90 kilometres (56 mi) to the southwest of the Schirmacher Oasis
Schirmacher Oasis
The Schirmacher Oasis is a 25 km long and up to 3 km wide ice-free plateau with more than 100 fresh water lakes. It is situated in the Schirmacher Hills on the Princess Astrid Coast in Queen Maud Land in East Antarctica, and is on average 100 metres above sea level...

.

The lake is approximately 6.5 kilometres (4 mi) long and 2.5 kilometres (1.6 mi) wide and has a surface area of 11.4 square kilometre (10 square kilometre is also reported). Its maximum depth is 169 metres (554.5 ft). It is permanently covered with ice, which has an average thickness of 3 metres (9.8 ft) in summer. The lake is dammed by the Anuchin Glacier
Anuchin Glacier
Anuchin Glacier is a glacier draining southward to Lake Unter-See in the northern part of the Gruber Mountains, Queen Maud Land. It was discovered, and plotted from air photos, by the Third German Antarctic Expedition, 1938–39...

, and meltwater from the Anuchin Glacier is the main source of water. The lake has no outlet. Water is lost through sublimation and ablation
Ablation
Ablation is removal of material from the surface of an object by vaporization, chipping, or other erosive processes. This occurs in spaceflight during ascent and atmospheric reentry, glaciology, medicine, and passive fire protection.-Spaceflight:...

 of the ice cover. The lake is categorized as an ultra-oligotroph
Oligotroph
An oligotroph is an organism that can live in an environment that offers very low levels of nutrients. They may be contrasted with copiotrophs, which prefer nutritionally rich environments...

ic lake.

History

Isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...

 studies have established that the lake has always had a permanent ice cover. Further, studies carried out during the austral
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...

 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 the Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...

 period when it emerged from a melt-water pond.

Studies of Lake Untersee have revealed that there are a number of large boulders which dam the lake. Geodetic
Geodesy
Geodesy , also named geodetics, a branch of earth sciences, is the scientific discipline that deals with the measurement and representation of the Earth, including its gravitational field, in a three-dimensional time-varying space. Geodesists also study geodynamical phenomena such as crustal...

 studies carried out during two summer seasons indicated that the boulders move at an annual rate of 1.1–3.9 m (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.

The lake was first discovered by the 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. Hermichen et al. (1985), E. Kaup et al. (1988) and A. Loopmann et al. (1988).

Research

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 and unstratified
Lake stratification
Lake stratification is the separation of lakes into three layers:# Epilimnion - top of the lake.# Metalimnion - middle layer that may change depth throughout the day.# Hypolimnion - the bottom layer....

. However, studies performed in the summer of 1991–92 found significant stratification in a 500 metres (1,640.4 ft) wide trough in the southeastern part of the lake, where it is up to 105 metres (344.5 ft) deep. There were sharp vertical gradients of temperature, pH, dissolved oxygen and electrical conductivity. While a thermocline
Thermocline
A thermocline is a thin but distinct layer in a large body of fluid , in which temperature changes more rapidly with depth than it does in the layers above or below...

 was recorded at a depth between 40 metres (131.2 ft) and 50 metres (164 ft), an oxycline followed at 70–80 m (229.7–262.5 ft), with a chemocline
Chemocline
A chemocline is a cline caused by a strong, vertical chemistry gradient within a body of water. A chemocline is analogous to a thermocline, the border at which warmer and cooler waters meet in an ocean, sea, lake, or other body of water...

 extending from 80 metres (262.5 ft) to bottom of the lake. Below 80 metres (262.5 ft), the water column was anoxic and smelled of hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

. The presence of hydrogen sulfide was associated with decreased sulfate
Sulfate
In inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...

 concentrations, indicating that it probably arose from bacterial reduction of sulfate.

The salt content of the upper levels of the lake is about 50 times that of glacial melt water. Salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...

 increased below 80 metres (262.5 ft), with sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

 ion concentration and electrolytic conductivity
Conductivity (electrolytic)
The conductivity of an electrolyte solution is a measure of its ability to conduct electricity. The SI unit of conductivity is siemens per meter ....

 more than doubling. The lake is highly alkaline (pH 10.4) down to a depth of 70 metres (229.7 ft); below this depth, pH drops, reaching the slightly acidic value of 6.1 at maximum depth. The proportion of methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

 in the sediment at the lake bottom is the highest recorded for any lake in the world, according to NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

 scientists.

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 . 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.

Expeditions

In November and December 2008, the "Tawani Foundation 2008 Antarctic International Expedition" headed by Richard Hoover of NASA's Marshall Space Flight Center
Marshall Space Flight Center
The George C. Marshall Space Flight Center is the U.S. government's civilian rocketry and spacecraft propulsion research center. The largest center of NASA, MSFC's first mission was developing the Saturn launch vehicles for the Apollo moon program...

 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 other moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

s and planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...

s 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 of extremophile
Extremophile
An extremophile is an organism that thrives in physically or geochemically extreme conditions that are detrimental to most life on Earth. In contrast, organisms that live in more moderate environments may be termed mesophiles or neutrophiles...

 microorganisms in the lake's waters, including a chemolithotroph that metabolises hydrogen.

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 the Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

 regolith
Regolith
Regolith is a layer of loose, heterogeneous material covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, some asteroids, and other terrestrial planets and moons.-Etymology:...

 and poles; monitor global climate change; and to evaluate methods for detecting hydrocarbon contamination and subsequent bio-remediation in a fragile, endangered ecosystem”. 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.

Experiments conducted have examined the metagenomes
Metagenomics
Metagenomics is the study of metagenomes, genetic material recovered directly from environmental samples. The broad field may also be referred to as environmental genomics, ecogenomics or community genomics. Traditional microbiology and microbial genome sequencing rely upon cultivated clonal cultures...

 of eukaryote
Eukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...

s; identified Prokaryote
Prokaryote
The prokaryotes are a group of organisms that lack a cell nucleus , or any other membrane-bound organelles. The organisms that have a cell nucleus are called eukaryotes. Most prokaryotes are unicellular, but a few such as myxobacteria have multicellular stages in their life cycles...

s and viruses inhabiting the lake;
provided evidence of virus-mediated horizontal gene transfer and adaptive metabolic or cold protective phenotype
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...

 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 using laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

-induced fluorescence
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...

 emission (L.I.F.E.) imaging techniques.

Two scientific divers were also part of this team. Dale Andersen, with the SETI Institute
SETI Institute
The SETI Institute is a not-for-profit organization whose mission is to “explore, understand and explain the origin, nature and prevalence of life in the universe”. SETI stands for the "search for extraterrestrial intelligence". One program is the use of both radio and optical telescopes to search...

’s Carl Sagan Center for the Study of Life in the Universe, and Ian Hawes of Aquatic Research Solutions dove in Lake Untersee to study its unique microbial communities.

A 270° image of Lake Untersee with the 2008 Tawani expedition camp can be found at http://gigapan.org/gigapans/7b0c7c5c7397379af609dadef8afe11e/

External links

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