Hydrothermal vent

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A hydrothermal vent

A hydrothermal vent is a fissure in a planet's surface from which geothermally heated water issues. Hydrothermal vents are commonly found in places that are also volcanically active, where hot magma is relatively near the planet's surface.

Hydrothermal vents are abundant on Earth because it is both geologically active and has large amounts of water on its surface. Common land types include hot springs, fumaroles and geysers. The most famous hydrothermal vent system is probably Yellowstone National Park in the United States.

Relative to the majority of the deep sea, the areas around hydrothermal vents are biologically productive, often hosting complex communities fueled by the chemicals dissolved in the vent fluids. Chemosynthetic archaea form the base of the food chain, supporting diverse organisms, including giant tube worms, clams, and shrimp.

Active hydrothermal vents are believed to exist on Jupiter's moon Europa, and ancient hydrothermal vents have been speculated to exist on Mars.^[1]

1 Exploration
2 Physical properties
3 Biological communities
4 References
5 See also
6 External links

[edit] Exploration

In 1949 a deep water survey reported anomalously hot brines in the central portions of the Red Sea. Later work in the 1960s confirmed the presence of hot, 60 °C, saline brines and associated metalliferous muds. The hot solutions were emanating from an active subseafloor rift. The highly saline character of the waters were not hospitable to living organisms. The brines and associated muds are currently under investigation as a source of mineable precious and base metals.

Submarine hydrothermal vents (black smokers in this case) were discovered along the Galapagos Rift, a spur of the East Pacific Rise, in 1977 by Jack Corliss, Jerry van Andel, and Robert Ballard through the use of deep sea submersibles. Despite their inaccessible location on ocean floors, many have been thoroughly mapped and explored.

In 2005 Neptune Resources NL, a mineral exploration company, applied for and was granted 35,000 km² of exploration rights over the Kermadec Arc in New Zealand's Exclusive Economic Zone to explore for seafloor massive sulfide deposits, a potential new source of lead-zinc-copper sulfides formed from modern hydrothermal vent fields.

[edit] Physical properties

Hydrothermal vents in the deep ocean typically form along the Mid-ocean ridges, such as the Mid-Atlantic Ridge. These are locations of upwellings of ascending mantle plumes occur between two tectonic plates at a divergent boundary.^[2]

The water that issues from seafloor hydrothermal vents consists mostly of sea water drawn into the hydrothermal system close to the volcanic edifice through faults and porous sediments or volcanic strata, plus some magmatic water released by the upwelling magma.

In terrestrial hydrothermal systems the majority of water circulated within the fumarole and geyser systems is meteoric water plus ground water that has percolated down into the thermal system from the surface, but it also commonly contains some portion of metamorphic waters, sedimentary formational brines and magmatic water that is released by the magma. The proportion varies from location to location.

The water emerges from a hydrothermal vent at temperatures ranging up to 400°C, compared to a typical 2°C for the surrounding deep ocean water. The high pressure at these depths significantly expands the thermal range at which water remains liquid, and so the water doesn't boil. Water at a depth of 3,000 m and a temperature of 407°C becomes supercritical.^[3] However the increase in salinity pushes the water closer to its critical point.

Some hydrothermal vents form roughly cylindrical chimney structures. These form from minerals that are dissolved in the vent fluid. When the super-heated water contacts the near-freezing sea water, the minerals precipitate out to form particles which add to the height of the stacks. Some of these chimney structures can reach heights of 60 m.^[4] An example of such a towering vent is "Godzilla", a structure in the Pacific Ocean near Oregon that rose to 40 m before it fell over.

The initial stages of a vent chimney begin with the deposition of the mineral anhydrite. Sulfides of copper, iron and zinc then precipitate in the chimney gaps, making it less porous over the course of time. Vent growths on the order of 30 cm per day have been recorded.^[5]

Chimney structures that emit a cloud of black material are called "black smokers", named for the dark hue of the particles they emit. The black smokers typically emit particles with high levels of metal sulfides. Vents that emit lighter-hued minerals have also been discovered, and these are named "white smokers". They are typically lower in temperature than black smokers, and are deficient in copper, iron and hydrogen sulfide, while being rich in zinc.^[5]

[edit] Biological communities

A hydrothermal vent community depends on chemosynthetic bacteria for food. The water that comes out of the hydrothermal vent is both rich in dissolved minerals and chemosynthetic bacteria. These bacteria use sulfur compounds to produce organic material through the process of chemosynthesis.

The bacteria then grow into a thick mat which attracts other organisms such as amphipods and copepods which graze upon the bacteria directly. Larger organisims such as snails, shrimp, crabs, tube worms, fish, and octopuses form a food chain of predator and prey relationships above the herbivores. The ecosystem so formed is reliant upon the continued existence of the hydrothermal vent field as the primary source of energy, which is dissimilar to the wider Earth where solar energy is the basis for life.

Tube worms are a main part of a hydrothermal vent. The tube worms are unique in that they directly absorb nutrients into their tissues. The two species that inhabite a hydrothermal vent are Tevnia jerichonana, and Riftia pachyptila.

Over 300 new species have been discovered at hydrothermal vents.[1]