Information about Hydrothermal Vent

A hydrothermal vent, also called a "black smoker", is a fissure in a planet's surface from which geothermally heated water issues. Hydrothermal vents are commonly found near volcanically active places, tectonic plates that are moving apart, ocean basins, and hotspots.

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]

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.^[2] The brines and associated muds are currently under investigation as a source of mineable precious and base metals.

Submarine hydrothermal vents, specifically "black smokers", were discovered along the Galapagos Rift, a spur of the East Pacific Rise, in 1976 by a group of marine geologists studying ocean temperatures. The measured temperatures and collected evidence provided the scientists with enough information to conclude that the findings were from a hydrothermal vent plume. In 1977, geologists returned to the rift and used ALVIN, an ONR research submersible from Woods Hole Oceanographic Institute, to see the hydrothermal vent communities with their own eyes. In that same year, scientist Peter Lonsdale published the first scientific paper on hydrothermal vent life.

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.

The discovery of a vent in the Pacific Ocean offshore of Costa Rica, named the Medusa hydrothermal vent field (after the the serpent-haired Medusa of Greek mythology), was announced in April 2007.^[3]

Physical properties

Hydrothermal vents in the deep ocean typically form along the Mid-ocean ridges, such as the Mid-Atlantic Ridge. These are locations where upwellings of ascending mantle plumes occur between two tectonic plates at a divergent boundary.^[4]

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.^[5] 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.^[6] 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.^[7]

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 sulfur-bearing minerals, or sulfides. "White smokers" refer to vent that emit lighter-hued minerals, such as barium, calcium, and silicon. These vents also tend to have lower temperature plumes.

Biological communities

A hydrothermal vent community depends on chemosynthetic bacteria for food. The water that comes out of the hydrothermal vent is rich in dissolved minerals and supports a large population of 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 organisms such as snails, shrimp, crabs, tube worms, fish, and octopi 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 differs from most surface life on Earth which is based on solar energy. However, although it is often said that these communities exist independently of the sun, some of the organisms are actually dependent upon oxygen produced by photosynthetic organisms. Others are anaerobic as was the earliest life.

''"Enumeration of the anaerobic metal(loid)-resistant microbial community associated with hydrothermal vent animals indicates that a greater proportion of the bacterial community associated with certain vent fauna resists and reduces metal(loid)s anaerobically than aerobically, suggesting that anaerobic metal(loid) respiration might be an important process in bacteria that are symbiotic with vent fauna. [1] Some theories indicate that life originated at hydrothermal vents from inorganic precursors.

Tube worms form an important part of the community around a hydrothermal vent. The tube worms, like parasitic worms, absorb nutrients directly into their tissues. This is because tube worms have no mouth or even a digestive tract, so the bacteria live inside them. There are approximately 285 billion bacteria per ounce of tubeworm tissue. Tubeworms have red plumes which contain hemoglobin. Hemoglobin combines hydrogen sulfide and transfers it to the bacteria living inside the worm. In return the bacteria nourish the worm with carbon compounds. The two species that inhabit a hydrothermal vent are Tevnia jerichonana, and Riftia pachyptila. One community has been discovered dubbed 'Eel City', which consists predominantly of eels. Though eels are not uncommon, as mentioned earlier invertebrates typically dominate hydrothermal vents. Eel City is located near Nafanua volcanic cone, American Samoa.^[8]

Other examples of the unique fauna who inhabit this ecosystem are a snail armored with scales made up of iron and organic materials, and the Pompeii worm (Alvinella Pompejana), which is capable of withstanding temperatures up to 80°C (176°F).

Over 300 new species have been discovered at hydrothermal vents.^[9]

References

• Glyn Ford and Jonathan Simnett, Silver from the Sea, September/October 1982, Volume 33, Number 5, Saudi Aramco World Accessed 17 October 2005
• Neptune Minerals Ltd webpage - Exploring SMS deposits
• Ballard, Robert D., 2000, The Eternal Darkness, Princeton University Press.
• http://www.botos.com/marine/vents01.html#body_4
• Anaerobic respiration on tellurate and other metalloids in bacteria from hydrothermal vent fields in the eastern pacific ocean

See also

• Black smoker
• Cold seep
• Fumarole
• Geyser
• Hot springs
• Lost City
• Origin of life
• Submarine volcano

External links

• Hydrothermal Vent Systems Information from the Deep Ocean Exploration Institute, Woods Hole Oceanographic Institution
• A new type of hydrothermal vent
• Vent geochemistry
• Everything you wanted to know about hydrothermal vents and the deep sea — Provided by New Scientist.
• a good overview of hydrothermal vent biology, published in 2006
• Images of Hydrothermal Vents in Indian Ocean- Released by National Science Foundation