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A black smoker in the Atlantic Ocean


A black smoker or sea vent, is a type of hydrothermal vent found on the ocean floor. They are formed in fields hundreds of meters wide when superheated water from below Earth's crust comes through the ocean floor. This water is rich in dissolved minerals from the crust, most notably sulfides. When it comes in contact with cold ocean water, many minerals precipitate, forming a black chimney-like structure around each vent. The metal sulfides that are deposited can become massive sulfide ore deposits in time.

Black smokers were discovered in 1977 on the East Pacific Rise by scientists from Scripps Institution of Oceanography. They were observed using a small submersible vehicle called Alvin. Now black smokers are known to exist in the Atlanticmarker and Pacificmarker Oceans, at an average depth of 2100 meters. The most northerly black smokers are a cluster of five named Loki's Castle, discovered in 2008 by scientists from the University of Bergenmarker at 73 degrees north, on the Mid-Atlantic Ridge between Greenland and Norway. These black smokers are of interest as they are in a more stable area of the Earth's crust, where tectonic forces are less and consequently fields of hydrothermal vents are less common.

The water at a vent can reach , but does not usually boil at the seafloor because the water pressure at that depth exceeds the vapor pressure of the aqueous solution. The water is also extremely acidic, often having a pH value as low as 2.8 — approximately that of vinegar. Each year 1.4 × 1014 kg (370 trillion gallons) of water is passed through black smokers.

Ecosystems



Although life is very sparse at these depths, black smokers are the center of entire ecosystems. Sunlight is nonexistent, so many organisms — such as archaea and extremophiles — convert the heat, methane, and sulfur compounds provided by black smokers into energy through a process called chemosynthesis. More complex life forms like clams and tubeworms feed on these organisms. The organisms at the base of the food chain also deposit minerals into the base of the black smoker, therefore completing the life cycle.

A species of phototrophic bacterium has been found living near a black smoker off the coast of Mexicomarker at a depth of . No sunlight penetrates that far into the waters. Instead, the bacteria, part of the Chlorobiaceae family, use the faint glow from the black smoker for photosynthesis. This is the first organism discovered in nature to use a light other than sunlight for photosynthesis.

New and unusual species are constantly being discovered in the neighborhood of black smokers: for instance, the Pompeii worm in the 1980s, and a scaly-foot gastropod in 2001 during an expedition to Indian Oceanmarker's Kairei hydrothermal vent field. The latter uses iron sulfides (pyrite and greigite) for the structure of its dermal sclerites (hardened body parts), instead of calcium carbonate. The extreme pressure of 2500 m of water (approximately 25 megapascals or 246.73 atmosphere) is thought to play a role in stabilizing iron sulfide for biological purposes. This armor plating probably serves as a defense against the venomous radula (teeth) of predatory snails in that community.

See also



References

  1. Beatty, et al., 2005




  • PMID 11557843
  • PMID 15967984


External links




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