Black smoker



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 Atlantic and Pacific Oceans, at an average depth of 2100 meters. The temperature of the water at the vent can reach 400 °C, 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 &mdash; approximately that of vinegar. Each year 1.4 &times; 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 &mdash; such as archaea and extremophiles &mdash; 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 Mexico at a depth of 2500 m. 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 (Beatty, et al., 2005).

New and unusual species are constantly being discovered in the neighborhood of black smokers: for instance, the Pompeii worm in the 1980s, and an armor-plated gastropod in 2001 during an expedition to Indian Ocean'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. This snail, which is unique in its kind, has not yet been named.