Hydrothermal Vent

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Introduction

Hydrothermal Vent, spring of hot water on the deep ocean floor. The water is heated in Earth’s crust by volcanic magma or in the mantle by a process called serpentinization (a chemical reaction between water and certain minerals). Heated water circulating up through the crust becomes enriched with minerals and chemicals. The minerals precipitate out when the hot water meets the cold water and intense pressure on the ocean floor, forming chimneylike and towerlike structures. The enriched hot water also provides food and energy for extremophile microorganisms that use chemical processes (chemosynthesis) instead of sunlight (photosynthesis) to produce food. Other life forms in turn use the microorganisms and their byproducts as food, forming unusual ecosystems known as hydrothermal vent communities.

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Types of Hydrothermal Vents

Scientists have found hydrothermal vents in many geologically active areas of the ocean floor around the globe. At places where the seafloor crust is spreading apart from plate tectonics, seawater sinks deep into cracks in the ocean floor. The seawater is superheated in volcanic rock in the crust to temperatures up to 400°C (760°F). The water becomes chemically acidic, leaching minerals from surrounding rocks. Carrying mainly iron and sulfur minerals, the dark, mineral-rich solution can emerge in chimneylike structures called “black smokers.” Thick deposits of minerals rich in copper, iron, manganese, and zinc can form. Hydrogen sulfide is the main chemical used by microorganisms around the vents to produce food from carbon compounds.

Another type of hydrothermal vent occurs when seawater reacts with the mantle under the ocean crust. This process is not volcanic and heat comes instead from chemical reactions when rocks rich in magnesium and iron oxidize to produce serpentinite and other minerals. The water that emerges from the seafloor at such sites is relatively cool compared to water at magma-heated spots, and is chemically alkaline. Calcium carbonate and magnesium-containing minerals in the water precipitate out to form large, white, towerlike structures. Hydrogen and methane in the water provide food and energy for microorganisms at such sites.

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Study of Hydrothermal Vents

Hot springs on the ocean floor were proposed to exist in 1965, as part of the developing theory of plate tectonics. Scientists discovered the first hydrothermal vent on the ocean floor in 1977 near the Galápagos Islands in the Pacific Ocean, using the submersible craft Alvin. Undersea hydrothermal vents have since been found around the Pacific Ocean basin, along the mid-Atlantic ridge in the Atlantic Ocean, as well as at sites in the Indian Ocean, the Arctic Ocean, and elsewhere. Scientific research about hydrothermal vents involves the fields of geochemistry, geology, oceanography, marine biology, and microbiology.

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The discovery of marine life food chains that begin with chemosynthesis instead of photosynthesis was an important scientific breakthrough. Such organisms may provide clues about the origin of life on Earth and the possibility of life in space (see Astrobiology). Many unusual life forms such as archaea microbes and giant tube worms have been identified from hydrothermal vents. Similar communities of animals that depend on chemosynthesis have also been found around cold seeps—spots on the ocean floor where methane and hydrogen sulfide seep up from hydrocarbon and other organic deposits. Temperatures at cold seeps are the same as those in surrounding seawater.