Hydrothermal vents

Hydrothermal vents are places where hot fluids (up to 752°F [400°C]) related to volcanic activity are released from the ocean floor. Because of the high pressure exerted by the water at depth on the sea floor, hydrothermal fluids can exceed 212°F (100°C) without boiling. The most visible indications of on-going volcanic activity are the plumes of hot fluids issuing from hydrothermal vents, which have been directly observed by scientists in deep-sea submersible vessels. Oceanographer Jack Corliss is credited with discovering the seafloor geysers in volcanic ridges in the Pacific Ocean in 1977.

These vents can occur as cracks in the top of cones of basalt (a dark, fine-grained rock that makes up most of the earth's crust). Or, the vents can issue from chimney-like structures that extend upward from the ocean floor. Some vents have lower fluid temperatures and release light-colored precipitates of silica; these vents are called "white smokers." But often, the fluids are black due to the presence of very fine sulfide mineral particles that precipitate out as the fluids cool. The sulfides present in these "black smokers" may contain amounts of iron , copper , zinc, and other metals that have been dissolved from underlying fresh basalt and concentrated in the hot solutions. These minerals can accumulate around the vents as sulfide deposits in mounds or chimney shapes up to 148 ft (45 m) high.

Hydrothermal vents usually occur along mid-ocean ridges where erupting basalt cools and creates new sea floor. The exact locations of the vents are controlled by cracks and faults in the basaltic rock. Isolated hydrothermal vents have also been found on seamounts and in Lake Baikal in Siberia.

Along the mid-ocean ridges, the heat of the magma that rises continuously from the mantle to form new oceanic crust causes water to convect through the top mile or two (2–3 km) of oceanic crust over many thousands of square miles. Down-convected ocean water encounters hot rocks at depth, is heated, yields up its dissolved magnesium , and leaches out manganese, copper, calcium , and other metals. This hot, chemically altered brine then convects upward to the ocean floor, where it is cooled and its releases most of its dissolved minerals as solid precipitates. This process makes the concentrations of vanadium, cobalt, nickel, and copper in recent sea-floor sediments near mid-ocean ridges 10–100 times greater than those elsewhere, and has formed many commercially important ores.

Two of the metals transported in large quantities by sea-floor circulation (i.e., calcium and magnesium) are important controllers of the carbon dioxide (CO2) balance of the ocean and thus of the atmosphere. A volume of water approximately equal to the world's oceans passes through the hydrothermal mid-ocean ridge cycle every 20 million years.

In the late 1980s, a mysterious illumination coming from some hydrothermal vents not visible to human eyes was discovered, and it has yet to be explained. Scientists at first thought the light was thermal radiation from the hot water, but other explanations have been proposed including crystalloluminescence (salt in the water responding to the heat) or chemiluminescence (from energy released during chemical reactions in the water). The faint glow is certainly important to the life forms around the vents.

The vents support living communities called ecotones that are transition zones between the hot vent water and the surrounding cold ocean water. The unusual forms of sea life that surround the hydrothermal vents include giant clams, tube worms, and unique types of fish that thrive on the energy-rich chemical compounds transported by hydrothermal fluids from the vents. This is the only environment on Earth supported by a food chain that does not depend on the energy of the sun or photosynthesis and lives by chemosynthesis instead. If the light source is sufficient to cause photosynthesis on the ocean floor, this is the only known photosynthesis not initiated by the Sun. Scientists have also found an apparently blind species of shrimp around the vents; instead of eyes, the shrimp has light-sensing patches on its back suggesting that evolution adapted the creature to the faint light source. Microbes called hyperthermophiles have also been found in vent water. The heat from the vents and the unusual life forms have prompted speculation that life on Earth originated on the sea floor near the vents or repopulated the planet after asteroid impacts. In fact, astrobiologists greatly interested in research on the origins of life prompted by these deep-sea finds.

See also Bedrock; Hot spot; Volcano.

Hydrothermal Vents

A hydrothermal vent is a geyser that is located on the floor of the sea. The first such vent was discovered in 1977 on the floor of the Pacific Ocean. Since then, vents have been discovered at a variety of locations in the Pacific Ocean, Atlantic Ocean, Indian Ocean, and even in the water under the polar ice cap.

The vents tend to be located deep in the ocean. For example, in the Atlantic Ocean, some 7,000 ft (2,134 m) beneath the surface, hydrothermal vents are associated with underwater mountain chain called the Mid-Ocean Ridge. This ridge is geologically active with an upwelling of hot magma and volcanic activity. The tectonic plate movements cause faulting and the seawater that enters the cracks is superheated by the molten magma. The superheated water and steam and spews out through hydrothermal vents.

Some vents, known as “black smokers,” spew out a black-colored mixture of iron and sulfide. “White smokers” eject a whitish mix of barium, calcium, and silicon.

This eruption through the hydrothermal vents is continuous, in contrast with the sporadic eruptions of surface geysers. The material that emerges from hydrothermal vents is extremely hot (up to 750°F [398.89°C]) and is very rich in minerals such as sulfur. The minerals can precipitate out of solution to form chimneys. The construction of a chimney can occur quickly. Growth of 30 ft (9 m) in 18 months is not unusual. The tallest of these chimneys that has been measured was the height of a 15 story building.

A vibrant community of bacteria, tubeworms that are unique to this environment, and other creatures exists around hydrothermal vents. The entire ecosystem is possible because of the activity of the bacteria. The work of Holger Jannasch (1927-1998) at the Woods Hole Oceanographic Institution, established that these bacteria utilize sulfur to produce energy in a process of chemosynthesis that does not require direct light from the sun. The chemical energy is then available for use by the other life forms, which consume the bacteria, or consume the organisms that rely directly on the bacteria for nourishment. For example, the tubeworms have no means with which to take in or process nutrients. Their existence relies entirely on the bacteria that live in their tissues.

Research lead by scientists at Woods Hole is progressing to catalogue the life at hydrothermal vents, particularly the bacterial varieties, and to genetically compare the bacteria from different locations around the globe. An expedition planned for 2007 will for the first time study the hydrothermal vents in the Arctic Ocean.

Hydrothermal vents

A hydrothermal vent is a geyser that is located on the floor of the sea. The first such vent was discovered in 1977 on the floor of the Pacific Ocean. Since then, vents have been discovered at a variety of locations in the Pacific and Atlantic Oceans.

The vents tend to be located deep in the ocean. For example, in the Atlantic ocean, some 7000 feet beneath the surface, hydrothermal vents are associated with underwater mountain chain called the Mid-Ocean Ridge. This ridge is geologically active with an upwelling of hot magma and volcanic activity. The tectonic plate movements cause faulting and seawater that then enters the cracks is superheated by the molten magma. The superheated water and steam and spews out through hydrothermal vents.

Some vents, known as "black smokers," spew out a black-colored mixture of iron and sulfide. "White smokers" spew out a whitish mix of barium, calcium, and silicon.

This eruption through the hydrothermal vents is continuous, in contrast with the sporadic eruptions of surface geysers. The material that emerges from hydrothermal vents is extremely hot (up to 750° F [398.89° C]) and is very rich in minerals such as sulfur. The minerals can precipitate out of solution to form chimneys. The construction of a chimney can occur quickly. Growth of 30 feet in 18 months is not unusual. The tallest of these chimneys that has been measured was the height of a 15 story building.

A vibrant community of bacteria , tubeworms that are unique to this environment, and other creatures exists around hydrothermal vents. The entire ecosystem is possible because of the activity of the bacteria. These bacteria have been shown, principally through the efforts of the Holger Jannasch (1927–1998) of Woods Hole Oceanographic Institution, to accomplish the conversion of sulfur to energy in a process that does not utilize sunlight called chemosynthesis. The energy is then available for use by the other life forms, which directly utilize the energy, consume the bacteria, or consume the organisms that rely directly on the bacteria for nourishment. For example, the tubeworms have no means with which to take in or process nutrients. Their existence relies entirely on the bacteria that live in their tissues.

See also Chemoautotrophic and chemolithotrophic bacteria; Extremophiles; Sulfur cycle in microorganisms

Hydrothermal vents

Hydrothermal vents are hot springs located on the ocean floor. The vents spew out water heated by magma, molten rock from below the earth's crust. Water temperatures of higher than 660°F. have been recorded at some vents.

Water flowing from vents contains minerals such as iron, copper , and zinc. The minerals fall like rain and settle on the ocean floor. Over time, the mineral deposits build up and form a chimney around the vent.

The first hydrothermal vents were discovered in 1977 by scientists aboard the submersible Alvin. The scientists found the vents near the Gal ápagos Islands in the eastern Pacific Ocean. Other vents were discovered in the Pacific, Atlantic, and Indian oceans.

In 2000, scientists discovered a field of hydrothermal vents in the Atlantic Ocean. The area called the "Lost City" contained 180-feet tall chimneys. These were the largest known chimneys.

Hydrothermal vents are located at ocean depths of 8,200 to 10,000 feet. The area near a hydrothermal vent is home to unique animals. They exist without sunlight and live in mineral-levels that would poison animals living on land. These unique animals include 10-foot-long tube worms, 1-foot-long clams, and shrimp.

[Liz Swain ]