Deep Sea Vents
7 Wonders of the Underwater World
Hydrothermal vents are locally very common because the earth is both geologically active and has large amounts of water on its surface and within its crust. Under the sea, hydrothermal vents may form features called black smokers. Relative to the majority of the deep sea, the areas around submarine hydrothermal vents are biologically more productive, often hosting complex communities fueled by the chemicals dissolved in the vent fluids.[3]
	White smokers at Champagne Vent on Dominica.[1]

 

Deep Sea Vents and Life's Origins

Bacteria found deep in the ocean in the volcanic regions of mid-ocean ridges suggest a possible scenario for the beginning of life on earth.

Ocean water seeps into cracks created by sea-floor spreading at the mid-ocean ridges and is heated by magma from inside the earth. Water in these hydrothermal vents reaches temperatures of 375 degrees C and higher and is rich in dissolved minerals. The hot water rises from the vents in geysers and meets cold ocean water, causing minerals to precipitate out of solution as the water cools. In some places compounds of iron and sulfides form "chimneys" on top of the vents. Such an extreme environment seemed unlikely to support life given the conditions of temperature, pressure, and absence of light for photosynthesis.

In 1977, Alvin, one of the first manned submersible vessels that could withstand extreme deep-sea pressures, made dives to the ocean floor during which its crew made a surprising discovery -- an ecosystem surrounding the hydrothermal vents of the mid-ocean ridges.

Bacteria called chemoautotrophs are the producers in the food chain, oxidizing sulfides to provide energy for synthesizing organic compounds. Species of tube worms, clams, mussels, and other organisms are the consumers. These communities cannot rely directly on photosynthesis, because sunlight cannot penetrate such depths. However, the oxygen dissolved in ocean water is produced by photosynthesis near the surface of the ocean.

The appearance of bacteria in these extremely hot, high-pressure, and dark environments has caused scientists to speculate that hydrothermal vents or places like them might be sites of the earliest appearance of life on earth -- fueled by water, energy from chemical reactions, and a rich supply of resources.[2]

Physical properties
Hydrothermal vents in the deep ocean typically form along the Mid-ocean ridges, such as the East Pacific Rise and the Mid-Atlantic Ridge. These are locations where two tectonic plates are diverging and new crust is being formed.

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. 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. 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.

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 vents that emit lighter-hued minerals, such as those containing barium, calcium, and silicon. These vents also tend to have lower temperature plumes.

An April 2007 exploration of the deep-sea vents off the coast of Fiji found those vents to be a significant source of dissolved iron. [3]