Saturday, November 13, 2010

The Deep Sea Vents

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In the blackness of night, on a remote part of the planet, a volcano erupts. Thick plumes of what looks like black smoke billow from it. Escaping magma blankets the terrain; temperatures soar to more than 600o F. deep cracks formed around the volcano, and superheated water seeps from them.

Local residents do not evacuate the area. While the magma is fatal to them, the hot water is not, and thousands are able to thrive in a seemingly hellish habitat.

The violent eruption, which has been going on for weeks, is not typical volcanic activity. It is happening at a deep-sea vent more than 8,000 feet below the surface of the ocean.

Deep-sea vents are also known as deepwater seeps, deep-sea springs, and hydro-thermal vents. Found at the bottom of the ocean, they are created by volcanic and tectonic activity in areas where huge hostile plates are converging or spreading apart. Magma erupts along the margins of these plates, usually slowly, but sometimes with such ferocity that it creates instant lava lakes. The thick black smoke is actually a plume of metal-rich, superheated water billowing out of the silt- and sediment-covered, gray-and-black chimney-an underwater volcano. Hope

Under thousands of pounds of pressure per square inch, sea water gradually seeps into the vents, where it is superheated and filled with manganese and other minerals before it is eventually returned to the ocean. This discovery has led some scientists to speculate that each drop of sea water circulates through the earth's crust, by way of the vents, every 10 to 20 million years. Before the discovery of the vents, most scientists thought that all of the minerals in the sea were dropped into the ocean by continental rivers.

Because no sunlight reaches the depths where the vents are found, these underwater wonders are visible only in the floodlights of a manned submersible such as Alvin. This three-person submarine, which can descend 12,800 feet below sea level, first took photographs and research scientists to see vents along the Galapagos rift in 1977, when the original discovery was made.

The residents of the vent community, although surely not the prettiest creatures, are perhaps the most fascinating of all the world's underwater wonders from a scientific perspective. At the geothermal vents, marine biologists have an opportunity to study a food chain that functions without sunlight. Most biologists had once believed that only sunlight, through photosynthesis, could support life on Earth. At the vents, however, life begins with bacteria that metabolize hydrogen sulfide. The bacteria, in turn, become food for the other animals in the vent community.

Among the 300 species of life found near the vents, perhaps the best documented life forms are the giant red-tipped tube worms-12-foot-tall creatures whose 300,000 tentacles strain food from the water. By comparison, tube worms in shallow ocean have a dozen or so tentacles and grow only a few inches long.

Blind crabs and shrimp, which don't need to see in a lightless world, live among octopuses that eat crabs and mussels. Equally fascinating residents include pink ventfish, sea cucumbers, sponges, and brittle stars, flowerlike animals that use their fine appendages to anchor themselves to rocks.

Mussels are among the 48 documented species of mollusks found in vent communities. And some specimens of giant clams that live in this environment measure almost ten inches in length.

How does a vent become colonized? Some species, while in their larval stage, travel tremendous distances through a virtually lifeless and totally lightless realm to colonize and new vent on the seafloor. But other species first travel to the surface to feed before settling down at a new deep-sea vent.

Several of these vents have been found and explored in both the Pacific and the Atlantic, while others likely remain hidden a mile or more below the sea surface and await discovery. Scientists who study the life-forms near the vents believe that the bacteria there, as insignificant as they may seem to most people, may provide clues to how life first formed on this planet so many millions of years ago.