Smoking in the Dark
by Robin Meadows
The deep-sea hot springs known as hydrothermal ventsare found along the oceans' ridges, a total of 46,000 miles of submarine mountain ranges that extend north to south through all the major seas. These ridges grow where the massive tectonic plates of the earth's crust are pulling apart. As the plates separate, lava flows in between them, adding new sea floor at up to seven inches per year. The newly formed crust is made of dark, glassy lava that cracks as it cools. Water seeps through these cracks, picking up heat and minerals from the molten rock that lies beneath the crust. This water then spouts back out through the vents.
The water ranges from 50 to 700 degrees F, depending on the type of vent. Even at temperatures above 212 degrees F, however, the water is superheated rather than boiling because the pressure is so great (250 atmospheres) at the depths where vents have been found--from 2,600 to 20,000 feet (the deepest the sea gets is about 35,000 feet). While the temperature of the hotter vents' water is far too high for animals to live in, this superheated water mixes so rapidly with the near-freezing surrounding water that most vent animals live at temperatures close to 35 degrees.
Vents are home to a great diversity of life: more than 250 known species of free-living bacteria and about 300 newly described animal species. These animals typically live within about 30 yards of their vent.
Not surprisingly, vents in different parts of the world tend to have different animals. For example, the giant tubeworms live only along the East Pacific Rise, which lies off the western coasts of Mexico and South America. Shrimp predominate at vents along the Mid-Atlantic Ridge, and barnacles, limpets, and snails predominate at the Mariana vents of the western Pacific.
(ZooGoer 25(3) 1996. Copyright 1996 Robin Meadows. All rights reserved.)
