Researchers have discovered dazzling white limestone structures rising from the ocean floor that may play a critical role in maintaining ocean chemistry. The sunken rock formations, reported in the 12 July issue of Nature, spit out lukewarm water a short distance away from the better known undersea ridge vents, where scorching hot water spews from the sea floor.
In recent years, researchers have found hints that hydrothermal vents could appear on old, cool oceanic crust near the newer, more active ridge centers. But limited surveys of the dark and rugged sea floor near ocean ridges had failed to detect the suspected vent fields. So oceanographer Deborah Kelley of the University of Washington, Seattle, and her colleagues were delighted last year to encounter a bright white structure on a small plateau a little over a dozen kilometers away from the Mid-Atlantic Ridge when they were investigating a large undersea mountain in the research submersible Alvin. Further exploration revealed that the formation was just one of a cluster of more than 30 similar structures spread over an area larger than a football field. They named the spooky landscape "Lost City" because it lies in an area known as the Atlantis Mastiff.
Water that will be expelled from Lost City's vents is initially sucked into the earth through nearby cracks that scar the ocean floor. It is heated to up to 70°C by the residual heat of the crust--still hot from its formation long ago--and by chemical reactions with crustal rocks. These reactions raise the pH of the water, making it basic. When the water reaches the surface, limestone settles out of the solution, forming the sparkling formations. More than a million years of accumulation have built a menagerie of exotic structures, including a tower as tall as an 18-story building.
With this first find in hand, oceanographer Karen Von Damm of the University of New Hampshire, Durham, says more "off-axis" vent fields should now be easier to find. "There's a lot of terrain on the Mid-Atlantic ridge," she says, "but we now have a better sense of where to look." And if they show up, that would strengthen the idea that vast numbers of such vents could be playing a key role in determining ocean chemistry.