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American Association for the Advancement of Science

Ocean eddies' roots churn up deep sea

The giant tubeworm, Riftia pachyptila, surround a black-smoker chimney gushing chemically and thermally altered seawater.
[ Woods Hole Oceanographic Institution]

Swirling currents called eddies can reach deep below the ocean's surface, where they stir up heat, larvae and chemicals from deep fissures in the sea floor and spread them across hundreds of kilometers, new findings suggest.

Scientists have known that the products of these fissures, called hydrothermal vents, must be dispersed into the oceans somehow. After all, vents are an important source of calcium, magnesium and iron, which are found throughout seawater. Likewise, vent ecosystems have somehow exchanged genes despite the distance between them.

Shortly after an eruption, vent life replenishes itself through the settlement of larvae sometimes from distant sources. Small tubeworms (Tevnia) and limpet gastropods begin to cover the new glassy basalt crust.
[ Woods Hole Oceanographic Institution]

Despite decades of research, however, the actual means of travel for this material has remained unclear.

Using sediment traps on the sea floor, Diane Adams of Woods Hole Oceanographic Institution and the National Institutes of Health and her colleagues monitored the flux of larvae and chemicals near the East Pacific Rise, off the coast of Central America. They noticed that more larvae and chemicals arrived when current flow increased.

Satellite data showed that these currents were induced by "mesoscale" eddies, which are somewhat like a hurricane in the atmosphere, hundreds of kilometers across. Thus, although the deep sea is often considered separate from the surface ocean and the atmosphere, it now appears to be profoundly affected by these eddies, which are generated at the surface.

This research appears in the 29 April 2011 issue of the journal Science.