Printed from “The Discovery of Hydrothermal Vents - 25th Anniversary CD-ROM” ©2002 Woods Hole Oceanographic Institution

INTO THE FUTURE: Vents Around the World

What’s in a name?
Since 1977, scientists have discovered some 40 vent sites around the globe. Many have interesting names. A site near the “Garden of Eden” on the Galápagos Rift was named “East of Eden” (which is also a novel by John Steinbeck). In the Atlantic, the seafloor topography near the “Broken Spur” site has a series of “spurs” coming off the ridge. The “Lucky Strike” vent site was found by chance when scientists were dredging up samples of seafloor rocks. “Snake Pit” was named after the slithering mass of white, eel-like fish that scientists found living there.

In 2000, Japanese scientists discovered the first vent site in the Indian Ocean and named it after their research vessel “Kairei.” Several months later, a U.S. expedition found another Indian Ocean vent site and named it “Edmond,” in memory of John Edmond, a renowned chemist from MIT who had recently died. Edmond participated in the original 1977 Galápagos cruise and was a pioneer and leader of hydrothermal vent research.

So far, most vents have been found on volcanically active mid-ocean ridges with newly made seafloor crust. But that may be only because scientists have focused their search for vents on ridges. In December of 2000, on an expedition led by Donna Blackman of Scripps Institution of Oceanography and Jeff Karson of Duke University, scientists in Alvin were surprised to find a vent field in the Atlantic Ocean that was tens of miles away from a ridge, on million-year-old seafloor crust. It had skyscraper-like structures, many stories high that were made of white carbonate material, not dark sulfide minerals. They called this unique vent site “Lost City.”

No such thing as a ‘typical’ vent
Why are vent sites so different? That’s a big question scientists have been trying to answer.

Some vent fields have black smokers. Others have “white smokers,” which belch slightly cooler, but still superheated fluids without dark mineral particles. At still other vent sites like the Galápagos, warm (but not superhot) vent fluids seep out of seafloor cracks (but not in chimneys).

How do massive mineral-rich deposits form at vent sites like TAG on the Mid-Atlantic Ridge, but not at others? Why did white, silica-rich deposits form at “Cauliflower Gardens” near Galápagos vents, but not at TAG?

Why does the chemical composition of vent fluids vary from place to place? What causes vent sites to turn on and to turn off? Each vent sites is unique because each is a result of a unique combination of interacting forces. In different places on the seafloor, the movement of Earth’s tectonic plates creates different seafloor topography, different sorts of cracks in the seafloor, and different amounts of volcanic activity. All these factors combine to create differences in vents—and perhaps differences in the communities that live around them.


What do kangaroos and tubeworms have in common?
Why do different kinds of animals live at vents in different oceans? Why are clams and tubeworms seen so commonly at Pacific Ocean vents, but not seen on the northern Mid-Atlantic Ridge? Why are shrimp found teeming around Atlantic vent sites, but only in small numbers at Pacific vents?

The same sort of thing happens on land, too. Koalas and kangaroos live only in Australia. That’s because animals on Australia became separated from other animal populations when Australia separated from an ancient supercontinent and became an island. Did something similar happen on the bottom of the ocean? Did seafloor spreading and the creation of mid-ocean ridges separate animal populations and cause them to evolve differently? Was the evolution of vent animals shaped by the movement of continents, which may have cut off connections between oceans and changed ocean circulation patterns?

On land, a variety of factors have created the unique ecosystems in Africa and the Amazonian rain forest. Do subtle differences in the chemistry of vent fluids, or seafloor rocks, or some other factors create different vent ecosystems?

The “biogeography” of vents—that is, where and why animal populations are distributed around the world’s oceans—remains a great mystery.

Vent-hopping
How vent animals are distributed around the world’s oceans also remains a mystery.

Vent animals flourish when the hydrothermal vents are active, but they are doomed if the vents shut down. The animals’ only hope of avoiding extinction is to send out tiny larvae to find and colonize other active vent sites. But vent sites are often isolated oases amid a cold ocean desert.

How do these larvae travel through the oceans? Are they carried away by buoyant plumes of hydrothermal vent fluids, or by deep current currents? Do the large, deep faults that break the global mid-ocean ridge into segments create barriers to larval migration? How do they avoid getting eaten? Do traces of toxic metal particles in hydrothermal plumes deter predators? How do the larvae find new vents? Are there chemical clues that allow them to home into a new home? How do they survive potentially long journeys before they find a suitable vent?

In 2001, a team of scientists, which included Lauren Mullineaux of Woods Hole, Craig Young of Harbor Branch Oceanographic Institution, and Adam Marsh and Donal Manahan of the University of Southern California, found an answer to the last question. They showed that tubeworm larvae could survive for 38 days—potentially long enough to locate another active vent before they run out of food.

Scientists are still pursuing answers to the other fascinating questions.