Geotimes - July 2002 - Hydrothermal Vents

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News Notes

Oceanography
Revisiting the first hydrothermal vents

Scientists on board the research vessel Atlantis in the Galápagos spoke via satellite to journalists at the meeting of the American Geophysical Union on May 29. The research expedition marked the silver anniversary of the 1977 discovery of deep-sea hydrothermal vents.

On this return trip, the researchers wanted to learn how the original Galápagos vent fields and their fauna had changed. To their surprise, the most famous and best-studied vent field in the region, Rose Garden, is now gone. The scientists suspect lava flows paved over the field. Nearby, a young vent community is claiming residency with small clams and mussels as well as one-inch long tubeworms growing on larger tubeworms. Disappointed over the loss of Rose Garden, but hopeful that the young vent field will develop as a community, the scientists named the new site Rosebud.

Alvin samples a clump of tubeworms at the Rosebud vent site. WHOI, courtesy of the Galapagos Rift 2002 Expedition.

“Rose Garden provided the earliest foundation for our understanding of hydrothermal vent communities,” says biologist Tim Shank, chief scientist for the Woods Hole Oceanographic Institution (WHOI). “Rosebud is a young vent field 350 meters west of Rose Garden. It appears to have younger lava sheet flows over older flows.”

Biologists first discovered Rose Garden in 1979, finding bouquets of 2-meter long tubeworms living off the low-temperature hydrothermal fluids coming out of the cracks in the lava. That same year, a separate expedition off the tip of Baja California, Mexico, discovered chimney-like formations precipitated from minerals under high temperatures associated with the hydrothermal vent fields. These chimneys, called “black smokers,” emanated hot, black plumes of iron, sulfide and other minerals. Later, cooler “white smokers,” where seawater is thought to mix with the fluid, were discovered spewing water rich in silica.

The tall chimneys are now considered characteristics of a hydrothermal vent area. But in the last 25 years, scientists had not yet seen high-temperature vents in the Galápagos. As part of this silver anniversary expedition, they also hoped to search unexplored areas for new vent fields and black smokers.

A return expedition to the Galápagos in 1985, using WHOI’s three-person deep submergence vehicle Alvin, found that mussels had overtaken Rose Garden. Extensively mapped during the next five years, Rose Garden became a case study for how vent communities change over time.

On this year’s expedition, the scientists created 1-meter vertical resolution bathymetry maps using a robot called ABE, Autonomous Benthic Explorer. Free of any tether to the ship, ABE navigates a pre-selected route above the seafloor, taking conductivity, temperature and depth measurements as well as mapping the seafloor surface using sonar. The sensitivity of ABE allowed the scientists to track down another area where the hydrothermal venting provided about as much warmth to the ocean as a candle outside. Specifically, ABE had detected a trail of water .01 to .02 degrees warmer than the ambient ocean temperature.

On June 2, the Alvin crew reported finding two extinct black chimneys with shiny metal sulfide crystals. Susan Humphris of WHOI explained on the cruise’s Dive and Discover Web page that such crystals only form when vent fluid temperatures reach 200 degrees Celsius, making these chimneys the first evidence of high-temperature vents along the Galápagos Rift. They also identified another new vent site, still unnamed, with large mussels and clams.

Cindy Van Dover, the only woman and scientist trained to pilot Alvin, checked out the Web page from her office at the College of William and Mary in Williamsburg, Va. “This is exciting stuff,” she says. Van Dover was part of the 1985 mission to Rose Garden and says its burial provides a better understanding of how frequently lava can obliterate a site. Prior to Rosebud’s discovery many biologists suggested that tubeworms were the first colonizers to a vent site, while others considered the vent communities more like a lottery where, competing for space, whatever species wins takes charge. Rosebud’s diverse community of young tubeworms, mussels and clams, “breaks down the dogma that tubeworms come in first,” Van Dover says.

Christina Reed

Check out the Dive and Discover Web page.

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