MAJOR DISCOVERIES: A Changed View of Life
An entirely new way to sustain life
Since 1977, scientists have surely learned this: If youve seen one vent, you definitely havent seen them all. Scientists have found that hydrothermal vent sites around the globe are as unique as cities around the world. Honolulu and Denver are both cities, but they have many differences. The same is true of vent sites.
The early 1979 cruises first hinted that vents sites are not all alike. At Galápagos Rift, shimmering, 23°C (73°F) fluids gushed out of the seafloor. But 1,800 miles away, at 21°N on the East Pacific Rise, 350°C (662°F) black smoke belched out of tall mineral chimneys. The more vents scientists found, the more differences they observed.
Scientists have also found that different kinds of animals live at different vents-much the way the populations of Tokyo and Paris dont closely resemble each other.
For example, tubeworms or clams are common at Pacific vents, but not at vents along the Mid-Atlantic Ridge. There, the vents are teeming with billions of shrimp, and anemones are common.
Until very recently, scientists had never had a chance to explore vents in the ocean between the Atlantic and Pacificthe Indian Ocean. In 2000, they found more of a mixed population. There were shrimp, as in the Atlantic, but also snails and barnacles usually seen just in the Pacific.
Scientists have also discovered that even at the same vent site, populations can shiftas Americas did, for example, after the first European colonists arrived. In 1979, Scripps scientist Robert Hessler saw a lush community of tubeworms at the Galápagos Rift vent site called Rose Garden. When he returned in 1985, the tubeworms were gone. The neighborhood had been overrun by mussels and clams, which out-competed the tubeworms for food.
Oases that blink on and off
Sometimes vent sites change because something devastating happens-like the ancient Roman city of Pompeii after Mount Vesuvius erupted.
In April 1991, scientists in Alvin were in the right spot at the right time to witness something extraordinary-the aftermath of a very recent seafloor eruption. They were diving on the East Pacific Rise at the 9° 50N vent site. The expedition was led by Rachel Haymon of the University of California at Santa Barbara and Dan Fornari, then at Lamont-Doherty Geological Observatory and now at Woods Hole Oceanographic Institution.
The scientists had surveyed the same site two years earlier with the ARGO camera system, which is towed near the seafloor via a cable attached to a surface ship. They found large, thriving animal communities.
But in 1991, the scientists returned to find a wide area of scorched and mangled tubeworms. Some tubeworms were encased in a fresh lava flow that had poured out of the seafloor and overrun the vent community. The area was covered with gray, ash-like deposits. They called the site Tubeworm Barbecue.
The bottom waters around the site were swirling with white particles. It looked like an underwater blizzard! The white material turned out to be material produced by bacteria. Great streams of it were being blown out of holes in the volcanic seafloor. The scientists called these seafloor features snow blowers. Huge quantities of microbes and microbial debris were being blasted into the ocean and rising more than 100 feet above the seafloor. In many places, the seafloor quickly became coated with a layer of microbes nearly 10 centimeters (4 inches) thick.
The scientists had come upon a seafloor volcanic eruption that had happened only weeks or days before.
Tubeworm Barbecue showed that vent sites are dynamic. They come and go, and they change. Volcanic heat creates nourishing hydrothermal fluids to launch and sustain animal communities. But volcanic forces can also wipe out the animals in an instant. Throughout the vast worlds ocean, volcanic eruptions occur almost daily. So it is very likely that somewhere on the seafloor, a vent site is being extinguished today. And somewhere else, a new vent site is being born.