Scientists Return to Galápagos Sea Vents
By Bijal P. Trivedi
National Geographic Today
|May 29, 2002|
Twenty-five years ago, the discovery of deep sea hydrothermal vents, one and a half miles below the ocean surface, near the Galápagos Islands revolutionized biology and captivated the world with pictures of thriving ocean floor gardens covered with towering, red-plumed tube worms, giant clams and ghostly white crabs.
To mark the silver anniversary, this week a team of biologists and geologists is revisiting the Galápagos Rift to compare the current inhabitants with those documented in previous years. They will also explore neighboring waters 200 miles west of the site for "high-temperature black smokers"dramatic geological forms that shoot super-heated, inky black plumes of water out of the ocean bed and may have nurtured the first life on Earth.
Life Around the Vents
"The western site, which we believe may be home to black smokers, may host a whole collection of new life-forms that we have never seen," said Stephen Hammond, a geologist and chief scientist for the National Oceanic and Atmospheric Administration's Office of Ocean Exploration. "Who knows what we'll find?"
The unexpected discovery 25 years ago of abundant life in the freezing, pitch-black waters of the deep ocean dramatically changed how we think about the requirements for life, said Jim Yoder, director of the Division of Ocean Sciences at the National Science Foundation. "Here was an entire food web that depended on chemical energy from the earth rather than energy from the sun." Yoder said that this is one of the most significant discoveries in oceanography in the last 50 years.
Vents occur where there is volcanic activity. The cracks in the seafloor allow water to percolate through the ocean crust where it is heated by nearby chambers of magma. The super hot watersometimes 750ºF (400ºC)dissolves metals and salts as it travels through rocks, eventually rising and gushing out of the hydrothermal vents. These searing vent cocktails are responsible for the chemistry of the world's oceans.
Among the bouquet of chemicals pouring out of the vents is hydrogen sulfidea poisonous gas which is toxic to most land-based life. But to the creatures living around the vents, hydrogen sulfide is the source of life. Some bacteria, never seen before the discovery of the vents, use the gas for an energy source. These bacteria are the base of the food chaincrabs, clams and tube wormsand all other vent creatures depend on these microbes for life.
Scientists believe that these vent systems were common 3.85 billion years ago, when the earliest life-forms are thought to have emerged. Possibly the hydrogen-sulfide-eating bacteria near the vents today may resemble these earliest life-forms.
Since the Galápagos vents were discovered in 1977, hundreds of other vents have been identified in oceans around the world. But the inaccessibility of these sites and the hostile conditions of the vent environments mean that scientists still don't have a firm understanding of how life changes in these places, said Tim Shank, a biologist at the Woods Hole Oceanographic Institution (WHOI) and co-chief of the expedition. "We don't even know how long the vents remain active," Shank said.
Looking for the Rose Garden
The current expedition will seek out a 0.6-acre (.24-hectare) plot of red-plumed white tube worms called the "Rose Garden," which is fed by nutrients from hydrothermal vents. The site was meticulously mapped in 1985, and was studied extensively until 1990. And now scientists now want to see whether the garden's inhabitants have changed and whether the vents feeding the area are still active.
On Sunday, a dive to the ocean floor in a three-man sub called Alvinone of only five deep-sea vehicles in the world able to prowl depths of 4,500 meters (14,764 feet) or greaterfailed to discover the Rose Garden. The garden was last seen in 1990, before civilians had access to the Global Positioning System, which enables very accurate location determination. "Looking for such a small site along the ocean floor is like trying to find a needle in a haystack," said Shank, a veteran of over 30 deep-sea dives.
During this first dive, the team did discover a garden possibly less than one year old with tiny tube worms, mussels and clams all living together. "It was very unusual," Shank said. In vent communities observed thus far, these three creatures are not usually seen together when the garden is young. Within the garden was a dense patch of anemones, their two-inch (five-centimeter) tentacles resembling a translucent shag rug. "The water was filled with debris and tiny worms floating around like a marine snow," Shank said, "and every 30 feet or so we saw bright red shrimpsome up to a foot in length."
Further exploration of the surrounding area during a dive on Monday revealed an old growth communitywith mature tube worms, mussels and clamson the perimeter of the new garden, suggesting that a fresh lava flow ploughed through an older garden. Plants and animals are colonizing the new flow just as they would be on land, said Dan Fornari, a geologist at WHOI, who traveled with Shank on the second dive.
The scientists used a net and Alvin's robotic claw to collect specimens from the garden, which they brought to the surface in a "biobox," also known as the "coffin," where samples remain cold. Among the bounty is a snail that Shank believes might be a new species.
But scientists are perplexed by the absence of the Rose Garden. "During this second trip we really should have seen it," Shank said. "We should have seen signs of a human presence if we were in the right spotsuch as the large steel weights that Alvin leaves behind after each mission." There have been around 25 dives to the Rose Gardenthat's 100 weights that should be scattered in the area, Shank said. "We haven't seen any of them."
"Sometime within the last 12 years the Rose Garden may have been paved over by a fast moving river of lavasomething like you might see on Hawaii," said Fornari. During the next few dives scientists will try to verify whether the garden has been buried.
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