Unlocking the Secrets of Ocean ‘Black Smokers’
There may be no harsher place for Earth life to survive--and no more difficult place to study it--than the sea floor vents called black smokers.
Crushing pressures, brutally hot water and corrosive gases sharply limit the time researchers can spend on site, even in deep-ocean submersibles, and corrode most sensors left behind.
But researchers brave those conditions to study the 300 or more bizarre species found at these light-less depths because many experts now believe that this is where life originated on Earth. Equally important, if there is life elsewhere in the solar system, such as on Jupiter’s moon Europa, it may very well be found in similar venues.
These exotic creatures may therefore not only provide new insights into our own origins, but may also show biologists what kinds of life to seek in the far reaches of our solar system.
Their study was made a little easier this summer when a team from the University of Washington and the American Museum of Natural History recovered the rock chimneys from four black smokers off the coast of the Pacific Northwest. The unprecedented recovery of these volcano-like accumulations of minerals will allow researchers to document the distribution of life throughout the chimney structure and collect bacteria from each microenvironment.
Using two ships and a remotely operated submersible, the team “surgically removed” 3,000 pounds of fragile rock from the ocean floor at the edge of the Juan de Fuca plate and lifted the four chimneys more than 7,500 feet to containers.
“That’s quite an engineering feat,” said biologist Craig Cary of the University of Delaware. “I applaud them.”
Back in their laboratories, geologists have already made surprising discoveries about how the chimneys grow and what they are made of. And biologists in the group have begun growing bacteria scraped from the chimneys that may be among the most primitive forms of life known.
“The important thing . . . is that we raised something alive and hot,” said earth scientist Edmond A. Mathez of the museum. “We can now study something about the maximum conditions at which life can exist.”
The vents, discovered two decades ago, are found at the edges of the planet’s massive tectonic plates, where molten magma lies just below the surface. Seawater seeps underground through cracks in the ocean floor and is heated to tremendous temperatures. The hot water dissolves rock and absorbs volcanic gases such as hydrogen sulfide.
When this superheated water rises into the frigid ocean waters, the sudden mixing of hot and cold causes the dissolved rocks to precipitate out, forming towering, chimney-like structures containing sulfide minerals, such as pyrite, chalcopyrite and sphalerite, as well as silicates.
The largest such chimney ever observed was 140 feet tall, but most break off before they reach such heights, leaving a rubble field around their base that also provides biological niches.
When the temperature of water emerging from the vents is above 575 degrees Fahrenheit, the sulfide minerals precipitate out as microscopic particles and give the water a billowing, cloud-like appearance that inspired the name black smokers.
Life at the vents is the only life on Earth that does not depend, either directly or indirectly, on energy from the sun. Instead, bacteria in the hot seawater get their energy from hydrogen sulfide in a process called chemosynthesis. They, in turn, are the base of a food chain that leads all the way up to exotic fish, all of which ultimately rely on the toxic volcanic fumes.
Perhaps the most exotic of the creatures at the black smokers are the Pompeii worms, Alvinella pompejana, which live in papery tubes on the sides of the chimneys. The tails of the worms inside the tubes are in water temperatures as high as 185 degrees Fahrenheit, while the heads are immersed in water that is only about 76 degrees.
The worms are not only the most heat-tolerant multicellular organisms known, but they also live in the highest temperature gradient ever observed--a 109-degree drop in temperature across their bodies that most biologists did not believe could be survived. How they survive this is still a mystery.
In their recent expedition, the researchers used metal cages designed and built by Le Olson of the University of Washington. Using a remotely operated submersible, the team maneuvered the cages over the chimneys, which were strapped inside the cages with steel cable.
After the base of each chimney was severed with a chain saw, the structures were raised 7,500 feet to the surface. One was an old, cold structure that was not venting fluids, two were venting fluids hot enough (up to 176 degrees) to support a wide variety of life and the fourth was an active black smoker.
The fourth one, called Finn, “was still smoking and steaming when it reached the surface,” said geologist John Delaney, a co-leader of the expedition.
When the researchers went back to Finn’s “stump” 3 1/2 days later, they found that a new cone had grown about 4 1/2 feet high. “That really surprised us,” Delaney said. After two weeks, another visit to install instruments showed that it was already 15 feet high.
The laboratory studies have also yielded some surprises, he noted. Although they expected the cones to be composed primarily of metal sulfides, the scientists found that the first one they studied “was just loaded with clay. . . . We never expected it to be caught in the chimneys,” Delaney said.
They also discovered that the chimneys grow larger when scalding water seeps through cracks in the chimney, depositing its dissolved minerals on the outside of the structures.
One of the chimneys will be placed on display this winter at the American Museum of Natural History in New York City. The expedition will also be the subject of a documentary next spring on PBS.
More information about the expedition can be obtained at the Web sites of the American Museum of Natural History (www.amnh.org), the University of Washington (www.ocean.washington.edu/outreach/revel) and PBS television (www.pbs.org/wgbh/nova/abyss).
