Lost City Expedition
Life from Rocky Reaction
based on University of Washington Oceanography release
The bizarre hydrothermal vent field discovered a little more than two years ago surprised scientists not only with vents that are the tallest ever seen –the one that’s 18 stories dwarfs most vents at other sites by at least 100 feet — but also because the fluids forming these vents are heated by seawater reacting with million-year-old mantle rocks, not by young volcanism.
|The Mid-Atlantic Ridge is one of the earth’s largest undersea mountain ranges at a length of nearly 6,200 miles. The dots represent active hydrothermal sites.
The field is unlike any seen before, according to chief scientist Deborah Kelley, a University of Washington associate professor of oceanography, and co-chief scientist Jeff Karson, a Duke University professor of earth and ocean sciences. Both have visited fields of black-smoker hydrothermal vents that scientists have been studying since the 1970s.
The remarkable Lost City hydrothermal vent field, so named partly because it sits on a seafloor mountain named the Atlantis Massif, was discovered in the middle of the Atlantic Ocean about 1,500 miles off the East Coast of the United States during an expedition that wasn’t even looking for hydrothermal vents.
"Perhaps a good analogy," explains Kelley, "may be to imagine flying a small plane by radar in the dark through a redwood forest with no map and no easy way to locate yourself. If you fly down near the tree trunks it is very difficult to see the rest of the grove, but if you fly high, the individual trees can be spotted by radar. In a very similar way, this is the method we used for exploring the Lost City."
Now the two scientists who were the first to travel in a submersible to the field after its serendipitous discovery Dec. 4, 2000, are leading a National Science Foundation-funded expedition to map and further investigate the field.
A Web site launched today will follow the 24 scientists onboard an exploration vessel, the Atlantis, during their 32-day expedition that starts April 21.
Erupting Life, But Not Volcanic
The Lost City is distinctive in part because the mighty 180-foot vent at the site, which scientists named Poseidon, is so much larger than previously studied black-smoker vents that mostly reach 80 feet or less. The tallest black-smoker chimney ever seen was a 135-foot vent off the coast of Washington (which toppled in recent years).
In contrast to black-smoker vents that are a darkly mottled mix of sulfide minerals, Lost City vents are nearly 100 percent carbonate, the same material as limestone in caves, and range in color from a beautiful clean white to cream or gray.
The differences are because hydrothermal venting –a process in which water circulates into the seafloor, gaining heat and chemicals until there is enough heat for the fluids to vent back into the ocean — doesn’t appear connected to volcanic activity and magma chambers. This is unlike most systems at mid-ocean ridge spreading centers. That’s where very young seafloor is created often dramatically during volcanic eruptions and vented water can be as hot as 700 F.
A fast spreading center will realign every 5-10 years, while more rare realignments like at Poseidon happen only once every 5,000 to 20,000 years.
Lost City is nine miles from the nearest spreading center and sits on 1.5 million-year-old crust. Heat generated by chemical changes in the rocks appears to drive venting: seawater permeates deeply into the fractured surface of the mantle rocks where it transforms the mineral olivine into a new mineral, serpentine. The heat is not as great as that at volcanically active sites but is enough to power hydrothermal circulation and produce vent fluids of 105 to 170 F.
Life At Home in Lost City
Lost City vent fluids support a community of microorganisms believed to live off the gases methane and hydrogen, both byproducts of serpentinization. This leads Kelley, Karson and others to speculate that life on this planet may have started in just such an environment, particularly since so much more mantle rock was exposed to seawater early in Earth’s history. And the same could be happening on other worlds.
|University of Washington oceanographer Deborah Kelley contrasts the white porous (almost wasp-nest-like) texture of a sample from the Lost City’s carbonate chimneys with a sample from the sulfide chimneys studied since the 1970s.
Credit: University of Washington
"The Lost City carbonate vents host diverse and very dense microbial communities," notes Kelley. "The organisms form thick biofilms that cover the mineral surfaces. We believe that these systems will host extensive microbial communities that may include methane- and hydrogen-oxidizing bacteria."
It is believed that a third of the Earth’s total biomass resides hundreds of meters below the oceans. Cell densities as high as a billion cells per cubic centimeter have been estimated.
"Unfortunately, instruments are not yet developed to characterize microbial populations," says Kelley, although culturing samples back in the lab has shown heat-loving microorganisms adapted to thrive in the thermophilic (50-70 C) and mesophilic (25 C) temperature ranges. "The long term goal is to develop seafloor observatory sites that will allow long term investigation of how volcanoes support life on the seafloor, and how submarine earthquakes affect the output of gases from the seafloor and microbial life. These are the types of questions that are of planetary scope . Perhaps learning how to examine such questions will provide useful guides to exploration of other planets."
The team leaves Barbados April 21 on board the Atlantis, operated by Woods Hole. It takes five days to reach the ocean above Lost City where researchers will use the submersible Alvin and an unmanned Autonomous Benthic Explorer.
Among those on the expedition will be lead pilot Pat Hickey, who took Kelley and Karson in the Alvin to see Lost City the day after it was first spotted during routine surveying using an unmanned, remotely operated vehicle. There was time for just a single dive before the expedition ended and bad weather began so scientists can only say the field is 300 feet by perhaps 1,700 feet and has roughly 30 vent structures. Since then the field has been visited by a U.S. film crew, which conducted no science, and a Russian group, which did limited sampling.
Work this month and next includes studying the waters above the field looking for clues to help find other Lost City fields and visiting a neighboring mountain that looks promising. Researchers also will grow and examine microorganisms recovered from the chimneys.
The project includes scientists, engineers and students from the University of Washington, Duke University, Woods Hole Oceanographic Institution, U.S. National Oceanic and Atmospheric Administration, Switzerland’s Institute for Mineralogy and Petrology and Japan’s National Institute of Advanced Industrial Science and Technology. Collaborators include: Jeff Karson, Duke University, Co-PI and diver during the discovery; Matt Schrenk (an astrobiology graduate student at the UW School of Oceanography); P.J. Cimino (a NASA Space grant undergraduate); and John Baross, also a faculty member in astrobiology and oceanography.