Lost City Life Methane-Powered
Scientists who named the spot Lost City knew they were looking at something never seen before when the field was serendipitously discovered in December 2000 during a National Science Foundation expedition to the mid-Atlantic.
This week in Science, researchers publish for the first time findings about the gases produced at Lost City and the organisms that make their living off them. Both are so different from so-called black-smoker hydrothermal vents that they may provide a whole new avenue for looking for the earliest life on Earth and for signs of life on other planets, according to Deborah Kelley, University of Washington oceanographer and lead author of the Science article.
Further, she says, Lost City microbes appear to live off bountiful methane and hydrogen. Absent is carbon dioxide, the key energy source for life at black-smoker vents. And there is little hydrogen sulfide and only very low traces of metals, on which many of the microbes at the other kind of vents depend. The difference in what's available is because water circulates through the Lost City hydrothermal vent field via serpentinization, a chemical reaction between seawater and the mantle rock on which Lost City sits. The resulting fluids are 105 F to 170 F. At the other kind of field, first discovered in the early 1970s, volcanic activity or magma drives venting and fluids can reach 700 F. The vents at such sites are often referred to as black smokers because some emit hot, mineral-laden fluid that looks like dark, billowing smoke when it hits the icy cold seawater.
Carbonate minerals from fluids at Lost City drape nearby cliffs in brilliant white and form vents ranging in shape from tiny toadstools to the 18-story column, named Poseidon, which dwarfs most known black smoker vents by at least 100 feet. Some places resemble the sort of deposits one might see in spectacular caves with spires and smoothly rippled surfaces in a complex three-dimensional array, says Duke University's Jeffrey Karson, co-author on the paper.
In surprising contrast, researchers discovered Lost City has a diversity of "larger" organisms that's as high, or higher, than any known black-smoker vent sites. Missing from Lost City are the tubeworms, abundant shrimp and other readily observed organisms that heavily blanket some black smokers. The high diversity revealed itself only after a 2003 expedition when the biology team led by Woods Hole Oceanographic Institution's Timothy Shank analyzed water samples "vacuumed" from around the vents.
"There aren't a lot of each kind of animal, most are only a centimeter in size and have translucent or invisible shells so it's no wonder we didn't suspect the actual diversity," says Kelley, who was chief scientist on the expedition, which like the 2000 voyage was funded by the National Science Foundation. Other large organisms include crabs, corals and fish.
Although nobody has yet found another field like Lost City, Kelley says she's 100 percent sure others exist because there are so many other places mantle rock has been thrust up through the seafloor, exposing it to seawater and serpentinization.
Even more such rocks were present on early Earth, Kelley says.
"We don't, in most places, have access to early Earth conditions so if we can understand the chemical reactions, sources of energy and how fluids circulate through Lost City, it may give us insight into how life started on this planet," Kelley says.
The work being published was funded by the NSF, NASA Astrobiology Institute and a Swiss national science grant.
"The findings are an exciting example of NSF's commitment to discovery through basic research," said Bilal Haq, director of NSF's marine geology and geophysics program. "Lost City shows us that geological, chemical and biological processes are intimately linked at a primal environment, and lends strong support to the need for interdisciplinary approaches to scientific research."
Other co-authors are Gretchen Früh-Green, Swiss Federal Institute of Technology; Dana Yoerger, John Hayes, Kate Buckman, Sean Sylva and Mike Jakuba, Woods Hole Oceanographic Institution; David Butterfield and Kevin Roe, University of Washington and Pacific Marine Environmental Laboratory's Joint Institute for the Study of Atmosphere and Ocean; Matthew Schrenk, Eric Olson, Giora Proskurowski, Ben Larson, Kristin Ludwig, Deborah Glickson, William Brazelton, Marvin Lilley and John Baross of the University of Washington; and Alex Bradley and Roger Summons, Massachusetts Institute of Technology.
The field was named Lost City in part because it sits on a seafloor mountain named the Atlantis Massif and because researchers were using the Woods Hole Oceanographic Institution's vessel the Atlantis when the field was discovered. The field is about 300 by 1,000 feet, has 30 large vents, some 10 to 60 meters tall, and hundreds of smaller structures. Steep cliffs behind the field are shingled with carbonate.