Other
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.v43c..01k&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #V43C-01
Other
1030 Geochemical Cycles (0330), 3035 Midocean Ridge Processes, 4805 Biogeochemical Cycles, Processes, And Modeling (0412, 0414, 0793, 1615, 4912), 4832 Hydrothermal Systems (0450, 1034, 3017, 3616, 8135, 8424)
Scientific paper
The serendipitous discovery of the Lost City Hydrothermal Field at 30N on the Mid-Atlantic Ridge significantly changed our views about where and how life is sustained on our planet. Investigation of this site shows that it is like no other yet discovered, hosting carbonate chimneys that tower up to 60 m above the seafloor. The field rests on 1-2 my old crust, at a water depth of 800 m and is underlain by variably deformed and altered peridotite with lesser gabbro. An intense interdisciplinary field program in 2003 and a follow-on investigation in 2005 show that geological, biological, and chemical processes are strongly intertwined at this site. Serpentinization reactions in the subsurface produce pH 9-11, 40- 91° C fluids enriched in methane, hydrogen, and other hydrocarbons. Mixing of the high pH fluids with seawater forms nearly monomineralic towers of calcite, aragonite, and brucite. In contrast to the rich diversity of microorganisms typically found in black smoker environments, the warm, porous interiors of the chimneys are dominated by a single phylotype of organisms related to Methanosarcinales, which may be capable of both methane oxidation and production. Other microbes, including an organism related to an anaerobic methane-oxidizing phylotytpe (ANME-1) are present in moderate temperature environments such as the flanges (40° C to 70° C), where there is sustained mixing of pure vent fluids and seawater. They are also present in cool carbonate vein environments (<40° C) that cut the serpentinite bedrock. Bacterial colonies grow on the outside of diffusely venting chimneys where they form white to light grey filamentous strands several centimeters in length. Based on 16S rDNA clone libraries there is a relatively high diversity of organisms in these zones that include Eubacteria as well as Archaea. In contrast to the dense macrofaunal assemblages that typify most known high-temperature vent environments, the biomass at Lost City is much smaller. The animals that live within the pores and small cavities on the outsides of the chimneys are typically <1 cm in size, with transparent to translucent shells that make them very difficult to see in the field. These animals include a variety of gastropods, polychaetes, and amphipods. Rare, larger animals include crabs, shrimp, sea urchins, eels, and a diverse array of corals. Current assessment at Lost City shows that 58% of the fauna are endemic to this vent environment. The discovery of seafloor hydrothermal ecosystems that do not require magmatic heat may have important implications in our search for life on other planets. The certainty that water exists, and has existed, on Mars where there is good evidence for rocks rich in olivine, and the presence of a liquid ocean on Europa, raises the question of whether systems similar to the Lost City Hydrothermal Field may be present (or were once present) elsewhere in the solar system.
2003/2005 Science Teams D. S.
Kelley
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