HR: 1330h
AN: B12A-0770    [PDF]
TI: Preliminary Geochemistry of Volatile Species From Active Vents at the Lost City Hydrothermal Field
AU: * Proskurowski, G
EM: giora@u.washington.edu
AF: University of Washington, UW School of Oceanography, Seattle, WA 98195 United States
AU: Lilley, M D
EM: lilley@ocean.washington.edu
AF: University of Washington, UW School of Oceanography, Seattle, WA 98195 United States
AU: Olson, E J
EM: olson@ocean.washington.edu
AF: University of Washington, UW School of Oceanography, Seattle, WA 98195 United States
AU: Larson, B
EM: blarson@ocean.washington.edu
AF: University of Washington, UW School of Oceanography, Seattle, WA 98195 United States
AB: The Lost City Hydrothermal Field is a unique site of hydrothermal venting, as the energy driving circulation is provided solely from exothermic reactions between seawater and the underlying ultramafic rocks. These serpentinization reactions produce large amounts of hydrogen, and the resulting reducing conditions favor methane as the dominant carbon volatile species. Samples taken during the return visit to Lost City in the Spring of 2003 provide the opportunity to characterize the volatiles of an ultramafic hosted hydrothermal system without a magmatic contribution. Preliminary results from fluids sampled using non-gas-tight major samplers indicate high levels of hydrogen (mmol/kg) and methane (hundreds of umol/kg), and abundant low molecular weight hydrocarbons (hundreds of nmol/kg). While the ratio of methane to higher organics (on the order of 100:1) is similar to results from sedimented mid-ocean ridge hydrothermal fluids, the lack of organic rich sediments at Lost City requires an alternate source of light hydrocarbon gases. Abiotic synthesis of low molecular weight hydrocarbons through Fischer-Tropsch type reactions is a potential pathway, and has been invoked in the high-temperature ultramafic system at Rainbow. However, the relatively cool temperature of venting at Lost City ($<$100$\deg$C) may provide a kinetic barrier to this type of reaction. Biological production may be an active mechanism of methane production, but it is unlikely that higher organics are formed this way. It is our hope that a careful analysis of the concentrations and isotope ratios of the collected gasses from major-pairs and gas-tight samplers at Lost City will lead to a better understanding of the flow of carbon at Lost City, and provide a model for other, yet undiscovered systems driven by the reaction of cold seawater with cold mantle rocks.
DE: 1045 Low-temperature geochemistry
DE: 1060 Planetary geochemistry (5405, 5410, 5704, 5709, 6005, 6008)
DE: 3035 Midocean ridge processes
DE: 4806 Carbon cycling
SC: Biogeosciences [B]
MN: 2003 Fall Meeting