HR: 14:55h
AN: V43C-06    [Abstracts]
TI: Production of Isotopically Heavy Dissolved Organic Carbon in the Lost City Hydrothermal Vent Field
AU: * Lang, S Q
EM: sqlang@u.washington.edu
AF: School of Oceanography, University of Washington, Box 355351, Seattle, WA 98195
AU: Butterfield, D
EM: david.a.butterfield@noaa.gov
AF: Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, 7600 Sand Point Way, Seattle, WA 98115
AU: Hedges, J
V43C-06 AF: School of Oceanography, University of Washington, Box 355351, Seattle, WA 98195
AU: Lilley, M
EM: lilley@ocean.washington.edu
AF: School of Oceanography, University of Washington, Box 355351, Seattle, WA 98195
AB: The Lost City is a peridotite-hosted vent field distinctly different from other known hydrothermal systems. Fluids from Lost City are warm (40 to 90°C), reducing, highly alkaline (pH 9 to 11), and enriched in hydrogen, methane and other hydrocarbons [1]. Tall carbonate chimneys host dense microbial communities which have been implicated in methane and sulfur cycling [1]. The concentration and composition of organic matter in this environment has important ramifications for resident microbial communities as both a potential carbon source and as a potential electron donor. Additionally, organic components can serve as tracers of subsurface processes such as microbial autotrophic production or heterotrophic uptake which may otherwise be difficult to detect. Water samples were collected from the Lost City vent field in the summer of 2003 and analyzed for dissolved organic carbon (DOC) concentrations. Across the field, concentrations fell primarily along a single mixing line between the hydrothermal endmember fluids and local background seawater. Endmember fluids contain up to 95 μM DOC, more than twice the concentration in local background seawater. The presence of a single, field-wide mixing line suggests that the majority of the excess carbon is added at depth, with minimal interaction from the carbonate chimneys. To constrain its source, we analyzed the stable carbon (¹³C) isotopic composition of the DOC, which ranged from typical seawater values of -22.2 ‰ (VPDB) to -10.0 ‰ in the most hydrothermally pure samples. The excess DOC has a similar isotopic composition to both the methane in the fluids [2] and the lipids of methane-cycling archaea isolated in the chimney [1]. Ongoing molecular measurements will help constrain the potential sources of organic carbon to this system. [1] Kelley, D.S. et al. (2005) A Peridotite-Hosted Ecosystem: The Lost City Hydrothermal Field. Science. 307 (5714). [2] Proskurowski, G., Lilley, M.D., Frueh-Green, G.L., Olsen, E.J., and Kelley, D.S. (2004) The Use of Stable Hydrogen Isotopes as a Geothermometer in Hydrothermal Systems. Eos, Trans. American Geophysical Union 85(47): Fall Meeting Suppl. Abstract #B13A-0200
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 1055 Organic and biogenic geochemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005