HR: 1340h
AN: V13A-1440    [Abstracts]
TI: Toward long-term geochemical sampling of gases and deep fluids in subduction zone fore-arcs: New instrument developments
AU: * Tryon, M D
EM: mtryon@ucsd.edu
AF: Scripps Institution of Oceanography, 9500 Gilman Dr, 0244, La Jolla, CA 92093-0244 United States
AU: Labonte, A L
EM: alabonte@ucsd.edu
AF: Scripps Institution of Oceanography, 9500 Gilman Dr, 0244, La Jolla, CA 92093-0244 United States
AU: Fueri, E
EM: efuri@ucsd.edu
AF: Scripps Institution of Oceanography, 9500 Gilman Dr, 0244, La Jolla, CA 92093-0244 United States
AU: Hilton, D R
EM: drhilton@ucsd.edu
AF: Scripps Institution of Oceanography, 9500 Gilman Dr, 0244, La Jolla, CA 92093-0244 United States
AU: Brown, K M
EM: kmbrown@ucsd.ede
AF: Scripps Institution of Oceanography, 9500 Gilman Dr, 0244, La Jolla, CA 92093-0244 United States
AB: We present preliminary results of an on-going instrument development study aimed at quantifying the rate of elemental loss to the ocean/atmosphere in active fore-arc margins. Work on subduction zones to date has focused on elemental fluxes associated with magmatism at the arc front. For example, the flux of carbon output along the strike of the Central America arc is $\sim$ 5 x 10$^{7}$ mol/yr/km, or ~14% of that potentially available by input via the trench (Shaw et al., EPSL, 2003). This result indicates that carbon is (a) efficiently recycled to the (deeper) mantle, i.e. the mantle beyond the zone of arc magma generation, and/or (b) lost in the fore-arc region. There are few constraints on elemental losses at the fore-arc region; the present work, therefore, is motivated by quantifying the flux of volatiles (and other species) lost in the early stages of the subduction cycle. This will allow a qualitative assessment of the importance of deep recycling and contribute to an increased understanding of the hydrogeology of active margins. The Chemical and Aqueous Transport (CAT) meters (Tryon et al., Deep Sea Research, 2001) used in this study record a time series of flow rates by injecting a tracer at a constant known rate into the flow stream through the instrument and by sampling downstream of this point for tracer dilution. They also collect a time series of seep fluids in copper coils and maintain them at seafloor pressure during recovery. The Optical Flow Meter (OFM) measures flow by determining the time-of-flight of a tracer pulse injected into the flow stream. An osmotic pump is used to sample fluids in a manner similar to the CAT meters. A series of tests utilizing both sets of instruments has been conducted at the Extrovert Cliffs site in Monterey Bay during 2004. Sites chosen range from diffuse flow sites with output rates of 10s of cm/yr to highly focused visibly flowing sites: all localities are covered by extensive microbial mats and chemosynthetic clams. Our coupled data sets of aqueous flow rate and geochemical/volatile composition allow us to estimate geochemical fluxes at these sites. Our next deployment of the instrumentation will target seeps off the Costa Rica margin.
DE: 8045 Role of fluids
DE: 4806 Carbon cycling
DE: 1030 Geochemical cycles (0330)
DE: 1050 Marine geochemistry (4835, 4850)
DE: 1094 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting