HR: 15:25h
AN: B23G-08    [Abstracts]
TI: Particulate Organic Carbon and Iron Speciation within Deep-Sea Hydrothermal Plumes
AU: * Toner, B M
EM: btoner@whoi.edu
AF: Woods Hole Oceanographic Institution, Department of Marine Chemistry and Geochemistry, 266 Woods Hole Rd., Woods Hole, MA 02543,
AU: Fakra, S C
EM: sfakra@lbl.gov
AF: Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, CA 94720,
AU: Manganini, S J
EM: smanganini@whoi.edu
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics, 266 Woods Hole Rd., Woods Hole, MA 02543,
AU: Moffett, J W
EM: jmoffett@usc.edu
AF: University of Southern California, Department of Biological Sciences, 3616 Trousdale Parkway, Los Angeles, CA 90089,
AU: German, C R
EM: cgerman@whoi.edu
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics, 266 Woods Hole Rd., Woods Hole, MA 02543,
AU: Edwards, K J
EM: kje@usc.edu
AF: University of Southern California, Department of Biological Sciences, 3616 Trousdale Parkway, Los Angeles, CA 90089,
AB: Geophysical and geochemical models indicate that mid-ocean ridge hydrothermal venting may be a quantitatively significant component of the global Fe budget. Direct measurements demonstrate that seawater interactions with hydrothermal plumes exert quantitative controls on the elemental oceanic cycling of numerous trace elements and isotopes including essential nutrients and micronutrients. The chemical reactivity of hydrothermal plumes has been attributed, but not firmly linked, to the formation and surface reactivity of Fe oxide minerals. Despite the overwhelming evidence that plume particulate Fe is a key factor in ocean chemistry, essentially nothing is known of Fe speciation within plumes, outside of sulfide mineralogy. In addition, due to the analytically challenging nature of the plume particles, little is known about the mechanisms behind the biogeochemical processes catalyzed by these materials. Although a role for organic C (Corg) in Fe speciation and mobility in the deep-sea has been hypothesized, Corg sources and speciation in plumes remain largely unknown. The present study examines Fe and C speciation in plume particles at the nanometer scale using scanning transmission X- ray microscopy (STXM) combined with C 1s and Fe 2p near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The results offer evidence for direct interactions between Fe and C in plume particles; Fe(II), Fe(III), and C occur in close spatial proximity within plume particle aggregates. Iron(II) is co-located with C, and is stable in the presence of dissolved O2 on timescales that exceed the calculated "half-life" (with respect to oxidation) for Fe(II) in seawater. Organic C matrices coat micrometer scale Fe-rich particles and physically entrap nanometer scale Fe-rich particles. Our results suggest a new and broader conceptual model for the source of trace-element reactive surfaces in hydrothermal plumes is required, one that includes Corg in addition to the long-hypothesized Fe oxide particles. Our study has wide ranging implications for long-range Fe oceanic transport, oceanic trace element distributions, and deep-sea and sub-seafloor microbial C fixation.
DE: 0448 Geomicrobiology
DE: 3035 Midocean ridge processes
DE: 4832 Hydrothermal systems (0450, 1034, 3017, 3616, 8135, 8424)
DE: 4850 Marine organic chemistry (0470, 1050)
DE: 4851 Oxidation/reduction reactions (0471)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting