HR: 0800h
AN: B31C-0508    [Abstracts]
TI: Bamboo Coral Gorgonin: Surface Water Geochemical Records From the Organic Nodes of a Deep Water Coral
AU: * Myrvold, C R
EM: myrvold@geology.ucdavis.edu
AF: Department of Geology, University of California Davis, One Shields Ave., Davis, CA 95616,
AU: Hill, T M
EM: tmhill@ucdavis.edu
AF: Department of Geology, University of California Davis, One Shields Ave., Davis, CA 95616,
AU: Spero, H J
EM: spero@geology.ucdavis.edu
AF: Department of Geology, University of California Davis, One Shields Ave., Davis, CA 95616,
AU: Guilderson, T P
EM: tguilderson@llnl.gov
AF: Center for Acceleration Mass Spectrometry, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550,
AB: Deep-sea bamboo corals (family Isididae) found on seamounts on the California margin (37°22'N to 31°54'N) have the potential to record annual to subannual changes in water mass chemistry over decades to centuries. These corals are composed of calcite internodes precipitated from the surrounding intermediate water (as evidenced by D¹⁴C values), and organic nodes formed from the organic matter of the coral's food source. Both organic and inorganic portions of the skeleton are precipitated annually, with growth rates of ~100 microns/year. Geochemical analyses of the organic nodes of living corals collected in 2004 and 2007 (800- 2200m water depth) exhibit post-bomb radiocarbon values of >80 per mil D¹⁴C on the outer edge of the organic nodes, suggesting that the organic matter is surface-derived; pre-bomb spike values range from -81.3 per mil to -116.9 per mil in the interior of the coral organic node. Carbon isotopic values of recently precipitated organic nodes range from -16.5 per mil to -18.8 per mil. Nitrogen isotopic values from the organic nodes range between 13.8 per mil and 18.9 per mil, reflecting a zooplankton-derived N source that is strongly affected by water column denitrification processes. Organic node carbon isotopic variability in a 300+ yr old specimen exceeds 3 per mil, suggesting changes in productivity along the California margin during this time period. Organic geochemical analyses of several long-lived corals has the potential to provide century scale, high-resolution records of surface water productivity, nutrient dynamics and biogeochemical cycling along the California margin.
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 1040 Radiogenic isotope geochemistry
DE: 4912 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4805)
DE: 4916 Corals (4220)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting