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ricketts

HR: 1340h
AN: B33A-1020
TI: Effects of Carbon Dioxide Hydrate Emplacement on Deep-sea Foraminiferal Assemblages
AU: * Ricketts, E R
EM: e_ricketts@umail.ucsb.edu
AF: Department of Geological Sciences and the Marine Science Institute, University of California, Santa Barbara, Santa Barbara, CA 93106 United States
AU: Kennett, J P
EM: kennett@geol.ucsb.edu
AF: Department of Geological Sciences and the Marine Science Institute, University of California, Santa Barbara, Santa Barbara, CA 93106 United States
AU: Hill, T M
EM: tmhill@ucdavis.edu
AF: Department of Geology, University of California, Davis, Davis, CA 95616 United States
AU: Barry, J P
EM: barry@mbari.org
AF: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039 United States
AB: Two studies, conducted in cooperation with the Monterey Bay Aquarium Research Institute (using the R/V Western Flyer and the ROV Tiburon), investigated effects of carbon dioxide hydrate emplacement and associated dissolution products on foraminifera at two sites (3600m and 3100m) off the California margin. Foraminifera are ideal for these investigations because of differing test composition (calcareous and agglutinated) and thicknesses, and diverse epifaunal and infaunal depth preferences. The pH of each site was monitored by Seabird CTDs. Suites of sediment push-cores were collected and stained (to distinguish live from dead). These included control cores and multiple experimental core types (corral, distal, and proximal). Core length differed between the two studies in part to assess the effective depth of penetration of CO2 within the sediments. Effects of CO2 emplacement on foraminiferal assemblages have been tracked both vertically (10-20cm below the sea floor) and horizontally (up to 50m from CO2 injection sites), and between live and dead individuals. Results from these experiments are in accordance on several major effects: 1) increased mortality and dissolution as a consequence of CO2 hydrate exposure; 2) total number of foraminifera in the sample decreases; and 3) resistance to dissolution varies with depth and species. Down-core trends (to 10cm bsf) for the 3600m study show: 1) an exponential decrease of tests with depths; 2) percent agglutinated forms decline and calcareous forms increasingly dominate with depth; 3) agglutinated diversity decreases with depth; and 3) assemblages in experimental cores become increasingly similar with depth to those in control cores. Down-core trends for the 3100m study show: 1) a uniform distribution of tests to a depth of 14cm; 2) below 14cm there is a linear increase in test abundance per centimeter; and 3) deep penetration of carbonate dissolution (up to 16cm) in assemblages in experimental cores. These results suggest that while the overall effects of mortality and dissolution of foraminifera are similar, emplacement effects vary between sites, with shallower assemblages better demonstrating the true magnitude due to the predominantly calcareous forms. Both sites experienced a small overall reduction in ocean pH as well as large excursions resulting from CO2 injection. Exposure to this low pH plume caused increased mortality and dissolution of calcareous foraminifera as far as 50m from the injection site. These results imply almost complete initial mortality and dissolution upon CO2 hydrate emplacement in the corrals.
DE: 0485 Science policy (6620)
DE: 4858 Population dynamics and ecology
DE: 4902 Anthropogenic effects (1803, 4802)
DE: 4930 Greenhouse gases
DE: 9355 Pacific Ocean
SC: Biogeosciences [B]
MN: Fall Meeting 2005