HR: 0800h
AN: PP51B-0600    [Abstracts]
TI: Carbon Isotopic Signatures in Benthic Foraminifera Bio- and Tanathocenosis From Methane-Soaked Gas-Hydrate-Bearing Sediments in Guaymas Basin, Gulf of California
AU: * Herguera, J
EM: herguera@cicese.mx
AF: CICESE, Carretera TransPeninsular Km 107, Ensenada, BC 22850 Mexico
AU: Perez, E
EM: geperez@isugw.indstate.edu
AF: Natural History Museum, Cromwell Rd, London, SW7 5BD United Kingdom
AU: Paull, C
EM: paull@mbari.org
AF: MBARI, 7700 Sandholdt Rd, Moss Landing, CA 95039-9644 United States
AU: Ussler, B
EM: methane@mbari.org
AF: MBARI, 7700 Sandholdt Rd, Moss Landing, CA 95039-9644 United States
AU: Peltzer, E
EM: etp3@mbari.org
AF: MBARI, 7700 Sandholdt Rd, Moss Landing, CA 95039-9644 United States
AB: Here we report on recent results from an extensive ROV-based exploration along the NE transform margin of the Guaymas Basin in the Gulf of California to characterize patterns of carbon isotopic assimilation into the benthic foraminiferal tests along known gradients of present methane venting. Cores were retrieved from: a (i) vigorous methane venting site visible by a continuous emanation of gas bubbles from the seafloor at 1,582 m depth of water, (ii) beds of living calyptogenid clams, (iii) white bacterial mats, commonly found on exposed strata on the flanks of the basin, and (iv) background sites at the same depth in the neighboring slopes of Guaymas Basin. Rose bengal-stained and non-stained specimens of Uvigerina peregrina (Up), Planulina wllerstorfi (Pw), Globobulimina pacifica (Gp), and Bulimina mexicana (Bm) were hand-picked and their carbon and oxygen isotopic ratios were determined. Dissolved inorganic carbon isotopic values measured in several pore water samples extracted from sediments range between -2.9% to -35.85%. The most depleted values indicate that while some methane derived carbon has entered the authigenic DIC pool within the seafloor sediments during early diagenesis, there is no record of the assimilation of this carbon on the calcitic shells of living benthic foraminifera. Here we will further compare the carbon isotopic composition of stained (living) foraminifera shells and non-stained tests to show the patterns of carbon assimilation and early diagenetic imprint of both assamblages. These results question the extent to which strong carbon isotopic depletion signals in the geological record are features recorded by living foraminifera or the result of a posterior diagenetical imprint.
DE: 1051 Sedimentary geochemistry
DE: 3004 Gas and hydrate systems
DE: 4924 Geochemical tracers
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005