Isotopic evidence for the incorporation of methane-derived carbon into foraminifera from modern methane seeps, Hydrate Ridge, Northeast Pacific

Details Isotopic evidence for the incorporation of methane-derived carbon into foraminifera from modern methane seeps, Hydrate Ridge, Northeast Pacific Isotopic evidence for the incorporation of methane-derived carbon into foraminifera from modern methane seeps, Hydrate Ridge, Northeast Pacific

Nov 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004gecoa..68.4619h&link_type=abstract

Geochimica et Cosmochimica Acta, Volume 68, Issue 22, p. 4619-4627.

Computer Science

8

Scientific paper

The presence of modern methane seeps at Hydrate Ridge, offshore Oregon, provide an opportunity to study the influence of methane seeps on the ecology and geochemistry of living foraminifera. A series of cores were collected from the southern summit of Hydrate Ridge in 2002. Samples were preserved and stained to determine the δ13C composition of three species of live (stained) and dead benthic foraminifera: Uvigerina peregrina, Cibicidoides mckannai, and Globobulimina auriculata. Specimens were examined under light and Scanning Electron Microscopy (SEM) and exhibit no evidence of diagenesis or authigenic carbonate precipitation. Individual living foraminifera from seep sites recorded δ13C values from -0.4‰ to -21.2‰, indicating the isotopic influence of high methane concentrations. Average δ13C values (calculated from single specimens) range from -1.28 to -5.64‰ at seep sites, and -0.81 to -0.85‰ at a control (off seep) site. Two distinct seep environments, distinguished by the presence of microbial mats or clam fields, were studied to determine environmental influences on δ13C values. Individual foraminifera from microbial mat sites exhibited more depleted δ13C values than those from clam field sites. We interpret these differences as an effect of food source and/or symbiotic microbes on foraminiferal carbon isotopic values, acting to magnify the negative δ13C values recorded via the DIC pool. No statistical difference was found between δ13C values of live vs. dead specimens. This suggests that authigenic carbonate precipitation did not play a dominant role in the observed isotopic compositions. However, a few dead specimens with extremely negative δ13C composition (<-12‰) do indicate potential evidence for an authigenic influence on the recorded δ13C composition.

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