Organic and carbon isotope biogeochemistry of California coastal sediments.

摘要

Five studies examined various aspects of carbon cycling in two different marine sedimentary environments. Four of these considered sediment biogeochemistry and microbial ecology near natural hydrocarbon seepage (the Isla Vista seep). The fifth study involved the development and application of a new method for measuring total amounts of, and stable carbon isotopes in, dissolved organic carbon (DOC) of interstitial waters.; Sediments at the Isla Vista seep were the most oxygen-limited and had high sulfate reduction rates compared with two non-seep sediments. Compounds which could be used to fuel subsurface anaerobic metabolism were limited. Although detected in high concentrations, sediment methane contribute insignificantly to sulfate reduction. Pore-water acetate was also detected in high concentrations at the seep, and acetate metabolism could potentially account for greater than one-third of total sulfate reduction there. The proportion of acetate assimilated to cellular carbon was lower, while water-soluble metabolites were higher, in seep sediments.; Fossil, {dollar}sp{lcub}14{rcub}{dollar}C-depleted carbon from hydrocarbon seepage was detected in varying amounts in total organic, dissolved inorganic, and meiofaunal and macrofaunal carbon from sediments at three sites near the seep. Using natural {dollar}sp{lcub}14{rcub}{dollar}C abundances and mass balance considerations, estimates of fossil carbon mineralization or incorporation into faunal biomass were made.; Development and subsequent application of a new method of DOC analysis showed that DOC exhibited a concentration maximum in the surface layer of a hypersaline microbial mat, contrasting with invariable total organic and dissolved inorganic carbon profiles. Isotopic abundances of DOC were {dollar}sim{dollar}8 per mil lighter at 1.5-2.0-cm depth than in the mat surface (0-0.5 cm) indicating that it was the most isotopically dynamic of the three major carbon pools.