Isotope Studies of Methane Sources in Large Marine Anoxic Basins

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ABSTRACTOCE-0099280This study sets out to better constrain the global biogeochemical cycle of methane, CH4, by a consideration of the isotopic composition of oceanic source end members. Recent renewed interest in several aspects of the geochemistry of marine methane clathrates poses a number of intriguing problems that the proposed isotopic information is likely to inform. Methane, in the form of submarine gas hydrates, potentially represents the largest known reservoir of hydrocarbons on the planet. It is important to fully understand the methane cycle in the oceans for at least two reasons, i) evaluation of its potential as an energy source, and ii) evaluation of the propensity of its past and future outgassings from the ocean to effect large scale climatic change. Methane is a powerful greenhouse gas, with a radiative impact approx. 25 times that of CO2. The investigators on this project will measure the natural isotopic composition of methane (d 13C-CH4 and d 2H-CH4 in addition to some measurements of D 14C-CH4) from the water column as well as suspected end-member sources in sediments in order to construct composition mixing models. The work takes advantage of the restricted circulation of anoxic basins such as the Black Sea, using the overlying water column to integrate the effects of different sources of and processes taking place on CH4 as it passes through the water column. The study will build on and extend preliminary measurements on d 13C-CH4 and d 2H-CH4 made on samples collected from a 1988 Black Sea expedition.