Particle-Associated and Water-Column Methane Cycling in the Upper Ocean

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ABSTRACTOCE-9911649The biogeochemistry of the production, cycling, and loss methane, an important greenhouse gas, in the world ocean is very imperfectly understood. Several lines of evidence suggest that the oceanic pycnocline (the vertical zone in which seawater density increases relatively rapidly with depth) is a zone of particularly intense methanogenesis. Suspended particulates, which tend to accumulate in this zone and thus offer an interface for the microbial activity driving methanogenesis, may provide the sites where this chemical activity is concentrated. In this project, investigators from the University of Hawaii will study the details of particle-associated and water-column methane production in the pycnocline of the eastern tropical North Pacific, including the possibility that methane production and oxidation is driven algal exudates. The field study will occupy stations along a well documented oxidation-reduction gradient extending from the upwelling-induced anoxic zone offshore of Mexico and extending to the oxygen minimum of the Pacific central gyre, thus covering a range of oxygen concentrations, particle loading rates, and dissolved inorganic nitrogen levels. The study will also examine the role of nitrifying bacteria and the importance of dissolved inorganic nitrogen concentration in methane oxidation.