9416626 Devol In this project, the investigator will address one of the major questions on the global carbon cycle: What determines the extent to which organic carbon produced by primary production in the world ocean survives mineralization and is buried in seafloor sediments? The project will continue the investigator's past work in two regions of the western Pacific margin, one off the U.S. Pacific Northwest, the other off the coast of northwestern Mexico. It has commonly been assumed that the amount of particulate organic matter near the sediment-water interface determines the rate of organic mineralization, or oxidation; the process is mediated by heterotrophic bacteria that use either dissolved oxygen or nitrate as oxidant. However, in this study the investigator will also explore the possibly that, when water column oxygen concentrations are low, the concentrations of dissolved oxygen and nitrate (rather than organic matter) may actually control mineralization rates. To clarify these issues, the project will involve field measurements of the rates of organic sedimentation, chemical reactions in the sediments, and (by direct measurement) solute fluxes across the sediment-water interface.
