Processes controlling organic carbon turnover and sequestration in the land-ocean margin off the Atchafalaya River/Louisiana Shelf

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Under this funding, the PI will attempt to determine the role of organic matter compositions in controlling carbon sequestration and turnover by quantitatively investigating how different organic carbon (OC) fractions are cycled within a well-characterized sediment system: the Atchafalaya River/Louisiana Shelf. Specifically, the study will trace the changes in concentration and composition of four major OC pools of contrasting origin, particle characteristics (e.g. density), and reactivity: (i) vascular plant debris, (ii) soil organic matter, (iii) ancient fossil kerogen, and (iv) marine organic matter remains. The objectives of the work are to determine the distribution of the four OC pools within the Atchafalaya River/Louisiana Shelf dispersal system, to follow the concentration changes and compositional transformations of these OC pools along the dispersal system, and to determine the sequestration rates and compositional changes of the four OC pools during burial in the Louisiana shelf. The study consists of field sampling followed by lab studies to determine: (a) density fractionation of sediments, (b) elemental (carbon, nitrogen) compositions, (c) stable carbon and radiocarbon isotopic compositions, (d) 13C-NMR characterization of organic isolates, and (e) biomarker concentrations and isotopic signatures.