In spite of their importance as sites of long-term burial of organic matter (OM), key questions remain regarding the factors controlling carbon sequestration in river subaqueous deltas. One of the salient, but poorly understood, features of these river-dominated ocean margins (RIOMARs) is their highly dynamic nature. Specifically, we lack quantitative understanding of the role that perturbation events, such as floods, play in the OM biogeochemistry of RIOMAR systems. To address this knowledge gap, we propose to analyze the composition of OM in sediments from the Po River prodelta (Italy) that were emplaced during a 100-year flood. We propose to conduct a series of analyses designed to test specific aspects of a conceptual model of non-steady state biogeochemical OM cycling in coastal margins. We will specifically test the effects of key physical forcings (sediment deposition, physical and biological reworking, and microbial activity) on the processes responsible for the cycling and ultimate fate of OM in the flood deposit. We will investigate changes in the physical properties and composition of a variety of OM constituents including organic carbon, organic nitrogen, isotopes, as well as specific biochemical classes (fatty acids, cutin, lignin and amino acid products). Our approach will be to select sites and zones of the sedimentary column that experienced intense and clear changes in order to test hypotheses regarding the effects of these post-depositional processes. Our proposed work will provide novel insights into the role that major floods play on the cycling and fate of organic matter in RIOMAR sediments. This area of research is critical to several ongoing international programs (e.g. North American Carbon Program, Carbon&Water, MARGINS) designed to understand global organic carbon cycle, and more specifically to define the connections between terrestrial and marine environments.
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