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    River discharge and sedimentation drive progressive bottom-water hypoxia and redox reorganization in eastern Arabian Sea shelf sediments

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    Date
    2026
    Author
    Sivan, K.
    Mazumdar, A.
    Peketi, A.
    Verma, S.
    Mishra, Shubhshree
    Zatale, A.
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    Abstract
    Continental shelf sediments play a critical role in global biogeochemical cycling, serving as major sites for organic carbon burial as well as sulfur and trace element transformations. Here, we employ a multiproxy analysis of a sediment core from the seasonally hypoxic shelf off the west coast of India to reconstruct depositional and diagenetic redox evolution and evaluate how river discharge, water column stratification, and upwelling influence shelf biogeochemistry. Sedimentary characteristics, such as grain size and organic carbon content, indicate a shift toward enhanced terrestrial siliciclastic input and organic matter burial associated with intensified southwest monsoon rainfall, river discharge, and upwelling during the late Holocene. Redox-sensitive metal records reveal a progressive intensification of suboxic conditions, consistent with increased terrestrial siliciclastic flux and organic matter burial. A decrease in U enrichment, along with decreasing U/Th and Mo/Mn ratios in the uppermost sediments (?30.5 cmbsf), suggests a recent weakening of reducing conditions. Pyrite sulfur isotope ratios further capture a transition from bioturbated, open-system diagenesis under relatively oxic conditions to more closed-system behavior under intensified hypoxia, driven by changes in sulfate replenishment and benthic activity. Together, these results highlight that bottom water redox conditions on seasonally hypoxic continental shelves are governed by the coupled effects of terrestrial input, stratification, upwelling, and organic matter burial. The multiproxy approach presented here provides a process-based framework for interpreting sedimentary archives of coastal deoxygenation and offers insights applicable to other seasonally oxygen-deficient margin systems, as well as to ancient marginal-marine environments characterized by fluctuating redox conditions.
    URI
    https://doi.org/10.1016/j.chemgeo.2026.123415
    https://www.sciencedirect.com/science/article/pii/S0009254126001841
    http://drs.nio.res.in/drs/handle/2264/9673
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