Substantial Accumulation of Chemically Oxidizable Organic Carbon in Continental Margin Sediments

Abstract The balance between organic carbon (OC) sequestration and oxidation regulates the oceanic carbon cycle, and OC reactivity determines its susceptibility to remineralization or long‐term burial. However, the stability of sedimentary OC on continental margins remains poorly understood. Here, we quantify chemically oxidizable and oxidation‐resistant OC fractions and their compositions across the East China Continental Margins (ECCM) using a chemical oxidation approach. Burial fluxes of oxidizable and oxidation‐resistant OC across the ECCM are estimated at 11.8 (interquartile range: 8.5–15.5) and 10.8 (interquartile range: 6.9–14.1) Mt C yr −1 , respectively. Oxidation‐resistant OC is overwhelmingly terrestrial (>90%) but derived from contrasting sources, whereas oxidizable OC is predominantly marine‐derived, and has approximately sixfold higher OC loadings than oxidation‐resistant OC. Global synthesis of 1,102 marine sediments shows that ∼61.6 ± 24% of sedimentary OC is oxidizable, indicating that continental margins act as transient reservoirs of reactive OC that are highly susceptible to environmental perturbation.