Evaluation of Sedimentary Organic Carbon Reactivity and Burial in the Eastern China Marginal Seas

Dynamic physicochemical interactions along continental margins create complex organic carbon (OC) cycles that have a significant impact on the global climate but remain enigmatic; in particular, the OC burial behaviors in mud areas are still unclear. Herein, the molecular and bulk properties of sedimentary OC (SOC) were investigated in eastern China marginal seas to better understand the fate of SOC. The source discrimination analysis showed that SOC was mainly derived from indigenous production and experienced strong heterotrophic alteration, as indicated by low glucosamine/galactosamine ratios (<3) and the relatively high contribution of bacterial OC (similar to 25%). The South Yellow Sea mud area (SYSMA) and East China Sea mud area (ECSMA) both represented hot spots for SOC burial, but the SYSMA exhibited lower SOC reactivity than the ECSMA because of intense degradation in the water column. Although the net particulate OC deposition flux in the ECSMA was approximately 5 times that of the SYSMA, the SOC burial efficiencies (similar to 35%) of these two areas were similar due to the presence of cold water masses and cyclonic eddies in the SYSMA (which are beneficial for the storage of SOC) and the active remineralization driven by the priming effect and intense physical reworking in the ECSMA. As human disturbance and global climate change intensify, the role of distal mud areas (represented by the SYSMA) in SOC burial may become increasingly prominent, while the SOC burial in inner shelf mobile mud areas (such as the ECSMA) affected by large rivers may be significantly reduced.