Distribution, sources and burial flux of sedimentary organic matter in the East China Sea

Distribution of total organic carbon (TOC), total nitrogen (TN), stable isotope ratio of organic carbon and nitrogen (δ13C and δ15N) in 31 surface sediments were examined to quantitatively discriminate the source and burial of sedimentary organic matter (SOM) in the East China Sea (ECS). Results show that high content of TOC and TN occurred in the southern inner shelf and the northeast area due to the transport of organic matter (OM) from the Changjiang (Yangtze) River southwards by the Zhejiang Fujian Coastal Current (ZFCC) and the delivery from the old Huanghe (Yellow) River estuary by the Subei Coastal Current (SbCC), respectively. The significant relationship of TOC to clay provided evidence that the fine-grained sediment was the primary carrier for SOM from the inner shelf to open sea. The TN varied proportionally to the TOC with the neglected intercept, suggesting that most of nitrogen measured was related to the SOM and the influence of the sorption of inorganic nitrogen was insignificant. The seaward enrichment of δ13C and seaward depletion of C/N and δ15N illustrated the decrease of terrestrial OM (TOM) and the increase of marine OM (MOM). The close of average C/N ratio to the Redfield ratio indicated the minor role of terrestrial plant debris in the SOM. Distribution of bulk OM properties was ascribed to the terrestrial and marine input by the shelf circulation and phytoplankton with the contributions of 76.1% MOM and 23.9% TOM to SOM, respectively. The burial flux of OC ranged within 0.34–7.56 mg/(cm2·a) (averaged 2.80 mg/(cm2·a)) and enriched along the shore and in the fine-grained area, manifesting the significant input of the land-based sources and the effect of shelf mud depositional process on the fate of SOM. The sharp seaward decrease of burial fluxes of terrestrial and marine OC gave evidences that the majority of organic carbon were settled in the inner shelf with the small fraction of them further transported eastwards.