210Pb, 137Cs and 239,240Pu in East China Sea sediments: sources, pathways and budgets of sediments and radionuclides

Profiles of 210Pb, 137Cs and 239,240Pu measured in 83 sediment cores collected from various sedimentary regimes in the East China Sea were analyzed to elucidate the sources, routes and budgets of sediments as well as these radionuclides. Distributions of sedimentation rates and nuclide inventories reveal alongshore transport of sediments, 137Cs and 239,240Pu from the mouth of the Yangtze River toward the south, largely confined to the inner-shelf area (water depth <70 m). Mass balance calculations suggest that the East China Sea is a sink for the particle-reactive 210Pb and 239,240Pu, with about one-sixth of their sedimentary budgets supplied via boundary scavenging. In contrast, due to lower affinity of 137Cs for particles and rapid turnover of the shelf water, the East China Sea serves as a source for 137Cs. About two-thirds of the cumulative input of 137Cs have been transported out of the East China Sea, leaving the remaining one-third stored in the bottom sediments and the overlying water column. As for the sediment budget, mass balance cannot be established due to a shortfall in sediment supply of more than 30% based on a comparison between input terms documented thus far and the sedimentation flux derived from this study. It is very likely that we have overestimated the sediment burial flux or that long-distance transport from the Yellow River’s dispersal system to the East China Sea is underestimated. Alternatively, the imbalance could be explained by the discrepancy between sediment input and output on decadal to centennial timescales.