Sedimentation dynamics off the Changjiang Estuary: Radiochemical observations

Sedimentation dynamics off the Changjiang Estuary, from seasonal to decadal time scales, was elucidated using a multitracer approach. Sediment cores collected from the study area commonly show a fluffy surficial layer which, based on the Be-7 data, is accumulated rapidly by flood sedimentation in the summer time. The depth of 7 Be penetration is generally consistent with Pb-210-defined surface mixed layer. This layer can be easily resuspended in the subsequent winter monsoon season and transported to the inner-shelf region in the Louth. Below the surface mixed layer, profiles of Pb-210 show exponential decrease with depth, which can be simply explained by constant sedimentation at each site on longer (decadal to centennial) time scales. The derived sedimentation rates in the study area vary from less than 0.11 g(.)cm(-2.)yr(-1) to over 1 g(.)cm(-2.)yr(-1). Being consistent with the topography and the current flow in the study area, the spatial pattern of sedimentation rate and nuclide inventories reveal the pathways of sediments and two areas of enhanced sedimentation. Results of this study suggest that the amount of Changjiang-derived sediments stored in the estuarine area and the Hangzhou Bay may be less than previously thought.