Sedimentation and lateral transport of ~(210)Pb over the East China Sea Shelf

摘要

~(210)Pb is an effective tracer of constraining particle transport and sedimentation in shelf regions. To reveal the spatial pattern of ~(210)Pb over the East China Sea (i.e. ECS) Shelf, ~(210)Pb in the surface sediments were examined at 11 stations, as well as ~(234)Th and ~(210)Pb in the water column at four stations. Overall, the plume zone of the Yangtze River along the coastline is a source area of ~(210)Pb for the outer shelf, exporting 0.46 dpm cm~(-2) year~(-1) at least, which accounts for about 25 % of ~(210)Pb input into this region. In the southern ECS Shelf to the north of the Taiwan Strait, the focusing factor (f) values are higher than unity, indicating a sink area of ~(210)Pb. Boundary scavenging of ~(210)Pb contributes 0.36 dpm cm~(-2) year~(-1) to this sink area on the basis of a mass balance model evaluation. Lateral transport of ~(210)Pb to this region, quantified by ~(234)Th and ~(210)Pb in the water column, varied from 3.34 to 6.39 dpm cm~(-2) year~(-1) with an average of 4.83 dpm cm~(-2) year~(-1), also supporting its sink characteristic. To the southwest of the Cheju Island, the f values were less than unity, revealing a source region of ~(210)Pb. The average export flux of ~(210)Pb from this region was 1.64 dpm cm~(-2) year ~(-1). Therefore, ~(210)Pb sedimentation/settling showed significantly heterogeneous sedimentation of particulate matter over the ECS Shelf.