and in settling particles collected by time-series sediment traps in the Okinawa Trough

Abstract Settling particles were collected from two locations in the Okinawa Trough (Stn. SST-1: 29–23.3°N, 128–14.5°E; Stn. SST-2: 28–08.2°N, 127–11.4°E) in the East China Sea continental margin from March 1993 to February 1994 by using time-series sediment traps and then analyzed for 210 Pb . A few samples also were analyzed for 234 Th . Sediment samples collected at the same locations also were analyzed for 210 Pb . There was a clear tendency for 210 Pb concentrations in settling particles to increase with depth. 210 Pb fluxes showed large seasonal variations and increased with depth, with an especially large increase near-bottom. 234 Th fluxes also showed a general tendency to increase with depth. Ratios of the annual mean 210 Pb flux to the 210 Pb deficiency flux were only 0.14 at SST-1 and 0.13 at SST-2 in the 600 m traps and 0.53 at SST-1 and 0.59 at SST-2 in the 800 m traps, showing a strong 210 Pb flux deficit attributable to advective export from these sites. The annual mean 210 Pb fluxes in the near-bottom traps were 2.30 times higher at SST-1 and 1.47 times higher at SST-2 than the 210 Pb deficiency flux. These results might be attributable to lateral transport of particles that slowly slid down on the continental slope nepheloid layer while scavenging 210 Pb . The annual net rates of laterally transported 210 Pb were estimated to be 78.8 dpm/m 2 / day at SST-1 and 37.5 dpm/m 2 / day at SST-2 in the near-bottom layer. These rates were 3.5 times higher at SST-1 and 1.5 times higher at SST-2 than 210 Pb flux observed in upper traps, indicating that lateral transport processes play a significant role in material transport on the continental margin in the East China Sea.