Large particle flux of 239 240Pu on the continental margin of the East China Sea

Settling particles were collected from three locations in the East China Sea continental margin and analyzed for 239 240 Pu. Two types of sediment traps were used, cylindrical traps and conical time-series traps. Surface sediment samples collected from five locations were also analyzed for 239 240 Pu. Data from cylindrical traps showed there was a clear tendency for total mass fluxes to increase with depth at all three stations, and there was an especially large increase near the bottom. 239 240Pu concentrations in settling particles increased with depth from 1.76 mBq g at 97-m depth to 3.00 mBq g at 120-m depth and ranged from approximately 3 to 4 mBq g at depths greater than 120 m. 239 240Pu concentrations collected in the near-bottom traps were approximately two times higher than those in the underlying surface sediments. Like total mass fluxes there was a clear tendency for 239 240Pu fluxes to increase with depth at every station, and the highest 239 240Pu fluxes were observed near the bottom. 239 240Pu concentrations in the time-series traps had little variation throughout the sampling period, though the total mass fluxes showed a large variation. A high variability of 239 240Pu fluxes occurred in very short period of time Ž1 2 day.. The large fluxes of 239 240Pu might be attributed to episodic lateral transport of particles that flow down the continental slope with the nepheloid layer which was considered to be significant for 239 240Pu transport on the continental slope in the East China Sea.