Abstract
241Am in the marine environment originated mainly from the decay of 241Pu. 241Am and Pu isotopes are highly particle-reactive elements and those are therefore removed from the water column by scavenging onto settling particles. Compared with intensive studies of Pu isotopes, distributions and behavior of 241Am in the ocean have been poorly investigated. The objectives of this study are to measure the activities of 241Am, 239+240Pu and 210Pb in settling particles and surface sediments and to discuss the removal of reactive radionuclides by scavenging on the continental margin of the East China Sea. Settling particle samples were collected at four stations. Two types of sediment traps were used, cylindrical traps and conical time-series traps. Sediment samples were collected with a multiple core sampler. The 241Am activities in settling particles ranged from 2.6 to 7.3 mBq/g, indicating that they increased gradually with increasing trap depth. The 241Am/239+240Pu activity ratios were 1.5 at 100-m depth and 2.1 at 600-m depth. The 241Am fluxes ranged from 1.5 to 170 mBq/m2/day and increased with depth, with an especially large increase near-bottom. The activities and fluxes of 241Am showed large seasonal variations. There was a tendency for 241Am activities and 241Am/239+240Pu activity ratios in surface sediments (0-1 cm) to increase almost linearly with depth. This tendency was in good agreement with that of 210Pb. All these results can be attributed to enhanced 241Am scavenging by particles and removal near the front between the Kuroshio Current and the East China Sea shelf water. It appears that the same removal mechanism occur between 241Am and 210Pb.
