Enhanced boundary scavenging of Am on the continental margin of the East China sea.

The Am concentrations were determined by sector field high-resolution inductively coupled plasma mass spectrometry for settling particles and surface sediments collected on the continental margin in the East China Sea to discuss the behavior of Am in the studied area. A large and regular increase was noted from 97 m depth to 592 m depth in Am concentrations in settling particles from the cylindrical sediment traps, whereas only a slight increase in Pu concentrations was evident. The gradual increase in Am/Pu activity ratios from the cylindrical trap settling particles also was observed. These results were attributed to Am being scavenged by settling particles at a more rapid scavenging rate than Pu. There was an obvious tendency for Am fluxes to increase linearly with depth with the highest fluxes at near-bottom, and these fluxes were due to large advective import to the near-bottom. There was a tendency for Am concentrations in surface sediments to increase almost linearly with depth, showing the same tendency as Pb concentrations, and this tendency indicated that the enhanced boundary scavenging of Am as well as Pb occurred in the East China Sea continental slope region due to the greater abundance of reactive finer particles. The Am concentrations in settling particles from the time-series sediment trap ranged from 1.05 to 4.20 mBq g, showing large variation. The Am concentrations from the time-series trap varied inversely with the total mass fluxes, indicating that Am concentrations were diluted by particles when mass flux increased. The Am fluxes showed large time-series variations and these variations were primarily controlled by mass flux variation. It seems that the high total mass flux events are due to resuspension of the underlying surface sediments and episodic lateral transport of particles that flow down the continental slope in the East China Sea.