Enhanced boundary scavenging of 241Am on the continental margin of the East China sea

The 241Am 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 241Am in the studied area. A large and regular increase was noted from 97 m depth to 592 m depth in 241Am concentrations in settling particles from the cylindrical sediment traps, whereas only a slight increase in 239+240Pu concentrations was evident. The gradual increase in 241Am/239+240Pu activity ratios from the cylindrical trap settling particles also was observed. These results were attributed to 241Am being scavenged by settling particles at a more rapid scavenging rate than 239+240Pu. There was an obvious tendency for 241Am 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 241Am concentrations in surface sedi-ments to increase almost linearly with depth, showing the same tendency as 210Pb concentrations, and this tendency indicated that the enhanced boundary scavenging of 241Am as well as 210Pb occurred in the East China Sea continental slope region due to the greater abundance of reactive finer particles. The 241Am concentrations in settling particles from the time-series sediment trap ranged from 1.05 to 4.20 mBq g-1, showing large variation. The 241Am concentrations from the time-series trap varied inversely with the total mass fluxes, indicating that 241Am concentrations were diluted by particles when mass flux increased. The 241Am 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.

Automated summary

The behavior of 241Am in the studied area of the East China Sea was investigated by analyzing settling particles and surface sediments. The results showed that 241Am concentrations increased with depth in settling particles, and the increase was attributed to a more rapid scavenging rate. The concentrations of 241Am in surface sediments also increased with depth, indicating enhanced boundary scavenging.