Enhanced boundary scavenging of 241Am on the continental margin of the East China sea. (December 2022)

• Record Type: Journal Article
• Authors: Yamada, Masatoshi; Zheng, Jian
• Is Part Of: Journal of environmental radioactivity. Volume 255(2023)
• Publication Date: 2022-12
• Subjects: Sediment trap experiment -- 241Am -- Settling particle -- Boundary scavenging -- Western North Pacific ocean -- East China Sea; Radioactivity -- Periodicals; Radiation, Background -- Periodicals; Radioecology -- Periodicals; Radioactive pollution -- Periodicals; Environmental Pollutants -- Periodicals; Radioactive Pollutants -- Periodicals; Radioactivity -- Periodicals; Radioécologie -- Périodiques; Pollution radioactive -- Périodiques; Fond de rayonnement -- Périodiques; 539.752
• DOI: 10.1016/j.jenvrad.2022.107044
• Languages: English
• ISSNs: 0265-931X

Abstract

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