title: Anthropogenic Pu distribution in Tropical East Pacific.
abstract: The geographical distribution of the anthropogenic radionuclides (238)Pu and (239+240)Pu in the Tropical East Pacific in 2003 was studied from the viewpoint of material migration. We measured the contents of Pu isotopes in seawater and in sediment from the sea bottom. The distributions of Pu isotopes, together with those of coexisting nitrate and phosphate species and dissolved oxygen, are discussed in relation to the potential temperature and potential density (sigma-θ). The Pu contents in sediment samples were compared with those in the seawater. Horizontal migration across the Equator from north to south was investigated at depths down to ~800m in the eastern Pacific. The Pu distribution at 0-400m correlated well with the distribution of potential temperature. Maximum Pu levels were observed in the subsurface layer at 600-800m, corresponding to the depth where sigma-θ≈27.0. It is suggested that the Pu distribution depends on the structure of the water mass and the particular temperature and salinity. The water column/sediment column inventory ratio and the vertical distribution of Pu may reflect the efficiency of scavenging in the relevant water areas.
authors.affiliation: Research Facility Center for Science and Technology, University of Tsukuba, 1-1-1 Ten-nodai, Tsukuba, Ibaraki 305-8577, Japan. kinoshita@tac.tsukuba.ac.jp
authors.forename: Norikazu
authors.initials: N
authors.lastname: Kinoshita
authors.forename: Takahiro
authors.initials: T
authors.lastname: Sumi
authors.forename: Kiyotaka
authors.initials: K
authors.lastname: Takimoto
authors.forename: Mika
authors.initials: M
authors.lastname: Nagaoka
authors.forename: Akihiko
authors.initials: A
authors.lastname: Yokoyama
authors.forename: Takashi
authors.initials: T
authors.lastname: Nakanishi
mesh_terms: D019015:Geologic Sediments / Q000737:chemistry; D010140:Pacific Ocean; D011005:Plutonium / Q000032:analysis*; D011834:Radiation Monitoring; D011847:Radioactive Fallout / Q000032:analysis* / Q000706:statistics & numerical data; D012623:Seawater / Q000737:chemistry; D014329:Tropical Climate; D014872:Water Movements; D014875:Water Pollutants, Radioactive / Q000032:analysis*; D014878:Water Pollution, Radioactive / Q000706:statistics & numerical data*
chemical_list: D011847:Radioactive Fallout; D014875:Water Pollutants, Radioactive; D011005:Plutonium