title: Delivery mechanism of (134)Cs and (137)Cs in seawater off the Sanriku Coast, Japan, following the Fukushima Dai-ichi NPP accident.
abstract: To assess the delivery mechanism of radiocesium emitted from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP), we examined vertical profiles of (134)Cs, (137)Cs, and (228)Ra concentrations and the (228)Ra/(226)Ra ratio in the water columns off the Sanriku Coast in the northwestern Pacific Ocean, in July 2012, along with their surface lateral variations in July 2009. Radiocesium concentrations exhibited maximum peaks (3-5 mBq/L for (134)Cs) at depths of 100-200 m, accompanied by high (228)Ra concentrations (0.6-0.8 mBq/L) in comparison with shallower depths (∼0.4 mBq/L). Taking the circulation patterns of currents in the area into account, it was inferred that radioactive depositions were supplied to the (228)Ra-rich Tsugaru Warm Current Water (TWCW) in the offshore area of the Sanriku Coast following the FDNPP accident, and that after the spring of 2011, this water (∼26.5σθ) was covered by lower density surface water, which helped intrude its way to depths of 100-200 m.
authors.affiliation: Low Level Radioactivity Laboratory, Kanazawa University, Nomi, Ishikawa 923-1224, Japan. Electronic address: mutsuo@llrl.ku-unet.ocn.ne.jp.
authors.forename: M
authors.initials: M
authors.lastname: Inoue
authors.affiliation: Low Level Radioactivity Laboratory, Kanazawa University, Nomi, Ishikawa 923-1224, Japan; Japan Marine Science Foundation, Minato, Mutsu, Aomori 035-0064, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Kofuji
authors.affiliation: Fisheries Research Agency, National Research Institute of Fisheries Science, Fukuura, Kanazawa, Yokohama 236-8648, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Fujimoto
authors.affiliation: Low Level Radioactivity Laboratory, Kanazawa University, Nomi, Ishikawa 923-1224, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Furusawa
authors.affiliation: Low Level Radioactivity Laboratory, Kanazawa University, Nomi, Ishikawa 923-1224, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Yoshida
authors.affiliation: Low Level Radioactivity Laboratory, Kanazawa University, Nomi, Ishikawa 923-1224, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Nagao
authors.affiliation: Low Level Radioactivity Laboratory, Kanazawa University, Nomi, Ishikawa 923-1224, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Yamamoto
authors.affiliation: Low Level Radioactivity Laboratory, Kanazawa University, Nomi, Ishikawa 923-1224, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Hamajima
authors.affiliation: Fisheries Research Agency, National Research Institute of Fisheries Science, Fukuura, Kanazawa, Yokohama 236-8648, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Minakawa
mesh_terms: D002586:Cesium / Q000032:analysis*; D002588:Cesium Radioisotopes / Q000032:analysis; D062406:Fukushima Nuclear Accident; D007564:Japan; D010140:Pacific Ocean; D011834:Radiation Monitoring; D011847:Radioactive Fallout / Q000032:analysis; D011886:Radon / Q000032:analysis*; D012621:Seasons; D012623:Seawater / Q000032:analysis; D013051:Spectrometry, Gamma; D014872:Water Movements; D014875:Water Pollutants, Radioactive / Q000032:analysis*
chemical_list: D002588:Cesium Radioisotopes; D011847:Radioactive Fallout; D014875:Water Pollutants, Radioactive; D002586:Cesium; D011886:Radon
keywords: (228)Ra; Fukushima Dai-ichi nuclear power plant accident; Off Sanriku Coast; Radioactive deposition; Radiocesium; Tsugaru warm current