title: Numerical simulation on the long-term variation of radioactive cesium concentration in the North Pacific due to the Fukushima disaster.
abstract: Numerical simulations on oceanic (134)Cs and (137)Cs dispersions were intensively conducted in order to assess an effect of the radioactive cesium on the North Pacific environment with a focus on the long-term variation of the radioactive cesium concentration after the Fukushima disaster that occurred in March 2011. The amounts of (134)Cs and (137)Cs released into the ocean were estimated using oceanic monitoring data, whereas the atmospheric deposition was calculated through atmospheric dispersion simulations. The highly accurate ocean current reanalyzed through a three-dimensional variational data assimilation enabled us to clarify the time series of the (134)Cs and (137)Cs concentrations in the North Pacific. It was suggested that the main radioactive cesium cloud due to the direct oceanic release reached the central part of the North Pacific, crossing 170°W one year after the Fukushima disaster. The radioactive cesium was efficiently diluted by meso-scale eddies in the Kuroshio Extension region and its concentration in the surface, intermediate, and deep layers had already been reduced to the pre-Fukushima background value in the wide area within the North Pacific 2.5 years after the Fukushima disaster.
authors.affiliation: Sector of Nuclear Science Research, Japan Atomic Energy Agency, Japan. Electronic address: kawamura.hideyuki@jaea.go.jp.
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Kawamura
authors.affiliation: Sector of Nuclear Science Research, Japan Atomic Energy Agency, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Kobayashi
authors.affiliation: Sector of Nuclear Science Research, Japan Atomic Energy Agency, Japan.
authors.forename: Akiko
authors.initials: A
authors.lastname: Furuno
authors.affiliation: Meteorological Research Institute, Japan Meteorological Agency, Japan.
authors.forename: Norihisa
authors.initials: N
authors.lastname: Usui
authors.affiliation: Meteorological Research Institute, Japan Meteorological Agency, Japan.
authors.forename: Masafumi
authors.initials: M
authors.lastname: Kamachi
mesh_terms: D000392:Air Movements; D002586:Cesium / Q000032:analysis*; D002588:Cesium Radioisotopes / Q000032:analysis; D062406:Fukushima Nuclear Accident; D008962:Models, Theoretical; D010140:Pacific Ocean; D011834:Radiation Monitoring / Q000379:methods*; D011847:Radioactive Fallout / Q000032:analysis*; D018788:Radioactive Hazard Release; D013997:Time Factors; D014872:Water Movements; D014875:Water Pollutants, Radioactive / Q000032:analysis*
chemical_list: D002588:Cesium Radioisotopes; D011847:Radioactive Fallout; D014875:Water Pollutants, Radioactive; D002586:Cesium
keywords: (134)Cs; (137)Cs; Data assimilation; Fukushima Daiichi nuclear power plant; Long-term variation; Oceanic dispersion