Fukushima-derived radiocesium in the waters of the Northwest Pacific Ocean in the winter of 2011

Abstract

To understand the transport of Fukushima Dai-ichi Nuclear Power Plant Accident (FDNPPA)-derived nuclear contaminated water, which will be discharged into the Pacific Ocean in the future, the distributions of 134Cs and 137Cs in seawater in the public areas east of Japan in winter 2011 were reported in this study. The ranges of 134Cs and 137Cs activities were <MDA (Minimum Detectable Activity) -68.9 Bq/m3 and 1.3–85.9 Bq/m3, respectively. The average decay corrected FDNPPA-derived 134Cs/137Cs activity ratio was 0.97. The FDNPPA-derived radiocesium existed in the seawater at a relatively high level at most stations. The 134Cs and 137Cs activities were comparable throughout the upper 50 m at each station. The FDNPPA-derived radiocesium was mainly distributed north of 36.5°N due to the boundary formed by the Kuroshio Extension. The temporal variations of FDNPPA-derived 134Cs and 137Cs suggested that their environmental half-lives in the study area were 61 d and 63 d in the period of June 2011 to June 2012, respectively.