Impacts of Fukushima Daiichi Nuclear Power Plant accident on the Western North Pacific and the China Seas: Evaluation based on field observation of 137Cs

Abstract

After the Fukushima nuclear accident (FNA), ¹³⁷Cs activities of seawater in the Western North Pacific (WNP) and China Seas were determined in order to examine whether ¹³⁷Cs derived from FNA across the Kuroshio was still existed and if there were any indications of FNA's impact. High ¹³⁷Cs activities at 200-500m were observed in the south of Kuroshio during 2015, indicating ¹³⁷Cs from FNA could cross the Kuroshio. Surface ¹³⁷Cs activities were on average 1.43±0.42Bqm^-3 for WNP, 1.11±0.14Bqm^-3 for South China Sea (SCS) and 1.10±0.29Bqm^-3 for East China Sea (ECS) during 2011-2015. The activities and inventories of ¹³⁷Cs were almost identical before and after the FNA, indicating the impacts of FNA on the WNP and China Seas were minor. The effective environmental half-lives of ¹³⁷Cs in surface seawater were firstly estimated to be 14.4±1.7yrs for ECS and 16.9±2.1yrs for SCS.

Keywords: (137)Cs; China Seas; Fukushima nuclear accident; Kuroshio; Western North Pacific.