Transport of suspended radiocesium in coastal area off Fukushima

Otosaka, Shigeyoshi*  ; Suzuki, Takashi  ; Tsuruta, Tadahiko  ; Misono, Toshiharu   ; Dohi, Terumi   ; Mino, Yoshihisa*; Sukigara, Chiho*; Ito, Yukari*; Kanda, Jota*; Ishimaru, Takashi*

A time-series sediment trap was deployed from October 2017 to June 2018 at a station located in southeast of the Fukushima Daiichi Nuclear Power Plant to clarify the transport process of suspended radiocesium from the coast to the offshore area. Sinking particles of 39 periods were collected by this experiment. Radiocesium was detected from sinking particles throughout the observation period, and the concentration showed clear seasonal variation. The observed flux of radiocesium showed maxima in winter (December-January) and spring (March-April). From detailed analysis of physical and chemical characteristics of sinking particles, it was found that sinking particles were composed of biological particles with relatively low degradation in winter and fine-grained terrestrial particles in spring. Especially in spring, high radiocesium flux was observed, and it was presumed due to lateral transport of radiocesium-bound lithogenic particles from the coastal area to the offshore. However, the effect of redistribution of radiocesium in seabed sediments by this process is considered to be limited.