Temporal variation of cesium isotope concentrations and atom ratios in zooplankton in the Pacific off the east coast of Japan.

After the Fukushima Daiichi Nuclear Power Plant accident in March 2011, concentrations of cesium isotopes (Cs, Cs, and Cs) were measured in zooplankton collected in the Pacific off the east coast of Japan from May 2012 to February 2015. The time series of the data exhibited sporadic Cs concentration peaks in zooplankton. In addition, the atom ratio of Cs/Cs in zooplankton was consistently high compared to that in ambient seawater throughout the sampling period.

The Contribution of Sources to the Sustained Elevated Inventory of (137)Cs in Offshore Waters East of Japan after the Fukushima Dai-ichi Nuclear Power Station Accident.

We have evaluated the contribution of sources of (137)Cs to the inventory of radiocesium in waters (surface area: 6160 km(2), water volume: 753 km(3)) off Fukushima Prefecture and neighboring prefectures from May 2011 to February 2015. A time-series of the inventory of (137)Cs in the offshore waters revealed a clearly decreasing trend from May 2011 (283.4 TBq) to February 2015 (1.