Impacts of the Fukushima nuclear accident on the china seas: Evaluation based on anthropogenic radionuclide 137Cs

In order to evaluate the impact of the Fukushima nuclear accident on the China Seas, seawater samples from the South China Sea (SCS), the East China Sea (ECS) and the Yellow Sea (YS) were collected in April-June 2011, and their Cs-137 activities were measured using low-background gamma-spectrometry. Cs-137 activities in the study area ranged from 0.75 +/- 0.07 to 1.43 +/- 0.08 Bq m(-3) with an average of 1.12 +/- 0.08 Bq m(-3). Cs-137 activities initially increased from the nearshore to the inner shelf, and subsequently decreased from the inner shelf to the outer shelf. Vertical profiles showed higher Cs-137 activities at the surface but lower activities at depth in the ECS, suggesting atmospheric input of Cs-137. As such, the distribution pattern of Cs-137 in the region was presumably determined by a combination of atmospheric deposition and subsequent mixing between different water masses including the coastal currents, the Yangtze River plume and the Taiwan Warm Currents. Based on the inventory of 93 Bq m(-2) and the atmospheric deposition flux of Cs-137 in the ECS of 32.2 mBq m(-2) d(-1) (5.4-42.9 mBq m(-2) d(-1)) which we estimated, we derived the residence time of Cs-137 in the upper water column to be 66 d (45-95 d). We concluded that in terms of Cs-137, the ECS was less impacted by the Fukushima accident as compared to the Chernobyl accident. The released amount of Cs-137 into the ECS from the Fukushima accident was minute