Anthropogenic Radionuclides in Seawater of the Japan Sea : The Results of Recent Observations and the Temporal Change of Concentrations

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Between 1996 and 2002, a wide-area research project on anthropogenic radionuclides was carried out in an area covering the Japanese and Russian Exclusive Economic Zones of the Japan Sea, through a collaboration of Japanese and Russian institutes. The aim was to investigate the migration behavior of anthropogenic radionuclides (90Sr, 137Cs, and 239+240Pu) in the sea. Four expeditions conducted in the Japan Sea between 2001 and 2002 found that the observed concentrations and distributions of radionuclides were similar to those found in previous investigations. Inventories estimated from the concentration data indicate that larger amounts of these radionuclides accumulate in the Japan Sea seawater (by a factor of 1.5–2.1) than are supplied by global fallout in the same latitude belt. Further, we found that the 90Sr and 137Cs concentrations in the intermediate layer show temporal variations with time scales of 1 to several years. The results of cross-analysis using the data of 137Cs and dissolved oxygen suggest that the distribution and variation of radionuclide concentrations in the intermediate layer may reflect water mass movement in the upper part of the Japan Sea.
社団法人日本原子力学会の論文
2005-01-25