Study on material/seawater circulation in the Japan Sea using environmental radionuclides

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We analysed 236U concentration and distribution as well as its chemical state in samples obtained from the Sea of Japan and its surroundings to establish 236U as new oceanographic tracer. 236U concentration in all samples were determined with high precision, which made clear that much smaller samples are sufficient. Our results show that the main source of 236U in the Sea of Japan is direct inflow through Tsushima-strait and that 236U stays in dissolved form in the water column. The depth profile of 236U as well as the diffusion coefficient were found to be similar to the ones of 137Cs, which was widely used as an oceanographic tracer isotope in former research. This suggests that the long-lived anthropogenic radionuclide 236U has a huge potential to replace the short-lived 137Cs as oceanographic tracer. Furthermore, the distributions of 236U suggested a possibility of deep-water formation with the subduction of surface water.