Anthropogenic radionuclides in sediment in the Japan Sea: distribution and transport processes of particulate radionuclides

Distributions of anthropogenic radionuclides (90Sr, 137Cs and 239+240Pu) in seabed sediment in the Japan Sea were collected during the period 1998–2002. Concentration of 90Sr, 137Cs and 239+240Pu in seabed sediment was 0.07–1.6 Bq kg−1, 0.4–9.1 Bq kg−1 and 0.002–1.9 Bq kg−1, respectively. In the northern basin of the sea (Japan Basin), 239+240Pu/137Cs ratios in seabed sediment were higher and their variation was smaller compared to that in the southeastern regions of the sea. The higher 239+240Pu/137Cs ratios throughout the Japan Basin were considered to reflect production of Pu-enriched particles in the surface layer and substantial sinking of particulate materials in this region. In the southern regions of the Japan Sea (<38°N), both inventories and 239+240Pu/137Cs ratios in sediment were larger than those in the other regions. In the southern Japan Sea, observations suggested that supply of particulate radionuclides by the Tsushima Warm Current mainly enhanced accumulation of the radionuclides in this region.