Host: The Japan Radiation Research Society
Co-host: Asian Association for Radiation Research
Distribution of 137Cs in the western North Pacific Ocean in the water column has been studied for long time since 1960s. The major source of anthropogenic radionuclides in seawater in the Pacific Ocean is global fallout from atmospheric nuclear weapons tests. 137Cs, one of long-lived radionuclides originating from atmospheric weapons tests still exists especially in the upper layers of the Ocean. Concentration data of 137Cs are also valuable to establish baselines applicable for dose assessments from consumption of marine food products and for understanding other geochemical processes in the ocean. A core of 137Cs concentration in a layer 200-500 m around 20 deg. N is found. In terms of density, it is in a layer sigma 25.0-26.5 with an core center at ca. 26.0. The core of 137Cs concentration around 20 deg. N coincides with the density of lighter variety of Central Mode Water (CMW), then this core might formed by subduction of CMW. The concentrations at this core seem to be still increasing. This southward transport process might control longer half-residence time of 137Cs surface water concentration and water column inventory in the equatorial region.
