Analysis of 137Cs and 239,240Pu concentrations in surface waters of the Pacific Ocean

Geographical and temporal variations of anthropogenic radionuclides, 137Cs and 239,240Pu, in surface waters of the North Pacific Ocean were studied using the HAM database, which is a comprehensive data set on 137Cs, 239,240Pu, and other anthropogenic radionuclides. The geographical distributions suggest that 137Cs and 239,240Pu concentrations in surface waters of the Pacific Ocean in the 1960s were controlled by global fallout from the 1961–1962 US and former USSR atmospheric nuclear weapons tests. The changes in surface 137Cs concentrations in the Pacific that occurred after 1970 were caused by physical processes. In the 1990s, surface 137Cs showed a homogeneous distribution throughout the Pacific. Biogeochemical and physical processes are important factors controlling surface 239,240Pu concentrations. The time-series data on anthropogenic radionuclides suggest that wind-driven circulation, subduction, and upwelling of Pacific surface and subsurface waters control the geographic distributions of anthropogenic radionuclides and their fates.