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

Geographical and temporal variations of anthropogenic radionuclides, Cs-137 and Pu-239,Pu-240, in surface waters of the North Pacific Ocean were studied using the HAM database, which is a comprehensive data set on Cs-137, Pu-239,Pu-240, and other anthropogenic radionuclides. The geographical distributions suggest that Cs-137 and Pu-239,Pu-240 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 Cs-137 concentrations in the Pacific that occurred after 1970 were caused by physical processes. In the 1990s, surface Cs-137 showed a homogeneous distribution throughout the Pacific. Biogeochemical and physical processes are important factors controlling surface Pu-239,Pu-240 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. (C) 2003 Elsevier Ltd. All rights reserved.