A millennium perspective on the contribution of global fallout radionuclides to ocean science.

Five decades ago, radionuclides began to enter the ocean from the fallout from atmospheric nuclear weapons tests. The start of the 21st century is an appropriate vantage point in time to reflect on the fate of this unique suite of manmade radionuclides--of which more than two-thirds arrived at the surface of the oceans of the planet. During these five decades much has been learned of the behavior and fate of these radionuclides and, through their use as unique tracers, of how they have contributed to the growth of basic knowledge of complex oceanic physical and biogeochemical processes. Some of the highlights of the ways in which fallout radionuclides have given new insights into these processes are reviewed in the historical context of technological and basic ocean science developments over this period. The review addresses major processes involved, such as physical dispersion and mixing, particle association and transport of reactive nuclides, biological interactions, and mixing and burial within ocean sediments. These processes occur over a range of scales ranging from local to global. Finally, an account is given of the present spatial distribution within the oceans of the various components of the fallout radionuclide suite.