Anthropogenic radionuclides as tracers of climate change in the Pacific Ocean

Abstract Anthropogenic radionuclides introduced into the ocean through atmospheric nuclear weapons testing, nuclear accidents, and controlled releases from nuclear facilities are powerful tracers of ocean circulation. Because their input histories are temporally well constrained, they provide time markers that can be used to quantify water-mass transport, mixing, and ventilation, processes that regulate ocean heat and carbon uptake. The Pacific Ocean, the largest and one of the most intensively sampled basins, provides an exceptional setting for applying radionuclide tracers to climate-relevant ocean dynamics studies. Here, we synthesize how tritium, cesium-137, and plutonium isotopes have been used, together with ocean general circulation and particle-scavenging models, to constrain basin-scale transport, inter-basin exchange among the Pacific, Indian, and Atlantic Oceans, and multidecadal changes in vertical mixing and eddy activity associated with a warming and increasingly stratified upper ocean.