239,240Pu/137Cs ratios in the water column of the North Pacific: a proxy of biogeochemical processes.
Anthropogenic radionuclides in seawater have been used as transient tracers of processes in the marine environment. Especially, plutonium in seawater is considered to be a valuable tracer of biogeochemical processes due to its particle-reactive properties. However, its behavior in the ocean is also affected by physical processes such as advection, mixing and diffusion. Here we introduce Pu/(137)Cs ratio as a proxy of biogeochemical processes and discuss its trends in the water column of the North Pacific Ocean. We observed that the (239,240)Pu/(137)Cs ratio in seawater exponentially increased with increasing depth (depth range: 100-1000 m). This finding suggests that the profiles of the (239,240)Pu/(137)Cs ratios in shallower waters directly reflect biogeochemical processes in the water column. A half-regeneration depth deduced from the curve fitting the observed data, showed latitudinal and longitudinal distributions, also related to biogeochemical processes in the water column.
Hirose
Katsumi
K
Geochemical Research Department, Meteorological Research Institute, Nagamine 1-1, Tsukuba, Ibaraki 305-0052, Japan. khirose@mri-jma.go.jp
Aoyama
Michio
M
Povinec
Pavel P
PP
D002588:Cesium Radioisotopes / Q000032:analysis*; D010140:Pacific Ocean; D011005:Plutonium / Q000032:analysis*; D011834:Radiation Monitoring; D012623:Seawater / Q000737:chemistry*; D014872:Water Movements; D014875:Water Pollutants, Radioactive / Q000032:analysis*
D002588:Cesium Radioisotopes; D014875:Water Pollutants, Radioactive; D011005:Plutonium