Distribution and behavior of plutonium isotopes in Western Pacific marginal seas

Abstract Due to atmospheric nuclear weapon tests carried out by various countries and the ground-level test series conducted at Marshall Islands by the US, marine environments have been extensively contaminated by plutonium over the Western Pacific marginal seas, especially in the China Seas. The released plutonium isotopes can serve as geochemical tracers for various physical and biogeochemical ocean processes. In this critical review, the source term, temporal-spatial distribution and geochemical behavior of plutonium isotopes in seawater and sediments in the China Seas are summarized and discussed, and then they are compared to those in the neighboring seas. A database of plutonium activity concentrations, isotope ratio, and inventories in marine environments in the China Seas is established. We concluded that global fallout and the Pacific Proving Grounds were still the major source of plutonium in the China Seas. The spatial distributions of plutonium in the China Seas indicated surface plutonium activity concentration in sediments in estuary area is lower than that in shelf region, and we thus clarified that plutonium in seawater in nearshore area is scavenged more efficiently than in open sea. Finally, future research needs for plutonium in marine environments are discussed.