Transport pathway of Pacific Proving Grounds-derived Pu into the western Indian Ocean

Abstract

The ^239+240Pu concentrations and ²⁴⁰Pu/²³⁹Pu atom ratios in seawater from the eastern Indian Ocean were determined to identify their Pu sources and to propose the transport pathway of Pacific Proving Grounds-derived Pu. In the West Australia Basin, the ^239+240Pu concentration increased with depth; a subsurface maximum was identified at 200 m depth and then decreased gradually with depth; its water column inventory was 32.8 Bq/m²; the mean ²⁴⁰Pu/²³⁹Pu atom ratio was 0.242. These high atom ratios proved the presence of close-in fallout Pu from Pacific Proving Grounds nuclear tests. This is the first study by anyone on Pu atom ratios in the Indian Ocean.