Plutonium AMS measurements in Yangtze River estuary sediment

The Yangtze River is the largest single source of sediment to the continental shelf of the East China Sea. The quantity of material exported by the river is expected to decrease substantially as a consequence of an extensive continuing program of dam construction within the river catchment. We report here AMS measurements of plutonium isotope concentrations and ratios for selected depth increments from a sediment core, collected from the sub-aqueous delta of the Yangtze River estuary. The Pu derives from atmospheric nuclear weapons testing in the 1950s and 1960s, and is potentially a useful tracer of sediment deposition times in the marine environment. The results show considerable structure in the depth-concentration profile, and offer an excellent opportunity to compare Pu with the more commonly used ¹³⁷Cs isotopic tracer. The AMS data show superior sensitivity and indicate that the ²⁴⁰Pu/²³⁹Pu ratio can provide a check on the deposition dates. The changes in the ²⁴⁰Pu and ²³⁹Pu concentrations and the ²⁴⁰Pu/²³⁹Pu ratios with sediment depth all indicate the possibility of using Pu as a geochronological tool for coastal sediment studies.