A method for the sequential measurement of yttrium-90 and thorium-234 and their application to the study of rapid particle dynamics in aquatic systems

James T. Waples and Kent A. Orlandini

Limnol. Oceanogr. Methods 8:661-677 (2010) | DOI: 10.4319/lom.2010.8.0661

ABSTRACT: 234Th/238U activity ratios have been used for decades in marine and freshwater systems as a tracer for particle flux—where disequilibrium between particle-reactive 234Th (half-life: 24.1 d) and its conservative parent 238U measures particle removal rates on a time scale of days to weeks. A new tracer that we have developed utilizes 90Y/90Sr activity ratios—where disequilibrium between particle-reactive 90Y (half-life: 64 h) and its conservative parent 90Sr measures particle removal rates on a time scale of hours to days. When both tracers (90Y/90Sr and 234Th/238U) are used in tandem, net particle removal rates on both time scales are measured. Here, we present a detailed set of instructions for the sequential measurement of 90Y and 234Th in a water sample and demonstrate how the use of these two chronometers can be applied to deconstruct sediment resuspension in Lake Michigan.