APPLICATION OF A GENERALIZED SCAVENGING MODEL TO THORIUM ISOTOPE AND PARTICLE DATA AT EQUATORIAL AND HIGH-LATITUDE SITES IN THE PACIFIC-OCEAN

A generalized trace metal scavenging model has been applied to particle cycle and Th-234 data at three equatorial Pacific sites, and to dissolved and particulate Th-228, Th-230, and Th-234 profiles at a single high-latitude station. The one-dimensional (and here steady state) model consists of two particle classes, small (suspended) and large (sinking). It is driven by particle primary production and parameterized from particle and tracer concentration and flux data. The model has been used to determine, as functions of depth, (1) rates of particle remineralization; (2) aggregation and disaggregation of the small and large-particle classes, respectively, and (3) adsorption and desorption rate constants of thorium. The results are insensitive to the assumed large particle sinking rate of 150 m d-1. The profiles of all three tracers at Station P are described satisfactorily by a single set of model parameters. The adsorption rate constant, normalized for the effect of particle concentration, is enhanced in the upper 100 m of the water column by a factor of 2 or greater at all sites. Values of this and the other major model parameters are consistent with earlier results for a variety of oceanic environments.