Michael P. Bacon and K. Cochran; Woods Hole Oceanographic Institution and State University of New York, Stony Brook

"Thorium Isotopes as Indicators of Export Flux and Particle Dynamics in the Southern Ocean: Joint Global Ocean Flux Study"

This proposal requests funding for a study of spatial and temporal variations in the distributions and particulate fluxes of ²³⁴Th and ²²⁸Th as part of the Joint Global Ocean Flux Study (JGOFS) in the Southern Ocean. These thorium isotopes serve as ocean tracers that yield fundamental information about the rates of biogeochemical processes that govern the production and fate of biogenic particles in the oceanic water column. Participation in six of the process cruises is proposed: Oct.-Nov. 1996, Jan. or Feb. 1997, Apr. 1997, and Aug.-Sept. 1997 in the Ross Sea; Nov.-Dec. 1997 and Mar. 1998 in the Polar Front Zone. Each cruise will require two participants from this project. Measurements of ²³⁴Th will be made at sea by beta- and gamma-counting; measurements of ²²⁸Th will be made ashore by alpha-spectrometry. The data will be interpreted within the context of biological rate measurements and other data to be collected during the study and will be used to provide estimates of export fluxes of organic matter, carbonate, and silica from the euphotic zone; to quantify transformation processes such as aggregation and disaggregation in the water column; and to test biogeochemical models.