FLUXES OF RA-226 AND BARIUM IN THE PACIFIC-OCEAN - THE IMPORTANCE OF BOUNDARY PROCESSES

The Ra-226/Ba ratio in particles collected in sediment traps decreases with depth. Fluxes of Ba and Al increase with depth. These observations cannot be explained by simple vertical processes. Instead they require a component to the deep flux which originates at the ocean margins. We suggest that the deep traps are enriched in Ba through the advection of barite originally precipitated in biologically productive regions of the ocean margin. This source is less important for Ra-226 because some is lost by radioactive decay between the precipitation of barite on the margin and outward transport. The boundary flux is an important source of material to the deep sea. From Ra-226 fluxes in the upper 1000 m of the water column, we estimate that the residence time of Ra-226 in the upper ocean is 400 years. The removal of Ra-226 in the particle flux is approximately balanced by the upwelling of waters enriched in Ra-226.