Scavenging, cycling and removal fluxes of 210Po and 210Pb at the Bermuda Time-series Study site

Quantifying relative affinities of Po and Pb in different populations of marine particulate matter is of great importance in utilizing Po as a tracer for carbon cycling. We collected and analyzed water samples for the concentrations of dissolved and total Po and Pb from the upper 600 m of the water column at Bermuda Timeseries Study site (September 1999 to September 2000) to investigate their seasonality of concentrations and their activity ratio (Po/Pb activity ratio, AR). Sinking particles collected in sediment traps at depths of 500 m, 1500 m, and 3200 m from the Oceanic Flux Program (OFP) time-series sediment traps were analyzed over a period of 12 months (May 1999 to May 2000). The objective was to compare the deficiencies of Po with respect to Pb in the water column to that measured in the sediment traps and to assess the relative affinities of Po and Pb with different particle pools. Inventories of Po in the upper 500 m water column varied by a factor of 2, indicating seasonal variations of particulate flux dominated the removal of Po. The Po/Pb ARs in the dissolved phase were generally less than the secular equilibrium value (1.0) in the upper 600 m, while were generally greater than 1.0 in the particulate phase, indicating higher removal rates of Po relative to Pb by particulate matter. The measured fluxes of Po and Pb in the 500 m, 1500 m, and 3200 m traps increased with depth, while the Po/Pb ARs decreased with depth except from May-August 1999. From the measured fluxes of Po and Pb at these three traps and the concentrations of Po and Pb in the water column, this region appears to be a sink for Pb which is likely brought-in by lateral advection.