Biogeochemical controls on PCB deposition in Hudson Bay

PCB concentrations, congener patterns, and fluxes were examined in 13 dated and organically characterized (C, N, delta(13)C, delta(15)N) marine sediment cores from Hudson Bay, Canada, to investigate the importance of organic matter (OM) supply and transport to PCB sequestration. Drawdown of PCBs, supported by marine primary production, is reflected in elevated summation operatorPCB concentrations and more highly chlorinated PCB signatures in surface sediments underlying eutrophic regions. Sediments in oligotrophic regions, which are dominated by "old" marine OM, have lower PCB concentrations and weathered signatures. For the surface of Hudson Bay, average atmospheric deposition appears to be very low (ca. 1.4 pg summation operatorPCBs cm(-2) a(-1)) compared to fluxes reported for nearby lakes (ca. 44 pg summation operatorPCBs cm(-2) a(-1)). (210)Pb fails to provide a means to normalize the fluxes, highlighting important differences in the biocycling of (210)Pb and PCBs. Unlike (210)Pb, atmospheric PCB exchange with the water's surface is partially forced by the aquatic organic carbon cycle. The extremely low atmospheric deposition of PCBs to the surface of Hudson Bay is likely a reflection of the Bay's exceptionally low productivity and vertical carbon fluxes. If future marine production and vertical flux of carbon increase due to loss of ice cover or change in river input as consequences of global warming, PCB deposition would also increase.