Oceanic deep water formation as a sink of persistent organic pollutants

The formation of deep oceanic waters occurs as part of the global thermohaline circulation due to gradients in salinity and temperature, and moves surface waters, including persistent organic pollutants (POPs), directly to the deep Ocean. For the four main deep water formation regions, removal fluxes of polychlorinated biphenyl (PCB) congeners were calculated based on their surface water concentrations and deep water formation rates. PCB fluxes were higher in the Norwegian Sea (ca. 420 kg/yr) than in the Labrador, Ross and Weddell Seas (ca. 140-160 kg/yr each). In the four regions considered, more PCBs were removed due to deep water formation (ca. 870 kg/yr) than by the settling of PCBs associated to organic carbon (ca. 320 kg/yr), whereas the settling flux dominates on a basin scale. Several POPs could serve as tracers for oceanic deep water plumes, as they have only been produced for a few decades.