The formation of surface-active organic complexes of copper in coastal marine waters

The importance of surface-active organic matter on the speciation of copper in coastal seawater was examined over a 22 month period in Massachusetts Bay. Concentrations of copper associated with dissolved surface-active organic matter ranged from 15 pmol/kg during winter (0.67% of total dissolved copper) to 850 pmol/kg (18% of total dissolved copper) at the peak of primary production during a spring bloom and, following a spring bloom, accounted for 36% of the total dissolved copper concentration. Association of copper with surface-active organic matter may have occurred by direct complexation with surface-active organic ligands or indirectly via organic-organic interactions with non-surface-active organic complexes of copper. Although total dissolved copper at the site was inversely related to salinity, indicative of freshwater/continental sources, the amount of copper bound to surface-active organic matter was significantly correlated with estimated rates of phytoplankton primary production (r2 = 0.78). The primary source of surface-active organically bound copper in Massachusetts Bay is apparently in-situ biological production and not export of anthropogenic/freshwater ligands from continental sources. Although they represent a small but significant fraction of the total copper species present in coastal seawater, surface-active forms of copper assume added importance due to their active role in the transport and biogeochemical cycling of this element.