Organic complexation of copper in deep-sea hydrothermal vent systems

Here we report, for the first time, that strong organic complexation plays an important role in the chemical speciation of copper in hydrothermal vent systems including medium temperature outlets, diffuse vents with an adjacent hydrothermal biocommunity, and local mixing zone with seawater. Samples from three deep-sea hydrothermal vent areas show a wide concentration range of organic copper-binding ligands, up to 4000 nM, with very high conditional stability constants (log K'(Cu'L) = 12.48 to 13.46). Measurements were usually made using voltammetric methods after removal of sulfide species under ambient seawater conditions (pH 7.8), but binding still occurs at pH 4.5 and 2.1. The voltammetric behaviour of our hydrothermal samples is compared with that of glutathione (GSH) a known strong Cu-binding ligand, as a representative of an organic thiol. Our results provide compelling evidence for the presence of organic ligands, including thiols, which form complexes strong enough to play an important role in controlling the bioavailability and geochemical behaviour of metal ions around hydrothermal vents.