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RESEARCH ARTICLE
Contents Vol 4(2)

Organic complexation of copper in deep-sea hydrothermal vent systems

Sylvia G. Sander A D , Andrea Koschinsky B , Gary Massoth C , Matthew Stott C and Keith A. Hunter A
+ Author Affiliations
- Author Affiliations

A Marine and Freshwater Chemistry, Department of Chemistry, University of Otago, PO Box 56, Dunedin, New Zealand.

B Geosciences and Astrophysics, School of Engineering and Science, Jacobs University Bremen, Campus Ring 8, Bremen D-28759, Germany.

C GNS Sciences, Wairakei Research Center, 114 Karetoto Road, Wairakei, New Zealand.

D Corresponding author. Email: sylvias@chemistry.otago.ac.nz

Environmental Chemistry 4(2) 81-89 https://doi.org/10.1071/EN06086
Submitted: 28 December 2006  Accepted: 22 March 2007   Published: 17 April 2007

Environmental context. Deep-sea hydrothermal vents represent a natural habitat for many extremophile organisms able to cope with extreme physical and chemical conditions, including high loads of heavy metals and reduced gases. To date, no information is available on the level and role of organic complexation of metals in these systems, which will have consequences on the bioavailability and precipitation or mineralisation of metals. In this work, we give evidence for the presence of organic molecules, including thiols, capable of forming complexes with copper strong enough to compete against sulfide present at high levels in hydrothermal systems.

Abstract. 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.

Additional keywords: copper complexation, electrochemistry (analysis), geochemistry (organic), hydrothermal vents, thiols.


Acknowledgements

This work was funded by two University of Otago Research Grants. The work was also supported by grants from the priority program 1144 of the German Science Foundation. This is publication no. 10 of the priority program 1144 ‘From Mantle to Ocean: Energy-, Material- and Life-cycles at Spreading Axes’ of DFG. G. Massoth and M. Stott’s participation on the SWEEP VENTS expedition was supported by the FRST funded ‘Mineral Wealth of New Zealand and its Exclusive Economic Zone (C05X0406)’ program. Thanks are due to Captain M. Kull, the officers and the crew of the R/V METEOR as well the ROV QUEST crew (Universität Bremen) for their excellent co-operation during the M60/3 and M68/1 cruises. We would also like to acknowledge Metrohm for lending a VA663 stand during the M68/1 cruise. Thanks to JAMSTEC, the operator of the YOKOSUKA and SHINKAI 6500 and the funding agency for the SWEEP VENTS expeditions, as well as the Captain, officers and crew of the YOKOSUKA. Special thanks to C. de Ronde, GNS, NZ, J. Ishibashi, University of Kyushu, Japan and D. Butterfield, University of Washington, USA for enabling the sampling and for supplying additional information on the Brothers volcano samples. We also thank Brook Nunn and the anonymous reviewers for their comments, which greatly improved the quality of the manuscript.


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