Chemical speciation of copper and zinc in surface waters of the western Black Sea

• Published in: Marine chemistry Vol. 76; no. 4; pp. 233 - 251
• Main Authors: Muller, François L.L., Gulin, Sergei B., Kalvøy, Åshild
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.12.2001; Elsevier Science
• Subjects: Bacteria; Black Sea; Copper speciation; Earth sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Geochemistry; Mineralogy; Organic ligands; Physical and chemical properties of sea water; Physics of the oceans; Silicates; Stripping voltammetry; Trace metals; Water geochemistry; Zinc speciation; East Mediterranean; Black Sea; MED, Black Sea; Copper speciation; Stripping voltammetry; Organic ligands; Zinc speciation; Black Sea; Trace metals; sea water; particulate matters; ligands; salinity; trace metals; voltammetry; Space remote sensing; metals; concentration; alkalinity; speciation; surface water; suspended materials; modern; hydrochemistry; radiometry; pH; temperature; copper; dissolved materials; residence time; Mediterranean Sea; zinc; Th-234
• ISSN: 0304-4203; 1872-7581
• DOI: 10.1016/S0304-4203(01)00060-3

The chemical speciation of Cu and Zn was investigated by voltammetric titration methods in the surface waters (∼10 m) of the western Black Sea during an Istanbul–Sevastopol cruise conducted in November 1998. Supporting parameters (temperature ( T), salinity ( S), pH, alkalinity (Alk), suspended particulate matter (SPM) and dissolved and particulate 234Th) were obtained in order to distinguish hydrographic features against involvement of the metals in biogeochemical processes. In the Turkish continental slope region, the cruise track intersected a narrow vein of colder water originating on the western shelf. The core of this cold water vein was characterised by a relatively low salinity, higher specific alkalinity and higher metal (especially Cu) and metal-binding ligand concentrations. A very large portion of Cu (93–99.8%) and Zn (82–97%) was organically complexed. The degree of complexation was highest in shelf waters and lowest in the central gyre. Titration data for Cu were modelled by two classes of organic binding ligands characterised by ( C L1=3–12 nM, log K 1′=13.1–13.9) and ( C L2=20–70 nM, log K 2′=9.4–11.2). These ligands occurred mainly in the ‘dissolved’ phase, as defined by 0.4-μm filtration. The stronger Cu-binding ligand seemed to be produced in situ in response to Cu concentration, whereas the weaker Cu-binding ligand appeared to be derived from terrestrial sources and/or reducing shelf sediments. Titration results for Zn were generally represented by one class of ligands ( C L1=8–23 nM, log K 1′=9.4–10.2), which were almost uniformly distributed between the ‘dissolved’ (78±8%) and the particulate phase (22±8%). The concentration of these strong Zn-binding ligands showed a very good correlation with SPM ( r 2=0.64), which improved when the dissolved ligands alone were considered ( r 2=0.78). It is hypothesised that these ligands were produced in situ by the bacterial breakdown of particulate organic matter.