On the possibility of iodide oxidation in the near-surface of the Black Sea and its implications to iodine in the general ocean

• Published in: Deep-sea research. Part I, Oceanographic research papers Vol. 48; no. 11; pp. 2397 - 2412
• Main Authors: Truesdale, Victor W, Watts, Simon F, Rendell, A.R
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.11.2001; Elsevier; Pergamon Press Inc
• Subjects: Bacteria; Black Sea; Earth sciences; Earth, ocean, space; Entrainment model; Exact sciences and technology; External geophysics; Geochemistry; Iodate; Iodide; Marine; Mineralogy; Oceanography; Oxidation; Physical and chemical properties of sea water; Physics of the oceans; Redox modelling; Silicates; Sulfur; Water geochemistry; Middle East; Azov Sea; Turkey; East Mediterranean; Black Sea; Bosporus; MED, Black Sea; Iodate; Iodide; Entrainment model; Redox modelling; Sulfur; Black Sea; advection; sea water; models; oxidation; halides; iodides; surface water; hydrochemistry; Asia; iodates; sulfur; iodine; Mediterranean Sea
• ISSN: 0967-0637; 1879-0119
• DOI: 10.1016/S0967-0637(01)00021-8

Iodide oxidation to iodate in near-surface waters of the open oceans is an elusive process, and an unequivocal demonstration of it would simplify modelling of the marine iodine system. In the open ocean, the upward advection of iodate complicates any mathematical treatment of the problem. In this context, the high concentration (0.1 μM) of iodate in the Black Sea surface waters suggested that this Sea might be a place where oxidation might be demonstrated. Hydrologically, the surface waters of the Black Sea appear to be downstream of the deeper waters and, given the latter's anoxicity, the surface waters seemed likely to gain most of their iodine as iodide by upward advection. To test this further, prior to experimentation, an iodine budget for the near-surface waters, based upon the latest hydrological model of the Sea was prepared; this predicts a minimum oxidation flux of 3.89×10 −4 mol I m −2 a −1. The chemistry of this oxidation is discussed in the light of existing knowledge of the sulfide system. It is argued that as the redox potential of the IO 3 −/I − and I 2/I − couples at pHs typical of the Black Sea (7.75) are much higher than that of the sulfate–sulfide couple, iodide is probably oxidized in the near-surface domain. This contrasts with sulfide oxidation in the suboxic zone. The possible role of nitrifying bacteria in the oxidation is discussed.