On the possibility of iodide oxidation in the near-surface of the Black Sea and its implications to iodine in the general ocean |
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| Institution: | 1. State Key Laboratory of Pollution Control and Resource Reuse, Key Laboratory of Yangtze Water Environment, Ministry of Education, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, P.R. China;2. Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, P.R. China;3. Department of Safety, Health and Environmental Engineering, National Kaohsiung University of Science and Technology, Kaohsiung 824, Taiwan, R.O.C.;4. Shanghai Chengtou Raw Water Co., Ltd., Shanghai 200125, P.R. China;5. College of Environmental and Chemical Engineering, Shanghai University of Electric Power, Shanghai 200090, P. R. China;6. School of Chemical Science and Engineering, Key Laboratory of Road and Traffic Engineering of Ministry of Education, Tongji University, Shanghai 200092, P.R. China;7. State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing, 210023, P. R. China;1. Instituto de Oceanografía y Cambio Global, IOCAG, Universidad de Las Palmas de Gran Canaria, ULPGC, Spain;2. CNRS, Univ Brest, IRD, Ifremer, LEMAR, F-29280 Plouzane, France;3. Laboratoire de Météorologie Physique, UMR 6016, CNRS, Université Clermont Auvergne, 63178 Aubière, France;4. CNRS, SIGMA Clermont, Institut de Chimie de Clermont-Ferrand, Université Clermont Auvergne, F-63000 Clermont-Ferrand, France;5. Observatoire de Physique du Globe de Clermont-Ferrand, UAR 833, CNRS, Université Clermont Auvergne, 63178 Aubière, France |
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| Abstract: | 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 IO3?/I? and I2/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. |
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