ELSEVIER Marine Chemistry 48 (1995) 151-156 Iodine speciation in the northwestern Mediterranean Sea: method and vertical profile R.C. Tian’, E. Nicolas zyxwvutsrqponmlkjihgfedcbaZYXWVUTSR Laboratoire de Physique et Chimie Marines, Universitt Pierre et Marie Curie, B.P. 08, La Dame, 06230 Villefranche sur Mer, France Received 19 April 1994; revision accepted 15 September 1994 Abstract Iodine speciation analysis was carried out upon seawater samples collected in July 1993 at the zyxwvutsrqponmlkjihgf DYFAMED station (43”25’N, 7”52’E) located in the northwestern Mediterranean Sea. Dissolved iodate and iodide were directly determined by differential pulse polarography and cathodic stripping square wave voltammetry, respectively, and organically bound iodine was estimated by wet-chemical oxidation with sodium hypochlorite. Iodate is the predominant species ranging from 416 nM in surface waters to 480 nM in bottom waters. Iodide is present in significant concentrations up to 60 nM in surface waters, undetectable between 500 and 1000 m depth and present in very low but measurable concentrations (about 6 nM) in deep waters. The vertical profile of total free iodine demon- strates observable removal from surface waters, slight enrichment at about 200 m depth and constant there below. Up to 40 nM of organically bound iodine has been estimated between 20 to 30 m. Factorial analysis of different iodine species with biologically relevant parameters provided strong evidence for iodine biophilic features. 1. Introduction Iodine is a minor chemical element in seawater with total concentration between 400 and 500 nM. It is a biophilic element (Wong et al., 1985) with concentration factors of about 1200 in mixed plankton (Bowen, 1966) and up to lo4 in brown algae (Mauchline and Templeton, 1964; Bruland, 1983). It is present in seawater principally in two chemical species: iodate (IO:) and iodide (I-) (Wong, 1991). Iodate is the thermodynamically stable form in oxygenated waters. Consequently, iodide should not be detectable in surface waters (Rebello et al., 1991). But significant quantities of iodide is often observed in the euphotic layer with concentration up to 250 nM (Nakayama et al., 1989). This thermodynamic disequilibrium in the euphotic layer is widely considered of bio- mediated origin (Jickells et al., 1988; Luther et al., 1988). With its particular geographical and hydro- logical features, the Mediterranean Sea represents an interesting site for studies of biogeochemical processes in marine environments (BCthoux and Copin-Mont&gut, 1988). But up to now, few, if any, studies of iodine speciation have been carried out in the Western Mediterranean Sea. Ullman et ‘Corresponding author’s present address: Institut Maurice al. (1990) have reported their results of iodine Lamontagne, B378, C.P. 1000, Mont-Joli, Qukbec, Canada analysis in the Eastern Mediterranean Sea. We G5H 324. Tel.: l-1418-775-0521. Fax: l-418-775-0542. present here the results of analyses of I-, IO;, 0304-4203/95/$07.00 0 1995 Elsevier Science B.V. All rights reserved SSDZ 0304-4203(94)00048-4