Iodine speciation: a potential indicator to evaluate new production versus regenerated production

Vertical profiles of iodide, iodate and total free iodine were determined monthly for one year (from July 1993 to June 1994) at the DYFAMED permanent station located in the northwestern Mediterranean Sea. Dissolved iodate and iodide were directly determined by differential pulse polarography and cathodic stripping square wave voltammetry, respectively. Iodate is the predominant species, ranging from 390 nM in surface waters to 485 nM in deep waters. Iodide is present in significant concentrations up to 80 nM in surface waters and from undetectable levels to several nanomolar (< 10 nM) in deep waters. Concentrations of total free iodine are slightly lower in surface waters (467–478 nM with an average of 472 nM) than in deep waters (475–486 nM with an average of 481 nM). Considerable variations in iodine speciation were observed. Iodide concentrations in surface waters were relatively low and stable from February to April (about 20 nM), increased up to 80 nM from May until November, and then decreased from December to February. Comparison between iodide abundance and primary production demonstrates that the transformation from iodate to iodide in surface waters is linked to the regenerated production. The stability of regenerated iodide in surface seawater makes iodide a potential indicator to evaluate new production vs regenerated production.