MODEL EXPERIMENTS ON THE DIURNAL CYCLING OF IODINE IN SEAWATER

Model experiments were performed to examine the influence of photochemical and biological processes on the iodine speciation in seawater. Artificial seawater and natural seawater samples were exposed to (1) sun light and (2) intensive UV-irradiation and the iodine speciation was determined. Furthermore, outdoor cultures of unfiltered seawater (slightly fertilized with phosphate and nitrogen) were maintained for 45 h, iodate and iodide concentrations being determined every 3 h. The experiments show that sunlight does not create any measurable change in iodine speciation; only intensive (artificial) UV-radiation does. In seawater, containing a natural mixture of phyto- and zooplankton, there are pronounced daily variations between iodide and iodate of 5-8 nM/h, obviously related to photosynthesis and respiration.