MODEL EXPERIMENTS ON THE DIURNAL CYCLING OF IODINE IN SEAWATER

Model experiments were performed to examine the influence of photochem ical and biological processes on the iodine speciation in seawater. Ar tificial 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 (slig htly fertilized with phosphate and nitrogen) were maintained for 45 h, iodate and iodide concentrations being determined every 3 h. The expe riments show that sunlight does not create any measurable change in io dine speciation; only intensive (artificial) UV-radiation does. In sea water, containing a natural mixture of phyto- and zooplankton, there a re pronounced daily variations between iodide and iodate of 5-8 nM/h, obviously related to photosynthesis and respiration.