Non-Volatile Dissolved Organic Iodine in Marine Water
An analytical scheme for the determination of marine DOI has been established. The concentration of DOI is estimated as total iodine (TI) minus total inorganic iodine (TII). The concentration of total iodine is determined as [special characters omitted] after DOI has been oxidized to inorganic iodine quantitatively by intensive UV-irradiation and all the inorganic iodine in the samples had been converted to [special characters omitted] by the addition of NaClO. Production of DOI in seawater can
... be via both non-phytoplankton and phytoplankton related processes. In the former, iodide is converted to DOI. In the latter, most likely, iodate is converted to DOI. Naturally occurring phytoplankton in shelf break water contribute more to the production of DOI than that in the open ocean. DOI can be rapidly decomposed when exposed to sunlight. The half life of the photolysis was only on the order of hours. The product of the photolysis is iodide, while iodate concentration remains constant. In a sample, at least 70% of DOI can be decomposed by UV-A to visible light. In the stratified water column of the Chesapeake bay, high concentrations of DOI could only be found in the surface mixing layer. While normalized total inorganic iodine appeared depleted in surface water, normalized total iodine had little change in the water column. A box model calculation for the Chesapeake Bay water column demonstrates that iodate in the incoming open ocean water is the major source of DOI in the estuary. In the slightly stratified James River estuary, DOI was the dominant species of iodine, where iodate was absent below the salinity of 15. From the riverine input (0.0) to the Chesapeake Bay mouth (18.6), total iodine displayed a linear relationship with salinity. Thus, iodine behaved conservatively in the investigated environment. Instead of the removal or addition of iodine from solid phase, it was the species conversion among the dissolved forms which led to more or less non-conservative behavior of the individual species.