Oceanic waters contain predominantly the stable form of iodine (iodate), but significant amounts of iodide are found in surface waters. Iodine is incorporated in a reduced form into phytoplankton in the photic zone of the ocean. Some of this iodine can be transported to oceanic sediments in particulate organic carbon and to the atmosphere as volatile forms, but much remains in the upperwater column where iodide accumulates due to remineralization of particulate organic carbon. Iodide oxidation to iodate is not an important chemical process in seawater. Preliminary results show detectable speciation changes over a year at one location due to oceanic mixing. This research will investigate the use iodine speciation as an indicator of primary productivity. The changes noted above, in conjunction with sediment trap iodine analyses, will be monitored over time at a time series location to understand iodine and carbon cycling. Precise methods for the measurement of both iodide and iodate are now available for a study of this type.
