THE UPTAKE OF IODATE BY MARINE-PHYTOPLANKTON

Several studies have suggested that phy,toplankton play a role in the iodine cycle. Using a short-term incubation technique for determining the uptake of iodate by phytoplankton, cultures of Thalassiosira ocean ica Hasle, Skeletonema costatum (Greville) Cleve, Emiliania huxleyi (L ohmann) Hay and Mohler, and Dunaliella tertiolecta Butcher were found to be capable of assimilating iodate at rates ranging from 0.003 to 0. 24 nmol IO3-.mu g chlorophyll a(-1).h(-1). The kinetics for the uptake of iodate can be modeled, and the similarity between the model and ex perimental results suggests that there is a steady state between iodat e uptake and release of dissolved iodine from the cells, presumably in the form of iodide. Two experiments were conducted in the Sand Shoal Inlet of the Cobb Bay estuary (37 degrees 15' N, 75 degrees 50' W). Th e uptake of iodate was 0.26 and 0.08 nmol IO3-.mu g chlorophyll a(-1). h(-1) during high and low tide, respectively. Using field estimates ba sed on measured levels of iodate in the estuary, we estimate that phyt oplankton can take up as much as 3% of the ambient pool of iodate on a daily basis and the entire pool in about 1 month. Thus, phytoplankton can be a significant component of the global iodine cycle by mediatin g changes in the speciation of iodine in the marine environment.