Dissolved iodine speciation in surface seawater at a coastal Antarctic site has been studied over a period spanning three austral summers. The sampling site is biologically productive, with a summertime algal bloom accompanying strong seasonal variations in physical and chemical parameters. The results suggest a seasonal cycle in which iodide concentrations increase and iodate concentrations decrease during the summer, though the magnitude of these changes appears to be subject to considerable interannual variability. Iodide concentrations were typically very low, with minimum values of 10 to 20 nM at the beginning and end of the ice-free summer periods and summertime maxima of about 35 nM in 2005/06, 150 nM in 2006/07 and 82 nM in 2007/08. More detailed observations of iodide and iodate concentrations made during summer 2005/06 demonstrated that the accumulation of iodide was strongly correlated with integrated biological primary productivity, with an implied I/C assimilation ratio of 1.6 × 10−4.