Dissolved iodate and total iodine during an extreme hypoxic event in the Southern Benguela system

Dissolved iodate and total iodine were studied in St Helena Bay, South Afri ca, during a period of acute hypoxia, following upwelling off Cape Columbin e. Despite the generally high concentrations of chlorophyll a (10-30 mg m(- 3)) total iodine concentration was essentially constant in the main part of the Bay, and similar to that found elsewhere in the oceans. Occasional, lo wer concentrations of total iodine (0.28 to 0.42 mu M) were found with exce ptionally high chlorophyll a concentrations (500 mg m(-3)) in shallow water s. In contrast, iodate was found to be reduced to iodide at both the surfac e and the bottom of the Bay. The implications of these changes are discusse d, given that the surface waters reflect sustained eutrophication while the bottom waters are hypoxic as a result of the organic-rich sediment from th e waters above. (C) 2000 Academic Press.