PHOTO-REDUCTION OF FE (III) BY DISSOLVED ORGANIC-SUBSTANCES AND EXISTENCE OF FE (II) IN SEAWATER DURING SPRING BLOOMS

Fe(III) in seawater was readily reduced to Fe(II) in sunlight in the presence of hydroxycarboxylic acids, such as sugar acids. Tartaric, gluconic, glucaric acids and glucaric acid-1,4-lactone gave higher reduced Fe(II) concentrations and a more rapid increase for a short illumination time than other acids. The reduced Fe(II) concentration was found to be greater at 5-degrees-C than at 20-degrees-C. In sunlight the reduction of Fe(III) in seawater occurred even at low concentration of the hydroxycarboxylic acids (1-mu-M). From field observations, 0.02-0.04-mu-M of dissolved Fe(II) appeared in oxic surface seawater during spring blooms in Funka Bay (Japan) during 1987, 1988 and 1989 as a result of vertical water mixing by which Fe(III) from sediments was transported to the surface. These observations may result from photo-reduction of Fe(III) in the presence of hydroxycarboxylic acids which were possibly released by phytoplankton during spring blooms.