DIEL VARIATIONS IN IRON SPECIATION IN NORTHERN AUSTRALIAN SHELF WATERS

Iron in northern Australian shelf waters was found predominantly in fi ne (< 0.2 mu m) 8-hydroxyquinoline-reactive form or in larger (> 1.0 m u m) particulate form. Partitioning into the larger size fraction domi nated during a period of high turbidity following a cyclonic resuspens ion event. Only a small component of the iron pool reacts rapidly with the strong ferrous binding agent ferrozine. The concentration of the ferrozine-reactive component is strongly dependent on light intensity with maximum concentration observed at peak light intensity. The close correlation between ferrozine-reactive iron concentration and light i ntensity suggests a fine balance between Fe(III) reduction and Fe(II) oxidation with the steady state concentration observed being strongly influenced by light induced changes in redox kinetics. An observed lac k of association between particulate iron concentrations and the conce ntration of ferrozine-reactive iron suggests that the soluble rather t han the particulate iron pool is most influenced by light. The chromop hore may be an Fe(III)-organic complex with the strong iron binding li gand that is now recognised to be present in seawater.