ABSTRACT
This chapter presents the results of specific (photo)redox processes involving iron and manganese in surface seawaters. It attempts to assess the conjunctive effects of these processes in seawaters. The chapter presents and discusses the results of diurnal studies of iron and manganese speciation and partitioning between filterable and nonfilterable phases in a variety of marine systems. Thermodynamically, both iron (Fe) and manganese (Mn) are expected to predominate in oxidized form in seawater with iron present as Fe(III) oxyhydroxides and manganese present as Mn(III) and/or Mn(IV) oxides. The marine systems chosen for study are such that investigations are conducted on a unique water mass with mixing between water masses minimized as much as possible. Diurnal studies of the partitioning of manganese between 0.22-µm filtrand and filtrates indicate a strong dependency on light intensity. This is to be expected given the ability of light to retard both Mn(II) oxidation and to induce the reductive dissolution of Mn(III,IV) oxides.
