COPRECIPITATION ACCUMULATION DISTRIBUTION OF MANGANESE AND IRON, AND ELECTROCHEMICAL CHARACTERISTICS OF MN IN CALCAREOUS SEAWATER

A study of manganese and iron associated with particulate matter in seawaters derived from the English Channel (and North Sea). Sequential extraction procedures have been used to identify geochemical processes that govern Mn and Fe coprecipitation/accumulation/distribution in different particulate phases (carbonate; FeMn(hydr)oxides; organic matter and residual phase). The oxidation states of Mn and Fe, some mechanisms of bonding and the magnetic characteristics of particles have been investigated by Mossbauer spectroscopy, electron spin resonance(ESR) spectroscopy, and mass susceptibility balance. The effect of pH and redox potential on stability of different dissolved and particulate Mn species was also examined. In the these calcareous seawaters, manganese (II) is predominantly bound to the carbonate phase (calcite) in the form of MnxCa1-xCO3. However the persistent occurrence of Mn in oxidation states > 2 in these particles has suggested the existence of manganese(III) in the polymeric FeOOH structures as an ''intermediate'' entity during Mn(II) oxidation in the sea. The activity coefficient of the entity ''MnOOH'' in FeOOH has been evaluated and p epsilon-pH diagrams of Mn have been proposed under marine conditions.