Mn(III) is an aquatic player

Chemical oceanographers, who long dismissed Mn(III) as a fleeting and thus inconsequential oxidation state of manganese in marine systems, will now have to rethink those assumptions. Mn(III) is actually relatively abundant in the oxygen-poor waters of the Black Sea and the Chesapeake Bay, according to a survey conducted by George W. Luther III and Robert E. Trouwborst of the University of Delaware and their colleagues (Science 2006, 313, 1955). Although Mn(III) can be stabilized with chelating agents in aqueous solutions in the laboratory, it's been widely assumed this species quickly disproportionates to soluble Mn(II) and particulate MnO₂ in open waters. Instead, the researchers have found that soluble Mn(III) concentrations can reach as high as 5 µM in oxygen-poor waters. In some sampling locations, previously overlooked Mn(III) accounts for 100% of the total dissolved Mn pool. Formed either by Mn(II) oxidation or by MnO₂ reduction, Mn(III) in marine environments is stabilized by as-yet-uncharacterized natural ligands, the researchers surmise.