Publication Date:
2019-09-23
Description:
Manganese (Mn) is a required element for oceanic phytoplankton as it plays a critical role in photosynthesis, through its unique redox chemistry, as the active site in photosystem II and in enzymes that act as defences against reactive oxygen species (ROS), most notably for protection against superoxide (O2-), through the action of superoxide dismutase (SOD), and against hydrogen peroxide (H2O2) via peroxidases and catalases. The distribution and redox speciation of Mn in the ocean is also apparently controlled by reactions with ROS. Here we examine the connections between ROS and dissolved Mn species in the upper ocean using field and laboratory experimental data. Our results suggest it is unlikely that significant concentrations of Mn(III) are produced in the euphotic zone, as in the absence of evidence for the existence of strong Mn(III) ligands, Mn(II) reacts with O2- to form the short lived transient manganous superoxide, MnO2+, which may react rapidly with other redox species in a similar manner to O2-. Experiments with the strong Mn(III) chelator, desferrioxamine B (DFB), in seawater indicated that the Mn(III) species is unlikely to form, as the pre-cursor Mn(II) complex under natural ambient conditions due to the high side reaction of DFB with Ca.
Type:
Article
,
PeerReviewed
Format:
text
Format:
text
Format:
text
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