Manganese distribution is variable in the coastal waters of the Northwest Atlantic

Academic Writing

Published in The Journal of Geophysical Research: Oceans, 2020.

Oldham, V. E., Lamborg, C. H., & Hansel, C. M. (2020). The spatial and temporal variability of Mn speciation in the coastal Northwest Atlantic Ocean. Journal of Geophysical Research: Oceans, 125, e2019JC015167. https://doi.org/10.1029/2019JC015167

2020_Carignan(nee Oldham)_MnNorthwestAtlantic.pdf

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Manganese (Mn) is an essential micronutrient in seawater and an important player in the reactions of many other biologically relevant elements. The role of Mn in seawater is governed by its speciation: oxidation state (+2 to +4 in natural systems) and coordination environment. Manganese speciation is dominated by three species: soluble Mn(II), soluble Mn(III)‐ligand complexes, and solid Mn oxides. Most studies of Mn in seawater focus only on solid versus soluble phase speciation, but this does not adequately describe the redox cycling of Mn because each species has unique chemistry in seawater. Here, we add to the limited studies that examine the speciation of Mn in seawater and find that Mn(III)‐ligand complexes dominate our four coastal sites. This is important because Mn(III)can donate or accept electrons, making it particularly reactive and versatile. The complex cycle of Mn in coastal waters is dominated by each site's unique biology, the light regime, and water mixing processes. In addition, we examine the speciation of Mn over a diel cycle and find that Mn speciation changes dramatically from day to night, likely a mixing response. Thus, we find that the cycling of Mn is more variable over space and time than previously thought