Abstract
Knowledge of the chemical speciation of particulate manganese (pMn) is
important for understanding the biogeochemical cycling of Mn and other
particle-reactive elements. Here, we present the synchrotron-based X-ray
spectroscopy-derived average oxidation state (AOS) of pMn in the surface
Arctic Ocean collected during the U.S. GEOTRACES Arctic cruise (GN01) in
2015. We show that the pMn AOS is less than 2.4 when sampled during the
day and more than ~3.0 when sampled at night. We
hypothesize that an active light-dependent redox cycle between dissolved
Mn and particulate Mn(III/IV) exists during the day-night cycle in the
surface Arctic Ocean, which occurs on the timescale of hours. The
magnitude of observed pMn AOS is likely determined by the net effect of
the length of the previous night and integrated light level before the
end of pMn sampling.