Mn and Fe Content of Microbial Carbonates from Lake Fryxell, Antarctica

[Mn] and [Fe] are highly variable in microbial carbonates from Lake Fryxell, McMurdo Dry Valleys, Antarctica. Carbonates precipitate in pore space inside photosynthetically-active microbial mats, and as such are subject to spatial and temporal fluctuations in local redox which affect the behavior of Mn and Fe. [Mn] and [Fe] are lowest in carbonates from the shallowest depth samples where pore waters are typically supersaturated with oxygen, likely due to sequestration into insoluble oxide phases, and highest at the deepest sampling point where pore waters are usually suboxic to anoxic. Mn and Fe concentrations and the Mn/Fe ratio in these carbonates are otherwise independent of depth, and do not correlate to cathodoluminescence intensity.