δ13C, δ18O, and Triple Oxygen Isotopes of Benthic Microbial Carbonates from Perennially Ice-Covered Lake Fryxell, Antarctica

Microbial carbonates from Lake Fryxell, McMurdo Dry Valleys, Antarctica show slight (~0-3‰) enrichment in 13C, likely due to preferential uptake of 12C by metabolically-active microbes. Carbonate δ18O is highly variable, with a range of ~24‰ across all samples. Large differences in δ18O can be found at subsampling sites only hundreds of microns to a few millimeters apart. Triple oxygen isotopes suggest mixing of a modified marine fluid with lake waters in benthic pore spaces as a potential mechanism for this isotopic variability.