Stable isotopes
Carbonate δ18O in this depth range is highly variable and does not follow a clear trend with depth. Carbonate δ18O values span >20‰, and carbonate δ18O does not match predicted values for precipitation in isotopic equilibrium with the Lake Fryxell water column (Figure 6). Carbonate δ18O does not co-vary with δ13C. At the shallowest depths (8.9-9.0 m), average carbonate δ13C values are similar to calculated values for precipitation in isotopic equilibrium with the DIC pool. From 9.3-9.7 m, carbonate δ13C at nearly all sampling sites is approximately 0-3‰ heavier than expected from precipitation in isotopic equilibrium with DIC (Figure 6).