Figure 6. δ13C and δ18O of Lake Fryxell carbonates. Carbonate δ13C is, on average, enriched relative to expected values for precipitation in isotopic equilibrium with water column DIC (closed symbols). Carbonate δ18O is also enriched relative to expected equilibrium values and varies over a range of >20‰. δ13C follows an overall increasing trend with depth, while δ18O does not covary with depth or with δ13C.