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).