Calculated carbon-system parameters and comparison with Earth system model results for the PETM. Pairing pH and DIC (A) with records of temperature, salinity, and surface pressure, we calculate surface-ocean calcium carbonate-saturation state (Ω calcite) (B), pCO2 (C), and alkalinity (D). Presented runs of the Earth system model cGENIE (10) (red) include enhanced organic carbon burial during the recovery period in order to better match the more rapid recovery of δ13C.