Paleoaltimetry: A Review of thermodynamic methods

This review presents the use of conserved thermodynamic variables to estimate paleoaltitudes. The method based on conservation of moist static energy (the combined internal, latent heat, and gravitational potential energy of moist air) is discussed. This method exploits the physical relation between of the wind fields and the spatial and vertical distributions of both temperature and humidity. Given the climatological distributions of these three atmospheric fields, the method identifies moist enthalpy (the combined internal and latent heat energies of air) as a thermodynamic variable that varies with height in the atmosphere in a predictable fashion. To use this method, the major requirements are: (1) a priori knowledge of the spatial distribution of moist static energy for the paleoclimate and (2) the ability to estimate moistenthalpy in the paleo-environment for two isochronous locations: one at sea level, the other at some unknown elevation. As presented here, the method incorporates basic physical principles of atmospheric science and inferences of paleoclimates from plant leaf physiognomy. Assuming that expected errors estimated from present-day relationships between physiognomy and enthalpy apply to ancient climates and fossil leaves, an uncertainty estimate of ± 910 m in the paleoaltitude difference between two isochronous fossil assemblage locations can be assessed.