HOW ACCURATE ARE STABLE ISOTOPE BASED ESTIMATES OF PALEOALTIMETRY: RESULTS FROM ISOTOPE ENABLED CLIMATE MODELS

Stable isotope based estimates of paleoaltimetry require a number of assumptions, many of which are difficult to assess through data alone. We use an isotope-enabled fully coupled atmosphere-ocean general circulation model (the Hadley centre climate model, HadCM3L) to investigate the role of changing circulation and local recycling in determining the isotopic signature over the Tibetan plateau. The model is configured with Early Eocene (Lutetian, ~45Ma) paleogeographies and a number of topographic scenarios are modelled. The different topographic scenarios represent uncertainties in the reconstructions, and include representation of valley systems and differences in the southern part of the plateau. Even with these relatively modest changes in the height, changes in delta-18O can be large. Typical variations can be +/- 3 per mille which corresponds to an elevation uncertainty of about 1km. Larger changes to the topography can make even bigger differences to the estimated elevations, with changes in circulation altering the best location for estimating the low altitude reference site.