Modern precipitation δ18O and trajectory analysis over the Himalaya-Tibet Orogen from ECHAM5-wiso simulations

Variations in oxygen isotope ratios (O-18) measured from modern precipitation and geologic archives provide a promising tool for understanding modern and past climate dynamics and tracking elevation changes over geologic time. In areas of extreme topography, such as the Tibetan Plateau, the interpretation of O-18 has proven challenging. This study investigates the climate controls on temporal (daily and 6h intervals) and spatial variations in present-day precipitation O-18 (O-18(p)) across the Tibetan Plateau using a 30year record produced from the European Centre/Hamburg ECHAM5-wiso global atmospheric general circulation model (GCM). Results indicate spatial and temporal agreement between model-predicted O-18(p) and observations. Large daily O-18(p) variations of -25 to +5 occur over the Tibetan Plateau throughout the 30 simulation years, along with interannual O-18(p) variations of similar to 2. Analysis of extreme daily O-18(p) indicates that extreme low values coincide with extreme highs in precipitation amount. During the summer, monsoon vapor transport from the north and southwest of the plateau generally corresponds with high O-18(p), whereas vapor transport from the Indian Ocean corresponds with average to low O-18(p). Thus, vapor source variations are one important cause of the spatial-temporal differences in O-18(p). Comparison of GCM and Rayleigh Distillation Model (RDM)-predicted O-18(p) indicates a modest agreement for the Himalaya region (averaged over 86 degrees-94 degrees E), confirming application of the simpler RDM approach for estimating O-18(p) lapse rates across Himalaya.