Modern precipitation δ 18 O and trajectory analysis over the Himalaya‐Tibet Orogen from ECHAM5‐wiso simulations

Variations in oxygen isotope ratios (δ 18 O) 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 δ 18 O has proven challenging. This study investigates the climate controls on temporal (daily and 6 h intervals) and spatial variations in present‐day precipitation δ 18 O (δ 18 O p ) across the Tibetan Plateau using a 30 year record produced from the European Centre/Hamburg ECHAM5‐wiso global atmospheric general circulation model (GCM). Results indicate spatial and temporal agreement between model‐predicted δ 18 O p and observations. Large daily δ 18 O p variations of −25 to +5‰ occur over the Tibetan Plateau throughout the 30 simulation years, along with interannual δ 18 O p variations of ~2‰. Analysis of extreme daily δ 18 O 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 δ 18 O p , whereas vapor transport from the Indian Ocean corresponds with average to low δ 18 O p . Thus, vapor source variations are one important cause of the spatial‐temporal differences in δ 18 O p . Comparison of GCM and Rayleigh Distillation Model (RDM)‐predicted δ 18 O p indicates a modest agreement for the Himalaya region (averaged over 86°–94°E), confirming application of the simpler RDM approach for estimating δ 18 O p lapse rates across Himalaya.