Modern precipitation δ~(18)O and trajectory analysis over the Himalaya-Tibet Orogen from ECHAM5-wiso simulations

摘要

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.