Isotopic evidence in modern precipitation for the westerly meridional movement in Central Asia

Abstract

The seasonal and inter-annual variations of stable isotopes in alpine precipitation in arid Central Asia is of great help to understand the modern hydrological processes and climate proxy in the westerly-dominant region. In this study, we measured the 3-year precipitation isotope values at a site located on the southern Tianshan Mountains in Central Asia. The δ18O values of precipitation show a statistically significant relationship with air temperature (R2 = 0.58). The trajectory diagnostics indicate the strong influence of westerly moisture, although the local trajectories do exist. According to the 3-year isotope records in the sampling site, the δ18O values of precipitation correlated with the meridional circulation index, while the correlation with the zonal circulation index is generally weak. An isotope-enabled GCM is used to analyze the correlation between the δ18O values in summer precipitation and the meridional and zonal wind speeds on a longer time scale; there is a strong correlation between the δ18O values and the meridional wind speed for the upwind direction. The findings indicate the meridional movement of mid-latitude westerly can be sensitively recorded in the modern precipitation in arid Central Asia, and the inter-annual variability of precipitation isotopes in Central Asia can not only be attributed to temperature effect.