Isotopic dynamics of precipitation and its regional and local drivers in a plateau inland lake basin, Southwest China

摘要

Shrinkage of plateau lakes under climate strength has drawn growing attention. Because of its intricate implication to hydro-meteorological condition and climate system, stable isotopes in precipitation (e.g. δ~2H_p and δ~(18)O_p) provide us a powerful tool to understand the climate-hydrologic dynamics in shrinking lakes. However, how the regional atmospheric circulation, moisture sources and local fractionation processes drive isotopic variability from temporal to spatial scale has rarely been reported for remote plateau lakes. Hence, we collected a total of 98 rainfall samples at the south and the north shores of Chenghai lake, Yunnan-Guizhou Plateau to study the potential driving forces of precipitation isotope variability during the wet season of 2019. Based on backward trajectories of air masses obtained from HYSPLIT model, 68% of moisture came from δ~(18)O depleted ocean (Indian Ocean, Bay of Bengal, South China Sea and Pacific Ocean), and the rainout process promoted the isotopic depletion when moisture arrived at the study basin. Evapotranspiration increased the heavy isotope ratios in precipitation originated from continents (northern China inland and western continents). The temporal dynamics of δ~(18)O_p and δ~2H_p were in phase with the convection activities intensity underlined the influence from large-scale atmospheric circulation. Local meteorological factors played a secondary role in isotope variability. Precipitation amount-effect strongly affected isotope ratios while mild anti-temperature effect was observed at daily scale. Interestingly, the rainfall isotope ratios showed different mechanisms in govern at lake south shore and north shore, with a distance of 19 km in between. This south-to-north difference can be explained by either lower 1.03% sub-evaporation in the south shore or 7% of recycled moisture contributing to precipitation in the north shore. Our findings discover the driving forces for δ~(18)O_p variation and provide solid interpretations for hydro-climate change in Southwest China.