Implications of variations in δ18O and δD in precipitation at Madoi in the eastern Tibetan Plateau

Abstract

Event-based rain and snow samples were collected from May 2009 to April 2010 at Madoi in the eastern Tibetan Plateau, and the stable isotopic compositions (δ18O and δD) of these samples were analyzed. The local meteoric water lines (LMWLs) based on individual samples and monthly weighted means were δD = 8.37δ18O + 11.86 (R2 = 0.97, n = 175) and δD = 8.80δ18O + 20.16 (R2 = 0.98, n = 11), respectively. Although fluctuations of the isotopic compositions in precipitation throughout the year were high, monthly amount-weighted means revealed seasonal signals. According to the monthly averaged data, the δ18O values decreased distinctly from June to July, indicating that summer monsoon circulation can significantly influence precipitation in this region. The high d-excess values from May to June and from October to November were probably the result of local moisture recycling. Apart from moisture sources, the δ18O and d-excess values in precipitation were also affected by subcloud evaporation/sublimation, which could be inferred from their relationships with different temperature and relative humidity ranges. The results of this study augment the understanding of the water cycle in the eastern Tibetan Plateau.