Seasonal deuterium excess in Nagqu precipitation: influence of moisture transport and recycling in the middle of Tibetan Plateau

A total of 198 precipitation samples were collected at Nagqu on the central Tibetan Plateau in 2000. Based on the isotope data from individual samples, the local meteoric water line was established: delta D = 7.7 delta O-18-4.6 (r(2 =) 96, p < 0.0001). Stable isotope data from precipitation exhibit a seasonal variability in deuterium excess. The study indicated that the influence of moisture transport and recycling on seasonal variation of d-excess in precipitation events is potentially significant. During summer precipitation, the lower d-excess values are usually related to warm and humid Indian Ocean moisture transport. In spring and winter, due to the cold and dry westerly and northern moisture transport, d-excess values in precipitation are usually higher. The d-excess in summer precipitation is also influenced by the secondary evaporation between cloud base and ground during precipitation events, as well as the admixture of water vapor from evapotranspiration over the continent along the storm trajectories. The results also suggested that the d-excess values in precipitation at Nagqu displayed an obvious transition due to its location on the central Tibetan Plateau.