Indian monsoon influences altitude effect of δ18O in precipitation/river water on the Tibetan Plateau

The delta O-18 variation in precipitation acquired from 28 stations within the network of Tibetan Observation and Research Platform (TORP) is studied, with the focus on the altitude effect of delta O-18 in river water during monsoon precipitation in an effort to understand the monsoon influence on isotopic composition in annual river water. It is found that delta O-18 in precipitation on the Plateau is influenced by different moisture sources, with significant Indian monsoon influence on delta O-18 composition in plateau precipitation and river water. The delta O-18 of water bodies in the monsoon domain is generally more depleted than that in the westerly domain, suggesting gradual rainout of southwesterly borne marine moisture in the course of long-distance transportation and lifting over the Himalayas. The lapse rate of delta O-18 in river water with altitude is the largest during monsoon precipitation, due to the increased temperature vertical gradient over the southern Plateau region controlled by monsoon circulation. The combination of delta O-18 in river water in monsoon (wet) and non-monsoon (dry) seasons shows a larger lapse rate than that in non-monsoon (dry) season alone. As the altitude effect of delta O-18 in precipitation and river water on the Tibetan Plateau results from the combined effect of monsoon moisture supply and westerly moisture supply, the delta O-18 composition and its altitude effect on the Plateau during monsoon seasons should be considered in the reconstruction of paleoelevation of the Tibetan Plateau.