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

Abstract

The δ18O 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 δ18O 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 δ18O in precipitation on the Plateau is influenced by different moisture sources, with significant Indian monsoon influence on δ18O composition in plateau precipitation and river water. The δ18O 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 δ18O 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 δ18O 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 δ18O in precipitation and river water on the Tibetan Plateau results from the combined effect of monsoon moisture supply and westerly moisture supply, the δ18O composition and its altitude effect on the Plateau during monsoon seasons should be considered in the reconstruction of paleoelevation of the Tibetan Plateau.