Oxygen isotope variation in the water cycle of the Yamzho lake Basin in southern Tibetan Plateau

Given the potential use of stable isotope in the paleoclimate reconstruction from lacustrine records as well as in the local hydrology cycle, it is crucial to understand the processes of stable isotope evolution in catchment in the Tibetan Plateau region. Here we present a detailed study on the water oxygen isotope based on 2 years observation including precipitation, river water and lake water in the Yamzho Lake, south of the Tibetan Plateau. Temporal variation of local precipitation delta(18)O shows an apparent "monsoon cycle". In monsoon season, delta(18)O in waters is lower. In non-monsoon season, delta(18)O in precipitation and lake water is higher and higher river delta(18)O exists in spring, probably reflecting the effect of land surface evaporation, together with the higher delta(18)O values in spring precipitation. It is also found that the surface lake water delta(18)O varies seasonally and annually. The lower lake water delta(18)O in the late summer is apparently related to the summer monsoon precipitation. The mean delta(18)O value of lake water in 2007 is 1.2% higher than that in 2004, probably due to the less monsoon precipitation in summer of 2007, as can be confirmed from the precipitation data at the Langkazi meteorological data. It is also found that an obvious shift of vertical lake water delta(18)O reflects the fast mixture of lake water. delta(18)O values of lake water are over 10% higher than those of precipitation and river water in this region due to the evaporation fractionation. The modeled results show that the evaporation process of the lake water is sensitive to relative humidity, and the present lake water delta(18)O reflects a relative humidity of 51% in the Yamzho Lake. It shows that the lake will take 30.5 years to reach present lake water delta(18)O given a large shift in the input water delta(18)O. The modeled results also reveal that surface lake water temperature and inflow delta(18)O have slight effect on the isotopic balance process of lake water in the Yamzho Lake.