Variations of water stable isotopes (δ 18O) in two lake basins, southern Tibetan Plateau

Abstract

δ18O measurements based on systematic sampling and isotopic modeling have been adopted to study the controls of stable isotopes in lakewater in two lake basins (lakes Yamdrok-tso and Puma Yumtso) at two different elevations on the southern Tibetan Plateau. Temporally, δ18O values in precipitation and lake water display a seasonal fluctuation in both lakes. Spatially, δ18o values in the two lake basins increase by 10%from the termini of glaciers to the lake shores, by ~1%from the lake shores to the lake center and by 0.4% from the water surface to depth in these lakes. The clear annual δ18O variations indicate that lake water mixes sufficiently in a short time. Model results show that glacial meltwater and surface lake-water temperature are not the dominant factors in the balance process of stable isotopes in lake water. Equilibrium δ18o values decrease by 0.8%for Yamdrok-tso lake and 0.6% for Puma Yum-tso lake when glacial meltwater contributions to these lakes shrink by 60%. δ18o ratios increase rapidly during the initial stages and take a longer time to approach the equilibrium value.