Variable apparent hydrogen isotopic fractionation between sedimentary n-alkanes and precipitation on the Tibetan Plateau

The hydrogen isotope ratio values of sedimentary leaf wax n-alkanes (delta D-wax) have been considered a reliable proxy for precipitation isotope ratios (delta D-P) across various transects on a global basis. Records of delta D-wax have been used to infer past changes in hydrology, climate and altimetry, assuming nearly constant apparent hydrogen isotopic fractionation (epsilon(wax-P)) between sedimentary leaf wax components and precipitation. Here, we present the results of an analysis of delta D-wax values from the surface sediments of 22 lakes across a precipitation and vegetation gradient on the Tibetan Plateau. The delta D-wax values correlated significantly with mean annual precipitation delta D (r 0.90) and summer precipitation delta D (r 0.91), suggesting that delta D-wax can record delta D-P in very dry regions. However, epsilon(wax-P) varies with annual precipitation as well as with relative humidity. Calculation using Craig-Gordon isotope models showed that the variable epsilon(wax-P) values likely resulted from intensive soil evaporation and plant evapotranspiration in this relatively arid region. This implies that variable isotopic fractionation should be taken into consideration when reconstructing paleohydrology, paleoclimate and paleoaltimetry. (C) 2018 Elsevier Ltd. All rights reserved.