Local effects on soil leaf wax hydrogen isotopes along a west to east transect through the Pamirs, Tajikistan

Understanding the control mechanisms that affect soil leaf wax hydrogen isotopes is crucial when interpreting these data in the context of paleoclimatic reconstructions. Within a pilot study we aimed to evaluate the regional controls on leaf wax δ2H in the Central Asian Pamir Mountains (Tajikistan), a region characterized by pronounced hydroclimatic gradients. Soil and tap water samples were collected along a ca. 1000 km west-east-gradient, spanning ca. 3100 m of altitude difference. The results give evidence of variable environmental control on soil leaf wax δ2H values in different sub-regions of the study area. In the western and central Pamirs, the plant lipids mirror the signal of a mostly riverine water source, with an isotopic signature mainly controlled by winter and spring precipitation. With ca. –1.3‰ change per 100 m altitude, soil leaf wax derived isotopic lapse rates in these samples are lower than in other Asian high-altitude settings and the global average, which confirms earlier findings from surface water analysis from the Pamirs. In contrast, soil samples from the shielded Karakul basin showed significantly higher δ2H values. Those most likely reflect the more positive isotope signal of a predominant summer precipitation in the arid eastern Pamirs, with potential additional enrichment due to local vapor recycling and soil- and leaf water evapotranspiration. While the predominant water source (precipitation vs river water) plays an important role on a local scale, the results further highlight the significance of regional climate effects on isotopic signals incorporated into leaf waxes.