Climatic controls on leaf wax hydrogen isotope ratios in terrestrial and marine sediments along a hyperarid to humid gradient

Abstract. The hydrogen isotope composition of leaf wax biomarkers (δ²H_wax) is a valuable tool for reconstructing continental paleohydrology, as it serves as a proxy for the hydrogen isotope composition of precipitation (δ²H_pre). To yield robust palaeohydrological reconstructions using δ²H_wax in marine archives, it is necessary to examine the impacts of regional climate on δ²H_wax and assess the similarity between marine sedimentary δ²H_wax and the source of continental δ²H_wax. Here, we examined an aridity gradient from hyperarid to humid along the Chilean coast. We sampled sediments at the outlets of rivers draining into the Pacific, soils within catchments and marine surface sediments adjacent to the outlets of the studied rivers and analyzed the relationship between climatic variables and δ²H_wax values. We find that apparent fractionation between leaf waxes and source water is relatively constant in humid/semiarid regions (average: −121 ‰). However, it becomes less negative in hyperarid regions (average: −86 ‰) as a result of evapotranspirative processes affecting soil and leaf water ²H enrichment. We also observed that along strong aridity gradients, the ²H enrichment of δ²H_wax follows a non-linear relationship with water content and water flux variables, driven by strong soil evaporation and plant transpiration. Furthermore, our results indicated that δ²H_wax values in marine surface sediments largely reflect δ²H_wax values from the continent, confirming the robustness of marine δ²H_wax records for paleohydrological reconstructions along the Chilean margin. These findings also highlight the importance of considering the effects of hyperaridity in the interpretation of δ²H_wax values and pave the way for more quantitative paleohydrological reconstructions using δ²H_wax.