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 (2Hwax) is a valuable tool for reconstructing continental paleohydrology, since it serves as a proxy for the hydrogen isotope composition of precipitation (2Hpre). To yield robust palaeohydrological reconstructions using 2Hwax in marine archives, it is necessary to examine the impacts of regional climate on 2Hwax and assess the similarity between marine sedimentary 2Hwax and the source of continental 2Hwax. 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 as well as soils within catchments and marine surface sediments adjacent to the outlets of the studied rivers and analyzed the relationship between climatic variables and 2Hwax values. We found that apparent fractionation between leaf waxes and source water is relatively constant in humid and semiarid regions (average: -121ĝ€¯‰). However, it becomes less negative in hyperarid regions (average: -86ĝ€¯‰) 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 2Hwax follows a non-linear relationship with water content and water flux variables, driven by strong soil evaporation and plant transpiration. Furthermore, our results indicate that 2Hwax values in marine surface sediments largely reflect 2Hwax values from the continent, confirming the robustness of marine 2Hwax records for paleohydrological reconstructions along the Chilean margin. These findings also highlight the importance of considering the effects of hyperaridity in the interpretation of 2Hwax values and pave the way for more quantitative paleohydrological reconstructions using 2Hwax.