This exploratory project aims to calibrate a new paleoaltimeter based upon the hydrogen isotope ratios of plant biomarkers. These ratios enable reconstruction of the isotopic signatures of paleoprecipitation, from which paleoelevations are inferred using a physically based isotope-elevation model. This approach is rooted in the systematic relationship between the hydrogen isotope composition of molecules that comprise the epicuticular waxy coating on plant leaves and the isotopic composition of precipitation. An evaluation of this new method is being carried out using plant-wax n-alkanes extracted from North American and Andean montane lakes representing a range of plant communities, hydrology and altitude. The modern lake sediments offer an ideal analog for the ancient lake environments often used for paleoaltimetry. Comparison of reconstructed precipitation hydrogen isotope ratios and elevation estimates with actual lake elevation and local precipitation composition will provide a powerful and direct means to evaluate hydrogen isotope ratios of plant-wax biomarkers as paleoelevation proxies. The role of plant physiology is being assessed by measuring the plant-wax hydrogen isotope composition in leaves roots and soils from monospecific stands of six different tree species, representing dominant Cenozoic taxa, grown under identical climate and water sources at the Siemianice Experimental Forest in Poland. These measurements allow evaluation of species-dependent differences in transpiration and isotopic fractionation accompanying plant-wax synthesis. Investigation of this new technique with modern samples is necessary before its widespread application as a paleoaltimeter.
Paleoelevation is a key variable in tectonics and climate research. Observation-based estimates provide a benchmark to compare with models of mountain formation and help constrain the complex interactions driving uplift, denudation and climate. A plant-wax hydrogen isotope ratio paleoaltimeter will broaden the types of samples amenable to paleoaltimetry while pioneering an interdisciplinary and novel application of biogeochemical tools to the study of tectonic systems. This research also indirectly addresses the challenges of discerning climate histories in the terrestrial environment, and has potential to offer insights to the consequences of human-induced changes in climate, terrestrial hydrology and the physical landscape.
