Can sedimentary leaf waxes record D/H ratios of continental precipitation? Field, model, and experimental assessments

D/H ratios of leaf waxes (δDwax) derived from terrestrial plants and preserved in lake sediments can provide important information on past continental hydrology. Ideally, δDwax can be used to reconstruct precipitation D/H ratios (δDP) which is a well-established paleoclimate proxy. However, many other factors, such as vegetation and relative humidity (RH), also affect δDwax variation. How the combination of these factors affects sedimentary δDwax is unclear. Here, we use a transect of 32 lake surface sediments across large gradients of precipitation, relative humidity, and vegetation composition in the southwestern United States to study the natural factors affecting sedimentary δDwax. δD values of C28n-alkanoic acids show significant correlation with δDP values (R2 = 0.76) with an apparent isotopic enrichment of ∼99 ± 8‰, indicating that sedimentary δDwax values track overall δDP variation along the entire transect. Leaf waxes produced by plants grown under controlled conditions (RH = 80%, 60%, 40%) show a small increase in D/H ratios as RH decreases, consistent with prediction from the Craig-Gordon model. However, the isotopic effect of RH on δDwax along the natural transect is partially countered by the opposing influence of vegetation changes. The correlation between δDwax and δDP values is significantly higher (R2 = 0.84) in the drier portions of the transect than in the wetter regions (R2 = 0.64). This study suggests that D/H ratios of sedimentary leaf waxes can be used as a proxy for precipitation δD variations, with particularly high fidelity in dry regions, although more studies in other regions will be important to further test this proxy.