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

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JUL 15

D/H ratios of leaf waxes (delta D-wax) derived from terrestrial plants and preserved in lake sediments can provide important information on past continental hydrology. Ideally, delta D-wax can be used to reconstruct precipitation D/H ratios (delta D-P) which is a well-established paleoclimate proxy. However, many other factors, such as vegetation and relative humidity (RH), also affect delta D-wax variation. How the combination of these factors affects sedimentary delta D-wax 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 delta D-wax delta D values of C-28 n-alkanoic acids show significant correlation with delta D-P values (R-2 = 0.76) with an apparent isotopic enrichment of similar to 99 +/- 8 parts per thousand, indicating that sedimentary delta D-wax values track overall delta D-P 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 delta D-wax along the natural transect is partially countered by the opposing influence of vegetation changes. The correlation between delta D-wax and delta D-P values is significantly higher (R-2 = 0.84) in the drier portions of the transect than in the wetter regions (R-2 = 0.64). This study suggests that D/H ratios of sedimentary leaf waxes can be used as a proxy for precipitation delta D variations, with particularly high fidelity in dry regions, although more studies in other regions will be important to further test this proxy. (c) 2008 Elsevier Ltd. All rights reserved.