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.
Can sedimentary leaf waxes record D/H ratios of continental precipitation?: Field, model, and experimental assessments
Year of Publication:
GEOCHIMICA ET COSMOCHIMICA ACTA