Can hydrogen isotopic ratios in plant lipids provide a quantitative proxy for aridity?

Abstract

Hydrogen-isotopic fractionations within the hydrol. cycle respond strongly to climatic variables, including evapn. We are investigating whether the D/H ratios of leaf-wax lipids can provide a quant. proxy for aridity, by sampling multiple plant species along a gradient of declining pptn. totals across southern California (from 1000 to 200 mm/yr pptn.). We observe a strongly aridity-dependent D/H enrichment of plant waters which reduces the apparent fractionation of leaf-wax lipids relative to source water (ranging from -120 to -60 per mil). However, the aridity signal is suppressed in leaf-wax lipids by an opposing 40 per mil decrease in the delta-D of pptn. along the storm track. Paleoaridity reconstructions from leaf-wax delta-D values will be most robust where the isotopic compn. of environmental waters is const. or independently constrained. Our multi-species and catchment scale approach also quantifies the potential influence of changing plant community assemblage on the sedimentary leaf-wax lipid isotopic signal.