GEOC 4 |
| Hydrogen-isotopic fractionations within the hydrological cycle respond strongly to climatic variables, including evaporation. We are investigating whether the D/H ratios of leaf-wax lipids can provide a quantitative proxy for aridity, by sampling multiple plant species along a gradient of declining precipitation totals across southern California (from 1000 to 200 mm/year precipitation). 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 precipitation along the storm track. Paleoaridity reconstructions from leaf-wax delta-D values will be most robust where the isotopic composition of environmental waters is constant 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. |
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Modern Calibrations and Terrestrial Applications of Stable Isotope Paleo Proxies
9:00 AM-12:10 PM, Sunday, August 19, 2007 Boston Park Plaza -- St. James Rm, Oral
Division of Geochemistry |