Effects of aridity and vegetation on plant-wax δD in modern lake sediments

Pratigya J. Polissar, Katherine H. Freeman

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126 Scopus citations

Abstract

We analyzed the deuterium composition of individual plant-waxes in lake sediments from 28 watersheds that span a range of precipitation D/H, vegetation types and climates. The apparent isotopic fractionation (ε;a) between plant-wax n-alkanes and precipitation differs with watershed ecosystem type and structure, and decreases with increasing regional aridity as measured by enrichment of 2H and 18O associated with evaporation of lake waters. The most negative ε;a values represent signatures least affected by aridity; these values were -125±5‰ for tropical evergreen and dry forests, -130‰ for a temperate broadleaf forest, -120±9‰ for the high-altitude tropical páramo (herbs, shrubs and grasses), and -98±6‰ for North American montane gymnosperm forests. Minimum ε;a values reflect ecosystem-dependent differences in leaf water enrichment and soil evaporation. Slopes of lipid/lake water isotopic enrichments differ slightly with ecosystem structure (i.e. open shrublands versus forests) and overall are quite small (slopes=0-2), indicating low sensitivity of lipid δD variations to aridity compared with coexisting lake waters. This finding provides an approach for reconstructing ancient precipitation signatures based on plant-wax δD measurements and independent proxies for lake water changes with regional aridity. To illustrate this approach, we employ paired plant-wax δD and carbonate-δ18O measurements on lake sediments to estimate the isotopic composition of Miocene precipitation on the Tibetan plateau.

Original languageEnglish (US)
Pages (from-to)5785-5797
Number of pages13
JournalGeochimica et Cosmochimica Acta
Volume74
Issue number20
DOIs
StatePublished - Oct 1 2010

All Science Journal Classification (ASJC) codes

  • Geochemistry and Petrology

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