TY - JOUR
T1 - Effects of aridity and vegetation on plant-wax δD in modern lake sediments
AU - Polissar, Pratigya J.
AU - Freeman, Katherine H.
PY - 2010/10
Y1 - 2010/10
N2 - 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.
AB - 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.
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U2 - 10.1016/j.gca.2010.06.018
DO - 10.1016/j.gca.2010.06.018
M3 - Article
AN - SCOPUS:78650213006
SN - 0016-7037
VL - 74
SP - 5785
EP - 5797
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 20
ER -