Estimating the hydrogen isotopic composition of past precipitation using leaf-waxes from western Africa


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james.collins [ at ] awi.de

Abstract

The hydrogen isotopic composition of plant leaf-wax n-alkanes (δDwax) is a novel proxy for estimating δD of past precipitation (δDp). However, vegetation life-form and relative humidity exert secondary effects on δDwax, preventing quantitative estimates of past δDp. Here, we present an approach for removing the effect of vegetation-type and relative humidity from δDwax and thus for directly estimating past δDp. We test this approach on modern day (late Holocene; 0-3 ka) sediments from a transect of 9 marine cores spanning 21°N-23°S off the western coast of Africa. We estimate vegetation type (C3 tree versus C4 grass) using δ13C of leaf-wax n-alkanes and correct δDwax for vegetation-type with previously-derived apparent fractionation factors for each vegetation type. Late Holocene vegetation-corrected δDwax (δDvc) displays a good fit with modern-day δDp, suggesting that the effects of vegetation type and relative humidity have both been removed and thus that δDvc is a good estimate of δDp. We find that the magnitude of the effect of C3 tree - C4 grass changes on δDwax is small compared to δDp changes. We go on to estimate δDvc for the mid-Holocene (6-8 ka), the Last Glacial Maximum (LGM; 19-23 ka) and Heinrich Stadial 1 (HS1; 16-18.5 ka). In terms of past hydrological changes, our leaf-wax based estimates of δDp mostly reflect changes in wet season intensity, which is complementary to estimates of wet season length based on leaf-wax δ13C. © 2013 Elsevier Ltd.



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Eprint ID
32703
DOI https://www.doi.org/10.1016/j.quascirev.2013.01.007

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Collins, J. A. , Schefuß, E. , Mulitza, S. , Prange, M. , Werner, M. , Tharammal, T. , Paul, A. and Wefer, G. (2013): Estimating the hydrogen isotopic composition of past precipitation using leaf-waxes from western Africa , Quaternary Science Reviews, 65 , pp. 88-101 . doi: https://www.doi.org/10.1016/j.quascirev.2013.01.007


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