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

• Published in: Quaternary science reviews Vol. 65; pp. 88 - 101
• Main Authors: Collins, James A., Schefuß, Enno, Mulitza, Stefan, Prange, Matthias, Werner, Martin, Tharammal, Thejna, Paul, André, Wefer, Gerold
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.04.2013
• Subjects: African palaeoclimate; Hydrogen isotopic composition of precipitation; Leaf-waxes; Organic geochemistry; ASE, Africa; African palaeoclimate; Leaf-waxes; Organic geochemistry; Hydrogen isotopic composition of precipitation
• ISSN: 0277-3791; 1873-457X
• DOI: 10.1016/j.quascirev.2013.01.007

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. ► Leaf-wax δD can be corrected for the effects of vegetation and evapotranspiration. ► C3 tree versus C4 grass changes are not the main control on leaf-wax δD variations. ► Wet season intensity was generally increased during the mid-Holocene. ► Wet season intensity was shifted southeastwards during the Last Glacial Maximum.