Articles | Volume 12, issue 12
Research article
29 Jun 2015
Research article |  | 29 Jun 2015

Coupling δ2H and δ18O biomarker results yields information on relative humidity and isotopic composition of precipitation – a climate transect validation study

M. Tuthorn, R. Zech, M. Ruppenthal, Y. Oelmann, A. Kahmen, H. F. del Valle, T. Eglinton, K. Rozanski, and M. Zech

Abstract. The hydrogen isotopic composition (δ2H) of leaf waxes, especially of n-alkanes (δ2Hn-alkanes), is increasingly used for paleohydrological and paleoclimate reconstructions. However, it is challenging to disentangle past changes in the isotopic composition of precipitation and changes in evapotranspirative enrichment of leaf water, which are both recorded in leaf wax δ2H values. In order to overcome this limitation, Zech M. et al. (2013) proposed a coupled δ2Hn-alkanes–δ18Osugar biomarker approach. This coupled approach allows for calculating (i) biomarker-based "reconstructed" δ218O values of leaf water (δ218Oleaf water), (ii) biomarker-based reconstructed deuterium excess (d-excess) of leaf water, which mainly reflects evapotranspirative enrichment and which can be used to reconstruct relative air humidity (RH) and (iii) biomarker-based reconstructed δ218Oprecipitation values.

Here we present a climate transect validation study by coupling new results from δ2H analyses of n-alkanes and fatty acids in topsoils along a climate transect in Argentina with previously measured δ18O results obtained for plant-derived sugars. Accordingly, both the reconstructed RH and δ218Oprecipitation values correlate highly significantly with actual RH and δ218Oprecipitation values. We conclude that compared to single δ2Hn-alkane or δ18Osugar records, the proposed coupled δ2Hn-alkane–δ18Osugar biomarker approach will allow more robust δ218Oprecipitation reconstructions in future paleoclimate research. Additionally, the proposed coupled δ2Hn-alkane–δ18Osugar biomarker approach allows for the establishment of a "paleohygrometer", more specifically, the reconstruction of mean summer daytime RH changes/history.

Short summary
Stable water isotopes (18O/16O and 2H/1H) are invaluable proxies for paleoclimate research. Here we use a coupled 18O/16O and 2H/1H biomarker approach based on plant-derived sugars and n-alkanes. Applying this innovative approach to a topsoil transect allows for (i) calculating the deuterium-excess of leaf water as a proxy for relative humidity and (ii) calculating the plant source water isotopic composition (~precipitation). The approach is validated by the presented climate transect results.
Final-revised paper