Articles | Volume 12, issue 12
Biogeosciences, 12, 3913–3924, 2015
Biogeosciences, 12, 3913–3924, 2015

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. Tuthorn1, R. Zech2, M. Ruppenthal3, Y. Oelmann3, A. Kahmen4, H. F. del Valle5, T. Eglinton2, K. Rozanski6, and M. Zech1,7 M. Tuthorn et al.
  • 1Department of Soil Physics and Chair of Geomorphology, University of Bayreuth, Universitätsstr. 30, 95440 Bayreuth, Germany
  • 2Geological Institute, ETH Zurich, Sonneggstrasse 5, 8092 Zurich, Switzerland
  • 3Geoecology, University of Tübingen, Rümelinstr. 19–23, 72070 Tübingen, Germany
  • 4Department of Environmental Sciences – Botany, University of Basel, Schönbeinstrasse 6, 4056 Basel, Switzerland
  • 5Ecología Terrestre, Centro Nacional Patagónico (CENPAT), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Boulevard Brown 2825, U9120ACF Puerto Madryn, Argentina
  • 6Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, Kraków, Al. Mickiewicza 30, 30–059 Kraków, Poland
  • 7Institute of Agronomy and Nutritional Sciences, Soil Biogeochemistry, Martin-Luther University Halle–Wittenberg, von-Seckendorff-Platz 3, 06120 Halle, Germany

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