Preprints
https://doi.org/10.5194/bg-2020-434
https://doi.org/10.5194/bg-2020-434

  22 Dec 2020

22 Dec 2020

Review status: this preprint is currently under review for the journal BG.

Validation of a coupled δ2Hn-alkane18Osugar paleohygrometer approach based on a climate chamber experiment

Johannes Hepp1,2,a, Christoph Mayr3,4, Kazimierz Rozanski5, Imke Kathrin Schäfer6, Mario Tuthorn7,b, Bruno Glaser2, Dieter Juchelka7, Willibald Stichler8, Roland Zech6,9,c, and Michael Zech2,10,d Johannes Hepp et al.
  • 1Chair of Geomorphology and BayCEER, University of Bayreuth, Universitätsstrasse 30, D-95440 Bayreuth, Germany
  • 2Institute of Agronomy and Nutritional Sciences, Soil Biogeochemistry, Martin-Luther-University Halle-Wittenberg, Von-Seckendorff-Platz 3, D-06120 Halle (Saale), Germany
  • 3Institute of Geography, Friedrich-Alexander-University Erlangen-Nürnberg, Wetterkreuz 15, D-91058 Erlangen, Germany
  • 4GeoBio-Center & Earth and Environmental Sciences, Ludwig-Maximilian University Munich, Richard- Wagner-Str. 10, D-80333 München, Germany
  • 5Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, Al. Mickiewicza 30, PL-30-059 Kraków, Poland
  • 6Institute of Geography and Oeschger Centre for Climate Research, University of Bern, Hallerstrasse 12, CH-3012 Bern, Switzerland
  • 7Thermo Fisher Scientific, Hanna-Kunath-Str. 11, D-28199 Bremen, Germany
  • 8Helmholtz Zentrum München, German Research Center for Environmental Health, Ingolstädter Landstrasse 1, D-85764 Neuherberg, Germany
  • 9Institute of Geography, Chair of Physical Geography, Friedrich-Schiller University of Jena, Löbdergraben 32, D-07743 Jena, Germany
  • 10Institute of Geography, Heisenberg Chair of Physical Geography with focus on paleoenvironmental research, Technische Universität Dresden, Helmholtzstrasse 10, D-01062 Dresden, Germany
  • apresent address: Chair of Geomorphology and BayCEER, University of Bayreuth, Universitätsstrasse 30, D-95440 Bayreuth, Germany
  • bpresent address: Thermo Fisher Scientific, Hanna-Kunath-Str. 11, D-28199 Bremen, Germany
  • cpresent address: Institute of Geography, Chair of Physical Geography, Friedrich-Schiller University of Jena, Löbdergraben 32, D-07743 Jena, Germany
  • dpresent address: Institute of Geography, Heisenberg Chair of Physical Geography with focus on paleoenvironmental research, Technische Universität Dresden, Helmholtzstrasse 10, D-01062 Dresden, Germany

Abstract. The hydrogen isotopic composition of leaf wax-derived biomarkers, e.g. long chain n-alkanes (δ2Hn-alkane), is widely applied in paleoclimatology research. However, a direct reconstruction of the isotopic composition of source water based on δ2Hn-alkane alone can be challenging due to the alteration of the soil water isotopic signal by leaf-water heavy-isotope enrichment. The coupling of δ2Hn-alkane with δ18O of hemicellulose-derived sugars (δ18Osugar) has the potential to disentangle this effect and additionally to allow relative humidity reconstructions. Here, we present δ2Hn-alkane as well as δ18Osugar results obtained from leaves of the plant species Eucalyptus globulus, Vicia faba var. minor and Brassica oleracea var. medullosa, which grew under controlled conditions. We addressed the questions (i) do δ2Hn-alkane and δ18Osugar values allow precise reconstructions of leaf water isotope composition, (ii) how accurately does the reconstructed leaf-water-isotope composition enables relative humidity (RH) reconstruction in which the plants grew, and (iii) does the coupling of δ2Hn-alkane and δ18Osugar enable a robust source water calculation?

For all investigated species, the alkane n-C29 was most abundant and therefore used for compound-specific δ2H measurements. For Vicia faba, additionally the δ2H values of n-C31 could be evaluated robustly. With regard to hemicellulose-derived monosaccharides, arabinose and xylose were most abundant and their δ18O values were therefore used to calculate weighted mean leaf δ18Osugar values. Both δ2Hn-alkane and δ18Osugar yielded significant correlations with δ2Hleaf-water and δ18Oleaf-water, respectively (r2 = 0.45 and 0.85, respectively; p < 0.001, n = 24). Mean fractionation factors between biomarkers and leaf water were found to be −156 ‰ (ranging from −133 to −192 ‰) for εn-alkane/leaf-water and +27.3 ‰ (ranging from +23.0 to 32.3 ‰) for εsugar/leaf-water, respectively. Modelled RHair values from a Craig-Gordon model using measured Tair, δ2Hleaf-water and δ18Oleaf-water as input correlate highly significantly with measured RHair values (R2 = 0.84, p < 0.001, RMSE = 6 %). When coupling δ2Hn-alkane and δ18Osugar values the correlation of modelled RHair values with measured RHair values is weaker but still highly significant with R2 = 0.54 (p < 0.001, RMSE = 10 %). Finally, the reconstructed source water isotope composition (δ2Hs and δ18Os) as calculated from the coupled approach matches the source water in the climate chamber experiment (δ2Htank-water and δ18Otank-water). This highlights the great potential of the coupled δ2Hn-alkane18Osugar paleohygrometer approach for paleoclimate and relative humidity reconstructions.

Johannes Hepp et al.

 
Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

Johannes Hepp et al.

Johannes Hepp et al.

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