Coupling δ<sup>2</sup>H and δ<sup>18</sup>O biomarker results yields information on relative humidity and isotopic composition of precipitation – a climate transect validation study

Abstract

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" δ2Hδ18O values of leaf water (δ2Hδ18Oleaf 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 δ2Hδ18Oprecipitation 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 δ2Hδ18Oprecipitation values correlate highly significantly with actual RH and δ2Hδ18Oprecipitation values. We conclude that compared to single δ2Hn-alkane or δ18Osugar records, the proposed coupled δ2Hn-alkane–δ18Osugar biomarker approach will allow more robust δ2Hδ18Oprecipitation 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.

The effect of 18O‐labelled water vapour on the oxygen isotope ratio of water and assimilates in plants at high humidity

“…Finally, our findings have important implications for ecophysiological and hydrological sciences using oxygen (and potentially also hydrogen) isotopes of various plant biomarkers such as cellulose, hemicellulose and n‐alkanes to decipher temporally and spatially integrated information about past environmental conditions and associated plant functional responses (Hepp et al ., ; Tuthorn et al ., ). This is especially important for organic molecules derived from plants, sediments, or soils in regions and seasons that experience high humidity conditions (e.g.…”

Don-alkane biomarkers in soils/sediments reflect theδ2H isotopic composition of precipitation? A case study from Mt. Kilimanjaro and implications for paleoaltimetry and paleoclimate research

“…Also climatically driven changes of deuterium content in local precipitation as well as changes of temperature with altitude need to be taken into account. A way out of this dilemma could be a coupled δ 2 H-δ 18 O approach in terrestrial and lacustrine paleoclimate studies as suggested by Zech et al [67], Hepp et al [82] and Tuthorn et al [83].…”

Leaf Wax δD and δ13C in Soils Record Hydrological and Environmental Information Across a Climatic Gradient in Israel

“…However, individual plants show considerable δ 13 C wax and δD wax variability even within species or plant functional type, and thus, plant δ 13 C wax and δD wax distributions contain significant variability uncorrelated with environmental parameters (e.g., Sachse et al, 2012). The n-alkanes are durable molecules; they withstand weathering and to some extent bacterial degradation (e.g., Chikaraishi & Naraoka, 2006;Nguyen Tu et al, 2011;Pond et al, 2002;Tuthorn et al, 2015;Zech et al, 2011), and are incorporated into the sedimentary cycle and accumulate in soils and lakes (e.g., Lichtfouse et al, 1998;Pedentchouk et al, 2006). Throughout this process, leaf waxes are integrated over space and time, and soil δ 13 C wax and δD wax variability is reduced.…”