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The oxygen isotopic composition of cellulose is a valuable proxy in paleoclimate research. However, its application to sedimentary archives is challenging due to extraction and purification of cellulose. Here we present compound-specific δ 18 O results of hemicellulose-derived sugar biomarkers determined using gas chromatography–pyrolysis–isotope ratio mass spectrometry, which is a method that overcomes the above-mentioned analytical challenges. The biomarkers were extracted from stem material of different plants ( Eucalyptus globulus , Vicia faba and Brassica oleracea ) grown in climate chamber experiments under different climatic conditions. The δ 18 O values of arabinose and xylose range from 31.4‰ to 45.9‰ and from 28.7‰ to 40.8‰, respectively, and correlate highly significantly with each other ( R = 0.91, p 18 O hemicellulose (mean of arabinose and xylose) correlate highly significantly with δ 18 O leaf water ( R = 0.66, p 18 O cellulose ( R = 0.42, p R = −0.79, p R = −0.66, p 18 O enrichment of leaf water. While relative air humidity controls most rigorously the evapotranspirative 18 O enrichment, the direct temperature effect is less important. However, temperature can indirectly exert influence via plant physiological reactions, namely by influencing the transpiration rate which affects δ 18 O leaf water due to the Peclet effect. In a companion paper (Tuthorn et al., this issue) we demonstrate the applicability of the hemicellulose-derived sugar biomarker δ 18 O method to soils and provide evidence from a climate transect study confirming that relative air humidity exerts the dominant control on evapotranspirative 18 O enrichment of leaf water. Finally, we present a conceptual model for the interpretation of δ 18 O hemicellulose records and propose that a combined δ 18 O hemicellulose and δ 2 H n -alkane biomarker approach is promising for disentangling δ 18 O precipitation variability from evapotranspirative 18 O enrichment variability in future paleoclimate studies. |
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