Data_Sheet_2_Leaf Waxes and Hemicelluloses in Topsoils Reflect the δ2H and δ18O Isotopic Composition of Precipitation in Mongolia.DOCX

Compound-specific hydrogen and oxygen isotope analyzes on leaf wax-derived n-alkanes (δ2Hn–alkane) and the hemicellulose-derived sugar arabinose (δ18Oara) are valuable, innovative tools for paleohydrological reconstructions. Previous calibration studies have revealed that δ2Hn–alkane and δ18Oara reflect the isotopic composition of precipitation, but – depending on the region – may be strongly modulated by evapotranspirative enrichment. Since no calibration studies exist for semi-arid and arid Mongolia so far, we have analyzed δ2Hn–alkane and δ18Oara in topsoils collected along a transect through Mongolia, and we compared these values with the isotopic composition of precipitation (δ2Hp–WM and δ18Op–WM, modeled data) and various climate parameters. δ2Hn–alkane and δ18Oara are more positive in the arid south-eastern part of our transect, which reflects the fact that also the precipitation is more enriched in 2H and 18O along this part of the transect. The apparent fractionation εapp, i.e., the isotopic difference between precipitation and the investigated compounds, shows no strong correlation with climate along the transect (ε2H n–C29/p = −129 ± 14‰, ε2H n–C31/p = −146 ± 14‰, and ε18O ara/p = +41 ± 2‰). Our results suggest that δ2Hn–alkane and δ18Oara in topsoils from Mongolia reflect the isotopic composition of precipitation and are not strongly modulated by climate. Correlation with the isotopic composition of precipitation has root-mean-square errors of 13.4‰ for δ2Hn–C29, 12.6 for δ2Hn–C31, and 1.2‰ for δ18Oara, so our findings corroborate the great potential of compound-specific δ2Hn–alkane and δ18Oara analyzes for paleohydrological research in Mongolia.

针对叶蜡源正构烷烃（n-alkanes）的化合物特异性氢同位素分析（δ²Hₙ–alkane）以及半纤维素源糖阿拉伯糖（δ¹⁸Oₐᵣₐ），是古水文重建领域极具应用价值的创新性技术手段。既往校准研究表明，δ²Hₙ–alkane与δ¹⁸Oₐᵣₐ可反映降水的同位素组成，但受区域差异影响，其信号或会受到蒸发蒸腾富集作用的强烈调控。鉴于迄今尚无针对半干旱与干旱蒙古地区的相关校准研究，本研究对沿蒙古样带采集的表层土壤中的δ²Hₙ–alkane与δ¹⁸Oₐᵣₐ进行了分析，并将测得值与降水同位素组成（δ²Hₚ–WM与δ¹⁸Oₚ–WM，均为模型数据）及多项气候参数开展对比。在样带干旱的东南部区域，δ²Hₙ–alkane与δ¹⁸Oₐᵣₐ的数值更为偏正，这一现象反映出该区域降水的²H与¹⁸O富集程度同样更高。表观分馏εapp（即降水与目标化合物间的同位素差值）沿样带未表现出与气候的显著相关性：ε²Hₙ–C29/p = −129 ± 14‰，ε²Hₙ–C31/p = −146 ± 14‰，ε¹⁸Oₐᵣₐ/p = +41 ± 2‰。本研究结果表明，蒙古地区表层土壤中的δ²Hₙ–alkane与δ¹⁸Oₐᵣₐ可直接反映降水的同位素组成，且未受到气候因素的强烈调控。δ²Hₙ–C29、δ²Hₙ–C31与降水同位素组成的相关分析均方根误差分别为13.4‰、12.6‰及1.2‰，因此本研究结果证实，化合物特异性δ²Hₙ–alkane与δ¹⁸Oₐᵣₐ分析技术在蒙古地区古水文研究中具备巨大应用潜力。