Table_1_Leaf Waxes and Hemicelluloses in Topsoils Reflect the δ2H and δ18O Isotopic Composition of Precipitation in Mongolia.XLSX

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 = +44 ± 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 2.2‰ for δ18Oara, so our findings corroborate the great potential of compound-specific δ2Hn–alkane and δ18Oara analyzes for paleohydrological research in Mongolia.

对由叶片蜡衍生出的碳链烷烃（δ2Hn-烷烃）和半纤维素衍生出的阿拉伯糖（δ18Oara）进行特定的氢氧同位素分析，是进行古水文重建的宝贵创新工具。以往的研究校准表明，δ2Hn-烷烃和δ18Oara反映了降水的同位素组成，但根据地区不同，可能受到蒸发蒸腾增强作用的显著调节。鉴于迄今为止在半干旱和干旱的蒙古地区尚无校准研究，我们对沿蒙古地区横断面采集的表层土壤中的δ2Hn-烷烃和δ18Oara进行了分析，并将这些值与降水（δ2Hp-WM和δ18Op-WM，模拟数据）和多种气候参数的同位素组成进行了比较。δ2Hn-烷烃和δ18Oara在横断面干旱的东南部地区更为正值，这反映了该部分降水的2H和18O富集程度也更高。显性分馏系数εapp，即降水与所研究化合物之间的同位素差异，与横断面沿线的气候无强相关性（ε2H n-C29/p = −129 ± 14‰，ε2H n-C31/p = −146 ± 14‰，以及ε18O ara/p = +44 ± 2‰）。我们的结果表明，蒙古表层土壤中的δ2Hn-烷烃和δ18Oara反映了降水的同位素组成，且不受气候的强烈调节。与降水同位素组成的关联，均方根误差分别为δ2Hn-C29的13.4‰，δ2Hn-C31的12.6，以及δ18Oara的2.2‰，因此我们的发现证实了特定化合物δ2Hn-烷烃和δ18Oara分析在蒙古古水文研究中的巨大潜力。