Abstract Plant-derived n-alkyl lipids are well-preserved in sedimentary archives, and their stable hydrogen isotope ratio (δDwax) is a proxy for precipitation δD and climate. Net fractionation of H isotopes between plant source water and n-alkyl lipids (ewax/water) is the largest uncertainty for interpreting this proxy and depends on plant type and environment. Although popular proxies, n-alkanoic acids (n-acids) are less frequently calibrated in modern environments than n-alkanes. We constrain the net fractionation (ewax/MAP – Mean Annual Precipitation) for the northern boreal forest based on n-C24,26,28 acids in topsoils from a 13-site network in Yukon, Alaska and Northwest Territories (60–68°N). n-Acid homologue distributions for common boreal plants (gymnosperm trees, shrubs, forbs, C3 grasses and mosses) show that soil n-acids are dominated by mosses, but with a reduced carbon preference index compared to fresh mosses, possibly owing to post-depositional degradation. Regionally averaged ewax/MAP values are −93 ± 10‰, −101 ± 11‰ and −95 ± 11‰ for n-C24,26,28 acids, respectively, which are similar to values reported from low and high latitude regions. We find that ewax/MAP for n-C26,28 acids (but not n-C24) is significantly (p ≤ 0.05) smaller with increasing latitude and decreasing mean annual temperature, factors that covary across our network. Since latitude is typically known for ancient deposits, we parsed the dataset to obtain latitude-specific ewax/MAP values for 60–64°N (−107 ± 8‰ for n-C26; and −101 ± 8‰ for n-C28) and 65–68°N (−94 ± 11‰ for n-C26; and −89 ± 10‰ for n-C28). These soil-derived values are relevant for hydroclimate reconstructions using fossil n-acids in paleosols from a comparable paleoflora and latitude.

中文翻译：

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北方北方森林土壤中正链烷酸中氢同位素的净分馏

摘要 植物来源的正烷基脂质在沉积档案中保存完好，其稳定的氢同位素比（δDwax）是降水δD和气候的代表。植物源水和正烷基脂质（蜡/水）之间 H 同位素的净分馏是解释该代理的最大不确定性，取决于植物类型和环境。尽管流行的代理，正链烷酸（n-酸）在现代环境中的校准频率低于正链烷烃。我们根据来自育空、阿拉斯加和西北地区 (60–68°N) 的 13 个站点的表土中的 n-C24,26,28 酸来限制北方北方森林的净分馏（蜡/MAP – 平均年降水量） ）。常见北方植物（裸子植物、灌木、杂种、C3 草和苔藓）表明土壤 n-酸以苔藓为主，但与新鲜苔藓相比，碳偏好指数降低，可能是由于沉积后降解。n-C24、26、28 酸的区域平均蜡/MAP 值分别为-93 ± 10‰、-101 ± 11‰ 和-95 ± 11‰，与低纬度和高纬度地区报告的值相似。我们发现 n-C26,28 酸（但不是 n-C24）的 ewax/MAP 随着纬度的增加和年平均温度的降低而显着（p ≤ 0.05）更小，这些因素在我们的网络中是共变的。由于纬度通常以古代沉积物而著称，因此我们解析了数据集以获得 60–64°N 的纬度特定 ewax/MAP 值（n-C26 为 -107±8‰；n-C28 为 -101±8‰）和 65–68°N（n-C26 为 -94 ± 11‰；n-C28 为 -89 ± 10‰）。