Abstract An increasing number of studies from high latitude settings use the stable hydrogen isotope ratio (δ2H) of plant leaf waxes to quantify changes in past precipitation. Calibration of modern vegetation and source water use from these landscapes is important to more accurately reconstruct past hydroclimate variability using sedimentary leaf wax δ2H values. Here, we determine plant-water fractionations from 12 sites along a south-north transect in central Alaska, from Fairbanks to Deadhorse (64-70°N). We characterize the δ2H values of n-alkanes and n-alkanoic acids from modern plants and their xylem and leaf water δ2H values, as well as plant source water using surface soils, a soil core, and previously collected meteoric water data from the region. We find both transpiration (eLW/XW) and biosynthetic (ewax/LW) fractionation are sensitive to environmental controls with latitude, with increased leaf transpiration and biosynthetic fractionation to the north, potentially due to increased summer sunlight hours. Soil water δ2H values show near linear 2H enrichment toward the surface associated with evaporation, with the δ2H value ∼40 cm matching mean annual precipitation (MAP). Average net fractionation was calculated using xylem water and chain length weighted wax δ2H values (ewax/XW) and we find nearly the same mean values for both n-alkanes, −112 ± 27‰, and n-alkanoic acids, −110 ± 23‰, from 12 common high latitude vascular plants. To provide the range of likely net fractionations along this transect, we also calculate the average net fractionation using MAP, finding values are less negative than using xylem waters (ewax/MAP, −89 ± 28‰ for n-alkanes, and −86 ± 24‰ for n-alkanoic acids). To compare across studies, we determined the average ewax/MAP of n-alkanes from all available high latitude calibration studies and found more 2H enriched (smaller fractionations) for C27 (-87 ± 29‰), C29 (-87 ± 32‰), and C31 (-91 ± 31‰) than those of global ewax/MAP homolog averages. This new work in Alaska contributes to our growing understanding of plant water-wax fractionation in the high latitudes and is potentially important for the use of sedimentary δ2H values for paleoprecipitation estimates.

中文翻译：

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阿拉斯加北部-苔原横断面现代植物中的氢同位素分馏

摘要 越来越多来自高纬度地区的研究使用植物叶蜡的稳定氢同位素比 (δ2H) 来量化过去降水的变化。从这些景观中校准现代植被和源水使用对于使用沉积叶蜡 δ2H 值更准确地重建过去的水文气候变化非常重要。在这里，我们确定了阿拉斯加中部从费尔班克斯到戴德霍斯 (64-70°N) 沿南北横断面的 12 个地点的植物-水分馏。我们表征了现代植物中正构烷烃和正构烷酸的 δ2H 值及其木质部和叶水 δ2H 值，以及使用表层土壤、土壤核心和先前从该地区收集的大气水数据的植物源水。我们发现蒸腾作用 (eLW/XW) 和生物合成 (wax/LW) 分馏对纬度的环境控制很敏感，北方的叶子蒸腾作用和生物合成分馏增加，这可能是由于夏季日照时间增加。土壤水 δ2H 值显示出与蒸发相关的表面近线性 2H 富集，δ2H 值 ~40 cm 与平均年降水量 (MAP) 匹配。使用木质部水和链长加权蜡 δ2H 值 (ewax/XW) 计算平均净分馏，我们发现正构烷烃 -112 ± 27‰ 和正链烷酸 -110 ± 23 的平均值几乎相同‰，来自12种常见的高纬度维管植物。为了提供沿该断面可能的净分馏范围，我们还使用 MAP 计算平均净分馏，发现值比使用木质部水（蜡/MAP，正构烷烃为-89±28‰，正链烷酸为-86±24‰）的负面影响小。为了比较研究，我们从所有可用的高纬度校准研究中确定了正构烷烃的平均蜡/MAP，并发现 C27 (-87 ± 29‰)、C29 (-87 ± 32‰) 更多的 2H 富集（较小的分馏） , 和 C31 (-91 ± 31‰) 比全球蜡/MAP 同系物平均值高。阿拉斯加的这项新工作有助于我们加深对高纬度地区植物水蜡分馏的了解，并且对于使用沉积 δ2H 值进行古沉淀估计具有潜在的重要意义。我们从所有可用的高纬度校准研究中确定了正构烷烃的平均蜡/MAP，发现 C27 (-87 ± 29‰)、C29 (-87 ± 32‰) 和 C31 (- 91 ± 31‰) 比全球 ewax/MAP 同系物平均值高。阿拉斯加的这项新工作有助于我们加深对高纬度植物水蜡分馏的理解，并且对于使用沉积 δ2H 值进行古沉淀估计具有潜在的重要意义。我们从所有可用的高纬度校准研究中确定了正构烷烃的平均蜡/MAP，发现 C27 (-87 ± 29‰)、C29 (-87 ± 32‰) 和 C31 (- 91 ± 31‰) 比全球 ewax/MAP 同系物平均值高。阿拉斯加的这项新工作有助于我们加深对高纬度地区植物水蜡分馏的了解，并且对于使用沉积 δ2H 值进行古沉淀估计具有潜在的重要意义。