Abstract The hydrogen isotopic composition (δ2H values) of plant waxes preserved in the sedimentary record is a useful proxy for past hydroclimate, but a number of known biological and environmental factors can confound the climate signal this proxy records. High-latitude ecology and environmental conditions differ from those of the better-studied low latitudes, and the influence of arctic conditions on factors that affect δ2H records of climate is poorly constrained. Direct observations of arctic plant waxes and their δ2H values, particularly from aquatic plants, are very limited. Here we present a study of n-alkane and n-alkanoic acid homologue distributions, δ2H values, and δ13C values from west Greenland, including measurements of terrestrial and aquatic plants, algae, and Nostoc (colonial cyanobacteria). By examining samples collected from the same region and season, we focus on climate-independent factors that may affect the δ2H values of sedimentary plant waxes. We observe that the average abundance of leaf n-alkyl lipids (C20-C31) in common terrestrial plants from this region exceeds that in aquatic sources by up to 30×. We also note weaker source specificity in n-alkanoic acids than in n-alkanes. A comparison of these data with surface sedimentary plant waxes from a lake within the study area, previously reported by McFarlin et al. (2019), indicates that at this site both mid-chain and long-chain sedimentary waxes are likely to derive from dominantly terrestrial sources, particularly biased towards the genus Salix. Abundance-weighted isotope data reveal that while terrestrial plants show taxonomic trends in δ2H values, the amplitude of these trends is unlikely to exceed the error of the proxy (the standard deviation on calculated eapp). n-Alkane eapp values are more variable in aquatic than in terrestrial sources, with median values ranging from −115‰ in n-C31 to −143‰ in n-C21. However, because sedimentary waxes at our study site are most similar to terrestrial plants for all homologues (in isotopic composition and proportional abundance), the large variability in aquatic eapp is unlikely to strongly impact sedimentary wax δ2H values here and in comparable environments. Our findings do not support using comparisons of mid- and long-chain homologues to infer differences between lake water and precipitation without independent validation of the source of mid-chain waxes. Nevertheless, we show that homologue abundance, δ2H values, and δ13C values of sedimentary n-alkanes can inform wax-based reconstructions of paleoclimate at high latitudes. This work provides new insights into the wax contributions from west Greenland plant communities and highlights important areas for future studies of arctic plants and plant wax proxies.

中文翻译：

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格陵兰西部沉积植物蜡记录来源和气候信号的现代约束

摘要 沉积记录中保存的植物蜡的氢同位素组成（δ2H 值）是过去水文气候的有用代表，但许多已知的生物和环境因素可能会混淆该代表记录的气候信号。高纬度生态和环境条件与研究较好的低纬度不同，北极条件对影响气候δ2H记录的因素的影响很少受到约束。对北极植物蜡及其 δ2H 值的直接观察非常有限，特别是来自水生植物。在这里，我们对格陵兰西部的正构烷烃和正构烷酸同系物分布、δ2H 值和 δ13C 值进行了研究，包括对陆生和水生植物、藻类和 Nostoc（菌落蓝藻）的测量。通过检查从同一地区和季节收集的样本，我们关注可能影响沉积植物蜡的 δ2H 值的气候独立因素。我们观察到该地区常见陆生植物的叶正烷基脂质 (C20-C31) 的平均丰度比水生植物高 30 倍。我们还注意到正链烷酸比正链烷烃的来源特异性更弱。将这些数据与来自研究区域内湖泊的表层沉积植物蜡进行比较，先前由 McFarlin 等人报道。(2019)，表明在该地点，中链和长链沉积蜡都可能主要来自陆地来源，特别是偏向于柳属。丰度加权同位素数据显示，虽然陆生植物的 δ2H 值显示出分类趋势，但 这些趋势的幅度不太可能超过代理的误差（计算出的 eapp 的标准偏差）。水生来源的正烷烃 eapp 值比陆地来源的变化更大，中值范围从 n-C31 的 -115‰ 到 n-C21 的 -143‰。然而，由于我们研究地点的沉积蜡与所有同系物的陆生植物最相似（同位素组成和比例丰度），水生 eapp 的巨大变异不太可能强烈影响这里和可比环境中的沉积蜡 δ2H 值。我们的研究结果不支持使用中链和长链同源物的比较来推断湖水和降水之间的差异，而无需独立验证中链蜡的来源。尽管如此，我们表明同源丰度、δ2H 值、沉积正构烷烃的 δ13C 和 δ13C 值可以为高纬度古气候的蜡基重建提供信息。这项工作提供了对西格陵兰植物群落蜡贡献的新见解，并突出了北极植物和植物蜡代理未来研究的重要领域。