Dual isotope evidence for sedimentary integration of plant wax biomarkers across an Andes-Amazon elevation transect
Dual isotope evidence for sedimentary integration of plant wax biomarkers across an Andes-Amazon elevation transect
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DOI：
10.1016/j.gca.2018.09.007
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发表时间：
2018-12
影响因子：
5
通讯作者：
S. Feakins;Mong Sin Wu;C. Ponton;V. Galy;A. West
中科院分区：
文献类型：
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作者：
S. Feakins;Mong Sin Wu;C. Ponton;V. Galy;A. West
热带山地地区的降水、生物生产、侵蚀和沉积物输出的速率往往很高，这些因素共同将物质从地貌中转移到下游的沉积沉积物中。植物蜡生物标志物可以用来研究有机质的来源，并经常被用来替代沉积矿床中过去的气候和环境。为了了解植物蜡是如何从潮湿的热带山地集水区获得的，我们测量了沿海拔样带的土壤中正构烷烃和正构烷酸的稳定碳和氢同位素组成(δ13C和δD)，以及秘鲁安第斯山脉东侧马德雷·德迪奥斯河网内的沉积物，排水面积为75,400 km2和6 公里。土壤产生了植物蜡δ13C(C29n-烷烃和C30n-烷酸在矿物层中分别为+1.75和+1.31‰Km−1)和δD值(分别为−10和−12‰Km−1)在3.5 公里海拔样带上的系统趋势，这与以前从树冠叶中报道的趋势相似，尽管我们在植物和土壤中发现了δ13C值之间的偏差。河流悬浮沉积物在雨季一般遵循集水高程(C29n-烷烃和C30n-烷酸的δ13C：+1.03和+0.99‰Km−1和δD：−10到−7‰Km−1)定义的土壤同位素梯度，在旱季下降，限制较少。在少数河流悬浮物中，成岩贡献和深度分选影响当时烷烃的δ13C信号。我们的双同位素、双化合物类和季节性采样方法显示，在植物蜡质出口方面没有安第斯优势，相反，在这个非常潮湿、森林覆盖的集水区，植物蜡质的来源与上游集水区的空间整合预期大致相同，因此在面积上具有低地优势，指导热带山地地区的古环境重建。双同位素方法提供了对高度信号的交叉核对，并可以解决可能与古气候记录中的植被变化或干旱有关的模糊性。此外，植物蜡中编码的海拔效应为古高程测量提供了一种新的双同位素生物标志物方法。
Tropical montane regions tend to have high rates of precipitation, biological production, erosion, and sediment export, which together move material off the landscape and toward sedimentary deposits downstream. Plant wax biomarkers can be used to investigate sourcing of organic matter and are often used as proxies to reconstruct past climate and environment in sedimentary deposits. To understand how plant waxes are sourced within a wet, tropical montane catchment, we measure the stable C and H isotope composition (δ13C andδD) ofn-alkanes andn-alkanoic acids in soils along an elevation transect and from sediments within the Madre de Dios River network along the eastern flank of the Peruvian Andes, draining an area of 75,400 km2and 6 km of elevation. Soils yield systematic trends in plant waxδ13C (+1.75 and +1.31‰ km−1, for the C29n-alkanes and C30n-alkanoic acids respectively in the mineral horizon) andδD values (−10 and −12‰ km−1, respectively) across a 3.5 km elevation transect, which approximates trends previously reported from canopy leaves, though we find offsets betweenδ13C values in plants and soils. River suspended sediments generally follow soil isotopic gradients defined by catchment elevations (δ13C: +1.03 and +0.99‰ km−1andδD: −10 to −7‰ km−1, for the C29n-alkanes and C30n-alkanoic acids respectively) in the wet season, with a lowering in the dry season that is less well-constrained. In a few river suspended sediments, petrogenic contributions and depth-sorting influence then-alkaneδ13C signal. Our dual isotope, dual compound class and seasonal sampling approach reveals no Andean-dominance in plant wax export, and instead that the sourcing of plant waxes in this very wet, forested catchment approximates that expected for spatial integration of the upstream catchment, thus with a lowland dominance on areal basis, guiding paleoenvironmental reconstructions in tropical montane regions. The dual isotope approach provides a cross-check on the altitudinal signals and can resolve ambiguity such as might be associated with vegetation change or aridity in paleoclimate records. Further, the altitude effect encoded within plant waxes presents a novel dual-isotope biomarker approach to paleoaltimetry.