Sediment residence time reveals Holocene shift from climatic to vegetation control on catchment erosion in the Balkans
Sediment residence time reveals Holocene shift from climatic to vegetation control on catchment erosion in the Balkans
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DOI：
10.1016/j.gloplacha.2019.04.005
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发表时间：
2019-06-01
影响因子：
3.9
通讯作者：
Leng, Melanie J.
中科院分区：
文献类型：
--
作者：
Francke, Alexander;Dosseto, Anthony;Leng, Melanie J.
了解土壤系统在地质时间尺度上的演变，对于预测未来景观发展具有根本重要性，因为全球变暖和人类活动的影响日益加剧。在这里，我们使用一种创新的铀同位素为基础的技术相结合的有机碳同位素和元素比率的沉积物从奥赫里德湖（北马其顿/阿尔巴尼亚）重建土壤系统的演变在湖泊的集水区在过去类似于16,000卡年BP。铀同位素被用来估计古沉积物的停留时间，定义为粉砂和粘土大小的碎屑物质的形成和最终沉积之间经过的时间。年表是基于新的隐石层在沉积序列中确定。将同位素和元素数据与来自相同样品材料的沉积特性和花粉进行比较，以根据气候强迫、植被发展和人为土地利用，更好地了解过去的流域侵蚀和景观演变。在晚冰期和全新世早期，当大部分流域被开阔的植被覆盖时，潮湿的气候促进了碎屑物质的流动，古沉积物停留时间较短。这是由于风化层较深部分被薄土侵蚀所致。碎屑物质与较长的古沉积物的停留时间，说明较厚的土壤浅侵蚀沉积在干燥的气候。气候变化和土壤侵蚀之间的耦合终止于早全新世中期过渡的铀同位素比值的显着变化表明，集水区的侵蚀主要是由浅侵蚀厚的土壤。这种变化表明，在山坡侵蚀的门槛是跨越，可能是由于植被覆盖的重大变化，防止在较高海拔的薄土壤的深度侵蚀。流域侵蚀的阈值并不反映随着时间的推移，土壤发育，逐渐增加，在晚冰期至全新世变暖，直到人类的土地利用在晚全新世促进减少土壤发育和土壤退化。总的来说，我们观察到，土壤系统的演变是逐步控制气候，植被，并最终由人类土地利用在过去类似的16,000年。
Understanding the evolution of soil systems on geological time scales has become fundamentally important to predict future landscape development in light of rapid global warming and intensifying anthropogenic impact. Here, we use an innovative uranium isotope-based technique combined with organic carbon isotopes and elemental ratios of sediments from Lake Ohrid (North Macedonia/Albania) to reconstruct soil system evolution in the lake's catchment during the last similar to 16,000 cal yr BP. Uranium isotopes are used to estimated the paleosediment residence time, defined as the time elapsed between formation of silt and clay sized detrital matter and final deposition. The chronology is based on new cryptotephra layers identified in the sediment sequence. The isotope and elemental data are compared to sedimentary properties and pollen from the same sample material to provide a better understanding of past catchment erosion and landscape evolution in the light of climate forcing, vegetation development, and anthropogenic land use.During the Late Glacial and the Early Holocene, when wide parts of the catchment were covered by open vegetation, wetter climates promoted the mobilisation of detrital matter with a short paleo-sediment residence time. This is explained by erosion of deeper parts of the weathering horizon from thin soils. Detrital matter with a longer paleo-sediment residence time, illustrating shallow erosion of thicker soils is deposited in drier climates. The coupling between climatic variations and soil erosion terminates at the Early to Mid-Holocene transition as evidenced by a pronounced shift in uranium isotope ratios indicating that catchment erosion is dominated by shallow erosion of thick soils only. This shift suggests a threshold is crossed in hillslope erosion, possibly as a result of a major change in vegetation cover preventing deep erosion of thin soils at higher elevation. The threshold in catchment erosion is not mirrored by soil development over time, which gradually increases in response to Late Glacial to Holocene warming until human land use during the Late Holocene promotes reduced soil development and soil degradation. Overall, we observe that soil system evolution is progressively controlled by climatic, vegetation, and eventually by human land use over the last similar to 16,000 years.