Quantifying the response of rapidly eroding landscapes to climate change with cosmogenic nuclides

在地球上的许多地区，全球变暖和与之相关的水文循环变化影响着河流总径流量以及洪水的频率和规模。流量的变化可能会立即影响河流的输送能力，但气候变化如何影响山坡的沉积物供应还不是很清楚。在这个项目中，我们想要测量印度亚穆纳河填海梯田中的宇宙核素浓度，以确定山坡侵蚀速率的时间变异性，并揭示喜马拉雅地区快速侵蚀的地貌对过去气候变化的反应。我们将在野外测绘和地形建模的基础上，通过重建山谷填充物的几何形状和体积来补充我们的地球化学方法。通过几何重建，我们可以评估影响输沙能力的纵向河道剖面中泥沙储量的空间分布和时间变化。此外，我们将使用不同的地质年代学方法来获得沉积和切割旋回的准确年代学，并将这些数据与沉积学观测相结合，以推断沉积物的来源和来源，并结合基于树叶蜡中稳定同位素的古水文重建。这些数据，结合我们的体积估计和山坡的侵蚀历史，使我们能够重建随时间推移的沉积物收支平衡，绘制山谷沉积期间环境条件的综合图景，并测试喜马拉雅景观如何对气候变化做出反应的现有模型。该项目的预期成果将有助于评估当今气候变化的影响，以及评估第四纪气候波动对喜马拉雅地区侵蚀的影响以及假定的对新生代晚期气候变化的反馈。

In many regions on Earth, Global Warming and the associated changes in the hydrological cycle affect total river runoff and the frequency and magnitude of floods. Changes in discharge are likely to immediately affect the transport capacity of rivers, but how climatic changes affect the supply of sediments from hilllopes is not well understood. In this project, we want to measure cosmogenic nuclide concentrations in fill terraces of the Yamuna River, India, to determine the temporal variability of hillslope erosion rates and to unravel how a rapidly eroding landscape in the Himalaya has responded to climatic changes in the past. We will supplement our geochemical approach with a reconstruction of the geometry and volume of the valley fill, based on field mapping and topographic modeling. The geometrical reconstruction allows us to assess the spatial distribution of sediment storage and temporal changes in the longitudinal channel profile, which affects the sediment transport capacity. Furthermore, we will use different geochronological methods to obtain an accurate chronology of the aggradation-and-incision cycle, and combine these data with sedimentological observations for inferring the source and origin of the sediments, and with paleo-hydrologic reconstructions based on stable isotopes in leaf waxes. These data, combined with our volume estimate and the erosional history of hillslopes, allow us to reconstruct the sediment budget through time and draw a comprehensive picture of the environmental conditions during the period of valley aggradation and to test existing models of how Himalayan landscapes respond to climate change. The expected results of this project will help assessing the impacts of present-day climate change, and evaluating the consequences of Quaternary climate fluctuations for erosion in the Himalaya and the postulated feedbacks on Late Cenozoic climate change.