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

在地球上的许多地区，全球变暖和相关的水文循环变化影响了河流径流总量以及洪水的频率和强度。流量的变化可能会立即影响河流的运输能力，但气候变化如何影响丘陵沉积物的供应还不是很清楚。在这个项目中，我们想要测量印度亚穆纳河填充物阶地中的宇宙成因核素浓度，以确定山坡侵蚀速率的时间变化，并揭示喜马拉雅地区快速侵蚀的景观是如何对过去的气候变化做出反应的。我们将在野外测绘和地形建模的基础上，对山谷填充物的几何形状和体积进行重建，以补充我们的地球化学方法。几何重建使我们能够评估泥沙储存量的空间分布和纵向河道剖面的时间变化，这影响了输沙能力。此外，我们将使用不同的年代学方法获得沉积-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，推断沉积物的来源和成因，并基于叶蜡的稳定同位素进行古水文重建。这些数据，结合我们的体积估算和山坡的侵蚀历史，使我们能够重建随时间变化的沉积物预算，并绘制出山谷退化期间环境条件的全面图景，并测试喜马拉雅景观如何响应气候变化的现有模型。该项目的预期结果将有助于评估当前气候变化的影响，并评估第四纪气候波动对喜马拉雅地区侵蚀的影响以及对晚新生代气候变化的假设反馈。

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.