Landscape sensitivity to past and future climate: Solving the intermittency puzzle

了解气候变化如何影响塑造地球表面的侵蚀过程是地球科学家的一个关键目标。流域水通量和沉积物输运的不稳定性的限制很少，但在实现这一目标方面至关重要。现有的数据表明，满岸泥沙输移率，如果持续下去，将意味着千年沉积通量的数量级大于沉积档案或侵蚀估计中观察到的。因此，在一个变暖的世界里，风暴的增加会导致河流运输的不稳定性略有下降，这可能会大大增加侵蚀率和沉积物的输出。该项目旨在通过综合利用现代河流的实地数据、地质地层学和数值模拟来解决“不透明度难题”，从而为景观和沉积物路径系统对环境变化的敏感性提供新的限制：1）使用希腊现代集水区的约束条件，学生将计算河岸泥沙输运能力和水流量，使用已发表的和新的测量集水区几何形状和沉积物粒度。之所以选择这个地方，是因为它的半干旱气候是很好的研究，因为在科林斯地区的IODP数据具有独特的约束全新世沉积速率与特殊的保真度。通量估计值将与全新世沉积量和集水区平均侵蚀率估计值进行比较，以计算实际沉积通量与潜在岸流通量的比率，如果它们在同一时期持续存在的话-即沉积物输移通量比率。这些沉积物迁移率将直接与目前的降雨分布和关于风暴事件频率的历史数据进行比较。2)这些现代数据集将与干旱系统的地质实例进行严格比较。我们将重点关注始新世河流沉积-新生代最温暖的时代。在西班牙比利牛斯山脉研究良好的范例将被选为比较。这些系统具有已知的沉积体积和保存完好的河道结构，能够重建满岸流条件。沉积物输运的不稳定性将比较中，晚始新世的气候重建和现代的例子。3)最后，学生将使用一个耦合模型的集水盆地系统，在帝国开发与外部合作者布鲁克，其中包括降雨的不稳定性和渗透阈值，模拟沉积物路由系统响应降雨量的变化。将利用上述地质数据校准关键输入，预测未来一系列情景下降雨/风暴的演变情况，对合成景观演变和侵蚀通量进行正演模拟。研究结果将用于解决不稳定性难题，并确定流域对增强风暴的脆弱性。

Understanding how changing climate affects erosional processes that shape the planet's surface is a key goal for geoscientists. Constraints on the intermittency of water flux and sediment transport in catchments are rare, but are of critical importance in reaching this goal. The data that exist indicate that bankful sediment transport rates, if sustained, would imply millennial sediment fluxes orders of magnitude greater than that observed in depositional archives or from erosional estimates. Consequently, small reductions in the intermittency of fluvial transport, caused by enhanced storminess in a warming world, could significantly enhance erosion rates and sediment export. This project aims to solve the 'intermittency puzzle' by using a combination of field data from modern rivers; geological stratigraphy; and numerical modelling to provide new constraints on landscape and sediment routing system sensitivity to environmental change: 1) Using well constrained modern catchments in Greece, the student will calculate bankfull sediment transport capacities and water discharges, using published and new measurements of catchment geometry and sediment grain size. This locality is selected because its semi-arid climate is well-studied and because IODP data in the Corinth area have uniquely constrained Holocene sedimentation rates with exceptional fidelity. Flux estimates will be compared with Holocene depositional volumes and catchment average erosion rate estimates to calculate the ratio of actual sediment fluxes to potential bankful fluxes, were they to be sustained over the same time period - the sediment transport intermittency ratio. These sediment transport intermittencies will be directly compared with the present-day distribution of rainfall and historical data on the frequency of storm events. 2) These modern data sets will be compared critically to geological examples of arid systems. We will focus on Eocene fluvial deposits - the warmest Epoch of the Cenozoic. Well-studied exemplars in the Spanish Pyrenees will be selected as comparators. These systems have known depositional volumes, and well preserved channel architectures which enable bankful flow conditions to be reconstructed. Sediment transport intermittency will be compared to climate reconstructions for the mid and late Eocene and to modern examples. 3) Finally, the student will use a coupled model of a catchment-basin system, developed at Imperial with external collaborator Brooke, which includes rainfall intermittency and an infiltration threshold, to model sediment routing system response to rainfall variability. Predictions of how rainfall/storminess may evolve in the future for a range of scenarios will be used to forward model synthetic landscape evolution and erosional fluxes, using the geological data above to calibrate key inputs. The results will be used to solve the intermittency puzzle and identify catchment vulnerability to enhanced storminess.