Collaborative Research: Timescales and drivers of floodplain disequilibrium at climatic transitions

该奖项的全部或部分资金根据《2021 年美国救援计划法案》（公法 117-2）提供。河流和洪泛区对其所经过的景观和环境产生重大影响。这些系统表现出一系列的形式和特征（形态），这些形式和特征（形态）由松散岩石（沉积物）的可用性和河流输送沉积物的能力之间的平衡控制。由于气候对这些变量起着主要控制作用，随着地球气候变暖，洪泛区的形态预计将发生重大变化。在气候变暖的情况下，沉积物供应量通常会相对于运输能力而下降，而泛滥平原的特点是垂直切割较旧的沉积物，形成称为河流阶地的阶梯式景观特征。这项研究的目的是加深我们对洪泛区如何应对过去不同程度和时间尺度的气候变化的理解，以增强我们预测未来变化程度的能力。这一目标将通过确定河流阶地形成的时间并将其与地球近代地质历史中已知的气候变化进行比较来实现。该项目还支持为来自历史上代表性不足的群体的中学生举办关于景观演变的夏季研讨会，开发一个关于梯田形成的易于理解的本科生虚拟实地项目，以及促进社区实地研讨会分享项目结果。具体的研究问题包括：（1）需要多长时间和强度的气候变化才能推动洪泛区形态的重大变化？ (2) 在气候驱动的重大变化之后，洪泛区需要多长时间才能建立新的、稳定的形态？ (3) 非气候机制在多大程度上抵消或加强气候对洪泛区过程的控制？这些问题将通过解决苏格兰东部河流阶地中保存的约 14,000 年洪泛区扩张和退化的时间，并将其与主要和次要气候转变和冰川作用的时间进行比较来解决。苏格兰东部是开展这项工作的理想地点，因为它的构造不活跃，具有良好的气候年代学，经历了大陆冰盖和高山冰川作用，并且包含河流阶地序列。平台年代学将利用放射性碳、光激发光和宇宙成因核素暴露测年法来开发。将比较具有相同气候和冰川历史但具有不同流域特性的实地地点之间河流形态变化的时间和持续时间，以确定非气候变量如何影响侵蚀和退化循环。该研究还将探讨先前冰川侵蚀对影响洪泛区形态和现代沉积物路径的作用。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Rivers and floodplains significantly influence the landscapes and environments through which they pass. These systems exhibit a range of forms and characteristics (morphologies) controlled by a balance between the availability of unconsolidated rock (sediment) and the river’s capacity to transport that sediment. As climate exerts a major control on these variables, floodplain morphologies are expected to undergo major changes as Earth’s climate warms. Under a warming climate, sediment supply often declines relative to transport capacity and narrowing floodplains are characterized by vertical cutting through older deposits creating stair-stepped landscape features called river terraces. The goal of this study is to deepen our understanding of how floodplains have responded to different magnitudes and timescales of climatic changes in the past to enhance our ability to predict the extent to which they will change in the future. This goal will be achieved by determining the timing of river terrace formation and comparing it to known climate shifts throughout Earth’s recent geological past. The project also supports a summer workshop on landscape evolution for middle school girls from historically underrepresented groups, the development of an accessible undergraduate virtual field project on terrace formation, and the facilitation of a community field workshop to share project results.Specific research questions include: (1) What duration and intensity of climatic change is required to drive significant changes to floodplain morphology? (2) How long does it take for floodplains to establish new, stable morphologies after significant climate-driven changes? (3) To what extent do non-climatic mechanisms counter or enhance climatic controls on floodplain processes? These questions will be addressed by resolving the timing of ~14,000 years of floodplain aggradation and degradation preserved in river terraces in eastern Scotland and comparing them against the timing of major and minor climatic transitions and glaciations. Eastern Scotland is an ideal location to undertake this work because it is tectonically inactive, has an excellent climate chronology, has undergone both continental ice sheet and alpine glaciation, and contains river terrace successions. The terrace chronology will be developed using radiocarbon, optically stimulated luminescence, and cosmogenic nuclide exposure dating. A comparison of the timing and duration of river morphology changes between field sites with the same climatic and glacial history, but with different catchment properties, will be undertaken to determine how non-climatic variables influence aggradation and degradation cycles. The research will also address the role of prior glacial erosion on influencing floodplain morphology and modern sediment routing.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.