Ocean process-driven sediment transport in submarine canyons along the northern Cascadia margin: Morphological control of triggers

“卡斯卡迪亚北部边缘海底峡谷中海洋过程驱动的沉积物运输：触发因素的形态控制”海底峡谷充当沿海和深海之间的主要公路，输送足够的水、营养物质和沉积物，对地质、生物和气候产生全球影响。就像陆地上的峡谷一样，海底峡谷是巨大的、被侵蚀的山谷，但它们不是被河流雕刻出来的。取而代之的是，海底峡谷是由类似雪崩的泥沙和水流向下流动形成的。科学家们在预测这些流动的开始和行进距离方面面临挑战。该项目旨在确定华盛顿海岸外这些水流的物理过程，并了解峡谷结构的差异如何影响总体上的水流。将在两个海底峡谷安装一套海底仪器，以记录沉积物重力流通过它们时的情况。这些数据非常罕见，极大地有助于理解流动力学，并使开发预测流动发生地点和时间的数值模型成为可能。将在阿斯托里亚峡谷和奎诺峡谷维护六个海底仪器包，这两个峡谷都由哥伦比亚河供应，为期一整年。将从两个峡谷收集沉积物岩心，在那里将识别和分析来自过去沉积物-重力流的事件层，以确定它们的组成和历史频率。研究人员预测，河流洪水和海洋风暴事件(大浪、大风)可能会在今天引发这些峡谷的主要沉积物重力流，但峡谷地形的差异在不同条件下会触发沉积物重力流。海底峡谷几乎存在于每个大陆边缘，是全球重要的海洋混合、沉积物输送以及沿海和深海环境之间营养交换的场所。地球上的海底峡谷是由密度驱动的水和沉积物流动维持的，但触发流动的机制-及其向下流动的演变-仍然没有被很好地理解。这个项目考察了沿卡斯卡迪亚边缘的两个峡谷的沉积路径，这两个峡谷在形态上截然不同，但拥有相同的河流来源--哥伦比亚河。这项研究的实验设计包括有针对性的仪器部署、全面的海底取心调查和沉积物重力流动的水动力学模拟。该项目旨在增进对现代海平面高位下峡谷沉积过程的了解，并限制地形和海洋扰动在引发海底再悬浮和密度驱动水流方面的作用。在Astoria和Quinault峡谷，将研究来自河流来源的海底沉积物负荷、通过波和流能量的水深聚焦触发水流以及跨越远处峡谷系统的同步下坡输送作为峡谷地形的函数。研究人员预测，相对深水峡谷环境中的沉积沉积可能是通过海洋触发形成的，目的是对这种流动的下坡极限施加定量限制。他们还预测，不同峡谷形态的过程会导致沉积物在区域上同步和异步地分布在深处。这一裁决反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

“Ocean process-driven sediment transport in submarine canyons along the northern Cascadia margin: Morphological control of triggers”Submarine canyons act as a major highway between the coastal and deep ocean, transporting enough water, nutrients, and sediment to have a global impact on geology, biology, and climate. Just like canyons on land, submarine canyons are large, eroded valleys, but they are not carved by rivers. Instead, submarine canyons are carved by downslope-flowing currents of sediment and water akin to an avalanche. Scientists are challenged in predicting the onset and distance traveled by these flows. This project aims to identify the physical processes in these flows off the coast of Washington and learn how differences in canyon structure can affect the flows generally. A set of seafloor instruments in two submarine canyons will be installed to record sediment gravity flows as they pass through them. These data are quite rare and greatly aid understanding of flow mechanics and enable development of numerical models that predict where and when flows occur. Six seafloor instrument packages will be maintained in Astoria Canyon and Quinault Canyon, both fed by the Columbia River, for a complete year. Sediment cores will be collected from both canyons, where event-layers from past sediment-gravity flows will be identified and analyzed for their composition and historical frequency. The researchers predict that river floods and marine storm events (large waves, strong winds) can trigger major sediment gravity flows in these canyons today, but differences in canyon terrain trigger sediment-gravity flows under different conditions. Submarine canyons are present along nearly every continental margin and are the sites of globally significant ocean mixing, sediment transport, and nutrient exchange between the coastal and abyssal environment. Earth’s submarine canyons are maintained by density-driven flows of water and sediment, but the mechanisms that trigger flows—and their downslope flow evolution—are still not well understood. This project examines the pathways of sediment through two canyons along Cascadia Margin which are morphologically distinct yet share the same fluvial source, the Columbia River. This study’s experimental design includes a targeted instrument deployment, comprehensive seabed coring survey, and hydrodynamic modeling of sediment gravity flows. The project is intended to advance knowledge of canyon sedimentary processes under modern high stands in sea level and constrain the role of morphology and oceanographic disturbance in initiating seabed resuspension and density-driven flow. Seafloor sediment loading from fluvial sources, triggering of flows by bathymetric focusing of wave and current energy, and synchronous downslope transport across distant canyon systems will be studied as functions of canyon morphology in Astoria and Quinault Canyons. The investigators predict that sedimentary deposits in relatively deep-water canyon environments may be created via oceanic triggering, and aim to place quantitative constraints on the downslope limit of such flows. They also predict that processes in differing canyon morphologies result in deposits that are both regionally synchronously and asynchronously emplaced at depth.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.