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

“沿着北卡斯卡迪亚边缘的海底峡谷中海洋过程驱动的沉积物运输：触发器的形态控制”海底峡谷充当沿海和深海之间的主要高速公路，运输足够的水、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，海底峡谷是被侵蚀的巨大山谷，但它们不是由河流雕刻而成的。相反，海底峡谷是由类似雪崩的沉积物和水的下坡水流雕刻而成的。科学家们在预测这些流的开始和移动距离方面面临挑战。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水流。将在两个海底峡谷中安装一套海底仪器，记录通过峡谷的沉积物重力流。这些数据非常罕见，极大地帮助理解流动力学，并使数值模型的发展能够预测流动的发生地点和时间。阿斯托里亚峡谷和奎诺峡谷的六个海底仪器包将被维持整整一年，这两个地方都由哥伦比亚河提供水源。沉积物岩心将从两个峡谷收集，在那里，过去沉积物重力流的事件层将被识别并分析其组成和历史频率。研究人员预测，河流洪水和海洋风暴事件（大浪，强风）可以在今天的这些峡谷中引发主要的沉积物重力流，但峡谷地形的差异在不同条件下引发沉积物重力流。海底峡谷几乎沿着每个大陆边缘存在，是全球重要的海洋混合、沉积物运输和沿海和深海环境之间的营养交换的场所。地球上的海底峡谷是由密度驱动的水流和沉积物维持的，但引发水流的机制——以及它们的下坡水流演化——仍然没有得到很好的理解。该项目考察了沿着卡斯卡迪亚边缘的两个峡谷的沉积物路径，这两个峡谷在形态上是不同的，但共享同一河流来源，哥伦比亚河。本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的水动力学建模。该项目旨在提高对现代高海拔下峡谷沉积过程的认识，并限制地形和海洋扰动在海底再悬浮和密度驱动流启动中的作用。在阿斯托里亚峡谷和奎诺峡谷，将研究来自河流源的海底沉积物负荷、波流能量的深海聚焦引发的流动以及跨越遥远峡谷系统的同步下坡运输。研究人员预测，相对深水峡谷环境中的沉积沉积物可能是通过海洋触发形成的，并旨在对这种水流的下坡极限进行定量约束。他们还预测，不同峡谷形态的作用过程会导致区域同步和深度不同步的沉积。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.