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

“海洋过程驱动的沉积物运输在海底峡谷沿着卡斯卡迪亚北方边缘：触发器的形态控制“海底峡谷作为沿海和深海之间的主要公路，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，海底峡谷是巨大的、被侵蚀的山谷，但它们不是被河流雕刻出来的。相反，海底峡谷是由沉积物和水的下坡流雕刻而成的，类似于雪崩。科学家们在预测这些流动的开始和传播距离方面面临挑战。这个项目的目的是确定这些流的物理过程，在华盛顿海岸和学习的差异，峡谷结构可以影响流量一般。将在两个海底峡谷安装一套海底仪器，记录沉积物通过峡谷时的重力流。这些数据是非常罕见的，极大地帮助理解流动力学，并使数值模型的发展，预测何时何地发生流动。六个海底仪器包将在阿斯托里亚峡谷和奎诺峡谷维持一整年，这两个峡谷都由哥伦比亚河供水。将从这两个峡谷收集沉积物岩心，确定和分析过去沉积物重力流的事件层的成分和历史频率。研究人员预测，河流洪水和海洋风暴事件（大浪，强风）今天可以在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一个大陆边都存在，是全球重要的海洋混合、沉积物搬运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流和沉积物维持的，但是触发水流的机制及其下坡流的演变仍然没有很好的理解。本项目研究沉积物通过两个峡谷的路径沿着卡斯卡迪亚边缘是形态上不同的，但共享相同的河流源，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，全面的海底取芯调查，以及沉积物重力流的流体动力学建模。该项目旨在增进对现代高海平面下峡谷沉积过程的了解，并限制地貌和海洋扰动在引发海底再悬浮和密度驱动流动方面的作用。将研究来自河流源的海底沉积物负荷、波能和海流能的测深聚焦引发的水流以及跨越遥远峡谷系统的同步下坡输运，作为阿斯托里亚和奎诺尔特峡谷峡谷形态的函数。研究人员预测，相对深水峡谷环境中的沉积物可能是通过海洋触发产生的，并旨在对此类流动的下坡限制进行定量限制。他们还预测，在不同的峡谷形态的过程中，在区域同步和异步侵位在depth.This奖项反映了NSF的法定使命，并已被认为是值得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的支持。

“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.