Understanding the Dynamics of Wave- and Current-supported Turbidity Currents via High-performance High-fidelity Numerical Simulations

大陆边缘是碳、氮、氧和其他地球化学上重要物质的主要反应器。在沿海海洋中，其中一些物质与颗粒物质有关，颗粒物质的移动取决于波浪和水流对沉积颗粒的再悬浮和搬运。因此，了解和量化沉积物穿越大陆架的物理过程是准确估计这种地球化学上重要物质的全球预算的核心。在大陆架，表面波和沿岸流移动海底沉积物，造成再悬浮。由于沉积物的重量，这产生了具有比纯海水更高的有效密度的浑浊（沉积物/水）水的混合物。密度较大的浑浊沃茨倾向于向下游流动，形成所谓的波浪和水流支持的浊流（WCSTC），这是将沉积物从内陆架运送到内陆架的过程之一。WCSTC的发展是一个相对较小规模的过程，不能解决区域尺度的数值模式和他们的列入需要准确的参数化的发展。最近的现场观测，实验室实验和数值模拟提供的证据表明，在传统的概念化的WCSTCs的一些假设可能不成立，这可能有显着的影响跨大陆架颗粒物输送量。根据这些观测结果，这项工作将调查沿岸流和沉积物粒度分布对WCSTC的作用，并将开发适用于区域尺度数值模型的改进参数化。后者将有助于更准确地估计区域和全球范围的地球化学收支。此外，这项工作将提供关于缓慢移动的WCSTC向自动悬浮或自加速浊流过渡的见解，这些浊流对海底基础设施（电缆，管道）造成危害风险。一名研究生将得到该项目的支持，并将在海岸过程，环境流体力学和高性能计算方面接受均衡的培训。一名本科生将被招募，并将接受使用高性能计算平台，数据可视化和物理海洋学的基本培训。开发的数值模型将公开提供给科学界和工程界使用，该项目的主要假设是，沿大陆架的海流与波浪结合在一起时，在大规模跨大陆架迁移中发挥主要作用。这项研究将建立在大涡模拟（LES）上，使用能够模拟精细尺度过程并产生高保真结果的高性能计算机。模拟将侧重于评估沉积物沉降速度对波浪边界层内沉积物浓度的作用。此外，还将评估波浪、水流和WCSTC下坡速度之间的非线性相互作用。 模拟数据将用于开发WCSTC在区域尺度模型中的参数化。知识价值包括基于物理上一致的概念化的跨大陆架颗粒物传输的量化，确定影响WCSTC动态的关键参数，以及数据综合以提供更好的WCSTCs.This奖项的参数化反映了NSF的法定使命，并已被认为是值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估的支持。

The continental margin is a major reactor of carbon, nitrogen, oxygen, and other geochemically important material. In the coastal ocean some of this material is associated with particulate matter the movement of which depends on the resuspension and transport of sedimentary particles by waves and currents. Understanding and quantifying the physical processes that route sediments across the shelf are therefore central to accurately estimating global budgets of such geochemically important material. In the continental shelf, surface waves and coastal currents mobilize benthic sediments and cause resuspension. This creates a mixture of turbid (sediment / water) water with an effective density higher than that of pure seawater due to the weight of the sediment. The denser turbid waters tend to flow downslope, creating the so-called wave- and current-supported turbidity currents (WCSTCs), which are among the processes that route sediments from the inner to the outer shelf. WCSTC development is a relatively small-scale process that cannot be resolved by regional-scale numerical models and their inclusion requires the development of accurate parameterizations. Recent field observations, laboratory experiments, and numerical simulations have provided evidence that some of the assumptions in conventional conceptualization of WCSTCs perhaps do not hold, which may have significant impacts on the amount of cross-shelf particulate matter transport. In light of these observations, this effort will investigate the role of alongshore currents and sediment size distribution on WCSTCs and will develop improved parameterizations suitable for regional-scale numerical models. The latter will help in more accurately estimating geochemical budgets at both regional and global scales. In addition, this effort will provide insights on the transition of slow-moving WCSTCs to auto-suspending or self-accelerating turbidity currents which impose hazard risk to submarine infrastructure (cables, pipelines). One graduate student will be supported by this project and will receive well-balanced training in coastal processes, environmental fluid mechanics, and high-performance computing. One undergraduate student will be recruited and will receive basic training in using high-performance computing platforms, data visualization, and physical oceanography. The developed numerical models will be publicly available for use by the scientific and engineering communities.The main hypothesis of this project is that along-shelf currents play a major role in massive cross-shelf transport when combined with waves. The study will be built on Large-Eddy Simulations (LES) using high-performance computers capable in simulating fine-scale processes and producing high-fidelity results. The simulations will focus on assessing the role of sediment settling velocity on sediment concentration inside the wave boundary layer. Also, the non-linear interaction between waves, currents and WCSTCs downslope velocity will be assessed. The simulation data will be used to develop WCSTCs’ parameterizations in regional-scale models. The intellectual merits include the quantification of cross-shelf particulate matter transport that is based on physically consistent conceptualization, identifying the key parameters that affect WCSTC dynamics, and data synthesis to provide better parameterization of WCSTCs.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.