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

大陆边缘是碳、氮、氧和其他重要地球化学物质的主要反应堆。在沿海海洋中，有些物质与颗粒物质有关，颗粒物质的运动取决于波浪和洋流对沉积颗粒的再悬浮和运输。因此，了解和量化使沉积物穿过大陆架的物理过程对于准确估计这种重要的地球化学物质的全球预算至关重要。在大陆架，表面波和沿岸流调动海底沉积物并引起再悬浮。这就产生了混浊(沉积物/水)水的混合物，由于沉积物的重量，其有效密度高于纯海水。密度较高的浑浊水倾向于向下流动，产生所谓的波浪和水流支持的浑浊流(WCSTC)，这是将沉积物从内陆架输送到外陆架的过程之一。WCSTC的发展是一个规模相对较小的过程，不能用区域尺度的数值模式来解决，要包括它们需要发展准确的参数化。最近的现场观测、实验室实验和数值模拟提供的证据表明，传统的WCSTCs概念化中的一些假设可能不成立，这可能对跨陆架颗粒物的运移量产生重大影响。根据这些观察，这项工作将调查沿岸流和沉积物尺寸分布对WCSTC的作用，并将开发适用于区域尺度数值模式的改进的参数。后者将有助于更准确地估计区域和全球两级的地球化学预算。此外，这项工作将为缓慢移动的WCSTC过渡到自动悬浮或自动加速的浊流提供见解，这将对海底基础设施(电缆、管道)构成危险风险。一名研究生将得到该项目的支持，并将接受海岸过程、环境流体力学和高性能计算方面的平衡培训。将招收一名本科生，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供科学界和工程界使用。该项目的主要假设是，当与海浪结合时，沿陆架流在大规模跨陆架输送中起主要作用。这项研究将建立在大涡模拟(LES)的基础上，使用能够模拟精细过程并产生高保真结果的高性能计算机。模拟的重点是评估泥沙沉降速度对波浪边界层内泥沙浓度的影响。此外，还将评估波浪、流和WCSTC下坡速度之间的非线性相互作用。模拟数据将被用来开发区域尺度模式中的WCSTC的参数化。这一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学术价值和更广泛的影响审查标准进行评估，认为值得支持。

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.