Collaborative Research: Investigating the Dynamics in Deep Valleys on the Seafloor With Numerical Experiments and Data Analysis

为了关闭海洋的全球翻转环流，高纬度稠密水的产生和下沉必须通过浮力增加和上升流来平衡其他地方。这两个过程都与底界混合密切相关，这意味着混合过程在地球气候系统中具有根本的重要性。此外，垂直运动是深海环流的主要驱动力，这意味着必须知道其空间分布，以便了解环流并建立环流模型。过去几十年中收集的观测资料表明，深海中最强的混合主要出现在覆盖整个海底50%以上的大洋中脊的粗糙地形附近。特别令人感兴趣的是许多山脊侧面峡谷（断裂带），它们每隔50公里左右切割缓慢扩张的山脊侧面。这些峡谷不仅是强混合的主要场所，它们也是惊人的规则和自相似的，持续的上侧翼流和溢出的无处不在的水深丘陵，作为沿轴流的门槛。尽管关于混合的空间分布和脊翼峡谷环流的观测取得了进展，但实际上对海洋垂直运动的空间分布一无所知。虽然目前的高分辨率海洋模式在许多领域取得了显着的进步，现实的上升流场的准确性仍然是一个重要的悬而未决的问题。MORs附近的动态行为，特别是在山脊侧翼峡谷的流动将通过使用数值模拟和现有的观测分析进行研究。除了提高我们的理解的横向环流和混合附近粗糙的地形，人们可以期待从这项研究的见解，以促进发展更准确的表示上升流和由此产生的深海环流在海洋环流models.Intellectual优点：湍流强烈依赖于域几何的细节。即使是分辨率最高的大型海洋模型也无法充分解决海底地形的所有精细尺度特征。因此，粗糙地形引起的上升流的参数化和建模提出了一个根本性的挑战。脊翼峡谷的几何形状和相关流动的自相似性和规则性可以极大地促进大尺度模型中相关阻力和混合的表示。这些流量的数值模拟是一个新的事业，这将揭示形式阻力，水力控制和时间依赖性强迫在分层流多sills.Broader影响的重要性：从这个项目的结果将被传播的形式在期刊上的文章，在国家和国际科学会议上的演讲，并通过一个项目网站。最终，更好地了解MORs上的流动动力学将导致更好地理解和模拟海洋环流。由于海洋模型被用来预测各种尺度的环流模式，这项研究的结果可能会对气候建模产生更广泛的影响，最终会通过影响政策来影响社会。该项目的结果也可能有助于提高我们对热液“产品”，包括热量、地球化学示踪剂和动物幼虫的扩散的理解。这项研究将为物理海洋学的一名博士生和一名女博士生提供支持。

In order to close the global overturning circulation of the ocean, the production and sinking of dense water at high latitudes must be balanced elsewhere by buoyancy gain and upwelling. Both these processes are intimately linked to diapycnal mixing, which implies that mixing processes are fundamentally important in the Earth's climate system. Additionally, vertical motion is a primary driver for the abyssal circulation, which implies that its spatial distribution must be known in order to understand and model the circulation. Observations collected during the last few decades indicate that the strongest mixing in the deep ocean is primarily found near the rough topography of mid-ocean ridges (MORs), which cover more than 50% of the entire sea-floor. Of particular interest are the many ridge-flank canyons (fracture zones) that incise the flanks of slow-spreading ridges every 50 km or so. Not only are these canyons the main sites of strong mixing, they are also strikingly regular and self similar, with persistent up-flank flows and overflows across the ubiquitous bathymetric hills that act as sills for the along-axial flows. In spite of the observational advances regarding the spatial distribution of mixing and the circulations in ridge-flank canyons, virtually nothing is known about the spatial distribution of vertical motion in the ocean. While current high resolution ocean models have made significant strides towards realism in many areas, the accuracy of the upwelling field remains as one of the important outstanding problems. The dynamics acting near MORs, and in particular the flows in the ridge flank canyons will be investigated by using numerical modeling and analysis of existing observations. In addition to improving our understanding of the lateral circulation and the mixing near rough topography, one could expect insights from this study to contribute towards developing more accurate representations of upwelling and the resulting abyssal circulations in ocean general circulation models.Intellectual Merits: Turbulent flows are strongly dependent on the details of domain geometry. Even the highest resolution large-scale ocean models cannot adequately resolve all the fine-scale features of bottom topography. As such, parameterization and modeling of upwelling induced by rough topography poses a fundamental challenge. The self-similar, regular nature of the geometry of the ridge-flank canyons and the associated flows may greatly facilitate representation of the associated drag and mixing in large-scale models. The numerical modeling of these flows is a novel undertaking, which will reveal the importance of form drag, hydraulic control and time-dependent forcing in stratified flows over multiple sills.Broader Impacts: The results from this project will be disseminated in the form of articles in journals, presentations in national and international scientific meetings, and via a project website. Ultimately, a better understanding of flow dynamics on MORs will lead to an improved understanding and modeling of the ocean general circulation. As ocean models are used to predict circulation patterns at a variety of scales, the results from this study may have the broader impact of aiding climate modeling, which can ultimately impact society by influencing policy. The results from this project may also help improve our understanding on the dispersal of hydrothermal "products", including heat, geochemical tracers and animal larvae. The study will provide support for both a PhD student and a female PhD recipient in physical oceanography.