Turbulent mixing by nearshore internal bores

学术价值：在过去的几年里，对内陆架更大范围物理的整体理解有了显著的进步，但在内陆架分层水域与海岸相互作用的浅海近岸地区，工作很少。迄今为止有限的观测，包括在蒙特利湾和马马拉湾的工作表明，瞬时混合和层结事件，可能与近海存在的内部波场的浅滩和破裂有关，极大地改变了这一具有生态重要性的海洋部分的物理环境。在这个项目中，将使用一套声学多普勒测速仪(ADV)和快速电导率/温度传感器在蒙特利湾南部10到30米的水中对周期性湍流钻孔和湍流锋面进行详细观测，以描述近岸湍流混合和层化事件的行为。ADV将安装在一个8米高的塔架上，并用电缆连接到岸上，以测量湍流变量，包括雷诺应力、湍流耗散和浮力通量。该塔将由一系列声学多普勒海流剖面仪和以其为中心的热电阻链进行补充，以提供这些流动的详细空间和时间视图，包括诊断其动力学。自动水下机器人将被用来绘制更大范围的温度和盐度变化地图。该项目旨在实现两个相关目标，以显著促进当前对近岸流动的理解：(1)展示这些类似钻孔的特征如何与地形和其他(如潮汐)气流相互作用，以及(2)根据现有的边界层和分层剪切湍流的动力学框架，检查在这种相互作用过程中产生的湍流。这一点具有重要意义，原因如下：(1)孔/锋似乎是向沿海上升流系统陆架区域近岸环境供应较深近海水域的重要机制。由于这些底层衍生水和近岸生态系统中受表层过程影响的水域之间的相互作用，这对于了解气候变化将如何影响这些生态系统非常重要，因为这些水域的溶解氧较低，酸度较高。(2)这些孔/锋被认为是内陆架近岸和最外层之间生物交换的重要机制。(3)垂直湍流混合对许多生态过程至关重要，如底栖放牧和浮游植物初级生产。该项目的研究人员将试验如何最好地利用沿海海洋观测系统，并通过参与斯坦福大学海洋解决方案中心，如何将它们的使用与政策制定者以及其他海洋生态学家和地球化学家的数据和信息需求联系起来。从教育的角度来看，拟议的工作将是劳动密集型的，因此将涉及许多斯坦福大学的研究生和本科生。除了直接参与该项目的两名学生外，至少还有四名研究生可能会参与现场工作，其中包括两名与调查人员一起工作的女博士生。作为该项目的一部分，将教授一个将围绕2013年5月的实验建立的研究生野外方法课程。最后，研究人员还将制作一部微型纪录片(见http://microdocs.org/)，关于内部钻孔对营养通量和近岸生态系统生产的重要性)。结合这段视频，他们将访问当地几所高中，主要是代表人数较少的地区，就海洋学、海洋健康和海洋职业机会做简短(30分钟)的陈述，在此期间，微纪录片将被呈现在课堂上。

Intellectual Merit: The overall understanding of the larger-scale physics of the inner shelf has advanced notably in the past few years, but there has been little work on the shallow nearshore regions where stratified inner shelf waters interact with the shore. Limited observations to date, including work in Monterey Bay and Mamala Bay, suggest that transient mixing and stratification events, presumably associated with the shoaling and breaking of internal wave fields present offshore, dramatically alter the physical environment in this ecologically important part of the ocean.In this project, detailed observations of periodic turbulent bores and fronts will be conducted in 10 to 30 m water in southern Monterey Bay using a set of Acoustic Doppler Velocimeters (ADV) and fast Conductivity/Temperature sensors to describe the behavior of nearshore turbulent mixing and stratification events. The ADVs will be mounted on an 8m high tower and cabled to shore, to measure turbulence variables including Reynolds stresses, turbulence dissipation and buoyancy fluxes. This tower will be supplemented by an array of Acoustic Doppler Current Profilers and thermistor chains centered on it to provide a detailed spatial and temporal view of these flows, including diagnosing their dynamics. An Automated Underwater Vehicle will be used to map larger-scale variations in temperature and salinity. The project is designed to accomplish two related goals that could substantially advance current understanding of flows in the nearshore: (1) Show how these bore-like features interact with topography and other (e.g. tidal) flows, and (2) Examine the turbulence produced during this interaction in light of existing dynamical frameworks of boundary layer and stratified shear turbulence.Broader Impacts: The local dynamics of the bore/relaxation front pattern that has been often reported in the literature can be the dominant source of variability in an ecologically important class of physical environments. This is significant for several reasons: (1) The bores/fronts appears to be an important mechanism by which deeper offshore waters are supplied to nearshore environments in shelf regions of coastal upwelling systems. Because of the interaction between these bottom derived waters and surface process affected waters in nearshore ecosystems, this is important for understanding how climate change will affect these ecosystems since these waters are low in dissolved oxygen and have high acidity. (2) These bores/fronts are thought to be an important mechanism for the exchange of organisms between the nearshore and the outermost regions of the inner shelf. (3) Vertical turbulent mixing is critical to many ecological processes such as benthic grazing and primary production by phytoplankton.The project's investigators will be experimenting with how to best use coastal ocean observing systems and, through their participation in Stanford's Center for Ocean Solutions, how to connect their use with the data and information needs of policy makers as well as those of other marine ecologists and geochemists.From an educational standpoint, the proposed work will be labor intensive and thus will engage a number of Stanford graduate and undergraduate students. Besides the two students directly involved in the project, at least four other graduate students will likely be involved in the field work, including two women Ph.D. students working with the investigators. As part of this project, a graduate field methods class that will be built around the May 2013 experiment will be taught. Finally, the investigators will also develop a microdocumentary (see http://microdocs.org/) on the importance of internal bores to nutrient fluxes, and nearshore ecosystem production. In conjunction with this video, they will visit several local area high schools in largely underrepresented districts to make short (30 min) presentations on oceanography, ocean health, and ocean career opportunities during which the microdocumentary will be presented to the classroom.