Turbulent mixing by nearshore internal bores

知识价值：在过去几年中，对内大陆架更大规模物理的整体理解有了显著的进步，但在分层的内大陆架水与海岸相互作用的浅水近岸地区，几乎没有工作。迄今为止有限的观察，包括在蒙特利湾和马马拉湾的工作，表明短暂的混合和分层事件，可能与近海内波场的浅滩化和破裂有关，极大地改变了海洋中这一生态重要部分的物理环境。在本项目中，将使用一套声波多普勒测速仪（ADV）和快速电导率/温度传感器对蒙特利湾南部10 - 30米水域的周期性湍流孔和锋面进行详细观测，以描述近岸湍流混合和分层事件的行为。ADVs将安装在一个8米高的塔上，用电缆连接到岸上，用于测量湍流变量，包括雷诺应力、湍流耗散和浮力通量。该塔将由声学多普勒电流分析器阵列和以其为中心的热敏电阻链进行补充，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。自动水下航行器将用于绘制温度和盐度的大范围变化。该项目旨在实现两个相关的目标，这些目标可以大大提高当前对近岸流动的理解：(1)显示这些钻孔状特征如何与地形和其他（例如潮汐）流动相互作用；(2)根据现有的边界层和分层剪切湍流的动力框架，检查在这种相互作用期间产生的湍流。更广泛的影响：文献中经常报道的钻孔/松弛锋模式的局部动态可能是生态上重要的一类物理环境变异性的主要来源。这有几个重要的原因：(1)钻孔/锋似乎是一个重要的机制，通过它，较深的近海水被供应到沿海上升流系统陆架区域的近岸环境。由于这些海底衍生水与近岸生态系统中受地表过程影响的水之间的相互作用，这对于了解气候变化将如何影响这些生态系统非常重要，因为这些水溶解氧含量低，酸度高。(2)这些孔/锋被认为是内陆架近岸和最外层生物交换的重要机制。(3)垂直湍流混合对底栖生物放牧和浮游植物初级生产等生态过程至关重要。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，并通过他们在斯坦福大学海洋解决方案中心的参与，如何将他们的使用与决策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，至少还有四名其他研究生可能会参与实地工作，其中包括两名与研究人员一起工作的女博士生。作为该项目的一部分，将围绕2013年5月的实验开设研究生实地方法课程。最后，调查人员还将制作一部微型纪录片（见http://microdocs.org/），介绍内孔对养分流动和近岸生态系统生产的重要性。为配合这段录像，他们将访问代表性不足地区的几所当地高中，就海洋学、海洋健康和海洋职业机会作简短（30分钟）的介绍，其间将向教室播放微纪录片。

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.