Collaborative Research: The Role of Canyons in Boundary Mixing and Exchange with the Ocean Interior

提出了一个现场程序，通过测量蒙特利潜艇峡谷和其他几个峡谷中的湍流、内波和星云状层来检查混合边界流体与分层内部的交换。将讨论几个问题：1.陆坡内波驱动的边界混合对海洋内部层结的净影响是什么？2.在峡谷中，湍流混合的精细尺度参数化是否由于(I)比在开阔海洋中发现的更相干的内波场或(Ii)与地形的相互作用而不足5倍？测量将包括用XCP进行全深度速度-温度剖面调查，用配备透射仪的LADCP/CTD测量水流和水的性质，用微结构剖面仪测量湍流混合的时间序列，给出了装有ADCP和热电阻链的系泊设备在底部120m处的速度和温度分布时间序列。这些数据将被用来(I)通过确定进出边界的内波能量通量以及边界层的湍流耗散率来量化边界层的能量收支，以及(Ii)描述云状层的分布。能量通量发散将被用来确定峡谷内的内部波源和汇，而潜在的外部源将被从深水通量中确定。此外，还将探索新的分析技术，包括：(1)利用能量通量共谱诊断近临界底坡的内波反射；(2)双相干法评价高低垂直波数之间的关系；(3)动量通量评价海底形态阻力；(4)层结通量和泥沙通量确定混合边界水与层结内部的交换。这项工作是与维多利亚大学的埃里克·昆泽合作进行的，他将进行微结构测量，并参与整个数据集的分析和解释。它将受益于ONR 2006年伊索计划期间在蒙特利湾南部斜坡上的最新建模工作和测量。智力上的优点：我们的动机是关于以下基本问题：(I)在边界上与层化内部混合的流体的交换及其在全球混合和温盐环流中的作用，以及(Ii)如何更好地对地形附近的内波驱动的湍流混合进行参数化。调查计划结合了空间覆盖和高频时间序列，以允许对重要性进行严格测试。横跨半日潮全周期的核心XCP图形将提供比实验室外迄今所获得的更好的空间和时间上的相干内波场的分辨率，以便更好地理解通过倾斜地形附近的内波场的能量级联。此外，在其他大陆坡峡谷的探索性测量将有助于将适用性扩展到全球范围。广泛的影响：多机构合作将促进对蒙特利峡谷和其他大陆坡峡谷混合过程的跨学科理解，这是当地营养物质、沉积物和化学示踪剂预算的重要方面。通过改进FineScale混合参数，它还将有助于大规模混合预算，并可能有助于气候模型预测。将通过支持研究生和参加外联活动来促进教育。

A field program is proposed to examine exchange of mixed boundary fluid with the stratified interior by measuring turbulence, internal waves and nepheloid layers in Monterey SubmarineCanyon and in several other canyons. Several questions will be addressed:1. What are the net effects of continental-slope internal-wave-driven boundary mixing on theinterior stratification of the ocean?2. Do finescale parameterizations for turbulent mixing fall short by a factor of 5 6 in canyons because of (i) a more coherent internal wave field than found in the open ocean or (ii) interactions with topography?Measurements will include full-depth velocity-temperature profile surveys with XCPs, time seriesof currents and water properties with transmissometer-equipped LADCP/CTD, time-series of turbulent mixing with a microstructure profiler, and a velocity and temperature profile time series of the bottom 120 m with a mooring equipped with ADCP and thermistor chain. These data will be used (i) to quantify the BBL energy budget by determining internal wave energy fluxes into and out of the boundary along with boundary-layer turbulent dissipation rates, and (ii) to characterize the distribution of nepheloid layers. Energy-flux divergence will be used to identify internal wave sources and sinks within the canyon while potential external sources will be identified from deep-water fluxes. In addition, new analysis techniques will be explored, including (i) the use of energy-flux co-spectra to diagnose internal wave reflection from the near-critical bottom slope, (ii) bi-coherence to evaluate relationships between high and low vertical wavenumbers, (iii) momentum-fluxes to evaluate bottom form drag, and (iv) stratification flux and sediment flux to determine the exchange of mixed boundary water with the stratified interior. This work is in collaboration with Eric Kunze at the University of Victoria, who will make the microstructure measurements and participate in analysis and interpretation of the whole data set. It will benefit from recent modeling efforts and measurements on the slope south of Monterey Bay during ONR's 2006 AESOP program.Intellectual Merit: We are motivated by fundamental questions concerning (i) the exchange of fluid mixed on the boundary with that in the stratified interior and its role in global mixing and the thermohaline circulation, and (ii) how to better parameterize internal-wave-driven turbulent mixing near topography. The survey plan combines spatial coverage and high-frequency timeseries to allow rigorous testing of significance. The core XCP pattern spanning a full cycle of the semidiurnal tide will provide better resolution of a coherent internal wavefield in space and time than hitherto achieved outside the laboratory in order to better understand the cascade of energy through the internal wave field near sloping topography. In addition, exploratory measurements in other continental slope canyons will aid in expanding applicability to a global scope.Broader Impacts: The multi-institutional collaboration will advance interdisciplinary understanding of mixing processes in Monterey Canyon and other continental slope canyons, an important facet for local budgets of nutrients, sediment, and chemical tracers. Through the refinement of finescale mixing parameterizations, it will also aid large-scale mixing budgets and,potentially, climate model predictions. Education will be advanced through the support of graduate students and participation in outreach activities.