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

通过测量蒙特雷海底峡谷和其他几个峡谷的湍流、内波和星云状层，提出了一个实地方案来研究混合边界流体与分层内部的交换。将讨论几个问题：1。大陆坡内波驱动的边界混合对海洋内部分层的净效应是什么？在峡谷中，湍流混合的精细尺度参数化是否因为(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达不到5.6倍？测量将包括使用XCPs进行全深度速度-温度剖面测量，使用配备传输计的LADCP/CTD进行电流和水性质时间序列测量，使用微观结构剖面仪进行湍流混合时间序列测量，以及使用配备ADCP和热敏电阻链的系泊系统进行底部120米的速度和温度剖面时间序列测量。这些数据将用于(i)通过确定进出边界的内波能量通量以及边界层湍流耗散率来量化BBL能量收支，以及（ii）表征星云层的分布。能量通量散度将用于确定峡谷内的内部波源和汇，而潜在的外部波源将从深水通量中确定。此外，还将探索新的分析技术，包括(i)利用能量通量共谱来诊断近临界底部斜坡的内波反射，（ii）双相干来评估高低垂直波数之间的关系，（iii）动量通量来评估底部形式阻力，以及（iv）分层通量和沉积物通量来确定混合边界水与分层内部的交换。这项工作是与维多利亚大学的Eric Kunze合作进行的，他将进行微观结构测量，并参与整个数据集的分析和解释。在ONR的2006年AESOP计划中，它将受益于最近在蒙特利湾南部斜坡上的建模工作和测量。智力优势：我们的动机是关于以下基本问题：(i)边界上混合流体与分层内部混合流体的交换及其在全球混合和温盐环流中的作用，以及（ii）如何更好地参数化地形附近的内波驱动湍流混合。调查计划结合了空间覆盖和高频时间序列，以允许严格的显著性测试。为了更好地理解斜坡地形附近内波场的能量级联，跨越整个半日潮周期的核心XCP模式将提供比迄今为止在实验室外获得的更好的空间和时间相干内波场分辨率。此外，在其他大陆斜坡峡谷的探索性测量将有助于扩大在全球范围内的适用性。更广泛的影响：多机构合作将促进对蒙特雷峡谷和其他大陆斜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。通过细化细尺度混合参数化，它还将有助于大规模混合预算，并可能有助于气候模式预测。教育将通过支持研究生和参与外展活动来推进。

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.