Collaborative Research: Systematic Direct Mixing Measurements within the Global Repeat Hydrography Program (SYSDMM)

迄今为止，在深海中获得的湍流剖面还不到一千个，而且只集中在少数几个地理区域。由于缺乏直接测量，混合的分布主要是通过具有已知局限性的代理和参数化来推断的。混合预算仍然缺乏约束。这个试点项目的目的是证明，在整个海洋深处，可以在全球海洋的广泛分布中获得系统的、重复的湍流混合序列。为了实现这一目标，该项目的研究人员将在全球重复水文测量计划操作的标准船载CTD/LADCPs包上部署chi-pods -“湍流混合仪”。在三年的时间里，将收集和分析几千个湍流剖面。chi-pods是独立的仪器，自2005年以来一直在赤道系泊处量化混合。他们使用快速响应热敏电阻和精密加速度计测量微尺度温度梯度，从中得到温度方差的耗散率，÷和热的涡流扩散率等示踪剂。与传统的基于剪切探头的速度微观结构测量不同，温度微观结构测量对平台振动不敏感，这是在具有表面表达或CTD玫瑰花结的系泊上部署的必要条件。CTD-chi-pod经过改进，可以在重复水文作业中轻松夹紧到标准玫瑰花结上，并且在最近的几次浅水试验中被证明是成功的。知识价值：海洋内部的潜流混合对上层海洋的热量和营养收支、深海环流和水质量分布有很强的影响。作为美国国家科学基金会资助的气候过程小组的一部分，开发和实施大尺度模型的周期混合参数化的初步尝试正在进行中。这一努力的最大障碍是难以置信的缺乏直接湍流观测，特别是覆盖整个水柱深度的观测。该项目将展示收集全球微观结构观测数据集的可行性和价值，这些数据集将在获取后尽快公开，并遵循重复的水文协议。这些数据将使pi以及更广泛的科学界能够更好地计算出平周期混合率的全球和区域平均值，探索控制海洋湍流地理分布的潜在动力学，评估盆地平均混合率的逐渐变化，评估正在广泛使用的细尺度剪切和应变混合参数化的不确定性和系统偏差。并验证湍流参数化，这将进入下一代的区域和气候模式。更广泛的影响：拟议的测量将是第一个全面的直接混合观测集，更广泛的社区可以轻松获得。这些测量可以被广泛的科学家用来限制从区域示踪剂预算到生物养分通量到全球能量学的一切。这些结果对于测试和改进正在为全球气候模式开发的湍流混合的参数化特别有用（http://www-pord.ucsd.edu/~jen/cpt/），因为在这种模式中，湍流混合率仍然是最具影响力的调谐参数之一。该项目将培训一名研究生，并让其他学生接触到公海观测技术。

To date, less than a thousand profiles of turbulence have been acquired in the deep ocean and these are concentrated in only a few geographic regions. As a result of this paucity of direct measurements, the distribution of mixing is inferred largely through proxies and parameterizations that have known limitations. Mixing budgets remain poorly constrained. The purpose of this pilot project is to demonstrate that systematic, repeated sequences of turbulent mixing over full-ocean depths can be obtained in a broad distribution throughout the global ocean. To accomplish this goal, the investigators in this project will deploy chi-pods - "turbulent mixing meters" on standard shipboard CTD/LADCPs package operated by the Global Repeat Hydrography Program. A few thousand turbulence profiles will be collected and analyzed over a three-year period. The chi-pods are self-contained instruments that have been quantifying mixing on equatorial moorings since 2005. They use fast response thermistors and precision accelerometers to measure microscale temperature gradients, from which the dissipation rate of temperature variance, ÷ and the eddy diffusivity of heat and other tracers. Unlike traditional velocity microstructure measurements based on shear probes, temperature microstructure measurements are not sensitive to platform vibration - a necessity for deployment on moorings with a surface expression or from a CTD rosette. The CTD-chi-pod has modifications that allow it to be easily clamped to a standard rosette with minimal impact during repeat hydrography operations, and has been proven successful in several recent pilot experiments in shallower waters.Intellectual Merit: Diapycnal mixing in the ocean interior has a strong influence on upper ocean heat and nutrient budgets, abyssal circulation, and water mass distributions. An initial attempt to develop and implement parameterizations of diapycnal mixing for large-scale models is underway as part of an NSF-funded Climate Process Team. The largest impediment to that effort is the incredible scarcity of direct turbulence observations, particularly those that cover the full water column depth. This project will demonstrate the feasibility and value of collecting a global dataset of microstructure observations that will be made publicly available as soon as possible after acquisition, following repeat hydrography protocols. The data will allow the PIs, as well as the broader scientific community, to calculate better global and regional averages of diapycnal mixing rates, explore underlying dynamics that control the geographic distribution of ocean turbulence, evaluate gradual changes in basin-averaged mixing rates, assess uncertainty and systematic bias in finescale shear and strain parameterizations of mixing that are becoming widely used, and validate turbulence parameterizations that will be going into the next generation of regional and climate models.Broader Impacts: The proposed measurements will be the first comprehensive set of direct mixing observations easily available to the broader community. These measurements can be used by a wide range of scientists to constrain everything from regional tracer budgets to biological nutrient fluxes to global energetics. The results will be particularly useful for testing and improving parameterizations of turbulent mixing being developed for global climate models (http://www-pord.ucsd.edu/~jen/cpt/), as diapycnal mixing rates remain one of the most influential tuning parameters in such models. This project will train one graduate student and give other students exposure to open-ocean observational techniques.