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

到目前为止，在深海中采集到的湍流剖面还不到1000个，而且这些剖面只集中在几个地理区域。由于缺乏直接测量，混合的分布在很大程度上是通过代理和参数推断的，这些参数具有已知的局限性。混合预算仍然没有得到很好的约束。这一试点项目的目的是证明，可以在全球海洋的广泛分布上获得全海洋深度上系统的、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计划操作的标准船上CTD/LADCP组件上部署CHI-Pod-“湍流混合仪”。在三年的时间里，将收集和分析数千条湍流剖面。X-Pod是一种自给自足的仪器，自2005年以来一直在量化赤道系泊设备上的混合情况。他们使用快速响应热敏电阻和精密加速度计来测量微尺度的温度梯度，由此得到温度变化的消散率，以及热量和其他示踪剂的涡流扩散率。与基于剪切探头的传统速度微结构测量不同，温度微结构测量对平台振动不敏感-这是在有表面表达的系泊设备上或从CTD玫瑰花环上部署的必需品。CTD-chi-Pod经过改进，在重复的水文测量操作中，它可以很容易地夹在标准花环上，而影响最小，并且在最近的几个浅水试验中被证明是成功的。智力优势：海洋内部的昼夜混合对上层海洋的热量和营养平衡、深海环流和水质量分布有很大的影响。作为美国国家科学基金会资助的气候过程小组的一部分，为大型模式开发和实施昼夜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令人难以置信的缺乏直接湍流观测，特别是那些覆盖整个水柱深度的观测。该项目将展示收集微结构观测的全球数据集的可行性和价值，该数据集将在采集后尽快公开，并遵循重复的水文学协议。这些数据将使PI以及更广泛的科学界能够计算出更好的全球和区域日平均混合率，探索控制海洋湍流地理分布的潜在动力，评估盆地平均混合率的逐渐变化，评估正在广泛使用的精细尺度混合切变和应变参数的不确定性和系统偏差，并验证将进入下一代区域和气候模式的湍流参数。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营养通量再到全球能量学的一切。这些结果将特别有助于测试和改进为全球气候模式(http://www-pord.ucsd.edu/~jen/cpt/)，)开发的湍流混合的参数，因为昼夜混合率仍然是此类模式中最有影响的调整参数之一。该项目将培养一名研究生，并让其他学生接触到远洋观测技术。

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.