Inferring Ocean Mixing Rates from Hydrography and Turbulent Energy Sources

概述：海洋混合发生在小到分子水平的最小海洋尺度上，但总的来说，它对大尺度海洋环流产生影响，包括翻转环流、对大气变化响应的时间尺度以及热量和碳的吸收。该项目的目标是通过综合混合、水文观测、通风率和湍流能量源的直接观测，绘制全球海洋混合率图。该项目的方法是将水文反演技术与年龄示踪剂和小规模混合参数化相结合，以估计全球混合率并减少其剩余的不确定性。将开发一种强有力地诊断海洋混合率的水文反演技术，包括潮汐混合和混合能源等小尺度过程的约束，并将反演方法应用于已经收集的来自世界各地海洋的观测资料。该项目与了解海洋如何输送示踪剂数量，以及年龄示踪剂放射性碳捕获的物理、生物和化学过程的相互作用有关。知识价值：海洋混合率以前已经从至少四个不同的信息来源估计出来：1)对微观和精细尺度结构的直接观测，2)基于海洋过程（如潮汐、内波和湍流）的混合参数化，3)大尺度水文观测和地转平衡的反演，以及4)考虑年龄示踪剂（如放射性碳及其平流和扩散输送的记录）。这些估计中的每一个都具有显著的不确定性，将开发一种原始方法来估计混合率，该方法同时考虑了来自这四个来源的信息，并采用数学严格的逆技术。在不久的将来，确定海洋混合的空间变异性的原位测量将太少，因此打破这一僵局的最佳希望是在建模和分析框架中综合多种形式的已收集数据。由此产生的全球三维扩散率图将与具体的水深特征和海洋过程有关，这些特征和过程被设想为导致侧重于特定区域的过程研究。全球空间地图还将作为目前最好的扩散率地图的基准，并将作为规划新的就地测量运动的指南。更广泛的影响：改进海洋混合率的估计对于重建和预测海洋对热量和碳的吸收以及确定海洋参与气候变率的活跃程度尤为重要。海洋混合的空间分布影响着海洋环流隔离深渊的效果，与已经被隔离但可能在未来几百年内重新出现的碳的命运有关。由此产生的全球混合率可以在气候模拟中规定，并可能减少这些模式中海洋成分的主要不确定性。在许多气候过程固有的长时间尺度上，一个更真实的模拟海洋是关键。该项目的成果将输出到美国国家科学基金会资助的加州大学戴维斯分校KeckCAVES团队的一个补充项目中，在那里，与计算机科学家的合作将有助于以一种扩大科学参与和广泛传播气候科学的方式将结果可视化。此外，该项目将主要支持一名年轻的研究人员在建立一个研究小组的初期阶段。

Overview: Ocean mixing occurs at the smallest ocean scales down to the molecular level, yet in aggregate, it exerts influence over the large scale ocean circulation, including the overturning circulation, the timescale of response to atmospheric changes, and the uptake of heat and carbon. The goal of the project is to map ocean mixing rates globally in a way that synthesizes direct observations of mixing, hydrographic observations, ventilation rates, and turbulent energy sources. The approach of the project is to combine techniques for inverting hydrography with the inclusion of age tracers and a small-scale mixing parameterization in order to estimate global mixing rates and to reduce its remaining uncertainty. An hydrographic inversion technique that diagnoses ocean mixing rates robustly, the inclusion of constraints from small-scale processes such as tidal mixing and the sources of energy for mixing, and application of the inversion method to already-collected observations from around the world ocean will be developed. This project is relevant to understanding how the ocean transports tracer quantities, and the interaction of physical, biological, and chemical processes as captured in the age tracer, radiocarbon.Intellectual Merit: Ocean mixing rates have been previously estimated from at least four different sources of information: 1) direct observation of micro- and fine-scale structure, 2) parameterizations of mixing based upon knowledge of ocean processes such as tides, internal waves, and turbulence, 3) inversion of large-scale hydrographic observations and geostrophic balance, and 4) consideration of age tracers such as radiocarbon and their record of advective versus diffusive transports. Significant uncertainties are inherent to each of these estimates, and an original method will be developed to estimate mixing rates that takes into account information from these four sources simultaneously with a mathematically-rigorous inverse technique. Too few in-situ measurements will be made in the near future to determine the spatial variability of ocean mixing, so the best hope to break this impasse is to synthesize the many forms of already-collected data in a modeling and analysis framework. The resulting global three-dimensional maps of diffusivity will be related to specific bathymetric features and ocean processes, which are envisioned to lead to process studies that focus on particular regions. The global spatial map will also serve as a present-day benchmark of the best current maps of diffusivity, and will serve as a guide by which to plan new in-situ measurement campaigns.Broader Impacts: Improved estimates of ocean mixing rates are especially important to reconstruct and predict the ocean uptake of heat and carbon, and the determination of how actively the ocean participates in climate variability. The spatial distribution of ocean mixing influences just how well the ocean circulation acts to isolate the abyss, with relevance to the fate of carbon that has already been sequestered but can potentially re-emerge in the next few hundred years. The resulting global mixing rates can be prescribed in climate simulations and may reduce a major uncertainty in ocean component of these models. A more realistic simulated ocean is key on the long timescales inherent to many climate processes. The output of the project will be exported to a complementary NSF-funded project of the KeckCAVES team at UC Davis, where collaboration with computer scientists will help visualize the results in a way that will broaden participation in science and broadly disseminate climate science to the general public. In addition, this project would primarily support a young investigator in the beginning stages of building a research group.