Changes in Internal Wave Driven Diapycnal Mixing

海洋是人为变暖的最大汇，其中很大一部分热量在深海中积累。了解是什么推动了这种深度变暖，以及气候系统将如何对此做出反应，对于准确预测未来海洋将如何吸收人为热量至关重要。一个重要的过程是不同密度的海洋混合（潜流混合），这既取决于也直接影响海洋内的热量分布。然而，据我们所知，目前还没有研究利用观测来探索海洋混合如何随着气候变化而变化，而气候变化将直接影响热量在未来如何被吸收和储存在海洋中。这项研究的最终目标是首次对过去几十年来海洋的混合变化进行观测估计。除了支持一名早期职业观察学家外，还将支持一名本科生暑期学生。海洋内部的大部分混合是由于内部重力波的产生、传播和破裂都取决于背景分层。这种背景分层是由海水的温度和盐度变化演变而来的，海水的温度和盐度随海洋位置的不同而变化。由内波引起的混频预计也会发生变化。然而，尚不清楚这是否会对海洋的能量或热量预算做出实质性贡献。该项目旨在为混合变化设定观测界限，解决以下问题：在气候尺度上，海洋中的潜周期混合在哪里以及在多大程度上发生了变化？这个变化大到足以影响深海的热量收支吗？计划的观测基础设施是否足以测量混合变化？这些问题将通过分析在全球重复水文调查期间收集的数据来解决。利用这些水文剖面，研究者将在全球范围内探索分层随时间的变化，并将这些观察结果与已知的水性质变化联系起来。然后，利用温度、盐度和压力数据对混合的估计，在水文剖面上计算出河床混合的变化和相关的不确定性。最后，将计算的混合变化应用于封闭深海盆地的热收支来考虑这些变化的重要性。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The oceans are the largest sink of anthropogenic warming, and a large portion of this heat is accumulating in the deep ocean. Understanding what is driving this deep warming, and how the climate system will respond to it, is vital to accurately forecasting how the ocean will take up anthropogenic heat in the future. One important process is ocean mixing between different densities (diapycnal mixing), which both depends on and directly affects heat distribution within the ocean. Yet to our knowledge there have been no studies using observations to explore how ocean mixing may be changing in response to climate change, which would directly affect how heat is taken up and stored within the ocean in the future. The ultimate goal of this study is to provide the first such observational estimate of mixing changes in the ocean over the last few decades. One undergraduate summer student will be supported on this grant, in addition to the support of an early career observationalist. Much of the mixing in the ocean interior is due to internal gravity waves whose generation, propagation, and breaking all depend on the background stratification. This background stratification evolves from changes in the temperature and salinity of the water, which vary by location in the ocean. The mixing due to internal waves is also expected to change. However, it is not known whether that will make a substantial contribution to the energy or heat budgets of the ocean. This project aims to place observational bounds on the change in mixing, addressing the questions: Where, and to what extent, is diapycnal mixing in the ocean changing on climate scales? Is this change large enough to influence abyssal heat budgets? Is the planned observational infrastructure sufficient for measuring the changes in mixing? These questions will be addressed through analysis of data collected during global repeat hydrographic surveys. Using these hydrographic sections, the investigator will explore the stratification change with time on a global scale, and link these observations to known water property changes. The change in diapycnal mixing and associated uncertainties will then be calculated over the hydrographic sections using estimates of mixing from temperature, salinity, and pressure data. Finally, the importance of these changes will be considered by applying the calculated changes in mixing to heat budgets of enclosed abyssal basins.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.