The Maintenance of Deep Circulation and Stratification in the Ocean

该项目将探索海洋深层层结和环流的维持机制。一个中心方面将是进一步发展和检验关于中深度和深海环流和分层的理论。对于中深度和深海的分层，还没有一套公认的理论。传统上认为，深部层结的维持是由不同温度和盐度性质的多个水团的存在和/或与经向翻转环流相结合的昼夜混合所维持的分层深渊。然而，最近的数值研究表明，在南极绕极航道再入的情况下，即使在极日扩散系数消失的极限情况下，深层层结也可以维持。如果这是真的，这将是一个重要的结果，无论是在基本层面上，还是因为它将对海洋混合和需要较大的昼夜扩散系数值，对于过去气候制度中的海洋行为和碳循环都有影响。研究人员已经开发了温跃层以下海洋分层的概念模型，该模型将进一步发展和推广为定量和可检验的机制理论。这一理论将通过数值模拟进行检验，并用来更好地理解结果是否适用于真实的海洋，以及在过去的气候中对海洋环流的影响是什么。理解海洋分层是海洋学中一个具有挑战性的基本问题。我们建议进一步发展一种新的理论，进行数值模拟，并与其他假设进行比较，以确定深层层结和相关的倾覆环流的原因。了解海洋分层和环流是改进预测海洋输送的数值模式的一个必要方面。深层环流也可能与二氧化碳的吸收和释放有关，是决定大气中二氧化碳水平的重要因素。因此，了解深层环流将有助于我们理解气候变化在很长时间尺度上的性质。这项提议将支持一名刚刚开始有前途的职业生涯的初级科学家。最后，首席调查员将修订一本教科书(Vallis 2006)，这本教科书已经被一些大学采用，用于教授大气和海洋动力学，他正在开始编写第二本本科生级别的关于海洋对气候的影响的书。

The project will explore the mechanisms of maintenance of the deep stratification and circulation of theocean. A central aspect will be to further develop and to test a theory for the mid-depth and abyssal circulation and stratification. There is no body of accepted theory for the stratification of the mid-depth and abyssal ocean. Traditionally, it has been supposed that the deep stratification is maintained by the presence of multiple water masses with different temperature and salinity properties and/or by diapycnal mixing which, in association with a meridional overturning circulation, can maintain a stratified abyss. However, recent numerical investigations have suggested that, in the presence of a re-entrant Antarctic Circumpolar Channel, deep stratification can be maintained even in the limit of vanishing diapycnal diffusivity. If true, this would be an important result both at a fundamental level and because of the implications it would have for ocean mixing and the need for large values of diapycnal diffusivity, for the behavior of the ocean in past climate regimes, and for the carbon cycle. The investigators have developed a conceptual model for the stratification of the ocean below the thermocline, which will be further developed and extended into a quantitative and testable mechanistic theory. The theory will be tested with numerical simulations, and used to better understand whether the results apply to the real ocean and what the consequences are for ocean circulation in past climates.Intellectual MeritUnderstanding the stratification of the ocean is a challenging fundamental problem in oceanography. We are proposing to further develop a novel theory and to perform numerical simulations, and to compare with alternative hypotheses, to determine the cause of the deep stratification and associated overturning circulation.Broader ImpactsThe deep circulation of the ocean transports heat meridionally and so is of direct importance to the climate system. Understanding the ocean stratification and circulation is a necessary aspect of improving numerical models that predict that transport. The deep circulation is also likely tied to the uptake and release of carbon dioxide, and is an important factor determining the levels of carbon dioxide in the atmosphere. Understanding the deep circulation will therefore help us to understand the nature of climate variability on very long timescales. The proposal will support a junior scientist at the threshold of a promising career. Finally, the lead investigator will be revising a textbook (Vallis 2006) that has been adopted by a number of universities for the teaching of atmospheric and oceanic dynamics, and he is beginning to write a second, undergraduate level, book on the ocean's impact on climate.