The dynamics of the ocean meridional overturning circulation.

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The ocean meridional overturning circulation (MOC) plays a key role in the climate system: it controls the amount of heat stored in the deep ocean and helps regulate the exchange of CO2 with the atmosphere. Yet, its response to changes in external atmospheric forcing is still poorly understood and modeled. Over the last twenty years, it has become clear that modeling the response of the MOC to climate change requires high spatial resolution. This is especially true in the Southern Ocean, where geostrophic turbulence around the Antarctic Circumpolar Current (ACC) must be explicitly resolved. Current computing power allows for a small number of eddy-resolving simulations modeling the MOC in global models. It does not, however, allow for a more thorough exploration of the parameter space, such as is required to fully understand the governing dynamics. Instead, such studies are typically carried out using more idealized models. As a result, there still exists a very wide gap between the idealized theoretical studies that attempt to understand the dynamics of the overturning circulation and the more realistic General Circulation Model (GCM) simulations that attempt to mimic accurately the MOC and predict its response to climate change. The overall goal of this proposal is to bridge this gap. To do this, we will apply a powerful two-way grid nesting approach to a GCM in order to consider a much wider range of model complexities and address the role of key processes that have been neglected in previous theoretical studies of the MOC. We will focus on various boundary conditions constraining the MOC and address the following questions: