Southern Ocean ventilation: connection to dynamic tracers and uptake of heat and carbon

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The Southern Ocean is globally important due to the Antarctic Circumpolar Current, connecting the three main ocean basins (Indian, Pacific, Atlantic) and leading to the global exchange of heat, carbon, and nutrients. The strong westerly winds in the Southern hemisphere lead to an upwelling of deep waters and thus the creation of mode and intermediate waters, such as Subantarctic Mode Water and Antarctic Intermediate Water. These mode waters spread northward and ventilate the subtropics, and hence can have an impact on the amount of heat and carbon transported around the globe. Mode waters are formed at the end of winter when the very deep mixed layers in the Southern Ocean shoal and leave behind a well-mixed, homogeneous layer of water. These mode waters are defined on certain density surfaces in different ocean basins by their low potential vorticity. The ventilation in the Southern Ocean will be investigated using the ECCOv4 global ocean circulation model to complete a set of adjoint sensitivity experiments and forward perturbation experiments. These experiments will be used to reveal how different surface forcing affects the formation of several mode waters in the Southern Ocean. The outcome from these experiments will be sensitivity maps that identify where forcing terms, such as heat flux and wind stress, have an impact on the formation of mode waters. We then plan to test these linear inferences using forward perturbation experiments. We also hope to provide physical insight into how ventilation affects the uptake of heat and carbon. This insight may be important to help identify which physical mechanisms may change in the Southern Ocean as the ocean warms through climate change.