| Summary: | The location of fronts has a direct influence on both the physical and biological processes in the Southern Ocean. Moreover, the Subtropical Front (STF) is believed play a key role in the global climate system. Model simulations have shown that a wind induced poleward shift of the STF may strengthen the Atlantic Meridional Overturning Circulation by allowing a stronger salt flux from the Indian to the Atlantic Ocean. This hypothesis has important implications for our future climate, as global warming scenarios predict an intensification and southward shift of the Southern Hemisphere Westerlies. Nonetheless, confirmation of the theory has been limited by a lack of data and also our poor dynamical understanding of fronts. In this thesis we produce a new working dynamical definition of the STF and study the relation of this and other Southern Ocean fronts to the winds and topography. We first explore the relative importance of bottom topography and winds for determining the location and structure of Southern Ocean fronts, using 100 years of a control and climate change simulation on the high resolution coupled climate model HiGEM. Topography has primary control on the number and intensity of fronts at each longitude. However, there is no strong relationship between the position or spacing of jets and underlying topographic gradients because of the effects of upstream and downstream topography. The Southern Hemisphere Westerlies intensify and shift south by 1.3° in the climate change simulation, but there is no comparable meridional displacement of the Antarctic Circumpolar Current’s (ACC) path or the fronts within its boundaries, even over flat topography. Instead, the current contracts meridionally and weakens. North of the ACC, the STF shifts south gradually, even over steep topographic ridges. We suggest the STF reacts more strongly to the wind shift because it is strongly surface intensified. In contrast, fronts within the ACC are more barotropic and are therefore more sensitive to the underlying topography. We ...
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