Dynamics and mixing of stratified rotating bottom boundary layers

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Enhanced turbulence in the vicinity of sloping bottom topography in stratified basins has an important effect on the dynamics of near-bottom currents, and is often also essential for basin-scale mixing. The prevailing view has been that near-bottom turbulence is energized primarily through either breaking internal waves or bottom friction. Results from a recent DFG project, however, have shown that differential advection in the bottom boundary layer may generate gravitationally unstable stratification, therefore triggering turbulent convection. This process, largely ignored in previous studies, was shown to provide an important additional energy source for near-bottom turbulence with a number of significant consequences for mixing inside bottom boundary layers. Insights gained from this previous study, focusing only on non-rotating systems, will be generalized in this proposal by including the effect of Earth's rotation. In contrast to previous investigations of the dynamics of near-bottom currents, the present project will emphasize the role of near-bottom turbulence due to shear-induced convection, and its implications for overall mixing. To this end, our expertise in turbulence modeling will be used for the analysis of rotating bottom boundary layers with the help of different types of idealized numerical models. These theoretical and numerical investigations will be complemented by the analysis of an already existing data set describing shear-induced convection in the bottom boundary layer on the North American shelf.