Dynamics of eddying abyssal mixing layers over sloping rough topography

Abstract ABSTRACT: The abyssal overturning circulation is thought to be primarily driven by small-scale turbulent mixing. Diagnosed watermass transformations are dominated rough topography “hotspots”, where the bottom-enhancement of mixing causes diffusive buoyancy flux diverge, driving widespread downwelling in interior—only overwhelmed an even stronger up-welling a thin Bottom Boundary Layer (BBL). These significantly underestimated one-dimensional (1D) sloping boundary layer solutions, suggesting importance three-dimensional physics. Here, we use hierarchy models generalize this 1D approach eddying flows over realistically topography. When applied Mid-Atlantic Ridge Brazil Basin, idealized simulation results roughly consistent with available observations. Integral budgets isolate physical processes that contribute strong BBL upwelling. downwards diffusion balanced upwelling along canyon sidewalls and surrounding hills. strengthened restratifying effects submesoscale baroclinic eddies blocking along-ridge thermal wind within canyon. Major topographic sills block along-thalweg from trough, resulting continual erosion trough’s stratification. We propose simple modifications model which approximate each these effects. provide local dynamical insights into mixing-driven overturning, but complete theory will also require non-local coupling basin-scale circulation.