From winds to eddies to diapycnal mixing of the deep ocean: the abyssal meridional overturning circulation driven by the surface wind-stress.




Stanley, Geoffrey John

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Previous numerical and theoretical results based on constant diapycnal diffusivity suggested the abyssal meridional overturning circulation (MOC) should weaken as winds over the Southern Ocean intensify. We corroborate this result in a simple ocean model, but find it does not hold in more complex models. First, models with a variable eddy transfer coefficient and simple yet dynamic atmosphere and sea-ice models show an increase, albeit slightly, of the abyssal MOC under increasing winds. Second, the abyssal MOC significantly strengthens with winds when diapycnal diffusivity is parameterized to be energetically supported by the winds. This tests the emerging idea that a significant fraction of the wind energy input to the large-scale ocean circulation is removed by mesoscale eddies and may then be transferred to internal lee waves, and thence to bottom-enhanced diapycnal mixing. A scaling theory of the abyssal MOC is extended to incorporate this energy pathway, corroborating our numerical results.



Diapycnal Mixing, Abyssal Circulation, Southern Ocean, Ocean Energetics, Westerly Winds, Meridional Overturning Circulation