We develop a simple model of the lower limb of the meridional overturning circulation in the Southern Ocean based on residual mean theory. We hypothesize that the strength of the lower limb (Ψ) is strongly controlled by the magnitude of abyssal diapycnal mixing (κ), and that of mesoscale eddy transfer (K). In particular, we argue that Ψ ∝ √ κK. The scaling and associated theory find support in ...