Turning ocean mixing upside down

The upwelling of abyssal waters through density surfaces in the deep ocean is not possible unless the sloping nature of the sea floor is taken into account. The bottom‐-intensified mixing arising from interaction of internal tides and geostrophic motions with bottom topography implies that mixing is a decreasing function of height in the deep ocean. This further implies that the diapycnal motion in the deep ocean is downward, not upwards as is required to balance the sinking of dense waters at high latitudes. This conundrum is resolved by appealing to the fact that the ocean does not have vertical side walls and upwelling can proceed along the sloping boundaries. The implications of this result for our understanding of the abyssal ocean circulation will be presented with a combination of numerical models and observations.