Abstract

The lower cell of the meridional overturning circulation (MOC) is sourced by dense Antarctic Bottom Waters (AABW), which form and sink around Antarctica and subsequently fill the abyssal ocean. For the MOC to ‘overturn’, these dense waters must upwell via mixing with lighter waters above. Here, we investigate the processes underpinning such mixing, and the resulting water mass transformation, using an observationally forced, high-resolution numerical model of the Drake Passage in the Southern Ocean. In the Drake Passage, the mixing of dense AABW formed in the Weddell Sea with lighter deep waters transported from the Pacific Ocean by the Antarctic Circumpolar Current is catalysed by energetic flows impinging on rough topography. We find that multiple topographic interaction processes facilitate the mixing of the two water masses, ultimately resulting in the upwelling of waters with neutral density greater than 28.19, and the downwelling of the lighter waters above.