The Southern Ocean is fundamental to the operation of the Earth system. It is the central connection among the major ocean basins and between the upper and lower layers of the global ocean circulation. It influences global climate and planetary-scale biogeochemical cycles, because the Southern Ocean accounts for half of the annual ocean uptake of anthropogenic carbon from the atmosphere [Rintoul et al., 2001; Le Quéré et al., 2007; Meredith et al., 2012]. The Southern Ocean also supplies nutrients that fertilize the majority of global ocean biological productivity north of 30°S [Sarmiento et al., 2004].