The Southern Ocean is vital to our understanding of the climate system. It is a key region for vertical and lateral exchanges of heat, freshwater, carbon, oxygen, and nutrients, with significant past and potential future global climate implications, especially around the latitudes of the Antarctic Circumpolar Current, which is the focus region for this session. The role of the Southern Ocean as a dominant player in heat and biogeochemical exchanges as well as its response to changing atmospheric forcing and increased Antarctic melting remains uncertain. Indeed, the sparsity of observations of this system and its inherent sensitivity to small-scale physical processes, not fully represented in current Earth System Models, result in large climate projection uncertainties and considerable discrepancies between observations and models. To address these knowledge gaps, the Southern Ocean is currently subject to investigations with increasingly advanced observational platforms as well as theoretical, numerical and machine learning techniques. These efforts are providing deeper insight into the three-dimensional patterns of Southern Ocean changes on sub-annual, multi-decadal and millennial timescales, as well as their potential future modifications under a changing climate. In this session, we welcome contributions concerning the role of the Southern Ocean in past, present, and future climates. These include (but are not limited to) small-scale physics and mixing, water mass transformation, gyre-scale processes, nutrient and carbon cycling, ventilation, ocean productivity, climate-carbon feedbacks, and ocean-ice-atmosphere interactions. We also welcome contributions on how changes in Southern Ocean circulation as well as heat and carbon transport affect lower latitudes and global climate more generally.