Abstract

Only a small fraction of the ocean is interacting with the atmosphere at any given time. This water is definitively found in the upper mixing layer of the ocean. When this water leaves the mixing layer and enters the ocean interior, it has ‘ventilated’ (this term arising from the abundance of oxygen in newly ventilated water). The Southern Ocean is an important ventilation site for heat and carbon and is likely to influence the outcome of anthropogenic climate change. We conduct an extensive backwards-in-time trajectory experiment (effectively calculating a 30 year ‘history’ of the Southern Ocean) to identify spatial and temporal patterns of ventilation. Temporally, almost all ventilation occurs between August and November. Spatially, ‘hotspots’ of ventilation account for 60% of open-ocean ventilation on a 30-year timescale; the remaining 40% ventilates in a circumpolar pattern. The densest waters ventilate on the Antarctic shelf, primarily near the Antarctic Peninsula (40%) and the west Ross Sea (20%); the remaining 40% is distributed across East Antarctica. Shelf-ventilated waters also appear to experience significant densification outside of the mixed layer.