Tipping Points in Southern Ocean Tracer Ventilation

The Southern Ocean with its steeply sloping isopycnals acts as a control valve through which climatically important tracers such as heat, freshwater, and CO₂ are transferred between the atmosphere and the ocean. The process which transports these climatically important tracers from the surface mixed layer into the ocean interior is known as ocean ventilation, and its dynamics are thought to be important for both the abrupt reorganisation of the ocean's global overturning circulation during the last glacial and deglacial period, and the uptake and storage of excess heat and CO₂, produced as a consequence of anthropogenic climate change, in future climate. Here I show how the interaction between Southern Ocean jets and topographic features can lead to a tipping point in Southern Ocean ventilation. For increasing winds, this interaction leads from a state in which tracers are confined to the surface mixed layer, to a tipping point beyond which tracers ventilate the ocean interior. For the Kerguelen Plateau, in the Indian sector of the Southern Ocean, this tipping point is reached for wind forcing predicted by climate models for the coming century. These results imply a prominent role for jet dynamics in understanding tipping points in the global climate system.