Opening the window to the Southern Ocean: the role of jet dynamics

The surface waters of the Southern Ocean act 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 that transports these tracers through the surface mixed layer into the ocean interior is known as ocean ventilation. Changes in ocean ventilation are thought to be important for both rapid transitions of the ocean’s global overturning circulation during the last deglaciation and the uptake and storage of excess heat and CO₂ as a consequence of anthropogenic climate change. I show how the interaction between Southern Ocean jets, topographic features, and ocean stratification can lead to rapid changes in Southern Ocean ventilation as a function of wind stress. For increasing winds, this interaction leads from a state in which tracers are confined to the surface mixed layer to a state in which tracers fill the ocean interior. For sufficiently high winds, the jet dynamics abruptly change, allowing the tracer to ventilate a water mass known as Antarctic Intermediate Water in the mid-depth Southern Ocean. Abrupt changes in Antarctic Intermediate Water ventilation have played a major role in rapid climate transitions in Earth’s past, and combined with the results presented here, this would suggest that jet dynamics could play a prominent role in contributing to, or even triggering, rapid transitions of the global climate system.