Southern Ocean [in “State of the Climate in 2017”]

In the climate system, the Southern Ocean is disproportionately important when it comes to its storage of heat and carbon. Modification of the upper Southern Ocean could have significant implications for the rate and magnitude of air–sea fluxes (of heat and carbon) and for the ventilation of the ocean interior, thereby altering the effects of climate warming on the ocean system as a whole. Here, we evaluate the state of the Southern Ocean in 2017 by first assessing the upper ocean as the interface between the atmosphere and ocean interior. We then discuss the changes in intermediate to deep water masses, which are critical pathways to moving heat and carbon to the ocean interior where it will (in general) remain for decades to centuries. Lastly, we report on the status of ocean acidification in the Southern Ocean using newly available biogeochemical observations.