The Southern Ocean is an important contributor to carbon cycling and is of most importance for our global climate. The capacity of the ocean to store and sequester carbon is set by the ocean circulation which transfers carbon in and out of the deep ocean. North of the Antarctic Circumpolar Current (ACC), anthropogenic carbon (Cant) is subducted and stored in the ocean interior, mainly in subantarctic mode and intermediate waters (SAMW-AAIW). South of the ACC, old carbon- and nutrient-rich deep water is brought to the surface via large-scale upwelling driven by the Westerly winds. In pre-industrial times, this later process used to release CO2, so-called natural carbon. However, the rise of atmospheric CO2 ever since suppresses this outgassing more and more transforming the upwelling regions into new sinks of anthropogenic carbon.

The physical mechanisms responsible for the transfers in and out of the ocean interior remain poorly understood. Here, we use biogeochemical eddy-resolving ocean simulations (1/10°) to investigate the mechanisms involved in Cant subduction north of the ACC and carbon outgazing south of the ACC.

First, we focus on the SAMW-AAIW subduction hotspots. In the high resolution model, mesoscale transient eddies appear to have little influence on the total Cant subduction in SAMW-AAIW, with the time-mean circulation contributing to 87% of the Cant subduction. The mechanism dominating the Cant transfer in SAMW-AAIW is Mesoscale Stationary Rossby Waves (SRWs). SRWs are generated when the strong ACC jets interact with topography and are not well reproduced in low spatial resolution models.

Secondly, we assess the role of ocean in controlling carbon fluxes south of the ACC. Hot spots of natural carbon outgassing and anthropogenic carbon uptake occur near topographic obstacles along the Polar Front. We discuss potential physical–biological mechanisms through which fronts merging and baroclinic instabilities may affect carbon fluxes and pathways.