Impact of Southern Ocean processes on atmospheric CO2 concentration

The Southern Ocean (SO) is believed to play a pivotal role in modulating atmospheric CO₂ concentrations, both across glacial/interglacial cycles and during abrupt climate shifts. Previous studies using coarse-resolution Earth system models have suggested that stronger southern hemisphere westerly winds enhance the upwelling of deep waters, which in turn increases CO₂ outgassing. However, mesoscale processes have a significant impact on Southern Ocean circulation. To better capture these dynamics, we assess the effects of changes in the position and strength of the southern hemisphere westerlies through a series of numerical simulations using the eddy-rich and eddy-permitting ocean, sea-ice, and carbon cycle model, ACCESS-OM2. Our results show that a 10% increase in southern hemispheric westerly wind stress leads to a 0.13 GtC/yr increase in Southern Ocean CO₂ outgassing. We also find that a poleward shift of the SH westerlies enhances CO₂ outgassing, with a sensitivity of 0.08 GtC/yr for a 5-degree poleward shift. 
We further compare the impact and timescale of the Southern Ocean carbon cycle changes driven by dynamic wind variations with those resulting from changes in Antarctic Bottom Water transport and iron fertilisation.