Response of the Southern Ocean Air‐Sea CO 2 Flux to Positive and Negative Emissions
Precious Mongwe, Jerry Tjiputra, Nadine Goris, Yeray Santana‐Falcón, Kyung‐Min Noh, Takamitsu ItoAbstract
We investigate the response and reversibility of Southern Ocean air–sea CO 2 fluxes to a symmetric atmospheric CO 2 increase and removal experiment, where atmospheric CO 2 is increased by 1% annually for 140 years, followed by a symmetric 1% annual decrease over 140 years, and then held at preindustrial levels for 50 years. During positive emissions, the Southern Ocean CO 2 sink strengthens and shifts poleward, with the Antarctic region becoming the dominant uptake area. Carbon dioxide removal reverses this spatial redistribution within approximately 100 years, restoring a subtropical‐dominated uptake structure; however, the Southern Ocean remains a net CO 2 source for at least 50 years after mitigation. This delayed recovery arises from the inefficient removal of anthropogenic dissolved inorganic carbon relative to heat, leading to persistent subsurface carbon storage and sustained reductions in CO 2 solubility. Model responses show a pronounced asymmetry between emission and removal phases, with a faster intensification of CO 2 uptake during ramp‐up than its recovery during ramp‐down. These differences are strongly controlled by preindustrial seasonal pCO 2 dynamics and ocean CO 2 buffering capacity: models with a weaker buffering capacity exhibit up to twice the sensitivity of air–sea CO 2 fluxes to atmospheric forcing. Seasonal cycle representation in the Subantarctic and Antarctic regions further separates models into thermally and non‐thermally dominated regimes, which govern both the magnitude and reversibility of the CO 2 sink under forcing. Overall, our results demonstrate that Southern Ocean carbon sink recovery under negative emissions is slow, spatially heterogeneous, and controlled by interior ocean memory and seasonal carbon‐cycle processes.