A Shift in the Mechanisms of CO2 Uptake under High Emissions in the Southern Ocean

The Southern Ocean is a key region for natural and anthropogenic carbon dioxide (CO₂) uptake, contributing about one-third of the global ocean's total annually. In the present climate, CO₂ uptake predominantly occurs in the Subtropics during winter, driven by gas solubility. South of the subtropical front, CO₂ uptake is driven by primary production during summer and is partly compensated by seasonal upwelling of CO₂-rich water driving outgassing in winter, with the largest effect in the Antarctic region. Using a suite of nine state-of-the-art Earth System Models under the high-emission scenario, we find that the region of dominant CO₂ uptake shift to the Antarctic region in the future. Ocean warming is projected to weaken gas solubility and diminish CO₂ uptake in the subtropics. South of the Polar Front, the warming-driven sea-ice melt and the accumulation of anthropogenic dissolved inorganic carbon in the upper ocean lead to the shutting down of seasonal CO₂ outgassing and shifting the carbonate system from being nonthermal to thermal-driven in winter. The Antarctic region will then operate in a hybrid mode of winter-summer CO₂ uptake, driven by solubility and primary production, respectively.

Reference: Mongwe, P., Gregor, L., Tjiputra, J., et al. (2024). Projected poleward migration of the Southern Ocean CO₂ sink region under high emissions. Commun Earth Environ, 5, 232. https://doi.org/10.1038/s43247-024-01382-y