Anomalous Summertime CO2 Sink in the Subpolar Southern Ocean Promoted by Early 2021 Sea Ice Retreat

In January 2022, a CARIOCA (CARbon Interface OCean Atmosphere) drifting buoy was deployed in the subpolar Southern Ocean, measuring hourly surface ocean fCO₂ (fugacity of carbon dioxide), for seventeen months. The buoy observed an anomalously strong air-sea fCO₂ disequilibrium, for over two months, near Bouvet Island. Lagrangian trajectories traced the waters back to the sea ice edge in November 2021, where a large phytoplankton bloom took place. We interpret that carbon depleted waters travelled to the subpolar region, and while air-sea CO₂ exchanges partly reduced the air-sea disequilibrium, a strong anomaly remained. Early sea ice retreat might have caused a large CO₂ sink farther north than usual in summer 2022.

Reference: Naëck, K., Boutin, J., Swart, S., et al. (2025). Anomalous summertime CO₂ sink in the subpolar Southern Ocean promoted by early 2021 sea ice retreat. Biogeosci., 22, 1947–1968. https://doi.org/10.5194/bg-22-1947-2025