Impact of air-ice CO2 fluxes on polar ocean carbon budgets: a bipolar data compilation

In Earth system models and ocean carbon budget assessments, sea-ice is still treated as an impermeable barrier rather than a dynamic interface mediating CO₂ exchange between the ocean and atmosphere. To quantify its contribution to the polar ocean carbon budget, we compiled over 6000 chamber-based air–ice CO2 flux collected across the Arctic and Southern Ocean between 2003 and 2021. This unprecedented database spans diverse sea-ice, snow, and seasonal conditions. Despite spatiotemporal limitations, this database enables a comprehensive reassessment of sea-ice’s role in the carbon budgets of polar oceans. Sea ice acts as a CO₂ source in winter and a sink in summer, as summer drawdowns offset most winter emissions. On an annual basis, sea-ice represents a small net CO₂ source of +4 Tg C yr⁻¹ in the Arctic and +2 Tg C yr⁻¹ in the Southern Ocean, refuting previous hypotheses of a major sea-ice carbon sink. Although these net fluxes remain negligible at basin scales relative to concurrent open-ocean uptake, our results highlight that sea-ice exchanges gases even in cold winter conditions. These exchanges may have critical implications for short-term, small-scale processes and for other trace gases, underscoring the need for continuous, process-resolving flux observations.