<p>As a critical region regulating air-sea gas exchanges, the polar Southern Ocean has important implications for deglacial atmospheric CO₂ rises. However, proxy data evidence is sparse to evaluate the respective roles of Southern Ocean biological and physical dynamics in affecting past air-sea CO₂ exchanges due to longstanding challenges in obtaining carbonate materials to reconstruct surface conditions in this region. Here, we circumvent these challenges by constraining polar Southern Ocean surface-water conditions based on preformed deep-water properties derived from paired carbonate ion-phosphate-oxygenation reconstructions during the last deglaciation. We show that polar Southern Ocean carbon losses coincided with increased deep-ocean preformed nutrient concentrations, highlighting reduced biological&#xa0;carbon utilization as a key process for deglacial CO₂ outgassing. By comparing total carbon losses with those attributable to biological processes, we further show that enhanced physically-driven air-sea gas exchanges in the polar Southern Ocean strongly drove CO₂ outgassing towards the end of the last deglaciation.</p>