Contributions of biological and physical dynamics to deglacial CO2 release from the polar Southern Ocean

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 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.