Storms drive outgassing of CO 2 in the subpolar Southern Ocean.

The subpolar Southern Ocean is a critical region where CO 2 outgassing influences the global mean air-sea CO 2 flux (F CO2 ). However, the processes controlling the outgassing remain elusive. We show, using a multi-glider dataset combining F CO2 and ocean turbulence, that the air-sea gradient of CO 2 (∆pCO 2 ) is modulated by synoptic storm-driven ocean variability (20 µatm, 1-10 days) through two processes. Ekman transport explains 60% of the variability, and entrainment drives strong episodic CO 2 outgassing events of 2-4 mol m -2 yr -1 . Extrapolation across the subpolar Southern Ocean using a process model shows how ocean fronts spatially modulate synoptic variability in ∆pCO 2 (6 µatm 2 average) and how spatial variations in stratification influence synoptic entrainment of deeper carbon into the mixed layer (3.5 mol m -2 yr -1 average). These results not only constrain aliased-driven uncertainties in F CO2 but also the effects of synoptic variability on slower seasonal or longer ocean physics-carbon dynamics.