Abstract
The subpolar Southern Ocean is a critical region where CO2 outgassing influences the global mean air-sea CO2 flux (FCO2). However, the processes controlling the outgassing remain elusive. We show, using a multi-glider dataset combining FCO2 and ocean turbulence, that the air-sea gradient of CO2 (∆pCO2) 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 CO2 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 ∆pCO2 (6 µatm2 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 FCO2 but also the effects of synoptic variability on slower seasonal or longer ocean physics-carbon dynamics.
Highlights
The subpolar Southern Ocean is a critical region where CO2 outgassing influences the global mean air-sea CO2 flux (FCO2)
This outgassing variability has been linked to climate-mode forced variations in wind-driven upwelling that comprises the surfacing of deep waters with high concentrations in dissolved inorganic carbon (DIC) resulting in widespread but variable outgassing of CO2 in the subpolar region, which counteracts the CO2 uptake flux[2,9,10]
The air-sea flux of CO2 is defined (Eq 1) as the product of the air-sea gradient of pCO2 (ΔpCO2 = pCO2sea − pCO2atm, where pCO2sea is the partial pressure of CO2 in the surface ocean and pCO2atm in the atmosphere), the temperature-dependent solubility Ks and the wind dependent air-sea gas transfer velocity Kw30
Summary
The subpolar Southern Ocean is a critical region where CO2 outgassing influences the global mean air-sea CO2 flux (FCO2). Extrapolation across the subpolar Southern Ocean using a process model shows how ocean fronts spatially modulate synoptic variability in ΔpCO2 (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 constrain aliased-driven uncertainties in FCO2 and the effects of synoptic variability on slower seasonal or longer ocean physicscarbon dynamics. Intense wind events drive turbulent entrainment of the deeper
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