Oxygen in the Southern Ocean From Argo Floats: Determination of Processes Driving Air-Sea Fluxes

Abstract

The Southern Ocean is of outsized significance to the global oxygen and carbon cycles with relatively poor measurement coverage due to harsh winters and seasonal ice cover. In this study, we use recent advances in the parameterization of air‐sea oxygen fluxes to analyze 9 years of oxygen data from a recalibrated Argo oxygen data set and from air‐calibrated oxygen floats deployed as part of the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project. From this combined data set of 150 floats, we find a total Southern Ocean oxygen sink of −183 ± 80 Tmol yr−1 (positive to the atmosphere), greater than prior estimates. The uptake occurs primarily in the Polar‐Frontal Antarctic Zone (PAZ, −94 ± 30 Tmol O2 yr−1) and Seasonal Ice Zone (SIZ, −111 ± 9.3 Tmol O2 yr−1). This flux is driven by wintertime ventilation, with a large portion of the flux in the SIZ passing through regions with fractional sea ice. The Subtropical Zone (STZ) is seasonally driven by thermal fluxes and exhibits a net outgassing of 47 ± 29 Tmol O2 yr−1 that is likely driven by biological production. The Subantarctic Zone (SAZ) uptake is −25 ± 12 Tmol O2 yr−1. Total oxygen fluxes were separated into a thermal and nonthermal component. The nonthermal flux is correlated with net primary production and mixed layer depth in the STZ, SAZ, and PAZ, but not in the SIZ where seasonal sea ice slows the air‐sea gas flux response to the entrainment of deep, low‐oxygen waters.