Extended Data Fig. 5: Heterogeneous surface-water CO₂ partial pressure (pCO₂) in the Southern Ocean.

a, Spatial surface-water pCO₂ during the preindustrial, based on the GLODAP data set¹⁵. Note that the data coverage is incomplete and should not be treated to reflect the annual mean conditions. b, Temporal surface water and atmospheric pCO₂ gradient (ΔpCO₂) at PS2498-1 from the South Atlantic. c, Temporal ΔpCO₂ at MD97-2106 from the South Pacific (see also ref. ¹⁰¹). Surface-water pCO₂ was heterogeneous in the Southern Ocean, both spatially and temporally. Despite the Southern Ocean being an overall source of CO₂ to the atmosphere, some surface ocean regions had lower pCO₂ than the atmosphere, possibly reflecting seasonal and hydrographical variations in surface conditions. When using surface data, this highlights the need to obtain data for different seasons at broad locations to gain complete information about the Southern Ocean’s role in atmospheric CO₂¹⁷. Literature data are plotted against their originally published age models.