evidence: The global net air–sea CO2 flux is a residual of large natural and anthropogenic CO2 fluxes into and out of the ocean with distinct regional and seasonal variations (Figs. 6 and B1). Natural fluxes dominate on regional scales but largely cancel each other out when integrated globally (Gruber et al., 2009). Mid-latitudes in all basins and the high-latitude North Atlantic dominate the ocean CO2 uptake where low temperatures and high wind speeds facilitate CO2 uptake at the surface (Takahashi et al., 2009). In these regions, the formation of mode, intermediate, and deep water masses transports anthropogenic carbon into the ocean interior, thus allowing for continued CO2 uptake at the surface. Outgassing of natural CO2 occurs mostly in the tropics, especially in the equatorial upwelling region, and to a lesser extent in the North Pacific and polar Southern Ocean, mirroring a well-established understanding of regional patterns of air–sea CO2 exchange (e.g. Takahashi et al., 2009; Gruber et al., 2009). These patterns are also noticeable in the Surface Ocean CO2 Atlas (SOCAT) data set, where an ocean fCO2 value above the atmospheric level indicates outgassing (Fig. S1).