Figure 7.10. Three main ocean carbon pumps govern the regulation of natural atmospheric CO₂ changes by the ocean (Heinze et al., 1991): the solubility pump, the organic carbon pump and the CaCO₃ ‘counter pump’. The oceanic uptake of anthropogenic CO₂ is dominated by inorganic carbon uptake at the ocean surface and physical transport of anthropogenic carbon from the surface to deeper layers. For a constant ocean circulation, to first order, the biological carbon pumps remain unaffected because nutrient cycling does not change. If the ocean circulation slows down, anthropogenic carbon uptake is dominated by inorganic buffering and physical transport as before, but the marine particle flux can reach greater depths if its sinking speed does not change, leading to a biologically induced negative feedback that is expected to be smaller than the positive feedback associated with a slower physical downward mixing of anthropogenic carbon. Reprinted with permission, copyright 1991 American Geophysical Union.