Figure 4. Aragonite mineral saturation state (Ω_arag) and buffer index in the coral calcifying fluid as functions of pH and [DIC].

(a) Ω_arag and (b) buffer index. The buffer index is given as mmol kg⁻¹ of H⁺ pumping (H⁺ loss or TA gain) per unit of pH upregulation. This index is calculated numerically with CO2SYS (ref. ³⁷) (see Methods section). Here [DIC]=1800 μmol kg⁻¹ is roughly the same as seawater value. pH is on the NBS scale.