Figure 3.

TA versus DIC plots (i.e., Deffeyes diagrams) showing the equilibrium pH at free scale (a) and pCO₂ in μatm (b) as contours. Both graphs show vectors for the addition of protons (vertically downward) and dissolution of calcium carbonate (slope 2:1). Notice that the resulting change in pH and pCO₂ for the same amount of calcite dissolved or acid added (same vector) differs because of differences in sensitivity (buffering). For instance, the ΔpH and ΔpCO₂ for proton additions are −0.074 and +136 μatm, respectively, at low buffering (high DIC/TA ratio), and −0.037 and +20.9 μatm at high buffering (low DIC/TA ratio). Similarly, for the calcite dissolution vector, the ΔpH values are 0.022 and 0.013 and the ΔpCO₂ values are −33.9 and −5.9 μatm for low and high buffering, respectively.