Carbonate compensation dynamics

Carbonate saturation (zsat) and compensation (zcc) depths change with deep‐ocean acidification and basification. We present simple, explicit, mechanistic formulas for the positions of these two critical depths. In particular zcc is expressed as a function of the mean dissolved carbonate ion concentration of the deep ocean, [CO3]D, the supply of dissolvable CaCO3, Fc, and the dissolution rate constant at the sediment‐water interface, kc, which we show to be essentially mass‐transfer controlled. Calculations reveal that zsat and zcc are today some ∼0.9 km apart and will rise and separate by as much as 1.7 km with acidification; conversely, if [CO3]D increases, zsat and zcc will deepen, but their separation will asymptote to ∼0.7 km.