Marine calcification as a source of carbon dioxide: Positive feedback of increasing atmospheric CO2

Calcification is a well‐recognized source of CO 2 to the surrounding water and thus a potential source of atmospheric CO 2 due to chemical equilibria involving the CO 2 species. The released CO 2 : precipitated carbonate ratio (Ψ) has recently been estimated to be 0.6 in seawater (taking into account the buffering capacity of the latter). We report an analytical expression enabling the computation of this ratio. Calculations show that the amount of CO 2 that must be released to equilibrate seawater increases with increasing partial pressure of CO 2 in seawater ( p CO 2 ), which results from human impact on atmospheric CO 2 . We show that at 15°C Ψ increased from 0.55 during the time of glaciation to 0.67 at present and would increase to 0.84 for a p CO 2 of 1,000 µ atm. Doubling the preindustrial p CO 2 value results in a total CO 2 source of ∼5 Gt C (taking into account the described buffering effect).