Simulated effect of calcification feedback on atmospheric CO(2) and ocean acidification

Ocean uptake of anthropogenic CO(2) reduces pH and saturation state of calcium carbonate materials of seawater, which could reduce the calcification rate of some marine organisms, triggering a negative feedback on the growth of atmospheric CO(2). We quantify the effect of this CO(2)-calcification feedback by conducting a series of Earth system model simulations that incorporate different parameterization schemes describing the dependence of calcification rate on saturation state of CaCO(3). In a scenario with SRES A2 CO(2) emission until 2100 and zero emission afterwards, by year 3500, in the simulation without CO(2)-calcification feedback, model projects an accumulated ocean CO(2) uptake of 1462 PgC, atmospheric CO(2) of 612 ppm, and surface pH of 7.9. Inclusion of CO(2)-calcification feedback increases ocean CO(2) uptake by 9 to 285 PgC, reduces atmospheric CO(2) by 4 to 70 ppm, and mitigates the reduction in surface pH by 0.003 to 0.06, depending on the form of parameterization scheme used. It is also found that the effect of CO(2)-calcification feedback on ocean carbon uptake is comparable and could be much larger than the effect from CO(2)-induced warming. Our results highlight the potentially important role CO(2)-calcification feedback plays in ocean carbon cycle and projections of future atmospheric CO(2) concentrations.