Multiple timescales for neutralization of fossil fuel CO2

The long term abiological sinks for anthropogenic CO 2 will be dissolution in the oceans and chemical neutralization by reaction with carbonates and basic igneous rocks. We use a detailed ocean/sediment carbon cycle model to simulate the response of the carbonate cycle in the ocean to a range of anthropogenic CO 2 release scenarios. CaCO 3 will play only a secondary role in buffering the CO 2 concentration of the atmosphere because CaCO 3 reaction uptake capacity and kinetics are limited by the dynamics of the ocean carbon cycle. Dissolution into ocean water sequesters 70–80% of the CO 2 release on a time scale of several hundred years. Chemical neutralization of CO 2 by reaction with CaCO 3 on the sea floor accounts for another 9–15% decrease in the atmospheric concentration on a time scale of 5.5–6.8 kyr. Reaction with CaCO 3 on land accounts for another 3–8%, with a time scale of 8.2 kyr. The final equilibrium with CaCO 3 leaves 7.5–8% of the CO 2 release remaining in the atmosphere. The carbonate chemistry of the oceans in contact with CaCO 3 will act to buffer atmospheric CO 2 at this higher concentration until the entire fossil fuel CO 2 release is consumed by weathering of basic igneous rocks on a time scale of 200 kyr.