MULTIPLE TIMESCALES FOR NEUTRALIZATION OF FOSSIL-FUEL CO2

The long term abiological sinks for anthropogenic CO2 will be dissolut ion in the oceans and chemical neutralization by reaction with carbona tes and basic igneous rocks. We use a detailed ocean/sediment carbon c ycle model to simulate the response of the carbonate cycle in the ocea n to a range of anthropogenic CO2 release scenarios. CaCO3 will play o nly a secondary role in buffering the CO2 concentration of the atmosph ere because CaCO3 reaction uptake capacity and kinetics are limited by the dynamics of the ocean carbon cycle. Dissolution into ocean water sequesters 70-80% of the CO2 release on a time scale of several hundre d years. Chemical neutralization of CO2 by reaction with CaCO3 on the sea floor accounts for another 9-15% decrease in the atmospheric conce ntration on a time scale of 5.5-6.8 kyr. Reaction with CaCO3 on land a ccounts for another 3-8%, with a time scale of 8.2 kyr. The final equi librium with CaCO3 leaves 7.5-8% of the CO2 release remaining in the a tmosphere. The carbonate chemistry of the oceans in contact with CaCO3 will act to buffer atmospheric CO2 at this higher concentration until the entire fossil fuel CO2 release is consumed by weathering of basic igneous rocks on a time scale of 200 kyr.