ADSORPTION OF CO2 ON MINERAL SURFACES AS A TERRESTRIAL CARBON SINK

Efforts to model global climate change rely heavily on our understanding of the global carbon budget. While knowledge of the carbon budget has greatly improved over the last decade, significant uncertainties still remain, especially with respect to terrestrial sources and sinks. Numerous potential sinks have been investigated including forest biomass, weathering reactions, soil organic material, soil pore water, lake sediments, agricultural impoundments, and even bacteria. Adsorption of CO₂ on mineral surfaces has not been seriously considered, perhaps because of the perception that it has been thoroughly studied and found to be insignificant, though few studies have actually been done on common natural minerals at earth surface temperatures. In our work, results of published adsorption on soils were coupled with our own measurements of adsorption on volcanic substrates as a basis for estimating adsorption in the soil zone in response to rising atmospheric CO₂ concentrations. Initial soil-CO₂ concentrations were estimated from a global soil and climate database to model adsorption at the scale of the North American continent. The North American terrestrial sink for the period of 2000 to 2005 has been estimated to be approximately 0.65 Pg/yr. Our model indicates that adsorption onto mineral surfaces in the upper 3 m could account for at least 8% of this sink, and possibly much more.