Soil-zone adsorption of atmospheric CO2 as a terrestrial carbon sink

Identifying and quantifying sources and sinks of CO2 is integral to developing global carbon budgets and effectively modeling climate change. Adsorption of CO2 onto mineral and soil surfaces has generally been regarded as an insignificant sink, though few studies have investigated adsorption on natural materials at temperatures and CO2 concentrations relevant to atmospheric or soil zone conditions. In this study, annual adsorption at the scale of North America was modeled for the upper 3 m of the Earth’s surface (the root zone) based on our own and published adsorption data, and results compared with reported estimates for the North American terrestrial carbon sink during 2000–2005. Our results suggest that adsorption can account for 1–3% of the average annual sink during these years. At smaller regional scales where more adsorptive deposits are present, such as volcanic ash or high-organic soils, the sink may be significantly larger.