Determining CO2 consumption from elemental change in soil profiles developed on carbonate and silicate rocks

Abstract

To further understand the roles of carbonate and silicate rocks in regulating the atmosphere/soil CO2 level, the flux of CO2 consumed by the chemical weathering of silicate and carbonate rocks was determined from the elemental change in soil profiles. Results showed that the chemical weathering of carbonate rocks mainly occurred at the rock-regolith interface, and that the further weathering of the residua soil on the carbonate rocks was similar to that of the granite profile. Chemical weathering of the silicate rocks occurred through the whole profiles. Therefore, CO2 consumed per volume by the silicate profiles [M sr (CO2)] and the residues on carbonate rocks [M cr (CO2)] were calculated based on the elemental weathering gradients. CO2 consumed by carbonate protolith [M cp (CO2)] was calculated from the elemental change at the rock-regolith interface. The M sr (CO2) were about tens to thousands orders of magnitude greater than M cr (CO2). Even so, this demonstrated that the residues on carbonate rocks could be a sink of CO2 on long-term scales. The M cp (CO2) was about four times larger than M sr (CO2), which demonstrated that carbonate rocks played a more important role in regulating the CO2 level than the silicate rocks did during the pedogenic process of the profiles.