Soil Inorganic Carbon Formation and the Sequestration of Secondary Carbonates in Global Carbon Pools: A Review

Soil inorganic carbon (SIC), a potential carbon sink especially in arid and semi-arid environments, contributes to soil development, landscape stability, carbon (C) sequestration, and global C dynamics but due to the lack of SIC scientific reporting in most C sequestration research, its importance is unclear. A detailed overview of primary and secondary carbonate occurrence, formation, and importance is much needed to understand the role of pedogenic (PC)/secondary carbonate (a common biogeochemically derived soil mineral over time) in the SIC. The mechanisms involved in the formation of PC including carbon dioxide (CO2) from microbial respiration and precipitation, silicate mineral weathering, dissolution, and reprecipitation are highlighted. The isotopic composition of carbonates related to biological C3 or C4 carbon fixation pathways and other paleoecologic and/or climactic factors responsible for new soil carbonate formation are discussed in detail. To address the lack of knowledge associated with SIC, this review attempts to highlight the currently known aspects of the literature, and briefly describe the formation and methodologies that can aid in addressing the research gaps surrounding SIC sequestration. The authors also suggest that greater focus needs to be provided on the actual measurement of SIC to develop a more comprehensive SIC inventory to provide sound data for future research direction, and modeling efforts and to predict C terrestrial storage and change efficiently.