Ramnarine, R., Wagner-Riddle, C., Dunfield, K. E. and Voroney, R. P. 2012. Contributions of carbonates to soil CO₂emissions. Can. J. Soil Sci. 92: 599-607. Carbon dioxide (CO₂) is released in soil as a by-product of microbial and root respiration, but soil carbonates may also be a source of CO₂ emissions in calcareous soils. Global estimates of inorganic carbon range from 700 to 900 Pg as carbonates stored in soils, representing a significant potential source of CO₂ to the atmosphere. While previous studies have focused on the total CO₂ efflux from the soil, our goal was to identify the various sources and their contribution to total CO₂ emissions, by measuring the isotopic signature of the CO₂ emitted from the soil. Calcareous Luvisolic silt loam soil samples were obtained from conventional tillage (CT) and no-tillage (NT) plots in southern Ontario, Canada. Soil samples (root- and residue-free) were laboratory-incubated for 14 d and the isotopic signature of the CO₂ (δ¹³C_CO2) released was analyzed using isotope ratio mass spectrometry. Isotopic measurement was essential in quantifying the abiotic CO₂ production from carbonates, due to the unique δ¹³C signature of carbonates and soil organic matter. A two-end member mixing model was used to estimate the proportion of CO₂ evolved from soil carbonates and soil organic matter decomposition. Analysis of emitted CO₂ collected after the 14-d incubation indicate that the proportion of CO₂ originating from soil inorganic carbon was 62 to 74% for CT soil samples, and 64 to 80% for NT soil samples. Further work is recommended in the quantification of CO₂ emissions from calcareous soils, and to determine the transferability of laboratory results to field studies.