Molecular-Level Mechanism of Phosphoric Acid Digestion of Carbonates and Recalibration of the 13C–18O Clumped Isotope Thermometer

The kinetic isotope effect (KIE) produced byphosphoric acid digestion reaction of carbonates has been well-studiedsince the start of stable isotope geochemistry, but its molecular-level mechanismremainselusive. Importantly, the validity of carbonate13C-18O clumped isotope thermometry, which is heavily based onthe phosphoric acid digestion treatment,need further study. The existing 47-T relationships calibrated by different groups are incompatible and generate substantial confusions in the community. Here we propose a new model of molecular-level mechanismofthe phosphoric acid digestion reaction of carbonates. This new model, which points out that there are three parallel pathways undergoing for the phosphoric acid digestion process,can explain a large part of discrepancies of the 47-T relationshipsobtained by different groupsat slightly different experimental conditions. Specifically, it provides different clumped isotope enrichment factors for reaction at 25C,70C and 90C than previous theoretical st...