CASPER: A modelling framework to link mineral carbonation with the turnover of organic matter in soil

Abstract Rapid formation of stable soil carbonates offers a potential biologically-mediated strategy for removing atmospheric CO 2 and forms a part of the negative emissions debate in a bid to maintain global temperatures of 1.5 °C. Microbial respiration in soil and respiration by plant roots leads to high partial pressure of CO 2 below ground. Given adequate supply of calcium in soil solution the sequestration of C into the mineral calcite (CaCO 3 ) can occur at rapid rates. We have coupled an established soil C model RothC to a simplified geochemical model so that this strategy can be explored and assessed by simulation. The combined model CASPER partitions CO 2 respired belowground into soil solution as HCO 3 − and simulates its reaction with Ca 2+ based on a particular dissolution rate for Ca-bearing minerals, with precipitation of calcite into soil pores as a consequence. Typical model output matches observed field rates of calcite accumulation over 5 years, namely 81 t ha −1 , with 19 t CO 2 ha −1 sequestered into the soil.