Regional potential of coastal ocean alkalinisation with olivine within 100 years

Abstract The spreading of crushed olivine-rich rocks in coastal seas to accelerate weathering reactions sequesters atmospheric CO 2 and reduces atmospheric CO 2 concentrations. Their weathering rates depend on different factors, including temperature and the reaction surface area. Therefore, this study investigates the variations in olivine-based enhanced weathering rates across 13 regional coasts worldwide. In addition, it assesses the CO 2 sequestration within 100 years and evaluates the maximum net-sequestration potential based on varying environmental conditions. Simulations were conducted using the geochemical thermodynamic equilibrium modeling software PHREEQC. A sensitivity analysis was performed, exploring various combinations of influencing parameters, including grain size, seawater temperature, and chemistry. The findings reveal significant variation in CO 2 sequestration, ranging from 0.13 to 0.94 metric tons (t) of CO 2 per ton of distributed olivine-rich rocks over 100 years. Warmer coastal regions exhibit higher CO 2 sequestration capacities than temperate regions, with a difference of 0.4 t CO 2 /t olivine distributed. Sensitivity analysis shows that smaller grain sizes (10 µ m) exhibit higher net CO 2 sequestration rates (0.87 t/t) in olivine-based enhanced weathering across all conditions, attributed to their larger reactive surface area. However, in warmer seawater temperatures, olivine with slightly larger grain sizes (50 and 100 µ m) displays still larger net CO 2 sequestration rates (0.97 and 0.92 t/t), optimizing the efficiency of CO 2 sequestration while reducing grinding energy requirements. While relying on a simplified sensitivity analysis that does not capture the full complexity of real-world environmental dynamics, this study contributes to understanding the variability and optimization of enhanced weathering for CO 2 sequestration, supporting its potential as a sustainable CO 2 removal strategy.