Alkalinity injection in stratified marine environment to assess the risk of carbonate precipitation: a numerical study

The permanent storage of carbon dioxide (CO2) is vital for achieving ambitious climate targets. Storing CO2 in the marine environment via coastal ocean alkalinity enhancement offers a promising pathway for large-scale, long-term sequestration. However, the safe discharge of alkaline solutions remains a critical challenge, as exceeding the seawater’s carbonate saturation state (Ω) can trigger secondary precipitation, reducing efficiency and posing ecological risks. This study presents a comprehensive dataset from high-fidelity Large Eddy Simulations (LES) investigating the near-field mixing of buoyant jets discharging alkaline solutions into stratified marine environments. By modeling the injection of Total Alkalinity (TA) and Dissolved Inorganic Carbon (DIC) as passive scalars, the resulting Reynolds-independent dataset is broadly applicable to various ocean alkalinity enhancement technologies and can be scaled with mass flow rate. Our results demonstrate that the aragonite saturation state (Ωa) rapidly decays below the critical precipitation threshold of Ωa < 7 within approximately 10–12 jet diameters. This decay rate is surprisingly poorly sensitive to ambient buoyancy and stratification conditions. To quantify the precipitation risk, we analyzed the residence time of water parcels within the supersaturated zone (Ωa > 7). The analysis reveals that residence times are on the order of one minute for a testcase plant, which is insufficient for significant carbonate nucleation, suggesting a negligible potential for secondary precipitation. In contrast to the saturation state decay, residence time is strongly influenced by ambient conditions: buoyancy forces reduce it, while stratification increases it. This work provides the first quantitative assessment of the near-field fluid dynamics and chemical behavior of alkaline jet discharges, offering critical insights for the design and operational safety of ocean alkalinity enhancement systems.