Modeling of near-source conditions of alkalinity injection in marine environment for precipitation assessment

The permanent sequestration of carbon dioxide via Ocean Alkalinity Enhancement offers a promising pathway for large-scale climate mitigation. However, the operational safety of alkaline discharges is contingent upon avoiding secondary calcium carbonate precipitation, which occurs when the seawater aragonite saturation state exceeds critical thresholds. This study investigates the near-field mixing dynamics of bicarbonate-enriched effluents using high-resolution Large Eddy Simulations across various seasonal stratification and buoyancy regimes. We implement a methodological framework that couples passive scalar transport of Total Alkalinity and Dissolved Inorganic Carbon with an equilibrium chemistry approach. By leveraging the linearity of transport equations and established Reynolds number independence, we present a non-dimensional formulation that allows for the scaling of results across diverse plant capacities and injection concentrations without the need for additional computational fluid dynamics runs. Our results indicate that while the spatial decay of the saturation state under threshold safety values are primarily governed by jet momentum, the residence time within the supersaturated zone is strongly modulated by ambient buoyancy and stratification. Even when accounting for turbulent fluctuations, via a conservative 95th-percentile analysis, the maximum residence times observed remained, for representative industrial scales, orders of magnitude below than the timescales required for carbonate nucleation and precipitation kinetics reported in the literature. These findings suggest that the risk of runaway secondary precipitation in the near-source region is negligible under the examined conditions, providing a scalable quantitative foundation for the design and environmental safety assessment of ocean alkalinity enhancement technologies.