Work

Integrating laboratory-based secondary precipitation thresholds with ocean biogeochemistry models to advance ocean alkalinity enhancement decision-making

Year: 2026

Type: preprint

Abstract: Ocean alkalinity enhancement (OAE) is a promising marine carbon dioxide removal strategy, yet its effectiveness depends on avoiding secondary abiotic precipitation that reduces alkalinity and carbon uptake. We conducted controlled microcosm experiments across temperature (7.5–29.5°C) and salinity (6.5–32.5) gradients to quantify NaOH-driven precipitation thresholds relevant to coastal OAE deployments. Higher temperatures accelerated precipitation and lowered the Ω ar threshold for precipitation, while lower salinities led to shifts in mineralogy mediated by pH, DIC, and Mg/Ca stoichiometry. Ω ar thresholds for CaCO₃ formation were substantially higher than previously reported, and runaway precipitation occurred only at temperatures ≥ 16°C under high alkalinity additions. Integrating experimentally-derived, temperature- and salinity-dependent saturation thresholds into a regional biogeochemical model produced substantial, spatially variable reductions in added alkalinity and atmospheric CO₂ uptake. These results provide operational bounds for safe and efficient OAE implementation and highlight the necessity of explicit precipitation parameterizations in predictive modeling frameworks.

Source: Research Square

DOI: 10.21203/rs.3.rs-10639502/v1