A new pathway to enhance the oceanic carbon sink: inorganic carbonate precipitation driven by calcium–alkali coupling

[Geoengineering News]

https://www.sciencedirect.com/science/article/abs/pii/S0301479726017548

Authors: Shan Shan Liu, Jin Ming Song, Xue Gang Li, Hua Mao Yuan, Li Qin Duan et al.

25 June 2026

https://doi.org/10.1016/j.jenvman.2026.130294

Highlights

•Novel calcium-alkali coupling converts DIC to CaCO3 for rapid oceanic CO2 removal.

•Field tests show 1000 m3 of seawater can sequester 77.6 kg of atmospheric CO2.

•Global shelf scaling suggests a carbon sink potential of 74 Pg C per application.

Abstract

Anthropogenic CO2 emissions are intensifying climate change, creating an urgent need for scalable and efficient strategies to enhance the oceanic carbon sink. This study proposes and evaluates a new calcium–alkali coupling pathway in which the co-addition of Ca2+ and OH− promotes the conversion of seawater dissolved inorganic carbon (DIC) into solid CaCO3. This process perturbs carbonate-system equilibrium and subsequently drives additional atmospheric CO2 uptake during system re-equilibration. Unlike conventional alkalinity-enhancement approaches that mainly retain absorbed CO2 as dissolved bicarbonate and carbonate species, the pathway examined here emphasizes carbonate precipitation as a major mode of DIC removal. Laboratory experiments, mesocosm simulations, and a 1000 m3 offshore field demonstration in the southern Yellow Sea were conducted to assess carbon-removal efficiency and short-term environmental responses. Under a dosing scheme of 1.79 mmol Ca2+ and 3.58 mmol OH− per litre of seawater, DIC in the 1000 m3 field system decreased by 1763 μmol kg−1 and was converted into CaCO3, corresponding to an estimated uptake of 77.6 kg atmospheric CO2. During the observation period, the monitored physicochemical parameters and trace-metal indicators showed only limited and controllable perturbations. A first-order scaling estimate based on this single-application, dose-dependent capacity suggests a theoretical carbon-sink enhancement potential of 2.48 Pg C on the Chinese continental shelf and 74 Pg C across global continental shelves. Because the carbonate system tended to relax toward its near-initial state after intervention, repeated applications may be feasible in principle and could provide considerable carbon-sink enhancement potential, although their long-term effectiveness, ecological consequences, and practical scalability require further evaluation. Overall, these results indicate that calcium–alkali coupling provides an efficient and mechanistically distinct pathway for engineered enhancement of the oceanic carbon sink.

Source: ScienceDirect