Probing salty waters: re-assessment of the early stages of calcium carbonate formation in seawater

Arns AI, Evans D, Schiebel R, Wolf S, Jantschke A, Hansen M, Leitner J, Vonhof H, Haug GH (2026)

Publication Type: Journal article

Publication year: 2026

Journal

Geochimica Et Cosmochimica Acta Meteoritical Society

Book Volume: 420

Pages Range: 323-339

DOI: 10.1016/j.gca.2026.03.048

Abstract

Calcium carbonate formation in the oceans is a major component of the global carbon cycle. Yet, nucleation and crystallisation in ionically-complex seawater are not well understood. Here, we investigate CaCO3 nucleation and growth using potentiometric titration experiments in model solutions directly relevant to marine calcifying organisms. We develop a new framework for the conceptual interpretation of titration experiments, based on influx and outflux of ions in a dynamic system, and demonstrate the influence of the seawater major ions on CaCO3 nucleation and precipitation dynamics. Before nucleation, we find a significant underrepresentation of Ca2+-CO32– interactions in state-of-the-art ion speciation models, suggesting strong ion association in solution, in seawater at conditions relevant to biomineralisation. After precipitation, structural, microscopic, and isotopic analyses indicate the presence of a nano-scale, disordered phase at precipitate surfaces, potentially contributing to crystal growth through particle attachment. The disordered phase forms at or in vicinity of crystal surfaces, and not as a distinct amorphous precursor in solution. Our findings show that ion association-driven processes during nucleation and crystal growth may be the usual case for inorganic aragonite formation in greatly supersaturated solutions, possibly implying this is the case for all or most (bio)carbonates, which is a significant conceptual shift for the understanding of carbonate formation in marine settings.

Authors with CRIS profile

Stephan Wolf

Involved external institutions

Max-Planck-Institut für Chemie (Otto Hahn Institut) / Max Planck Institute for Chemistry DE Germany (DE) Johannes Gutenberg-Universität Mainz (JGU) DE Germany (DE) University of Southampton GB United Kingdom (GB)

How to cite

APA:

Arns, A.I., Evans, D., Schiebel, R., Wolf, S., Jantschke, A., Hansen, M.,... Haug, G.H. (2026). Probing salty waters: re-assessment of the early stages of calcium carbonate formation in seawater. Geochimica Et Cosmochimica Acta, 420, 323-339. https://doi.org/10.1016/j.gca.2026.03.048

MLA:

Arns, Anthea I., et al. "Probing salty waters: re-assessment of the early stages of calcium carbonate formation in seawater." Geochimica Et Cosmochimica Acta 420 (2026): 323-339.

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