摘要:

Stable isotopes are widely used to reconstruct Earth’s history. Accurate applications require mechanistic knowledge of isotope fractionation during crystal formation via nucleation followed by growth, but isotope fractionation during nucleation has not been directly measured. By experimentally isolating crystal nucleation on organic films from growth in bulk solution, this study provides a measurement of isotope fractionation associated with nucleation, and finds that nucleation produces near-equilibrium isotope signatures, distinct from kinetic fractionation during growth. These findings extend isotope fractionation theory beyond growth-dominated low supersaturation regimes and provide a mechanistic basis for interpreting paradoxes in isotope fractionation which could not be explained by an ion-by-ion growth model. These results also have broad implications for isotope fractionation during biomineralization and interface-promoted nucleation.

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