Comment on "Maximilian Hansen, Denis Scholz, Bernd R. Schone, Christoph Spotl, Simulating speleothem growth in the laboratory: Determination of the stable isotope fractionation (δ13C and δ18O) between H2O, DIC and CaCO3" Chemical Geology 509 (2019) 20-44

In this comment it is shown that analysis of the fractionation constants of the DIC describing the enrichment of C-13 and O-18 along the flow path of a thin water layer flowing down an inclined marble plate precipitating calcite in analogy to precipitation to speleothems, enables one to decide whether the Rayleigh-Distillation-model or the kinetic model is valid. Appropriate analysis of epsilon(tot) values for carbon and oxygen as reported by Hansen et al. (2019) reveals the validity of the kinetic model and allows determining the constants epsilon(kin) and lambda. This is in contrast to findings of Hansen and coauthors and gives a deeper understanding of the meaning of kinetic fractionation during precipitation of calcite.