Quantifying sulfur speciation in magmatic-hydrothermal fluids

The paradigm could be framed as the thermodynamic framework used for modeling sulfur speciation in magmatic-hydrothermal fluids, specifically the role and properties of the trisulfur radical ion ([S3]-). The contested point is the validity of existing thermodynamic data and the interpretation of Raman spectra, which impacts the understanding of sulfur and metal transport in these fluids.

This preprint challenges a recent study (Farsang and Zajacz, 2025) which reported new sulfur speciation data and questioned the established thermodynamic properties of [S3]- and its role in metal transport. The preprint author, Pokrovski, argues that the conclusions of Farsang and Zajacz stem from inconsistent thermodynamic data, incorrect Raman spectra assignments, and a flawed experimental design. Pokrovski recalculates sulfur speciation using corrected data and parameters, demonstrating that [S3]- concentrations are significantly lower than proposed by Farsang and Zajacz, and undetectable by non-resonant Raman spectroscopy, thus seemingly reaffirming the existing thermodynamic data. This would suggest a Model Drift rather than a full-blown Model Crisis, as the core paradigm isn't necessarily challenged, but a specific interpretation of data within it, and the validity of a specific dataset is debated. However, there may be an element of Model Crisis, as the disagreement concerning the importance of the [S3]- ion could escalate if not resolved, potentially destabilizing some assumptions in the field. Therefore, I classify this paper as Model Drift/Model Crisis.