Unravelling biotic versus abiotic processes in the development of large sulfuric-acid karsts

Abstract In carbonate rocks, natural production of sulfuric acid can form karstic cavities. Where both epigenic and hypogenic speleogeneses have taken place, these processes are challenging to constrain, especially if there is more than one source sulfur involved. Thanks an innovative approach coupling geomorphology with measurements multiple sulfur, oxygen, strontium isotopes, our study two French Pyrenean caves quantifies the relative influence microbial thermochemical implied in sulfuric-acid production. Multiple isotopes reveal that sulfate speleothems derived from a mixing H2S hydrothermal water fossil previously trapped within cave host rock. We quantify percentages biotic abiotic place caves, paving way for similar studies other where usually only activity has been considered.