Sulphur stable isotope signature from sulphuric acid caves of Italy.

The study of sulphur stable isotope signatures in Sulphuric Acid Speleogenetic (SAS) caves gave rise to interesting information on both H2S sources and reactions involved in the sulphur cycle. In general, the stable isotope geochemistry of gypsum, sulphur and other sulphate by‐products found in underground SAS environments, provides the most robust evidence of present‐time and past SAS processes. Chemical signatures during sulphuric acid weathering can be influenced by microbial sulphate reduction (MSR) and/or thermochemical sulphate reduction (TSR). Studies on S isotope fractionation revealed large fractionations during MSR (from ‐30‰ to ‐70‰) with typical 34S‐depleted sulphides, whereas TSR shows smaller variations or no fractionation (δ34S values of SAS by‐products due to TSR are more or less similar to the original source of reduced sulphur). In the last two decades, the investigation on SAS caves around the world increased and produced interesting results. Italy hosts 25% of the worldwide known SAS caves, which are mainly located along the Apennine Chain, but also in Apulia, Sicily and Sardinia. In this contribution, we will report the new results from the study of the sulphur stable isotopes of sulphate and sulphur by‐products found in 18 SAS systems in Italy.