Characterization of undocumented CO2 hydrothermal vents in the Mediterranean Sea: implications for ocean acidification studies

In this paper, we present the first multidisciplinary description of an undocumented hydrothermal field located in Sicily (Southern Tyrrhenian Sea), at water depths ranging from 0 to 5 m. The area and the associated living communities were visually explored (snorkeling and SCUBA diving) in June 2021. Twenty sites were investigated for pH, alkalinity and nutrients analysis. Geochemical investigation of hydrothermal fluids gases revealed CO2 dominance (98.1%) together with low amount of oxygen and reactive gases. Helium isotope ratios (R/Ra =2.51) and δ13CCO2 (3) seem to confirm an inorganic origin of hydrothermal degassing of CO2 and the ascent of heat and deep-seated magmatic fluids to the surface. Values of pH ranged between 7.84 and 8.04, ΩCa between 3.68 and 5.24 and ΩAr from 2.41 to 3.44. Visual census of fish and megabenthos revealed the presence of 62 species among which five protected by SPA/BIO Protocol and two by the International Union for Conservation of Nature. This study represents the first step for the description of a suitable area of considerable interest for future ocean acidification experimental studies. ### Competing Interest Statement The authors have declared no competing interest.