The hypogenic caves: a powerful tool for the study of seeps and their environmental effects

Research performed in caves has shown the existence of significant effects of gas seeps, especially CO2 and H2S, within subterranean voids. Carbon dioxide causes important corrosive effects and creates characteristic morphologies (e.g., bell-shaped domes, bubbleʹs trails), but is not involved in the deposition of specific cave minerals. On the other hand, in carbonate environments, hydrogen sulfide when oxidized in the shallow sections of the aquifer generates important corrosion effects and is also responsible for the deposition of specific minerals of which gypsum is the most common. s performed in the last few years have shown that H2S seeps in caves are associated with rich and diverse biological communities, consisting of large numbers of endemic species. Stable isotope studies (carbon and nitrogen) have demonstrated that these hypogean ecosystems are entirely based on in situ production of food by chemoautotrophic microorganisms using energy resulting from the oxidation of H2S. gh located only 20 m under the surface, Movile Cave does not receive meteoric waters due to a layer of impermeable clays and loess that covers the Miocene limestone in which the cave is developed. In the Frasassi caves, where certain amounts of meteoric water seep into the limestone, the subterranean ecosystems are still isolated from the surface. As the deep sulfidic waters mix with the oxigenated meteoric waters, sulfuric acid limestone corrosion is accelerated resulting in widespread deposition of gypsum onto the cave walls. hese caves have raised a lot of interest for biological investigations regarding the chemoautotrophically based ecosystems, demonstrating the possibility of performing such studies in environments that are easily accessible and easy to monitor compared to the deep-sea environments where the first gas seeps were discovered.