Deep submarine gas vents in the aeolian offshore

Abstract

Consistent results, concerning the detection of deep submarine hydrothermal vents, were obtained during two cruises (1991 and 1996) offshore from the Aeolian Islands, by CTD profiling from sea surface down to seafloor, and water-sampling casts. In 1991 an echo sounder showed a wide plume at a depth of about 800 m, within which water samples displayed anomalies in He and NH a content, suggesting also the presence of a water-vapour phase. The latter, in 1996, was remarkably observed as a horizontally diffusing plume at about 350 m. Near-plume casts were characterised by high CO2 and CH4 and low O2 concentrations in seawater, disturbed light transmission profiles, and false bottom outputs appearing at ∼300–350 m down to the seafloor from the rosette-mounted altimeter. No significant temperature/salinity anomalies were noted during either events. These preliminary results show the presence of deep hydrothermal activity, over an area where, one century ago, the occurrence of submarine eruptions was detected.