Deep submarine gas vents in the Aeolian offshore

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 wa ter-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 4+ content, suggesting also the presence of a water-vapour phase. The latte r, in 1996, was remarkably observed as a horizontally diffusing plume at ab out 350 m. Near-plume casts were characterised by high CO2 and CH4 and low O-2 concentrations in seawater, disturbed light transmission profiles, and false bottom outputs appearing at similar to 300-350 m down to the seafloor from the rosette-mounted altimeter. No significant temperature/salinity an omalies were noted during either events. These preliminary results show the presence of deep hydrothermal activity, over an area where, one century ag o, the occurrence of submarine eruptions was detected. (C) 2000 Elsevier Sc ience Ltd. All rights reserved.