Focus

Discovery of a new submarine hydrothermal system off Zannone Island (western Pontine Archipelago, Tyrrhenian Sea)

A giant depression (0.5 km2) associated with hydrothermal activity has been recently discovered, on the seafloor surrounding Zannone Island (western Pontine Archipelago, Tyrrhenian Sea) at water depth ranging between 110 and 130 m, by CNR-IGAG researchers. This depression has been studied through very high resolution bathymetric data in the framework of the MaGIC project (http://www.magicproject.it/). Successively, during the research cruise "BOLLE 2014" aboard of the Urania R/V the site has been investigated integrating geophysical data (side scan sonar and seismic profiles) with ROV video observations and sedimentological, micropaleontological and geochemical analysis (water and gases) performed in collaboration with the researchers of the Earth Sciences Department (University of Rome, Sapienza), CNR-IGG and INGV (Palermo Section) in the framework of the Ritmare project (http://www.ritmare.it).
The giant depression is characterised by several hydrothermal features (e.g. authigenic deposits and pockmarks) and several CO2 fluid emissions associated with bacterial aggregations typical of extreme environments.
Evidence of active degassing, both continuous and intermittent, includes bubble and fluid releases from the floor and a plume rising about 70 m above the seafloor.
The hydrothermal manifestations off Zannone are rather similar to those found in the shallow-water surrounding Panarea Island; however the Zannone depression attain a much greater dimension (hundreds of meters) and morphological complexity. Their discovery represents the first evidence of active shallow-water seepage giant depressions in the Tyrrhenian Sea. In addition, the obtained results led to suppose that venting activity has been characterized by paroxysmal events producing collapse and/or explosive processes.
Factors peculiar to the study area (e.g., shallow water depth, coastline proximity, long-lasting venting activity) make the Zannone hydrothermal manifestations a strategic site for installation of a multi-disciplinary permanent seafloor observatory dedicated to study and monitoring of emission processes, to assess the venting hazard (e.g. possibility of hydrothermal explosions and slope instability) and environmental impact (e.g. organisms mortality, acidification process, CO2 input).