GAS VENTING RATES FROM SUBMARINE HYDROTHERMAL AREAS AROUND THE ISLANDOF MILOS, HELLENIC VOLCANIC ARC

Gas seeps were located, by echo sounding, SCUBA divers and ROV observa tions, at hydrothermal sites around the island of Milos, in the Hellen ic Volcanic Are. Samples were collected by SCUBA divers and by a ROV f rom water depths between 3 and 110 m. Fifty-six flow rates from 39 ind ividual seeps were measured and these ranged from 0.2 to 18.5 l h(-1) at the depth of collection. The major component, 54.9-91.9% of the gas , was carbon dioxide. Hydrogen (less than or equal to 3%), methane (le ss than or equal to 9.7%) and hydrogen sulphide (less than or equal to 8.1%) were also measured. Hydrothermal free gas fluxes from the subma rine hydrothermal areas around Miles were estimated to be greater than 10(10) moles y(-1). It was concluded that submarine gas seeps along v olcanic island arcs may be an important carbon dioxide source.