Shallow submarine gas manifestations in the Aegean Sea: preliminary catalogue and geochemical characterization

The Aegean area, like other regions of intense geodynamic activity, is characterised by extensive geogenic degassing. Gas manifestations widespread on land are also very frequent underwater. The present study aims at producing a first catalogue of these manifestations together with the geochemical characterization of the emitted gases. Sixty-one samples at 21 different sites have been collected by diving up to 15 m depth, mainly along the south Aegean active volcanic arc (SAAVA). The sites displayed very different gas fluxes. Most of them showed a very sluggish gas bubbling while a few had spatially large and strong bubbling. The most intense manifestation has been found at Kos Island along Paradise beach. Here a total output of about 2.7 tons/day from an area of about 250 m2 has been measured in September 2016. Samples have been analysed for their chemical (He, Ne, Ar, O2, N2, H2, H2S, CH4 and CO2) and isotopic (He, Ar, CO2-C, CH4-C, CH4-H) composition by gas chromatography and mass-spectrometry methodologies.