GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 1.3 273 CONTINUOUS GASCHROMATOGRAPHY HIGHLIGHTS PROCESSES GOVERNING GAS RELEASE FROM THE UNDERWATER FUMAROLES OF LEVANTE BAY (VULCANO ISLAND, ITALY) F. Sortino 1 , M.L. Carapezza 1 , A. Di Piazza 1 , A. Donatucci 2 , A. Gattuso 1 , M. Ranaldi 1,2 , L. Tarchini 1,2 1 INGV sez.ROMA1, Italy 2 Università RomaTRE, Italy We continuously analyzed a high-flow fumarole at Levante bay (Vulcano Island) with a gas-chromatograph at 10 minutes frequency for several days. The aim of this work was to assess short-term variations of the gas composition and possibly to relate such variations with environmental parameters, especially the cyclical period of tides and atmospheric pressure. Fumaroles, on the beach or bubbling in the sea, fed by a shallow hydrothermal system beneath Levante bay, have shown a different distribution in the last 50 years. In particular during the last decade, a migration of fumaroles was observed from the Faraglione towards north, accompanied by a prominent flow increase especially in the central part of the bay (Figg. 1A and B). The main component is carbon dioxide (98% v/v on average) with hydrogen sulphide, nitrogen, methane, oxygen and hydrogen as minor components. Helium is about 1 ppm, and carbon monoxide is present at fractional levels of ppm. A characteristic of the submarine bay fumaroles is the immediate reaction between the hydrogen sulphide and the, Italiano e nuccio, dissolved oxygen in the sea water that leads to the formation of colloidal sulfur giving the water the typical, easily identifiable, white color (Figg. 1A and B). Fumaroles or dry gases bubbling underwater are typically sampled by placing a funnel above and letting the gas flow inside the sampler. Specimens are then analyzed in the laboratory (Aliani et al., 2010, Capaccioni et al., 2007, Caracausi et al., 2005, Heinicke et al., 2009, Fig. 1 - A) View of Levante bay from the Faraglione; B) Aerial view of Levante bay; C) Sketch of the sampling system. Red star: chromatographic monitoring station (CSM); Yellow ellipse: analyzed submarine fumarole.