Organic and inorganic geochemistry of low temperature gas discharges at the Baia di Levante beach, Vulcano Island, Italy

Abstract

Discharge from subaereal and submarine gas vents of the Baia di Levante beach gases from the Vulcano Island were sampled for major and trace gas components in May and November 1995.Chemical compositions and equilibrium calculations suggest three different groups of CO 2 -rich gas emissions depending on their distance from the La Fossa crater: (1) gas vents close to the Faraglione area are characterised by high H 2 S contents, high calculated equilibrium temperatures based on inorganic species and relatively high proportion of alkene compounds; (2) gas vents close to Vulcanello are characterised by low calculated equilibrium temperatures and low amounts of alkenes; and (3) Pontile sample has the highest equilibrium CO 2 pressure (up to 68 bars) which may account for the observed absence of benzene. The relative large variability of H 2 S in the Baia di Levante beach gas discharge may be attributed to either different interactions between iron sulphides and weakly acid waters or catalytic effect of elemental sulphur on the de-hydrogenation of cyclo-hexane. Thermodynamic calculations suggest that the main inorganic species and CH 4 may have re-equilibrated at relatively shallow depth (10±200 m b.s.l. and 30±600 m b.s.l. for a lithostatic and hydrostatic pressure, respectively). The slow kinetics of reactions in the C n H 2n /C n H 2n12 systems, with respect to that of CH 4 ±CO±CO 2 , may explain the observed propene/propane ratios, which can only be reached at reaction temperatures of 300±3508C. This low speed of reactions can also explain the observed disequilibrium of C1±C4 alkanes. q

Geogenic and atmospheric sources for volatile organic compounds in fumarolic emissions from Mt. Etna and Vulcano Island (Sicily, Italy)

“…Light (C 2 ‐C 6 ) hydrocarbons occurring in low‐temperature gas discharges from Levante beach at Vulcano Island are ascribed to thermogenic processes [ Mangani et al , 1991; Capaccioni et al , 1995, 2001]. Schwandner et al [2004] found that the relative abundances of C 7 ‐C 12 n ‐alkanes in fumarolic fluids from La Fossa crater has a modus at C 8 , followed by a strong decrease of C 8+ concentrations resembling a Schulz‐Flory type distribution [ Satterfield and Huff , 1982], which is regarded as a indicator of catalytic Fischer‐Tropsch synthesis [ Salvi and Williams ‐ Jones , 1997].…”

Energetics of chemolithoautotrophy in the hydrothermal system of Vulcano Island, southern Italy

“…Bolognesi & D'Amore (1993) discounted seawater as a direct component of the system and concluded that the fumaroles owe their composition to the mixing of magmatic vapour and thermal meteoric water. Finally, Capaccioni et al (2001) argue that CO 2 -rich emissions in the Baia di Levante fall into several categories, depending on proximity to the crater, and differences in their calculated equilibrium temperatures, H 2 S contents and concentrations of hydrocarbons. More recently, Capasso et al (2001) formulated a model for the fumaroles at the Baia di Levante, in which ascending volcanic gases come into contact and react with a deep (∼ 200 m) thermal aquifer.…”

Metallic nanoparticle enrichment at low temperature, shallow CO2 seeps in Southern Italy

“…The resulting gas emissions from the hydrothermal aquifer are associated with magmatic fluids coming from the crater fumaroles and modified by low-temperature subsurface processes (Chiodini et al, 1995). The gas emissions are characterised by high CO 2 contents > 90% volume and a significant variability of H 2 S ranging from 0.8 to 2.5% volume (Capaccioni et al, 2001). The large variability of H 2 S in the gas discharge can be attributed to the interaction between metal sulphides and hydrothermally altered volcanic and weakly acid waters.…”