Microbial methane oxidation leading to extreme isotopic fractionation in thermal springs of central Greece

Risultato della ricerca: Other

Abstract

The Greek territory belongs to the geodynamically active Alpine-Himalayan orogenic belt. As such, it shows intenseseismic activity, active volcanic systems and areas of enhanced geothermal fluxes. One of these areas is the Sperchiosbasin and the northern part of Evia island in central Greece, which present widespread thermal manifestations(D’Alessandro et al., 2014). Five of them with temperatures from 33 to 80°C present bubbling gases whose dominatingspecies are either CO2 or N2. All gases contain from 27 to 4000 ppm of CH4. The isotopic composition of CH4 in thesegases covers a wide range with δ13C values ranging from -21.7 to +16.9 ‰ and δ2H values ranging from -124 to+301 ‰.The hottest manifestation displays the lowest isotopic values within the typical range of volcanic and geothermalsystems. All the remaining samples fit a methane oxidation trend reaching very positive values. If we consider thelowest values as the deep hydrothermal marker the obtained ΔH/ΔC values range between 5 and 13 which are close tothose typical of microbially driven oxidation (Kinnaman et al., 2007).Although the outlet temperature of the hottest manifestations is at the upper limit for methanotrophic microrganisms(Sharp et al., 2014), we can hypothesize that environmental conditions are not favorable for their survival at this sitewhile they can thrive in the other, strongly consuming methane and producing very positive isotopic values.D’Alessandro, W., Brusca, L., Kyriakopoulos, K., Bellomo, S., Calabrese S. (2014): A geochemical traverse along the "SperchiosBasin-Evoikos Gulf" Graben (Central Greece): origin and evolution of the emitted fluids. Mar. Petrol. Geol., 55, 295-308.Kinnaman, F.S., Valentine, D.L., Tyler, P.A. (2007): Carbon and hydrogen isotope fractionation associated with the aerobicmicrobial oxidation of methane, ethane, propane and butane. Geochim. Cosmochim. Acta, 71, 271-283.Sharp, C.E., Smirnova, A.V., Graham, J.M., Stott, M.B., Khadka, R., Moore, T.R., Grasby, S.E., Strack, M., Dunfield, P.F. (2014):Distribution and diversity of Verrucomicrobia methanotrophs in geothermal and acidic environments. Environ. Microbiol., 16,1867-1878.
Lingua originaleEnglish
Numero di pagine1
Stato di pubblicazionePublished - 2017

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