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Catalogue of the main gas manifestation of Greece: Geochemical characterisation and preliminary gas hazard assessment
Get PDFQuantification of gaseous emissions in geological systems is an important branch because it is a major source of greenhouse gas to the atmospheric budget. Of geological environments, there are two different categories: the first category includes emissions of the predominant carbon dioxide (CO 2), while the second includes emissions of the predominant methane (CH4). The Hellenic territory has a very complex geodynamic setting deriving from a long and complicated geological history. It is strongly characterized by intense seismic activity and enhanced geothermal gradient. This activity, with the contribution of an active volcanic arc, favours the existence of many cold and thermal gas manifestations. Geogenic sources release huge amounts of gases, which, apart from having important influences on the global climate, could also have a strong impact on human health. Geochemical studies based on the isotopic composition of carbon and hydrogen, along with helium isotopic ratios have become a good indicator of the origin of the gas. The isotopic ratio 13C/12C of CO 2 expressed in δ 13C (provides important information about the amount of CO 2 released from the Earth's crust or mantle. For methane, carbon and hydrogen isotopic compositions and C1/(C2+C3) hydrocarbon ratios can characterize the origin of methane: biogenic (thermogenic or microbial) or abiogenic. Helium isotopic ratios provide additional information about crustal or mantle origin of the gas. In the present work, a large set of chemical and isotopic data is presented aiming at the identification of areas with geogenic gas emissions and their characterization in terms of different gas composition and origin. The present catalogue should be the base for the estimation total nationwide geogenic CO 2 and CH4 fluxes
Microbial methane oxidation leading to extreme isotopic fractionation in thermal springs of central Greece
Get PDFThe Greek territory belongs to the geodynamically active Alpine-Himalayan orogenic belt. As such, it shows intense
seismic activity, active volcanic systems and areas of enhanced geothermal fluxes. One of these areas is the Sperchios
basin 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 dominating
species are either CO2 or N2. All gases contain from 27 to 4000 ppm of CH4. The isotopic composition of CH4 in these
gases 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 geothermal
systems. All the remaining samples fit a methane oxidation trend reaching very positive values. If we consider the
lowest values as the deep hydrothermal marker the obtained ΔH/ΔC values range between 5 and 13 which are close to
those 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 site
while 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 "Sperchios
Basin-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 aerobic
microbial 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
Gas manifestations of Greece: Catalogue, geochemical characterization and gas hazard definition
Get PDFLike other geodynamically active areas, Greece is affected by a large number of geogenic gas manifestations. These occur either in form of point sources (fumaroles, mofettes, bubbling gases) or as diffuse emanations. We produced a first catalogue of the geogenic gas manifestations of Greece also considering few literature data. Collected samples were analysed for their chemical (He, Ne, Ar, O2, N2, H2, H2S, CO, CH4 and CO2) and isotopic composition (He, C and N). Most of the sampled gas manifestation are found along the South Aegean active volcanic arc (32 sites) and in the majority they belong to the CO2 dominated group. Very few gas manifestations, N2- or CH4- dominated, are found along the most external units of the Hellenides orogen (Apulia domain - W and SW Greece), where generally compressive or transpersive tectonic prevails. On the contrary, gas manifestations (mainly CO2- dominated) are widespread along northern Greece (28 sites) and along Sperchios basin - north Evia graben (12 sites) which are characterised by extensional tectonic. Geogenic gases, apart from having important influences on the global climate, could have strong impact on human health. Gas hazard is often disregarded because fatal episodes are often not correctly attributed. Geodynamic active areas release geogenic gases for million years over wide areas and the potential risks should not be disregarded. A preliminary estimation of the gas hazard has been made for the last 20 years considering the whole population of Greece. In this period at least 2 fatal episodes with a total of 3 victims could be certainly attributed to CO2. This would give a risk of 1.3·10-8 fatality per annum. Such value, probably underestimated, is much lower than most other natural or anthropogenic risks. Nevertheless this risk, being unevenly distributed along the whole territory, should not be overlooked and better constrained in areas with high density of gas manifestations and high soil gas fluxes
High diversity of methanotrophic bacteria in geothermal soils affected by high methane fluxes
Get PDFVolcanic and geothermal systems emit endogenous gases by widespread degassing from soils, including CH4, a
greenhouse gas 25 times as potent as CO2. Recently, it has been demonstrated that volcanic/geothermal soils act
as source, but also as biological filter for methane release to the atmosphere. For long time, volcanic/geothermal
soils has been considered inhospitable for methanotrophic microorganisms, but new extremophile methanotrophs
belonging to Verrucomicrobia were identified in three different areas (Pozzuoli, Italy; Hell’s Gate, New Zealand;
Kamchatka, Russia), explaining anomalous behaviours in methane leakages of several geothermal/volcanic sites.
Our aim was to increase the knowledge of the relationship between methane emissions from volcanic/geothermal
areas and biological methane oxidation, by investigating a geothermal site of Pantelleria island (Italy). Pantelleria
Island hosts a high enthalpy geothermal system characterized by high temperature, high CH4 and very low H2S
fluxes. Such characteristics are reflected in potentially great supply of methane for methanotrophs and scarce presence
of inhibitors of their activity (H2S and NH3) in the Pantelleria soils. Potential methanotrophic activity within
these soils was already evidenced by the CH4/CO2 ratio of the flux measurements which was lower than that of
the respective fumarolic manifestations indicating a loss of CH4 during the gas travel towards the earth’s surface.
In this study laboratory incubation experiments using soils sampled at Favara Grande, the main hydrothermal
area of Pantelleria, showed very high methane consumption rates (up to 9500 ng CH4 h1 g1). Furthermore,
microbiological and culture-independent molecular analyses allowed to detect the presence of methanotrophs
affiliated to Gamma- and Alpha-Proteobacteria and to the newly discovered acidothermophilic methanotrophs
Verrucomicrobia. Culturable methanotrophic Alpha-proteobacteria of the genus Methylocystis were isolated by
enrichment cultures. The isolates showed a wide range of tolerance to pH (3.5 – 8) and temperatures (18 – 45 C),
and an average methane oxidation rate of 450 ppm/h. A larger diversity of proteobacterial and verrucomicrobial
methanotrophs was detected by the amplification of the methane mono-oxygenase gene pmoA.
This study demonstrates the coexistence of both the methanotrophic phyla Verrucomicrobia and Proteobacteria in
the same geothermal site. The presence of proteobacterial methanotrophs was quite unexpected because they are
generally considered not adapted to live in such harsh environments. Their presence at Favara Grande could be
explained by not so low soil pH values (> 5) of this specific geothermal site and by the high methane availability.
Such species could have found their niches in the shallowest part of the soils, were the temperatures are not so
high, thriving on the abundant upraising methane. Understanding the ecology of methanotrophy in geothermal
sites will increase our knowledge of their role in methane emissions to the atmosphere
Risks related to gas manifestations in the Hellenic territory
Get PDFLike other geodynamically active areas, Greece is affected by a large number of geogenic gas manifestations. These occur either in form of point sources (fumaroles, mofettes, bubbling gases) or as diffuse emanations. We produced a catalogue of the geogenic gas manifestations of Greece also considering few literature data. Collected samples were analysed for their chemical (He, Ne, Ar, O2, N2, H2, H2S, CO, CH4 and CO2) and isotopic composition (He, C and N). Geogenic gases, apart from having important influences on the global climate, could have strong impact on human health. Gas hazard is often disregarded because fatal episodes are often not correctly attributed. Geodynamic active areas release geogenic gases for million years over wide areas and the potential risks should not be disregarded. A preliminary estimation of the gas hazard has been made for the last 20 years considering the whole population of Greece. In this period at least 2 fatal episodes with a total of 3 victims could be certainly attributed to CO2. This would give a risk of 1.310-8 fatality per annum. Such value, probably underestimated, is much lower than most other natural or anthropogenic risks. Nevertheless this risk, being unevenly distributed along the whole territory, should not be overlooked and better constrained in areas with high density of gas manifestations and high soil gas fluxes
Gas geochemistry and preliminary CO2 output estimation from the island of Kos (Greece)
Get PDFSeveral gas samples have been collected from natural gas manifestations at the island of Kos. Most of them are found underwater along the southern coast of the island. On land two anomalous degassing areas have been recognized. These are characterised by lack of vegetation and after long dry periods by the presence of sulfate salts efflorescences. Almost all the gases are CO2-dominated (CO2 ranging from 88 to 99%) with minor amounts of N2 (up to 7%) and CH4 (up to 2.6%). Only the on-land manifestations have also significant contents of H2 (up to 0.2%) and H2S (up to 0.3%). Only one underwater manifestation is N2-dominated (61-99%) with CH4 (0.6-11%) and low CO2 (0.1-26%).
The isotopic composition of He shows values ranging from 0.84 to 6.72 R/RA indicating a sometimes strong mantle contribution with the highest values measured in two of the most strongly degassing areas (Paradise Beach and Volcania). C-isotopic composition of CO2 is in the range from -3.6 to 0.6 ‰ vs V.PDB with most of the values around -1‰ indicating a mixed mantle – limestones origin. Isotopic composition of CH4, ranging from -21.5 to 2.8‰ for C and from -143 to 36‰ for H, points to a geothermal origin with sometimes evident secondary oxidation processes.
CO2-flux measurements showed values up to about 10,000 g/m2/day in the areas of Volcania and Kokkino Nero and up to about 50,000 g/m2/day at Paradise beach. Preliminary CO2 output estimations gave values of 8.8 and 4 tons/day for the first two areas and of 2.7 tons/day for the latter. The total output of the island (15.5 tons/day) should be considered a minimum estimation because of the incomplete coverage of the area and is comparable to the other active volcanic/geothermal systems of Greece (Nisyros, Nea Kameni and Methana)
Preliminary results of systematic sampling of gas manifestations in geodynamically active areas of Greece
Get PDFGreece is located on a convergent plate boundary comprising the subduction of the African Plate beneath the Eurasian, while the Arabian plate approaches the Eurasian in a northwestward motion. It is considered to be one of the most tectonically active regions of Earth with a complex geodynamic setting, deriving from a long and complicated geological history. Due to this specific geological background, conditions for the formation of many thermal springs are favoured. In the past years, almost all the already known sites of degassing (fumaroles, soil gases, mofettes, gas bubbling in cold and thermal waters) located in the Hellenic area were sampled at least one time. Collected samples were analysed for their chemical (He, Ne, Ar, O2, N2, H2, H2S, CO, CH4 and CO2) and isotopic composition (He, C and N). Some of these sites have been selected for systematic sampling. Four of them have records longer than 10 years with tens of samplings also considering some literature data. Two of the sites are located in active volcanic areas (Santorini and Nisyros) while the other two are close to actively spreading graben structures with intense seismic activity (Gulf of Korinth and Sperchios basin). Results allowed to define long term background values and also some interesting variation related to seismic or volcanic activity
Origin of He and CO2 in the gas manifestations of Greece.
Get PDFIn the period from 2004 to 2017, more than 350 samples of free and dissolved gases were collected along the whole Hellenic area. Some literature data have also been taken into consideration (Rizzo et al., 2016). Samples have been analysed for their chemical and isotope composition. The concentrations range from 0.10 to 3370 μmol/mol for He, 600 to 995,000 μmol/mol for N2, 0.60 to 915,000 μmol/mol for CH4 and 17 to 1,002,000 μmol/mol for CO2, whereas the isotope values range from 0.01 to 7.10 for R/RA and -29.91 to +6.00 for δ13C-CO2. Considering the R/RA and 4He/20Ne ratios the atmospheric, mantle and crustal contributions for He have been calculated (Sano and Wakita, 1985). The highest mantle contribution (50 to 90%) is found in the South Aegean Active Volcanic Arc (SAAVA), whereas the lowest in continental Greece (0-20%). Atmospheric contribution is mostly negligible. Taking into consideration the geographical distribution of the gases, it is evident that the R/RA increases in areas characterized by: i) thin crust; ii) elevated heat flow values; iii) recent (Pleistocene-Quaternary) volcanic activity; and iv) deep routed extensional or transtensional regional faults. The highest values are therefore found along the SAAVA and the lowest in the western part of Greece. Furthermore, based on the CO2/3He and δ13C-CO2 values (Sano and Marty, 1995), the contribution of Sediment, Mantle and Limestone end-members for CO2 was determined. The majority of the collected samples present a prevailing limestone C component and only few samples have a prevailing mantle C component. However, with the present data, it is not possible to distinguish CO2 deriving from crustal and slab-related limestones. Additionally, due to the complex geodynamic history, the mantle C isotopic composition could be affected by subduction-related metasomatism and, similarly to the nearby Italian area (Martelli et al., 2008), the C isotope composition could be more positive. In this case, the mantle contribution is probably underestimated
The impact of volcanogenic emissions of major and trace elements at Mt. Etna, Sicily, on precipitation (rain and snow) chemistry
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