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  • 1
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    Gas geochemistry and CO2 output estimation at the island of Milos, Greece (2019)
    Details
    Publication Date: 2020-07-13
    Description: Twenty gas samples have been collected from the natural gas manifestations of Milos Island, the majority of which is found underwater along its coast. Furthermore, three anomalous degassing fumarolic areas (Kalamos, Paleochori and Adamas) have been recognized on-land. Almost all the gases are CO2-dominated with CO2 ranging from 88 to 99% vol for the samples taken underwater, while the on-land manifestations show a wider range (15–98%) due to air contamination. Methane reaches up to 1.0% vol, H2 up to 3.2% vol and H2S up to 3.5% vol indicating a hydrothermal origin of the gases. The isotope composition of He points out to mantle contributions up to 45%, while the C-isotope composition of CO2 (from−1.9 to +1.3‰vs. V-PDB with most of the values around −0.5‰) suggests a prevailing limestone origin. Isotope composition of CH4, ranging from−18.4 to−5.0‰vs. VPDB for C and from−295 to+7‰vs. V-SMOWfor H, points to a geothermal origin with sometimes evident secondary oxidation processes. Additionally, CO2-flux measurements showed high values in the three fumarolic areas (up to 1100, 1500 and 8000 g/m2/d at Kalamos, Paleochori and Adamas respectively) with the highest CO2-flux values (up to about 23,000 g/m2/d) being measured in the sea at Kanavas with a floating chamber. The south-western part of the island was covered with a lower density prospection revealing only few anomalous CO2 flux values (up to 650 g/m2/d). The total output of the island (30.5 t/d) is typical of quiescent closed-conduit volcanoes and comparable to the other volcanic/geothermal systems of the south Aegean active volcanic arc (Nisyros, Kos, Nea Kameni, Methana and Sousaki).
    Description: Published
    Description: 13-22
    Description: 4V. Processi pre-eruttivi
    Description: JCR Journal
    Keywords: Hydrothermal gases ; Stable isotopes ; Geogenic degassing ; Carbon dioxide ; 04.08. Volcanology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Estimation of the geogenic carbon degassing of Greece (2019)
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    Publication Date: 2019-06-24
    Description: Greece belongs to the most geodynamically active regions of the world and as such it has to be considered an area of intense geogenic degassing. Here we review all the papers already published in the scientific literature on both the geochemistry of gas manifestations and the CO2 and CH4 release, in an attempt to obtain the first nationwide inventory of the natural output of these carbon gases in Greece. The best studied and most exhaling area is the South Aegean Active Volcanic Arc (SAAVA), which releases more than 1.3×105 tons of CO2 per year. Continental Greece, on the contrary, is much less studied but may release CO2 in the same order of magnitude in its eastern-central and northern parts. The western and south-western parts of Greece are conversely the main areas in which methane and higher hydrocarbons degas. Methane output of Greece is much less constrained, but the presence of one of the biggest thermogenic gas seepages of Europe, which releases about 200 tons of CH4 per year to the atmosphere, underscores its potentially high contribution.
    Description: Published
    Description: 60-74
    Description: 6A. Geochimica per l'ambiente e geologia medica
    Description: JCR Journal
    Keywords: Geogenic degassing ; Carbon dioxide ; Methane ; Gas geochemistry ; 05. General
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    Degassing at the Volcanic/Geothermal System of Kos (Greece): Geochemical Characterization of the Released Gases and CO2 Output Estimation (2019)
    Details
    Publication Date: 2020-07-13
    Description: Forty five gas samples have been collected from natural gas manifestations at the island of Kos, the majority of which is found underwater along the southern coast of the island. On land, two anomalous degassing areas have been recognized. These areas are mainly characterised by lack of vegetation and after long dry periods by the presence of sulfate salt efflorescences. Carbon dioxide is the prevailing gas species (ranging from 88 to 99 %), whilst minor amounts of N2 (up to 7.5 %) and CH4 (up to 2.1 %) are also present. Significant contents of H2 (up to 0.2 %) and H2S (up to 0.3 %) are found in the on-land manifestations. Only one of the underwater manifestations is generally rich in N2 (up to 98.9 %) with CH4 concentrations up to 11.7 % and occasionally extremely low CO2 amounts (down to 0.09 %). Isotope composition of He ranges from 0.85 to 6.71 R/RA, indicating a sometimes strong mantle contribution; the highest values measured are found in the two highly degassing areas of Paradise Beach and Volcania. C-isotope composition of CO2 ranges from -20.1 to 0.64 ‰ vs V-PDB, with the majority of the values being concentrated around -1 ‰ and therefore proposing a mixed mantle – limestones origin. Isotope composition of CH4 ranges from -21.5 to +2.8 ‰ vs V-PDB for C and from -143 to +36 ‰ vs V-SMOW for H, pointing to a geothermal origin with sometimes evident secondary oxidation processes. The dataset presented in this work consists of sites that were repeatedly sampled in the last few years, with some of which being also sampled just before and immediately after the magnitude 6.6 earthquake that occurred on the 20th of July 2017 about 15 km ENE of the island of Kos. Changes in the degassing areas along with significant variations in the geochemical parameters of the released gases were observed both before and after the seismic event, however no coherent model explaining those changes was obtained. CO2-flux measurements showed values up to about 104 g×m-2×d-1 in the areas of Volcania and Kokkinonero, 5×104 g×m-2×d-1 at Paradise beach and 8×105 g×m-2×d-1 at Therma spring. CO2 output estimations gave values of 24.6, 16.8, 12.7 and 20.6 t×d-1 respectively for the above four areas. The total output of the island is 74.7 t×d-1 and is comparable to the other active volcanic/geothermal systems of Greece (Nisyros, Nea Kameni, Milos, Methana and Sousaki).
    Description: Published
    Description: ID 3041037
    Description: 6A. Geochimica per l'ambiente e geologia medica
    Description: JCR Journal
    Keywords: Carbon dioxide ; geothermal systems ; CO2 fluxes ; seismic activity ; 05.09. Miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    Geochemical characterisation of the thermo-mineral waters of Greece (2021)
    Springer
    Details
    Publication Date: 2022-06-22
    Description: Geothermal areas of Greece are located in regions affected by recent volcanism and in continental basins characterised by elevated heat flow. Many of them are found along the coast and thus, water is often saline due to marine intrusion. In the current study, we present about 300 unpublished and literature data from thermal and cold mineral waters collected along Greece. Samples were analysed for major ions, Li, SiO2 and isotopes in water. Measured temperatures range from 6.5 to 98°C, pH from 1.96 to 11.98, whilst Total Dissolved Solutes (TDS) from 0.22 to 51 g/L. Waters were subdivided into four main groups: i) thermal; ii) cold; iii) acidic (pH 〈5) and iv) hyperalkaline (pH 〉11). On statistical basis, the thermal waters were subdivided into subgroups according to both their temperature [warm (〈29 °C), hypothermal (29-48 °C), thermal (48-75 °C) and hyperthermal (〉75 °C)] and TDS [low salinity (〈4 g/L), brackish (4-30 g/L) and saline (〉30 g/L)]. Cold waters were subdivided basing on their pCO2 [low (〈0.05 atm), medium (0.05-0.85 atm) and high (〉0.85 atm)]. δ18O-H2O ranges from -12.7 to +2.7 ‰ vs. SMOW, while δ2H-H2O from -91 to +12 ‰ vs. SMOW being generally comprised between the Global Meteoric Water Line and the East Mediterranean Meteoric Water Line. Positive δ18O shifts with respect to the former are mostly related to mixing with seawater, while only for a few samples they point to high-temperature water-rock interaction processes. Only a few thermal waters gave reliable geothermometric estimates, suggesting reservoir temperatures between 80 and 260 °C.
    Description: Published
    Description: 2111–2133
    Description: 6A. Geochimica per l'ambiente e geologia medica
    Description: JCR Journal
    Keywords: Hydrogeochemistry ; Stable isotopes ; Carbon dioxide ; Geothermometry ; 03. Hydrosphere ; 03.04. Chemical and biological
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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