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The chemical composition of rainwater was studied in two highly-industrialised areas in Sicily (southern Italy), between June 2018 and July 2019. The study areas were characterised by large oil refining plants and other industrial hubs whose processes contribute to the release of large amounts of gaseous species that can affect the chemical composition of atmospheric deposition As in most of the Mediterranean area, rainwater acidity (ranging in the study area between 3.9 and 8.3) was buffered by the dissolution of abundant geogenic carbonate aerosol. In particular, calcium and magnesium cations showed the highest pH-neutralizing factor, with ~92% of the acidity brought by SO42− and NO3− neutralized by alkaline dust. The lowest pH values were observed in samples collected after abundant rain periods, characterised by a less significant dry deposition of alkaline materials. Electrical Conductivity (ranging between 7 µS cm−1 and 396 µS cm−1) was inversely correlated with the amount of rainfall measured in the two areas. Concentrations of major ionic species followed the sequence Cl− > Na+ > SO42− ≃ HCO3− > ≃ Ca2+ > NO3− > Mg2+ > K+ > F−. High loads of Na+ and Cl− (with a calculated R2 = 0.99) reflected proximity to the sea. Calcium, potassium, and non-sea-salt magnesium had a prevalent crustal origin. Non-sea salt sulphate, nitrate, and fluoride can be attributed mainly to anthropogenic sources. Mt. Etna, during eruptive periods, may be also considered, on a regional scale, a significant source for fluoride, non-sea salt sulphate, and even chloride.

Estimation of CO2 degassing from active tectonic structures and regional hydrothermal systems is essential for the quantification of presentday Earth degassing [Frondini et al., 2019 and references therein]. Due to the high solubility of CO2 in water, great amounts of deep inorganic carbon can be dissolved, transported, and released from regional aquifers. By applying a massbalance approach [Chiodini et al., 2000], different sources of the dissolved CO2 can be discriminated. The main source of degassing in Greece is concentrated in hydrothermal and volcanic areas. However, deep CO2 from active tectonic areas has not yet been quantified. A key point of this research is to investigate the possible deep CO2 degassing through the big karst aquifers of Greece. From May 2016, 156 karst springs were sampled along the greatest part of the Hellenic region. To discriminate the different carbon sources, we analyzed the chemical and isotopic composition of total dissolved inorganic carbon (TDIC). Results yield TDIC values from 1.89 to 21.7 mmol/l and δ13CTDIC from 16.61 to 0.91 ‰. On this basis, karst springs are clustered into two groups: (a) low TDIC and δ13CTDIC values and (b) intermediate TDIC and δ13CTDIC values. The carbon of the first group derives from organic source and dissolution of carbonates; whilst the second group shows a possible carbon input from deep source. This geogenic carbon is mostly related to high heat flux areas, often near active or recent (Quaternary) volcanic systems.

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. In terms of carbon, the territory is characterized by the high hydrothermal and volcanic activity of the South Aegean Active Volcanic Arc (SAAVA), and by widespread geological seeps of buried carbon dioxide and methane. In the present work, we investigate the island of Gyali located in the volcanic system Kos-Gyali-Nisyros. Nine gas samples have been collected on the island of Gyali in areas found both on land, in a small lake (∼2000 m2) along its beach, and in the sea close to the shore at shallow depths (

In 2017, La Palma Island entered a state of volcanic unrest, with nine pre-eruptive seismic swarms detected by the seismic monitoring network of the Instituto Geográfico Nacional (IGN) up to 2021, most of the events occurring at depths of 20-35 km. During this period, the IGN geochemical network detected significant changes in deep gas emissions. On 11 September 2021, the last and most energetic pre-eruptive unrest began with more than 1500 earthquakes located at 10-15 km depth and migrating upwards, accompanied by ground deformation with up to ~20 cm vertical inflation detected by the IGN deformation network (GNSS, Insar, tiltmeters). On 19 September 2021 at 15:08 UTC, a volcanic eruption began on the western flank of Cumbre Vieja in El Paso village. This was the first eruption in the island after 50 years of quiescence.The 2021 eruption has lasted almost three months, ending on 13-14 December 2021 (last activity at the time of this writing). It began as a SE-NW fissural eruption and rapidly evolved to construct a main volcanic edifice up to ~200 m high, with several craters partially overlapping in a SE-NW direction, and later it constructed a secondary cone with a horseshoe shape open to the NE. The eruptive activity has been both strombolian and effusive, sometimes alternating and many times simultaneous with different behaviour at different emission points, a typical situation being strong degassing and strombolian jet and ash emission from an upper crater simultaneous to emission of fluid lavas and lava lake formation and periodical overflowing from a lower crater. Significant volcanic plumes have reached up to 8500 masl (typical value of 3000-3500 masl), and a large set of successive basanitic lava flows has been emitted to the west, developing a volcanic lava-fan covering ~12 km2 (~3000 buildings) and reaching the sea at several points along the western coast of La Palma.During the eruption, the IGN geochemical monitoring network included four stations measuring diffuse radon/thoron in soil, one station measuring diffuse CO2 flux in soil, an infrared thermal camera coupled with a visual camera and six water sampling points, regularly sampled for water composition, dissolved radon content, total and isotopic composition of dissolved gas (5 points) and free gas (1 point). Physical-chemical parameters (pH, Eh, T, EC, alkalinity) were also regularly measured in situ at these points. In this work we present the obtained dataset and first results. Changes in dissolved gas, mainly H2 and He, were recorded before and during the eruption. In two radon/thoron stations, abrupt increases in both gaseous species related to the eruptive process were also detected. Changes in dissolved radon in water were also observed at some of the sampling points. Finally, the analysis of the thermal image set can be used to monitor the surface volcanic activity in correlation with visual images and geophysical signals (volcanic tremor).

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, while Total Dissolved Solutes (TDS) from 0.22 to 51 g/L. Waters were subdivided into four main groups: (1) thermal; (2) cold; (3) acidic (pH 11). On statistical basis, thermal waters were subdivided into subgroups according to both their temperature [warm ( 75 °C)] and TDS [low salinity ( 30 g/L)]. Cold waters were subdivided based on their pCO2 [low ( 0.85 atm)]. δ18O–H2O ranges from − 12.7 to + 2.7‰ versus SMOW, while δ2H–H2O from − 91 to + 12‰ versus 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 these shifts 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.

Verrucomicrobial methanotrophs are a group of aerobic bacteria isolated from volcanic environments. They are acidophiles, characterized by the presence of a particulate methane monooxygenase (pMMO) and a XoxF-type methanol dehydrogenase (MDH). Metagenomic analysis of DNA extracted from the soil of Favara Grande, a geothermal area on Pantelleria Island, Italy, revealed the presence of two verrucomicrobial Metagenome Assembled Genomes (MAGs). One of these MAGs did not phylogenetically classify within any existing genus. After extensive analysis of the MAG, we propose the name of “Candidatus Methylacidithermus pantelleriae” PQ17 gen. nov. sp. nov. The MAG consisted of 2,466,655 bp, 71 contigs and 3,127 predicted coding sequences. Completeness was found at 98.6% and contamination at 1.3%. Genes encoding the pMMO and XoxF-MDH were identified. Inorganic carbon fixation might use the Calvin-Benson-Bassham cycle since all genes were identified. The serine and ribulose monophosphate pathways were incomplete. The detoxification of formaldehyde could follow the tetrahydrofolate pathway. Furthermore, “Ca. Methylacidithermus pantelleriae” might be capable of nitric oxide reduction but genes for dissimilatory nitrate reduction and nitrogen fixation were not identified. Unlike other verrucomicrobial methanotrophs, genes encoding for enzymes involved in hydrogen oxidation could not be found. In conclusion, the discovery of this new MAG expands the diversity and metabolism of verrucomicrobial methanotrophs.

The Favara Grande is a geothermal area located on Pantelleria Island, Italy. The area is characterized high temperatures in the top layer of the soil (60°C), low pH (3–5) and hydrothermal gas emissions mainly composed of carbon dioxide (CO2), methane (CH4), and hydrogen (H2). These geothermal features may provide a suitable niche for the growth of chemolithotrophic thermoacidophiles, including the lanthanide-dependent methanotrophs of the phylum Verrucomicrobia. In this study, we started enrichment cultures inoculated with soil of the Favara Grande at 50 and 60°C with CH4 as energy source and medium containing sufficient lanthanides at pH 3 and 5. From these cultures, a verrucomicrobial methanotroph could be isolated via serial dilution and floating filters techniques. The genome of strain AP8 was sequenced and based on phylogenetic analysis we propose to name this new species Methylacidimicrobium thermophilum AP8. The transcriptome data at μmax (0.051 ± 0.001 h−1, doubling time ~14 h) of the new strain showed a high expression of the pmoCAB2 operon encoding the membrane-bound methane monooxygenase and of the gene xoxF1, encoding the lanthanide-dependent methanol dehydrogenase. A second pmoCAB operon and xoxF2 gene were not expressed. The physiology of strain AP8 was further investigated and revealed an optimal growth in a pH range of 3–5 at 50°C, representing the first thermophilic strain of the genus Methylacidimicrobium. Moreover, strain AP8 had a KS(app) for methane of 8 ± 1 μM. Beside methane, a type 1b [NiFe] hydrogenase enabled hydrogen oxidation at oxygen concentrations up to 1%. Taken together, our results expand the knowledge on the characteristics and adaptations of verrucomicrobial methanotrophs in hydrothermal environments and add a new thermophilic strain to the genus Methylacidimicrobium.

We report on original geochemical data, which combine the rainfall trace metal contents from three different areas of Mt. Etna, variably fumigated by the volcanic plume, and those from soils, collected over the whole volcano. Trace element contents in rainfall appear mostly related to acidic ash leaching, while only for the most volatile elements (Cu, Zn, Cd, Pb, As, Sb, Tl, Se) we suggest a derivation from magmatic degassing. We analyzed separately the labile fraction of soil samples, considered the fraction bioavailable to plants and soil organisms living in. The complexing medium used to extract the bioavailable fraction simulates the growth environment of plant roots.The contents of trace elements in the bioavailable fraction from soil samples showed peculiar patterns, apparently unrelated to the plume fumigation. The transition metal contents in the bioavailable fraction account for less than 15 % of the pseudo-total fraction and the highest contents were measured in the less acidic soil samples and farthest from the summit craters. In particular, high Fe, Mn, Co, Ni, Pb, Zn, Cd contents were paralleled by high soil organic carbon concentrations, which increased in the samples collected downwind the summit vents. Concerning immobile elements, their abundance in the bioavailable fraction was related to the degree of alteration of soils. Two elements, Se and Tl, were enriched in soil samples collected at closer distance from the summit vents. Their origin is probably related to the plume deposition.The study highlighted that the accessibility of plants to potentially harmful trace elements present in the soil is not simply related to the exposure to pollutants, but also to their fate in the pedogenetic environment.

In the framework of the “Save the Etna World” research project, which investigates the impact of the volcanic activity on the surrounding environment, three bulk collectors were deployed on the flank of the Mt. Etna volcano to collect the meteoric depositions. The sampling sites were at distances between 5.5 and 13 km from the summit vents of the volcano on its eastern flank, that is the most exposed to the volcanic plume due to the high-altitude prevailing winds direction. The sites were selected in order to have a gradient of exposition with respect to the volcanic emissions, the most exposed being CIT, the intermediate ILI and the least NIC. Samples were collected monthly from July 2017 to July 2018 and analysed for major ions and for a large suite of trace elements. The influence of volcanic emissions is evidenced by the low pH of the collected depositions in the most exposed site, showing values mostly below 3.5 and never exceeding 5.72. The lowest values are related to high fluoride, chloride and sulfate concentrations in the collected water, deriving from the acid gases (HF, HCl and SO2) of the volcanic plume. The other two sites show pH values in range from 3.95 to 7.21. While the lowest values indicate a lower but significant volcanic influence, the highest values can be related to the dissolution of geogenic (mainly carbonate) particulate of local or regional (Saharan) origin. The latter process is evidenced by high concentrations of Ca and HCO3 in the samples with the highest pHs. Trace elements show almost all higher concentrations in the most exposed site. Highly volatile elements like Pb, Te and Tl, which are known to have strong enrichment factors in volcanic plumes with respect to the average upper crust composition, are found at CIT at concentrations always at least one order of magnitude higher than at NIC. Also lithophile elements like Si, Al, Ti and Fe are sometimes strongly enriched at CIT deriving from the interaction of the acid gases of the plume with the occasionally emitted volcanic ash. These new results confirm the importance of meteoric deposition as main carrier of volcanogenic elements to earth’s surface. “Etna World” is a fascinating natural laboratory, and the study of atmospheric depositions in this peculiar environment allows to understand better the general processes that influence the cycles of trace metals. Furthermore, the quantitative estimation of both emission and deposition of volcanogenic elements is a key factor for complementary studies on the geochemical mobility of trace elements and their distribution between atmosphere, soils, vegetation, and lastly, animals and humans in active volcanic areas.

Geochemical features of the geothermal and mineral waters from Apuseni Mountains, RomaniaAlin-Marius Nicula1, Artur Ionescu1,2, Cristian-Ioan Pop1, Carmen Roba1, Walter D’Alessandro3, Ferenc Lazar Forray4, Iancu Oraseanu5, Calin Baciu1 1Babes-Bolyai University, Faculty of Environmental Science and Engineering, Str. Fantanele nr. 30, 400294, Cluj-Napoca, Romania (marius_alin92@yahoo.com)2University of Perugia, Department of Physics and Geology, Via A. Pascoli 06123, Perugia, Italy3Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Via Ugo la Malfa, 153,90146 Palermo, Italy4Department of Geology, Babes-Bolyai University, Kogalniceanu 1, 400084 Cluj-Napoca, Romania5Romanian Association of Hydrogeologists, Bucuresti, Romania The Apuseni Mountains are located in the western part of Romania and separate the Pannonian Basin from the Transylvanian Basin. These mountains are famous and intensely studied for their important non-ferrous metal resources. Few data were published about the geothermal potential of this area. More works have been dedicated to mineral waters, while the geothermal waters are only briefly described, without sufficient emphasis on them. The current research is focusing on the two categories, cold mineral and geothermal water in the Apuseni Mountains, compared to the surrounding areas, in order to better understand their genesis and the general context of the geothermalism in the study region. A preliminary survey of these waters was done in 2019 taking water and gas samples from 41 sources.The pH varies between 6.00 and 9.02 and, the lowest values have been measured in the CO2-rich waters of the Southern Apuseni Mountains. Water temperatures vary between 11.1 ○C and 81 ○C. In the southern part of the Apuseni Mountains, the geothermal waters are of the calcium bicarbonate type (Ca-HCO3), while in the north-western part, the sodium bicarbonate type (Na-HCO3) is more common. The water sources from the north-western part are close to the Pannonian Basin and show features comparable to the thermal waters of this basin. Conductivity values show significant variations between 142 and 2040 µS/cm, but regional homogeneities were observed. The highest concentration of bicarbonate was measured in one of the localities of the northern study area (Beiuş Depression - 3318.4 mg/L). The dissolved heavy metal concentrations (Zn, Pb, Cd, Cr, Ni, Cu, Fe) in the water samples were also measured. For all the investigated waters, the heavy metal content was low. The highest concentrations were recorded for Fe 342.90 µg/L and Zn 86.14 µg/L. The isotopic data (δ18O and δ2H) demonstrate the meteoric origin of the thermal waters.Some springs and wells release free gases. The gas chromatographic analyses show the prevalence of N2 and CO2, with minor amounts of CH4 in the water sources close to the Pannonian Basin. The isotope composition of Helium shows values between 0.9 and 2.18 R/Ra indicating a prevailing crustal source with a significant mantle component. In the case of δ13C-CO2 the values range between -12.7 and -6.1 ‰ vs.V-PDB, indicating that the CO2 originates possibly from a limestone source.

The Duvalo locality is located in the SW of the Republic of North Macedonia, in the Ohrid region, near the village of Kosel. It is an area of strong soil degassing, called “volcano” by the local people despite volcanic activity has never been documented in the recent geologic history of the area [1]. A large area (thousands of sqm) shows signs of strong alteration and is devoid of vegetation. Until the 19thcentury sulphur was mined from this area [1].In August 2019, a campaign of soil CO2 flux measurements and soil gas sampling was made. Duvalo is sometimes referred to as an active geothermal feature but no signs of enhanced geothermal gradient were found and the soil temperatures at 50 cm depth in this campaign were always within the range of local mean air temperatures. Soil CO2 flux values ranged from 1.3 to 59,000 g/m2/d and can be modelled with the overlapping of 3 or 4 flux populations. A possible biological background is estimated in 6.8±1.8 g/m2/d while the other populations are characterized by an anomalous average flux ranging from 180 to 33,000 g/m2/d. The CO2 total emission, estimated both with a statistical and geostatistical approach, provided similar values in the order of 50 t/d. This has to be considered as a minimum value because only areas with evident signs of alteration have been investigated. Nevertheless, the estimated output is quite high for an area unrelated with recent volcanism or geothermal activity.The chemical composition of soil gases shows: CO2 (96.6%), N2 (1.8%), H2S (0.6%) and CH4 (0.3%) as the main gases. The present composition is almost indistinguishable from previous analyses made in 1957 and 1977 [1] pointing to a stability of the system in last decades. The isotope compositions indicate for CO2 (δ13C -0.2 ‰) a pure carbonate rock origin, for CH4 (δ13C -34.4 ‰ and δ2H -166 ‰) a thermogenic origin and for He (R/RA 0.10) a pure crustal origin.The H2S released at Duvalo may be produced by either microbial or thermochemical sulphate reduction favoured by hydrocarbons whose presence can be inferred by the uprise of thermogenic methane. Partial oxidation of H2S during its upflow, producing sulphuric acid, may be responsible of the production of abundant CO2 through dissolution of carbonate rocks. Similar processes have been evidenced also in other parts of North Macedonia [2]. These gases rise up through the N–S trending normal faults bordering the seismically active Ohrid basin graben [3] being released to the atmosphere through the soils of Duvalo “volcano”.This research was funded by: DCO Grant n. 10881-TDB “Improving the estimation of tectonic carbon flux”; GINOP-2.3.2-15-2016-00009 ‘ICER’ project and PO-FSE Sicilia 2014–2020 (CUP: G77B17000200009).References[1] Markovski B. et al., 2018. Duvalo a geological phenomenon near Ohrid. DOI: 10.18509/AGB.2020.05[2] Temovski M., 2017. Hypogene Karst in Macedonia. In: Klimchouk et al. (eds.), Hypogene Karst Regions and Caves of the World, Springer[3] Hoffmann N. et al., 2010. Biogeosciences, 7, 3377–3386

The complex geology of Greece includes two important parallel running ophiolitic belts. The Othrys Massif in central Greece belongs to the westernmost of them. In the current study, 33 water samples from cold hyperalkaline and hypothermal (T < 40°C) alkaline springs and 30 gas samples (either dissolved or free) were collected at 17 different sites in and around this wide ophiolite outcrop, aiming to determine the origin of fluids and evidence gas-water-rock interaction processes taking place in the area. Water samples were analysed for their chemical (major ions and trace elements) and isotope (d18O-H2O, d2H-H2O) composition. They can be subdivided into alkaline (pH 11 and Ca-OH composition). Trace elements generally showed very low concentrations and mostly inversely correlated with pH. Gases were analysed for their chemical (He, Ne, Ar, H2, O2, N2, CH4, C2H6, CO2 and H2S) and isotope (d13C-CH4, d2H-CH4, d13C-CO2) composition. Samples from alkaline waters were mainly dominated by CH4 (from 128,000 to 915,000 μmol/mol), while hyperalkaline waters showed a N2-rich composition (from 727,000 to 977,000 μmol/mol). Methane had a wide range of isotope compositions (d13C-CH4 from -74.5 to -14.5 and d2H-CH4 from -343 to -62 ). Alkaline waters present the most negative isotope values for CH4, evidencing a biogenic (both thermogenic and microbial) origin. Many of the hyperalkaline waters had CH4 isotope values compatible with an abiogenic origin through serpentinization processes but occasionaly very negative values were recorded, indicating sometimes a clear biogenic contribution. Finally, few samples both from alkaline and hyperalkaline waters showed some evidence of secondary oxidation processes.

Monogenetic eruptions are the most common volcanic activity in the world. However, unrest monitoring data are scarce due to the long intervening quiescence periods. This study analyzes unrest signals recorded in one of the largest monogenetic fields in the Canary Islands, Cumbre Vieja (La Palma). Two seismic swarms were registered in October 2017 and February 2018 with b-values of 1.6 ± 0.1 and 2.3 ± 0.2 respectively suggesting an intense magmatic fluids contribution, gas and/or magma. Both swarms were linked to changes in gas emissions. Increases in hydrogen concentration, and (R/Ra)c up to 7.52 ± 0.05, were recorded before the first swarm, at the sampling point closest to where seismicity was located, indicating a deep gas input. After the second swarm, increases in (R/Ra)c and thoron soil concentration were recorded at two locations. This dataset is compatible with a stalled magmatic intrusion at ca. 25 km depth, with an estimated volume between 5.5·10−4 km3 and 3·10−2 km3.

Samples of efflorescences and encrustations of hydrothermal origin were collected at Sousaki (Greece) and analysed for their mineralogical (XRD) and chemical composition. Solutions obtained both from mineralization with HNO3 and from leaching with deionised water were analysed for major (ICP-OES), minor and trace metals (ICP-MS) and sulfate contents (IC). Results evidence the dependence of the chemical and mineralogical composition on micro-environmental conditions i.e. humidity, oxygen-rich or -poor environment, exposed or sheltered from meteoric agents. In fact, the presence of highly soluble sulfate minerals with elevated contents of many metals (e.g. Mg, Al, Fe, Mn, Cr, Ni, etc.) further underscores the important influence of hydrothermal activity on elements' mobility, whilst the sometimes very high concentrations in toxic elements like Al, Cr, Ni suggest also possible environmental impacts.

I was lucky enough to meet Mariano Valenza in September 1995. I was hitchhiking on the highway that leads from Cefalu to Palermo to go back home. I had spent my summer holidays in the beautiful and wild Madonie mountains. An off-road vehicle (a Land Rover Defender) stopped and a refined gentleman with a curious and charismatic gaze offered me a ride. During our journey, we chatted pleasantly and he told he was originally from that area. When I told him, I was a Geology student, he smiled at me and said Then we will meet again soon, I am going to be your Teacher of Geochemistry!. After a few weeks the lessons began and I met again Professor Valenza in Via Archirafi 36, at the University of Palermo. I will never forget the first introductive lesson of his course: ... we are going to study how the chemical elements have formed in the stars, and how these elements have spread out on our planet; we are going to study the chemical- physical laws regulating their geochemical cycles and how they move in between the atmosphere, the hydrosphere and the lithosphere. We will also learn how the isotopes of these elements allow us to date the geological phenomena and the age of our own planet Earth; ...let's imagine that we are ourselves made of billions and billions and billions of atoms, and it is statically possible that one of Napoleon atom could be here, in this class room!. I was truly fascinated and I discovered my passion for this interesting subject.In via Archirafi 36, in the historical building of the University of Palermo, once home of the Istituto di Mineralogia, I have graduated and got a Ph.D. in Geochemistry, and still nowadays I am working there. In these last 25 years I have learnt to know the stories of different personalities and their scientific researches, which have been hidden and looked after in the ancient building of the University for almost one century. With this article, we would like to remember Professor Mariano Valenza, by telling some stories about him and some others told by himself. Amongst these extraordinary stories we have focused on the one of a little-known scientist, Ludovico Sicardi (1895 - 1987), a modest man who followed his passion for volcanoes. In his field, he was a true innovator and the present research in the field of the geochemical surveillance of volcanos is deeply in debt to him. The Scuola di Geochimica dei Fluidi, born in the '70s at the University of Palermo, has the most debt of gratitude to him, but also the one which has treasured best his memory. This special paper is dedicated to Professor Valenza, who was one of the founders of this school and, before that, the teacher of most of this piece's authors. He had preserved, beside the historical memory, also many documents, photos, and the scientific equipment used by Sicardi for his studies.Sergio Calabrese, Palermo, March 2020

The Favara Grande nature reserve on the volcanic island of Pantelleria (Italy) is known for its geothermal gas emissions and high soil temperatures. These volcanic soil ecosystems represent “hot spots” of greenhouse gas emissions. The unique community might be shaped by the hostile conditions in the ecosystem, and it is involved in the cycling of elements such as carbon, hydrogen, sulfur, and nitrogen. Our metagenome study revealed that most of the microorganisms in this extreme environment are only distantly related to cultivated bacteria. The results obtained profoundly increased the understanding of these natural hot spots of greenhouse gas production/degradation and will help to enrich and isolate the microbial key players. After isolation, it will become possible to unravel the molecular mechanisms by which they adapt to extreme (thermo/acidophilic) conditions, and this may lead to new green enzymatic catalysts and technologies for industry., Volcanic and geothermal environments are characterized by low pH, high temperatures, and gas emissions consisting of mainly CO2 and varied CH4, H2S, and H2 contents which allow the formation of chemolithoautotrophic microbial communities. To determine the link between the emitted gases and the microbial community composition, geochemical and metagenomic analysis were performed. Soil samples of the geothermic region Favara Grande (Pantelleria, Italy) were taken at various depths (1 to 50 cm). Analysis of the gas composition revealed that CH4 and H2 have the potential to serve as the driving forces for the microbial community. Our metagenomic analysis revealed a high relative abundance of Bacteria in the top layer (1 to 10 cm), but the relative abundance of Archaea increased with depth from 32% to 70%. In particular, a putative hydrogenotrophic methanogenic archaeon, related to Methanocella conradii, appeared to have a high relative abundance (63%) in deeper layers. A variety of [NiFe]-hydrogenase genes were detected, showing that H2 was an important electron donor for microaerobic microorganisms in the upper layers. Furthermore, the bacterial population included verrucomicrobial and proteobacterial methanotrophs, the former showing an up to 7.8 times higher relative abundance. Analysis of the metabolic potential of this microbial community showed a clear capacity to oxidize CH4 aerobically, as several genes for distinct particulate methane monooxygenases and lanthanide-dependent methanol dehydrogenases (XoxF-type) were retrieved. Analysis of the CO2 fixation pathways showed the presence of the Calvin-Benson-Bassham cycle, the Wood-Ljungdahl pathway, and the (reverse) tricarboxylic acid (TCA) cycle, the latter being the most represented carbon fixation pathway. This study indicates that the methane emissions in the Favara Grande might be a combination of geothermal activity and biological processes and further provides insights into the diversity of the microbial population thriving on CH4 and H2. IMPORTANCE The Favara Grande nature reserve on the volcanic island of Pantelleria (Italy) is known for its geothermal gas emissions and high soil temperatures. These volcanic soil ecosystems represent “hot spots” of greenhouse gas emissions. The unique community might be shaped by the hostile conditions in the ecosystem, and it is involved in the cycling of elements such as carbon, hydrogen, sulfur, and nitrogen. Our metagenome study revealed that most of the microorganisms in this extreme environment are only distantly related to cultivated bacteria. The results obtained profoundly increased the understanding of these natural hot spots of greenhouse gas production/degradation and will help to enrich and isolate the microbial key players. After isolation, it will become possible to unravel the molecular mechanisms by which they adapt to extreme (thermo/acidophilic) conditions, and this may lead to new green enzymatic catalysts and technologies for industry.

The eruption of Mt. Etna which occurred on December 24th 2018 was characterized by strombolian activity and fire fountains, emitted by the New South-East Crater and along a fissure that propagated towards the SE. The influence of volcanic emissions on atmospheric deposition was clearly detectable at several kilometres from the source. Wet and dry (bulk) deposition samples were collected each month, through a network of eleven collectors, in the areas of Milazzo, and Priolo between June 2018 and June 2019. They were analysed for major ions and trace elements concentrations. The pH values range from 3.9 to 8.3, while the EC values range from 7 to 396 μS cm-1. An extensive neutralization of the acidity has been recognised mainly due to the suspended alkaline dust particles, which have a buffering role in rainwater. A high load of Na+ and Cl- was observed at all sites, related to the closeness of the study areas to the coast, showing a high positive correlation (R2 = 0.989) along the line of Na+/Cl- ratio in seawater. During the eruption, the volcanic plume was carried by the winds for long distance (more than 300 km) affecting the area of Priolo but not that of Milazzo, which was upwind with respect to Mt. Etna. The impact of volcanic HF was clearly recognised in the samples collected after the eruption. Volcanic SO2 and HCl had a lower impact due to the overwhelming input of anthropogenic sulfate and marine chloride. On the contrary, the signature of the Mt. Etna eruption can be well recognised in the high concentrations of certain trace elements in the samples collected immediately after the eruption. The strongest contrast between affected and non-affected samples was recognised in Al, Cd, and especially in the volatile elements Tl and Te, which are typically enriched in volcanic emissions. The results showed that volcanic eruptions might have a relevant effect on the atmospheric chemistry and on the composition of rainwater up to distances of 80 km from the emission vents.

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. V-PDB for C and from −295 to +7‰ vs. V-SMOW for 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).

We investigated the geochemical features of the gases released from the Kizildag ophiolitic complex (Hatay, Turkey). Twenty-three samples both dissolved in hyperalkaline waters and free gases (bubbling gases and dry seeps) were collected. Samples were analysed for their chemical (He, H-2, O-2, N-2, CH4 and CO2) and isotopic (He, delta C-13-CH4, delta H-2-CH4, delta H-2-H-2) composition including the content and C-isotopic composition of C-2 to C-5 alkanes in free gases. Analytical results evidence H-2 production through low temperature (

Hyperalkaline mineral springs related to active continental serpentinization are a theme of growing interest since they may contain significant amounts of abiotic gas and have important implications for energy resource exploration, subsurface microbiology and astrobiology. We report the discovery of a new hyperalkaline (pH∼12) spring issuing in the Agioi Anargyroi monastery at Ermioni (Greece), connected to serpentinization of peridotites of the Argolis ophiolite. Two water samples have been collected from separated springs and analysed for the chemical composition of major, minor and trace elements, and isotopic composition (2H and 18O) of water by IC, ICP-OES, ICP-MS and IRMS, and for the chemical (H2, O2, N2, CH4, CO2 and C2H6) and isotopic (He, δ2H-CH4 and δ13C-CH4) composition of dissolved gases. The Iliokastron Melange Unit, comprising abundant serpentinized harzburgite, represent the aquifer feeding the hyperalkaline springs. The isotopic composition of water indicates a recent meteoric recharge probably through the close by and stratigraphically higher limestones of the Faniskos Unit. The Ca-OH water composition resulted to be similar to other hyperalkaline waters of Greece and worldwide. Although the concentrations of dissolved H2 are very low (tens of nmol/L) compared to other gases collected in similar manifestations, the concentrations of CH4 are considerable (38–314 μmol/L) and display isotopic compositions indicating a substantial if not exclusive abiogenic origin. Methane oxidation is also hypothesized in one of the two springs.

Biomonitoring techniques have been widely used in environmental studies to monitor anthropogenic pollutants. Recently such techniques have been also applied to ascertain the impact of contaminants naturally released by volcanic activity (Calabrese et al., 2015; Arndt et al., 2017). In the present study a biomonitoring survey has been performed in different sites around Nyiragongo and Nyamulagira (D.R. Congo), active volcanoes in the western branch of the East African Rift. We applied both active and passive biomonitoring techniques in order to investigate the release of some harmful chemical elements by Nyiragongo and Nyamulagira: the former was performed by exposing moss-bags (Sphagnum sp.) as active accumulators of volcanic gases and particles. At the same time, additional samples were collected from Amaranthus viridis and Senecio sp. leaves, as well as liquid samples from squeezed banana tree (Musa paradisiaca and Musa nana). Both Amaranthus viridis and banana are plants widespread in the study area and locally edible. While Amaranthus viridis is solely used as vegetable, banana is starchy and additionally used for juice and wine production. The liquid from squeezed banana tree is further used for cooking and drinking in some localities around Nyiragongo and Nyamulagira during the dry season. Any presence of volcanogenic harmful elements in these plants would lead to potential health risk for the population living around these volcanoes. These plants can thus be used to assess the environmental impact and the human health hazard associated with Nyiragongo and Nyamulagira volcanic emissions. All leave samples were gently isolated, dried and powdered avoiding metal contamination for acid microwave extraction (HNO3 + H2O2). Solutions were analyzed for major and trace elements by inductively coupled plasma spectrometry (ICP-MS and ICP-OES) for 49 elements. Preliminary results show a clear fingerprint of volcanic emissions both in the exposed moss bags and in the collected plants. Several elements (Al, As, Ba, Bi, Fe, Mo, Sb, Se, Sr, Te, Tl, Pb) are strongly enriched in the mosses exposed to the volcanic emissions with the highest enrichment measured close to the summit crater. However, evidences of metal bioaccumulation are also found in downwind sites (e.g. Kingi village, at several km from the volcanic source). Leaves of the studied plants also reflect the geographical dispersion of the volcanic plume, especially for highly volatile elements in high temperature volcanic environments such as Tl, Te, Bi, Se, Cu, As, Cd, S. Also alkali metals showed a significant increase in their concentrations, probably because of their affinity for the halide species which are often carried by particles (ashes, pele’s hair and tears, lithics) produced by the spattering and fracturing at the lava lake surface. The liquid water from banana samples has high concentrations of nutrients (Na, K, Mg, Ca, Cl) and trace metals (B, Ba, Cs, Rb, Zn, Tl). The preliminary results clearly highlighted a potential hazard for the population that live close to the Nyiragongo and Nyamulagira volcanoes. Calabrese et al., 2015, Chemosphere, 119, 1447-1455 Arndt et al., 2017, JVGR, 343, 220-232

The final composition of the atmosphere results from several processes and exchanges between all the Earth’s spheres. Some of these are widely known and others, such as the methane degassing from hydrothermal areas, are still understudied. Methane plays a key role in climate change being an efficient greenhouse gas. Although it would be crucial, the total CH4 output from geogenic sources is still not well defined; limitations in CH4 output estimations are due to many factors concerning a scarce dataset availability, difficulty in direct measurements, and interaction with methane-consuming microbiota in the soil. Often, the CH4 flux estimation was obtained indirectly, e.g. cross-correlating CO2/CH4 or H2O/CH4 values of the main gaseous manifestations with measured CO2 or H2O fluxes (Etiope et al., 2007). These methods are commonly used but, although acceptable in principle, may lead to strong over- or under-estimated values. This is particularly true when referred to hydrothermal systems like Nisyros Island (South Aegean Active Volcanic Arc, Greece) showing a wide range in the fumarolic CO2/CH4 ratios. Nisyros’ Island total CH4 output has been previously estimated indirectly in 54 tons/year (Etiope et al., 2007). In 2013, a gas prospection was carried at Lakki Plain, the main exhalative area. Methane flux values were measured at 130 sites ranging from –3.4 to 1420 mg/m2 day. Data were processed by sGs approach and the total flux was estimated in 1 ton/year. Soils were sampled at 10 sites with different T (27 to 70 C), pH (1.4 to 3.7) and gas composition (e.g. H2S from 0.3 to 3.6%). They were used for incubation experiments carried on an atmosphere enriched in methane. Consumption was detected in a range from 5 to 40 ng CH4/gDW hour, with higher values in samples with milder environmental conditions (lower temperature and H2S contents and higher pH). The present study indicates that the previous estimate at Nisyros Island, made by cross-correlating CO2 output data with the CO2/CH4 ratios of its gaseous manifestations, has been excessively large. This result is not a surprise, over-estimation of the CH4 output has been evidenced also for Pantelleria Island (Italy) and Sousaki (Greece). Also in these cases high methanotrophic activity in the soil has been confirmed, indicating a good efficiency of the soil to act as natural filter for GHG (D’Alessandro et al., 2009; 2011; Gagliano et al., 2014). Notwithstanding, the hydrothermal areas are a significant source of CH4 but probably their contribution has been overestimated. Differences in the estimations derive from both disregarding methanotrophic activity within the soils and from an incorrect, and sometimes forced by the data availability, mean CO2/CH4 ratio of the fumarolic emissions used for the indirect estimation. A lot has still to be done to assess the global hydrothermal CH4 burden, but the importance of direct CH4 flux measurements has to be underscored.

The study area is close to the boundary of three tectonic plates (Anatolian, Arabian, and African plates) and is characterized by important tectonic lineaments, which consist mainly of the Dead Sea Fault (DSF), the Karasu Fault, and the East Anatolian Fault (EAF) systems. To understand the origin of soil gas emanation and its relationships with the tectonics of the Amik Basin (Hatay), a detailed soil gas sampling was systematically performed. Together with CO2 flux measurements, > 220 soil gas samples were analyzed for Rn and CO2 concentrations. The distribution of soil Rn (kBq/m(3)), CO2 concentration (ppm), and CO2 flux (g/m(2)/day) in the area appears as a point source (spot) and/or diffuses (halo) anomalies along the buried faults/fractures due to crustal leaks. The results revealed that Rn and CO2 concentrations in the soil gas show anomalous values at the specific positions in the Amik Basin. The trace of these anomalous values is coincident with the N-S trending DSF. CO2 is believed to act as a carrier for Rn gas. Based on the Rn and CO2 concentrations of soil gases, at least three gas components are required to explain the observed variations. In addition to the atmospheric component, two other gas sources can be recognized. One is the deep crust component, which exhibits high Rn and CO2 concentrations, and is considered the best indicator for the surface location of fault/fracture zones in the region. The other component is a shallower gas source with high Rn concentration and low CO2 concentration. Moreover, He isotopic compositions of representative samples vary from 0.94 to 0.99 Ra, illustrating that most samples have a soil air component and may have mixed with some crustal component, without significant input of the mantle component. Based on the repeated measurements at a few sites, soil gas concentrations at the same site were observed to be higher in 2014 than in 2013, which may be associated with the activity of the DSF in 2013-2014. This suggests that soil gas variations at fault zone are closely related to the local crustal stress, and hence are suitable for monitoring fault activities. (C) 2017 Elsevier B.V. All rights reserved.

Volcanoes emit SO2, CO2, and H2S, but also trace elements gases and particles such as As, Cd, Cr, Cu, Hg, Ni, Pb, and Sb. Active moss bag biomonitoring, an easy to apply and low budget method, was used to determine trace element release from volcanic areas of different geological context and climates. Exposure height variations (0.7–1.6 m above ground) due to different availability of natural tie points did not affect the results. Accumulation was linear for exposure durations from three days to nine weeks, so values were comparable by normalization to moss exposure time. Uncovered moss bags showed higher accumulation than co-exposed covered ones because of additional dust and wet deposition while washout by rain was negligible. The selection of a specific moss significantly affected element accumulation with moss of lower shoot compactness accumulating more. For all volcanic areas, highest accumulation was found for S (1–1000 μmol·(g·d)− 1), followed by Fe and Mg (0.1–10 μmol·(g·d)− 1), Sr, Ba, Pb, Cr, Li (10− 4–10− 1μmol·(g·d)− 1), then Co, Mo and the volatile elements As, Sb, Se, Tl, Bi (10− 6–10− 2μmol·(g·d)− 1). For most elements, open conduit volcanoes (Etna, Stromboli, Nyiragongo) showed higher moss accumulation rates than more quiescent hydrothermal areas (Vulcano > Nisyros > Yellowstone National Park) and a correlation of S, Fe, and Pb from eruptive ash and lava emissions. For some volatile elements (S, As, Se), higher accumulation was observed within fumarolic fields compared to crater rims of open conduit volcanoes which is a relevant information for risk assessment of tourist exposure to volcanic gases.

We have performed leaching experiments on the fine ( Our results place the first constraints on the mobilisation of toxic elements from volcanic ash, which are necessary to assess the associated potential health risk of volcanic areas.

A comprehensive hydrogeochemical study of the cold and thermal groundwaters of the presently quiescent volcanic system at Methana was undertaken that involved collecting 71 natural water samples. Methana is a peninsula in Peloponnesus, Greece whose arid climate and hydrological situation is similar to that of the nearby small islands of the Aegean Sea. Similarly, the chemical and isotopic compositions of its water are dominated by the mixing of seawater with meteoric water both through direct intrusion and meteoric recharge. However, the simple mixing trends at Methana are modified by water–rock interaction processes, enhanced by the dissolution of endogenous CO2, which lead to strong enrichments in alkalinity, Ca, Ba, Fe and Mn. The thermal waters show very high salinity that is sometimes close to that of seawater [total dissolved solids (TDS) = 8.5–40 g/l]. Although the cold groundwaters sometimes also show elevated TDS values (up to 6.3 g/l), their overall quality is acceptable due to the trace metal and nitrate contents mostly being below acceptable limits. While the saltiest groundwaters are not acceptable for human consumption, they are used for irrigation without exerting toxic effects on plants, which is probably due to the high permeability of the soils not supporting salt accumulation and salinity-resistant crops being cultivated.

The time series of geochemical data available for the network of wells and drainage galleries at Mt. Etna has been analyzed to identify the changes in water chemistry related to the input of volcanic CO 2 and those related to hydrogeological dynamics. The dynamics of hydrological systems is mainly affected by changes in the rainfall, since this influences the yields of both springs and drainage galleries and the height of the water table of unconfined aquifers. In addition, the characteristics of hydrological systems can change with the fluid pressure. These mechanisms are probably enhanced by changes in the crustal strain, which can cause interbasin transfer of water. The changes in water circulation are paralleled by variations in physicochemical characteristics of groundwater, since water transfer probably occurs among water bodies with different temperatures and compositions. Based on the above mechanisms, the contribution of different water types has been estimated according to their chemical composition: it has been assumed that water circulating in the volcanic pile has a typical HCO 3 − -rich composition, whereas Cl − , SO 4 = , and NO 3 − could be contributed by rainfall, anthropogenic pollution, and sedimentary fluids rich in Na + and Cl − . The compositionally different end members have been identified based on the results of factor analysis, which allowed those chemicals accounted for by a single water end member to be grouped within the same factor. In some cases the SO 4 = enrichment is related to the dissolution of SO 4 = -bearing alteration minerals contained in volcanic sequences, and in such cases this is associated with HCO 3 − . We hypothesize a binary mixing between the HCO 3 − -rich volcanic end member and an end member polluted with Cl − , SO 4 = , and NO 3 − related to water circulation at shallow levels. These two end members are identified by their HCO 3 − /( Cl − + SO 4 = + NO 3 − ) ratio and Cl − , SO 4 = , and NO 3 − contents measured at each sampling site. The extent of mixing between these different water types changes over time, probably due to changes in their circulation patterns, with water being transferred from/to water bodies with different compositions. Once the proportion of the HCO 3 − content related to the binary mixing is determined, we can compute the amount of HCO 3 − related to the variable input of CO 2 over time into the aquifer. The obtained temporal trends are—over a long time period—synchronous in the two sectors of the volcano where the maximal CO 2 degassing occurs, namely the Paterno-Belpasso area on the southwestern flank and the Zafferana-S. Venerina area on the eastern flank. This provides evidence for a common deep mechanism underlying the CO 2 variations that is related to the dynamics of the volcano. Some inconsistent trends are observed in the two sectors during specific periods, such as in 2012, which is probably due to the marked dynamics affecting the eastern flank compared to the more stable southwestern one.

The 87 Sr/ 86 Sr ratio was investigated in groundwater circulating in the volcanic edifice of Mt. Etna in order to estimate the possible contribution of deep brines circulating in the sedimentary basement. Samples from 14 sites were collected and analyzed for their chemical composition and Sr-isotope ratios. While the most common approach of coupling 87 Sr/ 86 Sr ratios with the concentration of dissolved Sr is not effective in distinguishing between the deep brine and seawater contributions, we suggest that the Sr/Cl ratio is a useful complementary parameter that needs to be considered when attempting to clearly identify the Sr sources. The obtained data indicate that the Sr-isotope signature of groundwater is determined by the volcanics hosting the aquifer. The volcanic isotopic signature is modified by very small amounts of brines ( 87 Sr/ 86 Sr ratio typical of sedimentary environments, but only at sites where the groundwater circulates almost in contact with the sedimentary basement. Conversely, the contribution of seawater is completely ruled out since this should produce a higher concentration of chloride. The proposed approach is potentially very effective for tracing the circulation of groundwater not only at Mt. Etna but also at volcanic edifices that overlie a bedrock with different 87 Sr/ 86 Sr ratios as well as at volcanic islands where freshwater overlies seawater.

Fractions of the volatiles ascending from magma chambers meet groundwaters flowing away from the volcano summit and are carried to great distance as dissolved gases. The complex interactions between ascending magmatic volatiles, tectonic structures, heterogeneities in rock permeability and flow lines of aquifers deeply affect the dispersion of the dissolved species. Studying the spatial distribution of such species can therefore provide valuable information on the circulation of fluids inside volcanic edifices. Our study focussed on the composition of dissolved inert gases (He, Ne and N2) and He isotope ratio (3He/4He) in groundwaters circulating at Mt Etna volcano (Italy), because the concentrations of these species differ markedly between magmatic and shallow (crustal and atmospheric) sources, and they do not interact chemically with rocks. We identified groundwaters that flow through anomalously degassing areas associated with clearly evident or known tectonic structures. These waters show a typically magmatic He isotope composition (high 3He/4He ratios) and high proportions of dissolved magmatic gases (He and CO2) compared to the atmospheric ones (Ne and N2). Downstream of the degassing structures, along the hydrological outflows, we found groundwaters that are progressively enriched in atmospheric-derived gases (Ne and N2) and exhibited lower 3He/4He ratios. On this basis, we set up a model of unidimensional dispersion-advection of inert volatile solutes, coupled with a two-layer model for the dynamic exchange of volatiles through the aquifer–atmosphere interface. The model is able to quantitatively explain the progressive dilution of the magmatic signal over distances of several kilometres from the source location of the anomaly towards the final part of the flow lines at the coast. Typical hydrogeological parameters such as the flow velocity, rock permeability and rate of air–groundwater interaction can be constrained, and underground pathways of waters can be identified. Waters that are anomalously rich in magmatic tracers with respect to their peripheral position along the flow lines reflect arrival of deep gases from below, and they therefore offer a powerful tool for revealing hidden tectonic structures.

Forty-five gas samples have been collected from natural gas manifestations at the island of Kos—the majority of which are found underwater along the southern coast of the island. On land, two anomalous degassing areas have been recognized. These areas are mainly characterized by the lack of vegetation and after long dry periods by the presence of sulfate salt efflorescence. Carbon dioxide is the prevailing gas species (ranging from 88 to 99%), while 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 of 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 at around -1‰ and therefore proposing a mixed mantle—limestone 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 of up to about 104 g×m−2×d−1 in both the areas of Volcania and Kokkino Nero, 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 those of the other active volcanic/geothermal systems of Greece (Nisyros, Nea Kameni, Milos, Methana, and Sousaki).