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Coatepeque (on the E slope of Santa Ana Volcano), Ilopango (inside Ilopango Caldera) and Chanmico (associated with San Salvador Volcano) are volcanic lakes in El Salvador, showing a thermocline at a relatively shallow depth (from 30 to 40 m, from 20 to 40 m and from 5 to 15 m depth, respectively) and anoxic conditions below 33, 24 and 4 m depth, respectively. The Na+–Cl− composition of the Coatepeque and Ilopango lakes, displaying TDS values up to 1226 and 1216 mg/L, respectively, is likely due to hydrothermal fluids that feed these two lakes, as also confirmed by Cl−/Br− molar ratios ≤ 650, high As, B, Li and Si contents and Cl−/SO42− ratio > 1. The Mg2+–HCO3− water composition of Lake Chanmico, whose TDS values were between 566 and 856 mg/L, suggests water-rock interaction processes with mafic/ultramafic rocks variably affected by serpentinization processes, which produced high Mg2+, Si and B concentrations. Waters at depth were characterized by the presence of CO2 from an extra-lacustrine source, as suggested by δ13C-CO2 values significantly less negative than those typically related to biogenic processes, albeit this gas was found in smaller quantities when compared to those recorded in other meromictic lakes hosted in quiescent volcanic systems (e.g. Lake Kivu in DRC, Monticchio, Albano and Averno lakes in Italy, Hule and Rio Cuarto lakes in Costa Rica, Lake Pavin in France). The occurrence of CH4, whose concentrations in Lake Chanmico were up to two orders of magnitude higher than those recorded in Coatepeque and Ilopango lakes, suggests bacterial methanogenesis.

The Campo de Calatrava Volcanic Field (CCVF) located in central-southern Spain (along with Selva-Emporda in Catalonia, NE Spain) is regarded as one of the most important CO emitting zones in Peninsular Spain. Here, we report and evaluate new molecular and isotopic geochemistry of thermal waters and COrich gas discharges from the CCVF. Locally, these CO-rich fluid emissions represent the remnants of the past volcanic activity that affected this area from the late Miocene through the Quaternary, with the most recent events occurring in the Holocene. The locations of discharging fluids and previous volcanic centers appear to be aligned along well-defined NW-SE and NNW-SSE lineaments, with subordinate trends in the ENE-WSW direction. The chemical and isotopic composition of the thermal waters suggests a meteoric origin, dominated by three distinct geochemical facies: 1) HCO-Mg(Ca) type waters, associated with a relatively shallow aquifer and related to the interaction of meteoric waters with CO-rich gases, alkaline volcanic products, and sedimentary formations, 2) SO(Cl)-Ca(Mg) type waters, which stems from the two rivers (Guadiana and Jabalón) that drain Triassic evaporitic rocks before entering the study area, and 3) HCO-Na type waters, hosted in deep geopressurized CO-rich reservoirs within the Ordovician basement rocks. The Sr/Sr isotopic compositions (ranging between 0.70415 and 0.71623) and δS-SO values (+10.7 to +18.3‰ vs. CDT) of CO-rich fluids are consistent with interactions between water and either the Paleozoic basement, Triassic evaporites, Quaternary volcanic rocks, or a combination thereof. Dissolution of a CO-rich gas phase into the aquifer produces low pH values (down to 5.4) and enhances water-rock interactions causing relatively high salinity (Total Ionic Salinity: up to ∼185 meq/L). Carbon dioxide is by far the most abundant gas constituent (up to 992 mmol/mol) and is dominated by mantle-derived sources as indicated by the combination of relatively high helium isotopic ratios (up to 2.7 R/Ra), high isotopic ratios of carbon in CO (ranging between −6.8 and −3.2‰ V-PDB), and the carbon isotopic signature of TDIC (from −6.8 to +2.2‰ vs. VPDB). In the last two decades, numerous (CO-rich) gas blowouts have occurred in the area during well drillings, suggesting the presence of a geopressurized gas reservoir at relatively shallow depth., The Municipality of Almagro is gratefully acknowledged for the help provided during the sampling activities. We would like to thank Dr. Luis Perez del Villar for his help during the first sampling fieldwork at CCVF. We wish to thank D. Melero Cabañas who accompanied us in the field to collect the water samples during the first survey. Many thanks are also due to the personnel of Amphos21 (J. Bruno, A. Cedez, F. Grandia) and Ciudad de la Energia (D. Angel) and F. Capecchiacci (Dept. Earth Science of Florence) for their help during the second survey. We would like to acknowledge the comments and suggestions provided by two reviewers, who greatly improved an early version of the manuscript. This work was partially funded by Ciudad de la Energia (Resp. OV; Grant contract: ALM-08-006) and the Laboratory of Stable Isotopes and Fluid Geochemistry of the Department of Earth Sciences (University of Florence).

Red wood ants are ecologically important species in Europe that form large colonies. Their nest mounds are characterized by stable microclimatic conditions, that are favourable to the development of rich invertebrate and microbial communities. Through their respiration processes, all these inhabitants contribute to the total gas emissions of the mounds. Quantifications of red wood ant mounds CO2 production are only available from Northern and Central Europe, and the Alps, where these ants are common. During the second half of the last century some species were transplanted from the Alps to southernmost sites, where they were not present, to be employed as biocontrol agents. No information on the contribution of these low-latitudes populations to the local forest CO2 production is available. The microbial communities living within red wood ant mounds are also poorly known. In this study, we investigated the CO2 gas emissions and the microbiome of the mounds of an introduced population of the red wood ant Formica paralugubris in a Southern Europe montane forest. We found that ant mounds produced more CO2 than the forest soil, and that their CO2 efflux as well as internal concentration were higher during summer than winter, with a lighter CO2 carbon isotopic signature in summer than winter, likely due to an increased ant activity. Moreover, the top part of the mound was characterised by higher CO2 efflux and lower CO2 internal concentration compared to the bottom, probably due to its internal structure and conditions. The isotopic signature of the mound material was similar between summer and winter, suggesting a metabolic similarity of the microbial communities. Also, we estimated the ants' relative contribution to the total mound CO2 production to be 83%, whereas the microbiota CO2 contribution was estimated at 17%. Finally, the mound microbiome composition varied between summer and winter, though no seasonal difference in the diversity indexes or beta-diversity was found. Our results demonstrate the impacts of the introduced red wood ants on the carbon dynamics of the recipient ecosystem.

Sicily hosts many natural manifestations that include thermal waters, gas discharges and mud volcanoes. Due to the significant geodynamic and geological differences, the fluid discharges along a NE-WS–oriented transect that run from the Peloritani Mts. to the Sciacca Plain shows a large variability in water and gas chemical and isotopic compositions. The studied waters are characterized by Ca-HCO3, Ca(Mg)-SO4, Ca-Cl and Na-Cl compositions produced by distinct geochemical processes such as water-rock-gas interactions, mixing between deep and shallow aquifers and seawater and direct and reverse ion exchanges. The gas chemistry is dominated by CO2 to the east and CO2-N2 to the west of the study area, whereas the central part shows mud volcanoes discharging CH4-rich gases. Water isotopes suggest that the thermal waters are fed by a meteoric recharge, although isotopic exchange processes between thermal fluids and host rocks at temperature >150°C are recognized. Accordingly, liquid geothermometry suggests equilibrium temperatures up to 220°C. The carbon in CO2 and helium isotopes of the emissions from the westernmost sector of Sicily indicate that these two gases consists of up to 40 % of a mantle component, the latter decreasing to the east down to 10% where CO2 of thermometamorphic origin dominates. Accordingly, conceptual models of the fluid circulation for the western, central and eastern sectors are proposed. The regional geothermal reservoir, hosted in carbonates in the western sector and locally outcropping, is of low to medium temperature. Higher temperature conditions (up to 200-220°C) are suggested by geothermometry and probably related to deeper levels of the system. Sicily can be regarded as a potentially suitable area for future investigations to evaluate specific activities aimed at exploiting the geothermal resource.

This study was aimed to test a new methodological approach to carry out measurements of gaseous elemental mercury (GEM) diffusively emitted from soils in hydrothermal-volcanic environments. This method was based on the use of a static closed-chamber (SCC) in combination with a Lumex® RA-915M analyzer that provides GEM measurements in a wide range of concentrations (from 2 to 50,000 ng m-3). Gas samples were collected at fixed time intervals from the SCC positioned on the ground (time-series samples). The Lumex® inlet port was equipped with a three-way Teflon valve allowing the free entrance of air through a carbon trap, in order to: (i) prevent disturbance to the Lumex® operative flow rate (10 L min-1) during the injection of the gas samples from the SCC and (ii) minimize the instability of the baseline signal induced by possible variations of GEM concentrations in air. In the lab, known amounts of GEM, pipetted from a vessel containing an Hg-saturated air in equilibrium with liquid mercury at 27 °C, were injected in the Lumex® via the modified inlet port to construct a calibration curve. The latter was used to calculate the amount of GEM in the SCC (KSCC) from the corresponding GEM concentrations measured by the Lumex® analyzer. The KSCC values of the time-series samples were proportionally increasing with the GEM fluxes (φGEM), thus φGEM values were computed according to the following equation: φGEM=(dKSCC/dt)/A, where A is the basal area of the SCC and dt is the time interval of the time-series sampling. Up to 214 φGEM measurements were carried out at Solfatara crater (Campi Flegrei, southern Italy), a hydrothermally altered tuff cone characterized by an anomalous diffuse soil emission of GEM-rich geogenic gases. The measured φGEM values varied up to 4 orders of magnitude, from 1,296, corresponding to the sensitivity of the method at the selected sampling time interval (1 min), to 1,957,500 ng m-2 day-1, and were consistent with those recently measured in this crater using a different method. In the field, 10 replicates were carried out in 5 selected sites, allowing to demonstrate that the proposed method has a high reproducibility (RDS < 4%). The φGEM and φCO2 values, the latter being measured in the same 214 sites by using the accumulation chamber method, showed a low correlation, although both gases were originated from the same deep source. This suggests that GEM and CO2 soil fluxes are differently affected by environmental parameters, such as soil humidity and temperature, which have a strong effect on the release of GEM from the soil, whereas they do not play a significant role in the diffuse degassing of CO2. The measured fluxes were used to compute the CO2 and GEM total outputs (402 and 5.41 × 10-6 t day-1, respectively) from the study area (92,000 m2) and to construct contour maps showing the spatial distribution of the φCO2 and φGEM values. By modifying the geometry of SCC and the time interval of the sampling series, the proposed method can be applied to the measurements of GEM soil fluxes in other geological systems and man-made environments. This study was aimed to test a new methodological approach to carry out measurements of gaseous elemental mercury (GEM) diffusively emitted from soils in hydrothermal-volcanic environments. This method was based on the use of a static closed-chamber (SCC) in combination with a Lumex® RA-915M analyzer that provides GEM measurements in a wide range of concentrations (from 2 to 50,000 ng m_3). Gas samples were collected at fixed time intervals from the SCC positioned on the ground (time-series samples). The Lumex® inlet port was equipped with a three-way Teflon valve allowing the free entrance of air through a carbon trap, in order to: (i) prevent disturbance to the Lumex® operative flow rate (10 L min_1) during the injection of the gas samples from the SCC and (ii) minimize the instability of the baseline signal induced by possible variations of GEM concentrations in air. In the lab, known amounts of GEM, pipetted from a vessel containing an Hg-saturated air in equilibrium with liquid mercury at 27 _C, were injected in the Lumex® via the modified inlet port to construct a calibration curve. The latter was used to calculate the amount of GEM in the SCC (KSCC) from the corresponding GEM concentrations measured by the Lumex® analyzer. The KSCC values of the time-series samples were proportionally increasing with the GEM fluxes (fGEM), thus fGEM values were computed according to the following equation: fGEM¼ (dKSCC/dt)/A, where A is the basal area of the SCC and dt is the time interval of the time-series sampling. Up to 214 fGEM measurements were carried out at Solfatara crater (Campi Flegrei, southern Italy), a hydrothermally altered tuff cone characterized by an anomalous diffuse soil emission of GEM-rich geogenic gases. The measured fGEM values varied up to 4 orders of magnitude, from 1,296, corresponding to the sensitivity of the method at the selected sampling time interval (1 min), to 1,957,500 ng m_2 day_1, and were consistent with those recently measured in this crater using a different method. In the field, 10 replicates were carried out in 5 selected sites, allowing to demonstrate that the proposed method has a high reproducibility (RDS < 4%). The fGEM and fCO2 values, the latter being measured in the same 214 sites by using the accumulation chamber method, showed a low correlation, although both gases were originated from the same deep source. This suggests that GEM and CO2 soil fluxes are differently affected by environmental parameters, such as soil humidity and temperature, which have a strong effect on the release of GEM from the soil, whereas they do not play a significant role in the diffuse degassing of CO2. The measured fluxes were used to compute the CO2 and GEM total outputs (402 and 5.41 _ 10_6 t day_1, respectively) from the study area (92,000 m2) and to construct contour maps showing the spatial distribution of the fCO2 and fGEM values. By modifying the geometry of SCC and the time interval of the sampling series, the proposed method can be applied to the measurements of GEM soil fluxes in other geological systems and man-made environments.

Paola Ridge, along the NW Calabrian margin (southern Tyrrhenian Sea), is one of the few reported deep sea sites of precipitation of authigenic carbonates in the Tyrrhenian Sea. Here, the changing composition of the seeping fluids and the dynamic nature of the seepage induced the precipitation of pyrite, siderite and other carbonate phases. The occurrence of this array of authigenic precipitates is thought to be related to fluctuation of the sulfate-methane transition zone (SMTZ). Concretions of authigenic minerals formed in the near sub-bottom sediments of the Paola Ridge were investigated for their geochemical and isotopic composition. These concretions were collected in an area characterized by the presence of two alleged mud volcanoes and three mud diapirs. The mud diapirs are dotted by pockmarks and dissected by normal faults, and are known for having been a site of fluid seepage for at least the past 40 kyrs. Present-day venting activity occurs alongside the two alleged mud volcanoes and is dominated by CO2-rich discharging fluids. This discover led us to question the hypothesis of the mud volcanoes and investigate the origin of the fluids in each different domed structure of the study area. In this study, we used stable isotopes (carbon and oxygen) of carbonates coupled with rare earth element (REE) composition of different carbonate and non-carbonate phases for tracing fluid composition and early diagenesis of authigenic precipitates. The analyses on authigenic precipitates were coupled with chemical investigation of venting gas and sea-water. Authigenic calcite/aragonite concretions, from surficial sediments on diapiric structures, have depleted 13C isotopic composition and slightly positive δ18O values. By contrast, siderite concretions, generally found within the first 6 m of sediments on the alleged mud volcanoes, yielded positive δ13C and δ18O values. The siderite REE pattern shows consistent LREE (light REE) fractionation, MREE (medium REE) enrichment and positive Gd and La anomalies. As shown by the REE distribution, the 13C-depleted composition and their association with chemosymbiotic fauna, calcite/aragonite precipitated at time of moderate to high methane flux close to the seafloor, under the influence of bottom seawater. Authigenic siderite, on the other hand, formed in the subseafloor, during periods of lower gas discharges under prolonged anoxic conditions within sediments in equilibrium with 13C-rich dissolved inorganic carbon (DIC) and 18O-rich water, likely related to methanogenesis and intermittent venting of deep-sourced CO2.

In this study, the chemical and isotopic composition of thermo-mineral springs from the Rosario de la Frontera hydrothermal system was used to construct a conceptual model describing the source regions the thermal fluids and the chemical-physical processes controlling the chemistry of waters and dissolved gases during their underground circulation. The main hydrothermal reservoir, hosted within the Cretaceous Pirgua Subgroup deposits, is fed by meteoric water and shows a Na-HCO3 composition produced by water-rock interactions involving sedimentary formations mostly consisting of conglomerates and sandstones, which are interbedded with alkaline volcanic rocks and shales and limestone deposits. This aquifer also receives significant contributions of crustal CO2 and He from mantle degassing, the latter being likely favored by the regional tectonic assessment that is characterized by a deep detachment (at about 10km depth) in the basement of the Santa Bárbara thick-skinned thrust system and a thinned lithosphere. The uprising thermal fluids mix with a relatively high salinity Na-Cl dominated aquifer produced by the interaction of meteoric water with the Tertiary Anta Formation evaporite. The temperatures of the hydrothermal reservoir, estimated with water geothermometers, are up to 130°C, which are consistent with the thickness of the hydrothermal circuit (2700-3000m) and the relatively high local geothermal gradient (~40°C/km). These results suggest that the heat stored in the fluid phase of RFHS is up to ~1×1018J, a value significantly higher (20%) than that previously estimated assuming an average reservoir temperature of 90°C. Fil: Chiodi, Agostina Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Investigaciones en Energía no Convencional. Universidad Nacional de Salta. Facultad de Ciencias Exactas. Departamento de Física. Instituto de Investigaciones en Energía no Convencional; Argentina Fil: Tassi, F.. University of Florence. Department of Earth Sciences; Italia. Institute of Geosciences and Earth Resources; Italia Fil: Baez, Walter Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Investigaciones en Energía no Convencional. Universidad Nacional de Salta. Facultad de Ciencias Exactas. Departamento de Física. Instituto de Investigaciones en Energía no Convencional; Argentina Fil: Maffucci, R.. Università di Roma; Italia Fil: Invernizzi, C.. Institute for Dynamics of Environmental Processes; Italia Fil: Giordano, G.. Università di Roma; Italia. Institute for Dynamics of Environmental Processes; Italia Fil: Corrado, S.. Università di Roma; Italia Fil: Bicocchi, G.. University of Florence. Department of Earth Sciences; Italia Fil: Vaselli, O.. University of Florence. Department of Earth Sciences; Italia. Institute of Geosciences and Earth Resources; Italia Fil: Viramonte, Jose German. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Investigaciones en Energía no Convencional. Universidad Nacional de Salta. Facultad de Ciencias Exactas. Departamento de Física. Instituto de Investigaciones en Energía no Convencional; Argentina Fil: Pierantoni, P.P.. University of Camerino; Italia

Fil: Chiodini, Giovanni. Istituto Nazionale Di Geofisica E Vulcanologia. Italia. Fil: Liccioli, Caterina. Universidad Nacional de Rio Negro. Instituto de Investigaciones en Paleobiologia y Geologia; Argentina. Río Negro, Argentina Fil: Vaselli, Orlando. Universita Degli Studi Di Firenze; Italia Fil: Calabrese, Sergio. Università di Palermo; Italia Fil: Tassi, Franco. Universita Degli Studi Di Firenze; Italia Fil: Caliro, Stefano. Istituto Nazionale Di Geofisica E Vulcanologia; Italia Fil: Caselli, Alberto Tomás Universidad Nacional de Rio Negro. Instituto de Investigaciones en Paleobiologia y Geologia; Argentina. Río Negro, Argentina Fil: Agusto, Mariano R. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: D'alessandro, Walter. Istituto Nazionale Di Geofisica E Vulcanologia; Italia Fil: Liccioli, Caterina. Consejo Nacional de Investigaciones Científicas y Técnicas. Río Negro, Argentina. Fil: Caselli, Alberto Tomás Consejo Nacional de Investigaciones Científicas y Técnicas. Río Negro, Argentina. A geochemical survey of the main thermal waters discharging in the southwestern part of the Domuyo volcanic complex (Argentina), where the latest volcanic activity dates to 0.11 Ma, has highlighted the extraordinarily high heat loss from this remote site in Patagonia. The thermal water discharges are mostly Na-Cl in composition and have TDS values up to 3.78 g L− 1 (El Humazo). A simple hydrogeochemical approach shows that 1,100 to 1,300 kg s− 1 of boiling waters, which have been affected by shallow steam separation, flow into the main drainage of the area (Rio Varvarco). A dramatic increase of the most conservative species such as Na, Cl and Li from the Rio Varvarco from upstream to downstream was observed and related solely to the contribution of hydrothermal fluids. The equilibrium temperatures of the discharging thermal fluids, calculated on the basis of the Na-K-Mg geothermometer, are between 190 °C and 230 °C. If we refer to a liquid originally at 220 °C (enthalpy = 944 J g− 1), the thermal energy release can be estimated as high as 1.1 ± 0.2 GW, a value that is much higher than the natural release of heat in other important geothermal fields worldwide, e.g., Mutnovsky (Russia), Wairakei (New Zealand) and Lassen Peak (USA). This value is the second highest measured advective heat flux from any hydrothermal system on Earth after Yellowstone. A geochemical survey of the main thermal waters discharging in the southwestern part of the Domuyo volcanic complex (Argentina), where the latest volcanic activity dates to 0.11 Ma, has highlighted the extraordinarily high heat loss from this remote site in Patagonia. The thermal water discharges are mostly Na-Cl in composition and have TDS values up to 3.78 g L− 1 (El Humazo). A simple hydrogeochemical approach shows that 1,100 to 1,300 kg s− 1 of boiling waters, which have been affected by shallow steam separation, flow into the main drainage of the area (Rio Varvarco). A dramatic increase of the most conservative species such as Na, Cl and Li from the Rio Varvarco from upstream to downstream was observed and related solely to the contribution of hydrothermal fluids. The equilibrium temperatures of the discharging thermal fluids, calculated on the basis of the Na-K-Mg geothermometer, are between 190 °C and 230 °C. If we refer to a liquid originally at 220 °C (enthalpy = 944 J g− 1), the thermal energy release can be estimated as high as 1.1 ± 0.2 GW, a value that is much higher than the natural release of heat in other important geothermal fields worldwide, e.g., Mutnovsky (Russia), Wairakei (New Zealand) and Lassen Peak (USA). This value is the second highest measured advective heat flux from any hydrothermal system on Earth after Yellowstone.

The lithium-rich brines of the Salar de Olaroz in the Central Andes of NW Argentina are considered to be of great economic and strategic interest. This study focused on the fluid source(s) and geochemical processes governing the chemical and isotopic characteristics of the surficial waters of Olaroz (residual brines, ephemeral lakes, rivers and tributary streams), aiming to define the mechanisms leading to such a huge Li reservoir. The chemistry of the Rosario River, which is one of the main sources of recharge of the Salar de Olaroz, is mostly controlled by fluid inputs from hydrothermal systems located north of the salar (in the volcanic areas of Rosario de Coyaguayma, Pairique, and Cono Panizo). The hydrothermal fluids are characterized by relatively high Li concentrations, as they interact with Li-rich rocks pertaining to Miocene – Pliocene volcanic formations, Ordovician sedimentary deposits, and, possibly, pre-Ordovician crystalline basement. In the salar, the hyperarid climate regulates the relative proportion between supplied waters and evaporation, inducing deposition/dissolution of salts, which controls the concentrations of main ions in brines and ephemeral lakes. Hence, the peculiar combination of a Li-rich primary source, the hydrothermal scavenging by geothermal fluids that feed the Rosario River, and secondary concentration processes affecting the surficial water within the salar leads to the formation of the huge Li reservoir characterizing this area.

We investigated the effect of microbial activity on the chemistry of hydrothermal fluids related to the Vicano-Cimino system, central Italy. The database included the composition and delta C-13 CO2 and delta C-13 CH4 values for soil gas from an area characterized by intense degassing of fluids having a deep origin. The delta C-13 CH4 values along vertical profiles in the soil indicated that CH4 was controlled by microbial oxidation occurring at shallow (< 50 cm) depth, where free O-2 was available. This was consistent with the vertical gradients of CH4, H2S and O-2 concentrations. The delta C-13 CO2 values in soil gas, characterized by a composition similar to that of the hydrothermal fluids, were not significantly influenced by biodegradation. On the contrary, gas strongly affected by air contamination showed a significant delta C-13 CO2 fractionation. Microbial activity caused strong consumption of hydrothermal alkanes, alkenes, cyclics and hydrogenated halocarbons, whereas benzene was recalcitrant. Oxygenated compounds from hydrocarbon degradation consisted of alcohols, with minor aldehydes, ketones and carboxylic acids. A predominance of alcohols at a high rate of degassing flux, corresponding to a short residence time of hydrothermal gas within the soil, indicated incomplete oxidation. N-bearing compounds were likely produced by humic substances in the soil and/or related to contamination by pesticides, whereas alpha-pinene traced air entering the soil. The study demonstrates that microbial communities in the soil play an important role for mitigating the release to the atmosphere of C-bearing gases, especially CH4, through diffuse soil degassing, a mechanism that in central Italy significantly contributes to the discharge of CO2-rich gas from deep sources. (C) 2015 Elsevier Ltd. All rights reserved.

The chemical composition of volatile organic compounds (VOCs) in soil gases from the Solfatara crater (Campi Flegrei, Italy) was analyzed to investigate the effects of biogeochemical processes on gases discharged from the hydrothermal reservoir and released into the atmosphere through diffuse degassing. The chemistry of fluids from fumarolic vents, which represent preferential pathways for fluid uprising, was also reported for comparison. Oxidation-reduction and hydration-dehydration reactions, as well as microbial activity, strongly affected the composition of C-4-C-9 alkanes, alkenes, S-bearing compounds and alkylated aromatics, especially in those sites where the soil showed relatively low permeability to uprising fluids. Other endogenous organic compounds, such as benzene, phenol and hydrofluorocarbons were able to transit through the soil almost undisturbed, independently on the gas emission rate. Products of VOC degradation mainly consisted of aldehydes, ketones, esters, ethers and, subordinately, alcohols. Cyclic compounds revealed the occurrence of VOCs produced within sedimentary formations overlying the hydrothermal reservoir, whereas the presence of chlorofluorocarbons (CFCs) was likely related to air contamination. The results of the present study highlighted the strict control of biogeochemical processes on the behavior of hydrothermal VOCs that, at least at a local scale, may have a significant impact on air quality. This information could be improved by laboratory experiments conducted at specific chemical-physical conditions and in presence of different microbial populations. (C) 2015 Elsevier Ltd. All rights reserved.

We have analyzed the carbon isotopic composition of CO 2 , methane, ethane, propane and n-butane, the hydrogen isotopic composition of methane as well as total concentrations of gas constituents contained in the Mediterranean volcanic–hydrothermal discharges of Nisyros (Greece), Vesuvio, La Solfatara, Ischia and Pantelleria (all Italy) to determine the origin of the hydrocarbons. Isotopic criteria conventionally used for hydrocarbon classification suggest thermogenic origins, except for Pantelleria, for which an abiogenic origin is indicated. These findings would imply that thermogenic sources can provide methane/(ethane + propane) concentration ratios as high as those usually observed for microbial hydrocarbons. However, additional consideration of gas concentration data challenges the suitability of conventional criteria for the classification of hydrocarbons emanating from hydrothermal environments. Methane seems to be in close equilibrium with co-occurring CO 2 , whereas its higher chain homologues are not. Therefore, it cannot be excluded that methane on the one hand and ethane, propane and n-butane on the other hand have distinct origins. The carbon isotopic composition of methane might be controlled by the carbon isotopic composition of co-occurring inorganic CO 2 and by hydrothermal temperatures whereas the carbon isotopic composition of the higher n-alkanes could correspond to the maturity of organic matter and/or to the residence time of the gasses in the source system.

The Vicano-Cimino Volcanic District (VCVD) is related to the post-orogenic magmatic activity of the peri-Tyrrhenian sector of Central Italy. The chemical and isotopic compositions of 333 water discharges and 25 gas emissions indicate the occurrence of two main sources: 1) cold Ca-HCO3 to Ca(Na, K)-HCO3 type waters from relatively shallow aquifers hosted in volcanic and sedimentary formations; and 2) thermal Ca-SO4(HCO3) type waters located in a deep CO2-pressurized reservoir, hosted in carbonate-evaporite rocks and separated from the shallow aquifers by thick sequences of low-permeability formations. Carbon dioxide is mainly produced by thermal metamorphic decarbonation within the deepest and hottest parts of the carbonate-evaporite reservoir (delta C-13-CO2 from - 3.1 to + 2.2% vs. VPDB), likely affected by a mantle-rooted CO2. Release of CO2-rich gases from the deep aquifer into the overlying shallow aquifers produces high-CO2 springs and bubbling pools. The spatial distribution of thermal waters and CO2-rich cold discharges is strongly controlled by fractures and faults located in correspondence with buried structural highs. Stable isotopes (delta D and delta O-18) suggest that meteoric water feeds both the shallow and deep reservoirs. The relatively low R/R-a values (0.27-1.19) indicate that He is mainly deriving from a crustal source, with minor component from the mantle affected by crustal contamination related to the subduction of the Adriatic plate. Consistently, relatively high N-2/Ar and N-2/He-3 ratios and positive delta N-15-N-2 values (from 0.91 to 5.7 parts per thousand vs. air) characterize the VCVD gas discharges, suggesting the occurrence of a significant "excess" nitrogen. Isotopic compositions of CH4 (delta C-13-CH4 and delta D-CH4 values from - 28.9 to - 22.1 parts per thousand vs. VPDB and from - 176 to - 138 parts per thousand vs. VSMOW, respectively), and composition of light alkanes are indicative of prevalent thermogenic CH4, although the occurrence of abiogenic CH4 production cannot be excluded. The delta S-34-H2S values (from + 9.3 to + 11.4 parts per thousand vs. VCDT) are consistent with the hypothesis of H2S production from thermogenic reduction of Triassic anhydrites. Gas geothermometry in the H2O-H-2-Ar-H2S system suggests that the VCVD gases equilibrated in a liquid phase at redox conditions controlled by interactions of fluids with the local mineral assemblage at temperatures lower (2000 m) geothermal wells. This confirms that secondary processes, i.e. steam condensation, gas dissolution in shallow aquifers, re-equilibration at lower temperature, and microbial activity, significantly affect the chemistry of the uprising fluids. Thermal water chemistry supports the occurrence in this area of an anomalous heat flow that, coupled with the recent demographic growth, makes this site suitable for direct and indirect exploitation of the geothermal resource, in agreement with the preliminary surveys carried out in the 1970's-1990's for geothermal exploration purposes. (C) 2014 Elsevier B.V. All rights reserved.

This work reports the results of an integrated investigation on Holocene faulted deposits exposed on the northeastern Lake Langano in the central sector of the Main Ethiopian Rift (MER). The Lake Langano is part of a closed basin and thus it is highly sensitive to climate fluctuations. The present study explored the foot of the Haroresa escarpment, where coarse-grained slope deposits interbedded with thin lake shore shell-rich coarse sands are well exposed. Stratigraphical analysis of these deposits, integrated with radiocarbon dating carried out on lacustrine gastropod Melanoides tubercolata shells, points to significant lake level fluctuations forced mainly by climate oscillations. These have been interplaying during the early and middle Holocene with a structurally-controlled threshold separating an embayment of the Lake Langano to the south, from the small perched Lake Haro Bu-a basin to the north. Significant differences in the 13 C/ 12 C isotopic ratio have been identified in the M. tubercolata shells collected on the opposite sides of such a threshold. The time-space variations of the isotopic signature of the shells are referred to the mutual relationships between the two main different CO 2 sources (i.e., microbial activity and deep mantle degassing) dissolved in the lake water.

A geochemical survey of thermal waters collected from submarine vents at Panarea Island (Aeolian islands, southern Italy) was carried out from December 2002 to March 2007, in order to investigate (i) the geochemical processes controlling the chemical composition of the hydrothermal fluids and (ii) the possible relations between the chemical features of the hydrothermal reservoir and the activity of the magmatic system. Compositional data of the thermal water samples were integrated in a hydrological conceptual model, which describes the formation of the vent fluid by mixing of seawater, seawater concentrated by boiling, and a deep, highly-saline end-member, whose composition is regulated by water-rock interactions at relatively high temperature and shows clear clues of magmatic-related inputs. The chemical composition of concentrated seawater was assumed to be represented by that of the water sample having the highest Mg content. The composition of the deep end-member was instead calculated by extrapolation assuming a zero-Mg end-member. The Na-K-Ca geothermometer, when applied to the thermal end-member composition, indicated an equilibrium temperature of approximately 300 degrees C, a temperature in agreement with the results obtained by gas-geothermometry. (c) 2008 Elsevier Ltd. All rights reserved.