Search

Developing appropriate monitoring strategies in long-quiescent volcanic provinces is challenging due to the rarity of recordable geochemical and geophysical signals and the lack of experienced eruptive phenomenology in living memory. This is the case in the Massif Central (France) where the last eruptive sequence formed the Pavin's Group of Volcanoes, about 7 ka ago. There, current evidence of a mantle activity reminiscence is suggested by the presence of mineral springwaters, mofettes, and soil degassing. It appears fundamental as a prerequisite to decipher the evolution of the gas phase in the magmatic system at the time of the eruptive activity to understand the meaning of current local gas emissions. In this study, we develop an innovative approach coupling CO2 densimetry and geochemistry of fluid inclusions from products erupted by the Pavin's Group of Volcanoes. 3D imagery by Raman spectroscopy revealed that carbonate forming in fluid inclusions may lead to underestimation of CO2 density in fluid inclusions by up to 50% and thus to unreliable barometric estimates. Fortunately, we found that this effect may be limited by focusing on fluid inclusions with a small diameter (

Submarine hydrothermal systems along active volcanic ridges and arcs are highly dynamic, responding to both oceanographic (e.g., currents, tides) and deep-seated geological forcing (e.g., magma eruption, seismicity, hydrothermalism, and crustal deformation, etc.). In particular, volcanic and hydrothermal activity may also pose profoundly negative societal impacts (tsunamis, the release of climate-relevant gases and toxic metal(loid)s). These risks are particularly significant in shallow (

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.

Soil bacteria rank among the most diverse groups of organisms on Earth and actively impact global processes of carbon cycling, especially in the emission of greenhouse gases like methane, CO2 and higher gaseous hydrocarbons. An abundant group of soil bacteria are the mycobacteria, which colonize various terrestrial, marine and anthropogenic environments due to their impermeable cell envelope that contains remarkable lipids. These bacteria have been found to be highly abundant at petroleum and gas seep areas, where they might utilize the released hydrocarbons. However, the function and the lipid biomarker inventory of these soil mycobacteria are poorly studied. Here, soils from the Fuoco di Censo seep, an everlasting fire (gas seep) in Sicily, Italy, were investigated for the presence of mycobacteria via 16S rRNA gene sequencing and fatty acid profiling. The soils contained high relative abundances (upto 34 % of reads assigned) of mycobacteria, phylogenetically close to the Mycobacterium simiae complex and more distant from thewell-studied M. tuberculosis and hydrocarbon-utilizing M. paraffinicum. The soils showed decreasing abundances of mycocerosic acids (MAs), fatty acids unique for mycobacteria, with increasing distance from the seep. The major MAs at this seep were tentatively identified as 2,4,6,8-tetramethyl tetracosanoic acid and 2,4,6,8,10-pentamethyl hexacosanoic acid. Unusual MAs with mid-chain methyl branches at positions C-12 and C-16 (i.e., 2,12-dimethyl eicosanoic acid and 2,4,6,8,16-pentamethyl tetracosanoic acid) were also present. The molecular structures of the Fuoco di Censo MAs are different from those ofthe well-studied mycobacteria like M. tuberculosis or M. bovis and have relatively δ13C-depleted values (−38 ‰ to −48 ‰), suggesting a direct or indirect utilization of the released seep gases like methane or ethane. The structurally unique MAs in combination with their depleted δ13C values identified at the Fuoco di Censo seep offer a new tool to study the role of soil mycobacteria as hydrocarbon gas consumers in the carbon cycle.

Quantifying the CO2 flux sustained by low-temperature fumarolic fields in hydrothermal/volcanic environments has remained a challenge, to date. Here, we explored the potential of a commercial infrared tunable laser unit for quantifying such fumarolic volcanic/hydrothermal CO2 fluxes. Our field tests were conducted between April 2013 and March 2014 at Nea Kameni (Santorini, Greece), Hekla and Krýsuvík (Iceland) and Vulcano (Aeolian Islands, Italy). At these sites, the tunable laser was used to measure the path-integrated CO2 mixing ratios along cross sections of the fumaroles' atmospheric plumes. By using a tomographic post-processing routine, we then obtained, for each manifestation, the contour maps of CO2 mixing ratios in the plumes and, from their integration, the CO2 fluxes. The calculated CO2 fluxes range from low (5.7 ± 0.9 t d−1; Krýsuvík) to moderate (524 ± 108 t d−1; La Fossa crater, Vulcano). Overall, we suggest that the cumulative CO2 contribution from weakly degassing volcanoes in the hydrothermal stage of activity may be significant at the global scale.

The geologic emissions of greenhouse gases (CO2 and CH4) give an important natural contribution to the global carbon budget. However, the contribution of these emissions to the global carbon cycle and their possible role on the climate change remain still poorly quantified (Guliyev and Feizullayev, 1997; Milkov, 2000; Etiope et al., 2015 and references therein). Methane, the most abundant organic compound in Earth's atmosphere, may be created either from existing organic matter or synthesized from inorganic molecules. Accordingly, it can be differentiated in two main classes: a) biotic (either microbial or thermogenic) and b) abiotic. For this study, 115 gas samples of fumarolic, thermal and cold discharges from all over the Hellenic territory were collected and both chemical (CO2, H2S, CH4, N2, O2, Ar, H2 and light hydrocarbons) and isotopic (13C-CO2, 13C-CH4, D-CH4) analyses were performed, in order to investigate the genetic processes that produced CH4 in fluids related with the complex geodynamic setting of Greece. On the basis of the spatial distribution of the gas discharges and their type of emission, the whole dataset was subdivided into 3 main “domains”, as follows: 1) Volcanic Arc (VA) - 34 samples; 2) External Hellenides (EH) - 23 samples of cold emissions and of hyperalkaline aqueous solutions; 3) Internal Hellenides (IH) - 62 samples of cold and geothermal emissions. Almost each group is characterized, as long as subdivided in 3 groups based on the type of emission (on-land free or dissolved gases and subaqueous gases) and a 4th group includes literature data.

Greece, a country characterised by intense seismic and volcanic activity, has a complex geodynamic and geological setting that favours the occurrence of many gas manifestations. In this study, we address the origin of CH4 and light hydrocarbons in cold and thermal emissions discharging along the Hellenic territory. Also, we investigate their possible relationship with the main geochemical composition of the gases and the different geological settings of the sampling sites. For this purpose we collected 101 new samples that were analysed for their chemical (O2, N2, CH4, CO2, He, Ne, Ar, H2, H2S and C2-C6 hydrocarbons) and isotopic (R/RA, δ13C-CO2, δ13C-CH4 and δ2H-CH4) composition. Results show that CH4 presents a wide range of concentrations (from

The Hellenic territory has a very complex geodynamic setting from a long and composite geological history, giving rise to an intense seismic activity deriving and favoring the occurrence of many cold and thermal gas manifestations. Geogenic sources release huge amounts of gases, which have a significant impact on the global balance of the subaerial Carbon Cycle. The study of the geochemistry of the natural gas emissions of the Greek territory is actually underway. In the present work, we focus on methane and light hydrocarbons (C2-C6) to define their origin. Concentrations of methane range from < 2 to 915,200 mmol/mol and its isotopic ratios cover a wide range (d13C from -79.8‰ to +16.9‰; dD from -298‰ to +264‰) indicating different origins or secondary post-genetic processes. Samples from gas discharged located in the Ionian coast and northern Aegean Sea have a prevailing microbial origin, as also shown by the lack of C4+ hydrocarbons and the high C1/(C2+C3) ratios. On the contrary, cold and thermal gas manifestations of central and northern Greece display a prevalent thermogenic origin. Methane in gases released along the active volcanic arc seems to be abiogenic in origin, since they show low C1/(C2+C3) ratios, as well as relatively high C6H6 concentrations. However in these gases, significant thermogenic contribution cannot be excluded. Gases collected in the geothermal areas of central Greece (Sperchios basin and northern Euboea) are likely affected by strong secondary oxidation processes, as suggested by their highly positive C and H isotopic values (up to +16.9‰ and +264‰ respectively) and low C1/(C2+C3) ratios. Incubation experiments on water and sediments of some of these springs reveal that the oxidation of methane is microbially driven.

A new eruption started at Stromboli on 6 August 2014, which had been preceded by 2 months of increased Strombolian activity and several lava overflows from the craters. The eruption was characterized by a lava effusion in Sciara del Fuoco from a fracture at 650 m above sea level that lasted until 13-17 November. Here we present the first geochemical observations of this eruption, based on the soil CO2 flux in the summit area and on 3He/4He ratios in the thermal waters near Stromboli village. We infer that this eruption was triggered by the gradual replenishment of the feeding system by a CO2- and 3He-rich magma at the end of 2013 and after June 2014, suggested by the increase in 3He/4He ratio before eruption, which reached its highest value since 2007. We thus infer that this eruption was unusual, and we finally speculate on the evolutionary scenario of posteruption.

No abtract available

Quantifying the flux of magma derived CO2 dissipated by fumarolic fields at dormant volcanoes is fundamental to assess their current state of hydrothermal activity and, therefore, the likelihood of a future phreatic/magmatic eruption. There is, in fact, documented evidence that gas fluxes, and CO2 flux in particular, can increase substantially during volcanic unrests and prior to eruption, due to either degassing of new ascending magma or changes in the hydrothermal system physical regime. Quantifying CO2 emissions is relatively straightforward at open-conduit volcanoes with high-temperature gas venting, which release high enough quantities of SO2 remotely measurable with UV spectroscopy and where CO2 flux can then be obtained by scaling to fumarole CO2/SO2 ratios. Less actively degassing systems (T less than 300 C), in contrast, release sulphur predominantly as H2S, that is far more difficult to detect optically than SO2, and other procedures are therefore necessary. The main point is that many dormant volcanic systems worldwide fall in this second category. Here we present the first CO2 budget estimates for two dormant volcanoes displaying intense fumarolic activities: La Soufriere of Guadeloupe (Lesser Antilles arc) and Campi Flegrei (Naples, Italy). Both volcanic systems have produced voluminous pyroclastic eruptions in the past and have shown signs of unrest during the last decades (phreatic eruptions at La Soufriere; occasional seismic swarms, extensive degassing and ground uplift at Campi Flegrei). While the CO2 output by diffuse soil degassing is relatively well known at both systems, no accurate CO2 budget for their fumarolic exhalations has been obtained so far. For quantifying this budget we used a portable MultiGAS sensor system that allowed us to determine the horizontal/vertical concentration profiles of CO2 (plus H2O, SO2, H2S and H2) along cross-sections of the gas plumes generated by the fumarolic activity, perpendicular to the plume transport direction. Gas sampling data at 0.5 Hz and simultaneous GPS positioning provided us with the required temporal/spatial resolution to map the chemical heterogeneity of plumes. By integrating over the entire plume section, and scaling to measured plume transport speed (for thermal/UV/video imaging), the CO2 fluxes were calculated. The validity of this methodology was also tested at Campi Flegrei by comparison with independent CO2 flux estimates which we obtained with a Tuneable IR Laser (good match between the two independent flux estimates). Our results show that fumarolic CO2 emissions are significant at both volcanoes (e.g. 1000 t/day at Campi Flegrei, about as much as from diffuse soil degassing, and 30 to 60 t/day at La Soufriere). We propose that the experimental procedure described above can be applied to many other comparable volcanic targets worldwide in order to improve our knowledge of the budget for global volcanic CO2 emissions.

The geodynamics of the central Mediterranean is characterized by the interaction between the European plate and the African one. In this setting Sicily is a sector of the Appenine-Maghrebide accretionary prism, which is located between two areas affected by extensional tectonics (Sicily Channel to the south and the Thyrrenian back arc basin to the north). In the present study we present the first dataset of helium isotopic composition measured in fluids released from the central-western Sicily.With the aim to constrain the transfer system of fluids in this area we relate the results of geochemical investigations with the stratigraphy and structural setting, derived from field geology, deep boreholes and new seismic reflection, gravimetry and magnetometry data. Significant mantle-derived helium (0.4

Introduction In the last decades, the use of near-infrared room-temperature diode lasers for gas sensing has grown significantly. The use of these devices, for instance in combination with optical fibers, is particularly convenient for volcanic monitoring applications [1,2]. Here, we report on the first results of the application of an open-path infrared tunable laser-based at Campi Flegrei (Southern Italy). Such Diode-laser-based measurements were performed, during two field campaigns (october 2012, and january 2013), in the attempt to obtain novel information on the current degassing unrest of Solfatara and Pisciarelli fumarolic fields. Results and Discussion At each site, we used an ad-hoc designed measurement geometry, using a TDLS (a Gas Finder unit) and several differently positioned retroreflectors (mirrors), to scan the fumaroles’ plume from different angles and distances. From post-processing of the data (acquired at 1 hz), we derived tomographic maps of CO2 concentrations in the plume and, by integration and combination with plume transport speed (from video cameras), we inferred the CO2 flux directly. The so-calculated fluxes, the first ever obtained at Campi Flegrei, average of 500 tons/day, and support a significant contribution of fumaroles to the total CO2 budget. The cumulative (fumarole [this study] +soil [3]) CO2 output from Campi Flegrei is finally evaluated at 1600 tons/day. [1] Gianfrani L. et al. (2000). Appl. Phys. B-Rapid Common. 70, 467-470. [2] Richter D. et al (2002), Optics and Lasers in Engineering, Volume 37, Issues 2–3, Pages 171-186. [3] Chiodini G. et al. (2010), Journal of Geophysical Research, Volume 115, B03205, doi:10.1029/2008JB006258.

The geodynamics of the central Mediterranean is characterized by the interaction between the European plate and the African’s. In this setting Sicily is a sector of the Appenine-Maghrebide accretionary prism, which is located between two areas affected by extensional tectonics (Sicily Channel to the south and the Thyrrenian back arc basin to the north). Significant mantle-derived helium (0.4