Geogenic carbon dioxide degassing from active tectonic areas of the Balkan Peninsula

Sin dagli anni ’70, la ricerca scientifica ha evidenziato una forte relazione tra il degassamento di carbonio profondo e le aree tettonicamente attive, sottolineando l’elevata importanza del contributo di queste emissioni nella quantificazione del carbonio globale. La Penisola Balcanica presenta grandi aree caratterizzate da degassamento di carbonio di origine mantellica, da attività vulcaniche Quaternarie, da un’elevata sismicità e da strutture tettoniche a scala regionale. Purtroppo, la stima del degassamento di anidride carbonica profonda in quest’area è ancora poco studiata. La ricerca di questa tesi di dottorato si è focalizzata sulla (i) stima dell’output di carbonio profondo dalle grandi sorgenti carsiche della Grecia, e sulla (ii) caratterizzazione della composizione chimica e isotopica delle principali manifestazioni gassose della Macedonia del Nord. Inoltre, è stato condotto anche uno studio sull’impatto dei processi geogenici ed antropogenici sulla qualità delle acque dei grandi sistemi carsici della Grecia. Negli acquiferi carsici delle Grecia sono state riconosciute tre principali composizioni chimiche dell’acqua: (i) bicarbonato-calcica per le sorgenti continentali; (ii) cloruro-sodica per le sorgenti in area di costa, (iii) solfato-calcica dovuta a processi di dissoluzione di gesso all’interno dell’acquifero. I risultati, in termini di specie maggiori ed elementi in traccia, sono stati comparati con i limiti sulle acque potabili imposte dalle Direttive della Comunità Europea, CE/98/83 e CE/2020/2184, i quali raramente vengono superati tranne per quei parametri che risentono della influenza dell’intrusione marina (Conduttività Elettrica, Na, Cl, B). In queste sorgenti, sono stati rivelati elevati valori di nitrato, sebbene sempre al di sotto del limite di potabilità. Per quanto riguarda la composizione chimica dei gas disciolti e liberi, l’azoto risulta essere il gas dominante, con concentrazioni fino a 985,300 µmol mol-1. Il δ13CTDIC varia tra -16.6 ‰ e -0.10 ‰ (vs. V-PDB), mentre il δ13CCO2, misurato nel gas libero, varia da -29.9 ‰ a -7.41 ‰ (vs. V-PDB). La composizione isotopica dell’elio è stata misurata solo in pochi campioni (R/RA = 0.20 - 0.33), con valori che indicano una sorgente principalmente crostale. Applicando il bilancio di massa del carbonio, è stata fatta una stima del carbonio endogenico (1.43 × 109 mol a-1), la quale sorgente potrebbe essere associata a diverse sorgenti, tra cui termo-metamorfismo di carbonati indotto dall’intrusione di corpi magmatici di età Quaternaria e/o strutture tettoniche regionali. La ricerca condotta in Macedonia del Nord rappresenta un primo catalogo delle principali manifestazioni gassose presenti nell’area, sebbene ancora incompleto. Le manifestazioni gassose campionate, comprendenti sia sistemi caldi sia sistemi freddi, sono stati suddivisi in tre gruppi: (i) dominati in N2; (ii) dominati in CO2; (iii) ricchi in H2S. Queste categorie sono ben separate geograficamente, associate, soprattutto, al regime tettonico estensionale e, spesso, associati alle aree di confine tra le principali unità geotettoniche. Il δ13CCO2 varia tra -15.7 ‰ e +1.0 ‰, mentre i valori di R/RA variano da 0.1 a 1.8, suggerendo un’origine perlopiù crostale con un contributo mantellico fino al 20%. La composizione isotopica del metano presenta valori di δ13CCH4 tra -57.8 ‰ e -7.2 ‰ e valori di δ2HCH4 tra -303 ‰ e -80 ‰. Inoltre, misure di flusso di CO2 al suolo sono state condotte a Duvalo Kosel, Petkoniva e Botun. Per quanto riguardo Duvalo Kosel, un’area studiata in dettaglio, si è stimato una emissione di CO2 di 66.9 t × d-1. A Petkoniva and Botun sono state condotte delle misure preliminari, limitate ad aree caratterizzate da forte alterazione del suolo e mancanza di vegetazione, rivelando un flusso di CO2 di 0.20 t × d-1 a Petkoniva e di 0.59 t × d-1 a Botun.Since the 1970s, scientific research evidenced the close relationship between deeply-derived carbon degassing and active tectonic zones, highlighting the utmost importance of tectonic degassing contribution within the global carbon cycle. Large-scale degassing of mantle-derived carbon, Quaternary volcanic activity, seismic activity, and regional active fault systems are widespread in the Balkan Peninsula. However, the estimation of geogenic CO2 release from this area is currently still poorly quantified. This PhD research is focused on (i) the estimation of endogenous carbon release from the main karst hydro-systems of Greece and on (ii) the chemical and isotopic characterization of the main gas manifestation in North Macedonia. Moreover, a study about the geogenic and anthropogenic processes affecting the water quality of Hellenic karst aquifers was carried out. Three main water types were recognized in the Hellenic karst aquifers: (i) calcium-bicarbonate for hinterland springs; (ii) sodium-chloride for coastal springs; (iii) calcium-sulfate derived from gypsum dissolution. Results in terms of major ions and trace elements were compared with the drinking water limits set by the Directive 98/83/EC and the Directive 2020/2184/EC, which are rarely exceeded except for parameters related to marine intrusion along the coastal areas (EC, Na, Cl, B). In these springs, the highest nitrate levels are also found, though always below the drinking water limit. Regarding the chemical composition of the dissolved and free gases collected in the above-mentioned springs, the nitrogen is the dominant gas (up to 985,300 µmol mol-1). The δ13CTDIC varies between -16.6 ‰ and -0.10 ‰ (vs. V-PDB), whereas the δ13CCO2 in free gases ranged from -29.9 ‰ to -7.41 ‰ (vs. V-PDB). The isotopic composition of helium was measured in few samples (R/RA = 0.20 - 0.33), with values indicating a mainly crustal source. An estimation of the endogenous carbon (1.43 × 109 mol a-1) released from these systems was carried out, applying the isotope-carbon mass balance. The geogenic source of carbon may be associated to multiple sources, such as thermo-metamorphism of buried carbonates associated to intrusions of Quaternary magmatic bodies and/or regional tectonic structures. The research about the gas manifestations in North Macedonia represented a first catalogue, although still incomplete. The collected gas manifestations, comprising both thermal and cold systems, were subdivided in three groups: (i) N2-dominated group; (ii) CO2-dominated group; (iii) H2S-rich group. These categories are geographically well separated, mainly, related to the extensional tectonic regime of the area and, sometimes, associated with boundaries between the major geotectonic units. The δ13CCO2 varies between -15.7 ‰ and +1.0 ‰, whereas the R/RA values vary from 0.1 to 1.8, suggesting a prevailing crustal source with a mantle contribution up to 20%. On the other hand, the isotope composition of methane showed δ13CCH4 values ranging between -57.8 ‰ and -7.2 ‰ and δ2HCH4 varying from -303 ‰ to -80 ‰. Furthermore, soil CO2 flux measurements were carried out at Duvalo Kosel, Petkoniva and Botun. Regarding the former, a detailed investigation was carried out, estimanting a total CO2 output of 66.9 t × d-1. A preliminary investigation was done at Petkoniva and Botun, limited only to patches with heavy soil alteration and devoid of vegetation, revealing a CO2 output of 0.20 t × d-1 at Petkoniva and of 0.59 t × d-1 at Botun

Preliminary study on geogenic degassing through the big karstic aquifers of Greece

Non-volcanic degassing contributes to the C-cycle by providing on a global scale a significant amount of CO2 emitted through diffuse earth degassing processes (Kerrick et al 1995). Due to the elevated solubility of the CO2 in water, in the areas where high CO2 fluxes directly affect regional aquifers, most of it can be dissolved, transported and released by groundwaters. Therefore, quantification of this contribution to the atmosphere has a substantial implication for modeling the global carbon cycle. According to Chiodini et al. (2000), total dissolved inorganic carbon (TDIC) concentrations and δ13CTDIC values of groundwaters are useful tools to both quantify the geogenic degassing and distinguish the different carbon sources. This approach was proved to be valid for central Italy and can possibly work for continental Greece; due to similar geodynamic history. Greece is considered one of the most geodynamically active regions and is characterized by intense geogenic degassing. The main source of degassing in the Hellenic area is concentrated on hydrothermal and volcanic environments (Daskalopoulou et al., 2019), however, the impact of geogenic CO2 released by tectonically active areas shouldn’t be disregarded. Aim of this work is to quantify the CO2 degassing through aquifers hosted in the carbonate successions in the Hellenic region. 95 karst, thermal and cold waters were collected in the northern and central part of Greece with some of which being characterized by bubbling of CO2-rich gases. Results show that karst waters have a typical Ca-HCO3 composition. Thermal and cold waters show two different compositions: some samples are characterized by Ca-HCO3 composition suggesting the presence of a carbonate basement, whilst others have a prevailing Na-HCO3 composition. On the basis of TDIC concentrations and δ13CTDIC values, the springs are divided into two groups. The first group includes karst waters and some of thermal waters and is characterized by low TDIC concentrations and negative δ13CTDIC values. This group shows no evidence of deep CO2 contributions, whereas the carbon of these waters derives from dissolution of carbonate minerals by organic derived CO2. Remaining samples belong to the second group and present intermediate to high TDIC concentrations and δ13CTDIC values, indicating a possible input of inorganic CO2. Some of these springs are characterized by gas bubbling at discharge, suggesting an extensive degassing

Estimation of CO2 release from thermal springs to the atmosphere

Introduction Geodynamically active regions have long been recognized as areas of anomalous Earth degassing [Irwin and Barnes, 1980]. Areas found at plate boundaries are characterized by seismic, volcanic and geothermal activity as well as ore deposition. These processes are enhanced by the circulation of hydrothermal fluids in the crust, which transport volatiles from the deep crust or mantle to the surface [King, 1986]. Kerrick and Caldera, [1998], were the first to indicate the significant contribution of the CO2 degassing by extensional tectonic and hydrothermal activity in metamorphic belts during the Phanerozoic. Moreover, further studies concerning gas emissions from diffuse degassing tectonic structures on various geological regimes suggested in their majority elevated CO2 concentrations [Klusman, 1993]. In fact, it is worth noting that the estimated global hydrothermal CO2 flux from subaerial geothermal environments can be comparable to that of direct volcanic discharges [Kerrick et al., 1995; Seward and Kerrick, 1996]. Study Area The back-arc geothermal fields of Greece include, among others, the Tertiary sedimentary basins of both Sperchios Basin and north Euboea, which are located in central Greece. Their tectonic activity contributes in crust thinning [Papadakis at al., 2016 and references therein] and elevated heat flow values [Fytikas and Kolios, 1979]. These geothermal anomalies due to the tectonic activity and the geological and volcanic regime are expressed as hot springs (Ypatis, Psoroneria, Thermopyles and Kamena Vourla in Sperchios Basin and Edipsos and Ilion in north Euboea). Tectonics of central Greece seems to be of particular interest as major fault structures are found in the area. Sperchios Basin was formed through the activity of WNW-ESE trending faults [Georgalas and Papakis, 1966; Marinos et al., 1973], whilst the Sperchios tectonic graben itself is considered to be the extension of the North Anatolia strike-slip fault. Moreover, in the north Euboean Gulf, the major fault structures are those of the Atalanti Fault Zone (AFZ) that consist of several segments of normal faults, trending about NW-SE [Pavlides et al., 2004]. Materials and Methods Six groups of springs (Ypatis, Psoroneria, Thermopyles, Kamena Vourla, Edipsos and Ilion) were investigated in this study. Bubbling gases were sampled using an inverted funnel positioned above the bubbles and stored in glass flasks equipped with two stopcocks until analysis. Samples for dissolved gas analyses were collected in glass vials and were sealed underwater. In the laboratory, the concentrations of He, H2, H2S, O2, N2, CO2 and CH4, on the samples were analysed by an Agilent 7890B gas chromatograph with Ar as carrier. The total CO2 emitted through bubbling was measured at 6 different pools (Psoroneria, Psoroneria 2,Thermopyles, Leonidas, Kamena Vourla and Ilion), whereas at other springs (Koniavitis-Sperchios Basin, Edipsos-Damaria and Edipsos-Thermopotamos) an estimation of the release was made by visual inspection. The CO2 fluxes were measured using the floating chamber method [Mazot and Bernard, 2015] that was equipped with a portable fluxmeter (WEST Systems, Italy) based on the accumulation chamber method as suggested by Chiodini et al., [1998]. The flux data were processed with both the Graphical Statistical Approach (GSA) and the Stochastic Simulation Approach (SSA), with the latter being based on the algorithm of sequential Gaussian simulation [Deutsch and Journal 1998; Cardellini et al., 2003]. Zonal Statistics on the final CO2 flux maps was obtained using the ArcMap 10.3 (ESRI) Spatial Analyst tool and were used to estimate the total CO2 output to the atmosphere. Results and Conclusions Carbon dioxide is the prevailing gas species for the great majority of the under investigation sites, with only gases collected in the area of Kamena Vourla (Kamena Vourla and Koniavitis) being rich in N2. The total bubbling CO2 emission from the pools to the atmosphere ranged from 314 to 44,800 g/m2/day. At sites with greater surfaces, the CO2 release was estimated after performing direct measurements (28-Thermopyles, 74-Psoroneria) with the most elevated values being found in the areas of Thermopyles and Psoroneria (1 and 2 t/d, respectively) (Tab. 1); the maps were drawn following the SSA (Figure 1). The outgoing channels of the springs showed an elevated flow (> 250 l/s) of gas-charged water (> 15 mmol/l of dissolved CO2). Even though no bubbling was visible along the stream, the dissolved CO2 content sampled at different distances from springs of Psoroneria and Thermopyles, decreased up to an order of magnitude after few hundreds of metres, indicating an evident and intense, although not visible, CO2 degassing versus the atmosphere. Physico-chemical parameters (temperature and pH) along the outlet channels were also measured at the same sampling points showing correlations (negative in terms of temperature; T decreased from 33.1 to 30.3 and 40.8 to 39 °C, respectively and positive in terms of pH; pH increased from 6.11 to 7.05 and 6.05 to 7.70, respectively) with the distance. The CO2 output of the outgoing channels to the atmosphere was quantified considering thedifference between the initial and the final content of the dissolved CO2 as well as the water flow, obtaining values of > 10 t/d for Thermopyles and ~9 t/d for Psoroneria. Estimations were also made at Ypatis, Kamena Vourla, Koniavitis and Edipsos, where the mean values reached 1 t/d of CO2 for each spring. The obtained CO2 released from the bubbling pools to the atmosphere was directly compared with the one estimated from the outgoing channels (Tab. 1). The degassing along the outflow channel was almost always higher than the corresponding bubbling pool, sometimes even an order of magnitude, suggesting that most of the degassing is “hidden”. For each site the amount of CO2 released versus the atmosphere was calculated as (Figure 2): ΦtotCO2 = Φpool + Φstream The total CO2 released to the atmosphere as estimated for the study area is at ~ 30 t/d, with the major contribution deriving from the degassing along the outflow channels of the thermal springs. Such output is comparable and sometimes higher than that of each single active volcanic system along the South Aegean Volcanic Arc (15 - 38 t/d) and highlights the importance of “hidden” degassing along CO2 - oversaturated streams

Microbial impact on the isotope composition of methane in both thermal and hyperalkaline waters of central Greece

Introduction The different origins of methane can be subdivided in biogenic (either directly produced by microbial activity or deriving by decay of organic matter at T > 150\ub0C) and abiogenic (from pure inorganic reactions). Among the latter, one of the most debated origins comes from serpentinization processes of ultramafic rocks in ophiolitic sequences at low temperatures (T < 80 \ub0C). Moreover, further secondary processes (diffusion, inorganic or microbial oxidation, etc.) may also contribute and thus mask the original chemical and/or isotope composition. Primary and secondary processes acting on CH4 can be recognised mainly through its isotope (d13C and d2H) composition and the ratio between CH4 and C2+C3 light hydrocarbons [Bernard et al. 1978; Schoell 1980]. Microorganisms may be involved in the methane cycle not only as active producers but also as consumers. Methane oxidizing bacteria (or methanotrophs) are microorganisms with the ability to use methane as the only source of carbon for energy and biomass production. Methanotrophs are ubiquitous and play an important role in the global carbon cycle, acting as a natural filter between the subsoil and the atmosphere. They were isolated from several environments such as soils, wetlands, freshwater, marine sediments, water columns, groundwater, rice paddies, and peat bogs [Murrell and Jetten, 2009]. Some species were adapted also at extreme environments characterized by high temperature (up to 81.6 \ub0C), extremely low or high pHs (1.5-11) or even anaerobic conditions. Due to the fact that methanotrophs metabolize preferentially light isotopes, biologic methane oxidation brings sometimes to extremely positive d13C and d2H values [Cadieux et al., 2016]. The Greek territory belongs to the geodynamically active Alpine-Himalayan orogenic belt. As such, it shows intense seismic activity, active volcanic systems and areas of enhanced geothermal fluxes. One of these areas is the Sperchios Basin and the northern part of Euboea Island in central Greece, where thermal manifestations are widespread [D\u2019Alessandro et al., 2014]. The complex geology of Greece includes also two important parallel running ophiolitic belts, with the Othrys Massif (central Greece) belonging to the westernmost of them. In and around this wide ophiolite outcrop, some cold hyperalkaline and some hypothermal (T < 30\ub0C) alkaline waters are present. In the present paper we discuss data about chemistry and methane isotope composition of bubbling or dissolved gases in both thermal springs and hyperalkaline springs of Central Greece. Sampling and Analytical Methods Free bubbling gas samples were taken using an inverted funnel. All free gas samples were stored in Pyrex bottles with two vacuum stopcocks. Samples for dissolved gas analyses were collected in glass vials sealed underwater. In the laboratory, the chemical analyses were carried out by gaschromatography (Agilent 7890B GC System) using Ar as the carrier gas. Dissolved gases were extracted after equilibrium was reached at constant temperature with a host-gas (high-purity argon) injected in the sample bottle. The measurement precision was better than \ub15% for common gases and \ub110% for trace gases such as the alkanes. The chemical composition of the dissolved gas phase was obtained from the gas-chromatographic analyses taking into account the solubility coefficients (Bunsen coefficient \u201c\u3b2\u201d, ccgas/mlwater STP) of each gas specie, the volume of gas extracted and the volume of the water sample (details in Capasso and Inguaggiato, [1998] and Liotta and Martelli, [2012]). Starting from the total amount of dissolved gases (ccSTP/L) we calculated the relative abundances for every single gas species in equilibrium with the dissolved gas phase and expressed the analytical results in \u3bcmol/mol of gas at atmospheric pressure, allowing the comparison of dissolved gases with free gases. Carbon and hydrogen isotope compositions of CH4 were measured using a Thermo TRACE GC and a Thermo GC/C III interfaced to a Delta Plus XP gas source mass spectrometer. 13C/12C ratios are reported here as d13C values (\ub10.1 \u2030) with respect to the V-PDB standard. 1H/2H ratios are reported here as d2H values (\ub12 \u2030) with respect to the V-SMOW standard. The oxygen and hydrogen isotopic compositions of water were analysed on unfiltered samples with the use of Analytical Precision AP 2003 and FinniganMAT Delta Plus IRMS devices, respectively. The isotope ratios are expressed as the deviation per mil (\u3b4\u2030) from the reference V-SMOW. The uncertainties (\ub11\u2030 were \ub10.1% for \u3b418O and \ub11% for \u3b42H. Results Five thermal springs, with temperatures from 33 to 80\ub0C, were sampled in the study area. All show elevated fluxes of bubbling gases whose prevailing species are either CO2 or N2. Methane concentrations range from 27 to 4000 \u3bcmol/mol, whilst the isotope composition of CH4 covers a wide range with d13C values ranging from -21.7 to +16.9\u2030 and d2H values ranging from -124 to +370\u2030. Seven alkaline hypothermal waters were collected in five areas (Amplas, Platystomo, Kaitsa, Smokovo and Soulanta) while 10 hyperalkaline waters in two areas (Archani and Ekkara); all samples were collected from different springs and wells and some of the sites presented bubbling. All samples present low concentrations of H2 (from <2 to 2500 \u3bcmol/mol), CO2 (up to 26,000 but generally below 1000 \u3bcmol/mol) and O2 (up to 16,000 but generally below 3000 \u3bcmol/mol). Gases in alkaline waters (pH <10) are in their majority dominated by CH4 (from 128,000 to 915,000 \u3bcmol/mol). Hyperalkaline (pH > 11) waters are N2 dominated (from 727,000 to 977,000 \u3bcmol/mol) and have CH4 concentrations from 11,500 to 279,000 \u3bcmol/mol. Also all these samples display a wide range of isotope compositions of CH4 (d13C from -74.5 to -14.5 \u2030 and d2H from -343 to -62 \u2030). Discussion Thermal springs Methane in most of the bubbling gases found in the thermal waters of Greece display a small range in isotope composition close to -21\u2030 for carbon and to -130\u2030 for hydrogen [Daskalopoulou et al., 2018] and plot in the middle of the field of volcanic and geothermal systems (Figure 1). In the study area, only the hottest (Edipsos) of the thermal manifestations displays similar values. All the remaining samples fit a methane oxidation trend reaching extremely positive values (Figure 1). If we consider the lowest values as the deep hydrothermal marker the obtained \u394H/\u394C values range between 5 and 13 which are close to those typical of microbially driven oxidation [Coleman et al., 1981]. Although the outlet temperature of the hottest manifestations is at the upper limit for methanotrophic microrganisms [Sharp et al., 2014], we can hypothesize that environmental conditions are not favourable for their survival at this site. On the contrary, methanotrophs can thrive in the sites characterized by lower temperatures (33-65 \ub0C), strongly consuming methane. The most positive values were measured at Psoroneria and indicate a very high consumption fraction. Considering again the values of Edipsos as the deep hydrothermal marker, a Rayleigh fractionation modelling in a closed system and kinetic fractionation factors for microbial oxidation [Coleman et al., 1981] we estimate a consumption of more than the 75% of the initial CH4. Alkaline and hyperalkaline waters Alkaline waters present mostly isotope values for CH4 compatible with a biogenic origin (d13C from - 62.0 to -37.5 \u2030 and d2H from -247 to -154 \u2030). Only the sample of Kaitsa falls above the biogenic field, indicating possible fractionation due to CH4 oxidation (Figure 2). Most of the hyperalkaline waters have CH4 isotope values compatible with an abiogenic origin through serpentinization processes (Figure 2). But some of the CH4 collected in the hyperalkaline waters show values falling in the biogenic field, with at points, very negative d13C values (< -70\u2030). Methanogens were found also in other hyperalkaline waters taking advantage of the presence of sometimes very high hydrogen concentrations [Woycheese et al., 2015; Miller et al., 2018]. Also methanotrophs were rarely found in hyperalkaline waters [Woycheese et al., 2015; Miller et al., 2018] and their presence may justify the most positive values found in the study area (Figure 2)

Determinazione in continuo di CO2, CH4 e H2Ov in ambiente atmosferico attraverso tecnica ad assorbimento laser (UGGA)

Molti dei composti chimici presenti nell’atmosfera terrestre prendono il nome di “gas serra”. Queste specie gassose consentono alla radiazione solare di entrare liberamente nell’atmosfera e di trattenere parte della radiazione solare riflessa dalla superficie terrestre come energia termica. Nel corso del tempo si instaura un complesso equilibrio termico tra la quantità di energia inviata dal sole e quella irradiata dalla superficie. L’alterazione di questo equilibrio, con l’aumento di uno o più gas serra in atmosfera, porta a degli squilibri termici e un conseguente innalzamento delle temperature. Questo fenomeno è definito come “effetto serra”. I principali gas serra in natura che prendono parte a questo fenomeno sono: vapor d’acqua (H2Ov), anidride carbonica (CO2), metano (CH4), e ossido nitroso (N2O). Il vapore acqueo è il più potente gas serra ed è responsabile per circa due terzi dell’effetto serra naturale. Il secondo gas serra più importante è l’anidride carbonica. Il suo contributo è responsabile per il 5 - 20% dell’effetto serra naturale ed è la causa principale dell’effetto sera accelerato essendo il più emesso attraverso attività umane, difatti la sua concentrazione in atmosfera è aumentata del 142% dal livello pre– industriale al 2013 [WMO Greenhouse Gas Bulletin, n° 10: 06 November 2014]. Il terzo gas serra più importante è il metano. Anche se possiede un tempo di residenza in atmosfera breve e una concentrazione atmosferica bassa, è una molecola estremamente efficiente nell’assorbire il calore ed è responsabile per circa 8% dell’effetto serra, con picchi del 20% [G. Etiope et. al.,2008]. La concentrazione di metano in atmosfera è aumentata di 772ppb (parti per miliardo) dal periodo pre-industriale fino al 2013 [WMO Greenhouse Gas Bulletin, n° 10: 06 November 2014]. L’ossido nitroso ha una concentrazione atmosferica molto limitata ma un efficienza nel trattenere il calore molto elevata, circa 300 volte quella dell’anidride carbonica. Come abbiamo accennato, i gas serra possono essere di origine sia naturale che antropica. Elevate quantità di vapor d’acqua e anidride carbonica vengono rilasciate ogni anno in atmosfera dai sistemi vulcanici attivi, non solo durante i periodi eruttivi ma anche nei periodi di quiescenza. Emissioni naturali di metano in atmosfera sono legati al degassamento di vulcani di fango, largamente diffusi sull’intero pianeta. Recentemente l’organizzazione mondiale Intergovernmental Panel on ClimateChangedelle Nazioni Unite ha pubblicato una relazione internazionale (ICCP 2013) in cui, attraverso informazioni tecnicoscientifiche e socioeconomiche, ha valutato come il rischio del cambiamento climatico sia legato all’emissione di gas serra (principalmente CO2, H2O(v) e CH4), stimando che la temperatura media globale del suolo è aumentata di 0,6 ± 0.2K dalla fine del 19° secolo. L’IPCC rivela che: “c’è una nuova e più forte evidenza che gran parte del riscaldamento e dell’emissione di questi gas negli ultimi 50 anni siano attribuibili alle attività antropiche più che alle attività naturali” [Crosson, 2008]. Essendo l’effetto serra diventato un problema globale per la salute del pianeta è di fondamentale importanza disporre di strumentazioni analitiche per il monitoraggio di queste specie chimiche in atmosfera. Nel corso degli anni si sono utilizzate diverse tecniche analitiche per lo studio di questi gas in atmosfera al fine di capirne l’evoluzione. La tecnica più consolidata utilizzata per le misurazioni di specie gassose in atmosfera per oltre un decennio è stata la spettroscopia a raggi infrarossi non dispersiva (NDIRS). Nonostante la tecnica NDIRS abbia una buona precisione di misurazione per la maggior parte dei gas serra, questa tecnica risulta essere molto macchinosa e complessa in quanto necessita di frequenti azzeramenti e calibrazioni allungando notevolmente i tempi di analisi. Ultimamente in commercio sono stati introdotti dei nuovi strumenti molto più sensibili e precisi dei classici NDIRS. Questi strumenti, assimilabili ai vecchi spettrofotometri a doppio raggio, utilizzano una particolare cavità ottica Cavity Ringdown Spectroscopy (CRDS) che oltre ad offrire una maggiore sensibilità analitica, per un ampio numero di specie gassose, riducono i tempi analitici e non richiedono particolari operazioni di calibrazione. Alcuni di questi strumenti hanno come caratteristica principale, oltre la determinazione e quantificazione della specie gassosa, anche la determinazione della composizione isotopica, come ad esempio il Thermo Fischer Delta Ray per analisi del δ13C dell’anidride carbonica e il Picarro CRDS per l’analisi del δ13C del metano. Negli ultimi tempi questi strumenti al laser hanno esteso il loro campo di applicazione, difatti in aggiunta agli studi sulla qualità dell’aria, vengono anche impiegati per il monitoraggio di gas naturali, rilevamento di perdite nei giacimenti di carbone e studi sui flussi di gas dal suolo [Carapezza et. al., 2003]. In questo lavoro sono state testate le potenzialità in laboratorio ed in campagna del nuovo analizzatore Ultra-Portable Greenhouse Gas Analyzer (UGGA) prodotto da Los Gatos Research (LGR). Lo strumento è basato sull’implementazione della tecnica CRDS denominata “Off-Axis ICOS” che permette di determinare simultaneamente ed in continuo le concentrazioni di CO2, H2O(v) e CH4 in atmosfera all’interno di intervalli di concentrazioni dell’ordine dei ppm. Il lavoro ha avuto l’obiettivo di studiare gli errori e i tempi analitici per la determinazione delle concentrazioni di CO2, H2O e CH4 in atmosfera. Lo strumento è stato da prima testato in laboratorio e poi in campagna. Le analisi in laboratorio sono state svolte presso i laboratori analitici dell’Istituto Nazionale di Geofisica e Vulcanologia di Palermo. Le prospezioni sono state eseguite lungo percorsi urbani e periferici di Palermo e lungo la faglia della Pernicana, nella zona etnea, a cui sono state associate tramite un GPS (Global Position System) informazioni sulle coordinate geografiche

Impact of geogenic degassing on C-isotopic composition of dissolved carbon in karst systems of Greece

The Earth C-cycle is complex, where endogenic and exogenic sources are interconnected, operating in a multiple spatial and temporal scale (Lee et al., 2019). Non-volcanic CO2 degassing from active tectonic structures is one of the less defined components of this cycle (Frondini et al., 2019). Carbon mass-balance (Chiodini et al., 2000) is a useful tool to quantify the geogenic carbon output from regional karst hydrosystems. This approach has been demonstrated for central Italy and may be valid also for Greece, due to the similar geodynamic settings. Deep degassing in Greece has been ascertained mainly at hydrothermal and volcanic areas, but the impact of geogenic CO2 released by active tectonic areas has not yet been quantified. The main aim of this research is to investigate the possible deep degassing through the big karst aquifers of Greece. Since 2016, 156 karst springs were sampled along most of the Greek territory. To discriminate the sources of carbon, the analysis of the isotopic composition of carbon was carried out. δ13CTDIC values vary from -16.61 to -0.91‰ and can be subdivided into two groups characterized by (a) low δ13CTDIC, and (b) intermediate to high δ13CTDIC with a threshold value of -6.55‰. The composition of the first group can be related to the mixing of organic-derived CO2 and the dissolution of marine carbonates. Springs of the second group, mostly located close to Quaternary volcanic areas, are linked to possible carbon input from deep sources

Carbon degassing through karst hydrosystems of Greece

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

Duvalo (North Macedonia): A "volcano" without volcanic activity

T he 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”

Preliminary geochemical characterization of gas manifestations in North Macedonia

L ike most of the Balkan Peninsula, North Macedonia is a geodynamically active area. As such it has many hydrothermal features and gas manifestations. Until now, no systematic study about the geochemical characterization of the geogenic gases was made before in this country. In August 2019, 24 gas samples were collected in the study area. All, except one collected at Duvalo (soil gas), are gases bubbling or dissolved in thermomineral waters (temperatures from 12 to 66 \ub0C). They were analysed in the laboratory for their chemical (He, Ne, Ar, O2 , N2 , H2 , H2S, CH4 and CO2) and isotopic composition (\u3b413C-CO2, \u3b413C-CH4, \u3b42H-CH4 and R/RA). Most of the gases have CO2 as the main component (400-998,000 ppm) while the remaining are enriched in N2 (1300-950,000 ppm). Helium ranges from 0.3 to 2560 ppm while CH4 from 1.6 to 20,200 ppm. R/RA and 4He/20Ne ratios indicate a generally low atmospheric contamination, a prevailing crustal contribution and mantle contributions between 1 and 20% considering a MORB endmember. The highest mantle contributions are found in the SE part of the country very close to the sites that show the highest R/RA values in continental Greece [1]. This area is characterised by extensional tectonics and Plio- Pleistocene volcanism. A quite high mantle contribution (about 15%) is also found in two manifestations in the NW part of the country along a main normal fault system. With the exception of the sample of Smokvica, which has very low CO2 (1400 ppm) and \u3b413C-CO2 (-15.7 \u2030 V-PDB), all free gases show a relatively narrow range in \u3b413C-CO2 values (-4.6 to +1.0 \u2030 V-PDB) indicating the mixing between a mantle and a carbonate rock source. The isotope composition allows us to assign the CH4 origin to three sources. The largest group can be attributed to a hydrothermal origin (\u3b413C-CH4 around -20 \u2030 V-PDB and \u3b42H-CH4 around -100\u2030). Three samples collected in the SW part of the country have a thermogenic origin (\u3b413C-CH4 around -35 \u2030 V-PDB and \u3b42H-CH4 around -160\u2030 V-SMOW). Finally, one sample (Smokvica) with the highest values (\u3b413C-CH4 -7.2 \u2030 V-PDB and \u3b42H-CH4 -80\u2030 V-SMOW) may be attributed to abiotic processes in a continental serpentinization environment or to methane oxidation

Impact of Etna’s volcanic emission on major ions and trace elements composition of the atmospheric deposition

Mt. Etna, on the eastern coast of Sicily (Italy), is one of the most active volcanoes on the planet and it is widely recognized as a big source of volcanic gases (e.g., CO2 and SO2), halogens, and a lot of trace elements, to the atmosphere in the Mediterranean region. Especially during eruptive periods, Etna’s emissions can be dispersed over long distances and cover wide areas. A group of trace elements has been recently brought to attention for their possible environmental and human health impacts, the Technology-critical elements. The current knowledge about their geochemical cycles is still scarce, nevertheless, recent studies (Brugnone et al., 2020) evidenced a contribution from the volcanic activity for some of them (Te, Tl, and REE). In 2021, in the framework of the research project “Pianeta Dinamico”, by INGV, a network of 10 bulk collectors was implemented to collect, monthly, atmospheric deposition samples. Four of these collectors are located on the flanks of Mt. Etna, other two are in the urban area of Catania and three are in the industrial area of Priolo, all most of the time downwind of the main craters. The last one, close to Cesarò (Nebrodi Regional Park), represents the regional background. The research aims to produce a database on major ions and trace element compositions of the bulk deposition and here we report the values of the main physical-chemical parameters and the deposition fluxes of major ions and trace elements from the first year of research. The pH ranged from 3.1 to 7.7, with a mean value of 5.6, in samples from the Etna area, while it ranged between 5.2 and 7.6, with a mean value of 6.4, in samples from the other study areas. The EC showed values ranging from 5 to 1032 μS cm-1, with a mean value of 65 μS cm-1. The most abundant ions were Cl- and SO42- for anions, Na+ and Ca+ for cations, whose mean deposition fluxes, considering all sampling sites, were 16.6, 6.8, 8.4, and 6.0 mg m-2 d, respectively. The highest deposition fluxes of volcanic refractory elements, such as Al, Fe, and Ti, were measured in the Etna’s sites, with mean values of 948, 464, and 34.3 μg m-2 d-1, respectively, higher than those detected in the other sampling sites, further away from the volcanic source (26.2, 12.4, 0.5 μg m-2 d-1, respectively). The same trend was also observed for volatile elements of prevailing volcanic origin, such as Tl (0.49 μg m-2 d-1), Te (0.07 μg m-2 d-1), As (0.95 μg m-2 d-1), Se (1.92 μg m-2 d-1), and Cd (0.39 μg m-2 d-1). Our preliminary results show that, close to a volcanic area, volcanic emissions must be considered among the major contributors of ions and trace elements to the atmosphere. Their deposition may significantly impact the pedosphere, hydrosphere, and biosphere and directly or indirectly human health