• Kis, B., M., Baciu, C., Zsigmond, A-R., Kékedy-Nagy, L., Kármán, K., Palcsu, L., Harangi, Sz., 2020, Constraints on the hydrogeochemistry and origin of the CO2-rich mineral waters from the Eastern Carpathians – Transylvanian Basin boundary (Romania), Journal of Hydrology, 591, 125311



The Eastern Carpathians, along the Neogene to Quaternary volcanic chain, host important natural resources of mineral waters. Most of these are in the form of CO2-rich natural springs of different types, associated with CO2 gas emissions. In order to understand the origin of these waters, the natural processes responsible for the observed physical–chemical features and to check the exposure and vulnerability of the hydrogeological system to potential contamination and environmental changes, 121 mineral water springs and wells were investigated. The investigations performed, offered an insight on the processes affecting the waters after their infiltration that led to a wide range of chemical and isotopic compositions. The diversity in the geological structure of the area, alteration processes and interaction with CO2, all explain the variety of the hydrogeochemical facies of the investigated waters. Three major hydrogeochemical types that are the result of the geological variety of the study area and water–rock interaction were identified: Ca–Na–Mg–HCO3, Ca–Na–Mg/Na–Ca ± Mg–HCO3–Cl ± SO4, and Na–Cl waters. Further changes in the geochemical features are attributable to mixing between different water types during their ascent, enhanced by the tectonic setting of the area. Considering the isotopic composition (δ18O, δD) of the waters, most of them proved to be of meteoric origin. Extreme isotopic shifts towards enriched δ18O and δD values of +8.59 and −12.2‰ (V-SMOW) respectively were observed in the case of 11 springs. These shifts were attributed to the interaction of water with clay minerals and diagenesis. As most of these waters are of meteoric origin, their discharge may be influenced by meteorological factors. Moreover, the mixing of aquifers with very shallow waters most likely facilitates their exposure to external contamination.


  • Kis, B.M., Caracausi, A., Palcsu, L., Baciu, C., Ionescu, A., Futó, I., Sciarra, A., Harangi, SZ. 2019, Noble gas and carbon isotope systematic at the seemingly inactive Ciomadul volcano (Eastern-Central Europe, Romania): evidence for volcanic degassing, Geochemistry, Geophysics, Geosystems, 20, 6, 3019-3043



Ciomadul is the youngest volcano in the Carpathian‐Pannonian Region, Eastern‐Central Europe, which last erupted 30 ka. This volcano is considered to be inactive, however, combined evidence from petrologic and magnetotelluric data, as well as seismic tomography studies, suggests the existence of a subvolcanic crystal mush with variable melt content. The volcanic area is characterized by high CO2 gas output rate, with a minimum of 8.7 × 103 t/year. We investigated 31 gas emissions at Ciomadul to constrain the origin of the volatiles. The δ13C–CO2 and 3He/4He compositions suggest the outgassing of a significant component of mantle‐derived fluids. The He isotope signature in the outgassing fluids (up to 3.10 Ra) is lower than the values in the peridotite xenoliths of the nearby alkaline basalt volcanic field (R/Ra 5.95 Ra ± 0.01), which are representative of a continental lithospheric mantle and significantly lower than MORB values. Considering the chemical characteristics of the Ciomadul dacite, including trace element and Sr–Nd and O isotope compositions, an upper crustal contamination is less probable, whereas the primary magmas could have been derived from an enriched mantle source. The low He isotopic ratios could indicate a strongly metasomatized mantle lithosphere. This could be due to infiltration of subduction‐related fluids and postmetasomatic ingrowth of radiogenic He. The metasomatic fluids are inferred to have contained subducted carbonate material resulting in a heavier carbon isotope composition (δ13C is in the range of −1.4‰ to −4.6‰) and an increase of CO2/3He ratio. Our study shows the magmatic contribution to the emitted gases.


  • Serban M Sarbu, S.M., Aerts, J.W., Flot, J.F., Van Spanning, RJM, Baciu, C., Ionescu, A., Kis, B.M., Incze, R., Sikó-Barabási, S., Para, Z., Hegyeli, B., Atudorei, N.V., Barr, C., Nealson, K., Forray, F., Lascu, C., Fleming, E.J., Bitter, W., Popa, R., 2018, Sulfur Cave (Romania), an extreme environment with microbial mats in a CO2-H2S/O2gas chemocline dominated by mycobacteria, Journal of Speleology, 47, 2.



Sulfur Cave (Puturosu Mountain, Romania) is an extreme environment, unique for displaying life in a gas chemocline. The lower part of the cave is filled with CO2, CH4, and H2S of mofettic origin, while the upper part contains air that floats above the heavier volcanic gasses. S° and H2SO4 (from sulfur-oxidation) cover the cave wall at and below the CO2-H2S:O2 gas/gas interface. On the cave wall, near the interface the pH is < 1 and unusual microbial biofilms occur on the rock’s surface. We provide context information on the geology, mineralogy, chemistry and biology to better understand this unique environment. We have used X-ray diffraction, optical microscopy, scanning electron microscopy with EDAX capabilities, stable isotope analysis and 16S and 18S rDNA amplicon sequencing. The most common taxa in the microbial biofilms are Mycobacteria, Acidithiobacillus and Ferroplasmaceae. Liquid water in this system originates solely from condensation of water vapor onto the cave walls making inflow of organic carbon from outside unlikely. The most likely primary source of energy for this microbial community is sulfur oxidation with H2S and S° as main reductants and atmospheric O2 as the main oxidant. Ferric iron from the rock surface is another potential oxidant. In Sulfur Cave, gaseous CO2 (from mofettic emission) maintains the stability of the gas chemocline. Sulfur Cave biofilms can help the search for extreme life in the subsurface, near volcanic systems on Earth and Mars. The Sulfur Cave example shows that a habitable environment can be established underground in gas chemoclines near CO2-dominated gas discharge zones, where it can have a steady supply of water and energy.


  • Kis, B.M., Ionescu, A., Cardellini, C., Harangi, Sz., Baciu, C., Caracausi, A., Viveiros, F., 2017, Quantification of carbon dioxide emission of Ciomadul, the youngest volcano of the Carpathian-Pannonian Region (Eastern-Central Europe, Romania), Journal of Volcanology and Geothermal Research, 341, 119-130.



We provide the first high-resolution CO2 flux data for the Neogene to Quaternary volcanic regions of the entire Carpathian-Pannonian Region, Eastern-Central Europe, and estimate the CO2 emission of the seemingly inactive Ciomadul volcanic complex, the youngest volcano of this area. Our estimate includes data from focused and diffuse CO2 emissions from soil. The CO2 fluxes of focused emissions range between 277 and 8172 g d− 1, corresponding to a CO2 output into the atmosphere between 0.1 and 2.98 t per year. The investigated areas for diffuse soil gas emissions were characterized by wide range of CO2 flux values, at Apor Baths, ranging from 1.7 × 101 to 8.2 × 104 g m− 2 d− 1, while at Lăzărești ranging between 1.43 and 3.8 × 104 g m− 2 d− 1. The highest CO2 focused gas fluxes at Ciomadul were found at the periphery of the youngest volcanic complex, which could be explained either by tectonic control across the brittle older volcanic edifices or by degassing from a deeper crustal zone resulting in CO2 flux at the periphery of the supposed melt-bearing magma body beneath Ciomadul. The estimate of the total CO2 output in the area is 8.70 × 103 t y− 1, and it is consistent with other long (> 10 kyr) dormant volcanoes with similar age worldwide, such as in Italy and USA. Taking into account the isotopic composition of the gases that indicate deep origin of the CO2 emissions, this yields further support that Ciomadul may be considered indeed a dormant, or PAMS volcano (volcano with potentially active magma storage) rather than an inactive one. Furthermore, hazard of CO2 outpourings has to be taken into account and it has to be communicated to the visitors. Finally, we suggest that CO2 output of dormant volcanic systems has to be also accounted in the estimation of the global volcanic CO2 budget.


  • Italiano, F. Kis, B.M. (correspondent author), Baciu, C., Ionescu, A., Harangi, Sz., Palcsu, L., 2016, Geochemistry of dissolved gases from the Eastern Carpathians-Transylvanian Basin boundary, Chemical Geology, 469, 117-128.



We show the results of a study on the volatiles dissolved in mineral waters discharged over a 200 km-long transect along the Rodna-Bârgău area and Călimani-Gurghiu-Harghita volcanic chain (Eastern Carpathians, Romania). All of the collected mineral water samples carry dissolved gas with carbon dioxide content up to 1.99 cm3STP/gH2O, and helium content up to 2.3 × 10− 5 cm3STP/gH2O. Carbon (δ13CTDIC total dissolved inorganic carbon, ranging from − 15.6 to 5.32‰ vs. VPDB), He systematics (He isotopes in the range of 0.38–0.99 Ra, Ra = air-normalized 3He/4He ratio) and CO2/3He ratio spanning over four orders of magnitude from MORB-like values of 2.92 × 109 to crustal-type values of 3.02 × 1013, coherently indicate the presence of fluids from different crustal sources (e.g. sediments, hydrocarbon reservoirs) besides minor, but detectable contributions of mantle/magmatic-derived fluids (up to 16.45%). Our investigations show that the wide range of chemical and isotopic composition can be explained in terms of mixings among different gas sources feeding the groundwater and the contemporary occurrence of gas-water interactions like degassing and deposition of carbonates, affecting the circulating waters after their infiltration.


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