Geochemistry of the thermomineral waters in Greece

Many geothermal areas of Greece are located in regions affected by Miocene or Quaternary volcanism and in continental basins characterized by elevated heat flow. Moreover, the majority of them is found along the coast as well as in islands of the Aegean Sea and thus thermal water is often brackish to saline due to marine intrusion into coastal aquifer. In the present study, almost 300 thermal and cold mineral water samples were collected along the Hellenic territory with their physicochemical parameters (temperature, pH, electrical conductivity and Eh) and the amount of bicarbonates (titration with 0.1N HCl) being determined in situ. Additionally, gases, found either in free or dissolved ph…

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 dis…

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…

Natural and anthropogenic impacts on Greek karst water quality

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 tect…

CO2 release to the atmosphere from thermal springs of Sperchios Basin and northern Euboea (Greece): The contribution of “hidden” degassing

Abstract Greece is a region characterised by intense geodynamic activity that favours the circulation of hydrothermal fluids in the crust transporting volatiles from either the deep crust or the mantle to the surface. Elevated heat flow values are detectable at Sperchios Basin and North Euboea (central Greece), two areas defined by a system of deeply rooted extensional faults and Quaternary volcanic activity. This setting contributed to the formation of numerous hydrothermal systems, which are mostly expressed as CO2-rich thermal springs with intense bubbling. The CO2 output from six bubbling pools has been determined by flux measurements with the use of the floating chamber method. The hig…

Trace elements in thermomineral waters in Greece

Trace elements have a fundamental role in natural and anthropogenic systems. In waters, they present a great variability of concentrations that mostly depends on the degree of gas-water-rock interactions and geochemical conditions such as pH, temperature, redox and/or exchange reactions, etc. Even though, they are present in very low contents in host-rocks, elevated concentrations in ground or surface waters may have a hazardous impact on human health and thus, it is important to both quantify and understand their behavior in natural systems. Here we present the results of about 300 cold and thermal mineral waters collected along the entire Hellenic territory. Physicochemical parameters (te…

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°C) 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 °C). 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 rati…