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

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Abstract

Greece is a region characterised by intense geodynamic activity that favours the circulation of hydrothermalfluids in the crust transporting volatiles from either the deep crust or the mantle to the surface. Elevated heatflow values are detectable at Sperchios Basin and North Euboea (central Greece), two areas defined by a systemof deeply rooted extensional faults and Quaternary volcanic activity. This setting contributed to the formation ofnumerous 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 floatingchamber method. The highest bubbling CO2 output has been found at Thermopyles and Psoroneria (0.6 and 0.84t/d, respectively), where the outgoing channels have an elevated flow (>250 l/s) of gas-charged water (>15mmol/l of CO2). Although no bubbling is noticed along the stream, the CO2 content decreases by an order ofmagnitude after few hundreds of metres, indicating an intense degassing from the water. Taking into account thewater flow and the amount of CO2 lost to the atmosphere, the CO2 output of the outgoing channels is quantifiedin 12.5 t/d for Thermopyles and 9.23 t/d for Psoroneria. Output estimation has also been made for the othersprings of the area. The diffuse CO2 release from the outgoing channels has always been higher respect to that ofthe visible bubbling, suggesting that most of the degassing is “hidden”. Furthermore, the loss of CO2 from thewater has determined a shift in dissolved carbonate species as demonstrated by the pH increase along the channelthat led eventually to an oversaturation in carbonate minerals and therefore travertine deposition.The total CO2 output to the atmosphere of the study area is estimated at ~27 t/d, with the major contributionderiving from the degassing along the outflow channels of the thermal springs. Such output is comparable to thatof the single active volcanic systems along the South Aegean Active Volcanic Arc and highlights the importanceof “hidden” degassing along CO2-oversaturated streams.
Original languageEnglish
Number of pages11
JournalApplied Geochemistry
Volume119
Publication statusPublished - 2020

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