Tunable diode laser measurements of hydrothermal/volcanic CO₂ and implications for the global CO₂ budget

Abstract. 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.