Spatial domain analysis of carbon dioxide from soils on Vulcano Island: Implications for CO2 output evaluation

• Innovative use of a DeltaRay™ for in situ determination of δ13C(CO2) in soil gases.
• Sources of CO2 in soil gases identified by comparison of CO2 content and δ13C(CO2).
• Deep-origin CO2 quantified by CO2 flux, CO2 amount and δ13C(CO2) measurements.
• Sparsely released CO2 by soils has been quantified on Vulcano Island.
• Non-anomalous degassing zones release detectable amount of deep-origin CO2.

The carbon dioxide emissions of volcanoes have been targeted as effective contributors of CO2 to the atmosphere. However, different sources can be effective and active at the same time in the generation and release of CO2 in volcanic zones. Since isotopic fingerprinting of CO2 allows the precise identification of different sources, coupling carbon isotope and CO2 flux measurements enables the evaluation of the mass contribution of each source to the carbon dioxide emissions. This paper accounts for the first extensive spatial analysis of coupled measurements of carbon isotopologues of CO2 in the soil gases and CO2 fluxes discharged by soils on Vulcano Island. An innovative method has been designed, tested and fine-tuned in the laboratory to measure δ13C(CO2) values directly in field using a new type of laser-based isotopologues analyzer, namely a DeltaRay™ (Thermo Fisher Scientific). The method can be used to determine the carbon isotope composition across the full range of CO2 concentrations in the soil gases (0 – 100 vol%). These data have been combined with measurements of the CO2 contents in the soil gases to distinguish CO2 from deep origins from CO2 of biogenic origin in the inhabited area of Vulcano Porto. The method of evaluating the amount of deep-origin CO2 in the soil gases is widely applicable in volcanic and geothermal zones for evaluation and monitoring purposes for both gas and volcanic hazards.