On-field measurements of CO2 isotope composition of diffuse degassing from soils in volcanic areas: Delta-ray setup for direct measurements in the 0-100% vol. range.

Vienna

Volcanoes release carbon dioxide in the atmosphere and have been targeted as potential contributors to the global
warming. Despite the evidences lay against these conjectures, the accurate estimation of the release of CO2 of
volcanic origin in the atmosphere is currently unavailable because both not all the volcanoes of the world are
satisfactorily monitored, and the estimations available for monitored volcanoes are often discordant. At the same
time, the available estimate for the monitored volcanoes can be different according to the state of activity of the
volcano.Multiple sources can be effective in the release of CO2 in volcanic zones as demonstrated by the isotopic
fingerprinting of CO2. Better estimates of the amount of carbon dioxide released by different sources represent
one means of improving the accuracy of the estimation of the CO2 budget in environmental systems and reducing
the knowledge gaps related to the effects of the carbon cycle in the Earth-climate system. The coupled approach
of carbon isotope and CO2 flux measurements allows the precise identification of different sources, and enables
the evaluation of the mass contribution of each source to the carbon dioxide emissions.
From a volcanological perspective, it is well known that the amount of CO2 released by soils before and during
periods of unrest increases appreciably, similar to the amount of carbon dioxide released from the craters of the
volcanoes.
This study focuses on the application of a DeltaRayTM from Thermo Scientific, and reports the development of
an innovative method for directly determining in the field the isotope composition of carbon dioxide discharged
by soils at concentrations from atmospheric to 100 vol %. To settle the DeltaRayTM to the determination of the
isotope composition of soil gases, a sampling method has been designed to analyse the isotope composition of
the CO2 in a gas sample of unknown CO2 concentration, reduce the measurement operation time without loss of
accuracy, and measure the isotope composition of the CO2 without changing the instrument configuration.
The results of the first application on Vulcano (Aeolian Islands) are reported in order to evaluate the amount
of hydrothermal CO2 discharged by soils. The amount of hydrothermal CO2 released by soils is not negligible
because of the specific extent of the degassing surface. For the first time, the budget of the CO2 of hydrothermal
origin discharged by soils on Vulcano was computed separately from the contribution of the biogenic source, and
the data indicate a degassing area that is wider than that previously reported in the literature.
Furthermore, the synchronous and extensive investigation of both the spatial distribution of the carbon isotope
composition of CO2 and the CO2 flux provides a better assessment of the amount of CO2 of deep origin.
Monitoring of this type of CO2 represents a step forward in the evaluation of the volcanic hazard.