Publication Date:
2017-04-04
Description:
A new method combining measurements of soil CO2 flux and determinations of the carbon isotopic
composition of soil CO2 efflux was developed in order to qualitatively and quantitatively characterise the CO2
source feeding the soil CO2 diffuse degassing. The method was tested in March 2007 at the Solfatara of
Pozzuoli volcano degassing area (Naples, Italy) where more than 300 measurements of soil CO2 flux and
determinations of the carbon isotopic composition of soil CO2 efflux were performed, surveying Solfatara
crater and its surroundings. The wide range of CO2 flux and CO2 isotopic composition values (from 8.4 g m−2
d−1 to 28,834 g m−2 d−1, and from 0.73‰ to −33.54‰, respectively), together with their statistical
distributions suggests the occurrence of multiple CO2 sources feeding soil degassing. The combined
interpretation of flux and isotopic data allows us to identify and characterise two distinct gas sources: a
hydrothermal and a biogenic source. The soil CO2 from the hydrothermal source is characterised by a mean
δ13CCO2 of −2.3‰±0.9‰, hence close to the isotopic composition of the fumarolic CO2 (δ13CCO2=−1.48‰±
0.22‰) and by a mean CO2 flux of 2875 g m−2 d−1. The CO2 from the biogenic source is characterised by a
mean δ13CCO2 of −19.4‰±2.1‰, and by a mean CO2 flux of 26 g m−2 d−1, which are both in the range of the
typical values for biologic CO2 soil degassing. This reliable characterisation of the biogenic CO2 flux would not
have been possible by solely applying a statistical analysis of the CO2 flux values, which is commonly applied
in volcanological studies for the partitioning between background fluxes and anomalous CO2 fluxes. A map of
the Solfatara diffuse degassing structure was derived from the estimated threshold for the biogenic CO2 flux,
highlighting that soil degassing of hydrothermal CO2 mixed in different proportion with biogenic CO2 occurs
over a large area (~0.8 km2), which extends over the inner part of the Solfatara crater as well as the eastern
periphery, corresponding with a NW–SE fault system. The presented method and data analysis are important
means of surveillance of the volcanic activity.
Description:
Published
Description:
372–379
Description:
1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive
Description:
2.4. TTC - Laboratori di geochimica dei fluidi
Description:
4.5. Degassamento naturale
Description:
JCR Journal
Description:
reserved
Keywords:
CO2 soil degassing
;
CO2 flux
;
carbon dioxide
;
carbon isotopes
;
03. Hydrosphere::03.04. Chemical and biological::03.04.05. Gases
;
03. Hydrosphere::03.04. Chemical and biological::03.04.06. Hydrothermal systems
;
04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry
;
04. Solid Earth::04.08. Volcanology::04.08.01. Gases
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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