The role of the aquifer in soil CO 2 degassing in volcanic peripheral areas: A case study of Stromboli Island (Italy)

Abstract

The peripheral area of Stromboli Island, Italy, named “Scari”,was continuously studied between January 2009 and December 2010. Data on soil CO2 flux and the partial pressure of CO2 (pCO2) in equilibrium with the thermal aquifer linked to the magmatic system are presented. Soil CO2 fluxes range from 20 to 370 g m−2 d−1 and have been strongly affected by soil temperature variations. Soil CO2 flux data were filtered with respect to the soil temperature and the calculated values, called “residuals”, were considered to detect changes induced by the magmatic system. The pCO2 values change in a wide range from 0.03 to 0.6 (atm), showing rapid variations. The results of this study showthat in the volcanic peripheral area, the degassing process of soil CO2 is determined not only by the CO2 released directly from the magma but also by gas–water interactions in the aquifer. The aquifer is able to dissolve the high amount of CO2 discharged by the magmatic system. Moreover, the “residuals” of CO2 flux diffused from the soil show a delay on the order of ~1 month with respect to the pCO2 in equilibrium with the aquifer. The soil CO2 flux is therefore not directly linked to the uprising of magmatic CO2 but instead depends on the CO2 discharged fromthe aquifer, which buffers and modulates the volatile changes released by the magmatic system. © 2016 Elsevier B.V. All rights reserved