The role of the aquifer in soil CO2degassing in volcanic peripheral areas: A case study of Stromboli Island (Italy)

The peripheral area of Stromboli Island, Italy, named “Scari”, was continuously studied between January 2009 and December 2010. Data on soil CO2flux and the partial pressure of CO2(pCO2) in equilibrium with the thermal aquifer linked to the magmatic system are presented. Soil CO2fluxes range from 20 to 370 g m− 2d− 1and have been strongly affected by soil temperature variations. Soil CO2flux 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 pCO2values change in a wide range from 0.03 to 0.6 (atm), showing rapid variations. The results of this study show that in the volcanic peripheral area, the degassing process of soil CO2is determined not only by the CO2released directly from the magma but also by gas–water interactions in the aquifer. The aquifer is able to dissolve the high amount of CO2discharged by the magmatic system. Moreover, the “residuals” of CO2flux diffused from the soil show a delay on the order of ~ 1 month with respect to the pCO2in equilibrium with the aquifer. The soil CO2flux is therefore not directly linked to the uprising of magmatic CO2but instead depends on the CO2discharged from the aquifer, which buffers and modulates the volatile changes released by the magmatic system.