Carbon dioxide emission and heat release estimation for Pantelleria Island (Sicily, Italy)

Abstract

Detailed surveys of diffuse CO2 flux, soil temperature, thermal gradients, and sampling of high-T fumaroles were carried out in the Favare area and Lake Specchio di Venere on Pantelleria Island. Spatial patterns of diffuse CO2 emissions in the Favare area reflect structural discontinuities (faults, fractures or cracks in the soil) associated with the volcano-tectonic structures of the young Monastero Caldera (NNE–SSW to NE–SW trending). The estimated diffuse CO2 output from two adjacent sites in the Favare area (~ 93,000 m2) is 7.8 t d− 1 (equivalent to 2.62 kt a− 1), whereas that from the west shore of the lake (450 m2) is 0.041 t d− 1 (or 0.015 kt a− 1). The extrapolation of diffuse CO2 fluxes across the entire altered area of Favare suggests that CO2 emissions are ~ 19.3 t d− 1. The diffuse CO2 flux correlates with shallow soil temperatures, indicating a similar source for both the heat and volatiles from the underlying geothermal reservoir. Gas equilibria applied to fumarolic effluents define P–T conditions for this reservoir at 2–6 bar and 120–160 °C, in good agreement with measurements from exploratory wells in these areas (e.g., 135 °C at a depth of 290 m). Using the CO2 flux as a tracer for steam output, and consequently for heat flow, the calculated thermal energy for the shallow reservoir is 10–12 MW; this represents the minimum geothermal potential of the reservoir on Pantelleria island.