Conclusions

Earth’s CO2 emission in Italy includes both volcanic and non-volcanic emissions, present along Central-Southern peninsular Italy, and in Sicily. Measured CO2 fluxes totals to 35 - 60 Mt/y, including volcanic degassing (e.g., Etna, Stromboli, Vulcano, Vesuvio, Campi Flegrei, Ischia) and non-volcanic soil emission.

Deep carbon cycling in Italy depends on both degassing of a deep anomalous layer left by the Adria-Ionian slab retreat during Oligocene-Present times and on the formation of CO2-rich magmas. Slab rollback left a layer of anomalous, low-velocity mantle material at a depth of about 70-120 km, generated by melting of carbonate-rich sediments such as marls. Continuous loss of carbonate components from the retreating slab induced carbonate metasomatism and generated low melt fractions of carbonate-rich melts reflected by the low-velocity layer. This variation in mantle rheology has been preserved long after the end of volcanism possibly as a result of the increase of carbonate melting at higher temperatures, due to heating and decompression. Carbonate-rich melts are unable to reach the surface, since they degas to produce CO2 at depths shallower than 70 km. CO2 fluids are substantially immobile at these depths and tend to accumulate in the mantle. Deep lithospheric faults, such as the 41° Parallel Line are able to reach this layer provoking degassing and/or migration of CO2. This may rise to accumulate to the Moho or to be released to the surface.

The CO2 storage capability of the mantle reservoir beneath the western Mediterranean has been tentatively calculated by Frezzotti et al. (2009) at about 1.35 Mt of CO2 (equal to 5 Mt carbon) for each km3 of metasomatized mantle. Based on the extension of the low velocity wedge, and assuming a time scale of 30 Ma, CO2 mantle degassing beneath Italy would conservatively lead to a CO2 flux of about 70 Mt/y, which exceeds yearly natural CO2 emission in Italy.

The low velocity wedge beneath the western Mediterranean region represents an important natural cycled C reservoir which stores CO2 amounts in the order of 100 Gt. Since present day atmospheric CO2 reservoir is estimated at about 3000 Gt, recycling of carbon through CO2-mantle degassing in Italy represents a relevant process, which could be a noteworthy source of CO2 to the atmosphere.