Journal of the Virtual Explorer

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.