Massive emissions of deep CO ₂ coupled to the 2009–2018 Central Italy earthquakes.

Lake Trasimeno is a shallow, endorheic lake located in central Italy. It is the fourth Italian largest lake and is one of the largest endorheic basins in western Europe. Because of its shallow depth and the absence of natural outflows, the lake, in historical times, alternated from periods of floods to strong decreases of the water level during periods of prolonged drought. Lake water is characterised by a NaCl composition and relatively high salinity. The geochemical and isotopic monitoring of lake water from 2006 to 2018 shows the presence of well-defined seasonal trends, strictly correlated to precipitation regime and evaporation. These trends are clearly highlighted by the isotopic composition of lake water (δ¹⁸O and δD) and by the variations of dissolved mobile species. In the long term, a progressive warming of lake water and a strong increase of total dissolved inorganic solids have been observed, indicating Lake Trasimeno as a paradigmatic example of how climate change can cause large variations of water quality and quantity. Furthermore, the rate of variation of lake water temperature is very close to the rate of variation of land-surface air temperature, LSAT, suggesting that shallow endorheic lakes can be used as a proxy for global warming measurements.

We review the methods based on the measurement of CO₂ emissions for the computation of geothermal heat flow, both at a local (hydrothermal sites, a few km²) and regional scale (hundreds km²). At the local scale, we present and discuss the cases of the Latera caldera and Torre Alfina (Italy) geothermal systems. At Torre Alfina and Latera, the convection process sustains a CO₂ emission of ~1 kg s⁻¹ and ~4 kg s⁻¹, and heat flows of 46 MW and 130 MW, respectively. At the regional scale, we discuss the case of the central Apennine (Italy), where CO₂ mass and enthalpy balances of regional aquifers highlights a wide and strong thermal anomaly in an area of low conductive heat flow. Notably, the CO₂/heat ratios computed for the central Apennines are very similar to those of the nearby geothermal systems of Latium and Tuscany, suggesting a common source of CO₂-rich fluids ascribed to the Tyrrhenian mantle.

Variations of springs discharge due to seismic events are rather common. On 2016 October 30th a Mw 6.5 earthquake occurred 5 km NNE of Norcia Town (Central Italy), at a depth of around 9 km b.g.l. The Torbidone spring, dry since 1979, was re-activated after the Norcia earthquake, and its discharge rose up to 1.6 m3/s in thefollowing weeks. The Torbidone, with other minor springs, feeds the baseflow of the Sordo River (Nera River basin), the discharge of which increased up to 2m3/s after the earthquake. The seismic events did not affect only the Torbidone spring but also the entire groundwater circulation of the Nera River hydrogeological basin.We analyzed the Torbidone spring area and its geological framework using hydrogeological, structural and geochemical methods, to evaluate the causes of the perturbations and the possible system evolution.The main factors thought to be responsible for the perturbations are the changes of permeability and the variations of hydraulic head. The mechanisms of these hydrogeological changes are currently being studied in order to define a conceptual model consistent with the observed response of Torbidone spring to the seismic event.

Chemical weathering is the main natural mechanism limiting the atmospheric carbon dioxide levels on geologic time scales (>1 Ma) but its role on shorter time scales is still debated, highlighting the need for an increase of knowledge about the relationships between chemical weathering and atmospheric CO₂ consumption. A reliable approach to study the weathering reactions is the quantification of the mass fluxes in and out of mono lithology watershed systems. In this work the chemical weathering and atmospheric carbon dioxide consumption of ultramafic rocks have been studied through a detailed geochemical mass balance of three watershed systems located in the metaophiolitic complex of the Voltri Massif (Italy). Results show that the rates of carbon dioxide consumption of the study area (weighted average = 3.02 ± 1.67 × 10⁵ mol km⁻² y⁻¹) are higher than the world average CO₂ consumption rate and are well correlated with runoff, probably the stronger weathering controlling factor. Computed values are very close to the global average of basic and ultrabasic magmatic rocks, suggesting that Voltri Massif is a good proxy for the study of the feedbacks between chemical weathering, CO₂ consumption, and climate change at a global scale.