Shallow Submarine CO2 Emissions in Coastal Volcanic Areas Implication for Global Carbon Budget Estimates: The Case of Vulcano Island (Italy)

The Earth’s degassing is an important factor in evaluating global carbon budget estimates and understanding the carbon cycle. As a result, numerous studies have focused on this topic. However, current estimates predominantly focus on subaerial CO2 emissions and CO2 deep submarine emissions, particularly along mid-ocean ridges (MORs), whereas very few and only spatially limited estimates of shallow submarine CO2 emissions have been reported, despite being widespread features of the seafloor. This study reports the results of measuring the dissolved CO2 concentrations in shallow submarine environments along the coast of Vulcano Island (Aeolian Islands, Italy). For the areas exhibiting the highest concentrations, we calculated the amount of diffuse degassing by computing the sea–air CO2 flux. The results revealed extremely high dissolved CO2 concentrations, reaching up to 24 vol.% in areas with visible hydrothermal activity, including one location far from the island’s main crater. Notably, elevated CO2 levels were also detected in areas with minimal or no apparent hydrothermal discharge, indicating the occurrence of diffuse degassing processes in these areas. In addition, the calculated diffuse degassing flux was comparable in magnitude to the CO2 flux directly emitted into the atmosphere from the island’s main bubbling pools.