In a groundbreaking study published in Geology, researchers have proposed a novel method of carbon capture and storage (CCS) that has the potential to significantly contribute to global climate change mitigation efforts. The focus of this research is on the potential of offshore underwater volcanoes to serve as carbon sinks, with the capacity to sequester large quantities of carbon dioxide from the atmosphere.
The researchers, led by Ricardo Pereira, a geologist at the NOVA School of Science and Technology, and Davide Gamboa, a geologist at the University of Aveiro, focused their investigation on the Fontanelas volcano, an extinct volcanic formation located about 100 kilometers off the coast of Lisbon, Portugal. The undersea volcano, partially buried and peaking approximately 1,500 meters below sea level, demonstrated promising potential for CCS due to its geological makeup and location.
In the course of the study, the researchers estimated that the Fontanelas volcano could store between 1.2 to 8.6 gigatons of carbon dioxide. This volume of CO2 is equivalent to approximately 24 to 125 years of Portugal's industrial emissions. To put this in context, the Global CCS Institute reported that in 2022, a total of 42.6 megatons (0.0426 gigatons) of CO2 was removed from the atmosphere by international CCS efforts. Thus, the potential capacity of the Fontanelas volcano for CCS is substantial, presenting offshore underwater volcanoes as promising sites for future carbon capture initiatives.
The method of carbon storage proposed in the study relies on a process known as "in situ mineral carbonation." This process involves the reaction of CO2 with elements present in certain types of rocks, leading to the formation of new minerals that can safely and permanently store the carbon. Basaltic rocks, common in volcanic formations, are ideal for this process due to their high content of calcium, iron, and magnesium, elements which combine with CO2 to form minerals like calcite, dolomite, and magnesite.
What sets this approach apart from other CCS methods is the considerably shorter mineralization time. Traditional CCS projects often inject CO2 into porous sedimentary basins that are sealed to prevent gas migration. Over time, the carbon will form minerals, but this process can take decades or even centuries. In contrast, CO2 injected into volcanic basalts can mineralize much faster—potentially within a few years, making the process safer and more effective. Once the carbon is stored in minerals, concerns about potential leaks become irrelevant, as highlighted by Gamboa: "The faster it gets into a mineral, the safer it becomes, and once it’s a mineral, it is permanent".
The researchers used 2D and 3D seismic studies of the undersea volcano, produced during offshore oil exploration, as well as data from rock samples dredged from the area in 2008 to estimate the potential volume of CO2 that could be stored at this site. These samples contained naturally formed carbonate minerals, indicating that the necessary chemical reactions for carbon storage were already taking place. Additionally, the samples had up to 40% pore space, which could be used for carbon injection and mineralization. Low-permeability layers around the flanks of the volcano could aid in containing the CO2 before it is mineralized.
Although this research focused on the Fontanelas volcano, the authors emphasize that many other locations around the world may host similar offshore volcanoes that could be potential candidates for carbon capture and storage.