An extinct offshore volcano could hold gigatonnes of CO2.

What could be compared to 24–125 years of the country’s modern discharges?

According to the Global CCS Institute, international carbon capture and storage efforts will remove 42.6 megatons (0.0426 gigatons) of carbon dioxide from the atmosphere in 2022. The new study suggests that offshore underwater volcanoes could be a promising new location for carbon capture and storage, potentially allowing for the removal and storage of much larger quantities of the greenhouse gas from the atmosphere.

“We know that most nations, including Portugal, are putting forth attempts to decarbonize the economy and our human activities; this is a message that this might be one of the instruments to tackle the issue,” says Ricardo Pereira, a geologist at the NOVA School of Science and Innovation and co-creator of the review.

“We know that most countries, including Portugal, are attempting to decarbonize the economy and human activities; this is a message that this may be one of the tools available to address the problem.”

Ricardo Pereira, a geologist at the NOVA School of Science and Technology,

“In situ mineral carbonation” is the method used to store carbon dioxide in an extinct volcano. New minerals that securely and indefinitely store carbon dioxide are formed as a result of the reaction that occurs when carbon dioxide and certain kinds of rocks’ elements are mixed. The minerals calcite, dolomite, and magnesite are produced when carbon dioxide and elements like calcium, magnesium, and iron combine.

Rocks that contain a lot of calcium, iron, and magnesium are ideal candidates for this cycle —for example, the volcanic basalts that make up the greater part of the ocean bottom. Knowing this, the researchers chose an offshore volcano for a few reasons: the volcano’s structure could be ideal for carbon injection and storage, the rocks are suitable for the reactions involved, and the location is neither too close nor too far from large populations.

The majority of carbon capture projects have utilized the injection of carbon dioxide into sealed, porous sedimentary basins to prevent gas migration from reservoirs. In these cases, the carbon will ultimately begin to shape minerals, but just over longer timeframes — a very long time to hundreds of years. According to research published in 2016, 95 percent of the carbon dioxide injected into Icelandic underground basalts had mineralized within two years. The shorter mineralization time makes the process safer and more efficient because issues like potential leaks are no longer a concern once carbon is stored in minerals.

“What makes mineral carbonation really interesting is the time,” says Davide Gamboa, co-author of the study and a geologist at the University of Aveiro. The quicker it gets into a mineral, the more secure it becomes, and when it’s a mineral, it is long-lasting.”

Schematic cross-section of the Fontanelas spring of gushing lava, showing potential locales for carbon dioxide sequestration. Credit: Pereira and Gamboa, 2023

The scientists concentrated on the capacity potential at the old Fontanelas well of lava, which is somewhat covered 100 kilometers seaward from Lisbon, with a pinnacle 1500 meters beneath ocean level.

The authors used data from 2008 dredged samples and 2D and 3D seismic studies of the undersea volcano produced during offshore oil exploration to estimate the potential volume of carbon dioxide that could be stored at this location. Natural carbonate minerals were found in the dredged samples, indicating that the chemical reactions needed to store carbon were already taking place and that attempts to mineralize carbon in these rocks should succeed.

Additionally, the samples had up to 40% pore space, indicating that carbon dioxide could be injected and mineralized within the rocks. The researchers also say that low-permeability layers that were seen around the volcano’s flanks could help keep carbon dioxide from becoming mineralized.

While this study exhibited an enormous potential carbon stockpiling limit at the Fontanelas fountain of liquid magma, the creators noted that numerous different spots all over the planet might have comparable seaward volcanoes that could be contenders for carbon catch and capacity.

More information: Ricardo Pereira et al, In situ carbon storage potential in a buried volcano, Geology (2023). DOI: 10.1130/G50965.1

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