Exceptional eruptive CO2 emissions from intra-plate alkaline magmatism in the Canary volcanic archipelago

Alkaline mafic magmas forming intra-plate oceanic islands are believed to be strongly enriched in CO₂ due to low-degree partial melting of enriched mantle sources. However, until now, such CO₂ enhancement has not been verified by measuring CO₂ degassing during a subaerial eruption. Here, we provide evidence of highly CO₂-rich gas emissions during the 86-day 2021 Tajogaite eruption of Cumbre Vieja volcano on La Palma Island, in the Canary archipelago. Our results reveal sustained high plume CO₂/SO₂ ratios, which, when combined with SO₂ fluxes, melt inclusion volatile contents and magma production rates at explosive and effusive vents, imply a magmatic CO₂ content of 4.5 ± 1.5 wt%. The amount of CO₂ released during the 2021 eruptive activity was 28 ± 14 Mt CO₂. Extrapolating to the volume of alkaline mafic magmas forming La Palma alone (estimated as 4000 km³ erupted over 10 Ma), we infer a maximum CO₂ emission into the ocean and atmosphere of 10¹⁶ moles of CO₂, equivalent to 20% of the eruptive CO₂ emissions from a large igneous province eruption, suggesting that the formation of the Canary volcanic archipelago produced a CO₂ emission of similar magnitude as a large igneous province.