Constraining Soil Hydrothermal CO₂ Degassing Across the Changbaishan Volcanic Area: Insights From ¹³C‐¹⁴C Perspective

Abstract Soil hydrothermal CO 2 represents important forms of diffuse degassing in volcanic areas, but the corresponding CO 2 output remains unclear. Herein, we investigated geochemical features of soil gas, that is, soil gas components, carbon isotopic compositions of soil CO 2 (δ 13 C‐CO 2 and Δ 14 C‐CO 2 ), and soil CO 2 fluxes in the Changbaishan volcanic area (CHV). The geochemical characteristics of soil gas in diffuse degassing structures differed significantly from those in volcano‐affected structures. Specifically, soil CO 2 concentrations were up to 2.5 × 10 5 ppm, with δ 13 C‐CO 2 values ranging from −6.2‰ to −1.6‰ and Δ 14 C‐CO 2 values spanning from −996‰ to −845‰, showing significant hydrothermal CO 2 signatures. The isotopic mixing model was constructed to estimate the contribution of hydrothermal, biogenic, and atmospheric CO 2 to soil CO 2 . The results showed that soil CO 2 in diffuse degassing structures was predominantly derived from hydrothermal CO 2 , while soil CO 2 in the volcano‐affected structures was mainly derived from biogenic CO 2 . Combined with the soil CO 2 fluxes, it was concluded that the hydrothermal CO 2 output through soil degassing was 5.83 × 10 4 t yr −1 in CHV, significantly lower than previous estimates. We found that hydrothermal CO 2 release in CHV exceeded the CO 2 consumption through silicate weathering, thereby acting as the carbon source. We also estimated the hydrothermal soil CO 2 output from global volcanoes based on literature‐published values from 80‐degassing volcanoes, which was ∼150 Mt yr −1 . Our results highlighted the importance of conducting 13 C‐ 14 C investigations in global volcanic areas to replenish the database of hydrothermal CO 2 output in different forms and subsequently evaluate their climatic implications.