Soil CO2 flux in hydrothermal areas of the Tatun Volcano Group, Northern Taiwan

• Soil CO2 flux is measured in the Tatun Volcano Group, Taiwan.
• The flux spatial distribution is related to degassing pattern.
• Soil CO2 output from the TVG hydrothermal areas is estimated to be 113 t d− 1.
• Helium and carbon isotopes of soil gas reveal shallow degassing features.

We measured soil CO2 flux in the representative hydrothermal areas of the Tatun Volcano Group (TVG), to better understand the volcano's dynamic nature, and to estimate its soil CO2 degassing output. Results show that the average soil CO2 fluxes obtained at Da-You-Keng (DYK), Geng-Tze-Ping (GTP), She-Haung-Ping (SHP), and Tatun Natural Park (TNP) were 128 g m− 2 d− 1, 518 g m− 2 d− 1, 420 g m− 2 d− 1, and 25 g m− 2 d− 1, respectively. The range is comparable to other active volcanic/hydrothermal areas in the world. Along with Liu-Huang-Ku (LHK), where the soil CO2 flux is known, the total soil CO2 output from measured areas is evaluated at 82 t d− 1. Furthermore, a first total soil CO2 output from the whole hydrothermal areas of the TVG is roughly estimated at 113 t d− 1, which includes 15 t d− 1 mantle contribution. Considering the mantle-derived CO2 flux and H2O/CO2 ratio of fumarolic gas, thermal energy associated with the diffuse degassing at the TVG hydrothermal area is estimated at 8.2 MW. Carbon (δ13C) and helium (3He/4He) isotopic ratios of soil samples of the studied areas ranged from − 4.4 to − 6.7‰, and 2.45 to 6.98 RA, respectively. The extent of air involvement in the soil-degassing system, as constrained by the helium and carbon isotopic compositions, provides essential information for depicting regional degassing features of the hydrothermal areas.