Fault-related basins as carbon reservoirs: Soil CO2 emissions in the SE Korean Peninsula.

• Faults take topographical control to form sedimentary basins. • Mature basins yield a variety of soil. • Faults, basins, and soil affect CO 2 emissions. Carbon dioxide (CO 2) is one of the main components of greenhouse gases, and there is a great concern about emissions mainly from human activities. However, long term CO 2 emissions during the Earth's history are largely related to natural emissions by geological factors. Natural CO 2 emissions are mainly at highly permeable passages below the surface (e.g., volcanoes or faults). Unlike volcanoes, which actively release mantle-derived volatiles, faults can be affected by CO 2 of more diverse origins and are relatively lacking in research. Here, we note that it is important for CO 2 emissions that faults as channels with high permeability take topographical control to form sedimentary basins and produce mature soils. To this end, we performed CO 2 flux measurements in the Yangsan Fault System (YFS), Republic of Korea. As this fault is an active fault, topographical variations are clear and accessible. In the YFS, high spring CO 2 fluxes (119.5 g m−2 d-1 to 77,699.5 g m−2 d-1) were observed in Sector 1, and high soil CO 2 fluxes (0.5 g m−2 d-1to 1,240 g m−2 d-1) were observed along the Hyeongsan River in Sector 2. The carbon isotope composition indicates that the mantle contributes to fault-related spring CO 2 (δ13C = -14.03 ‰ to −7.44 ‰), and soil CO 2 comes from shallow biogenic sources (δ13C = –22.82 ‰ to −13.53 ‰) deposited in fault-forming basins. In addition, the helium isotope ratios indicative of the mantle contribution (3He/4He = 1.86 to 6.02 Ra) are shown in the gas samples of the springs. Furthermore, in a post-earthquake survey, we found temporal changes in soil CO 2 flux values near the epicenter, which may be related to the earthquake. A simple calculation of overall CO 2 emissions suggests that significant amounts of CO 2 (6.2 Mt yr−1) are being emitted along the YFS. Therefore, this study reports both large-scale structural degassing and biological CO 2 emissions from fault zones, providing implications for the role of sedimentary basins and soil types formed in fault zones. [ABSTRACT FROM AUTHOR]