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(searched for: doi:10.1016/j.earscirev.2019.102928)
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Chan Yeong Kim, Soonyoung Yu, Yun-Yeong Oh, Gitak Chae, Seong-Taek Yun, Young Jae Shinn
Published: 15 January 2021
Frontiers in Earth Science, Volume 8; https://doi.org/10.3389/feart.2020.599388

Abstract:
Temporal changes of soil CO2 flux (FCO2) and soil CO2 concentration ([CO2]v) were surveyed in a natural CO2 emission site to characterize the factors controlling the short-term temporal variation of geogenic FCO2 in a non-volcanic and seismically inactive area. Due to a lack of long-term monitoring system, FCO2 was discontinuously measured for three periods: Ⅰ, Ⅱ at a high FCO2 point (M17) and Ⅲ about 30 cm away. Whereas [CO2]v was investigated at a point (60 cm depth) for all periods. A 2.1 magnitude earthquake occurred 7.8 km away and 20 km deep approximately 12 h before the period Ⅱ. The negative correlation of FCO2 with air pressure suggested the non-negligible advective transport of soil CO2. However, FCO2 was significantly and positively related with air temperature as well, and [CO2]v showed different temporal changes from FCO2. These results indicate the diffusive transport of soil CO2 dominant in the vadose zone, while the advection near the surface. Meanwhile [CO2]v rapidly decreased while an anomalous FCO2 peak was observed during the period Ⅱ, and the CO2 emission enhanced by the earthquake was discussed as a possible reason for the synchronous decrease in [CO2]v and increase in FCO2. In contrast, [CO2]v increased to 56.8% during the period Ⅲ probably due to low gas diffusion at cold weather. In addition, FCO2 was low during the period Ⅲ and showed different correlations with measurements compared to FCO2 at M17, implying heterogeneous CO2 transport conditions at the centimeter scale. The abnormal FCO2 observed after the earthquake in a seismically inactive area implies that the global natural CO2 emission may be higher than the previous estimation. The study result suggests a permanent FCO2 monitoring station in tectonically stable regions to confirm the impact of geogenic CO2 to climate change and its relation with earthquakes.
, Robert Van Geldern, Anssi Myrttinen, Martin Zimmer, Johannes A. C. Barth, Bettina Strauch
Published: 26 November 2020
Scientific Reports, Volume 10, pp 1-9; https://doi.org/10.1038/s41598-020-77635-5

Abstract:
The relevance of CO2 emissions from geological sources to the atmospheric carbon budget is becoming increasingly recognized. Although geogenic gas migration along faults and in volcanic zones is generally well studied, short-term dynamics of diffusive geogenic CO2 emissions are mostly unknown. While geogenic CO2 is considered a challenging threat for underground mining operations, mines provide an extraordinary opportunity to observe geogenic degassing and dynamics close to its source. Stable carbon isotope monitoring of CO2 allows partitioning geogenic from anthropogenic contributions. High temporal-resolution enables the recognition of temporal and interdependent dynamics, easily missed by discrete sampling. Here, data is presented from an active underground salt mine in central Germany, collected on-site utilizing a field-deployed laser isotope spectrometer. Throughout the 34-day measurement period, total CO2 concentrations varied between 805 ppmV (5th percentile) and 1370 ppmV (95th percentile). With a 400-ppm atmospheric background concentration, an isotope mixing model allows the separation of geogenic (16–27%) from highly dynamic anthropogenic combustion-related contributions (21–54%). The geogenic fraction is inversely correlated to established CO2 concentrations that were driven by anthropogenic CO2 emissions within the mine. The described approach is applicable to other environments, including different types of underground mines, natural caves, and soils.
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