Diffuse emission of CO2 from the Langjiu Geothermal Field, Western Tibet

Abstract

The Earth's carbon cycle is closely related to climate change and global environmental changes. Emissions of CO2 from the solid Earth to the atmosphere through geological carbon cycling are an important source of atmospheric carbon. Therefore, it is of great importance to understand the current volcanic flux of carbon to the atmosphere, along with the factors that control this flux, to analyse climate stability. The Langjiu (LJ) geothermal field, which is located in the western region of the Lhasa terrane, is one of the four geothermal power plants in the Tibetan Plateau. In this study, the CO2 emissions and genesis from the geothermal field were quantitatively estimated. The results of this study indicate that the natural CO2 diffuse emission fluxes before and after the geothermal exploitation were 20.0 and 38.7 g m−2 d−1, respectively. The intensity of diffuse emission is close to that of other global geothermal fields. The endogenous CO2 emissions have increased significantly after geothermal exploration, indicating a greater contribution of endogenous CO2 emissions in the LJ geothermal field. Further, faults in the geothermal field could act as conduits for gas emission. The HeC isotope coupling model indicates that the CO2 in the LJ geothermal field is of crustal origin and have the addition of mantle fluids. The N2 in the LJ geothermal field is mainly of thermogenic origin. Our results show that natural CO2 emissions are an important source of CO2 input into the atmosphere. Although CO2 emissions can increase owing to anthropogenic activities (e.g. geothermal exploitation), natural CO2 emissions still have a high contribution to the atmosphere. The influence of natural CO2 emissions from the geothermal field should be assessed to achieve accurate CO2 inventories in geothermal settings.