Satellite Detection of Diffuse Tectonic CO2 Degassing in the East African Rift

Understanding the processes behind Earth’s CO2 degassing is crucial for clarifying how carbon is cycled by geologic processes on our planet. Earth’s carbon degassing results from magmatic and metamorphic processes controlled by large-scale plate tectonics. However, the nature and amount of diffuse CO2 fluxes from faults in continental rifts remain largely unconstrained. Recent research reports important CO2 fluxes from deep faults over 17 × 104 km2 in the East African Rift System (EARS), highlighting the need for a more detailed inventory of diffuse soil emissions. Across such extensive regions, only satellite observations can provide the broad measurement range needed to meet the observational requirements for long-term, large-scale overlay datasets. While space-based data provide extended coverage for large-scale identification of CO2 emission sources, to date, only the column-averaged total CO2 atmospheric content has been measured from space. Range-resolved measurements of CO2 concentration with the vertical accuracy needed to detect diffuse soil emissions are not available from space, preventing direct quantification of Earth degassing over large regions. In this paper, we focus on a new approach to measuring soil CO2 fluxes by a statistical deconvolution of column measurements of global atmospheric CO2 content. Anthropogenic increase, seasonal climatology at a small regional scale, and soil fluxes are measured without the use of ancillary measurements or model simulations. We combine petrology of fluid and melt phases in mantle rocks with a new satellite data analysis to reveal, for the first time, large CO2 fluxes from the lithospheric mantle to the atmosphere in a much wider region than previously considered (22.4 × 105 km2), including the Ethiopian and East African domes, where magmatism is no longer active or absent. We infer that diffuse soil emissions are measurable from space, and that Earth’s tectonic carbon fluxes are considerably more relevant than currently considered, with a crucial impact on the balance of the global carbon cycle.