Carbon dioxide flux and isotopic composition from sedimentary rock weathering, Draix-Bleone Critical Zone Observatory, France

The measurements and data contained here were obtained to study the release of carbon dioxide during the chemical weathering of sedimentary rocks. The primary aim of the research was to explore how these CO2 fluxes were related to environmental parameters (temperature, hydrology). Weathering of sedimentary rocks can result in CO2 release from the oxidation of rock organic carbon oxidation, but also due to the oxidation of sulfide minerals, production of sulfuric acid and subsequent release of CO2 from carbonate minerals. These rock-derived carbon sources are understudied, and form an important part of the geological carbon cycle. The CO2 flux measurements were made on 5 rock chambers (H4, H6, H7, H8 and H13) installed in the Draix-Bleone Critical Zone Observatory, France, on outcrops of Jurassic marls. Measurements and data were collected from December 2016 to May 2019. Regular visits to the site (~4 per year) returned data on total CO2 flux (see data in Total-CO2-flux.csv). This was explored as a function of temperature and ambient hydroclimate (precipitation). The datasets include the total CO2 flux measured at each visit to a chamber, and measurements of the internal chamber temperature. To determine the source of CO2 measured in the chambers, we trapped the CO2 using zeolite sieves and recovered it in the laboratory. The radiocarbon activity (reported as fraction modern, F14C) and its stable isotope composition (d13C) were measured from CO2 collected from chambers H4 and H6 over the sampling period (Radiocarbon-data.csv). These measurements were used in a mixing analysis to partition the source of CO2 between rock organic carbon and carbonate using a mixing model approach (Partitioned-CO2-fluxes.csv), as explained in full detail in the published paper Soulet et al., 2021, Nature Geoscience. We also measured the geochemical characteristics of the bedrocks that are undergoing weathering at the field site (rock-geochemical-composition.csv), including the organic carbon concentration, inorganic carbon concentration and their isotopic composition, and sulfur concentration. Finally, we measured environmental variables of interest: the chamber temperature (chamber-temperature.csv) and the air temperature at the Draix-Bleone observatory (Air-temperature-at-laval-le-plateau-weather-station.csv, respectively). This research was funded by a European Research Council Starting Grant to Robert Hilton (ROC-CO2 project, grant 678779) and Radiocarbon and stable isotope measurements were funded by the Natural Environment Research Council (NERC), UK, (NERC National Environmental Isotope Facility NEIF Radiocarbon Allocation 2074.1017) to Guillaume Soulet, Robert Hilton and Mark Garnett. Full details of data analysis and interpretation can be found in Soulet et al., 2021, Temperature control on CO2 emissions from the weathering of sedimentary rocks, Nature Geoscience