Figure 3

(A) Reconstruction of atmospheric pCO₂ prior to and during the early Toarcian CIE. In dependency of the carbon source and its isotopic signature different and partly contrasting CO₂ scenarios can be proposed. The best fit scenario is achieved for carbon sources enriched in ¹²C, suggesting that CIE and climate change were driven by carbon injections from cryosphere collapse⁹, or gas hydrates and wetlands¹⁷ (low pCO₂ scenario, blue and orange asterisks). Such a scenario agrees with stomata-based pCO₂ estimates¹⁰. Contribution from thermogenic methane released from fossil hydrocarbon sources would be plausible as well (moderate pCO₂ scenario, green and red  asterisks). On the contrary, scenarios invoking volcanic CO₂ emissions as primary driver of the early Toarcian carbon cycle perturbation are not supported by our data (high pCO₂ scenario, orange and red asterisks). Vertical grey bars indicate uncertainties of pCO₂ determinations. (B) Impact of pCO₂ levels and precipitation rates on the δ¹³C of land plant biomass (T-J: Triassic-Jurassic boundary; see supplementary information for additional information and references). Latitudinal climate and vegetation gradients cause offsets in δ¹³C absolute values.