Background Earth system state amplified Carnian (Late Triassic) environmental changes

Past major biological turnovers are coeval to large injections of CO2 into the atmosphere–ocean system that are often linked to the emplacement of Large Igneous Provinces. The impact of these CO2 pulses on ecosystems is however different at different times, and this difference is contingent on the initial boundary conditions. Here, we show how delayed vegetation recovery from the Permo–Triassic mass extinction (ca. 252 Ma) and continuing amalgamation of Pangaea, determined the style of the Late Triassic Carnian Pluvial Episode (ca. 233 Ma), a global climate change event linked to a major biological turnover and to the emplacement of the Wrangellia LIP. Our new biogeochemical modelling can reproduce changes in C and Sr isotopes only when we assume that high terrestrial productivity recovers in the Carnian, ∼15 Myrs after the Permo–Triassic crisis, consistent with the re-appearance of large coal swamps. In the model, this early Carnian expansion of the terrestrial organic C reservoir results in a drop of atmospheric pCO2 and global temperatures. Furthermore, climate modelling shows how the resulting low pCO2 conditions, coupled to the aridity of Pangaea, made the Carnian Earth system more susceptible to hydrological cycle enhancements following C inputs from coeval volcanism, thus explaining the nature of the Carnian Pluvial Episode.