Extremely elevated CO2 concentrations at the Triassic/Jurassic boundary

Although progress has been made in recent years in reconstructing the environmental conditions at the Triassic/Jurassic Boundary (TJB), published records of atmospheric CO2 concentrations have been of low resolution and/or based on multi-taxon estimates. This is addressed here by reconstructing CO2 concentrations across the TJB using stomatal frequencies of four phylogenetically and ecologically distinct plant groups from two depositionally, geographically and taphonomically separate boundary sections in East Greenland and Northern Ireland, with stomatal proxy methods and regression analysis. The resulting CO2 records then are compared with an additional existing TJB record from a geological section in Sweden. The final results indicate that pre-TJB (Rhaetian), the CO2 concentration was approximately 1000 ppm, that it started to rise steeply pre-boundary and had doubled to around 2000–2500 ppm at the TJB. The CO2 concentration then remained elevated for some time post-boundary, before returning to pre-TJB levels in the Hettangian. These results are in very good accordance with published C-isotope, fire and leaf dissection records, and clearly indicate steeply rising and lingering CO2 concentration at the TJB.

► The Triassic/Jurassic Boundary (TJB, 200 Mya) was a time of environmental upheaval.
► No published records of high-resolution atmospheric CO2 concentrations [CO2].
► Here, [CO2] across the TJB is reconstructed using the stomatal proxy method.
► Pre-TJB [CO2] was ~1000 ppm, and had doubled to ~2000–2500 ppm at the TJB.
► [CO2] remained elevated for some time, before returning to pre-TJB levels.