Fossil seed fern Lepidopteris ottonis from Sweden records increasing CO2 concentration during the end-Triassic extinction event.

SWEDEN; SKANE (Sweden)

The end-Triassic event (ETE), a short global interval occurring at the end of the Triassic Period (~201.5 Ma), was characterized by climate change, environmental upheaval, as well as widespread extinctions in both the marine and terrestrial realms. It was associated with extensive perturbations of the carbon cycle, principally caused by the volcanic emplacement of the Central Atlantic Magmatic Province in relation to the break-up of Pangea. The correlated change in atmospheric CO 2 concentrations (p CO 2) can be reconstructed with the stomatal proxy, which utilizes the inverse relationship between stomatal densities of plant leaves (here stomatal index (SI), which is the percentage of stomata relative to epidermal cells) and p CO 2. Fossilized Lepidopteris leaves are common and widespread in Triassic strata, thus offering great potential for high-resolution p CO 2 reconstructions. A dataset of leaf cuticle specimens belonging to the seed fern species Lepidopteris ottonis from sedimentary successions in Skåne (Scania), southern Sweden, provided the possibility of p CO 2 reconstruction at the onset of the ETE. Here, we tested the intra- and interleaf variability of L. ottonis SI, and estimated the p CO 2 during the onset of the ETE. Our findings confirm L. ottonis as a valid proxy for palaeo- p CO 2 , also when using smaller leaf fragments. Importantly, the statistical analyses showed that the SI values of abaxial and adaxial cuticles are significantly different, providing a tool to distinguish between the two sides and select cuticles for analysis. Reconstructed p CO 2 increased from ~1000 pre ETE to ~1300 ppm at the onset of the event, a significant increase of ~30% over a relatively short time period. The p CO 2 recorded here is similar to previously published estimates, and strongly supports the observed pattern of elevated p CO 2 at the onset of the ETE. • Extinct seed fern Lepidopteris ottonis from the End-Triassic Event (ETE), Sweden. • Testing statistical variation of stomatal indices based on large cuticle database. • Semi-quantitative p CO 2 estimates based on the stomatal ratio method. • Increase from ~1000 to ~1300 ppm in the Rhaetian. • Results support L. ottonis as a useful proxy for palaeo- p CO 2 reconstructions. [ABSTRACT FROM AUTHOR]

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