Impact of elevated UV-B radiation on Toarcian spores and pollen mutagenesis.

Studies on extant spores belonging to the family of clubmosses (e.g., Lycopodium) have shown that micro-FTIR spectroscopic analyses can reveal the quantity of UV-absorbing compounds (UACs) in the organic walls of the spores and thus be used to reconstruct UV-B radiation and the ozone layer degradation rates at the time of formation of the spore. Here, we present new data from Toarcian age sporomorphs from marine organic-rich marls to shales, deposited in the offshore to shoreface environments from a core from the Paris Basin, France, to evaluate the applicability of this method in the geological record. Our results are integrated with existing high-resolution geochemical and geodynamic data from the core to provide a comprehensive understanding of the system. Understanding the fluctuations in UV-B radiation during the Early Toarcian would allow us to understand whether Karoo and Ferrar Large Igneous Province activity resulted in the release of halides that triggered a depletion of the ozone column in the atmosphere, leading to increased UV-B exposure on Earth’s surface, potentially contributing to environmental and ecological perturbations on land and in the oceans. A quantitative palynofacies analysis performed on 32 samples from the core revealed the presence of anoxic conditions during the deposition of the deeper portion of the core, reflected in the abundance of AOM and lack of sporomorphs and marine elements in the palynological record. On the other hand, the palynological record shows a decrease in AOM and an increase in sporomorphs and marine elements at the passage from the Bifrons Zone to the Variabilis Zone, marking a shift to a shallower marine depositional environment characterised by enhanced continental inputs and decreased oxygen depletion. Previous studies of the early Toarcian Carbon Isotope Interval have revealed teratological pollen and spores from localities in the northern hemisphere, linking these mutations to prolonged exposure to enhanced UV-B radiation. Using micro-FTIR, sporomorph morphology analysis (via SEM), palynofacies models and integrating this with existing data we are able to better link changes in vegetation with LIP activity. Understanding the impact of volcanic activity on atmospheric chemistry and ozone thickness, which increases UV-B rays reaching Earth, would help us grasp their effects on life and how UV-B changes influence mutagenesis in organisms and eventually have a role in extinction events.