Vegetation response to climate change during an Early Jurassic hyperthermal event (Jenkyns Event) from Northern China (Ordos Basin)

The Early Jurassic Jenkyns Event (or Toarcian Oceanic Anoxic Event T-OAE) was an episode of global warming and C-cycle perturbation that affected both marine and terrestrial ecosystems, but the interplay between climate change and vegetation is not established in detail from sections outside of Europe. Here, abundance changes in spore-pollen assemblages from the lacustrine Anya succession in the Ordos Basin (North China) reveal a unique record of vegetation dynamics during the Jenkyns Event. Plant communities responded to the event with biodiversity losses and the reorganization of gymnosperm-dominated forests. Community-level shifts are observed from the Pliensbachian-Toarcian boundary, but the onset of the negative carbon excursion (NCIE) that marks the event is coeval with the most significant turnover: a switch from a high-diversity vegetation with conifers, seed ferns, cycads, bennettites and ferns to drought-adapted low-diversity flora with Cheirolepidiaceae. The demise of forests and lowland mire biomes resulted in deforestation with increased weathering and soil erosion that exacerbated the terrestrial ecosystem crisis already under stress from rising temperatures. Terrestrial recovery was initiated before the end of the Jenkyns Event with the resurgence of pioneer ferns and lycopsids that colonized disturbed habitats. Plant assemblages signal aridification at the onset of the event with frequent climatic oscillations and extreme weather patterns during the event itself. The main NCIE phase was preceded by a short-lived cooling phase in the earliest Toarcian. In the aftermath of the NCIE, Cheirolepidiaceae forests declined and a more stable biome developed with seed ferns and various conifers. This was contemporaneous with delta development and shallowing of the lake surrounded by lowland mires with ferns, clubmosses and horsetails. Comparison of floral patterns across the Jenkyns Event show that, although Cheirolepidiaceae dominated the event globally, there were differences in vegetation response between coastal and inland areas, and recovery patterns might differ regionally.