The Toarcian Oceanic Anoxic Event (T-OAE, ~183 Ma) was a profound global hyperthermal event in deep-time that triggered large-scale ocean deoxygenation and ecological disruption. Interestingly, the extreme climatic forces associated with this hyperthermal likely exerted an equivalent impact on terrestrial environment. Nonetheless, possible fluctuations in water-column redox, nutrient supply and other biogeochemical dynamics in the coeval lacustrine environment remain largely unknown. During expansion of paleo-lakes in the Sichuan Basin and Ordos Basin, which are typical terrestrial lake systems in the T-OAE, elevated  productivity and organic matter burial have been proposed as negative feedback helping to sequester excess atmospheric pCO₂. However, the mechanism driving organic matter accumulation in lacustrine environments, and their causal links to biogeochemical cycling and regional climate conditions are poorly understood.
Here, this study aims to elucidate the terrestrial geochemical response from mid- and high-latitude environments during the T-OAE through analyzing organic carbon content, major and trace elements, and chemical indices of weathering in lacustrine sediments. Results show that the bottom waters in the Sichuan Basin were anoxic-ferruginous or weakly euxinic during the T-OAE. Beneath these redox conditions, phosphorus (P) was efficiently recycled into the water-column via anaerobic organic matter remineralization and the reductive dissolution of Fe (oxyhydr)oxide minerals. The extensive recycling of P stimulated eutrophication by increasing the availability of reactive phosphorus. Conversely, the oxic or suboxic condition of the Ordos Basin demonstrate no significant change in phosphorus recycling throughout the event.
Furthermore, climate modeling results indicate that high-latitude regions experienced obvious warming and increased aridity during the T-OAE, whereas lower-latitude regions saw increased precipitation, promoting higher nutrient input, eutrophication, redox stratification, and enhanced primary productivity. By synthesizing geological evidence and climate modelling results from multiple regions and systems, this study reveals the patterns of climatic and ecological responses at different latitudes during the TOAE. These findings highlight the varied regional expressions and impacts of global climate events on land, providing critical insights into the mechaniams of  deep-time paleoclimate dynamics and offering a basis for predicting the regional consequences of future climate change.
 

T-OAE, Lacustrine redox condition, P cycling, Fe speciation