[B-CG07] Decoding the history of Earth: From Hadean to the present

[BCG07-09] Responses of the global carbon cycle to the eruption of large igneous provinces over the Phanerozoic time

★Invited Papers

*Yasuto Watanabe^1,2, Hironao Matsumoto³, Eiichi Tajika¹ (1.The University of Tokyo, 2.Meteorological Research Institute, 3.JAMSTEC)

Keywords:Phanerozoic, Large Igneous Province

Formations of large igneous provinces (LIPs) are voluminous magmatic events that are often ascribed to the upwelling of a mantle plume (e.g., Ernst et al., 2021). The eruption of LIPs strongly affects the climatic and environmental state of the ocean–atmosphere system by supplying greenhouse gasses (i.e. CO₂). Such CO₂ influxes would enhance the riverine nutrient supply and trigger the deoxygenation of the ocean, namely the ocean anoxic event (OAE). Many studies have previously explored the impact of the eruption of LIPs on the atmospheric composition and marine redox states (e.g., Beerling and Berner, 2002; Ozaki and Tajika, 2013). However, the factors that affect the magnitude of the LIP-related environmental fluctuation in the history of the Earth have not been systematically demonstrated. Here we investigate the response of the global carbon (C) and phosphorus (P) cycles to the eruption of LIPs using a biogeochemical model that considers the global C–P cycles and the land and marine biospheres. We validate the model by simulating the evolutions of the background climate state throughout the Phanerozoic and the response of the system to the actual LIP eruptions, such as the eruption of the Ontong Java Nui (OJN) at ~120 Ma. We discuss the different responses of the land and marine biospheres after the eruption of LIPs. We then evaluate the potential sensitivity of the global C–P cycles to the LIP-induced CO₂ influx for various ages over the Phanerozoic time.

We show that our biogeochemical model successfully simulates the long-term evolution of the background climate state over the Phanerozoic as consistent with the records of the past pCO₂ proxies (Foster et al., 2017) and the δ¹³C signals after the eruption of the OJN. We also show that the magnitude of the perturbation in the global C cycle after the LIP eruption depends on the terrestrial weatherability. The maximum atmospheric pCO₂ achieved after the eruption of LIP tends to be high during the Permian and Triassic, owing to the arid climate and low riverine runoff on Pangaea during this period (e.g., Goddéris et al., 2012). We also show that the riverine P supply rate is sensitive to the eruption of LIP when the terrestrial weatherability is high. This result indicates that the magnitude of the variations of atmospheric pCO₂ after the eruption of LIP are not necessarily related directly to the magnitude of the variations in the marine P cycle. We further show that the magnitudes of the variations of δ¹³C are also dependent on terrestrial weatherability. When the terrestrial weatherability is high, the positive δ¹³C signals after LIPs eruption is large and the negative δ¹³C signals are small. This may have led to the stronger positive δ¹³C signals relative to the negative δ¹³C signals after the eruption of LIPs during the Cretaceous than those during the Permian and Triassic. These findings would help to understand the dynamics of the global C–P systems after the eruption of LIPs during the Phanerozoic.