Can CO2 degassing explain the climate and biogeochemical perturbations during Cretaceous OAE2?

The Late Cretaceous is characterized by extreme greenhouse conditions with high temperatures and high atmospheric pCO2 that have been proposed to be directly linked to the emplacement of large igneous provinces (Caribbean and Madagascar LIP). As a result of these extreme conditions, an increase in organic carbon burial has been recorded on a global scale during Oceanic Anoxic Event 2 (OAE2, ~94.5 Ma), which has been linked to amplified continental weathering1,2 and increased marine nutrient availability. However, despite the event being well studied, a model that directly estimates the combined biogeochemical effects of LIP-derived CO2 input – and compares this to the combined geological record –is lacking. Here we use a new biogeochemical ocean-atmosphere-sediment multi-box model3 which produces a self-consistent estimate of the global C, O, Fe, S and P cycles across the marginal and deep ocean, and we explore the outputs of this model for carbon isotope excursions (CIEs) in carbonates and organic carbon as well as for high and low latitude paleo-sea-surface temperatures (SSTs) under a LIP CO2 degassing scenario for OAE2. The model results indicate that in order to reproduce both the global SST records and CIEs, the annual rate of volcanic input of CO2 must be higher than the estimated range from previously published research. Furthermore, to reproduce the magnitude of the positive CIEs, the model requires an additional source of bioavailable iron beyond that which is liberated through global weathering enhancement under high CO2. We investigate the possibility that hydrothermal input of Fe to the deep ocean during LIP activity helped boost productivity during OAE2, and suggest that the balance between tectonic inputs of CO2 and limiting nutrients may help explain why some OAEs are accompanied by positive carbon isotope excursions and some by negative excursions. References: 1 Pogge von Strandmann et al., 2013, Nature Geoscience 2 Nana Yobo et al., 2021, GCA 3 Zhao et al., 2023, Nature Geoscience