Astronomical forcing and anoxia during the Devonian: Insights from Earth system modeling

The Devonian period, spanning from 419 to 359 million years ago, was marked by a warmer-than-present climate and recurring ocean anoxic events (OAEs), with evidence increasingly suggesting a link between these events and astronomical forcing. Our study aims to investigate how astronomical forcing can initiate ocean anoxic events, revealing the spatial manifestation of these perturbations and assessing whether they remain regionally confined or escalate into global-scale phenomena. To this end, we employed the Earth System Model of Intermediate Complexity (EMIC) cGENIE, forced with spatially distributed continental reactive phosphorus fluxes. The coupling is performed offline with the dynsoil module of GEOCLIM, itself coupled to a statistical emulator of the Devonian climate, trained on a general circulation model (namely HadSM3). This coupling ensures the effects of more complex processes related to astronomical forcing that EMICs can hardly resolve. cGENIE is run transiently over a 1 Myr astronomical solution, crossing a 2.4 Myr eccentricity node, allowing us to capture the dynamic interplay between astronomical cycles and ocean oxygenation, mainly through the alteration of weathering. By exploring multiple variations of this astronomical solution, we aim to disentangle the respective contributions of individual astronomical parameters to the perturbation of the system. Furthermore, two experimental setups characterized by different atmospheric pCO₂ levels, one high (2000 ppm) and another low (500 ppm), are considered, enabling us to investigate the impact of astronomical forcing under both "warm" and "cold" Devonian climate scenarios.