On the impact of astronomical forcing on ocean anoxia

The Devonian is a warmer-than-present geological period spanning from 419 to 359 million years ago (Ma) characterized by 29 identified ocean anoxic/hypoxic events. Despite decades of extensive investigation, no consensus regarding the mechanisms responsible for ocean anoxia has been achieved. Our study contributes to this general research effort, focuses on the astronomical pacing of anoxia throughout the Devonian and is substantiated by growing geologic records suggesting a link between astronomical forcing and anoxic events during this period. To investigate the role of the astronomical forcing we used the Earth system Model of Intermediate Complexity (EMIC) cGENIE, which has proven to be a reliable choice to simulate ocean oxygen spatial patterns and values. In this project, we first tested the impact of continental configuration and ocean biogeochemistry (pCO$_2$, PO$_4$ and pO$_2$) on the equilibrium of the system and the related dissolved ocean oxygen concentration. Then, we produced an in-depth analysis of the astronomical forcing contribution to ocean anoxia for well-chosen continental reconstruction and biogeochemical quantities values. Our results indicate that variations in continental configuration, even small, can exert a strong impact on ocean anoxia, underscoring the influence of paleoreconstructions uncertainties on the biogeochemical tracers of cGENIE. The astronomical forcing reveals to be able to modify the nature of the equilibrium of the system, going from a single-state value solution to an oscillatory behaviour. Our findings also offer insights into potential ocean lockdown mechanisms, providing plausible explanations for the prolonged persistence of certain anoxic events over several hundred thousand years.