Idealized Earth system model analysis of the primary controls on shallow seafloor oxygenation

Sherry Xu, Pincelli Hull, Andy Ridgwell, Dominik Hülse

Key components of the Earth system, including climate, atmospheric oxygen, the strength of the biological pump, and continental configuration, have varied substantially through time. How these factors might have interacted to shape the evolution of marine life—particularly the availability of viable animal habitat—remains unclear. Here, we apply an Earth system model to investigate how tectonic and environmental factors interact to affect the availability of oxic shallow seafloor habitats. We use three idealized continental configurations and run ensembles of model simulations with varying atmospheric CO₂ and O₂, as well as organic matter sinking rates, to assess their coupled influence on seafloor oxygenation. While the dominant control on benthic oxygenation is the partial pressure of oxygen in the atmosphere (pO2), we find that the efficiency of the biological pump and continental configuration exert strong secondary influences, both directly and through nonlinear interactions. In contrast, atmospheric CO2 has only a weak direct effect, influencing benthic oxygenation primarily through interactions with other drivers. We further show that the sensitivity of seafloor anoxia to environmental perturbations is strongly state-dependent, with the largest responses to changes in organic matter sinking rate occurring at intermediate atmospheric pO2, and that ocean structure plays a key role in modulating this sensitivity. Our model results highlight the importance of the interaction of multiple boundary conditions for understanding marine oxygenation. The idealized model worlds presented here provide a framework for addressing broader questions of how different Earth system states have shaped the history of life, and vice versa.