MODELING THE CONTROLS ON MARINE HABITABILITY

Habitability of the ocean is shaped by a complex interplay of changing environmental (i.e., greenhouse warming, atmospheric oxygen levels, and evolving carbon, oxygen, and nutrient cycles) and tectonic (i.e., continental configuration) boundary conditions. Elucidating how these factors interact in determining the spatial distribution and fraction of the seafloor suitable for animal life is critical if we are to understand both the drivers of extinction as well as long-term evolutionary trends through the Phanerozoic. Here we present the results of an Earth system model analysis of how the key controlling factors combine to determine habitability.

We apply the cGEnIE Earth system model configured in three contrasting idealized continental configurations to explore tectonic drivers of habitability, and vary atmospheric CO₂, atmospheric O₂, and the ocean nutrient inventory (and hence the strength of the biological pump) to assess the role of changing environmental boundary conditions. These we combine in all possible permutations in a large ensemble of model experiments. We then evaluate the model results in terms of the extent and pattern of seafloor anoxia and euxinia. We find that certain boundary conditions are more influential than others in limiting the habitable space of each model world. For instance, the combination of a modern biological pump strength and low atmospheric O₂ leads to the lowest benthic habitat availability, and exerts a greater influence on seafloor anoxia than do continental configuration and atmospheric CO₂. Our idealized model results provide an empirical basis for addressing broader questions of how different Earth system states vary in their sensitivity to perturbations (i.e., massive carbon dioxide emissions), susceptibility to extinction, and overall suitability for life.