Dynamics of the Cretaceous Oceans: A Numerical Recipe

Recipe for OAE layer-cake: Take one whole fresh super-continent and break into pieces. Pick out the rock phosphate and place to one side. Immerse the continental fragments in seawater until the shelves and interior seaways are thoroughly flooded. Add a pinch of CO₂ and heat gently. While the ocean is warming and de-oxygenating, gradually stir in the phosphate that was put aside earlier. Keep stirring and adding CO₂ and phosphate until a thick black carbon crust suddenly forms. Remove the crust. Repeat to create as many carbon layers as possible before the cake starts to cool and the ocean re-oxygenates.

In this talk I will test this recipe using an Earth system model, discussing the potential role of sedimentary phosphate regeneration feedbacks in triggering carbon burial events, and the role of massive carbon burial in creating the necessary conditions to exit an OAE. I will also illustrate how the dynamics of entering and exiting an OAE depend on boundary conditions such as continental configuration and whether enhanced CO₂ out-gassing and weathering (and its attendant higher rate of nutrient supply to the ocean) is a sufficient trigger. Finally, in utilizing an isotope-enabled Earth system model (‘GENIE’ – http://mycgenie.seao2.org) in generating an OAE-like event, the plausibility of the recipe can be tested by analyzing the simulated phasing of climate, d¹³C, ocean redox, and carbon burial, which I will show contrasted with the geological record.