The Climate of Earth's Next Supercontinent: Stable Ocean Circulation States

Earth's continents assemble into supercontinents and subsequently disperse in cycles of 400 – 600 million years. The next supercontinent is predicted to form in about 250 million years. Previous studies of future supercontinent climate have focused on surface climate and atmospheric circulation only, so this study explores how small changes in astronomical forcing―future increased solar radiation and longer day lengths―could impact ocean circulation and climate. We simulated two scenarios using present-day or future astronomical forcing for one of the possible future continental arrangements, Aurica, using the fully-coupled climate model ROCKE-3D. Future orbital forcing leads to a 4.4°C rise in global surface temperatures and a shift towards an ice-free state. Ocean circulation transitions from a gyre-dominated state to an overturning circulation with deep water formation at subpolar latitudes, similar to present-day Earth's ocean circulation. This change in ocean circulation state is driven by interactions between the atmospheric circulation, altering rainfall and evaporation patterns, and changes in the transport of salt in the oceans. Our work adds to a growing body of evidence that, for the same continental configurations, multiple stable ocean circulation states may exist. We also emphasise that fully-coupled climate models (i.e., atmosphere and oceans) are needed to understand deep-time climate states.