Exploring Neoproterozoic climate and biogeochemical evolution in the SCION model

The Neoproterozoic Era (1000–539 Ma) saw extreme changes in climate and biogeochemical cycles, but the drivers of these changes remain poorly understood. In this paper, we extend the Spatial Continuous Integration (SCION) global climate-biogeochemical model beyond the Phanerozoic and into the Neoproterozoic using a set of GCM simulations to update the model's climate emulator and a plate tectonic model to estimate tectonic input fluxes. We use the model to explore to what degree changes in paleogeography and degassing rates—which are key drivers of Phanerozoic climate—can explain the broad pattern of Neoproterozoic environmental change. We find that while the known Neoproterozoic climate changes are generally within the model uncertainty envelope, and the model predicts cooling between the later Tonian and Earliest Cryogenian, we do not reproduce a clear greenhouse to icehouse transition here, or any long-term increases in atmospheric oxygen levels before the Ediacaran. Several key model limitations currently prevent it from testing these ideas in more detail and should be improved in future work. These include: dynamic continental lithology, climate simulations which include dynamic continental ice sheets, a more comprehensive estimate of degassing rates, a better representation of the evolution of primary producer groups (i.e. planktonic cyanobacteria and green algae) and the spatial structure of marine biogeochemistry, and a dynamic calcium cycle. We anticipate that these can all be tested in the future within the SCION framework.