SIMULATING CENOMANIAN CLIMATE WITH THE COMMUNITY EARTH SYSTEM MODEL

The Cenomanian (~100-94 Ma) was an interval of extreme warmth during the Cretaceous with ice-free polar regions and a significantly reduced meridional temperature gradient relative to present day. The warm climate of the Cenomanian, and the Cretaceous in general, is often ascribed to elevated GHG concentrations. By increasing CO₂, modeling studies have been able to replicate global-average temperature of the Cenomanian. However, the latitudinal temperature distribution remains difficult to simulate by way of greenhouse gas (GHG) concentrations alone, suggesting other factors such as ocean circulation and vegetation are partly responsible for the paleoclimate. Here we simulate the Cenomanian using a detailed paleogeographic reconstruction in NCAR's CESM model, which comprises CAM5, POP2, CICE4, and CLM4 with dynamic vegetation. For our baseline experiment, we hold CO₂ constant at 4-times preindustrial and maintain present day orbital configuration with an appropriately lowered solar constant. Preliminary model results show a reduced equator-to-pole temperature gradient, increased precipitation, and a global-average surface temperature roughly 9°C warmer than present day. In our results, a small amount of seasonal sea ice exists, mainly in the shallow Artic. We compare our outputs with those from a similarly configured Hadley Centre model (HadCM3) simulation to help identify common features of the Cenomanian climate. By combining several models and proxies, we create a robust representation of this unique climate as well as identify potential model deficiencies and proxy biases. These results are part of a series of 4 simulations that explore the importance of paleogeography in the proxy identified large-scale climate changes of the Cretaceous period.