EVOLUTION OF LATE CRETACEOUS MERIDIONAL TEMPERATURE GRADIENTS

During the Late Cretaceous, Earth’s climate experienced a shift from the warmest conditions of the past ~100 Myr, the Cenomanian-Turonian super-greenhouse (~100-90 Ma), to the relatively cooler greenhouse climate of the Campanian-Maastrichtian (~80-66 Ma). Despite considerable proxy data and climate modeling efforts, Late Cretaceous climate dynamics are still poorly understood. Existing temperature proxy data suggest that latitudinal temperature gradients were much shallower during the super-greenhouse as compared to today, although climate models often have difficulty reproducing these patterns. Here, we present the first carbonate clumped isotope (Δ₄₇) temperature estimates from fossil mollusks within the Western Interior Seaway (WIS) during the warmest, highest CO₂ interval of the Late Cretaceous, the Cenomanian-Turonian, together with new Δ₄₇ data from the lower CO₂ interval of the Campanian-Maastrichtian. Our Δ₄₇ temperatures agree well with previous proxy estimates (TEX₈₆ and δ¹⁸O) and confirm that the mid-latitudes experienced cooling of up to ~10°C during the Late Cretaceous. Combining all proxy data, from this study and previous including Δ_47, TEX₈₆ and δ¹⁸O, the absolute latitudinal gradient steepens significantly from the Cenomanian-Turonian (~0.07 °C/°latitude) into the Campanian-Maastrichtian (~0.4 °C/°latitude). This contrasts with prior model results of temperature gradients across these interval, which suggest very little change, and suggest that meridional climate dynamics representative of extreme greenhouse worlds have yet to be captured by climate models.