TEMPERATURE SEASONALITY IN CONTINENTAL NORTH AMERICA DURING THE EARLY EOCENE CLIMATIC OPTIMUM

Greenhouse climate equability has long been a paradox in paleoclimate research, but recent proxy and modeling work suggests that strong seasonality may be a feature of at least some greenhouse periods as well. The Paleogene is characterized by global greenhouse conditions punctuated by a series of hyperthermal events, which provides an ideal period for testing theoretical greenhouse equability by using new methods in high resolution paleothermometry to describe past temperature seasonality. Here we present the first multiproxy record of seasonal temperatures from floral assemblage, paleosol geochemistry, and carbonate clumped isotope thermometry from the Green River Basin (Wyoming, USA) during the Early Eocene Climatic Optimum (EECO). These paired temperature records allow for the reconstruction of past seasonality in the continental interior, which shows that temperatures were warmer in all seasons during the peak EECO and that mean annual range of temperature was high, similar to modern values (~26°C). Proxy data suggest increased seasonality during greenhouse events as compared to Eocene regional climate model results of the same region, which is similar to increased seasonality predicted by downscaled climate model ensembles for future high-emissions scenarios. Overall, these data and model comparisons have important implications for understanding greenhouse climates in general, and may be crucial for predicting future seasonal climate regimes and their impacts in continental regions.