Paleosol-Based Reconstruction Indicates Decoupling of Mean Annual Precipitation and Precipitation Intensity During the Paleocene-Eocene Thermal Maximum in the Uinta Basin, Utah

The Earth is transitioning to a state unprecedented in human history. This transition poses a challenge for predicting the future, as climate models require testing and calibration with real-world data from high greenhouse gas climates. Despite significant progress in climate modeling, changes in the precipitation remain highly uncertain. The Paleocene-Eocene Thermal Maximum (PETM) was the warmest period of the Cenozoic Era, and thus serves as an analog for a hydrological cycle altered by extreme greenhouse gas warming. Here, we use paleosol-based geochemical proxies to quantify changes in mean annual precipitation (MAP) during the PETM in the Uinta Basin, Utah. We find no change in MAP during this warming event. However, paleosol mass balance results track increased translocation of carbonates, increased clay illuviation, and increased accumulation of redox-sensitive elements. These results, along with shifts in fluvial stratigraphy, provide evidence for increased intensity and intermittency of extreme precipitation events that may be related to changes in the transport direction, seasonality, and moisture transport capability of the North American Monsoon. Surprisingly, changes in fluvial stratigraphy, clay illuviuation, and redoximorphy continued for 10⁵–10⁶ years after the PETM, suggesting persistent changes in precipitation intensity despite a decrease in global temperature. These findings provide further support for an intensification of the hydrological cycle during and after the PETM, provide evidence for a decoupling between mean and extreme precipitation, and indicate the importance of multi-proxy, regional studies for understanding the complexities of climate change.