Spatial patterns of temperature and hydroclimate during the Paleocene-Eocene Thermal Maximum: Fingerprints of a warmer world

The Paleocene-Eocene Thermal Maximum (PETM; ca. 56 Ma) is one of the best known hyperthermal events in Earth History. Numerous studies have investigated the changes in temperature and hydroclimate during this event, but a spatial picture has remained elusive given limited proxy coverage. Here, we use paleoclimate data assimilation to produce a spatial view of climate change during the PETM that is informed by both proxy and model information. The assimilation combines proxies for sea-surface temperature and surface air temperature with isotope-enabled modeling simulations conducted with iCESM 1.2. The assimilated product includes precipitation isotopes, facilitating comparison with plant wax hydrogen isotopic data. The reconstruction enables precise quantification of global mean surface temperature increase and polar amplification during the PETM; notably, the magnitude of global warming (6C) is larger than previously published estimates. Reconstructed patterns in precipitation show an increase in the tropics and mid-to-high latitudes, with decreases focused in off-equatorial and subtropical regions. We find that the isotopes of precipitation are more enriched during the PETM on a global basis, with depletion limited to areas of large precipitation increases. Even though the continental configuration is different, the patterns of climate change during the PETM mimic future projections, providing constraints on the reorganization of the climate system under elevated CO2 levels.