Global Changes in Terrestrial Vegetation and Continental Climate During the Paleocene-Eocene Thermal Maximum

Most studies of the response of terrestrial vegetation to climate change during the Paleocene-Eocene Thermal Maximum (PETM) have focused on individual sites and sections. To get a broader perspective we compiled published records of terrestrial pollen and spores across the Paleocene-Eocene transition at 38 sites around the globe. For the 10 sites with quantitative data PETM palynofloras were largely distinct in composition from those in the latest Paleocene or post-PETM early Eocene. We also inferred paleoclimatic conditions at each site from the distributions of nearest living relatives (NLRs) of fossil pollen taxa among present-day Koppen climate types. The NLRs of Paleocene high-paleolatitude palynotaxa are most diverse in cooler climates, whereas the NLRs of PETM taxa are more diverse in warmer, wetter climates. At middle-paleolatitudes NLRs of Paleocene palynotaxa are most diverse in warm, wet climates, whereas NLRs of PETM palynotaxa are most diverse in warm, seasonally dry climates. In the tropics there is little change from Paleocene to PETM in the climate distributions of NLRs. We compared changes in paleoclimate reconstructed from the Koppen distributions of the NLRs with those simulated from the Community Earth System Model (version CESM1.2). Paleoclimatic changes during the PETM inferred from palynological proxies are mostly consistent with modeled climate changes, including the expansion of temperate climates at the expense of cold climate types at high-paleolatitudes and the expansion of temperate and tropical climates in middle-paleolatitudes. Despite this concordance, modeled winter temperatures in continental interiors and high-paleolatitudes remain colder than those reconstructed from NLR distributions.