Global changes in terrestrial vegetation and continental climate during the Paleocene-Eocene Thermal Maximum

Studies of the response of terrestrial vegetation to climate change during the Paleocene-Eocene Thermal Maximum (PETM) generally have focused on individual sites and sections. To get a more global perspective 38 sites where terrestrial palynomorphs record the Paleocene-Eocene transition were compiled. At 10 sites for which quantitative counts of palynofloral composition were published PETM samples were largely distinct from latest Paleocene or post-PETM Eocene samples, but the type of floral change varies by latitude. We inferred climatic conditions at each site based on the distributions of nearest living relatives (NLRs) of fossil palynomorphs among Köppen climate types. At high-paleolatitudes NLRs of Paleocene palynotaxa are most diverse in cooler climates, whereas NLRs of PETM palynotaxa 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 in the climate distribution of NLRs of the fossil palynotaxa. Changes in Köppen climate reconstructed from palynofloras were compared to those simulated from Community Earth System Model (version CESM1.2). Inferences from palynological assemblages are mostly consistent with modelled climate changes. This includes the expansion of temperate climates at the expense of cold climate types at high-paleolatitudes, the expansion of temperate and tropical climates in middle-paleolatitudes and the expansion of arid and tropical climate types at low-paleolatitudes. Despite substantial similarity the continental interiors and high-paleolatitudes remain colder in the model than in the palynofloral reconstructions.