Impact of mid Eocene greenhouse warming on America's southernmost floras

A major climate shift took place about 40Myr ago-the Middle Eocene Climatic Optimum or MECO-triggered by a significant rise of atmospheric CO2 concentrations. The biotic response to this MECO is well documented in the marine realm, but poorly explored in adjacent landmasses. Here, we quantify the response of the floras from America's southernmost latitudes based on the analysis of terrestrially derived spores and pollen grains from the mid-late Eocene (similar to 46-34Myr) of southern Patagonia. Robust nonparametric estimators indicate that floras in southern Patagonia were in average similar to 40% more diverse during the MECO than pre-MECO and post-MECO intervals. The high atmospheric CO2 and increasing temperatures may have favored the combination of neotropical migrants with Gondwanan species, explaining in part the high diversity that we observed during the MECO. Our reconstructed biota reflects a greenhouse world and offers a climatic and ecological deep time scenario of an ice-free sub-Antarctic realm.

Automated summary

A research on the flora of southern Patagonia during the mid-late Eocene shows that the diversity of plant communities during the MECO period was on average 40% higher than in non-MECO periods, possibly due to the favorable combination of neotropical migrants with Gondwanan species in response to higher atmospheric CO2 concentrations and increasing temperatures.