Abstract
A major climate shift took place about 40 Myr 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 (~46–34 Myr) of southern Patagonia. Robust nonparametric estimators indicate that floras in southern Patagonia were in average ~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.
Highlights
A major climate shift took place about 40 Myr ago—the Middle Eocene Climatic Optimum or MECO—triggered by a significant rise of atmospheric CO2 concentrations
The Middle Eocene Climatic Optimum occurred about 40 million years ago, interrupting that cooling trend when vast amounts of CO2 were injected into the atmosphere, and sea surface temperature increased as much as 6 °C1
We detected three major groups of samples based on our cluster analysis using dinocyst frequency (Supplementary Data 1; Supplementary Fig. 3), probably driven by shifts in the most frequent species through the composite section: Enneadocysta dictyostila. This is a key species of the Middle Eocene Climatic Optimum (MECO) in the southernmost latitudes
Summary
A major climate shift took place about 40 Myr ago—the Middle Eocene Climatic Optimum or MECO—triggered by a significant rise of atmospheric CO2 concentrations. The Middle Eocene Climatic Optimum (or MECO) occurred about 40 million years ago, interrupting that cooling trend when vast amounts of CO2 were injected into the atmosphere, and sea surface temperature increased as much as 6 °C1. This warming event—widely recognized by a prominent perturbation in both oxygen and carbon stable isotopes—lasted about 500–600 Kyr[2,3]. Our study reinforces the importance of the fossil spore-pollen record to explore past diversity trends and represents a new explicit picture of how floras responded to a greenhouse event in America’s highest austral latitudes
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