Resilient tropical marine ecosystems during early Eocene global warming events

Biotic response across the Paleocene−Eocene Thermal Maximum (PETM; 56 Ma) is well documented, but information for other, lower-magnitude, early Eocene transient global warming events (hyperthermals) is sparse. We studied dinoflagellate cyst assemblages across six post-PETM hyperthermals (I1, I2, J, K, L1, and L2; 53.7−52.0 Ma) in the eastern tropical Atlantic Ocean. Remarkably, we observe no assemblage changes associated with the hyperthermals, which starkly contrasts the demise of eukaryotes during the PETM and harmful algal blooms associated with long-term warming during the Middle Eocene Climatic Optimum (ca. 40 Ma) at the same site. However, our results mimic observations of resilient calcareous nannoplankton assemblages to certain lower-magnitude hyperthermals in the tropical Pacific. We conclude that tropical early Eocene phytoplankton communities were resilient to multimillennial-scale warming of up to ∼1.5 °C.