Planktic foraminiferal response to the Early Eocene Climatic Optimum (EECO) from southern mid-to-high latitudes

The Early Eocene Climatic Optimum (EECO; ~53–49 Ma) records the warmest long-term global average tem- perature and CO2 levels of the Cenozoic and is punctuated by multiple transient global warming events (hyperthermals), providing a significant opportunity to investigate the impact of extreme heat on planktic foraminifera, a key group of marine calcifiers highly sensitive to paleoenvironmental changes. Studies on Atlantic and Pacific Oceans documented a dramatic decline in abundance and diversity of the symbiont-bearing genus Morozovella close to the EECO onset (J event), and a corresponding permanent increase in the abundance of Acarinina. We extend the record to southern high-latitude locations on the Australia margin to provide a global perspective on planktic foraminiferal resilience to the EECO. We present planktic foraminiferal biostratigraphy, quantitative abundance and dissolution from Hole 762C (Exmouth Plateau, Indian Ocean) and Site U1510 (Tasman Sea, Pacific Ocean). Despite core breaks, these sites record multiple hyperthermals within the EECO. Our results suggest that cooler conditions at higher latitudes may have mitigated the decline of Morozovella observed at Atlantic and tropical Pacific sites. At Hole 762C and Site U1510, Acarinina dominates the assemblage, demonstrating the greatest ecological flexibility. The disappearance of the genus Chiloguembelina from the K/X hyperthermal through the EECO in the studied sites may represent a global event as it occurred at the same level in the Atlantic and tropical Pacific. This study from higher southern latitudes enhances our understanding of global planktic foraminiferal resilience to the EECO underlying similarities and differences constrained by the diverse geological settings.