Planktic Foraminifera updated biostratigraphy and quantitative abundances from Hole 762C at the Early Eocene climatic optimum (EECO, c.53–49 Ma)

The Early Eocene climatic optimum (EECO; ~53–49 Ma) is the interval when Earth surface temperatures and atmospheric 𝑝CO2 reached the peak of the Caenozoic. This past Earth global warming scenario offers possible model systems for the coming warming trend. In this respect, planktonic Foraminifera, a major group of open-marine calcifiers, play an essential role in palaeoclimatology reconstructions as they are extremely sensitive to palaeoenvironmental changes. Previous studies on Atlantic and Pacific Oceans recorded a dramatic decline in abundance and diversity of the symbiont-bearing genus Morozovella close to the carbon isotope excursion (CIE) J event (EECO beginning), in opposition to a permanent increase in abundance of genus Acarinina. In addition, the Morozovellaspecies switched their coiling direction (the ability to add chambers in clockwise or counter-clockwise) from dextral to dominantly sinistral within 200–400 kyrs after the CIE K/X event. The record from Atlantic and Pacific Oceans also underlines diachroneities among planktonic foraminiferal biohorizons. Here we present planktonic foraminiferal biostratigraphy, quantitative abundance, and coiling direction from Hole 762C (Exmouth Plateau). This site records several CIEs below and within the EECO, though affected by some core breaks. The southern high latitude location in the northwest margin of Australia makes this site appropriate for outlining a global perspective of plank-tic foraminiferal resilience to the EECO. The new biostratigraphic data here suggested the importance of an Eocene zonal scheme revision that can solve the diachronicity problems. Our results also record the Morozovella change in coiling direction from the K/X event as previously documented. This study improves the knowledge on global planktonic foraminiferal resilience to the EECO and provides new insights for a thoroughgoing investigation of past global warmings that is essential to improve the understanding of the current climate changes.