Calcareous Nannofossils and Paleoclimatic Evolution Across the Eocene-Oligocene Transition at IODP Site U1509, Tasman Sea, Southwest Pacific Ocean

• Published in: Paleoceanography and Paleoclimatology
• Main Authors: Viganò, A., Dallanave, E., Alegret, L., Westerhold, T., Sutherland, R., Dickens, G. R., Newsam, C., Agnini, C.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2024
• Subjects: Antarc*; Antarctic; Antarctica
• Online Access: http://zaguan.unizar.es/record/132859; https://doi.org/10.1029/2023PA004738

The Eoceneâ€Oligocene transition (EOT; ∼34 Ma) was one of the most prominent global cooling events of the Cenozoic, coincident with the emergence of continentalâ€scale iceâ€sheets on Antarctica. Calcareous nannoplankton experienced significant assemblage turnover at a time of longâ€term surface ocean cooling and trophic conditions, suggesting causeâ€effect relationships between Antarctic glaciation, broader climate changes, and the response of phytoplankton communities. To better evaluate the timing and nature of these relationships, we generated calcareous nannofossil and geochemical data sets (δ18O, δ13C and %CaCO3) over a ∼5 Myr stratigraphic interval recovered across the EOT from IODP Site U1509 in the Tasman Sea, South Pacific Ocean. Based on trends observed in the calcareous nannofossil assemblages, there was an overall decline of warmâ€oligotrophic communities, with a shift toward taxa better adapted to cooler more eutrophic conditions. Assemblage changes indicate four distinct phases caused by temperature decrease and variations in paleocurrents: late Eocene warmâ€oligotrophic phase, precursor diversityâ€decrease phase, early Oligocene coldâ€eutrophic phase, and a steadyâ€state cosmopolitan phase. The most prominent shift in the assemblages occurred during the ∼550 kyrâ€long precursor diversityâ€decrease phase, which has relatively high bulk δ18O and %CaCO3 values, and predates the phase of maximum glacial expansion (Earliest Oligocene Glacial Maximum–EOGM).