Vegetation change across the Drake Passage region linked to late Eocene cooling and glacial disturbance after the Eocene–Oligocene Transition

• Main Authors: Thompson, Nick, Salzmann, Ulrich, López-Quirós, Adrián, Bijl, Peter K., Hoem, Frida S., Etourneau, Johan, Sicre, Marie-Alexandrine, Roignant, Sabine, Hocking, Emma, Amoo, Michael, Escutia, Carlota
• Format: Text
• Language: English
• Published: 2021
• Subjects: Antarctic; Drake Passage; Powell Basin; Weddell; Weddell Sea; Antarc*
• Online Access: https://doi.org/10.5194/cp-2021-84; https://cp.copernicus.org/preprints/cp-2021-84/

The role and climatic impact of the opening of the Drake Passage and how it affected both marine and terrestrial environments across the Eocene-Oligocene Transition (EOT ~ 34 Ma) period remains poorly understood. Here we present new terrestrial palynomorph data compared with recently compiled lipid biomarker (n-alkane) data from Ocean Drilling Program (ODP) Leg 113 Site 696 drilled on the margin of the South Orkney Microcontinent in the Weddell Sea, to investigate changes in terrestrial environments and paleoclimate across the late Eocene and early Oligocene (~ 37.6–32.2 Ma). Early late Eocene floras and sporomorph-based climate estimates reveal Nothofagus -dominated forests growing under wet temperate conditions, with mean annual temperature (MAT) and precipitation (MAP) around 13 °C and 1660 mm, respectively. A phase of latest Eocene terrestrial cooling at 35.5 Ma reveals a decrease in MAT by around 2 °C possibly linked to the opening of the Powell Basin. This is followed by an increase in Mesozoic sporomorphs together with a shift in terrestrial biomarkers and sedimentological evidence indicating ice expansion to coastal and shelf areas approximately 34.1 million years ago. However, major changes to the terrestrial vegetation at Site 696 did not take place until the early Oligocene, where there is a distinct expansion of gymnosperms and cryptogams accompanied by a rapid increase in taxa diversity following 33.5 Ma. This unusual expansion of gymnosperms and cryptogams is suggested to be linked to environmental disturbance caused by repeat glacial expansion and retreat, which facilitated the expansion of conifer and ferns. We conclude that the timing of glacial onset rather suggests that the event at site 696 is linked to the global cooling at the EOT and that latest Eocene regional cooling cannot directly be linked. Therefore, confirming that the opening of ocean gateways alone did not trigger Antarctic glaciation, even if ocean gateways may have played a role in stepwise cooling before the EOT.