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

Thompson, Alasdair, Salzmann, Ulrich, López-Quirós, Adrián, Bijl, Peter K., Hoem, Frida S., Etourneau, Johan, Sicre, Marie-Alexandrine, Roignant, Sabine, Hocking, Emma, Amoo, Michael and Escutia, Carlota (2021) Vegetation change across the Drake Passage region linked to late Eocene cooling and glacial disturbance after the Eocene–Oligocene Transition. Climate of the Past Discussions. cp-2021-84. ISSN 1814-9324

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The role and climatic impact of the opening of the Drake Passage and how it affected both marine and terrestrial 15 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, 20 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 25 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 30 if ocean gateways may have played a role in stepwise cooling before the EOT.

Item Type: Article
Additional Information: Funding information: NT received funding from the Natural Environment Research Council (NERC)-funded Doctoral Training Partnership ONE Planet [NE/S007512/1]. Funding for this research was also provided by the Spanish Ministry of Science and Innovation (grants CTM2014-60451-C2-1/2-P and CTM2017-89711-C2-1/2-P) cofounded by the European Union through FEDER funds. This work used Deep Sea Drilling Project archived samples provided by the International Ocean Discovery Program (IODP). We thank the staff at the Gulf Coast core repository (GCR) for assistance in ODP Leg 113 core handling and shipping. We thank CNRS for the salary support of MAS.
Uncontrolled Keywords: Disturbance (geology), Geology, Glacial period, Global cooling, Mesozoic, Paleoclimatology, Paleontology, Period (geology), Structural basin, Vegetation
Subjects: F700 Ocean Sciences
F800 Physical and Terrestrial Geographical and Environmental Sciences
F900 Others in Physical Sciences
Department: Faculties > Engineering and Environment > Geography and Environmental Sciences
Depositing User: Rachel Branson
Date Deposited: 19 Oct 2021 08:58
Last Modified: 21 Oct 2021 12:00

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