A high-resolution investigation of the eocene-oligocene climate transition: the dawn of the cenozoic icehouse world

• Main Author: Holmstrom, Max, Johan
• Format: Thesis
• Language: English
• Published: University of Southampton 2021
• Subjects: Antarctic; Antarc*; Newfoundland; Northwest Atlantic
• Online Access: https://eprints.soton.ac.uk/451560/; https://eprints.soton.ac.uk/451560/1/MJH_PhD_Thesis_Aug2021.pdf; https://eprints.soton.ac.uk/451560/2/Holmstrom_Permission_to_deposit_thesis_form_signed.docx

Global cooling and continental-scale expansion of Antarctic ice sheets occurred approximately 34 million years ago (Ma) during a period of climatic restructuring known as the Eocene-Oligocene Climate Transition (EOT). At this time, the Earth transitioned from the warm greenhouse climate state of the Eocene to the modern icehouse setting that still dominates today. Major changes in marine chemistry and ecosystems accompanied climate change and lowered sea levels, including deepening of the calcium carbonate compensation depth and accelerated turnover in marine plankton. Understanding of EOT climate change, however, is currently limited by the lack of welldated, continuous, and highly resolved marine geochemical records, especially from the Atlantic Ocean. New detailed EOT records are particularly needed to assess relationships between global climate change and potential driving mechanisms, such as changes in atmospheric CO2 and orbital configuration. Thus, with the aim of precisely evaluating the timing, magnitude, and pacing of the climate change leading up to and following the transition, I developed new high-resolution biostratigraphic, lithological, and foraminiferal stable isotope records from two sites in the Atlantic Ocean: (i) Integrated Ocean Drilling Program Expedition 342 Site U1411 on the Newfoundland Margin, Northwest Atlantic Ocean, and (ii) Ocean Drilling Program Leg 208 Site 1263 on Walvis Ridge, Southeast Atlantic Ocean. These records provide a new perspective both on the long-term and short-term climate evolution across the EOT, revealing a distinctive negative carbon isotope excursion at the onset of the EOT, high-amplitude climate cycles on short (~20–40 kyr) astronomical timescales, and a restructuring of the upper water column in the Northwest Atlantic across the EOT. In Chapter 2, a revised composite depth scale and astronomically tuned age model for Site U1411 is presented. The new age model is based on tuning of elemental records generated via Xray fluorescence (XRF) core scanning. ...