Global and Southern High Latitude Vegetation and Climate Change across the Paleogene: Insights from Plant Functional Type Diversity and Terrestrial Palynomorphs

Abstract

The Eocene Epoch (56-34 Ma) experienced significant climate and vegetation changes, encompassing the warmest temperatures of the Cenozoic Era during the early Eocene (~56.0-48.1 Ma) and ending in the onset of Antarctic glaciation during the Eocene-Oligocene Transition (34.44–33.65 Ma). Understanding the drivers of past climate change, and involved feedback mechanisms, is essential in order to comprehend the trajectory of future Earth climate. This thesis employs palaeovegetation to reconstruct environmental and climatic conditions, focusing on the two distinct time intervals of the early Eocene and the Eocene/Oligocene. Focusing on the warmth and high CO2 world of the early Eocene, this thesis utilises macro- and micro-fossil palaeobotanical records, coupled with new Plant Functional Type analysis, improving our understanding of vegetation zona>on and the ecological and climatic gradients governing them. This study uncovers disparities between previous climate model experiments and the plant fossil record, indicating wetter subtropics and a reduced equatorial ever-wet zone, while highlighting differences between the Northern and Southern Hemisphere climate and vegetation. Notably, it underscores the roles of precipitation and temperature seasonality in shaping biomes during the early Eocene. Secondly, this thesis explores the possible role of the Eocene/Oligocene opening of the Drake Passage in the Antarctic region and how this event affected terrestrial environments. This work analyses terrestrial palynomorphs from ODP Site 696 in the Weddell Sea, along with samples from Chilean Isla Riesco and the Brunswick Peninsula, reconstructing the timing and nature of vegetation changes across the region. Results reveal a synchronous latest Eocene regional cooling step before the onset of Antarctic glaciation and subsequent disturbance related vegetation change. Importantly, this stepwise cooling coincides with abrupt changes to marine environments linked to the opening of oceanic gateways, suggesting a causal link. Overall, while this study highlights how CO2 induced climate conditions highly moderate the distribution of vegetation through factors such as surface temperature and precipitation, it also reveals the potential influence of ocean currents on climate. Furthermore, it provides a refined picture of vegetation within the high CO2 world of the early Eocene, serving as both a crucial boundary condition and a tool for evaluating climate model predictions.

Date of Award	25 Jul 2024
Original language	English
Awarding Institution	Northumbria University Newcastle University
Supervisor	Ulrich Salzmann (Supervisor), Emma Hocking (Supervisor) & Neil Ross (Supervisor)