The Earth system changed significantly at the Eocene-Oligocene Transition (EOT), around 34 Million years ago. After gradual cooling through the late Eocene, there was a rapid expansion of ice over Antarctica associated with global cooling, recorded by multiple proxy records. This cooling was likely driven by declining atmospheric pCO2 levels; however, the underlying cause of the declining pCO2 remains a relatively open question, with the role of changing ocean gateways such as the Drake Passage still debated. Using a fully coupled 3-D climate model, this thesis explores the climatic and oceanic response of the Earth system to some of the major changes that occurred across the EOT. This was done by simulating the equilibrium climate response to multiple different sets of boundary conditions, for example different Antarctic ice sheet states, palaeogeographic reconstructions and atmospheric pCO2 levels. These simulations were used to address some fundamental questions regarding how the presence of the Antarctic ice sheet impacts on global and regional climate, and how sensitive palaeoclimate model simulations are to subtle changes in boundary conditions. It is shown that the inclusion of the Antarctic ice sheet in the model can result in high latitude warming, however, this response is highly sensitive to the boundary conditions used and the length of the model spin-up. To validate these model simulations (as well as simulations from other modelling groups) and to better understand the most plausible forcings and responses across the EOT, a large compilation of proxy temperature records was combined for the Southern Ocean and high latitude Southern Hemisphere. The evaluation suggests that modelled changes in response to opening of the Drake Passage are inconsistent with the temperature patterns recorded for the Southern Ocean, and that ice growth and pCO2 decline represent a more realistic mechanism of explaining the changes observed in the proxy records.
|Date of Award||25 Jun 2019|
- The University of Bristol
|Supervisor||A J Payne (Supervisor), Dan J Lunt (Supervisor) & Stephen Cornford (Supervisor)|