A Song of Ice and a Warm Southern Ocean: The paleoceanographic evolution of the Oligocene–Miocene Southern Ocean

Abstract

The Oligocene-Miocene (~34-5 Ma) was likely characterized by globally relatively warm temperatures, high and variable CO2 levels (300-750 ppm) and fluctuating Antarctic ice volumes, and can thus function as a past analogues for future climates, considering the projected atmospheric CO2 concentrations for the end of this century and beyond. Yet, fundamental questions remain about the past Southern Ocean structure and its role in the (in)stability of Antarctic ice-sheets from this critical deep time slice. With my collaborators, in this thesis, I provide this context by reconstructing the latitudinal SST gradients, variability and position of ocean frontal systems and oceanic environmental conditions of Tasmanian Gateway and Drake Passage regions of the Southern Ocean from the Late Eocene until Late Miocene (37-5 Ma) using new TEX86-based SSTs and dinoflagellate cyst assemblage data. By quantifying Oligocene to Miocene oceanic conditions from critical locations around Antarctica we provide new insights for an improved mechanistic understanding of Southern Ocean paleoceanographic evolution. This involves new reconstructions of Southern Ocean circulation and frontal system migrations during past warm Oligocene and Miocene climates, which shows us how the southern polar ocean operates under warmer-than-present-day conditions. The information on Southern Ocean sea surface temperature and ecology/environment provided in this thesis can be used as fundamental boundary condition to improve model simulations and to test the fitness of models simulating past oceanographic conditions.