Changes in Climate and Moisture Availability in the Antarctic Eocene, Oligocene, and Miocene: Evidence from Palynological and Stable Isotope Geochemical Analyses of the SHALDRIL and ANDRILL Cores

Abstract

Prior to the Late Eocene, the Antarctic continent experienced lush vegetation under temperate conditions. Just before the Eocene/Oligocene Boundary, the climate of the southernmost continent began to deteriorate dramatically. This cooling trend largely continued until most Antarctic vegetation disappeared, ~13.85-12.8 Ma. Classifying the nature and cause of Antarctica’s drastic climate change is essential for furthering our knowledge of Earth’s history, and also for grasping the potential effects of current and future climate shifts. Here, I present evidence from three new palynomorph-centric studies that deepen our understanding of Antarctic earth science, climate change, and of climate proxies. The first study involved analyzing the stable carbon isotopes (δ13C) of Nothofagidites fusca palynomorphs from the Late Eocene, Antarctic Peninsula region. We found that pollen Δ13C generally decreased through time, just prior to the Eocene/Oligocene Boundary, suggesting a decrease in water availability to plants. This decrease in moisture availability was likely caused by increased glaciation, decreased run off, decreased precipitation, or a combination of these factors. In the second study, the potential for using Nothofagus sp. pollen size as a proxy for changes in moisture availability was assessed. We found a significant relationship between pollen grain size and precipitation (as precipitation decreased, pollen size increased), suggesting this is a viable method for studying climate change. We then applied this method to Antarctic Eocene, Oligocene, and Miocene fossil Nothofagidites lachlaniae pollen and observed an overall increasing trend in pollen grain size from the Eocene through the Early Miocene, indicating that precipitation was decreasing in Antarctica during this time, and coincident with increased glaciation and decreased palynomorph abundance. Lastly, a standard palynological analysis was conducted on the lower sections of the ANDRILL 2A core from the Middle Miocene. Palynomorph abundance and diversity were generally sparse, indicating that the climate was likely cold and dry. However, two brief, warmer intervals were discovered prior to the Mid-Miocene Climatic Optimum. These data are compared with previously obtained palynological data from the upper section of AND-2A and with additional studies from the same core and other climate proxies (e.g. pCO2, leaf wax data, macro fossil presence, sedimentology, orbital cyclicity).