THE DEMISE OF ANTARCTICA'S LAST REFUGIUM: PALYNOLOGICAL EVIDENCE AND POTENTIAL MECHANISMS

The Antarctic Peninsula is considered to be the last region of Antarctica to have been fully glaciated as a result of Cenozoic climatic deterioration. As such, it was likely the last refugium for plants and animals that had inhabited the continent since it separated from the Gondwana supercontinent. Palynological data obtained from drill cores acquired during the SHALDRIL II campaign in the northernmost Peninsula region yield a record that, when combined with existing data, indicates progressive cooling and associated changes in terrestrial vegetation over the course of the past 37 million years. Mountain glaciation began in the latest Eocene, contemporaneous with glaciation elsewhere on the continent and a reduction in atmospheric CO₂ concentrations. This climate deterioration was accompanied by a decrease in diversity of the angiosperm-dominated vegetation that inhabited the northern Peninsula during the Eocene. A mosaic of beech and conifer-dominated woodlands and tundra continued to occupy the region during the Oligocene. By the middle Miocene, localized pockets of limited tundra still existed at least until 12.8 Ma. The transition from temperate, alpine glaciation to a dynamic, polythemal ice sheet took place during the middle Miocene. The northernmost Peninsula was over-ridden by an ice sheet during the late Miocene-early Pliocene interval. The long cooling history of the peninsula is consistent with the extended timescales of tectonic evolution of the Antarctic margin, involving the opening of ocean passageways and associated establishment of circumpolar circulation.