OLIGOCENE AND NEOGENE VEGETATION AND CLIMATE HISTORY OF THE ROSS SEA REGION, ANTARCTICA

Terrestrial palynomorphs (spores and pollen) recovered from Cape Roberts Project (CRP) drillholes in McMurdo Sound and from Sirius Group outcrop samples in the central Transantarctic Mountains reflect vegetational and climatic trends through the Oligocene and Neogene. Assemblages from CRP-1, CRP-2/2A and CRP-3 core samples span the latest Eocene through the Early Miocene, while Sirius Group samples may extend the record to the Late Pliocene. Palynological evidence suggests step-wise diversity reduction through the Oligocene and Neogene, consistent with increasing glaciation recorded in the sediments.

Early Oligocene palynomorph assemblages are much reduced in diversity from pre-existing Eocene cool temperate rainforest floras (Nothofagus-podocarp conifers-Proteaceae-ferns). The Early Oligocene vegetation might have looked similar to extant Magellanic Nothofagus woodland. Climatic conditions were likely cold temperate-periglacial, with warmest month mean daily temperatures at sea level about 10-12°C. This vegetation likely included low shrub or closed forest of Nothofagus and podocarp conifers, plus some other angiosperms and mosses.

Late Oligocene-Early Miocene assemblages reflect a mossy tundra vegetation, with dwarf woody plants (one or more species of Nothofagus and podocarp conifers) growing in more protected locations. The sparse Neogene vegetation grew in subpolar climates, with ~2-7°C warmest month mean temperatures. It probably resembled much of the vegetation growing on islands near the Antarctic Convergence today.