Fossil Plants from the Pliocene Sirius Group, Transantarctic Mountains: Evidence for Climate from Growth Rings and Fossil Leaves

Abstract

Fossil wood and leaves of Nothofagus beardmorensis Hill, Harwood and Webb occur within the Sirius Group in Antarctica, a sequence of Pliocene glacial sediments that crop out in the Transantarctic Mountains. Growth forms and tree rings in the wood and the morphology of the leaves indicate that these plants were deciduous dwarf trees that developed a prostrate habit with branches which spread across the ground surface. Despite their small size the narrow growth rings indicate that the trees were mature plants which grew very slowly under harsh conditions. Comparison with growing conditions and habits of prostrate shrubs at similar high latitudes in the arctic today suggests that mean annual temperatures in the Transantarctic Mountains were well below freezing, probably about -12C, with short summer growing seasons with temperatures of around 5C. This estimate for the Late Pliocene climate of Antarctica is considerably cooler than previous estimates based on these fossil plants.