Implications of a Pliocene stand of Nothofagus (southern beech) within 500 kilometres of the South Pole

Abstract

Branches, stems and roots of Nothofagus (southern beech) were reported from the Beardmore Glacier area (Sirius Formation) some 500 km from the South Pole. The Sirius Formation is a glacially derived unit which is considered Pliocene in age. We considered two scenarios by which a Nothofagus forest could flourish so close to the South Pole during the Pliocene. One scenario calls for the disappearance of this genus from Antarctica during the early Tertiary (Oligocene) and its re-introduction during a warm Pliocene interval. Seeds from modern Nothofagus, however, are not viable after submersion in sea water, are not carried by migrating birds and are not designed for long-distance wind transport. The second scenario involves survival of Nothofagus in Antarctic refugia through middle Tertiary glacial advances and its flourishing during a Pliocene warming. Excluding its occurrence in the Beardmore Glacier area, the known range of this genus in Antarctica is Cretaceous to Oligocene with some questionable occurrences in the early Miocene. The existing data do not support the refugia scenario. We also considered published speculations in which the closest modern analogue to the Beardmore Glacier Region, during the time that the Nothofagus represented by these specimens lived, was the coastal region of southern Chile where average annual temperatures are approximately 5°C and summer temperatures are of the order of 8–10°C. We incorporated these observations and speculations into a palaeoenvironmental model, assuming them to be valid; the results require Pliocene temperatures as warm as, or warmer than, the Cretaceous, a scenario which is not supported by the literature. We conclude, therefore, that the occurrence of Nothofagus in the Beardmore Glacier area is older than Pliocene. Instead, we suggest that it represents a relict assemblage which is probably no younger than Oligocene but which may have persisted into the early Miocene.