How likely was a green Antarctic peninsula during warm Pliocene interglacials? A critical reassessment based on new palynofloras from James Ross Island

The question whether Pliocene climates were warm enough to support a substantial vegetation cover on Antarctica is of great significance to the ongoing controversial debate on the stability or dynamism of Antarctic ice sheets during Neogene warm periods. Here we present a systematic palynological comparison of pollen and dinoflagellates assemblages of Pliocene diamictites from the northern Antarctic Peninsula. The sedimentary sequences are exceptionally well dated using a combination of 40Ar/39Ar and 87Sr/86Sr on interbedded lavas and pristine bivalve molluscs. The pollen bearing sediments were most probably deposited during warm and seasonally ice-free conditions. Pollen assemblages are dominated by Nothofagidites spp., Podocarpidites spp. and Cyathidites spp., suggesting contamination with older, pre-Neogene material. In order to distinguish between reworked and in-situ palynomorphs, we applied different methods, including fluorescence microscopy, which were used in previous publications to reconstruct potential Neogene vegetation. Our results indicate a purely Cretaceous and early Tertiary origin of pollen and spores and challenge previously published reconstructions of a Pliocene tundra vegetation on Antarctica.