New palynological data from the East Tasman Plateau (ODP Site 1172) indicate rapid earliest Oligocene warming.

Considered as one of the most significant climate reorganisations of the Cenozoic period, the Eocene-Oligocene (E/O) Transition (ca. 33.9-33.5 Ma) is characterised by global cooling coupled with glacial advance on Antarctica. Combined micropalaeontological (diatom and dinoflagellate) and sedimentological evidence hint of regional reorganisation of ocean currents around Antarctica, in association with the Eocene-Oligocene transition. The late Eocene to early Oligocene deepening of the Tasman Gateway resulted in the flow of warm surface waters from the Australo-Antarctic gulf into the southwestern Pacific Ocean.  However, the extent and effect of these changes in ocean circulation on regional terrestrial climate and vegetation across the E/O Transition is not readily known. Here, we present new well-dated, high resolution palynological (sporomorph) data from the East Tasman Plateau (ODP Site 1172) to reconstruct climate and vegetation dynamics from the late Eocene through to the early Oligocene. Results from our sporomorph data point to four vegetation communities occupying Tasmania under different precipitation and temperature regimes: (i) Paratropical rainforest along the coastlines and temperate rainforests at higher altitude of the hinterlands from 37.97-37.52 Ma; (ii) cool temperate forest expanding into areas previously occupied by the paratropical forests between 37.306-35.60 Ma; (iii) a complex mix of paratropical associations coexisting with frost-tolerant taxa, followed by a period of relative stability shown in the dominance of cold-temperate taxa from 35.50-33.36 Ma; (iv) a warm temperate forest present in the early Oligocene (33.25-33.06 Ma). Our sporomorph record showed a general cooling trend from the latest-middle Eocene to the late Eocene (37.97-35.60 Ma), fluctuations between warm and cold climates (35.50 – 34.19 Ma), a period of relative stable cooling across the E/O transition (33.94-33.5 Ma), and a rather unusual rapid warming right after the E/O transition (earliest Oligocene; 33.36 - 33.06 Ma). Our quantitative estimates of terrestrial temperature change and palaeoecological reconstructions show a close link with previously published dinoflagellate cyst data from this same study site, suggesting a possible vegetation and climate response to tectonic changes (most likely the tectonic opening and deepening of the Tasman Gateway ca. 35.5 Ma) and relative short-term regional reorganisation of ocean currents.

Keywords: Antarctica, Eocene-Oligocene Transition, sporomorph, temperate rainforest, Tasman Gateway