Environmental change during the last glacial on an ancient land bridge of southeast Australia

Aim: The Last Glacial Maximum (LGM) remains an enigmatic period in southeast Australia due to the limited spatial and temporal resolution of its palaeoclimatic records. A major feature of the LGM landscape was the existence of the Bassian Land Bridge, joining Tasmania with the mainland of Australia during periods of low sea level, and potentially facilitating increased biotic movement between these regions. To better understand biogeographical changes on the land bridge and in southeast Australia generally during the LGM, we present a 35 ka-year palaeoecological record from one of the larger islands of Bass Strait. Location: Bass Strait, southeast Australia. Taxon: Eucalyptus, Poaceae, Monotoca, Myriophyllum, Zygnemataceae, Botryococcus, Pediastrum. Methods: Pollen, charcoal, and non-pollen palynomorphs were analysed in a 1.75-m sediment core from truwana/Cape Barren Island, Bass Strait, to reconstruct changes in vegetation, fire regimes and lake levels on the Bassian Land Bridge. Results were then compared to existing palaeoenvironmental studies in the region to develop a broader context of the prevailing land bridge environment and the potential influence on biotic dispersals in Australia during the last glacial period. Results: Results suggest a major vegetation shift on the Bassian Land Bridge in response to the establishment of the LGM climate, with grassland expansion at the expense of woodland from ~29-11 ka. Floristic richness, biomass burned and lake levels also markedly decreased through this period, with the driest interval being ~25-18 ka. Dryland herbaceous taxa dispersed between the mainland and Tasmania when the landbridge was fully exposed. Main conclusions: In agreement with previous studies, our results show that the dry grassland that dominated southeast Australia (and Southern Hemisphere mid-latitude areas) during the LGM also extended across the Bassian Land Bridge. The prevailing environment on the land bridge is likely to have exerted a selective influence on biotic dispersals in Australia during glacial periods.