Vegetation, fire and climate history in central-western Tasmania (41°S), Australia, over the last ∼21,000 years

Abstract

We present high resolution pollen and macroscopic charcoal records from Basin Lake, a relatively small mid-latitude (42°S) lake located in central-western Tasmania, Australia, to examine vegetation, fire and climate change since and during the Last Glacial Maximum (LGM). We find dominance of cold-resistant alpine vegetation with buttongrass moorland and scant trees between ∼21.0-17.7 cal kyr BP, with local biomass burning and low lake levels between ∼21.0-20.0 cal kyr BP and a reduction in local biomass burning and a rise in lake levels between ∼20.0-17.7 cal kyr BP. These data suggest glacial-cold conditions during the last millennia of the LGM, with relatively humid conditions between ∼21.0-20.0 cal kyr BP and a further increase in humidity between ∼20.0-17.7 cal kyr BP. These shifts suggest an intensification of the South Westerly Winds (SWW) over the site between ∼20.0-17.7 cal kyr BP. An increase in cold-temperate rainforest taxa followed between ∼17.7-16.0 cal kyr BP along with lake-level lowering, suggesting a warm pulse and southward shift of the SWW at the beginning of the Last Glacial Termination (T1). Subsequent cold-temperate conditions and increased precipitation ensued between ∼16.0-14.9 cal kyr BP promoted by increased SWW influence. A rise in cold-resistant and hygrophilous rainforest taxa and lower biomass burning activity occurred between ∼14.9-12.8 cal kyr BP under colder conditions, enhanced precipitation and major SWW influence. A multi-millennial warm/dry interval began at ∼12.8 cal kyr BP with a decline in rainforest taxa, high fire activity and low lake levels and a further opening of the vegetation in response to elevated biomass burning between ∼11.1-8.9 cal kyr BP. We suggest a decline in the SWW influence that started at ∼12.8 cal kyr BP and accentuated between ∼11.1-8.9 cal kyr BP at the beginning of the Holocene. We detect increases in precipitation between ∼8.9-5.8, ∼3.4-1.9 cal kyr BP and the last ∼900 years, with declines in the intervening intervals. Our data indicate a pronounced and sustained fire-driven shift to a more open and shrub dominant landscape after ∼5.0 cal kyr BP, in synchronous with other pollen data from Tasmania's west, reflecting an increased efficacy of Aboriginal burning under more variable and overall reduced precipitation. Our climate inferences from Basin Lake are coherent with variations of the SWW identified in other terrestrial mid-latitudes records, suggesting synchronic changes in the SWW during and since the LGM.