Late Pleistocene and Holocene subtropical vegetation dynamics recorded in perched lake deposits on Fraser Island, Queensland, Australia

Abstract

The dune system of Fraser Island in subtropical Queensland, Australia, contains numerous perched lakes with organic-rich sediments. These lakes are located in the subtropics and their water levels are strongly influenced by precipitation. The lakes act as natural rainfall gauges, which make them highly sensitive to environmental change. Paleoecological and paleoclimatological investigations are performed on sediment cores from Lake Allom, a small perched lake on central Fraser Island. A detailed chronology is based on a series of closely spaced AMS-radiocarbon dates, supplemented with sedimentological information. Based on extrapolation, the chronology indicates an age range from ∼ 56 14C kyr BP to present, with a major hiatus occurring during the Last Glacial Maximum. Pollen analysis of the Lake Allom sediment record reveals strong changes between rainforest and open woodland vegetation. The Holocene portion of the record shows a stepwise vegetation development, from dry conditions in the early Holocene, to high lake levels and increasing forest between 5.5 and 3 cal kyr BP. At 3–2 cal kyr BP, a large diversification occurred towards the present-day heterogeneous sub-tropical rainforest vegetation, followed by a small rainforest decline at 0.45 cal kyr BP. Additionally, charcoal analysis indicates increases in fire occurrence contemporaneously with periods of drier vegetation and/or low lake levels. Part of the reconstructed vegetation changes can be related to local and regional factors including forest succession, dune formation, sea-level rise and human impact. Comparison with paleoclimate records from tropical and temperate regions indicates that the temporal and spatial dynamics of vegetation changes in eastern Australia are primarily controlled by climate variability. Particularly the increasing activity of the El Niño–Southern Oscillation (ENSO) during the late Holocene caused greater climate variability in eastern Australia, resulting in more heterogenous vegetation cover.