A 25 000-year record of aeolian sedimentation from eastern Australia: A proxy for climate variability

This thesis presents a high resolution record of aridity in eastern Australia for the past 25 000 (ka) calendar (cal) years developed from aeolian dust archives to determine the position and strength of the Australian south east dust transport pathway through this period. Aeolian dust archives were extracted from a lake sediment core collected from the exposed lake bed of Native Companion Lagoon in Southeast Queensland, Australia. Native Companion Lagoon is rain fed and all mineral sedimentation was believed to result from aeolian processes alone. The sediment core was sampled at 5 mm intervals, then dried and ashed. Sixteen AMS radiocarbon dates revealed a sedimentation rate of approximately 1 m 10 ka-1, resulting in a temporal resolution of circa 50 years. Aeolian sedimentation (ash record) and moisture content showed an inverse relationship, with periods of high aeolian deposition corresponding to low moisture content, and vice versa, for the majority of the 25 ka record. Phases of increased aeolian sedimentation are considered to represent periods of increased aridity and drought in central and eastern Australia, and disturbance of the local sand dunes which impound Native Companion Lagoon. The highly coherent nature of both the aeolian sedimentation and moisture content records suggests that both proxies are sensitive indicators of climate variability. Key palaeoclimate events shown in the record include the Last Glacial Maximum, Heinrich I, the Antarctic Cold Reversal, an early Holocene climatic optimum and the Neoglacial. Seventy three of the ashed samples underwent ICP-MS geochemical analysis using 44 trace elements. The results of the geochemical analysis were used for two purposes: a) to separate local and continental fractions of the aeolian sedimentation record, and then b) to provenance the far traveled dust content to source areas in eastern and central Australia. This was achieved by developing a model for separating local and continental dust fractions using five trace elements as proxies for continental dust. This five-element average approach is a unique technique for accurately defining the fartraveled component of the dust record. Once determined, the continental component of the aeolian sedimentation record was provenanced to source areas using a ternary mixing model. Fifteen trace elements were selected as suitable for use in the ternary mixing model, which mixed a south east Queensland sediment sample and two potential continental dusts. Variations in dominance of various central and east Australian dust source areas through time revealed significant variability in the position and strength of the south east dust transport corridor. Changes in the dominance of continental source areas were directly related to changes in local palaeoclimatic and environmental conditions in response to large scale global forcings of climate, and in turn changes in regional synoptic scale circulation patterns. Importantly, the Australian landscape is shown to respond quickly to changes in climate. This insight is essential for understanding both past and future impacts of a changing climate on the most arid inhabited continent other than Antarctica