Variability in dust emissions from Australia over the past 6000 years: a record of synoptic-scale circulation change and recent human activity
1, Hamish McGowan2, James Hooper1, Atun Zawadzki3, Balz Kamber4
1GeoQuEST Research Centre - School of Earth and Environmental Sciences, University of Wollongong, Wollongong, NSW, Australia, 2Climate Research Group, School of Geography, Planning and Environmental Management, The University of Queensland, Brisbane, Qld, Australia, 3Institute for Environmental Research, Australian Nuclear Science and Technology Organisation, Sydney, NSW, Australia, 4Department of Geology, School of Natural Sciences, Trinity College Dublin, Ireland, Dublin, Ireland
Records of dust emissions, as determined from deposition rates in sedimentary archives, have most often been interpreted to indicate the degree of aridity within dust source areas, where increased dust emissions occur in response to increased aridity. However, the controls on dust entrainment and transport are complex. In addition to aridity, broad-scale changes in sediment availability, windiness and surface conditions, e.g. vegetative cover, also influence dust output. Thus the response of dust to changing conditions through time is likely to be non-linear. Despite these difficulties, dust emissions can be used to reconstruct landscape response through time. In this study, rates of dust deposition are examined in peat mires dating from the mid to late Holocene and located downwind of the main dust producing regions of eastern and central Australia. These records show that dust output has varied by an order of magnitude during this period. This variability is ascribed to changes in specific source area conditions driven by climate variability. In particular changing dust emissions are interpreted to result from changes in the position of synoptic scale circulation features, possibly combined with the operation of teleconnections (e.g. ENSO), which control the advection of moisture into dust source areas. Changes in synoptic-scale circulation are inferred via reference to existing palaeo-climate records within dust source areas combined with geochemical fingerprinting of the provenance of dust deposited in the studied cores. A marked increase in dust output is apparent at c.150 years BP. This is interpreted to represent a change in the processes controlling dust emissions, where prior to 150 years BP dust emissions were driven by hydroclimate variability, while after this date human activity became a significant control on dust output. The date of onset of increased dust emissions corresponds to the development of widespread pastoralism over much of semi-arid central and south-eastern Australia. This resulted in widespread land-clearing (the removal of protective cover vegetation) and the introduction of hard-hooved animals, which broke up protective soil crusts. As a result, dust emissions over the past 150 years appear to have varied in response to human activity as well as hydroclimate variability. In addition, landscape ‘relaxation' to now altered environmental conditions may have also influenced patterns in recent dust emissions.