Dust emissions from eastern Australia during the mid to late Holocene record changing hydro-climatic conditions and landuse.

Abstract:

Dust emissions, determined from dust deposition rates in sedimentary archives, are sensitive indicators of landscape change in dust source areas. Changing patterns in dust output are most often interpreted to indicate changing aridity, where increased dust emissions occur in response to increased aridity. However, the controls on the degree of dustiness are complex and in addition to aridity include sediment availability and windiness. Sediment availability is influenced not only by climate, but also landuse. Despite this, dust emissions can be used to reconstruct landscape response through time. Rates of dust deposition downwind of the main dust producing regions of eastern and central Australia are examined in this study. Prior to agricultural development, dust emissions from this region appeared to be driven by changes in the position of synoptic scale circulation features combined with the operation of teleconnections. However, following widespread agricultural development dust output increased significantly, with patterns linked to human activity; although the influence of climate was still apparent. Different dust source regions appear to respond differently to spatial variability in climate. Dust emissions increased from central Australia desert after 4500 cal. BP, interpreted as a response to a northward positioning, and possible strengthening, of the baric ridge. Peak dust emissions from central Australia occurred at around 3500 cal. BP, coincident with a generally dry climate but also apparent peak El Niño Southern Oscillation (ENSO) variability. High ENSO variability is thought to have driven increased dust emissions as rapid changes between wet and dry sequences resupply sediment to dust source areas during wet phases, before it is entrained and transported during subsequent dry periods. By contrast, at the same time in more southerly latitudes (Australia’s western Murray-Darling Basin (MDB)) dust emissions were lower than at any other time. This is assumed to be associated with increased advection of moisture into the MDB during enhanced westerly circulation inhibiting dust entrainment. The records presented here imply that variability in hydro-climatology and landuse in Australia’s arid-lands have driven changes in dust output of up to ~20 times during the late Holocene.