Airborne dust traffic from Australia in modern and Late Quaternary times

Abstract

Abstract A review is provided of first-documented occurrences of dust transport within Australia for the last century, but which later on were considerably improved as a result of access to satellite observations and extensive ground observations. This was followed by the use of the HYSPLIT tracking models that enabled people to determine the major sources of dust in Australia. As a result of several important studies, the Lake Eyre Basin in central Australia is now considered to be the main source of dust entrainment, although other regions do contribute to dust production. This is followed by examination of the occurrence over the last few decades of dust transport and deposition within Australia and across the Tasman Sea, with dust being deposited even as far as New Zealand. After that, consideration is given to the deposition of dust not only at sea around Australia but also in New Zealand during the Holocene and Late Quaternary. As a consequence of these observations, a shift in the direction of dust plumes exiting Australia is noted. For example, during the Last Glacial Maximum (LGM), a substantial northerly shift of the Trans-Tasman dust plume is recorded and this coincides with stronger westerlies and an equatorward shift of oceanic fronts such as the Intertropical Convergence and Subpolar and Antarctic Fronts that were located closer to Australia compared to today. Strengthening of the winds during the LGM may have prevented dust plumes from travelling over the southern part of the Tasman Sea, even perhaps reaching Antarctica. Examination of the dust components in cores in the western Pacific Ocean would address this question. The second part of the paper examines the geochemical fingerprints of dusts from Australia, South America and those recovered from Antarctic ice cores. Examination of atmospheric conditions that prevailed in the Southern Ocean around Antarctica during a major dust storm event that occurred in Australia in October 2002 helps identify how dust can be entrained around cold fronts and eventually reach the Antarctic mainland. Once again, it appears that Australian dust did travel as far as Antarctica more frequently during the Holocene, than prior to that time. New Zealand as a dust source to some Antarctic sites is also discussed. Examination of the isotopic fingerprints in Antarctic ice cores point to South America being the main source of dust during the Last Glacial Maximum and previous glacial periods, with intermittent occurrences likely to have come from Australia and New Zealand as well. It is postulated that Australian dust plumes did travel mostly over the Tasman Sea, and eventually over the western Pacific Ocean during the LGM, and frequently less so towards Tasmania and the Southern Ocean as a result of the strengthening of the westerlies and their northward shift. It transpires that the dust flux from Australia was much higher during the glacial periods. It appears also that the dust plumes that traverse the eastern Indian Ocean remained unchanged during the LGM. Finally, this paper concludes by identifying that there is a need to either obtain larger dust samples from ice cores, or use more elaborate analytical techniques to combine more than two isotopes to fingerprint the origin of dusts recovered in ice cores. Perhaps a combination of not only isotopes, but also rare earth elements and major elements would eventually provide a better definition of atmospheric circulation in the Southern Hemisphere for comparison between glacial and interglacial periods.