Geochemical and microbiological fingerprinting of airborne dust that fell in Canberra, Australia in October 2002

Patrick De Deckker¹, Raeid M. M. Abed², Dirk de Beer², Kai-Uwe Hinrichs³, Tadhg O'Loingsig⁴, Enno Schefuß³, Jan Berend Stuut³, Nigel J. Tapper⁴ and Sander van der Kaars⁵

1 Research School of Earth Sciences, The Australian National University, Canberra ACT 0200, Australia
2 Max Planck Institute for Marine Microbiology, Celsiusstraße 1, 28359 Bremen, Germany
3 Department of Geosciences & MARUM - Center for Marine Environmental Sciences, University of Bremen, D-28334 Bremen, Germany
4 School of Geography and Environmental Science, Monash University Vic 3800, Australia
5 Department of Palynology and Climate Dynamics, Albrecht-von-Haller-Institute for Plant Sciences, University of Göttingen, Untere Karspüle 2, 37073 Göttingen, Germany

Figure 1. (A) SeaWiFS satellite image 09:00 hours local eastern standard time (EST) on 23 October 2002 (taken from McTainsh et al., 2005), showing the main dust plume passing over eastern Australia (note the smoke plumes from bushfires in south east Queensland and central east NSW, which indicate wind directions at the time of the event), (B): 13:25 hours EST - MODIS colour-optimised Red-Green-Blue image and (C) processed with the Miller Dust Enhancement Algorithm.

During the night of October 22-23, 2002, a large amount of airborne dust fell with rain over Canberra, located some 200 km from Australia's east coast, and at an average altitude of 650m. It is estimated that during that night about 6 g.m^-2 of aeolian dust fell. We have conducted a vast number of analyses to "fingerprint" some of the dust and used the following techniques: grain size analysis, SEM imagery, major, trace and rare earth elemental, plus Sr and Nd isotopic analyses, organic compound analyses with respective compound-specific isotope analyses, pollen extraction to identify the vegetation sources, molecular cloning of 16S rRNA genes in order to identify dust bacterial composition. DNA analyses show that most obtained 16S rRNA sequences belong mainly to three groups: Proteobacteria (25%), Bacteriodetes (23%), and gram-positive bacteria (23%).

In addition, we investigated the meteorological conditions that led to the dust mobilisation and transport using model and satellite data. Grain sizes of the mineral dust show a bimodal distribution typical of proximal dust, rather than what is found over oceans, and the bimodal aspect of size distribution confirms wet deposition by rain droplets. The inorganic geochemistry points to a source along/near the Darling River in NW New South Wales, a region that is characteristically semi-arid, and both the organic chemistry and palynoflora of the dust confirm the location of this source area. Meteorological reconstructions of the event again clearly identify the area near Bourke-Cobar as being the source of the dust. This study paves the way for determining the export of Australian airborne dust both in the oceans and other continents.

De Deckker, P., R. M. M. Abed, D. de Beer, K. Hinrichs, T. O'Loingsigh, E. Schefuß, J. W. Stuut, N. J. Tapper, and S. van der Kaars, 2008, Geochemical and microbiological fingerprinting of airborne dust that fell in Canberra, Australia, in October 2002, Geochem Geophys. Geosyst., 9, Q12Q10, doi:10.1029/2008GC002091.