Dust II

There is an increasing awareness in the importance of atmospheric dust loadings, and in particular the significant role they may play in climate change. The world’s deserts are major source regions of dust since the arid conditions and lack of vegetation enables deflation and entrainment of silt-sized sediment from a variety of materials (Middleton and Goudie, 2001). Human activities of grazing and vehicular use, for example, can increase the range of susceptible surfaces from which dust can be entrained.

Dust can influence climate in a number of ways. Goudie and Middleton (2001) advise that air temperatures may be affected through the absorption and scattering of solar radiation, marine primary productivity may be affected since dust may provide considerable quantities of iron, and changes in concentrations of condensation nuclei may influence cloud formation and in turn precipitation. Furthermore dust loadings may affect soil formation, calcrete formation, ocean sediment fluxes, and human health.

The Sahara provides the most substantial quantities of aeolian dust with emission estimates between 500 and 1000 Tg yr^-1 which makes up around 50% of the global total (Goudie, 2009). The Bodélé depression is the widely considered the most important source region in the Sahara and contributes a considerable proportion of the Saharan emissions. Saharan dust is comprised of a number of a number of different particles but is made up predominantly of SiO₂ and Al₂O₃. The dust flux generated in the Saharan region emphasises just how important geomorphologic processes are in the desert biome.

Entrained dust off the western coast of Africa, courtesy of NASA

Saharan dust has three main trajectories – over the North Atlantic to North and South America, northwards to southern Europe, and eastwards to the Middle East (Goudie and Middleton, 2001). The North Atlantic flux is the largest and large outbreaks can see dust transported to the Caribbean, US and Brazil. Dust concentrations have been recorded in Amazonia and corral reefs off Barbados, particularly noteworthy considering dust’s influence on nutrient dynamics and biogeochemical cycling of terrestrial and marine ecosystems.

So how does dust influence terrestrial and marine ecosystems? How will dust fluxes change in the face of climate change? Do humans significantly modify the extent of dust entrainment? How important are ‘dust hotspots’ such as the Bodélé depression? What are the other major source regions? Read on to find out………..!