Processes of Fine Particle Formation, Dust Source Regions, and Climatic Changes

Abstract

Copied as is: Atmospheric dust has been supplied by two main types of source region during the Quaternary. At times of maximum continental glaciation much dust was blown from outwash plains and braided river channels adjacent to continental ice sheets and valley glaciers in mid-latitudes. Dust flux from these sources was low in the Holocene and earlier interglacials. Arid regions have been important sources of dust during both glacial and interglacial periods. Based on observed variations in the abundance of dust in oceans cores, several authors have suggested that the flux of desert dust is directly related to the intensity or areal extent of continental aridity. However, this interpretation is bsed on an oversimplified view of the factors which control dust supply. It is argued in this paper that dust flux is greater from arid areas than hyperarid areas. Sudden increases in dust flux observed in ocean cores can be caused either by a change from semi-arid to arid or from hyperarid to arid conditions, or by changes in the pattern of meso- and macro-scale atmospheric processes which control dust dispersion. Conclusions: Large scale dust activity requires 1) a large area of bare, uncrusted and unarmoured silty sediment, 2) incidence of strong winds capable of entraining dust and dispersing it over large distances. At the present day favourable dust source areas are much less extensive than during glacial stages of the Pleistocene, when poorly sorted fluvioglacial outwash was deposited over thousands of square kilometres in mid-latitudes. --> areas with periodic floods obviously form the largest source areas of wind-blown dust. Modern day dust storms are almost twice as frequent in areas with a mean annual rainfall of 100-200 mm compared with drier and wetter areas (Goudie 1983).