Identifying Sources of Aeolian Mineral Dust: Present and Past - Mineral Dust: A Key Player in the Earth System - page 68

migration of grasslands into former desert regions. Pokras and Mix ( 1985 ) note that
the Melosira maximum in the late Holocene interglacial period is anomalous over
the past 150,000 year.

3.5 Conclusion

The study of dust is important, because this sediment has important effects on
the planetary radiation balance and biogeochemical cycles. Furthermore, geologic
records of past dust deposition have tremendous importance in paleoclimate studies.
Crucial to most investigations of dust in these contexts is identification of source
regions as the physical and chemical characteristics of suspended dust are strongly
governed by their surface provenance.
Particular geomorphic settings are the most favorable dust sources. These include
desiccated or ephemeral lakes, high- and low-relief alluvial systems, and aeolian
systems. Different landform systems exhibit varying potential as dust sources due
to the limitations on emission imposed by differences in the supply of fine sediment
(e.g., some geomorphic settings receiving sediment recharge from periodic flood
deposition) and in the availability of this sediment for entrainment. For example,
dry or ephemeral lakes may contain abundant fine-grained sediment, but will not
generate much dust if the surface is moist or if particles are cemented by salts or
clay minerals.
Many contemporary dust sources have been identified using high-resolution,
Earth-orbiting satellites. Satellites have provided a global assessment, establishing
topographic depressions in arid regions, usually far from populated areas, as the
most important dust sources and the presence of a “global dust belt.” MODIS and
MISR imagery give high-resolution records of dust sources on a regular basis. The
resolution of this imagery is sufficient that point sources (“hot spots”) of dust within
broader desert regions can be identified.
For studies of dust records of the past, identification of source areas requires
imaginative approaches. Physical properties of dust deposits, particularly loess, have
been used to identify aeolian sources for several decades. Mineralogy can also be
used to determine dust sources, even in deep-sea core records that are distant from
their sources on the continents. Dust collected along the African coast shows a
latitudinally variable clay mineral composition that closely matches the changes
in clay mineralogy of the major soil types of the African source regions, which are
in turn a function of the dominant soil-forming processes along a climatic gradient.
Geochemical methods have also been used to identify dust sources and isotopic
compositions (commonly for Nd, Sr, and Pb) have helped determine the sources of
dust in the Loess Plateau of China and Antarctic ice cores.
Dust sources can change over time, particularly on the scale of interglacial/glacial
cycles of the Quaternary. During glacial periods, growth of continental ice sheets
and expanded valley glaciers and mountain ice caps generated abundant glaciogenic
silt to a degree much greater than today. The record of this glacial-age dust source