Identifying Sources of Aeolian Mineral Dust: Present and Past - Mineral Dust: A Key Player in the Earth System - page 55

For example, lakes can be considered in four different states: wet, ephemeral,
dry (with consolidated sediments), and dry (with nonconsolidated sediments),
all characterized by a variable propensity to emit dust due to different degrees
of sediment availability and supply. A good review of studies focusing on the
geomorphic controls on dust emission processes is provided by Bryant ( 2013 ).

3.3.2 Aerosol Indexes (AI) Derived from the Orbiting TOMS

(Total Ozone Mapping Spectrometer)

Launch of the Nimbus 7 satellite with the onboard Total Ozone Mapping Spectrom-
eter (TOMS) in 1978 became a milestone in our ability to identify dust sources on a
global scale. Aerosol indexes (AI) derived from TOMS data demonstrated that broad
source areas for dust can be identified (Goudie and Middleton 2006 ; Middleton and
Goudie 2001 ;Prosperoetal. 2002 ; Washington et al. 2003 ). Prospero et al. ( 2002 )
used TOMS imagery from several years to generate a global map of dust source
areas. This, combined with observations made from MODIS and MISR imagery
(see discussion below), gives a worldwide picture of dust sources and their dominant
transport pathways. Indeed, what Prospero et al. ( 2002 ) refer to as a “global dust
belt” has been identified by this process (Fig. 3.2 ) with major dust source areas
including the Sahara and Sahel regions of Africa. The two most important dust
source areas in the world at present are in the Sahara: the Bodélé depression in
Chad and an area in the southwestern Sahara Desert region of Mali, Mauritania, and
Algeria. In addition, however, the Arabian Peninsula, Central Asia, desert basins in
China and central and southeastern Australia, the Mojave, Sonoran, and Chihuahuan
deserts and Great Plains region of western North America, and the Pampas and
Patagonian regions of southern South America also have been identified as major
dust sources over the past couple of decades. An important finding in the study by
Prospero et al. ( 2002 ) is that most dust source areas identified by interpretation of
TOMS imagery are dominantly in topographic depressions and remote from areas of
human settlement. Thus, they conclude that most areas of dust generation ( 75 %)

at present are the result of natural processes, rather than anthropogenic causes,
such as agriculture or urban development. Continued monitoring using TOMS and
other sensors can test whether this generalization holds true in the future. New
studies have already shown that different platforms, different algorithms for dust
assessment, and different time periods of imaging can change the picture of what
we consider to be the dominant dust sources globally. For example, Ginoux et al.
( 2012 ), using the moderate resolution imaging spectroradiometer (MODIS) “Deep
Blue” aerosol capability, report that a significant part of the Great Plains region of
North America is an important dust source, a region not identified as such in the
earlier study by Prospero et al. ( 2002 ), with TOMS.