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Fig. 3.5
Ternary diagram
showing abundances of
quartz, illite (mica), and
kaolinite in dust samples
collected off the coast of
Africa attributed to various
regions of origin (
shaded
polygons
) based on
back-trajectory analyses.
Also shown are values of dust
samples collected on
Barbados.
I/K
illite/kaolinite lines
(Data from Caquineau et al.
1998
,
2002
)
D
These results are consistent with the concept that dust collected on Barbados is
likely the result of integration of many individual dust sources in Saharan Africa
and the Sahel, well mixed after transport over not only much of Africa but also the
breadth of the Atlantic Ocean (Prospero and Lamb
2003
).
3.4.4
Geochemical Methods of Identifying Dust Sources
Geochemical methods of identifying dust sources are highly complementary to
mineralogical methods because geochemistry is a direct reflection of mineralogy.
The advantage of the geochemical approach is that it is highly quantitative;
analytical methods are now rapid, accurate, and precise, and trace elements can
often yield data about sources that are not apparent with mineralogy. Here we give
some examples of using this approach for identifying dust sources using samples
from both the marine and terrestrial environments. We caution, however, that the
mineralogy (and hence, the geochemistry) of dust being emitted from even a small
source area can change significantly from day to day and point source to point source
(Rojo et al.
2008
).
Olivarez et al. (
1991
), in a study of fine-grained sediments found in Pacific deep-
sea cores, sought to determine whether the particles were derived from LRT dust
or volcanic sources. Oceanic crust and other mafic volcanic rocks are enriched in
Sc and depleted in Th and La compared to average upper continental crust. Thus,
mafic rocks or particles derived from them will plot near the Sc pole on a ternary
diagram, whereas felsic rocks or particles derived from them will plot near the
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