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Aeolian dust inputs are represented by a high propor-
tion of quartz silt, which may have red-staining com-
pared with paler fluvial silts (Diester-Haass, 1976). An
increased abundance of aeolian silts has been attributed
to four main factors (Street, 1981; Stuut
et al.
, 2002):
enhanced wind strengths, changes in wind directions, a
thickening of the dust transporting layers of the atmo-
sphere and enhanced aridity in the source area (Warren
et al.
, 2007). Enhanced inputs of aeolian dust, and in some
cases dune sand, to Atlantic Ocean cores off west Africa
(Sarnthein and Diester-Haass, 1977; Kolla, Biscaye and
Hanley, 1979; Holz, Stuut and Hentrich, 2004), down-
wind from the Australian deserts (Thiede, 1979; Hesse
and McTainsh, 1999) and in the Arabian Sea (Kolla and
Biscaye, 1977) occurred within Quaternary cold periods.
The relationship holds for at least the last 600 000 years
(Emiliani, 1966; Bowles, 1975), while dust is detectable
almost back to 2 million years BP in some core sediments
(Parmenter and Folger, 1974).
Comparison of the spatial distribution of Holocene and
Late Quaternary aeolian deposits in the east Atlantic cores
(Figure 3.5) led Diester-Haass (1976) to propose a south-
ward shift and Kolla, Biscaye and Hanley (1979) the
southward expansion of the Sahara during the last glacial
maximum. The identification of freshwater diatoms in
later Quaternary Atlantic dust as far south as 20
◦
N, in-
terpreted as deflated material from dry lake floors by
Parmenter and Folger (1974), also supports the view of
Saharan extension at this time.
As well as indicating that some deserts were more ex-
tensive at various times during the last glacial cycle, and
in some cases centred on the last glacial maximum, the
widespread occurrence of aeolian dust in ocean cores also
suggests that conditions were windier (Sarnthein
et al.
,
1981; Hesse and McTainsh, 1999; Stuut
et al.
, 2002). The
size of aeolian dust particles may not, however, be a good
indication of the distance of travel as once supposed, for
Schroeder (1985) has shown that the size of mixed-nuclei
dust particles responds to water table fluctuations in the
source area, not travel distance, though using an end-
member model may allow wind- and water-transported
silts to be distinguished in ocean cores (Holz, Stuut and
Hentrich, 2004). The ratio of high- to low-density dust
particles, used by Diester-Haass (1976), may be a bet-
ter indicator of the transportation ability of the wind and
hence atmosphere circulation strengths at the time of de-
position.
Fluvial inputs to ocean-core sediments can in some con-
texts also provide an estimation of the extent of tropical
palaeoaridity (e.g. Hemming
et al.
, 1998). Sediments in
the offshore Amazon fan, dated to the last glacial period,
90
75
60
45
30
15
0
15
5
5
2
2
%
∆
Quartz
75
75
< 0%
0 - 2%
2 - 5%
5 - 10%
> 10%
2
2
5
5
1
10
10
1
10
10
5
5
0
0
2
2
1
10
10
1
10
10
5
5
5
5
60
2
2
60
2
2
5
5
2
2
1
10
10
5
5
45
45
2
2
2
2
0
0
0
0
5
5
2
2
0
0
5
5
2
2
2
2
30
30
2
2
5
5
1
10
10
15
15
2
2
1
10
10
5
5
1
10
10
5
5
2
2
2
2
0
0
0
0
0
0
2
2
0
0
5
5
2
2
15
15
0
0
0
0
2
2
2
2
30
30
2
2
0
0
2
2
5
5
2
2
0
0
45
45
2
2
0
0
2
2
0
0
2
2
60
60
90
75
60
45
30
15
0
15
Figure 3.5
Difference in quartz percentage in late glacial and
Holocene sections of Atlantic sediment cores. Enhanced late-
glacial concentrations in the northern hemisphere tropical zone
are interpreted as the product of dust inputs deflated from an
expanded Sahara and/or due to stronger circulation systems
(after Kolla, Biscay and Hanley, 1979).
sand and little kaolinitic clay (Damuth and Fairbridge,
1970). This has been interpreted as an indication of less
chemical weathering in source areas due to the spread of
aridity to the Brazilian Shield (Damuth and Fairbridge,
1970) or Amazon headwaters (Milliman and Summer-
hayes, 1975). A similar interpretation has been applied
to Late Pleistocene sediments from the Indian continen-
tal shelf (Hashimi and Nair, 1986). In other contexts the
variations in terrestrial component grain sizes in a core
have been used to infer the relative importance of aeo-
lian and fluvial system inputs over time and associated
