Subaquatic Dust Deposits - Mineral Dust: A Key Player in the Earth System - page 446

sediments in the eastern Pacific and in the numerous lakes of the Andes mountains
(e.g. Groot and Groot 1966 ; Heusser 1983 ; Markgraf 1993 ), in Australia from
sediments in the western Pacific and in Lynch's crater lake (e.g. Kershaw et al.
2003 , 2007 ), in north Africa from equatorial Atlantic sediments and presently dry
lakes (e.g. Dupont et al. 1989 ; Lézine 1989 ; Lézine and Casanova 1991 )andin
South Africa from marine sediments in the eastern Atlantic Ocean (e.g. Shi and
Dupont 1997 ; Dupont and Wyputta 2003 ; Rommerskirchen et al. 2006 ) as wel as a
desiccated lake (Partridge et al. 1993 ) and even Hyrax middens (Chase et al. 2011 ).
Although there is much debate about the transport mechanism of pollen (fluvial
versus aeolian), assemblages of the different pollen can be used to characterise
vegetation type, and downcore variability in the different vegetation types can be
interpreted in terms of environmental changes.
Homologous series of long-chain n -alkanes, n -alcohols and fatty acids are
typical lipids found in dust (Lepple and Brine 1976 ; Schefuß et al. 2003 ). These
lipids are the product of terrestrial higher plant epicuticular waxes (Eglinton and
Hamilton 1967 ) and are used by these plants as a protective coating on leaves and
stems. The wax particles are easily eroded off the surface of the leaves by wind,
especially by a sandblasting effect, and can then become airborne (Simoneit 1977 ).
Alternatively, decaying plant organic matter in soils can be lifted during dust storms
and transported by wind. The plant waxes have been found in marine sediments up
to 4 million years old and can be used to reconstruct environmental conditions in
the source areas of the dust (Martinez-Garcia et al. 2011 ).
Next to these organic proxies for wind-blown deposits, many studies use the
bulk chemistry of sediments as derived from core scanning and individual samples
to characterise aeolian dust. Bulk chemistry is in fact related to the particle size
but also potentially the density of the terrigenous particles (Bloemsma et al. 2012 ).
Using the isotope chemical composition of the aeolian sediment fraction (>10 m),
Meyer et al. ( 2011 ) managed to reconstruct the provenance changes of Saharan
dust throughout several geologic stages with well-established contrasting palaeo-
environmental conditions. Three periods were compared: (1) the Last Glacial
Maximum, which occurred about 20 kyr BP, was characterised by extreme aridity
and intensified atmospheric circulation; (2) the aforementioned African Humid
Period, which occurred about 10 kyr BP, was characterised by increased rainfall
and decreased atmospheric circulation relative to today; and (3) the present-
day situation, which is characterised by relatively dry conditions and “normal”
atmospheric circulation. All three periods obviously had an effect on the amount
and size of the material transported by winds, which is reflected in their differing
provenance (Meyer et al. 2011 , 2013 ).
Other isotopes like the Pb series ( 204 Pb, 206 Pb, 207 Pb and 208 Pb) were used to
characterise dust in sediment cores from the equatorial North Atlantic to reconstruct
increased dust input during the Last Glacial Maximum ( 18 kyr BP; Abouchami

and Zabel 2003 ). Great care should be taken using Pb isotopes in modern mineral
dust as combustion of long-chained hydrocarbons also emits considerable amounts
of Pb that end up in the marine sediment archive (e.g. Erlenkeuser et al. 1974 ;
Alleman et al. 2001 ).