Desert dust - Climatic Change in Deserts - page 155

et al., 2009 ). Hesse and McTainsh ( 2003 ) have reviewed work on modern dust-storms
and Quaternary eolian dust in marine cores. The marine record shows that the rate
of dust accumulation during the LGM was three times greater than it was during
the Holocene (Hesse, 1994 ). Hesse and McTainsh ( 2003 ) attributed this to weakened
Australian monsoon rains in the tropical north and a drier westerly circulation in
the temperate south. From 33 ka to 16 ka, there was a strong flow of dust to the
east and south over the southern half of the Australian continent. The northern limit
of the dust plume in eastern Australia appears to have extended about 350 km, or
3

, north of the present limit from 22 to 18 ka (Hesse, 1994 ; Hesse et al., 2004 ).
This is consistent with a northward shift of the high-pressure subtropical ridge (STR)
in glacial times to its present summer location near 35

°

S. The STR separates the
tropical easterly circulation from themid-latitude westerlies (Hesse, 1994 ; Hesse et al.,
2004 ).
Further evidence of major dust deflation during the LGM comes from Pleistocene
Lake Mungo in semi-arid western New South Wales. With a chronology solidly
founded on more than 200 14 C, TL and OSL ages, Bowler ( 1998 ) and Bowler and
Price ( 1998 ) showed that eolian dust ( Wustenquartz , or desert quartz dust) began
to accumulate in the lunettes on the eastern side of Pleistocene Lake Mungo and
adjacent lakes from about 35 to 16 ka, with a peak centred around the LGM, when
clay dunes and gypseous lunettes were actively forming on the downwind margins
of seasonally fluctuating lakes in many parts of semi-arid south-east and south-west
Australia immediately before and between 21 and 19 ka (Williams et al., 2009b ).
Major deflation of exposed lake-floor sediments coincided broadly with the time of
extreme aridity centred on the LGM (e.g., Lake Eyre: Magee and Miller, 1998 ). In two
marine cores off the coast of South Australia, Gingele and De Deckker ( 2005 ) found
evidence of enhanced wind-blown dust deposition at roughly 70-74 ka, 45 ka and
20 ka, all times of minimum insolation in these latitudes. These were also periods of
widespread lake desiccation, dune building and sparse vegetation cover in central and
southern Australia (Croke et al., 1996 ). Fine resolution analysis of a late Quaternary
dust record from eastern Australia offers support for the existence of two stadials
during the LGM (Petherick et al., 2008 ).

°

9.8 Influence of desert dust on local and regional climate
Except for the deserts of the North American Southwest (see Chapter 20 ), glacial
maxima were in general drier than today and interglacial maxima were as wet or wetter.
The deserts of North Africa, Arabia, central Asia, China, Patagonia and Australia all
display evidence of more vigorous eolian dust flux during glacial maxima. Nor should
it be forgotten that eolian dust might have an influence on local and regional climates.
In tropical West Africa, from 15 ka to about 7 ka, the rivers were mainly depositing
clays, and after 7 ka they mostly carried sands. Maley ( 1982 ) attributed this abrupt