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In-Depth Information
are the Lake Eyre Basin/Simpson Desert and the Murray-Darling Basin (Hesse and
McTainsh,
2003
), a pattern likely to have obtained in the past, with some modification.
There was enhanced dust flux to the east and south of the continent between 33 and
16 ka (Hesse,
1994
). Between 22 and 18 ka, the northern limit of the dust plume
was 350 km, or 3
, north of its present limit (Hesse,
1994
; Hesse et al.,
2004
),
consistent with a northward shift of the high-pressure subtropical ridge (STR) during
the LGM from its present summer location near 35
°
S. The STR separates the tropical
easterly circulation from the mid-latitude westerlies (Hesse,
1994
). Using present-day
measurements of dust flux, McTainsh and Lynch (
1996
) estimated that dust activity
in north-east Australia increased by 57 per cent and in the south-east by 52 per cent
during the LGM. They pointed out that these were probably underestimates, given
that they did not take into account increased sediment supplies to dust source areas
at that time. McTainsh and Strong (
2007
) found up to 65 per cent organic matter by
mass in modern dust, much of which was probably derived from biological crusts
that normally protect soils and dunes from deflation. During the cold, dry LGM, it is
probable that any existing crusts would also have been deflated.
Two exceptionally well-dated desert sites that span the Last Glacial Maximum are
the Willandra Lakes in arid western New South Wales, particularly Lake Mungo,
and the arid Flinders Ranges of South Australia, discussed in the next section. The
chronology for late Pleistocene Lake Mungo is based on more than 200 radiocarbon
and luminescence ages (Bowler,
1998
;BowlerandPrice,
1998
) and shows that wind-
blown dust began to accumulate in the lunettes on the eastern side of Lake Mungo and
associated lakes from around 35 until around 16 ka, with a peak during the LGM. Clay
dunes and gypseous lunettes were developing on the downwind margins of seasonally
fluctuating lakes inmany parts of semi-arid south-east and south-west Australia during
the LGM (Bowler,
1973
;Bowler,
1976
;Bowler,
1978b
; Bowler and Wasson,
1984
),
when the major deflation of dry lake-beds in the arid zone was underway (Magee and
Miller,
1998
).
In two marine cores off the coast of South Australia that span the last 170 ka,
Gingele and De Deckker (
2005
) documented three phases of enhanced dust flux into
the ocean at around 74-70, around 45 and around 20 ka. Each of these episodes
coincides with times of lake desiccation, dune accretion and sparse vegetation cover
in south-central Australia and with times of minimum insolation in these latitudes
(Croke et al.,
1996
; Gingele and De Deckker,
2005
; Williams et al.,
2009b
).
°
22.6.4 Late Quaternary wetlands
Reworked wind-blown dust also comprises a significant component of the late
Pleistocene fine-grained valley fills that have accumulated episodically since the
last interglacial in the arid Flinders Ranges of South Australia (Williams et al.,
2001
;
Williams and Nitschke,
2005
; Williams et al.,
2006a
; Williams and Adamson,
2008
;
