Australian deserts - Climatic Change in Deserts - page 435

2003a ; Kershaw et al., 2003b ; Kershaw et al., 2007 ). The climate remained cool and
dry until 19 ka, with open woodlands dominant. The peat humification record from
this site, also reflected in changing proportions of Cyperaceae and Poaceae, showed
1,500-year moisture cycles (Turney et al., 2004 ).
Pollen obtained from a marine sediment core located 60 km west of the Cape
Range Peninsula in semi-arid north-west Australia provides the only information
about the late Quaternary vegetation in this region (van der Kaars and De Deckker,
2002 ). Mean annual rainfall today is between 200 and 300 mm. The site lies near
the southern limit of the Australian summer monsoon today. Williams et al. ( 2009b )
refined the interpretation of the pollen record from this core using the transfer functions
of van der Kaars et al. ( 2006 ). The lowest mean annual precipitation and highest mean
maximum temperatures in the period before the LGM occurred from 35 to 33 ka. The
interval between 33 and 20 ka was the driest period of the 100 ka record, with almost
no summer rain, in accord with previous suggestions that the summer monsoon failed
to reach north-west Australia at this time (De Deckker et al., 2002 ; van der Kaars
and De Deckker, 2002 ). Coldest temperatures occurred between 26 and 24 ka (van
derKaarsetal., 2006 ). Conditions became slightly wetter and warmer from 20.4 to
14.2 ka and distinctly wetter after 14.2 ka, a change also seen at Lynch's Crater in
north-east Queensland. In addition, the reconstructed late Pleistocene discharge record
of the Fitzroy River and the onset of high lake levels in Lake Gregory in north-west
Australia led Wyrwoll and Miller ( 2001 ) to conclude that the summer monsoon had
become active there by 14 ka. This event reflects a global change in climate, with
the abrupt return of the summer monsoon in the headwaters of the Blue and White
Nile rivers at 14.5-14.0 ka (Williams et al., 2006c ; Williams, 2012a ). Furthermore,
deMenocal et al. ( 2000 ) identified a sharp decline in eolian dust input from the Sahara
into the Atlantic at this time, marking the start of what they termed the 'African Humid
Period', although as Gasse et al. ( 2008 ) correctly observed, not all of Africa became
humid at this time.
Playa lakes in the lower Darling Valley of semi-arid western New South Wales
contain pollen showing that the plant communities growing in this region after the
LGM (around 24-18 ka) were very different from those growing in the long interval
(around 70-24 ka) before then (Cupper, 2005 ). Pollen preserved in eight middens of
the stick-nest rat Leporillus in the arid northern Flinders Ranges of South Australia
show that woodlands were widespread and the climate was wetter from 8.8 to 5.3 ka
(McCarthy et al., 1996 ). During the preceding Pleistocene-Holocene transition, salt-
tolerant plants were dominant. This may reflect continued aridity after the LGM or a
change in rainfall seasonality at that time.
High-resolution U/Th ages from a speleothem in the Flinders Ranges, combined
with carbon and oxygen isotopic analysis, showed high effective precipitation at
around 11.5 and around 8-5 ka, with peak humidity at 7-6 ka (Quigley et al., 2010b ),
consistent with the stick-nest rat records of McCarthy et al. ( 1996 ). The present