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temperature data suggest that lower temperatures and reduced evaporation may have
been a factor in certain lakes being high during LGM times and for the persistence of
wetland ecosystems in the arid Flinders Ranges of South Australia (Williams et al.,
2001
).
Evidence from lakes may also throw some light on other controversial environ-
mental matters. There has been a long and still-unresolved debate as to whether the
demise of the megafauna in Australia was the result of human impact (direct or indir-
ect) or of climatic change. The arrival of prehistoric humans in Australia about 45,000
years (45 ka) ago seems to coincide with a wave of faunal extinctions, so on balance it
appears that humans were the causal agents. However, the environmental changes at
this critical time have always been poorly understood. A recent paper by Cohen et al.
(
2010b
) on late Quaternary aridification and the vanishing of Australia's mega-lakes
is a major contribution to this debate, in that it provides, for the first time, unequi-
vocal evidence that desiccation set in shortly after 45,000 years (45 ka) ago. Until
then, much of continental Australia was experiencing a very wet climatic phase with
vastly expanded lakes in what is now the arid interior. Cohen et al. (
2010b
)showed
that Lake Frome and a series of more northerly lakes were full, and overflowed into
a much expanded Lake Eyre at intervals until a final major transgression dated to
50-47 ka, after which lake levels fluctuated and became progressively lower. There
were renewed transgressions in Lake Frome late in MIS 3 (around 30 ka), and again
at 17, 13, 5 and 1 ka. Using local alluvial evidence and evidence from speleothems
in caves located, respectively, in the southern winter and northern summer rainfall
zones, they were able to show that southern sources of precipitation contributed to
run-off into Lake Frome during the 50, 30 and 17 ka lake transgressions. There was
also a tropical contribution to Lake Eyre via the Cooper and Diamantina rivers at
50-47 ka. The 13 ka and younger transgressions appear to represent northerly inputs
from tropical sources.
11.10 Conclusion
The early Holocene climates of the tropical northern deserts were generally wetter
than they are today, with the highest lake levels occurring around 9 ka. Similar climatic
conditions were true of the last interglacial around 125 ka. The desert environments no
doubt oscillated between these two extremes, with the interglacials slightly warmer
and very much wetter than today and the glacial maxima colder and mostly drier
than today. However, not all arid phases coincide with glacial maxima, nor do all
humid phases coincide with interglacial times. Some lakes show evidence of humid
glacial phases as well as arid glacial phases and humid interglacial phases as well
as dry interglacial phases. The evidence from Lake Chad illustrates this well, with
high levels at
30 ka to 18 ka, low LGM levels, high levels at 12-9 ka and low
levels after 4.5 ka (Servant and Servant-Vildary,
1980
). Lake Eyre in Australia was
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