Australia: The Land Where Time Began |
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The Last Interglacial – Australian
Deserts Quaternary
context The climate was much less stable in the
Pleistocene, the global circulation adjusting to the periodic growth and
decline of high latitude icesheets and glaciers. During this period
there was a repeated cycle of rapid global warming followed by a cooling
that was more gradual. A distinctive sawtooth pattern was formed by
these oscillations and with the warm peaks separated by about 100,000
years. The deep sea oxygen isotope record obtained from marine
foraminifera, which define a series of marine isotope stages, is the
cornerstone of this sequence of the Quaternary. By convention, the
glacial stages, which are cold and dry, are allocated even numbers, and
the interglacial stages, are given even numbers. These oscillations of
climate in Australian drylands have been found to be reflected in levels
of available moisture which vary with cyclical fluctuations. Lakes and
rivers across the arid interior are activated in interglacials and
active dunefields and blowing dust characterise the glacial phases which
are cold and drier. In terms of the natural prehistory of the deserts in
Australia, the most important of these climatic oscillations for
understanding this prehistory are the MIS 5, which encompasses the last
interglacial (substage 5.5 or 5e). The last significant imprint of
fluvial and lacustrine activity in the arid zone is the represented by
this period. This provides a key benchmark for comparison, Smith
suggesting that as conditions existing during the last interglacial can
be used as a best-case scenario for the conditions that are likely to
have prevailed at the time when the early colonists were moving into the
desert about 45,000 years ago. It represents, in this context, the upper
limit of the range of possibilities for these landscapes of the inland. The last time global climates were similar to those
of the present was during the last interglacial MIS 5.5 (Kukla et
al., 2002). It is the warmest
interglacial that has been recorded of the 800 ka recorded in the EPICA
Dome C ice-core (Masson-Delmotte et
al., 2010), being possibly
slightly warmer than the present. It has been conventionally dated to
132-115 ka (Shackleton et
al.,
2002), though age obtained with new thermal ionisation mass spectrometry
(TIMS) uranium/thorium (U/Th), coupled with a δ18O record of
precipitation obtained from Speleothems at Dongge Cave, China, have
narrowed the span to 129-120 ka (Yuan et
al., 2004). From 116-115 ka
it is shown by most records that a shift occurred to progressively
colder and drier conditions, with rapid climatic swings (Kukla et
al., 2002). As the world
entered another dry, windy glacial phase, about 71 ka, MIS 5 ended. This
time also saw a peak in the wind-borne dust at 70-60 ka, as recorded in
the Vostok ice core in Antarctica (Petit et
al., 2009). These shifts are
also seen in palaeoenvironmental records where they are registered in
various ways, such as a reduction of rain in global cold stages that
resulted in the drying of lakes and rivers, reduction of vegetation
cover, activation of sand dunes, and increased dust advection (Hesse,
Magee & van der Kaars, 2004: 118). Smith, Mike, 2013,
The Archaeology of Australia’s
Deserts, Cambridge University Press
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |