Australia: The Land Where Time Began

A biography of the Australian continent 

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).

Sources & Further reading

Smith, Mike, 2013, The Archaeology of Australia’s Deserts, Cambridge University Press


Author: M. H. Monroe
Last updated: 10/04/2014
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