Australia: The Land Where Time Began

A biography of the Australian continent 

Collapse of Prehistoric Aboriginal Society in Northwestern Australia Triggered by an ENSO Mega-Drought

One of the largest collections of rock art in the world is present in the Kimberley region, Western Australia, that is characterised by 2 distinct art forms; the anthropomorphic figures of the Gwion Gwion, or Bradshaw, paintings, that are fine-featured, and the Wandjina figures that are characterised by broad brush strokes. An age of at least 17,000 BP has been confirmed for the Gwion Gwion paintings by the most recent dates obtained by luminescence dating of mud wasp nests that were present on top of the Gwion Gwion paintings, with the most recent dates for these paintings being 7,000-5,000 BP, from near the mid-Holocene. It has been found by radiocarbon dating that there was a hiatus of at least 1,200 years following the latest of the Gwion Gwion until the earliest known appearance of the Wandjina rock art. In this paper the authors1 show that in the mid-Holocene an ENSO event triggered a collapse of the Australian summer monsoon which led to a mega-drought that lasted for about 1,500 years and it was this long period of continuous drought that triggered the society responsible for the Gwion Gwion rock art to collapse. The authors suggest the severity of the drought, that was enhanced by positive feedbacks resulting from changes in the conditions of the land surface and an increase of atmospheric aerosol loading, which led to a weakening or complete loss of monsoon rains. According to the authors this confirms a catastrophic upheaval that occurred in Aboriginal societies, caused by rapid natural variability of the climate, and they also suggest these heavy rains of the wet season could possibly fail again if there is significant change to the ENSO.

Conclusion

According to the McGowan, Marx, Moss, & Hammond1 they have shown the first evidence of significant rapid change in the monsoon over northwestern Australia that occurred during the Middle to Late Holocene. The Southern Hemisphere subtropical ridge was allowed to extend further to the north as the changes to the monsoon were linked to enhanced ENSO and associated breakdown of positive moisture-advection onto the Kimberley region. Prolonged aridity coeval with major change in rock art that resulted from the failure of the monsoon was confirmed by palynological and sedimentological evidence from the Black Springs site. The authors therefore concluded that a change in artists of the Kimberley rock art was the result of change of the northwest Australian monsoon that was forced by ENSO.

See Holocene Changes in Australian-Indonesian Monsoon Rainfall - Stalagmite Evidence from Trace element & Stable Isotope Ratios

Sources & Further reading

  1. McGowan, Hamish, Samuel Marx, Patrick Moss, and Andrew Hammond. "Evidence of Enso Mega-Drought Triggered Collapse of Prehistory Aboriginal Society in Northwest Australia." Geophysical Research Letters 39, no. 22 (2012): L22702.

 

Author: M. H. Monroe
Email:  admin@austhrutime.com
Last Updated 27/11/2013
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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading