Boats help beat desert climate change

Early Aborigines were either accomplished inland seafarers, or pretty good long-distance swimmers, as they coped with climate change in the middle of the Australian desert some 24,000 years ago.

A new international study has discovered that Australia's iconic Lake Mungo – which has been dry for the past 15,000 years – once held 250 per cent more water than previously thought, and was connected to a neighbouring lake for a brief period before the peak of the last ice age.  

The study was published today in the Public Library of Science journal PLOS ONE.

It was led by geologist Dr Kathryn Fitzsimmons from Germany's Max Planck Institute for Evolutionary Anthropology, La Trobe University archaeologist Dr Nicola Stern and geologist Professor Colin Murray-Wallace from the University of Wollongong.

Dr Stern said the mega lake was so large before the peak of the last ice age that water levels rose by five metres, creating an island between Lake Mungo and the adjacent lake. 

While it cut off people from their usual hunting grounds, artefacts found on the island – such as stone tools, burnt bones and multiple hearths – showed that people repeatedly visited the island to exploit its food resources.

Dramatic change

She said discovery of the mega-lake showed climate and landscapes can change suddenly and dramatically, and that people seemed to adapt pretty quickly to such changing conditions.

The study also revealed variation in the shorelines of the main lake compared with the former mega-lake, indicating possible warping by recent tectonic activity.

It noted while Australia was often perceived as tectonically stable, these observations highlighted the need to better understand the influence of stresses in the Earth's crust.

Lake Mungo is the best-known basin within the Willandra Lakes Region World Heritage Area in semi-arid south-eastern Australia. Its shoreline preserves Australia's oldest known human remains.  

The area's archaeology documents human behaviour over the last 50,000 years, while its sediments illustrate environmental change over 100,000 years. This provides a unique record of interactions between people and their environment over time.

The researchers say it had been assumed until now that Lake Mungo was once always filled to the same level from a neighbouring lake.

State of the art techniques

However, using the latest in differential global positioning systems and luminescence dating techniques, their study revealed an additional line of beach gravels five metres above the main shoreline.

Reconstructing the mega-lake using a digital elevation model, they discovered it was linked to the neighbouring lake at two overflow points, creating the island on which they found a lot of their evidence.

The researchers concluded that for the lake to fill to such levels, there most likely was a pulse of extremely high rainfall as the climate cooled, just prior to the peak of the last ice age.

'We know that the last ice age in Australia was cold and dry,' says Max Planck's Dr Fitzsimmons. 'Our results confront previous assumptions and indicate a non-linear transition into the ice age – implying that climate change is not always smooth.'

She said there was no evidence for watercraft use in Australia between colonisation of the continent more than 45,000 years ago, and 6,000 years ago.

Although no evidence of boats was found during their study, repeated visits to the island may represent indirect evidence for a resurrection of water-faring technologies following a pause of at least 20,000 years.

More about archaeology at La Trobe

Media contact: Ernest Raetz, 0412 261 919.