Saturday, 27 August 2016

Climate change data may help date Kimberley rock art

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Gwion-Gwion rock art at the Mitchell Plateau in the Kimberley. Gwion-Gwion rock art at the Mitchell Plateau in the Kimberley. Kimberley Foundation Australia
  • Researchers are analysing North Kimberley mound springs to chronicle climate change.
  • Early analysis suggests rock art styles changed when the climate became more habitable
  • Core samples turn up evidence of past bushfires and seasonal surface water

CORE samples from north Kimberley springs may provide rock art scientists with a timeline of the region's climate history to help figure out why there was a sudden changes in cave painting styles.

A rock art style, known as Gwion-Gwion paintings, incorporating lively stick figures is thought to date from a time of abundant rainfall and food when people could stay put for long periods.

Previous research found Gwion-Gwion paintings apparently stopped production roughly 5,000 years ago and that a different type of rock art, known as Wanjina, started to appear from 4000 years ago onwards.

It was thought that early humans stopped painting the Gwion-Gwion art because the region's climate started to dry out and so the people left the area and that their descendants returned when the climate stabilised and brought with them the Wanjina painting style.

Gwion-Gwion art in the north-west Kimberley. Credit: The Kimberley Foundation Australia.

 

Other researchers inferred climate change in this part of the Kimberley from climate records obtained at more distant sites.

However, the current research project saw University of Queensland scientists study unusual peat (decaying vegetation) mounds at four inland springs in the heart of Wanjina rock art country to shed light on local climatic history.

Paleoecologist Emily Field and her PhD program supervisor Hamish McGowan have preliminary dates from a 1.7m core taken from Black Springs on Drysdale River station, about 200km east of Wyndham.

Ms Field says the core is thought to represent 15,000 years of local climate history and shows vegetation changes indicated by fossilised pollens.

She says other climatic indicators in the core are specks of charcoal, suggesting bushfires, and cysts of the algae Pseudoschizaea showing the presence of seasonal surface water.

Based on this record she believes monsoon activity picked up about 14,000 years ago with a pronounced increase in rainfall from about 9,000 years before the present.

Emily Field testing water quality at Fern Pool, North Kimberley. Credit: Professor Hamish McGowan.

 

She says this rainfall appeared to persist until about 5,000 years ago, after which the climate becomes more variable and which correlates with the previous dating of the Gwion-Gwion paintings.

“We see sharp and pronounced fluctuations in vegetation assemblages and the organic contents of the sediments,” she says.

“We then see an arid phase beginning at 2,600 years before present where the vegetation in the savanna surrounding the spring becomes more open and we get large declines in the aquatic taxa.

“We also have increasing charcoal deposited in the sediments indicating an increase in burning likely related to this dry phase.”

Ms Field is now analysing cores taken from nearby Fern Pool and Gap Springs which so far show good correlations with the Black Springs climatic data.

Notes:

The research is funded by the Melbourne-based Kimberley Foundation, dedicated to studying and conserving Kimberley rock art.

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