Monitoring man-made emissions at Murujuga

Ancient art depicting now-extinct animals and some of the earliest known images of the human face have adorned the rocks at Murujuga for some 50,000 years.

The petroglyphs situated 1300km north of Perth in Western Australia have withstood the test of time, glacial and interglacial cycles and transformative environmental and climate changes.

Rising sea levels have shifted the coastline 160km east over the past 10,000 years, transforming Murujuga – or ‘hip bone sticking out’ in the Ngarluma-Yaburara language – from a rocky desert outcrop into a coastal habitat on the western edge of the Pilbara region.

Still, one to two million petroglyphs survived and they are considered to be the largest collection of Aboriginal engraved rock art in the world.

But there are fears human intervention and pollution is accelerating natural weathering at the location, which is recognised as a unique ecological and archaeological area by the WA government and was nominated as the next Australian UNESCO World Heritage Site last February.

Emissions caused by maritime shipping, terrestrial traffic, local industry and both planned burn-offs and uncontrolled bushfires may be doing untold damage to the area.

The Murujuga Aboriginal Corporation – a representation of the traditional custodians – have long protested the industrialisation of the area, saying it could lead to the gradual removal of Indigenous rock art from the site.

As recently as April, they expressed outrage over the commencement of construction on a fertiliser plant in the area, also known as the Burrup Peninsula.

While there have been several independent scientific studies undertaken into the effects of industrial air pollution on the petroglyphs since the mid-2000s, none have been conclusive, says the corporation’s acting CEO Travis McNaught.

“This led to the forming of the Murujuga Rock Art Monitoring Program, which will deliver a scientifically rigorous approach to monitoring, analysing and managing the rock art,” he told AAP.

Working with the WA government, the program will assess the impact of human-caused emissions and help determine what can be done to preserve the culturally and historically significant area.

Earlier this month, the Australian Nuclear Science and Technology Organisation (ANSTO) installed a 1500 litre atmospheric radon-222 detector at one of the 16 monitoring sites across the 100,000 hectares that make up Murujuga.

It has been rated the world’s best monitor by the World Meteorological Organisation for measuring global and regional atmospheric composition.

“We use radon as a natural atmospheric tracer, so it helps to distinguish the origins of different air masses and pollution,” says ANSTO’s Dr Scott Chambers, who installed the monitor.

This is to better understand the changing atmospheric composition on the rock and how that might affect the artwork.

“This is important in a place like the Murujuga region where meteorology is complex and there are many different pollution sources.”

These can be ‘natural’, such a sea salt, emissions from ocean plankton and bushfires; human-caused ‘direct’ emissions like pollution from gas rigs, ships, growing townships and local iron ore production; or secondary ‘indirect’ emissions like acid rain or changes to the ozone layer.

“In addition to helping distinguish between sources of natural or anthropogenic gases and aerosols that may impact the rock art, the high quality radon measurements will assist in determining changes in background greenhouse gas concentrations and improve the performance of leading global climate and chemical transport models,” Dr Chambers says.

Monitoring radon gas, which is emitted naturally from all rocks and soils, would also make it possible to establish which gases were locally-generated and which have come from distant sources or across the ocean.