Impacts of industrial emissions on rock art at Murujuga, Western Australia

The Murujuga Archipelago, Western Australia, hosts over one million petroglyphs that preserve indigenous knowledge spanning 50,000 years. This globally significant and newly UNESCO-listed world heritage site is co-located with heavy industry. Low values of pH on patinated rock surfaces have provoked concern that acid rain from reactive industrial emissions is dissolving the patina. Any such damage has negative consequences for rock art and implications for rock art conservation and the world heritage listing. This model is largely based on assumptions that rain in Murujuga is acidic and that the patinated surface provides the most sensitive record of damage. Via an innovative multidisciplinary statistically based integration of geochemical, environmental, and air-quality data, we show that the rain is not acidic, that rock surface pH patterns do not reflect current air-quality patterns, but that the porosity of the outer layer of granophyre rocks is elevated in areas where historic SO2 emissions were highest. These findings suggest that the acid deposition theory is flawed, that damage at Murujuga is likely historic, and that the outer layers of rock may provide a new sensitive and reliable monitor of damage that can be used at heritage sites worldwide.