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

Abstract The Murujuga Archipelago, Western Australia, hosts over one million petroglyphs preserving 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, with negative consequences for rock art, and implications for rock art conservation and the world heritage listing. That paradigm is based on the assumptions that rain in Murujuga is acidic and that damage would be recorded primarily by the patinated surface. 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, and 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 incorrect, that damage at Murujuga is likely historic, and that the patina substrate may provide a new sensitive and reliable monitor of damage that can be used at heritage sites worldwide.