EAGER: Development of a High-Resolution, Multi-Century Paleo-Fire Reconstruction from Tropical Australian Stalagmites

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Fire plays a critical role in ecology, especially in the dry tropics such as the savannas of northwestern Australia. The pace and extent of the burning of vegetation and litter (biomass) in a region reflects both human activities and the amount and timing of rain and lightning. Attempts to understand historic rates of biomass burning are hampered by few continuous records, records of fire at annual resolution, and records that span multiple centuries. This project explores a new method of recording the occurrence of historic fires by measuring traces of organic chemicals produced by fires that are captured within cave stalagmites. The project focuses on stalagmites in a well-studied cave in northwest Australian to develop a multi-century-long record of fire activity. In addition, these stalagmites provide a detailed record for constructing a 3000-year history of summer monsoon rainfall. By combining the records contained in the stalagmites, researchers will provide the first millennial record of the role of human activity and monsoonal rains in shaping the landscape and ecology of the dry tropics. This new methodology is a potentially transformative approach to characterize fire occurrence, and would be of general value in understanding the historic role of fire in other regions of the planet. Such information is extremely useful to land managers. This project will also provide research training for students at a primarily undergraduate US institution.Polycyclic aromatic hydrocarbons (PAHs), including fluoranthene, pyrene, benzo(a)pyrene and indeno(1,2,3-c,d)pyrene, are produced by burning of biomass and are characterized by high persistence in the environment. PAHs have been recovered from lake sediments spanning several millennia and prior studies have used them to reconstruct fire histories of the surrounding watershed. The investigators have developed a novel method for the extraction of PAHs from stalagmites and preliminary PAH analyses using high resolution 230Th-234U dating methods of the stalagmite carbonate were consistent with satellite maps of burn scars in revealing that 2004 was the only year to experience a burn over the cave. PAHs in these stalagmites may thus represent an important new high-resolution record of prehistoric fire activity in tropical karst regions such as Western Australia and can complement the monsoon rainfall reconstructions extracted from the same samples. This EAGER award will extend the analysis of fire-related organic compounds in these stalagmites through the 17th century to capture changes in burn activity associated with (1) changes in land use associated with European settlement in the 1880s, and(2 changes in monsoon activity associated with the transition from the Little Ice Age to the Modern Era.