C01_P04

Holocene fire recorded in dune footslope deposits at the Cooloola Sand Mass, Australia

Patton N^1,2, Shulmeister J^1,2, Hua Q³, Almond P⁴, Rittenour T⁵, Hanson J^1,2, Grealy A², Gilroy J², Ellerton D^2,6

¹School of Earth and Environment, University of Canterbury, Christchurch, New Zealand, ²School of Earth and Environmental Sciences, The University of Queensland, Brisbane, Australia, ³Australian Nuclear Science And Technology Organisation, Lucas Heights, Australia, ⁴Department of Soil and Physical Sciences, Lincoln University, Christchurch, New Zealand, ⁵Department of Geology, Utah State Luminescence Laboratory, Utah State University, Logan, USA, ⁶Department of Geological Sciences, Stockholm University, Stockholm, Sweden

Fire is one of the most dominant landscape disturbances on Earth. There are large and growing paleo-fire datasets, but they are strongly biased towards wetland areas (e.g., peat bogs, swamps and lakes). In this study, we investigate whether terrestrial depositions within the Cooloola Sand Mass coastal dune field, Australia, contain a reliable record of fire history. We excavated four profiles at the base of dune slipfaces (foot-slopes) and calculated charcoal concentrations for three size classes (180-250μm, 250-355μm and 355μm-2mm) at predetermined depth intervals. Bayesian age-depth models were constructed for these profiles using radiocarbon measurements on charcoal (n = 46) and basal OSL dates (n = 4). All records appeared intact with little evidence of post depositional mixing as demonstrated by minimal age-reversals and consistent trends in charcoal concentration and accumulation rates amongst size classes. Aggregating all four records, we generated a terrestrial fire history for the past ca. 7 ka that depicts five distinct peaks representing periods of increased local fire activity: ca. present-0.25, 0.4-1.2, 1.8-2.2, 2.6-3.6 and 5.2-6.7 ka. In general, the charcoal peaks increase in frequency after ca. 4 ka, possibly related to the onset of ENSO. Our findings parallel those recorded outside the dune field and highlight their utility as an ecological and geomorphological record that is abundant across the landscape. As dune fields are much more common than wetlands and lakes in semi-arid and arid areas, these deposits have the potential to increase the spatial resolution of fire records globally.