Bushfire impacts proposed Anthropocene markers in a southern hemisphere world heritage peatland

Humankind has left an indelible mark on natural ecosystems. This has fuelled proposals that we have exited the Holocene and entered the Anthropocene. The Anthropocene is commonly proposed to have commenced in the mid-20th century, marked by the presence of radionuclide fallout from above ground nuclear testing. Peatlands develop through progressive accumulation of partially decomposed plant material in saturated environments, and in Australia have a restricted distribution covering approximately 2.3 Mha. Detailed examination of a peat profile was conducted at Mount Banks, within the Greater Blue Mountains World Heritage Area, Australia. Soil chemistry, palynology, radiocarbon (¹⁴C), lead (²¹⁰Pb), plutonium (²³⁹Pu, ²⁴⁰Pu, and ²⁴¹Pu), and uranium (²³⁶U) isotopes were assessed to develop a record of environmental conditions into the proposed Anthropocene (mid-20th century). This site formed from the Meghalayan stage (1550 ± 30 years BP at 70 cm) and exhibited a relatively stable sedge and shrub vegetation community, interrupted with periods of fire through time which influences ²¹⁰Pb age-depth modelling. Peak radionuclide fallout (at 9.5 cm) occurred in the fibric zone and fallout levels of total plutonium and ²³⁶U were below global mean values, aligning with previous research in the Southern Hemisphere. To the best of our knowledge, this is the first study to examine the vertical distribution of fallout plutonium and uranium isotopes in south-eastern Australian montane peatlands. Peatlands face an uncertain future under projected climatic changes. Enhancing understanding of risks is essential to navigate the transition into the proposed Anthropocene and maintain these unique environments for the future.