Long-term climate dynamics and carbon cycling in eastern Australian from MIS5 to present

The last glacial cycle is a key period in the environmental and cultural history of the Australian continent, yet the climate of this time period remains poorly understood. Conflicting evidence from spatially disparate lacustrine records and discontinuous fluvial archives have hindered consensus on environmental change during this period. Here, we present two new, highly resolved organic sedimentary records from the Thirlmere Lakes (NSW) and Minjerribah (North Stradbroke Island, QLD) regions of eastern Australia that provide new constraints on long-term climate and environmental variability through the last glacial cycle.Australian aquatic systems often deviate from biogeochemical frameworks developed largely from Northern Hemisphere environments. The prevalence of low-nutrient conditions results in unusual carbon isotope signatures, complicating the identification of organic carbon sources and their transport between terrestrial and aquatic reservoirs. Through characterisation of modern aquatic carbon isotopes, we develop alternative threshold values for distinguishing organic matter sources and, in turn, demonstrate the utility of sedimentary stable carbon isotopes as robust tracers of environmental and climatic change in southern mid-latitude systems.Applying these newly developed isotope thresholds, we reconstruct millennial-scale climate variability in eastern Australia from Marine Isotope Stage 5 to the present. The resulting records reveal strong coupling between regional carbon cycling and Southern Hemisphere high-latitude climate, with limited evidence for Northern Hemisphere forcing. These findings highlight the importance of regionally calibrated carbon isotope frameworks and demonstrate the value of stable carbon isotopes for reconstructing past Earth system change in under-represented Southern Hemisphere environments.