Investigating the impact of millennial scale climate events on southern Australia during the Last Glacial Period

This project aimed to investigate how southern Australia was impacted by the AMOC driven millennial scale climate events of the Last Glacial Period.

Paleoclimate studies have demonstrated that abrupt millennial-scale climate events during the Last Glacial Period coincided with variations in the strength of the Atlantic Meridional Overturning Circulation (AMOC). These include Dansgaard-Oeschger events, which coincide with periods of AMOC strengthening, and Heinrich events, which coincide with AMOC weakening or collapse.  

Whilst numerous paleoclimatic studies have examined the global climatic and environmental consequences of these events, relatively few of these studies are based in the southern hemisphere, even fewer in Australia, with southern Australia largely overlooked. This is a problem, as there is currently very little understanding of how the southern Australian hydroclimate, fire regimes and vegetation was impacted by AMOC slowdown and/or shutdown in the past. Moreover, the scarcity of high resolution, temporally extensive paleoclimatic records in southern Australia constrains our capacity to understand interhemispheric leads & lags as well as the local response to rapid climate events.

To address these knowledge gaps, this project produced three new southern hemisphere mid-latitude paleoclimatic datasets and improved the age-constraints and proxy resolution on one existing published paleoclimatic dataset.

Three speleothems were analysed for this project- from Mammoth Cave (Southwest Western Australia), Kubla Khan Cave (Tasmania, Australia) and Hollywood Cave (South Island, New Zealand). We investigated the paleohydrology of these sites using stable isotope analysis (δ¹⁸O and δ¹³C), trace element analysis and geochronology (U-Th dating). The datasets from Mammoth Cave (38-14ka) and Kubla Khan (75-23 ka) have demonstrated hydroclimate excursions associated with millennial climate events, likely due to the meridional displacement of the South Westerly Winds. Extensive U/Th dating of the Hollywood Cave speleothem (73-11ka) has altered the pre-existing, published age model, with implications for the current interpretation of millennial climate event timing in the southern mid-latitudes.

A lake sediment sequence was also analysed as part of this project, to determine the vegetation, fire regime and hydroclimate impacts of AMOC driven millennial climate events. Lake Bullen Merri (western Victoria) was cored in early 2025, yielding 15m of lake sediment and ~36,000 years of climate history. Thirty-one 14C dates have been returned, providing a robust age-depth model. A suite of analyses have been applied to this sediment core; X-RF, magnetic susceptibility, loss on ignition, palynology, macroscopic and microscopic charcoal counting, biomarkers (n-alkanes, sterols, PAH’s) and leaf wax H-Isotope analysis. These results show significant hydroclimate & fire activity excursions throughout the past ~36,000 years, with higher resolution proxy analysis underway to highlight millennial/centennial scale excursions.

These results provide one of the first insights into the way southern Australia is impacted by millennial scale climate events, offering a valuable regional insight, as well as a point of comparison for interhemispheric studies.