Pollen, biomarker and stable isotope evidence of late Quaternary environmental change at Lake McKenzie, southeast Queensland

Unravelling links between climate change and vegetation response during the Quaternary is important if the climate–environment interactions of modern systems are to be fully understood. Using a sediment core from Lake McKenzie, Fraser Island, we reconstruct changes in the lake ecosystem and surrounding vegetation over the last ca. 36.9 cal kyr. Evidence is drawn from multiple sources, including pollen, micro-charcoal, biomarker and stable isotope (C and N) analyses, and is used to gain a better understanding of the nature and timing of past ecological changes that have occurred at the site. The glacial period of the record, from ca. 36.9 to 18.3 cal kyr BP, is characterised by an increased abundance of plants of the aquatic and littoral zone, indicating lower lake water levels. High abundance of biomarkers and microfossils of the colonial green alga Botryococcus occurred at this time and included large variation in individual botryococcene d13C values. A slowing or ceasing of sediment accumulation occurred during the time period from ca. 18.3 to 14.0 cal kyr BP. By around 14.0 cal kyr BP fire activity in the area was reduced, as was abundance of littoral plants and terrestrial herbs, suggesting wetter conditions from that time. The Lake McKenzie pollen record conforms to existing records from Fraser Island by containing evidence of a period of reduced effective precipitation that commenced in the mid-Holocene

Aquatic ecosystem response to late Pleistocene and Holocene climate variations : a palaeolimnological investigation of three lakes on Fraser Island, Australia

High resolution palaeoecological data is a valuable tool to determine past climate variability and ecological responses. This thesis examined the aquatic community response of three lakes on Fraser Island using biological and geochemical records for the last 18,000 years. The lake records demonstrate a trend of decreasing precipitation throughout the late Holocene, with increased climatic variability represented by episodic events. From these records, a more detailed knowledge of climate change in eastern Australia during the Holocene has been identified

Water quality changes in Lake McKenzie, Fraser Island, Australia: a Palaeolimnological approach

Surface water resources are highly valued for their ecological services and functions. However, their quality is under threat from anthropogenic activities and climate change. A detailed understanding of natural aquatic conditions and variability is rare. This is particularly the case in Australia where the variable climate produces significant ecological changes within natural thresholds and few long-term environmental data sets exist. Palaeoecology represents a means to identify natural fluctuations of aquatic ecosystems and provide long-term data for effective environmental management. This study uses a palaeoecological approach to identify biological and sediment changes in Lake McKenzie, Fraser Island, Australia. A sediment core was extracted from the lake and the fossil diatom assemblage and sediment particle size analysed. Inferred environmental changes were detected throughout the core that pre-date European impacts. The likely causes of these changes are climatic oscillations. Further dating is required to establish a detailed chronological record and identify the timing of detected environmental change at Lake McKenzie

Mid-Holocene palaeolimnological record of a Southern Hemisphere subtropical lake spanning the last ~6000 years: Lake Jennings, Fraser Island, Australia

The study of climate mechanisms in the Southern Hemisphere during the Holocene remains an area of active research that lacks the spatial and temporal connectivity characteristic of Northern Hemisphere research. The subtropical/temperate climate transition zone of eastern Australia provides a unique location to investigate long-term environmental changes during the Holocene. Lake Jennings on Fraser Island was used to investigate climate change in this transition zone using palaeolimnological techniques. The beginning of the Lake Jennings record (~6000 to 3500 cal. yBP), is characterised by fluctuations in geochemical signals, an abundance of sponge spicules, and a lack of diatom species. Results suggest gradually increasing precipitation and water depth, which affect nutrient cycling. However, the biological functioning of the lake is difficult to interpret due to the absence of diatoms, possibly a result of turbidity, dissolution and/or predation by freshwater sponges. During the late Holocene, ~3500 cal. yBP to present, precipitation and water depth of the lake decreases to present day levels. Within this section of the core nutrient cycling changes, as indicated by the geochemical results, and a series of more intense wet and dry events took place before stabilising at present day levels. Other palaeoecological studies within the Southern Hemisphere have noted changes in geochemical and biological attributes within similar latitudes, confirming the notion of climate forced environmental change in aquatic ecosystems. This continuous ~6000 year record from Lake Jennings shows distinct changes in aquatic communities, confirming a trend of drying in subtropical eastern Australia through the late Holocene