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dc.contributor.advisorTyler, Jonathan-
dc.contributor.advisorTibby, John-
dc.contributor.authorFalster, Georgina Maja-
dc.description.abstractAustralia’s climate is influenced by ocean-atmosphere interactions in the adjacent Indian, Pacific, and Southern oceans, as well as major atmospheric circulation patterns. Australian climates exhibit high inter-annual variability, arising in part from complex interactions between these drivers. Understanding the nature and drivers of Australian climate variability is not only important for land use and management, but also has global relevance, due to Australia’s contribution to the global terrestrial carbon budget. Measurements of Australian temperature and rainfall only extend back to the early 20th century, and hence do not capture the full range of natural climate variability. Proxy-based climate reconstructions are therefore required to understand Australian climate variability on long (centennial to millennial) time scales. The late Quaternary—defined in this thesis as 30 to 10 thousand years before the year 1950 (ka BP)—is a particularly informative interval. It encompasses large changes in global climate dynamics, including both the global Last Glacial Maximum (LGM; 23 to 19 ka BP) and subsequent deglaciation, allowing assessment of the Australian climate response to global change. However, the arid to semi-arid nature of most the continent is not conducive to sedimentary record accumulation, limiting spatial and temporal resolution of existing late Quaternary climate reconstructions. This thesis therefore presents both new late Quaternary palaeoclimate data and new methods for inferring past climate across the Australian continent, through the following research components: 1) A record of late Quaternary moisture balance, inferred from highly resolved x-ray fluorescence and organic carbon isotope measurements of a sedimentary sequence from Lake Surprise in south-eastern Australia (Chapter 3). The regional significance of this record is assessed using a Monte Carlo Empirical Orthogonal Function approach. 2) The high-resolution record is supported by three discrete quantitative temperature estimates, based on the clumped isotope composition (Δ47) of freshwater snail shells from Blanche Cave, also in south-eastern Australia (Chapter 6). Δ47 analysis allows calculation of the growth temperature of carbonate minerals (e.g. snail shells), independent of organism, carbonate phase, or formation water geochemistry. Carbonate Δ47 analysis therefore offers a uniquely direct estimate of past temperatures, that has not previously been applied in Australian palaeoclimate studies. 3) Clumped isotope analysis is highly susceptible to contamination, so this thesis provides a new pretreatment method for obtaining precise and accurate data from carbonates preserved within an organic-rich matrix (Chapter 2). 4) The influence of remote drivers of Australian climate often manifests in distinct spatial patterns of temperature or rainfall. However, the low spatial resolution of existing palaeoclimate records across the continent inhibits detection of spatio-temporal climate trends that would facilitate inference of these drivers. This thesis therefore evaluates the climate proxy potential of land snail shells in Australia, by combining flux balance models with clumped and stable isotope measurements of modern shells collected from a wide spatial and climatic gradient across the continent (Chapters 4 and 5). The palaeoclimate reconstructions provide a coherent record of climate variability prior to and throughout the late Quaternary, and suggest that drivers of south-eastern Australian climate have varied on multi-millennial time scales in response to major shifts in global circulation. Δ47 analysis of freshwater snail shells suggests that between ~41 and 32 ka BP, mean annual air temperatures at Blanche Cave decreased from approximately 12 ± 3.2 °C to 5 ± 4.4 °C i.e. almost ten degrees cooler than modern. These relatively low temperatures preceded a period of regional aridity between 28 and 18.5 ka BP as recorded at Lake Surprise. Together, the data suggest that the south-east Australian climate was probably responding to very different drivers to those that affect the modern climate, possibly dominated by cold Southern Ocean processes. Centennial- to millennial-scale hydroclimate variability was maintained throughout the 28–18.5 ka BP interval. Peak aridity between 21 and 18.5 ka BP probably represents the local expression of the global LGM. A rapid deglacial climate shift occurred between ~18.5 and 16 ka BP, culminating in warmer (15.5 ± 3.6 °C) and wetter conditions probably more like those of the present. The stable isotope geochemistry of modern land snail shells records precipitation amount via two mechanisms: (1) its influence on the δ18O of precipitation (a wet season signal), and (2) its effect on vegetation δ13C (an annual to multi-annual signal). Unlike freshwater snails, land snail Δ47 growth temperatures do not have a straightforward relationship with average air temperatures, but rather are useful for extracting the temperature influence from snail shell δ18O. This is the first study to report δ13C, δ18O, and Δ47 measurements from land snail shells spanning such a large climatic gradient, and also the first to investigate snail isotope-climate relationships across the variable and largely arid Australian environments. The isotope-climate relationships are robust irrespective of species or regional climatology. With land snails widely distributed in Australia, including in arid climates that lack other suitable proxies, these consistent relationships demonstrate that land snail shell isotopes will be a valuable tool for assessing spatio-temporal precipitation variability at a continental scale.en
dc.subjectclumped isotopesen
dc.subjectstable isotopesen
dc.subjectscanning XRFen
dc.subjectlast glacial maximumen
dc.titleReconstructing Australia’s late Quaternary climate from the geochemistry of lake sediments and snail shellsen
dc.contributor.schoolSchool of Physical Sciences : Earth Sciencesen
dc.provenanceThis electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at:
dc.description.dissertationThesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 2019en
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