School of Earth Sciences - Theses
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ItemCovariances in the weather and the influence on an Australian large-scale renewable electricity system( 2014)Sometime in the future Australia’s demand for electricity will undoubtedly need to rely on significant amounts of Renewable Electricity (RE). Fossil fuels are inherently non-renewable and their dwindling supply will force investment in alternatives. There is therefore a need to research how such increased penetrations of RE resources will be managed. Installed across large areas, a National Electricity Market (NEM) with increased contributions from RE will be affected by large-scale meteorological variability. The synoptic scale (100s-1,000s of km and days-weeks) weather systems are of particular interest. This thesis examines how synoptic scale weather variability might affect a future highly RE dependent Australia using two approaches. Approach one (Part 1 of the thesis) identifies the common synoptic scale weather systems from a reanalysis data set (ERA-Interim) and then analyses the availability of wind and solar associated with each weather type. Approach two (Part 2) utilises data from a regional model (ACCESS-R) as part of an electricity model that maximises the contribution of wind and solar electricity in meeting the demand of Australia. The influence of the weather systems identified in Part 1 on the optimised electricity network is then analysed. Part 1 of this thesis utilises the European Centre for Medium Range Weather Forecasting (ECMWF) reanalysis product ERA-Interim from 1989-2009 and for the Austral region (6S,105E) → (49.5S,165E). The Self-Organising Map (SOM) technique is then used to identify commonly occurring features in the ERA-Interim Mean Sea-Level Pressure (MSLP) field. The SOM technique converts the time series of MSLP to a time series of commonly occurring MSLP patterns, or weather types. The weather types are then analysed for their tendency to be associated with either high or low wind and solar potential. Some autumnal MSLP patterns are shown to be associated with very low wind speeds and solar irradiance for most of the Australian continent, while other summertime patterns show good potential for extracting wind and solar electricity. Following this an analysis of just the wind field demonstrates that decorrelation in the wind field is reached at a distance of approximately 1,300km. Part 2 of this thesis focuses on optimising renewable electricity capacity to meet electrical demand, using data from the Bureau of Meteorology’s high resolution regional weather model, ACCESS-R, for the period 2010-2011. The ACCESS-R data, in tandem with electrical demand data from the Australian Electricity Market Operator and a Genetic Algorithm, are utilised to investigate the influence of synoptic scale variability on a largely RE-based network. Wind and solar installations from locations across the ACCESS-R grid are optimally placed to maximise their contribution to meeting the electrical demand of 2010-2011. A gas-fired back-up system is deployed to cover moments when the combination of wind and solar cannot meet demand. The gas usage is made expensive to minimise its use, yet it is found that gas is still needed throughout the 2010-2011 period to cover moments when both the wind and solar are low. An investigation is then undertaken to determine any large-scale links to the minima in renewable generation. The common weather types identified in Part 1 are utilised in Part 2. By assigning SOM weather types to the 2010-2011 period it is shown that some regimes either adversely or favourably affect the net output of the optimised system. In particular, a late autumn and a summer weather type are shown to be significantly associated with very low RE output. The persistence and re-occurrence of low RE events shows that most episodes of low RE last for less than six hours and such low RE events have a mean return period of more than a week. Increasing the cost of transmission results in installed RE capacity contracting to four large wind stations and it is shown that the NEM region exhibits four distinct wind regimes. The wind regimes are highly uncorrelated and the minimum distance between regime locations reflects an approximate, but identical to Part 1, optimisation-based decorrelation length of 1,400km. In combination, Parts 1 and 2 of this thesis illustrate some of the issues that a future high penetration RE network might need to overcome. Knowledge of the influence of detrimental/favourable weather phenomena will be critical when designing and/or maintaining a large-scale renewable electricity network for Australia—in particular, knowledge of the decorrelation length-scale in the wind field.
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ItemInvestigating potential pathways to remediate thiocyanate-contaminated groundwater and wastewater at a Victorian gold mine( 2014)Thiocyanate (SCN-) is toxic to higher organisms, affecting the central nervous system, to cause irritability, nervousness, hallucinations, psychosis, mania, delirium and convulsions. This contaminant is commonly associated with gold mining activities and forms when cyanide, used for extraction of gold, reacts with reduced sulphur species in wastewater. Significant concentrations of thiocyanate have been detected in groundwater bores around the No. 2 Tailings Dam at Stawell Gold Mine in Victoria, with concentrations steadily increasing over time. Thiocyanate can be eliminated from groundwater and wastewater by oxidation to less harmful products such as ammonia and sulphate through chemical oxidation and biodegradation. Certain bacterial strains indigenous to thiocyanate-contaminated sites have demonstrated the ability to degrade thiocyanate and can be used to remediate contaminated land and water. Chemical and biological oxidation of thiocyanate was explored in this study through synthetic abiotic laboratory redox optimisation experiments and field-based injection experiments to determine the controls on thiocyanate degradation and potential pathways which could be implemented to remediate thiocyanate-contaminated groundwater and wastewater at the site. Analysis of site groundwater chemistry and aquifer properties revealed the presence of a plume of thiocyanate in acidic to near-neutral groundwater outside the tailings dam wall at monitoring bores SE12 and SE14 confined to the upper unconsolidated aquifer with low hydraulic conductivity (0.001-0.004 m/d) and low transmissivity (0.01-0.05 m2/d). The source of thiocyanate at the site was determined as the tailings dam. Inconclusive results from the nitrate reduction-thiocyanate oxidation experiments in synthetic and actual groundwater and wastewater suggests that nitrate may not form a redox couple with thiocyanate. However, in acidic solutions (pH 2) of Fe-EDTA and thiocyanate heated to 80°C, the Fe2+ was generated from thermal degradation of the Fe-EDTA compound, while thiocyanate was completely hydrolysed within 22 days. Catalysis of thiocyanate hydrolysis by iron reduction was not determined. However, solution pH and temperature were important factors, as thiocyanate hydrolysis did not proceed at pH 5.5 and 80°C. At pH 2, the hydrolysis of thiocyanate was faster at 80°C compared to 70°C. Thiocyanate-degrading microorganisms were not successfully stimulated in simulated injection (push-pull) experiments, as no appreciable decrease in thiocyanate concentrations was observed in groundwater or wastewater replicates.
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ItemThe palaeovegetation, palaeoclimate and biostratigraphy of South-eastern Australia during the Eocene Greenhouse to Oligocene Icehouse transition( 2014)The shift from the Eocene 'Greenhouse' to Oligocene 'Icehouse' conditions is a globally significant event. The Eocene – Oligocene boundary (33.9 million years ago) marks the onset of permanent large-scale glaciation in Antarctica and the onset of the current global climatic 'Icehouse‘ state. In the Austral-Antarctic region, the transition is well recorded in deep water marine carbon and oxygen isotopes, however in the terrestrial realm little is known of the nature of environmental change associated with this event. In Australia, this is partly due to a lack of precise methods of dating Paleogene terrestrial strata. The most common practice of dating terrestrial sediments is the application of Gippsland Basin‘s spore-pollen biostratigraphy. This research assessed the applicability of the Gippsland Basin‘s spore-pollen biostratigraphy to the Otway Basin. Results demonstrated Gippsland Basin‘s spore-pollen biostratigraphy provides inaccurate ages when applied to samples from the Otway Basin. In addition, results from pollen analyses combined with foraminifera, dinoflagellate, and calcareous nannofossils and other stratigraphic data were used to create a detailed climate history of this high palaeolatitude region (~60°S). The spore-pollen assemblage indicates the palaeovegetation of the Otway Basin was dominated by Nothofagidites spp., with an abundance of species from the families Myrtaceae, Casuarinaceae and Proteaceae. The Nothofagus-dominated mesothermal rainforest probably had an emergent layer of Podocarpaceae and Araucariaceae species and a diverse understorey of ferns. The palynological record of the Otway Basin shows no vegetation change occurred during the time prior to and across the Eocene-Oligocene boundary even though there is evidence of permanent continental–scale glaciation on Antarctica.
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ItemBiogeochemical arsenic cycling in the hydrothermal acid-sulfide springs at Waiotapu, New Zealand: implications for the evolution of arsenic resistance( 2014)Active acid-sulfide hot springs provide modern analogs for the geothermal systems of the early Earth where microbial metal(loid) resistance may have first evolved. One metal(loid) that potentially presented a critical geochemical challenge to the earliest biological processes is arsenic, present at high concentrations in the hot springs at Waiotapu on the North Island of New Zealand. Particularly of interest is the moderately acidic sulfidic Champagne Pool that features dissolved arsenic concentrations of up to 4.2 mg L-1. The biogeochemical arsenic cycle in Champagne Pool follows reaction paths that are not yet fully understood with respect to biotic versus abiotic contributions, but involve strong coupling to the biogeochemical sulfur cycle. In this PhD study, I quantified arsenic species at Champagne Pool via HPLC-ICPMS and detected arsenic oxyanions, arsenic thioanions and methylated arsenic species. Arsenite was the dominant species at Champagne Pool’s inner pool, rim and outflow channel (55% – 75% of total arsenic concentration), with dithio- and trithioarsenates forming 18% – 25% of total arsenic concentration. In the outflow channel, dimethylmonothioarsenate comprised up to 9% of total arsenic concentration, while on the highly siliceous outflow terrace „Artist’s Palette“, thioarsenates were the dominant species at 55% of total arsenic concentration. I also quantified the redox sensitive sulfur species sulfide, thiosulfate, sulfate and elemental sulfur via UV-VIS and HPLC-UV spectrometry. Sulfide and sulfate were measured at their maximum concentration in Champagne Pool and at the adjacent outflow terrace, respectively; whereas sulfite, not quantified in this study, could possible contribute up to 30% to the total sulfur concentration at the individual sites. Elemental sulfur, not included in the sulfur mass balance, reached its measured maximum concentration at the outflow terrace. Phylogenetic analysis of 16S ribosomal RNA genes of the whole microbial community obtained via metagenomic sequencing revealed the dominance of Sulfurihydrogenibium at all sites, with an elevated archaeal population including Thermofilum and Sulfolobus at the rim and outflow channel of Champagne Pool. This analysis revealed several phylotypes closely related to known sulfur oxidizing as well as sulfur reducing microorganisms. Functional gene analysis linked sulfur metabolizing genes to sulfur speciation results, supporting the potential for microbially mediated sulfur-dependent transformation of arsenite to thioarsenate species. Metagenomic analysis revealed genes encoding for the arsenate reductase ArsC at all sites, which, given the wide thioarsenate species distribution, suggests a possible early evolution for arsenate resistance in the absence of oxygen. Furthermore, the absence of the arsenite oxidase encoding gene aio at all sites suggests the priority of an arsenite detoxification mechanism over the energy conserving arsenite oxidation. Finally, the detection of methylated arsenic, a solely biogenic arsenic species, only at the outflow channel, and in conjunction with a significant increase in Aquificaceae, indicates a potential role for methyl transferases from this lineage in the evolution of thermophilic arsenic resistance. My PhD study highlights microbial contributions to coupled arsenic and sulfur cycling in an acid-sulfide hot spring that have implications for understanding the evolution of microbial arsenic resistance in sulfidic geothermal environments.
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ItemThermochronological and structural insights into the Mesozoic-Cenozoic tectonic evolution of the eastern Tibetan Plateau( 2013)This thesis explores the evolution of the eastern Tibetan Plateau (TP) in select areas, i.e. Yidun Arc, eastern Songpan-Ganze terrane (SGT), Longmen Shan (LMS) and Sichuan Basin (SB) using a combination of structural and thermochronological techniques. Results highlight the role of: (i) flat subduction of the Meso-Tethys in triggering crustal refrigeration and exhumation in the Yidun Arc; (ii) crustal strength discontinuities in transferring deformation in central Asia; (iii) inherited crustal architecture in forming the eastern TP margin; (iv) crustal extrusion in forming the post-collisional stress-regime and high elevations in the eastern TP; and (v) Late Cenozoic onset of the Asian monsoon in enhancing river incision in the southeastern TP. Thermochronology data from the Yidun Arc indicate a distinct phase of Late Jurassic-Early Cretaceous crustal refrigeration and exhumation, which is interpreted as resulting from flat subduction of the Meso-Tethys and subsequent Lhasa-Qiangtang collision along the Bangong suture. Such an interpretation is consistent with lithospheric features imaged by seismic data. Thermochronology data from the eastern SGT (including a deep >7 km borehole) point to a ubiquitous phase of Late Jurassic-Early Cretaceous cooling. This cooling is best explained by regional post-orogenic denudation, as a far-field response to Lhasa-Qiangtang collision to the south and extensive sinistral shearing along major faults bounding the SGT. Projecting these aforementioned events onto an Early Cretaceous paleogeographic terrane reconstruction, results in a new tectonic model, where shearing along the faults transferred strain related to the Lhasa-Qiangtang collision into central Asia. Structural and geochronological results from the southern LMS suggest that Early Cretaceous-Early Paleogene deformation of the LMS included a phase of crustal extension along its hinterland, and a phase of crustal shortening along its front, forming ~2-3 km thick foredeep deposits in the southwestern SB. This deformation assemblage is interpreted as the combined effect of failure of the LMS crustal wedge and clockwise rotation of the SGT. These results indicate that the pre-Cenozoic LMS was underlain by a thickened crust, which was further thickened by Late Cenozoic crustal shortening along a series of listric reverse-faults merging into a detachment seated at a depth of ~20-30 km. Thermochronology data from deep boreholes across a W-dipping reverse fault in the eastern SB point to a distinctive cooling episode in the hanging wall commencing at ~28 ± 3 Ma. This age constrains the timing of a Cenozoic shortening component along this structural belt corroborating that a phase of W-E shortening occurred in the eastern TP and SB. This finding is consistent with evidence supporting extrusion of the eastern TP. Enhanced river incision in the Yidun Arc (part of the southeastern TP) was initiated in the Early Miocene (~15-22 Ma). This timing is older than previous proposals for Late Miocene plateau formation and river incision elsewhere in the same region. It is concluded that the Early Miocene inception of river incision heralds the onset of surface uplift by continental subduction and extrusion, whereas Late Miocene incision was triggered by commencement of the Asian monsoon.
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ItemAerosol contributions to speleothem geochemistry( 2014)There is developing interest in cave aerosols due to the increasing awareness of their impacts on the cave environment and speleothems. This study presents the first multidisciplinary investigation into cave aerosols and their potential contribution to speleothem geochemistry. Aerosols are shown to be sourced from a variety of external emission processes, and transported into cave networks. Both natural (marine sea-spray, terrestrial dust) and anthropogenic (e.g. vehicle emissions) aerosol emissions are detected throughout caves. Internal cave aerosol production by human disruption has also been shown to be of importance in caves open to the public. Aerosols produced from floor sediment suspension and release from clothing causes short term high amplitude aerosol suspension events. Cave aerosol transport, distribution and deposition are highly variable depending on cave situation. Cave morphology, ventilation, and environmental conditions will influence how aerosols are distributed through cave networks. Aerosol deposition monitoring in Obir Cave, Austria has shown the significance of cave chamber size in aerosol transport, with large open chambers presenting higher levels of deposition. Modern monitoring of suspended aerosol concentrations, CO2 and temperature in Gough’s Cave, Cheddar Gorge have presented a strong relationship with cave ventilation processes. Temporal variations of aerosol levels have demonstrated the ability of aerosol monitoring to record seasonal ventilation shifts, beyond anthropogenic influences. Aerosol minima (based on 24 hours) provide a representation of natural aerosol baseline conditions without diurnal anthropogenic influences. Aerosols have shown a quicker recovery to natural background levels when compared to CO2 and T, making aerosols a sensitive and effective monitoring tool. When used in combination with more established monitoring methods, suspended aerosol monitoring is a beneficial addition to cave environmental studies. Theoretical modelling and calculations based on modern aerosol monitoring have established that aerosol contributions are highly variable. In some instances, modern aerosol supply is sufficient to account for speleothem geochemistry concentrations entirely. Aerosol contributions are of greatest significance under slow growth or hiatus scenarios and high aerosol deposition scenarios. Geochemical and stratigraphical analysis of a flowstone core from Gibraltar has highlighted the importance of hiatus events for future aerosol studies. Hiatus events provide a unique opportunity to investigate the type and amount of aerosol deposition and accumulation. Marine aerosol contributions have been quantified in the Gibraltar flowstone core and account for 18.5% of speleothem Sr. Sr isotopic analysis has confirmed the significance of marine aerosol contributions. Flowstone analysis has also demonstrated the ability of speleothems to record shifts in the supply of highly radiogenic terrestrial dust. Bio-aerosol deposits and bacterial colonisation have been identified as a potential source of trace element bioaccumulation and flowstone coloration in Yarrangobilly Caves, Australia. Bio-aerosols have shown to be deposited throughout cave networks. Inorganic aerosol deposition may provide a nutrient supply to cave surfaces allowing for, and sustaining microbial colonisation.
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ItemNeoproterozoic seas: ocean chemistry and marine carbonate mineralogy( 2014)The step-wise oxygenation of the ocean-atmosphere system is arguably one of the most profound processes in Earth history, affecting most surficial Earth processes. The last major oxygenation of the oceans is believed to have occurred in the Neoproterozoic Oxygenation Event (~800-540 Ma), and is implicated as a trigger for the rise of animal life. However, the timing of this event is not well constrained, both due to geochronological problems with Neoproterozoic stratigraphy; and because of the inherent uncertainty in ocean oxygenation proxies. Furthermore, there is now evidence for a more complex Neoproterozoic ocean chemical history, including return to strongly anoxic and ferruginous conditions. An additional complication in the understanding of Precambrian marine environments is the abundance of dolomite in Proterozoic successions. A recently discovered series of dolomitic reef complexes in the Neoproterozoic Adelaide Fold Belt, Australia, and Otavi Belt, Namibia, improve our understanding of Precambrian marine conditions. Stratigraphic and petrological analysis suggests that synsedimentary marine dolomite precipitation was pervasive within these reefs. Newly described dolomite cements have optical properties, chemical zonation and cathodoluminescent characteristics indicating that they were direct marine precipitates. Dolomite precipitation during marine diagenesis in these reef complexes suggests that the oceans of the Cryogenian were chemically different to those of the Phanerozoic. Marine dolomite precipitation appears to be linked to anoxic, magnesium-rich ocean conditions. These newly documented primary marine dolomite cements preserve information about conditions in the parent seawater via their petrographic properties and geochemistry. Being constrained by sedimentology, carbonate geochemistry provides a window into Cryogenian ocean chemistry and structure. Geochemical results reveal a pronounced chemical stratification where a thin veneer of oxic surface waters existed above a peritidal redoxcline with anoxic, strongly ferruginous seawater at depth. These conditions describe a ferro-sulfidic ocean and encompass some of the most extreme anoxia yet documented during the late Precambrian. A return to Archean-like ocean conditions at this time suggests large-scale disruption of the ocean system during the Neoproterozoic. These conditions may be linked to extreme climatic fluctuations at this time, perhaps induced by ocean stratification in this Neoproterozoic ‘Stagnant Earth’. When analysed in stratigraphic framework, variations in carbonate mineralogy provide a record of ocean oxygenation during the Neoproterozoic. New sedimentological and stratigraphic constraints for the Namibian Otavi Belt provides a context for this variation and has also led to the discovery of new Cryogenian reef complexes. When correlated with the Adelaidian succession, the distribution of marine cements in these sequences reflects changing seawater conditions. Pre-Sturtian, Neoproterozoic oceans precipitated both dolomite and aragonite and developed widespread marine anoxia prior to glaciation. Interglacial Cryogenian oceans were extremely anoxic and ferruginous, with widespread dolomite precipitation. In contrast, late Cryogenian and Ediacaran oceans hosted abundant aragonite precipitation recording a gradual decline in marine dolomitisation. The deepening of the oceanic chemocline during this interval suggests that these seas were likely to have been moderately oxygenated, paving the way for the large-scale radiation of animal life.
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ItemThe petrogenesis of Brazilian kimberlites and kamafugites intruded along the 125° lineament: improved geochemical and geochronological constraints on magmatism in Rondonia and the Alto Paranaiba Igneous Province( 2014)Despite a number of studies, the origin of ultrapotassic magmatism in Brazil remains contentious. In particular, problems relate to the timing of Cretaceous kimberlite and kamafugite magmatism within the Alto Paranaiba Igneous Province (APIP), the origin and relationship between the Cretaceous kimberlites and kamafugites, and the geochemical nature of the Permo-Triassic kimberlite magmatism. Many of these uncertainties arise as a consequence of either the implementation of now superseded analytical techniques or the use of highly altered samples. This study seeks to address these issues by performing state-of-the-art geochemical and geochronological analyses on a number of fresh kimberlite and kamafugite drill core samples situated along the 125° lineament. The first part of the thesis provides a comprehensive geochronological study of Brazilian kimberlites and kamafugites. This is built around a combination of the most recent U/Pb perovskite, Rb-Sr phlogopite, and Ar-Ar phlogopite dating techniques that together provide 33 age estimates, representing 22 separate intrusions, of which 11 are kimberlites and 11 kamafugites. The results are in broad agreement with previously published data, identifying a Permo-Triassic age for the Amazonian kimberlites, and kimberlites and kamafugites of Cretaceous age in the APIP. The new data from this study also support an age decrease from NW to SE within the APIP. However, data from this study suggest that this is not a continuous younging, instead indicating that two distinct magmatic episodes may exist. The data also reveal the presence of an “older” mid Cretaceous cluster (~88 Ma) encompassing Goias and the NW APIP (Southern Goiás and NW Minas Gerais) and a slightly younger Cretaceous cluster (~80 Ma) in the Central/Southern APIP. The importance of these new findings is discussed with reference to previously proposed petrogenetic models and casts doubt on the applicability of the plume-related hypothesis for ultrapossic magmatism in the region. In the second part of the thesis, an in-depth geochemical study of 15 kimberlites and 16 kamafugites from the APIP (27 samples) and Rondonia/Mato Grosso (4 samples) is presented. Bulk rock major and trace element data, together with Nd and Hf isotope determinations are combined with perovskite trace element, Sr and Nd isotope analyses in order to provide a comprehensive geochemical dataset. The elemental and isotopic similarity of the APIP kimberlite to South African transitional kimberlites, the APIP kamafugites to Ugandan and Chinese kamafugites and, for the first time, the Amazonian kimberlites to a mixture of South African Group I and transitional kimberlites is established. The overlapping range in Sr isotopic signatures identified between the APIP kimberlite and kamafugite magmas during previous bulk rock studies is confirmed by in situ perovskite analysis, with APIP kimberlites ranging between 70496 and 0.70596 and APIP kamafugites ranging between 0.70499 and 0.70574. Modelling suggests that this range can not result from contamination and must represent a heterogeneous source component, common in the formation of both rock types. It is argued that the combination of geochemical results is best explained by derivation of both rock types from the heterogeneous subcontinental lithospheric mantle. Kimberlites are believed to have been sourced from carbonated garnet lherzolite whereas the kamafugites were generated from phlogopite and clinopyroxene rich vein assemblages, with small volume MARID type metasomes indicated by the kamafugite Hf signatures. Finally, the geochronological and geochemical information is combined into a petrogenetic model: it is argued that the Cretaceous magmatism is likely not the result of plume heating but is instead a consequence of adiabatic decompression melting of the heterogeneous SCLM caused by extension. In parallel with the study of Brazilian ultrapotassic magmatism the thesis also investigates technical aspects of the U-Pb perovskite dating technique. Using a subset of Indian and Brazilian kimberlite samples, in situ perovskite dating was performed and combined with isotope dilution analysis of the co-magmatic, low uranium phase, titanomagnetite, in an attempt to improve precision of the Tera-Wasserburg regression. The inclusion of the titanomagnetite phase improved precision in all cases and enabled ages to be determined for the Indian samples without recourse to an assumed Stacey-Kramers common Pb value. The investigation also highlights some of the shortcomings associated with using an assumed Stacey-Kramers Pb value for young unradiogenic perovskite samples, whilst also highlighting the circularity of the commonly employed 207Pb correction method.
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ItemExploring the palaeoclimate potential of South East Australian speleothems( 2013)The paucity of palaeoclimatic data existing for the Southern Hemisphere and the regional bias of new data from the Northern Hemisphere has meant conclusions regarding the global response to the numerous climatic events of the last 20 kyr is both widely disputed and poorly understood. Despite being one of the Southern Hemisphere’s largest landmasses, Australia in particular displays a limited pool of palaeoclimatic information and the production of a new, robust record providing an insight into the response and timing of key climatic events is paramount to generating a more comprehensive characterisation and improved understanding of palaeoclimate in this region. Speleothems (cave deposits) are valuable archives of palaeoclimate variation, characterised by their extensive growth intervals and large geographic extent. They contain a multitude of ‘proxy’ records both directly and indirectly linked to climatic fluctuations and are typically robust, displaying high preservation potential with no post-depositional alteration. Key to their success is their amenability to radiometric dating, allowing the establishment of robust and reliable chronologies to which their multi-proxy records can be anchored. Consequently speleothems provide a clear opportunity to explore and expand palaeoclimatic knowledge at sites across the globe. This thesis describes and explains the use of state of the art technology to exploit relatively recent advances in U-series dating to construct reliable and detailed records of south east Australia’s response to palaeoclimatic fluctuations over the last 50 kyr using samples collected from cave sites from across the states of Victoria and New South Wales. 28 speleothem samples have been analysed in terms of both their coincident growth intervals and stable isotope variation to provide records with palaeoclimatic implications at a range of time scales. The production of a chronological template of speleothem growth intervals has enabled the assessment of south east Australia’s response to some of the key local and global millennial scale climatic events of the last glacial to interglacial transition and detailed stable isotope analysis of selected samples have been interpreted with the aid of a thorough cave monitoring programme, identifying increased variability in the region’s climate during the late Holocene. The palaeoclimatic records developed in this thesis represent a significant step forward in Southern Hemispheric palaeoclimatology. These records offer valuable new data for both palaeoclimatologists exploring south east Australia’s past climate and those investigating climatic fluctuations at a hemispheric to global scale. The high resolution and robust chronology of the records produced means that they provide a benchmark to which future records might be anchored.
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ItemHydrological extremes and consequences of climate change( 2013)In the design of infrastructure, risk has been – and often still is – assessed on the basis of long-term averages. Information on variation in hydrological extremes is required as the basis for informed decision-making, preparedness and possible adaptation. Long-term trends are fairly well understood for temperature but less well for precipitation. While climate models have become sophisticated tools for projecting future changes in our climate, their ability to replicate observed variations in precipitation is limited and it is therefore prudent to complement climate models through analysis of historical observations. Design rainfall is used as one of the required inputs for hydrological models in the design of structures such as dams and bridges. Design rainfall estimates are supplied in form of intensity-frequency-duration curves. Rainfall frequency analysis is almost invariably based on the assumption of a stationary climate. Sub-daily durations are of particular interest for urban applications. This thesis was strongly driven by the motivation to provide guidance to decision makers who have to account for non-stationarity in rainfall extremes. Non-stationarity in rainfall extremes comes about as a conflation of climate change and climate variability. Unlike for temperature extremes, rainfall extremes for Australia as a whole exhibit no clear increase or decrease in intensity over time but strong association with the El Niño-Southern Oscillation (ENSO). This has implications for the choice of suitable analysis techniques, e.g. sophisticated non-parametric techniques. Depending on the planning horizons both climate change and climate variability may have to be accounted for. The association of rainfall extremes with ENSO leads to an opportunity to develop statistical models to support decision-making on shorter time scales. Analysis of seasonality in frequency and magnitude of rainfall extremes revealed considerable variation across a set of sites in the southeast of Australia, implying different dominating rainfall-producing mechanisms and/or interactions with local topography. The strongest signal for an increase in extreme precipitation is found for short durations. Changes in rainfall extremes come about through a combination of changes in thermodynamical and dynamical variables. To assess large-scale changes in circulation, a classification technique (self-organising maps, SOM) was applied and synoptic types were identified. Rainfall extremes were then related to the synoptic type under which they occurred, to assess observed changes in the frequency of rainfall extremes. Rainfall extremes are typically preceded by conditions that are much wetter (both in absolute and relative terms) and warmer than the climatological average. These anomalies tend to be larger for shorter durations, and for rarer events. Given that increase in humidity exhibits strong regional variability and that it may be counteracted by changes in dynamics, it appears simplistic to state categorically that climate change will lead to an increase in extreme rainfall events and observed trends in rainfall extremes show a picture that is more complex. In summary, the combination of changes in thermodynamic and dynamic variables will define the change in frequency and intensity of rainfall extremes. The factors that are most relevant for the effect of climate change on rainfall extremes depend on geographical location.