School of Earth Sciences - Theses
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ItemInvestigating the causes of variations of temperature and precipitation extremes using observations and climate model data( 2015)Understanding how climate extremes have changed in the recent past and how they will change in the future is crucial for preparing for future climate change. Natural variability and anthropogenic climate change are both known to significantly influence the frequency and severity of temperature and precipitation extremes, so it is vital to better understand these effects. A case study of frost days in southern Australia first illustrates how short-term variations in climate can sometimes override any global warming signal for a period of time. Some unexpected frost day ‘increases’ are found over 1981-2011, despite a longer-term warming signal. A link to the concurrent precipitation decline and associated reduced cloudiness is identified for south-eastern Australia. The remainder of this thesis investigates variations and trends in the fraction of area experiencing daily temperature and precipitation extremes in four continental regions: Europe, North America, Asia and Australia, and the Northern Hemisphere. A new method based on existing extreme indices is used to investigate changes in five temperature and precipitation components, including maximum and minimum temperature components, and total precipitation, heavy daily precipitation and wet/dry day components. Near-global increases in area experiencing much-above-average warm days and nights and decreases in the area experiencing much-above-average cool days and nights are found. Over the Northern Hemisphere regions, increases in the area affected by wet extremes are also identified. For Australia, the spatial extent of precipitation extremes is primarily influenced by natural variability. Using simulations from eight global climate models under different radiative forcing scenarios, an anthropogenic contribution to the increases in area affected by warm temperature extremes is identified for all regions. Over Europe, an anthropogenic contribution to the increases in area affected by a much-above-average contribution of heavy precipitation to total annual precipitation was identified for a majority of models. However, trends in total precipitation extremes and wet/dry day extremes could not be reproduced under any forcing scenario. Climate model projections to 2100 under the high emission scenario indicate continued increases in the area affected by warm temperature extremes throughout the 21st century. By mid-century, the temperature components ‘saturate’, indicating that the extreme threshold determined relative to late 20th century conditions is likely to be exceeded almost every year. Continued increases in the area affected by a much-above-average heavy precipitation contribution are projected for all Northern Hemisphere regions, and to a lesser extent Australia. Projections for the total precipitation and wet/dry components vary between regions. Finally, the role of sea-surface-temperature forcing in driving variations and trends in the area affected by temperature and precipitation extremes is investigated. The greatest influence of sea surface temperatures is found for Australia, although a contribution is identified for all regions. Over Australia, El Niño-Southern Oscillation has a pronounced influence on the precipitation components. This thesis has investigated recent trends in the spatial extent of extremes in observations, and investigated their causes and future projections using climate model simulations. The utility of a spatial perspective for monitoring and investigating variations and changes in climate extremes is demonstrated by this work.
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ItemInvestigating stratospheric ozone change and associated impacts on circulation and climate( 2015)With stratospheric ozone on the path to recovery, understanding its future role in modulating Southern Hemisphere circulation and climate is essential. This work contributes to answering this question through both observational and modelling studies. First, a new Dobson Umkehr retrieval technique optimised for resolution was developed, with the retrievals contributing in the evaluation of the Australian Community Climate and Earth-System Simulator-Chemistry Climate Model (ACCESS- CCM). This model was used to investigate future Southern Hemisphere stratospheric ozone changes and associated dynamical and climate responses, particularly in the Southern Annular Mode (SAM), the tropopause height and quasi-stationary waves. For this purpose, four simulations were completed comprising of historical, future projection and sensitivity simulations with fixed ozone depleting substances and greenhouse gases (GHGs) at 1960 levels. These simulations also act as Australia’s contribution to the international Chemistry Climate Model Initiative. The Dobson Umkehr retrieval technique developed here uses all available data, unlike other algorithms, which use designated solar zenith angles (SZAs) from a single wavelength pair (C), out of three (A, C and D). Investigating a test case from Melbourne, the degrees of freedom for signal increased from 3.1 to 3.4 when using all C-pair SZAs, and up to 6.5 when using all available SZAs and wavelength pairs; a significant improvement over current operational methods. ACCESS-CCM evaluation shows excessive ozone but an accurate distribution, and a temporally persistent ozone hole. Comparison with the Dobson Umkehr retrievals, total column ozone observations, ERA-Interim reanalysis and past modelling studies shows ACCESS-CCM produces excess ozone at altitudes above 25 km for Melbourne, but with substantial improvements in Antarctic total column ozone over it’s precursors (CCMVal-2 UMUKCA models). Comparisons with Davis and South Pole ozonesondes display a large disparity in the vertical location of perturbed ozone. Maximum depletion is seen between 100–50 hPa in ozonesondes, compared to above 50 hPa in ACCESS-CCM. This difference is likely caused by cold model biases enhancing polar stratospheric cloud formation and subsequent chlorine release at high altitudes. The lack of supercooled ternary solution may be a cause of less depletion between 100–50 hPa. Despite these inadequacies, ACCESS-CCM is simulating the amount of historical Antarctic October ozone depletion, the SAM and 50 hPa zonal wind anomalies well compared to ERA-Interim and past modelling studies. This gives confidence that the model simulates reasonable ozone-induced circulation responses. The model shows that October averaged Antarctic ozone is returning to 1980 levels just after 2060. Increasing GHG and ozone concentrations act to delay and advance the breakup of the polar vortex respectively. Regression analysis shows that in the future, increasing GHGs and ozone concentrations drive an increase and decrease in the SAM index respectively, effectively cancelling each other out. Contrary to the SAM, the high latitude tropopause changes, while influenced heavily by ozone changes in the past, is dominated by increasing GHGs in the future. The phase of spring and summer wave 1 in TCO, 50hPa temperature and 10hPa zonal wind undergo an eastward shift due to both ozone depletion and GHG increases. The wave 1 phase influence from GHGs is seen to originate from the troposphere, and therefore is influenced heavily by Andes orography. This is not the case for ozone concentration changes, indicating that the main influence is through modulation of the stratospheric polar vortex. A decrease in the amplitude is also seen due to GHG increases, primarily due to a decrease in the amplitude of the tropospheric wave 1.
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ItemThe tectono-stratigraphic development of the Dublin Basin, Ireland( 2015)The Early Carboniferous stratigraphy of the Irish Midlands contains one of the world’s major carbonate-host Zinc-Lead Orefield’s, covering a region of approximately 8000km2. Despite the global significance of the region, genesis of mineralisation in the Irish Midlands is poorly understood. This stems from the difficulties associated with studying Carboniferous-aged stratigraphy, predominately resulting from the very limited amount of outcropping rock. To date, the majority of studies have relied heavily on sporadic coastal and quarry outcrop, as well as diamond drill holes. Another hindrance is the tendency for studies of carbonate-hosted ore deposits to focus on understanding the sulphide mineralisation and geology in the immediate vicinity of the mineral occurrence. However, the large-scale nature of the fluid flow systems that produce ore deposits suggest that understanding the nature of the host basin is equally as important. In this study, typical methods of stratigraphic analysis (drill core and outcrop logging) are integrated with recently acquired seismic reflection data and gamma ray logs to ascertain the stratigraphic and structural character of the Dublin Basin (the host basin to Irish Zn-Pb mineralisation). Geometric relationships between layers as revealed by seismic reflection, in conjunction with detailed lithological analysis has shown extensional tectonism was the main driving force of sedimentation in the Dublin Basin. The first episode of significant extensional tectonism occurred in the late Tournaisian (Moathill Event, ~348 Ma) and was accompanied by faulting and regional subsidence. Subsidence led to a basin-wide transgression and development of deeper marine conditions across the region. This was followed by a period of relative tectonic quiescence and initiation of a marine regression. The relative shallowing of ocean conditions produced a depositional environment ideal for the development of carbonate mudmounds (the Waulsortian Limestone). A second period of tectonism during the lower Viséan (Tober Colleen Event, ~345 Ma) resulted once again in significant subsidence across the basin, with a corresponding transgression (and drowning of the mudmounds). Importantly, the Tober Colleen Event was not accompanied by any major faulting. Previous tectonic interpretations of the Dublin Basin suggest that the Tournaisian was dominated by gentle subsidence and sagging, while most faults were produced as a result of Lower Viséan tectonism. The new view of tectonism revealed in this study has implications for arguments about the origin of Irish-type Zn-Pb deposits and the necessity (or not) for having active faulting during mineralisation.
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ItemMatrix effects in LA-ICP-MS: implications for in situ U-Pb geochronology( 2015)Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) is a widely available analytical technique used to resolve U-Pb age structures in morphologically complex minerals at the micron scale. Unfortunately, the matrix dependency of the ablation process remains one of the major drawbacks of the method, limiting the precision and accuracy of the U-Pb ratio determinations required for detailed geochronological studies. The aim of this thesis is to provide better understanding of the underlying causes of these ‘matrix effects’ as a key component in the development of strategies to correct for them. The approach comprises a series of studies involving detailed characterisation of ablation pit morphologies, quantification of ablation pit dimensions and evaluation of U-Pb signal ratios. Laser ablation experiments were performed on pure synthetic minerals (apatite, baddeleyite, rutile, titanite, zircon, among others) to assess the mechanism of material removal for different U-bearing mineral matrices. Results indicate that the response of a particular mineral to 193 nm laser radiation depends exclusively on the mineral’s crystal structure and lattice parameters. For minerals with a large unit-cell, the ablation is controlled by photochemical (non-thermal) mechanisms of material removal. In contrast, for minerals with very dense and progressively close-packed structures (at a atomic scale) the material removal process is increasingly controlled by thermal mechanisms. The degree of the U-Pb ratio fractionation observed during ablation of natural U- bearing accessory minerals is closely related to their ablation behaviour. Higher degrees of fractionation are associated with thermally controlled ablation of mineral matrices. In contrast, a significant reduction in the degree of U-Pb ratio fractionation occurs for minerals in which no signs of thermal processes during ablation were observed. Nevertheless, U-Pb ratio fractionations of up to 20% are still observed during ablation under photochemical material removal mechanisms. LA-ICP-MS analyses of several well-characterised zircon reference materials show that there are differences in material removal rate between them. Systematic errors in the LA-ICP-MS U-Pb age determinations of zircon samples (relative to their accepted ID-TIMS ages) are therefore introduced when the reference material used for system calibration ablates at a different rate. The results of this study suggest that differences in ablation rates observed between zircons account entirely for the matrix-related U- Pb age bias associated with the LA-ICP-MS dating method. Further investigation of the underlying causes of differences in ablation behaviour between zircon matrices indicates that an increase in laser penetration rate is associated with a decrease in the ability of a zircon crystal to withstand the thermo- mechanical stress induced during laser irradiation. Due to the marked decrease in elastic moduli of natural zircons with increasing radiation damage, the extent of damage accumulation is the dominant factor controlling the rate of laser material removal for partially damaged to highly metamict zircons. Thermal annealing of natural zircons at temperatures > 1000 °C results in more uniform ablation characteristics. There are slight differences in ablation rates between highly crystalline zircons of different trace element composition. The results of this study show that these variations are associated with differences in the degree of structural strain caused by the incorporation of trace elements into the zircon lattice. An investigation of the ablation behaviour of the mineral apatite shows differences in ablation rates between different apatites. A preliminary assessment indicates that there is not simple relationship between crystal unit-cell parameters and ablation rates. The lack of linear correlation may be associated with an increase in lattice strain caused by the incorporation of cations into the apatite structure which do not trigger changes in the unit-cell parameters.
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ItemMicrobial distribution and activity response to environmental gradients in a coastal acid sulfate soil system: implication for passive bioremediation by tidal inundation( 2015)Coastal acid sulfate soils (CASS) present a global environmental problem, damaging estuarine and coastal ecosystems by soil acidification and associated heavy metal contamination. In Australia, around $10 billion in "legacy" impacts remain from CASS effects, and Australia only contains about 18% of global CASS systems. Tidal inundation provides a potential treatment strategy, as seawater provides bicarbonate to neutralize acidity, and sulfate to trigger heterotrophic bacterial sulfate reduction (BSR), which forms more bicarbonate as well as promoting the precipitation of many heavy metals in iron sulfides. This process contributes more than 50% to acid neutralization. However, limited knowledge of spatial and temporal variability in microbial community composition, distribution and activity, in the context of hydrologically dynamic CASS systems, hinders evaluation and predictive modelling of remediation efficiency. In this study, 16s rRNA genes were used to identify microbial distribution, and 16s rRNA (cDNA) sequences were used to investigate microbial activity in a tidal inundation-treated CASS system during a tidal cycle. The results showed microbial distributions diverged from classical vertical redox stratification. Different metabolic guilds overlapped spatially, and their distributions were shaped by environmental parameters such as pH, Eh, water saturation, organic content, and mineral deposition. The positive correlation of biomass between iron and sulfate reducing bacteria suggests that high organic carbon content decreased microbial competition, and iron sulfide deposition favored both terminal electron-accepting pathways thermodynamically. Microbial activity patterns showed that low abundance microbial populations responded more quickly to environmental changes during tidal cycling. At the community level, low abundance, or “rare”, operational taxonomic units (OTUs) showed capacity for quick changes in overall metabolic activity. At the phylum or class levels, different activity patterns were observed between abundant (e.g., Deltaproteobacteria) and rare taxa, with some rare OTUs increasing their activity as they decreased in abundance, confirming a quick response to tidal cycling. These results suggest that microbial “resuscitation strategy” may play a key role in biogeochemical cycling in CASS environments. Microbial members were classified into early and delayed responders based on rRNA accumulation time. The activity patterns of microbial guilds were phylogenetically conserved at phylum/class/order levels across supra- to sub- tidal zones within the 20cm sampling depth over all tidal stages. Multiple metabolic strategies were observed, such as prey-predator relationship, endospore formation, photosynthesis, and N-, Fe-, S-related metabolisms. The taxonomy of early and delayed responders involved in different steps of organic matter degradation supported an ecological "niche" concept. In a high organic matter containing CASS ecosystem, conventional thermodynamically driven models will not be applicable for predicting microbial redox zonation. Instead, spatial-temporal variations in key environmental parameters will control microbial community structure. Tidal cycling imposes drying and rewetting cycles, cell resuscitation becomes a strategy to utilize energy in a more efficient way. This study provides detailed and new information about microbial species distribution and activity in a tidal inundation-treated CASS wetland.
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ItemDynamics and evolution of tropical cyclones( 2015)There are two scientific areas which have considerable bearing on tropical cyclone dynamics: convection processes and the processes operating in the hurricane boundary layer. The objective of this thesis was to examine a number of scientific issues related to these areas in an attempt to shed light on some unresolved issues and provide some general guidance to the modelling community. The issues examined in this thesis are model sensitivity to convective parameterisation (CP), small-scale model noise, and surface heat and moisture transfer in the boundary layer as it relates to hurricanes. A series of sensitivity experiments using numerical models were undertaken to investigate these issues. In the first study, tropical cyclone track sensitivity to model initial conditions, domain size, CP and shallow convection, was explored using the Weather Research and Forecasting model. Three case studies, each from different basins were selected: Rita (2005); Megi (2010) and Yasi (2011). To help identify any track deviations caused by the representation of convection, a potential vorticity diagnostic for tropical cyclone motion was applied to diagnose the cyclone motion from the dynamic fields and compare this against the simulated cyclone motion. The major findings showed several systematic sensitivities including, that model initial conditions cause less sensitivity in cyclone track compared to changing the CP, running the schemes without shallow convection results in negligible difference in track (except in the Grell-3D simulations), and the differences in the tracks using different CPs are attributed to simulated convective asymmetries, or in some cases other baroclinic processes from the vortex, such as diabatic heating. The second investigation expanded on the theme of track sensitivity to cumulus parameterisation. Here, a stochastic kinetic energy backscatter scheme was employed to stochastically perturb the model initial and lateral boundary conditions. The scheme accounts for a missing energy process in numerical models by introducing energy back into the model at the small-scale. The aim was to ascertain whether perturbing the dynamical fields of u and v wind, and temperature, resulted in more sensitivity to track and intensity than changing the cumulus scheme. Using a series of high resolution idealised simulations with the Weather Research and Forecasting model, we tested sensitivity to model initial conditions (e.g. domain size, initial vortex size and intensity) and stochastically perturbed and unperturbed runs with varying cumulus parameterisation specification. The major findings showed several systematic sensitivities, that the stochastically perturbed simulations produced weaker intensity storms than the unperturbed runs, the track sensitivity from changing the cumulus scheme is less than that arising from stochastic perturbation of the dynamic fields, and the perturbed simulations all produced a stronger westerly wind bias at 300 hPa with warmer inner core temperatures than the unperturbed runs. Results point to the possibility that including this stochastic scheme in modelling may in fact improve simulations of tropical cyclones. The final sensitivity study explored the importance of the ratio of the surface exchange coefficients of enthalpy (Ck) to drag (Cd) to hurricane potential intensity (PI). Unlike previous studies, the present study compared model results to PI theory for simulated intensity and consistency of the theory with internal storm structure. Hurricanes were simulated for a range of Cd and Ck values using the axisymmetric model CM1. The major findings showed a contraction of the radius of maximum wind in all sensitivity experiments where Ck and Cd were increased yet the Ck/Cd ratio maintained, that the redistribution of angular momentum in the boundary layer is a contributor to this structural change, and the gradient wind balance approximation of the Emanuel (1995) PI theory is not valid in certain conditions. Following on from the work of Bryan (2012), we showed as the Ck/Cd increases then the ability for supergradient overshoot increases, thus the inclusion of inertial (unbalanced) terms in PI theory is necessary. We established that the azimuthal vorticity has greater influence on the unbalanced terms than the contribution from the vertical velocity. We showed the initial vortex is unlikely to be as important in controlling the unbalanced terms as the Ck specification (the terms increase markedly for increasing Ck), whereas an increase in Cd leads to a decrease in the unbalanced terms. This results in substantial structure and intensity changes. The major conclusions of this thesis are that the clouds and precipitation represented by the CP scheme can affect the simulated track by deflecting the cyclone from its intended course; small-scale energy processes, often neglected from modelling, may improve hurricane simulations; and some surface heat and moisture exchange processes contradict some aspects of well-accepted theories.
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ItemTurbulence near deep convection( 2015)Deep convective clouds are one of the most important sources of turbulence that affect aviation. This type of turbulence does not only occur within clouds but also in the clear-air regions outside the cloud (so-called near-cloud turbulence [NCT]). NCT can occur significant distances from thunderstorms making it invisible and hard to detect using standard on-board or ground-based radars and is therefore a significant hazard to aircraft. Mechanisms that generate NCT are not yet fully understood and are the focus of this study. This thesis explores mechanisms behind turbulence that is generated around deep convection, with a focus on turbulence that is generated remotely from convection. Firstly, it investigates the generation of turbulence in the upper outflow regions of simulated idealised mesoscale convective systems (MCSs); sensitivity to vertical wind shear is also investigated. It then examines a case study of two actual turbulence encounters that occurred in the clear air outside mesoscale convective systems on 3 June 2005; these are examined using observations and convection-permitting simulations. In the idealised simulations without initial upper-level background shear, parameterised turbulence extends more than 100 km away from the main convective regions and is associated with Kelvin-Helmholtz (KH) instabilities that occur in the shear zones above and below the storm-induced upper-level outflow jet, which is centered near the tropopause. The simulations show KH-like billows within regions of low Richardson (Ri) number, as well as short-scale gravity waves that locally modulate the jet and contribute to further destabilisation and susceptibility to turbulence. These waves appear to be generated by the shear (i.e. KH) instability. Additional simulations with different initial upper-tropospheric wind shear show similar results, turbulence and dynamic instabilities that are also caused by the storm-induced upper-level outflow and associated enhanced vertical shear. However, in these simulations parameterised turbulence, low Ri regions and KH-like billows are found mainly below the outflow jet, as above the jet wind shear is weaker and stability is stronger. Convection-permitting simulations that examined the first observed turbulence encounter, which occurred on the south side of a warm-season MCS, showed that parameterised turbulence is generated more than 50 km away from the active convective regions. It is associated with a large-amplitude gravity wave that propagates ahead of the convective system, in the region with enhanced vertical shear that is caused by the storm-induced upper-level outflow. This wave amplifies, likely due to partial wave reflection, overturns and breaks down into turbulence. For the second case, turbulence occurs in the clear air and on the north-eastern side of the same MCS and is likely associated with both convection and large-scale (non-convective) forcing. Convection perturbs an environment already prone to turbulence (i.e. small background Ri) and the increase in wind shear due to the upper-level storm outflow contributes to a much larger and widespread area of low Ri, thus increasing turbulence likelihood. Other areas of simulated turbulence, which are not associated with the observed turbulence encounter, are entirely due to convectively-induced upper-level outflow.
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ItemOperational consensus forecasts and spatial verification methods( 2015)This thesis relates to multi-model consensus forecasts over Australia, at sites and on a high resolution spatial grid. In 2005, the Australian Bureau of Meteorology initiated efforts to investigate the use of multi-model consensus forecasts for operational forecasting. A bias-corrected and weighted operational consensus forecast (OCF) product was developed to produce daily site-scale screen-level temperature maxima and minima, ground-level temperature minima, evaporation, sunshine hours and rainfall total amount. The (automated) daily OCF product performed well in comparison to (human) operational forecasters. The success of the daily OCF product motivated work to extend the daily OCF scheme to produce instantaneous OCF values for aviation and fire-weather purposes (Chapter 2 of this thesis). A blending scheme was designed to cope with the intermittent availability of numerical weather prediction (NWP) forecasts throughout the 72 hour forecasting period. This enabled the use of models with different temporal resolutions, and benefited the consensus forecast in intervening time periods when those models were not available. In addition, the forecasting process at the Bureau was in the process of changing from site-scale forecasts manually written by operational forecasters to gridded forecasts generated automatically from NWP model output edited by operational forecasters. This change in forecasting paradigm produced a new need for high-resolution (approximately 5 km) ‘first-guess’ post-processed NWP data. This led to the question of whether the site-based OCF schemes could be extended to produce bias-corrected and weighted consensus forecasts across a high-resolution grid (without observations available at each grid-point) (Chapter 3 of this thesis). The site-scale OCF scheme was extended to produce ~5 km resolution consensus forecasts using a mesoscale surface analysis scheme as a proxy observation. The new ‘gridded’ OCF provided more accurate gridded numerical guidance to support the Australian Bureau of Meteorology’s grid-based forecast process. Producing a consensus product on a grid highlighted the importance of spatial errors in multi-model ensemble members. The OCF scheme was a Bayesian scheme that assumed unbiased and normal error distributions. Hence, spatial errors led to suboptimal consensus forecasts. Therefore an image registration algorithm used originally for medical imaging was adapted to detect and quantify spatial differences between meteorological forecasts, with a view to apply these differences to find a spatial consensus (Chapter 4 of this thesis).
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ItemDeep aquifer prokaryotic community responses to CO2 geosequestration( 2015)The cycling of many elements at or near the Earth’s surface, including nitrogen, sulfur, and carbon, is largely mediated by microorganisms. However, very little is known about microbial influences within the Earth’s deep subsurface (>1000 m). Understanding subsurface microbial responses to anthropogenic perturbations, such as injection of large amounts of supercritical-CO2 (scCO2) in geosequestration projects, is an important and topical area of study. Geosequestration is currently being trialed as a means to mitigate anthropogenic carbon pollution in the atmosphere. Recent studies on how microbes respond to scCO2 support the need to conduct field-scale analyses, and to monitor in situ the involvement of microbes before and after the injection of scCO2. The current thesis was developed around the CO2CRC Stage 2B Otway project; a leading field-scale demonstration of CO2 geosequestration in the Paaratte Formation of the Otway basin (~1400 m TVDSS; 60°C; 2010 psi), Australia. The thesis aimed to address how microbes respond in situ to the injection of 150 tons of scCO2 at the 16S rRNA gene, metagenomic, and phenotypic (chiefly, biofilm assays) levels. Microbial responses to scCO2 exposure are important to understand as certain selective adaptions may occur. If these adapted populations can convert scCO2 into CH4, or form biofilms that reduce aquifer permeability, the activities of these microbes may also influence scCO2 storage capacity. First-order analyses revealed a shift in microbial community structure from predominantly Firmicutes to Proteobacteria concurrent with the presence of residual organic compounds (i.e., polyethylene glycols) interpreted as residue from the drilling-fluid used during the emplacement of injection and sampling wells. Furthermore, Carboxydocella was identified as a native organism of the Paaratte Formation with autotrophic, thermophilic (~58°C), anaerobic, and carboxydotrophic physiological traits. A decline in carboxydotrophic gene abundance was observed with potentially significant impacts on the flow network of electrons (i.e., decline in H2 concentration) to the heterotrophic community members, including sulfur- oxidising and –reducing bacteria, and methanogens. Network analysis provided further insights into the physiology of the microbial community, including how key functional groups (e.g., autotrophic and heterotrophic carbon cyclers, and sulfur cyclers) may be integrated into the wider subsurface microbiome. Moreover, in vitro assays of biofilm formation confirmed that microbial populations and isolates representative of the Paaratte Formation were able to form biofilms, thus highlighting the potential for microbial influence on aquifer permeability and the residual sequestration of scCO2. This study firstly demonstrates a successful new in situ sampling approach for detecting deep subsurface microbial community changes associated with an scCO2 geosequestration event. Secondly, the resolution of high throughput genomic analyses presented in this study elucidated previously unknown microbial community dynamics within a subsurface biosphere. This response to field-scale scCO2 geosequestration forms the basis for further targeted investigations, particularly investigating the biogeochemical cycling of certain elements between different functional groups. The findings and methodology of this study has relevance and applications to other subsurface environments such as hydrocarbon rich reservoirs, radioactive waste storage sites, and high-CO2 natural analogue sites.
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ItemMeasurement and modelling of heat flow in the Gippsland Basin, Victoria( 2015)Geothermal energy has the potential to provide significant quantities of highly available power with little environmental impact. Enhanced geothermal system (EGS) technologies have the potential to become major contributors to global energy production, with a much wider geographic scope than the more established conventional geothermal systems. Certain favourable geological conditions have been recognised as providing improved prospectivity for EGS resources, primarily elevated heat flow rates and thermally insulating cover sequences. Most attention has been given to the location of regions having anomalously high heat flow, typically due to increased heat production in basement rocks such as granites rich in radiogenic isotopes. Little attention has been paid to extremes in thermal insulation, which offer an alternative but equally effective mechanism for increasing geothermal gradients and thus reducing the depth to a geothermal resource. Large and thick deposits of highly insulating coal present a unique thermal environment, where the commonly assumed one-dimensional relationship between surface heat flow and temperature at depth described by Fourier's Law is not maintained due to heat refraction -- a three-dimensional process. Understanding the effects of heat refraction due to thermal insulation and its effect on surface heat flow is a crucial element of exploration strategies in coal-bearing sedimentary basins. The onshore Gippsland Basin, and in particular the Latrobe Valley, is an ideal setting to study the effects of buried confined insulators on surface heat flow and thermal structure. This thesis combines the results of observational insights from empirical field data collection with mathematically driven insights of theoretical models, and simulation-driven insights of numerical finite-element modelling. Additionally, it explores the relatively modern paradigm of data-driven statistical science to generate predictions of rock properties from related intrinsic variables. Measured surface heat flow is moderately variable, with the ten most reliable calculations from borehole data having an interquartile range of 61--78 mW/m², with a mean and standard deviation of 72±14 mW/m², slightly higher than previous estimates. Groundwater advection identified in previous studies appears to affect the thermal structure of only the Cainozoic stratigraphy. Losses of up to 37 mW/m² in the vertical heat flow in the sandy Balook Formation of borehole Rosedale-301 represents a local maximum of heat transfer associated with groundwater advection. Only minor thermal effects are observed in the uppermost Mesozoic section, indicating a return to a dominantly conductive thermal regime there. The self-organising map technique was applied to the prediction of lithostratigraphy and thermal conductivity from well-log data. It successfully identified 91.3% of lithostratigraphy samples from a supervised mapping of well-log data. Mapping of thermal conductivity with corresponding well-log data produced more variable results compared with a petrophysical log interpretation technique over a large cohort of boreholes. However, the SOM analysis returned predicted values with a better correlation with measured values at sampled depths, required less pre-processing of log data, and was able to perform with non-standard log data and legacy tools. With further refinements of the technique, potential improvements may be made with its prediction performance of thermal conductivity and other rock properties. Heat flow theory applied to an idealised simulation of the Latrobe Valley coal seams showed that temperature increases of 35°C beneath the coal are possible over a reference model having no such insulation. Finite-element forward models of cross-sections and 3D volumes through the onshore Gippsland Basin identified highly variable surface heat flow, having up to ±30 mW/m² variance from the basal flux input. Complex patterns resulting from heat refraction were produced, with two common features indicative of confined insulators: 1. the greatest increase in subsurface temperature is correlated with the greatest decrease in surface heat flow, however, 2. surface heat flow tends to be slightly increased above the margins of buried insulators. The main implication from these results is the identification of an end-member insulation-dominated geothermal resource style, requiring new strategies for exploration and resource targeting.