School of Earth Sciences - Theses
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ItemNo Preview AvailableAntarctic sea ice and its interactions with high latitude weather and climate( 1998)Antarctic sea ice plays a major role in the earth system by greatly influencing the high latitude exchanges of heat, moisture and momentum between the ocean and atmosphere, as well as profoundly effecting the salt budget of the ocean, and thus the production of Antarctic Bottom Water, one of the driving mechanisms of worldwide oceanic circulation. With such considerable and far reaching impact, it is important to document its climatology, understand its variability and quantify its influence. Climatologies and trends of the Southern Ocean sea ice pack are presented using the most recent satellite observations available from the Defense Meteorological Program’s (DMSP) Special Sensor Microwave Imager (SSM/I). The analysis of these data show that Antarctic sea ice is highly variable in both time and space. Statistically significant increases in the sea ice extent, open water and ice areas have been determined from the SSM/I data for the 9 year period 1987 to 1996, a result which differs from the Scanning Multichannel Microwave Radiometer (SMMR) observations (1978-1987). The increasing trend in the SSM/I observations can be attributed to the large increases in sea ice observed in 1994-1995, as confirmed by an analysis of data from the ERS-1 satellite. The mean season length during these years has remained relatively unchanged. Regional trends, both in the sea ice concentration and in season length, showed vast spatial inhomogeneity. SSM/I data displayed increasing season length in the central Weddell Sea, Bellingshausen Sea and Balleny Islands regions, with decreasing length in the Amundsen Sea, eastern Ross Sea and in the coastal areas off Wilkes Land. Similar trends are observed in the seasonal sea ice concentration. In most cases, these trends are opposite to those observed in the SMMR data, which may be linked to the shift observed in the Amundsen Sea low after 1990. Comparisons with historical data would suggest that no large scale anomalous change has occurred in the Antarctic sea ice limits over the course of human observation. Furthermore, the degree of variability suggests great care is needed in interpreting large scale changes in sea ice conditions, and hence atmospheric or oceanic change, from locally observed anomalies. Case studies of the effect of individual cyclones upon the sea ice concentration show small but definite modification of the ice conditions. To further diagnose aspects of the thermodynamic and dynamic forcing upon the Antarctic pack, detailed analysis of the sea ice concentration variability has been conducted using spectral techniques, and the spectra have been compared to those of the European Centre for Medium Range Weather Forecasts (ECMWF) temperature and wind data. In all cases, and with the seasonal cycle removed, the sea ice concentration shows a bias towards longer timescales of variability than either the wind stress or surface air temperature. This “red shift” in its frequency spectrum is strongest with the wind stress, and weakest with the temperature. For longer period waves, this may be due to the formation of new ice by surface cooling or the moderation of melting by the cold surface water, whereas for shorter period waves, where wind stress dominates temperature and ice concentration respectively, time is required for winds to draw in warmer or cooler air, as well as to overcome the ice masses inertia and keel friction to open or close leads. Strong intraseasonal variability of the sea ice concentration is observed in the 20-25 day period, reflecting similar timescales of the temperature variability, as well as that of the energetic eddies of the Antarctic circumpolar current. Examination of the latitudinal variation of the sea ice concentration, temperature and wind stress spectra showed not only the importance of the north-south temperature gradient in influencing the variability, but also the seasonal changes in the semi annual oscillation of the circumpolar trough. Regional spectra showed clear differences between location, and reflected the influences of the atmosphere and ocean upon the sea ice pack. This is clearly shown in the Weddell Polynya region and off East Antarctica, with high variability in the synoptic timescales, and in the western Ross Sea where changes occur in timescales of greater than 20 days. In order to determine if satellite derived, real time sea ice concentration and distribution would be of benefit to operational numerical weather prediction (NWP) schemes, the effect of sea ice concentration change upon the atmosphere in synoptic timescales was examined using a general circulation model in conjunction with the Australian Bureau of Meteorology’s GASP analyses. Experiments were conducted with a typical July sea ice concentration and distribution, as well as slab concentrations of 0, 10, 25, 50, 80 and 100%. Results from 5-day numerical weather forecasts show that the central pressure, structure and tracks of individual cyclones are sensitive to the ‘switch on’ of different sea ice conditions. Composites of all forecasts made with each concentration showed considerable, and mostly statistically significant, anomalies in the surface temperatures and turbulent heat fluxes over the sea ice. The magnitudes of these changes varied monotonically with the area of open water. The largest changes were simulated closest to the coast for all concentrations except for the typical July sea ice run, which displayed maxima over the outer pack. Significant westerly anomalies were induced over the ice in all cases, as were reductions in mean sea level pressure. The July sea ice runs displayed a distribution of the mean sea level pressure anomaly different from all others, with maxima occurring in the central to outer pack. All other forecasts displayed maxima at the coast. The results suggest that sea ice concentration does induce anomalies in the atmospheric parameters in timescales of less than five days. Further, the use of a realistic distribution of sea ice concentration produces results distinct from the constant concentration forecasts. Hence it is suggested that real time Antarctic sea ice data may be of considerable benefit to numerical weather prediction models.
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ItemThe geology and geochemistry of the Agnew Intrusion: implications for the petrogenesis of early Huronian mafic igneous rocks in Central Ontario, Canada( 1996-07)The Early Proterozoic Agnew Intrusion is a well-preserved leucogabbronoritic to gabbronoritic layered intrusion that is a member of the East Bull Lake suite of layered intrusions (ca. 2490-2470 Ma) occurring in central Ontario. These intrusions are related to the development of the Huronian Rift Zone, which may be part of a much more widespread rifting event that involved the Fennoscandian Shield. Structural data suggest that these intrusions have been subjected to ductile deformation and are erosional remnants of one or more sill-like bodies originally emplaced along the contact between Archaean granitic rocks of the Superior Province and an Early Proterozoic Huronian continental flood basalt sequence in the Southern Province.
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ItemThe development of a high quality historical temperature data base for Australia( 1996)A high quality, historical surface air temperature data set is essential for the reliable investigation of climate change and variability. In this study, such a data set has been prepared for Australia by adjusting raw mean annual temperature data for inhomogeneities associated with station relocations, changes in exposure, and other problems. Temperature records from long-term stations were collaborated from the set of all raw data held by the Australian Bureau of Meteorology. These long-term records were extended by combining stations and manually entering previously unused archived temperature measurements. An objective procedure was developed to determine the necessary adjustments, in conjunction with complementary statistical methods and station history documentation. The objective procedure involved creating a reference time series for each long-term station, from the median values at surrounding, well-correlated stations. Time series of annual mean maximum and mean minimum temperatures have been produced for 224 stations, and the adjusted dataset has been made available to the research community. The adjusted data are likely to be more representative of real climatic variations than raw data due to the removal of discontinuities. The adjusted data set has been compared with previously used temperature data sets, and data sets of other parameters. The adjusted data set provides adequate spatial coverage of Australia back to 1910. Additional adjusted data are available prior to this date at many stations. Trends in annual mean maximum, minimum, the mean of the maximum and minimum, and the range between the maximum and minimum, have been calculated at each site. Maximum and minimum temperatures have increased since about 1950, with minimum temperatures increasing faster than maximum temperatures.
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ItemTransport, attenuation, and degradation of organic chemicals in a basaltic aquifer system near Melbourne, Australia( 1996)Groundwater in the Pliocene to Pleistocene fractured and jointed Newer Volcanics basaltic aquifer system beneath Melbourne's industrialised western suburbs is extensively contaminated by a wide variety of organic and inorganic compounds. Groundwater in Tertiary sediments underlying the Newer Volcanics is probably also contaminated by the same sources. The main objectives of this research were 1) to assess the types, concentrations, and distribution of contaminants in the Newer Volcanics aquifer system in Melbourne's western suburbs and at a selected contaminated site and 2) to determine contaminant transport, attenuation, and degradation processes affecting organic contaminants in this aquifer system. Contaminants detected in the Newer Volcanics aquifer system during this research include phenols, volatile organic compounds, polynuclear aromatic hydrocarbons, polychlorinated biphenyls, metals, and inorganic anions. The groundwater flow system in the study area comprises a single heterogeneous and anisotropic unconfined aquifer, and includes both the Newer Volcanics and underlying sedimentary units (the Brighton Group and the Werribee Formation), although hydraulic connection of these units to the volcanics is irregular. Groundwater flow in the Newer Volcanics is through vesicular and/or scoriaceous lava flow tops and bottoms, in intercalated fluvial deposits, and through the fractured and jointed lava flows. Locally (scale of less than I km square), the basaltic aquifer system may consist of hydraulically separated shallow and deep aquifer zones that are connected on a larger scale. The deep aquifer zones may be semi-confined to confined. Groundwater in the study area is recharged via throughflow from upgradient and infiltration of rainfall. Discharge from the Newer Volcanics in the study area is primarily to underlying sedimentary formations, but also to surface water features and directly to Port Phillip Bay. Several mechanisms which reduce contaminant concentrations are possible in the Newer Volcanics aquifer system. These include volatilisation, dispersion and diffusion, transient storage, matrix diffusion, sorption, hydrolysis, and biodegradation. However, the nature of porosity in the Newer Volcanics may significantly extend the lifetime of contaminant plumes via the processes of transient storage and matrix diffusion. The primary mechanisms of attenuation and degradation of organic contaminants in the Newer Volcanics aquifer system are probably biodegradation, matrix diffusion, sorption, and dispersion (for non-reactive contaminants) in order of decreasing effect. Biodegradation at the water table and discharge areas will also be significant because of atmospheric contact and increased dissolved oxygen concentrations. Because of the relative lack of organic carbon in the basaltic aquifer system, sorption will occur mainly to mineral surfaces in clay-rich zones and within the rock matrix (concurrent with matrix diffusion). In some cases, relatively undiluted contaminants may be transported along preferred flow paths to discharge locations where they may pose a potential threat to the environment prior to degradation or attenuation. It was found, at least with phenols and volatile organic compounds in groundwater at a study site, that contaminants are degraded and/or attenuated rapidly, probably via biodegradation, matrix diffusion, and sorption. Biodegradation testing of groundwater at this study site confirmed the existence of microorganisms in the aquifer system capable of aerobic degradation; indirect evidence may indicate the presence of anaerobes.
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ItemHigh resolution solar exposure estimates from geosynchronous satellite observations for climate and near real-time applications( 1998)This thesis describes research and development work undertaken to produce a satellite based near-real time high resolution (6 to 24 km) surface solar exposure estimation system. Physical models of radiative transfer within the atmosphere have been developed to produce the estimates of exposure for the entire Australian continent from full resolution hourly visible Geostationary Meteorological Satellite (GMS) Stretched-Visible and Infrared Spin Scan Radiometer (S-VISSR) data. This thesis describes the exposure estimation system, including details of the physical processes modelled. The accuracy of the exposure data is presented. The first high resolution climatology of exposure across Australia is also presented and discussed. Detailed charts of mean daily exposure for each month and annual mean daily exposure form part of the climatology, based on the period November 1990 to June 1994 inclusive. Annual and four-monthly charts are compared to the available Australian Bureau of Meteorology (BoM) National Climate Centre (NCC) Solar Radiation Atlas (1975) charts based on cloud and sunshine records for the period 1968 to 1974 inclusive. Generally the agreement is good, with the satellite system providing greater spatial and temporal (all months) detail, some significant differences and higher accuracy. The satellite climatology shows that minimum exposure in the far north occurs in February due to the monsoon even though the sub-solar point is at a similar latitude. During the monsoon, the exposure minimum over Cape York is seen to shift from the east to the west side. Considerable detail of coastal and orographic exposure gradients about the east and southeast coasts is available. Other features seen for the first time are also presented. For exposure estimation, the model of Diak and Gautier (1983) has been developed further and carefully tuned for use with GMS-4 data (1990 to 1994). Extensive changes have been made to this model to use data from GMS-5, which replaced GMS- 4 in May 1995. GMS-5 has a sensor response extending from the visible to the near-infrared. The GMS-5 based model now runs operationally within the BoM, using total precipitable water estimates from the BoM regional numerical weather prediction (NWP) system, and real-time ozone estimates from the local readout of the National Oceanographic and Atmospheric Administration (NOAA) satellites. The models perform best in clear-sky conditions, with the average deviation of spatially-averaged daily model estimates from surface-based point pyranometer data being less than 5% (less than 4% against available high quality pyranometer data). In cloudy conditions, the average percentage deviation is larger. Australia-wide estimates of the accuracy of satellite-based exposure estimates have been developed. Over most of the continent, typical cloud conditions lead to daily estimates being within 8% of collocated point pyranometer measurements. No other high-resolution data set is available for direct comparison. However, results achieved here are comparable to or better than those reported for other locations. In clear-sky conditions, results presented here are as accurate as measurements from well-maintained good-quality pyranometers. The spatial and temporal variability of the exposure data has also been examined. From this, it has been estimated that over typical Australian agricultural areas, daily satellite exposure estimates are more accurate than extrapolation from a high-accuracy pyranometer more than 20 to 50 km distant. The exposure data have already been used for crop modelling purposes, as an aid to siting of high-quality ground-based measurements for a solar-thermal power station feasibility study, and for hydrological modelling. Such applications, while briefly discussed, are outside the focus of this thesis.
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ItemTectonic geomorphology of the Bogong and Dargo High Plains region, east Victorian highlands, Australia( 1999)The Australian Alps, a sub-region of the Australian Eastern Highlands, have enigmatically high elevations of relief for a highland belt renowned for its ancient origins and landscapes. In debates over the Eastern Highlands history, the development and significance of the Alps have been under-represented. This study defines the morphological extent of the Australian Alps and investigates their tectonic and erosional development. The focus of investigation is the Bogong and Dargo High Plains area and the broader surrounding highlands region. The Cainozoic history of this area has not been investigated in detail since last century. The geological record of the region has substantial gaps, and the erosional history is the main indicator of tectonic change. A methodological structure different to traditional approaches is devised for this study. Cause and response are compared on a process geomorphology basis. Causes investigated are (1) intra-highland tectonics and (2) basin tectonics and sea level change. Denudational relief change is the main response investigated. Spinal and temporal comparison of quantitative results enables relationships to be determined. Peak height distribution and relief observations are used to define the morphological context of the Australian Alps. Within the Alps, the high plains area is used as a case study. Tectonic constructional morphology is investigated using peak height distributions, lineament analysis, tectonic landforms and lava offsets. A Cainozoic fault block is identified, and reactivated fault displacements are determined for bounding and intra-block faults. The erosional development of the area is determined and compared with the constructional morphology results. The sub-volcanic relief of the Bogong Volcanic Province is mapped and compared with post-volcanic stream incision. Guidelines are established for interpreting strath terraces and strath terrace long profiles are used to reconstruct the post-volcanic stream erosion development. Sources and magnitudes of oversteepened stream reaches in the present rivers are identified. Spatial and temporal relationships between fault reactivation and stream incision are determined, and the relative roles of active and passive tectonics are assessed. The tectonic and erosional development of the fault block is reconstructed in cross-sectional form. Finally, the proportion and nature of highland margin-derived stream incision is identified. This study finds that the Australian Alps were substantially affected by fault block uplift during Oligocene, with more minor phases in the Miocene and Pliocene. Broader highland margin warping accompanied fault block uplift. Uplift amounts varied between 150m and over 1000m according to proximity to major faults. Stream incision was upstream-increasing and periodic, with three incision phases during the Oligocene and Pliocene. The later phases include a possible isostatic rebound component. An additional incision phase unrelated to uplift occurred in the Gippsland Basin catchment during the Quaternary. The Australian Alps is delineated here as a separate entity within the Eastern Highlands, with its own tectonic history. Cainozoic uplift created the higher elevations and greater relief of the Alps. This history is not representative of the Eastern Highlands generally, and it should not be used as a guide to a ‘united’ Eastern Highlands uplift. The highlands consist of a ‘patchwork’ of landscape evolution scenarios, rather than a single tectonic province. More definable tectonic histories can be derived from erosional regions of geologically unrecorded time using a process geomorphology perspective. This study provides a suggested step towards redressing interpretation problems recognised in landscape evolution studies generally.