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 structural evolution, tectonics and hydrocarbons of the offshore Otway Basin, SE Australia( 2003)The offshore Otway Basin is part of Australia's passive southern margin, in which two separate rift-phases between the Tithonian? and Maastrichtian formed numerous depocentres. The research presented has analyzed and described the structural styles in the offshore Otway Basin and constructed a model of the basin's evolution since the Late Jurassic. The Otway Basin has been divided into four structural zones from north to south. Zone I comprises the onshore area and most of the shelf along the margin. Deep halfgraben developed during the first rift phase with characteristic horst and graben in Palaeozoic basement. To the south, zone I is bound by the Hinge Zone. Structural zone II covers the entire deepwater part of the Otway margin, characterized by a very thick Late Cretaceous section with pervasive Turonian faulting in the east and saucer-shaped depocentres in the west. Large halfgraben controlled deposition of the post-Turonian sedimentation in the eastern Otway Basin. Negative flower structures document strike-slip faulting. Strongly thinned lower laminated continental crust underlies this zone, limited to the south by the Outer Margin Highs. Domino faulting formed halfgraben and less commonly graben in Structural Zone III, the Outer Margin Highs. The base of the Outer Margin High sediments represents a regional decollement surface and domino faulting occurred along a second-generation decollement. Structural zone III is limited to the south by the continent-ocean-boundary with oceanic crust in structural zone IV. In the Shipwreck Trough, halfgraben died out against an accommodation zone which developed into the Shipwreck Fault with strike-slip offset .The regional stress regime indicate sinistral strike-slip movement along this fault zone. In the southwest Shipwreck Trough, four Turonian to early Coniacian syn-rift phases can be distinguished formed through footwall collapse to the north of the Hinge Zone. Differences in the amount of extension in the basin are accommodated along strike-slip faults such as the Shipwreck Fault. Sedimentation rates between 89 and 83 Ma increased whilst extension rates declined. Since approximately 83Ma sedimentation rates declined exponentially in phase with extension rates. Regionally, rapid Turonian extension formed a wide graben system between Antarctica and Australia. With the serpentinization of exhumed mantle peridotite in the Outer Margin Highs during the Coniacian in the east and Turonian in the west, the crustal deformation mechanism changed from mainly pure shear to simple shear along the newly established decollement. Fast spreading since the Mid Eocene caused gravitational collapse of the margin. Changes in heat flow possibly correlate with a change in deformation style in the continental crust. Parallel developments of sedimentation-rate and extension-rate suggest that most of the subsidence was structurally related. The Shipwreck Trough hydrocarbon fairway probably continues south into the Sorrell Basin. Possible stagnant conditions in deeper water offshore across the Hinge Zone might have enhanced the organic content of the Belfast Mudstone creating potential oil source rocks. Deepwater lntra-Paaratte reservoirs are not proven, but the alternating reflective to non-reflective seismic facies might indicate interbedded sands and shales. Large rollover anticlines would make excellent traps in the deepwater Otway Basin.
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ItemInvestigations into diamond drilling and rock drillability: microscale and fullscale impregnated bits( 1980)Drill bits having cutting edges formed of a matrix of sintered metal powder impregnated with diamond bort (the so called "impregnated" diamond bits) have the potential to greatly increase the economy of diamond drilling, due to low production costs and long bit life resulting from reconditioning of the cutting edges. However, little detailed research into the performance of impregnated bits has been conducted, and the capacity to predict their field behaviour is limited. As a contribution to the knowledge of impregnated bit performance, this project has studied basic relationships between thrust, rotational speed and the penetration of diamond bits into rock, with particular attention paid to the development of techniques suitable for laboratory testing using miniature impregnated bits. A conventional bench drill and a radial arm drill were modified and instrumented to enable operating conditions to be controlled and drilling parameters to be measured and monitored, for microscale and fullscale drilling using impregnated drill bits. Bit performance and drilling characteristics were studied for four rock types, and rock drillability studies were carried out on seven rock types. Statistical relationships between penetration rate, specific energy, torque and drilling distance that were determined enable projection of drilling data from a standard "sharp" condition. A wear measuring device was developed to assess matrix wear of the impregnated microbits. Reconditioning was done by drilling medium-strength, abrasive Stawell sandstone. Initial penetration rate increases linearly with increases in thrust and/or rotational speed, but only within a limited range, depending on rock type and the other operating parameters. Matrix contact with the rock surface, "clogging" of the diamonds, time-dependency, and strength of diamonds and the diamond-matrix bond play important roles in these phenomena. Comparison of rock drillability between that of microscale and fullscale bits shows a straight-line relationship indicating the possibility to predict drilling performance in the field. Uniaxial compressive strength, tensile strength, and Sklerograf hardness can be used as a preliminary, but not reliable guide, to predict drillability. Petrographic characteristics and the relative scale of diamond size to grain size of minerals affect rock drillability.
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ItemEnvironmental fate and transport of TNT in soil at the former explosives factory Maribyrnong( 2002)Highly toxic explosives compounds can potentially contaminate soil and groundwater and pose extended environmental hazard due to their persistence. Explosives contamination within soils was investigated at the former Explosives Factory at Maribyrnong (EFM), by sampling and spectrophotometric / HPLC analysis. The environmental fate and transport of 2,4,6-trinitrotoluene (TNT) was assessed via batch and microcosm testing to quantify the influence of key subsurface sinks, adsorption, and transformation, and hence evaluate natural attenuation as a remediation option. A five tonne crystalline TNT source zone was delineated within soils at the base of a TNT process waste lagoon. This source was found to be supplying aqueous TNT loading to subsurface soils and groundwater, with the resultant plume localised to the shallow clay sequence due to a combination of natural attenuation processes and hydrogeological constraints. Freundlich described sorptive partitioning was found to be the main TNT sink at EFM (KF= 29 mL/g), while transformation rates were moderate (3.86 x 10-4 hr-1) due to aerobic conditions, and TNT toxicity inhibiting microbial degradation. Slow groundwater migration toward the Maribyrnong River (0.7 m/yr) and upward hydraulic gradients within underlying sand and gravel aquifers serve to increase TNT residence time within the clay aquitard, leading to increased interaction with adsorptive substrates and microbes and/or elements of the soil matrix responsible for aerobic transformation. Remediation of the contaminated lagoon may involve removal and treatment/landfilling of the top 1m of soil, then refilling with an impermeable capping allowing ongoing natural attenuation of residual TNT at depth via anaerobic degradation and sorption.
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ItemAustralian Neoproterozoic glaciation: a study of the Sturtian glacial deposits in the Arkaroola region, Northern Flinders Ranges South Australia( 2005)The late Proterozoic Sturtian glacigenic succession exposed in the Arkaroola region of the Northern Flinders Ranges record the earliest of two global Neoproterozoic `Snowball' glacial events in the Adelaide Geosyncline, South Australia. Two stratigraphically disparate glacigenic units were recognised in the late Sturtian succession in the Arkaroola region, a subaerially deposited glacial till - the Merinjina Tillite, and an unclassified glaciomarine diamict unit. The Merinjina Tillite unit preserves a five-fold lithostratigraphy, hosting englacial melt-out deposits, glaciolacustrinal sediments and dominated by a massive to poorly-bedded tillite unit deposited directly from glacier ice. The glaciomarine diamictite preserves down-slope mass-flow deposits, as well as turbidite sequences, slumping and sediments from glacial fall-out including dropstones embedded in laminated muddy-shale and is interpreted as a basin-margin marine deposit. Palaeocurrent analyses across the Northern Flinders Ranges and stratigraphic reviews of analogous Sturtian glacigenic deposits elsewhere in the Northern Flinders Zone suggest palaeotidal influence from the north-north-west and indicate a north-north-west-sloping basin margin in the Northern Flinders Zone. Two major palaeoclimatic phases were recognised in glacigenic rocks the Arkaroola region. A glacial advance phase is represented by the advance of continental glacial sediments, across a topographically-elevated, subaerial surface and extending down-slope into a submarine basin. The other, represented regionally by dropstone shales, is interpreted as glacial retreat and the termination of Sturtian `Snowball Earth' conditions. A rise in palaeo-atmospheric temperatures is inferred, causing melting of continental and marine ice-sheets and resulting in a regionally-extensive marine transgression. The slight increase in water temperature during glacial retreat is believed to have triggered carbonate precipitation and the ultimate deposition of cap dolomites which overly the glacigenic sediments across the Adelaide Geosyncline.
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ItemThe major, trace and precious metal geochemistry of some Permian layered intrusions, Central Queensland( 1990)The Bucknalla Complex, previously known as the Westwood Layered Intrusion, is a small, 10 km2, layered, tholeiitic, mafic-ultramafic intrusion located 50 km southwest of Rockhampton that was emplaced into an active continental margin environment in the Permian. The complex comprises clinopyroxenites, olivine clinopyroxenites, wehrlites, troctolites, hornblende gabbros, gabbros, anorthosites, leucogabbros and dolerites. It is a saucer-shaped lopolith (2200 m X 6 km at maximum stratigraphic intersection) which intruded Lower Permian spilitic pillow lavas, cherts and tuffs of the Rookwood Volcanics during the Lower Permian. It has subsequently been tilted vertically and in a northeast direction. It consists of over 15 laterally discontinuous igneous units ranging in thickness from 1-50 m. Plagioclase is a cumulus phase throughout the intrusion while orthopyroxene is absent until the very uppermost levels of the stratigraphy. The chromium composition of magnetite analysed by electron microprobe has been found to mimic whole-rock mg# and is a good measure of the degree of fractionation of the rocks. Electron microprobe analyses of samples from two traverses perpendicular to layering reveal cryptic variation in the primary phases (olivine: Fo69-83; plagioclase: An54-97; clinopyroxene mg#: Cpx67-87) which is not a simple function of stratigraphic height. Background PPGE (Pd & Pt), Au, S and Cu values for the intrusion are high while IPGE (Ir & Ru) are low. A total of 120 analyses has produced the following range of values: Pd, 2-70 ppb; Pt, 3-40 ppb; Au, 1-20 ppb; Ir, 0.01-0.07 ppb; Ru, 0.2-0.6 ppb; S, 150-400 ppm and Cu, 40-600 ppm. Platinum, Pd and Au display good correlations with Cu, particularly at more elevated levels, while Ir and Ru are better correlated with whole rock Ni and Cr. Palladium, Pt, Au, Cu & S are elevated in rocks which have intermediate whole-rock mg# (47-60). These trends suggest that the PGE are, to some extent, controlled by fractionation and that the high melting point PGEs (Ir, Ru) were precipitated with the early crystallising phases, such as olivine and clinopyroxene, whereas Pt, Pd and Au were removed from the magma by sulphides. Mantle normalized metal plots for both the mineralized and unmineralized rocks of the Bucknalla Complex display similar trends. Both plots display the anomalous low Ir content, PPGE enrichment and the clear control of sulphides on the distribution of the PGEs and Au. The ratio Pd/Ir is extremely high (1800-9300) indicating extreme fractionation of the PGEs. These trends may, in part, reflect PGE abundances inherited from the source (i.e. relatively low degrees of partial melting) but were exaggerated by the extraction of the IPGE during the early stages of fractional crystallization and by the precipitation of a PPGE-enriched sulphide component. The Complex is known to host minor Pd-Pt-Au-Cu mineralization, disseminated throughout the intrusion. The mineralization consists of chalcopyrite and bornite and their alteration products digenite and covellite, electrum (Au-Ag alloy), Pd-As, Pd-Sb, Pd-S, michenerite (PdBiTe2) and sperrylite (PtAs2). A common host rock is olivine gabbro and the silicate minerals are generally fresh. The mineralization is considered to be primary magmatic for a number of reasons, foremost of which are (i) the clear association of the PGMs with intercumulus (magmatic-textured) fresh or relict Cu-sulphides and (ii) a continuum in Pd/Pt, Cu/Pd, and Cu/Pt ratios from background to mineralized samples which strongly suggests that the processes responsible for the enhanced PGE content of the Bucknalla Complex were also responsible for mineralization. In as much as the former must have been produced by magmatic processes it is concluded that the higher grade PGE-Cu-S mineralization was also caused by primary magmatic processes. A model is proposed in which mineralization is sporadically generated by influxes of small batches of PGE-rich S-undersaturated magma into a magma chamber in which the resident magma has reached S-saturation due to fractional crystallization processes. Other intrusions in the region, namely; the Eulogie Park Complex, the Fred Creek intrusion and the Boogargan intrusion, are not considered prospective for stratiform PGE mineralization due to their low background PGE tenor, low Pd/S and Pd/Se ratios and high S contents.
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ItemThe platinum-group element geochemistry and petrogenesis of the Heazlewood River mafic-ultramafic complex, Tasmania( 1990)The Heazlewood River mafic-ultramafic complex (HRC) comprises well-layered olivine- and orthopyroxene-rich cumulates, gabbronorite dykes, tonalites and low-Ti tholeiitic basalt and boninite lavas. The complex was emplaced as part of a large, low-angle thrust sheet during the middle Cambrian and subsequently deformed during the Devonian, so that the original stratigraphical relationships are obscured. The cumulate succession incorporates two distinct blocks, viz. the western HRC, comprising primitive adcumulates, and the eastern HRC, consisting of more evolved orthocumulates and mesocumulates. These two cumulate blocks are interpreted to represent stratigraphically equivalent parts of a single magma chamber. In this scenario, the western HRC represents an axial part of the intrusion where high heat flows, due to repeated injections of primitive magma, promoted the development of a compositionally zoned magma chamber. In contrast, the eastern HRC is believed to constitute a marginal facies of the intrusion, where sidewall cooling caused rapid crystallisation of successive magma additions and inhibited adcumulate growth and the formation of a compositionally stratified liquid column. Results from a detailed study of the mineral compositions and whole-rock geochemistry of the HRC suggest that all of the cumulates and most of the dykes and tonalites were derived from boninitic parental magmas. This hypothesis is substantiated by empirical models which were calculated using both major and trace element approaches. The models also show that the low-Ti basalts (second-stage melts) and boninites (third-stage melts) were probably derived from component-induced progressive partial melting of a MORB-depleted spinel lherzolite source. Partial melting of the refractory mantle source was initiated and sustained by the continued influx of slab-derived Si02-, LREE-, Zr-enriched hydrous fluids. The proposed petrogenetic model for the HRC is most consistent with an island arc setting for the complex, with melting occurring in MORB-depleted forearc lithosphere overlying a subduction zone. The HRC is not an ophiolite sensu stricto, despite the fact that it is more similar to the upper portions of the so-called 'island-arc ophiolites' (eg. Troodos) than to any other type of ultramafic intrusion. It is best perceived as a high-level boninitic magma chamber which developed immediately beneath a platform of genetically-related submarine lavas. The composition of the boninitic parental magmas was the principal control on the PGE geochemistry of the cumulate sequences. Despite representing PGE-enriched, S-undersaturated second-stage melts similar to the parental (U-type) magmas for the ultramafic portions of the Bushveld complex, the boninites were unable to form a Merensky-reef type PGE deposit because they did not come into contact with S-saturated (A-type) magmas. In the absence of cumulus sulphides, the PPGE (Pt, Pd, Rh) were partitioned into the residual liquids, whereas the IPGE (Os, Ir, Ru) were strongly fractionated into early-formed olivine-chromite cumulates. These features are highlighted by the extremely low IPGE tenor of the boninites, and the relatively high IPGE tenor of the dunites in comparison to the more evolved cumulates. Three types of chromitites are recognised in the HRC. Type I and type II chromitites occur as magmatic schlieren which probably formed during replenishment events. Type III chromitites occur as layers, pods and irregular patches developed in an unusual xenolith-bearing plagioclase peridotite. It is interpreted to have formed due to mixing between ascending xenolith-bearing, hydrous intercumulus liquids and resident ultramafic magma along the floor of the magma chamber. Chromitite occurrences in the HRC are enriched in PGE by up to two orders of magnitude relative to their ultramafic host rocks, and most strongly-enriched in Ru and/or Pt and Rh. Their PGE tenor reflects the early crystallisation of laurite, followed by Pt and Rh sulpharsenides, in response to increasing S and As activities which developed primarily due to magma mixing. The low Os and Ir abundances in the chromitites is believed to reflect their formation from Os- and Ir-depleted boninitic magmas. The HRC and the Adamsfield complex were the world's major suppliers of Os-Ir-Ru alloys during the early part of this century. The alloys occur in alluvial deposits that are spatially associated with primitive olivine-rich cumulate sequences. The latter are commonly suspected to represent the source for the alloys, but recent exploration programs have yet to define a bedrock occurrence of Os-Ir-Ru alloys in Tasmania. The results from the present study provide important constraints on the genesis of these alloys. Silicate inclusions found in the alloys suggest that they formed at mantle temperatures and pressures and were transported to crustal magma chambers by boninitic magmas. The alloys may have crystallised during ascent, or alternatively, represent residual mantle phases which became incorporated into the boninites during partial melting. Most of the observations pertaining to the Os and Ir geochemistry of the HRC suggest that the alloys probably occur in thin magmatic concentrations that were deposited along the base of the intrusion from the most primitive of the boninitic magmas involved in the generation of the cumulate sequences. Future exploration should focus on delineating the cumulate products of these primitive magmas and specifically, in defining the horizons which demarcate fresh influxes of these liquids.
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ItemStudies in Victorian Tertiary foraminifera neogene planktonic faunas( 1977)Planktonic foraminiferal faunas are described for the interval late Early Miocene to the Pleistocene, in the Tertiary basins along the southern margin of Victoria, including the Otway Basin, the Port Phillip Embayment, and the Gippsland Basin. Ninety-two foraminiferal taxa are identified. The faunas are dominated in the Early Miocene by globigerinid and globigerinoidid species, by unkeeled globorotalids in the Middle Miocene, and by keeled globorotalids for most of the Late Miocene. Unkeeled globorotalids are again important in the Early Pliocene, but keeled species again reappear in the Late Pliocene and the Early Pleistocene. One Pleistocene, two Pliocene, two Late Miocene, and two Middle Miocene planktonic foraminiferal zones are recognised on the first appearance of the following species: Orbulina suturalis, Globorotalia mayeri, Globorotalia acostaensis, Globorotalia conomiozea, Globorotalia puncticulata, Globorotalia viola, Globorotalia truncatulinoides. Subzones are identified by the extinction of Globorotalia peripheroronda, and by the appearance of Globigerina nepenthes and Globorotalia plesiotumida. Foraminiferal datum levels are used to correlate the Victorian sections with the Italian stratotype sections, the New Zealand late Tertiary, and the N-zonation of Blow, and hence into the palaeomagnetic and radiometric time scales. In the Tertiary basins, the maximum extent of marine deposition occurred in the Early Miocene, and despite subsequent sea level falls, continuous marine deposition is found through the Middle Miocene and most of the Late Miocene in the Otway Basin and the Port Phillip Embayment. Shallowing within the Middle Miocene is reflected by breaks in the Gippsland Basin sections, and lithological changes in other basins. A major sea withdrawal occurred near the top of the Miocene. Small scattered Pliocene deposits indicate short high sea level phases at the base of the Pliocene, in the middle of the Pliocene, and about the Pliocene - Pleistocene boundary.
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ItemThe weather and climate of Australia at the Last Glacial Maximum( 2005)The global climate has experienced four glacial cycles in the last 420,000 years, with each cycle characterised by a prolonged period of cooling culminating in maximal glaciation followed by a brief warm period. The most recent period of maximal glaciation is termed the Last Glacial Maximum (LGM) and occurred about 21,000 years ago. We currently live in one of the warm periods. The global climate is changing, and it is becoming more important to understand the extremes of the climate system and how well our modelling capability can capture those extremes. There has been a modelling intercomparison project established to examine how global general circulation models compare in simulating past climates, including the LGM. Analysis and comparison of these model results has been presented for many parts of the globe, but there has not been a comparison of the different model results over the Australian region. This thesis aims to fill that gap and explore the simulated LGM weather and climate of Australia and its drivers in more detail. Comparison with proxy evidence is also undertaken, and inconsistencies seen in the literature addressed. The Australian climate at the LGM was believed to be generally cooler, drier and possibly windier from proxy evidence in the literature. In the comparison done here the mean temperature and precipitation fields from most models show cooler and drier conditions, with some seasonal variability, but there are some strong outliers. It was found that the differences were not dependent on model resolution, but that the surface parameterisations were highly important for these fields. The shifts in the circulation were examined both in the model results and with a study of the non-linear link between the wind, surface moisture and dunes, which are a proxy for past winds. All the models simulate a southward shift in the westerlies in the Australian region. This is strongly driven byte prescribed sea-surface temperatures. Australia's current wind regime is conducive to dune building. However, the binding effect of soil moisture (or vegetation) is strong enough to limit present day movement, whereas in the drier climate at the LGM there was a capacity for sand movement. The analysis of dune orientations did not produce conclusive evidence for how the westerlies might have shifted at the LGM. An apparent enigma in the proxy evidence at the LGM is the high lake levels in Australia’s south east, while most inland lakes were dry. Previous authors believed that the precipitation was still low, but the high lake levels were driven by lowered potential evaporation. The hydrological cycle was generally depressed in the LGM simulations, but the potential for evaporation remained high. Thus an alternative hypothesis is posed based on increased run off due to a known shift in the vegetation types and a lag in the timing of the run off due to snowmelt. The analysis here shows that our capacity to simulate climates quite different from the present is still developing, but that model results can help explain apparent inconsistencies in the reconstruction of past climates from proxies.
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ItemAltitudinal distribution of vegetation in the headwaters of the Wongungarra River, Victoria( 1993)Changes in vegetation composition with respect to altitude were investigated in the sclerophyllous forests of the Australian mountain region. Vegetation was surveyed at 148 sites along two transects which were located to maximise variation in altitude and minimise the influence of environmental factors not directly related to altitude. The measurement, simulation, and estimation of environmental variables revealed that this aim was met except at the end-points of the transects where secondary influences are present.