School of Earth Sciences - Research Publications
Now showing items 1-12 of 495
Quantitative compaction trends of Miocene to Holocene carbonates off the west coast of Australia
(Taylor and Francis, 2021)
In this paper, we describe porosity variations in Miocene to Holocene carbonates off the west coast of Australia and assess their compaction trends. The porosity values were measured using discrete samples of Sites U1459–U1464 obtained by the International Ocean Discovery Program Expedition 356. The carbonate deposits have been influenced by a range of textures and diagenetic conditions throughout a nearly continuous sequence of geological ages from the Miocene to Holocene and at core depths from 0 to 1100 m below the seafloor. The collected samples were mostly grainstone, packstone, wackestone and mudstone textures. Dolostones and dolomitic carbonates were described at the Miocene intervals. Compaction trends were estimated exponentially and linearly based on cored sites, carbonate textures and dominant mineralogies (dolomite, calcite/aragonite). At all six sites, porosity distribution and reduction were generally depth-dependent. The porosity converged to about 30% between 750 and 1100 m, which suggests that the carbonates were close to the densest packing by mechanical compaction at a burial depth of ∼750 m. The porosity deviations are associated with textures and dominant mineralogies. Increasing mud content from grainstone to mudstone is a controlling factor for initial porosity and porosity reduction rate. Dolomitisation, dolomitic cementation, aragonite needle-rich mud and non-skeletal grains cause deviations from the depth-dependent compaction trends. Reflux-related cementation generally decreases porosity in Miocene dolomitic intervals. Higher porosity values of the Quaternary wackestone and mudstone at Site U1461 resulted from the presence of aragonite needle-rich mud hosting abundant micropores and from a high sedimentation rate. The occurrence of non-skeletal grains, such as ooids and peloids, as well as occasional meteoric exposure led to porosity inversion, occluding interparticle permeability and the creation of moldic pores.
Between a rock and a hard place: The burdens of uncontrolled fire for smallholders across the tropics
(Elsevier BV, 2021-09)
Once fire-resistant rainforests are becoming fire prone. Uncontrolled fires reflect new ecologies of the Anthropocene, driven by interactions of multiple actors and sectors across scales. They threaten the ecological integrity of tropical forests, impact global climate regimes and importantly cause considerable social and economic burdens. Numerous smallholder farming communities throughout the forested tropics experience the immediate place-based damages of uncontrolled fires and increasingly flammable landscapes. However, these burdens remain largely ‘invisible’ as leading narratives concentrate on losses accrued at aggregate scales, including to climate and biodiversity. Rather, smallholder farmers are often cast as culprits of contagion rooted in colonial condemnation of their customary fire-based agricultural practices. We use an environmental justice lens, notably the dimensions of recognition and distribution, to reveal the distributional burdens of uncontrolled fires for these land managers. We use empirical data from four case studies in three countries: Brazil, Madagascar and the Philippines, to explore the i) burdens of uncontrolled fire, ii) changing risks, iii) drivers and iv) responses to uncontrolled fire, and finally, the v) level of smallholder dependence on intentional fire. We show that place-based burdens of uncontrolled landscape fire are significant, including in landscapes where fire frequency is low. Burdens are both material and non-material and include infringements on food security, health, livelihoods, social relations and the burden of prohibitive fire policy itself. Equitable responses to uncontrolled fires must be sensitive to the distinctions between fire types. Further, we suggest that through bringing visibility to the place-based burdens of uncontrolled fires, we can begin to co-design resilient responses that avoid placing the final burden of risk reduction on to marginalized smallholder farming communities.
Warming Patterns Affect El Nino Diversity in CMIP5 and CMIP6 Models
(American Meteorological Society, 2020-10-01)
Given the consequences and global significance of El Niño–Southern Oscillation (ENSO) events it is essential to understand the representation of El Niño diversity in climate models for the present day and the future. In recent decades, El Niño events have occurred more frequently in the central Pacific (CP). Eastern Pacific (EP) El Niño events have increased in intensity. However, the processes and future implications of these observed changes in El Niño are not well understood. Here, the frequency and intensity of El Niño events are assessed in models from phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6), and results are compared to extended instrumental and multicentury paleoclimate records. Future changes of El Niño are stronger for CP events than for EP events and differ between models. Models with a projected La Niña–like mean-state warming pattern show a tendency toward more EP but fewer CP events compared to models with an El Niño–like warming pattern. Among the models with more El Niño–like warming, differences in future El Niño can be partially explained by Pacific decadal variability (PDV). During positive PDV phases, more El Niño events occur, so future frequency changes are mainly determined by projected changes during positive PDV phases. Similarly, the intensity of El Niño is strongest during positive PDV phases. Future changes to El Niño may thus depend on both mean-state warming and decadal-scale natural variability.
Contrasting Southern Hemisphere Monsoon Response: MidHolocene Orbital Forcing versus Future Greenhouse Gas-Induced Global Warming
(American Meteorological Society, 2020-11-15)
Past changes of Southern Hemisphere (SH) monsoons are less investigated than their northern counterpart because of relatively scarce paleodata. In addition, projections of SH monsoons are less robust than in the Northern Hemisphere. Here, we use an energetic framework to shed lights on the mechanisms determining SH monsoonal response to external forcing: precession change at the mid-Holocene versus future greenhouse gas increase (RCP8.5). Mechanisms explaining the monsoon response are investigated by decomposing the moisture budget in thermodynamic and dynamic components. SH monsoons weaken and contract in the multimodel mean of midHolocene simulations as a result of decreased net energy input and weakening of the dynamic component. In contrast, SH monsoons strengthen and expand in the RCP8.5 multimodel mean, as a result of increased net energy input and strengthening of the thermodynamic component. However, important regional differences on monsoonal precipitation emerge from the local response of Hadley and Walker circulations. In the midHolocene, the combined effect of Walker–Hadley changes explains the land–ocean precipitation contrast. Conversely, the increased local gross moist stability explains the increased local precipitation and net energy input under circulation weakening in RCP8.5.
Scope for predicting seasonal variation of the SPCZ with ACCESS-S1
Regional seasonal forecasting requires accurate simulation of the variability of local climate drivers. The South Pacific Convergence Zone (SPCZ) is a large region of low-level convergence, clouds and precipitation in the South Pacific, whose effects extend as far as northeast Australia (NEA). The location of the SPCZ is modulated by the El Niño-Southern Oscillation (ENSO) which causes rainfall variability in the region. Correctly simulating the ENSO-SPCZ teleconnection and its interplay with local conditions is essential for improving seasonal rainfall forecasts. Here we analyse the ability of the ACCESS-S1 seasonal forecast system to predict the SPCZ’s relationship with ENSO including its latitudinal shifts, zonal slope and rainfall magnitude between 1990 and 2012 for the December–January–February (DJF) season. We found improvements in ACCESS-S1’s SPCZ prediction capability compared to its predecessor (POAMA), although prediction of the slope is still limited. The inability of ACCESS-S1 to replicate seasons with a strong anti-zonal SPCZ slope is attributed to its atmospheric model. This has implications for accurate seasonal rainfall forecasts for NEA and South Pacific Islands. Future challenges in seasonal prediction facing regional communities and developers of coupled ocean–atmosphere forecast models are discussed.
Tropical forcing of Australian extreme low minimum temperatures in September 2019
We explore the causes and predictability of extreme low minimum temperatures (T ) that occurred across northern and eastern Australia in September 2019. Historically, reduced T is related to the occurrence of a positive Indian Ocean Dipole (IOD) and central Pacific El Niño. Positive IOD events tend to locate an anomalous anticyclone over the Great Australian Bight, therefore inducing cold advection across eastern Australia. Positive IOD and central Pacific El Niño also reduce cloud cover over northern and eastern Australia, thus enhancing radiative cooling at night-time. During September 2019, the IOD and central Pacific El Niño were strongly positive, and so the observed T anomalies are well reconstructed based on their historical relationships with the IOD and central Pacific El Niño. This implies that September 2019 T anomalies should have been predictable at least 1–2 months in advance. However, even at zero lead time the Bureau of Metereorolgy ACCESS-S1 seasonal prediction model failed to predict the anomalous anticyclone in the Bight and the cold anomalies in the east. Analysis of hindcasts for 1990–2012 indicates that the model's teleconnections from the IOD are systematically weaker than the observed, which likely stems from mean state biases in sea surface temperature and rainfall in the tropical Indian and western Pacific Oceans. Together with this weak IOD teleconnection, forecasts for earlier-than-observed onset of the negative Southern Annular Mode following the strong polar stratospheric warming that occurred in late August 2019 may have contributed to the T forecast bust over Australia for September 2019. min min min min min
Method uncertainty is essential for reliable confidence statements of precipitation projections
(American Meteorological Society, 2021-02-01)
Precipitation events cause disruption around the world and will be altered by climate change. However, different climate modeling approaches can result in different future precipitation projections. The corresponding ''method uncertainty'' is rarely explicitly calculated in climate impact studies and major reports but can substantially change estimated precipitation changes. A comparison across five commonly used modeling activities shows that, for changes in mean precipitation, less than half of the regions analyzed had significant changes between the present climate and 1.58C global warming for the majority of modeling activities. This increases to just over half of the regions for changes between present climate and 28C global warming. There is much higher confidence in changes in maximum 1-day precipitation than in mean precipitation, indicating the robust influence of thermodynamics in the climate change effect on extremes. We also find that none of the modeling activities captures the full range of estimates from the other methods in all regions. Our results serve as an uncertainty map to help interpret which regions require a multimethod approach. Our analysis highlights the risk of overreliance on any single modeling activity and the need for confidence statements in major synthesis reports to reflect this method uncertainty. Considering multiple sources of climate projections should reduce the risks of policymakers being unprepared for impacts of warmer climates relative to using single-method projections to make decisions.
Climate change and rural mental health: a social geographic perspective
(COLL MEDICINE & DENTISTRY JAMES COOK UNIV TOWNSVILLE, 2020-01-01)
CONTEXT: The objective of this commentary is to suggest ways in which current and future research on climate change and rural mental health can be enhanced by social geographic perspectives. As the effects of climate change escalate, the mental health of rural and remote communities will be placed at increasing risk. As such, it is imperative that academics and practitioners recognise the value of multidisciplinary approaches to tackling this issue. ISSUES: As social geographers, the authors of this commentary outline concepts from their field that they find helpful in understanding the relationship between people and places, and how these relations give rise to emotions that are responsive to environmental conditions. LESSONS LEARNED: Ultimately, the authors would like to prompt a re-thinking of 'social' as a category, which is usually confined to interpersonal interactions between humans and suggest a broadening of the concept to include both human and non-human worlds.
New Chronological Constraints from Hypogean Deposits for Late Pliocene to Recent Morphotectonic History of the Alpi Apuane (NW Tuscany, Italy)
<jats:p>A sedimentary sequence of fluvial deposits preserved in the Corchia Cave (Alpi Apuane) provides new chronological constraints for the evolution of the cave system and the timing and rate of uplift of this sector of the Alpi Apuane since the late Pliocene. Supported by magnetostratigraphic analysis performed on fine-grained fluvial deposits, and by radiometric dating of speleothems, we suggest that the deposition of fluvial sediments occurred between ~1.6–1.2 Ma. This implies that the host volume of rock was already located close to the local base level, adding key information about the recent tectonic evolution of the Alpi Apuane. A few before ~1 Ma, an erosive phase occurred due to the base-level lowering, followed by continuous speleothem deposition since at least 0.97 Ma. From that time, Monte Corchia uplifted at a maximum rate of ~0.5 mm/year, which is consistent with isostatic uplift mainly driven by erosional unloading. The petrographical study of the fluvial deposits highlights the presence of material derived from the erosion of rocks that today are absent in the cave’s catchment area, suggesting a different surface morphology during the Early Pleistocene. This study highlights the potential of cave sediments as archives for reconstructing the uplift history of mountain ranges.</jats:p>
Effects of Earthquakes on Flood Hazards: A Case Study From Christchurch, New Zealand
<jats:p>Earthquakes can influence flood hazards by altering the flux, volumes, and distributions of surface and/or subsurface waters and causing physical changes to natural and engineered environments (e.g., elevation, topographic relief, permeability) that affect surface and subsurface hydrologic regimes. This paper analyzes how earthquakes increased flood hazards in Christchurch, New Zealand, using empirical observations and seismological data. Between 4 September 2010 and 4 December 2017, this region hosted one moment magnitude (Mw) 7.1 earthquake, 3 earthquakes with Mw ≥ 6, and 31 earthquakes with local magnitude (ML) ≥ 5. Flooding related to liquefaction-induced groundwater pore-water fluid pressure perturbations and groundwater expulsion occurred in at least six earthquakes. Flooding related to shaking-induced ground deformations (e.g., subsidence) occurred in at least four earthquakes. Flooding related to tectonic deformations of the land surface (fault surface rupture and/or folding) occurred in at least two earthquakes. At least eight earthquakes caused damage to surface (e.g., buildings, bridges, roads) and subsurface (e.g., pipelines) infrastructure in areas of liquefaction and/or flooding. Severe liquefaction and associated groundwater-expulsion flooding in vulnerable sediments occurred at peak ground accelerations as low as 0.15 to 0.18 g (proportion of gravity). Expected return times of liquefaction-induced flooding in vulnerable sediments were estimated to be 100 to 500 years using the Christchurch seismic hazard curve, which is consistent with emerging evidence from paleo-liquefaction studies. Liquefaction-induced subsidence of 100 to 250 mm was estimated for 100-year peak ground acceleration return periods in parts of Christchurch.</jats:p>
Burial and Exhumation History of the Lujing Uranium Ore Field, Zhuguangshan Complex, South China: Evidence from Low-Temperature Thermochronology
<jats:p>The Zhuguangshan complex hosts the main uranium production area in South China. We report (U-Th)/He and fission track thermochronological data from Triassic–Jurassic mineralized and non-mineralized granites and overlying Cambrian and Cretaceous sandstone units from the Lujing uranium ore field (LUOF) to constrain the upper crustal tectono-thermal evolution of the central Zhuguangshan complex. Two Cambrian sandstones yield reproducible zircon (U-Th)/He (ZHe) ages of 133–106 Ma and low effective uranium (eU) content (270–776 ppm). One Upper Cretaceous sandstone and seven Mesozoic granites are characterized by significant variability in ZHe ages (154–83 Ma and 167–36 Ma, respectively), which show a negative relationship with eU content (244–1098 ppm and 402–4615 ppm), suggesting that the observed age dispersion can be attributed to the effect of radiation damage accumulation on 4He diffusion. Correspondence between ZHe ages from sandstones and granites indicates that surrounding sedimentary rocks and igneous intrusions supplied sediment to the Cretaceous–Paleogene Fengzhou Basin lying adjacent to the LUOF. The concordance of apatite fission track (AFT) central ages (61–54 Ma) and unimodal distributions of confined track lengths of five samples from different rock units suggest that both sandstone and granite samples experienced a similar cooling history throughout the entire apatite partial annealing zone (~110–60 °C). Apatite (U-Th-Sm)/He (AHe) ages from six non-mineralized samples range from 67 to 19 Ma, with no apparent correlation to eU content (2–78 ppm). Thermal history modeling of data suggests that the LUOF experienced relatively rapid Early Cretaceous cooling. In most samples, this was followed by the latest Early Cretaceous–Late Cretaceous reheating and subsequent latest Late Cretaceous–Recent cooling to surface temperatures. This history is considered as a response to the transmission of far-field stresses, involving alternating periods of regional compression and extension, related to paleo-Pacific plate subduction and subsequent rollback followed by Late Paleogene–Recent India–Asia collision and associated uplift and eastward extrusion of the Tibetan Plateau. Thermal history models are consistent with the Fengzhou Basin having been significantly more extensive in the Late Cretaceous–Early Paleogene, covering much of the LUOF. Uranium ore bodies which may have formed prior to the Late Cretaceous may have been eroded by as much as ~1.2 to 4.8 km during the latest Late Cretaceous–Recent denudation.</jats:p>
A Geospatial Database for Effective Mine Rehabilitation in Australia
The Australian landscape is affected by abandoned mines that pose environmental, public health and safety risks. To promote the beneficial reuse, rehabilitation and/or remediation of these sites and understand their spatial arrangement, we compiled, classified and analysed a country-wide geospatial database of all known inactive hard rock mine sites. Following extensive review and classification of disparate records of such sites that have been terminated, neglected or classified as heritage, plus those under care and maintenance in Australia, we assessed state-by-state reporting and cross-border rehabilitation requirements. This was enabled by the development of the Mining Incidence Documentation & Assessment Scheme (MIDAS) that can be used to catalogue and compare active or inactive mine data regardless of reporting conventions. At a national level, and with four case studies, we performed GIS-based spatial analyses and environmental risk assessments to demonstrate potential uses of our database. Analyses considered the proximity of sites to factors such as infrastructure and sensitive environmental receptors. As Australia struggles to manage the ongoing technical, socioeconomic and environmental challenges of effective mine rehabilitation, the insights enabled by this national-level spatial database may be key to developing coordinated responses that extend beyond state boundaries. Our classification and methodology are easily transferable, thereby encouraging more formalized, systematic and widespread documentation of abandoned mines worldwide.