School of Earth Sciences - Research Publications
Now showing items 1-12 of 376
Magnesium in subaqueous speleothems as a potential palaeotemperature proxy
(NATURE RESEARCH, 2020-10-06)
Few palaeoclimate archives beyond the polar regions preserve continuous and datable palaeotemperature proxy time series over multiple glacial-interglacial cycles. This hampers efforts to develop a more coherent picture of global patterns of past temperatures. Here we show that Mg concentrations in a subaqueous speleothem from an Italian cave track regional sea-surface temperatures over the last 350,000 years. The Mg shows higher values during warm climate intervals and converse patterns during cold climate stages. In contrast to previous studies, this implicates temperature, not rainfall, as the principal driver of Mg variability. The depositional setting of the speleothem gives rise to Mg partition coefficients that are more temperature dependent than other calcites, enabling the effect of temperature change on Mg partitioning to greatly exceed the effects of changes in source-water Mg/Ca. Subaqueous speleothems from similar deep-cave environments should be capable of providing palaeotemperature information over multiple glacial-interglacial cycles.
Major element data, Ar-40/Ar-39 step-heating and step-crushing data for anorthoclase megacrysts from the Newer Volcanic Province, south-eastern Australia
(ELSEVIER SCIENCE BV, 2018-08-01)
We provide the dataset associated with the research article "40Ar/39Ar ages of alkali feldspar xenocrysts constrain the timing of intraplate basaltic volcanism" Matchan et al. . This dataset contains major element data for 15 large anorthoclase xenocrysts ('megacrysts') collected from six Pleistocene eruption centres (Mount Leura, Mount Shadwell, Mount Noorat, Mount Franklin, Lake Keilambete and The Anakies (East Cone)) in the basaltic Newer Volcanic Province of south-eastern Australia. It also contains multi-collector (Argus VI) 40Ar/39Ar step-heating for 13 of these anorthoclase megacrysts. 40Ar/39Ar vacuo step-crushing experiment data is also provided for three of these megacrysts.
Experimental and simulation results of the adsorption of Mo and V onto ferrihydrite.
(Springer Science and Business Media LLC, 2019-02-04)
This study aims to highlight discrepancies between experimental and simulation linked to the mechanisms of Mo and V adsorption onto ferrihydrite (FHY) nanoparticles. We have measured adsorption capacities and uptake efficiencies and then fitted and compared these with outputs from various geochemical and adsorption models that were run as a function of pH, surface area (SA) and ferrihydrite particles size distributions. Our results revealed that the experimental data for the Mo system could be fitted very well, but this was not the case for the V system, when a model default value for the SA of FHY of 600 m2 g-1 was used. The discrepancy in the results for the V system can be explained by the lack of specific V species and/or associated constants in databases and variation in software versions, which change the outputted chemical species. Our comparative results also confirm that any experimental variables used as modelling inputs need to be checked carefully prior to any modelling exercises.
Pollen analysis of Australian honey
(PUBLIC LIBRARY SCIENCE, 2018-05-16)
Pollen analysis is widely used to verify the geographic origin of honeys, but has never been employed in Australia. In this study, we analysed the pollen content of 173 unblended honey samples sourced from most of the commercial honey producing regions in southern Australia. Southern Australian vegetation is dominated by Eucalyptus (Myrtaceae) forests and, as expected, most Australian honeys are palynologically dominated by Eucalyptus, while other important components include Myrtaceae taxa such as Corymbia/Angophora and the tribe Leptospermeae; plus Brassicaceae, Echium, Macadamia, and Acacia. An important feature of the honeys is the number of Myrtaceae pollen morphotypes per sample, which is generally high (mean = 4.6) compared to honeys produced outside of Australia, including Eucalyptus honeys produced in the Mediterranean region, and honeys produced in South America, which has its own rich indigenous Myrtaceae flora. In the latter regions, the number of Myrtaceae morphotypes is apparently generally ≤2. A high number of Myrtaceae morphotypes may be a feasible criterion for authenticating the origin of Australian honeys, since most Australian honey is produced by honey bees mainly working indigenous floral resources. Myrtaceae morphotype diversity is a convenient melissopalynological measure that could be applied even where detailed knowledge of the pollen morphology of the many component genera and species is absent. Palynological criteria developed in Europe for authenticating Eucalyptus honeys should not be relied upon for Australian honeys, since those criteria are not based on samples of Australian honey.
Biodegradation of thiocyanate by a native groundwater microbial consortium
(PEERJ INC, 2019-03-26)
Gold ore processing typically generates large amounts of thiocyanate (SCN-)-contaminated effluent. When this effluent is stored in unlined tailings dams, contamination of the underlying aquifer can occur. The potential for bioremediation of SCN--contaminated groundwater, either in situ or ex situ, remains largely unexplored. This study aimed to enrich and characterise SCN--degrading microorganisms from mining-contaminated groundwater under a range of culturing conditions. Mildly acidic and suboxic groundwater, containing ∼135 mg L-1 SCN-, was collected from an aquifer below an unlined tailings dam. An SCN--degrading consortium was enriched from contaminated groundwater using combinatory amendments of air, glucose and phosphate. Biodegradation occurred in all oxic cultures, except with the sole addition of glucose, but was inhibited by NH4+ and did not occur under anoxic conditions. The SCN--degrading consortium was characterised using 16S and 18S rRNA gene sequencing, identifying a variety of heterotrophic taxa in addition to sulphur-oxidising bacteria. Interestingly, few recognised SCN--degrading taxa were identified in significant abundance. These results provide both proof-of-concept and the required conditions for biostimulation of SCN- degradation in groundwater by native aquifer microorganisms.
Warming assessment of the bottom-up Paris Agreement emissions pledges
(NATURE PUBLISHING GROUP, 2018-11-16)
Under the bottom-up architecture of the Paris Agreement, countries pledge Nationally Determined Contributions (NDCs). Current NDCs individually align, at best, with divergent concepts of equity and are collectively inconsistent with the Paris Agreement. We show that the global 2030-emissions of NDCs match the sum of each country adopting the least-stringent of five effort-sharing allocations of a well-below 2 °C-scenario. Extending such a self-interested bottom-up aggregation of equity might lead to a median 2100-warming of 2.3 °C. Tightening the warming goal of each country's effort-sharing approach to aspirational levels of 1.1 °C and 1.3 °C could achieve the 1.5 °C and well-below 2 °C-thresholds, respectively. This new hybrid allocation reconciles the bottom-up nature of the Paris Agreement with its top-down warming thresholds and provides a temperature metric to assess NDCs. When taken as benchmark by other countries, the NDCs of India, the EU, the USA and China lead to 2.6 °C, 3.2 °C, 4 °C and over 5.1 °C warmings, respectively.
Greenhouse Gas Concentration and Volcanic Eruptions Controlled the Variability of Terrestrial Carbon Uptake Over the Last Millennium
(AMER GEOPHYSICAL UNION, 2019-06-01)
The terrestrial net biome production (NBP) is considered as one of the major drivers of interannual variation in atmospheric CO2 levels. However, the determinants of variability in NBP under the background climate (i.e., preindustrial conditions) remain poorly understood, especially on decadal-to-centennial timescales. We analyzed 1,000-year simulations spanning 850-1,849 from the Community Earth System Model (CESM) and found that the variability in NBP and heterotrophic respiration (RH) were largely driven by fluctuations in the net primary production (NPP) and carbon turnover rates in response to climate variability. On interannual to multidecadal timescales, variability in NBP was dominated by variation in NPP, while variability in RH was driven by variation in turnover rates. However, on centennial timescales (100-1,000 years), the RH variability became more tightly coupled to that of NPP. The NBP variability on centennial timescales was low, due to the near cancellation of NPP and NPP-driven RH changes arising from climate internal variability and external forcings: preindustrial greenhouse gases, volcanic eruptions, land use changes, orbital change, and solar activity. Factorial experiments showed that globally on centennial timescales, the forcing of changes in greenhouse gas concentrations were the largest contributor (51%) to variations in both NPP and RH, followed by volcanic eruptions impacting NPP (25%) and RH (31%). Our analysis of the carbon-cycle suggests that geoengineering solutions by injection of stratospheric aerosols might be ineffective on longer timescales.
Palaeobiogeographical affinities and palaeoceanographical significance of late Cretaceous Ostracoda (Crustacea) from Voluta-1, Otway Basin, southeastern Australia
(Informa UK Limited, 2020-11-04)
A continental shelf to upper continental slope ostracod fauna is documented from the late Cretaceous (late Turonian to Santonian) Belfast Mudstone in Voluta-1 of the Otway Basin, southeastern Australia. The fauna has palaeobiogeographical affinities with mid-late Cretaceous ostracod faunas of Western Australia, New Zealand, the Antarctic Peninsula and the Falklands Plateau. This distribution pattern probably reflects dispersal influenced by the opening of the Australo-Antarctic Gulf, and by clockwise gyre currents in the proto Southern Ocean. The presence of Philoneptunus sp. in this fauna suggests that the Australo-Antarctic Gulf was an important locus for deep sea colonization by Gondwanan neritic ostracod clades.
Polar Climate Change as Manifest in Atmospheric Circulation
(SPRINGER HEIDELBERG, 2018-12-01)
Purpose of Review: Dynamic manifestations of climate change, i.e. those related to circulation, are less well understood than are thermodynamic, or temperature-related aspects. However, this knowledge gap is narrowing. We review recent progress in understanding the causes of observed changes in polar tropospheric and stratospheric circulation, and in interpreting climate model projections of their future changes. Recent Findings: Trends in the annular modes reflect the influences of multiple drivers. In the Northern Hemisphere, there appears to be a "tug-of-war" between the opposing effects of Arctic near-surface warming and tropical upper tropospheric warming, two predominant features of the atmospheric response to increasing greenhouse gases. Future trends in the Southern Hemisphere largely depend on the competing effects of stratospheric ozone recovery and increasing greenhouse gases. Summary: Human influence on the Antarctic circulation is detectable in the strengthening of the stratospheric polar vortex and the poleward shift of the tropospheric westerly winds. Observed Arctic circulation changes cannot be confidently separated from internal atmospheric variability.
Plio‐Pleistocene Indonesian Throughflow Variability Drove Eastern Indian Ocean Sea Surface Temperatures
(American Geophysical Union (AGU), 2020-10)
Ocean gateways facilitate circulation between ocean basins, thereby impacting global climate. The Indonesian Gateway transports water from the Pacific to the Indian Ocean via the Indonesian Throughflow (ITF) and drives the strength and intensity of the modern Leeuwin Current, which carries warm equatorial waters along the western coast of Australia to higher latitudes. Therefore, ITF dynamics are a vital component of global thermohaline circulation. Plio‐Pleistocene changes in ITF behavior and Leeuwin Current intensity remain poorly constrained due to a lack of sedimentary records from regions under its influence. Here, organic geochemical proxies are used to reconstruct sea surface temperatures on the northwest Australian shelf at IODP Site U1463, downstream of the ITF outlet and under the influence of the Leeuwin Current. Our records, based on TEX86 and the long‐chain diol index, provide insight into past ITF variability (3.5–1.5 Ma) and confirm that sea surface temperature exerted a control on Australian continental hydroclimate. A significant TEX86 cooling of ~5°C occurs within the mid‐Pliocene Warm Period (3.3–3.1 Ma) suggesting that this interval was characterized by SST fluctuations at Site U1463. A major feature of both the TEX86 and long‐chain diol index records is a strong cooling from ~1.7 to 1.5 Ma. We suggest that this event reflects a reduction in Leeuwin Current intensity due to a major step in ongoing ITF constriction, accompanied by a switch from South to North Pacific source waters entering the ITF inlet. Our new data suggest that an additional ITF constriction event may have occurred in the Pleistocene.
A Cenozoic Great Barrier Reef on Australia's North West shelf
The Great Barrier Reef of Australia is the largest modern coral reef system on Earth. However, a similar-sized barrier reef (~2000 km long) existed on Australia's north-western margin in the middle Miocene and to some extent, still exists today. Seismic profiles reveal that this reef system was first initiated in the late Paleogene (~34–28 Ma) and reached its zenith as a prograding barrier reef during the middle Miocene (16–15 Ma). This giant reef system backstepped in the late Miocene (~10 Ma), forming a series of isolated atolls and pinnacle reefs. These remaining reefs were gradually extinguished, leaving only a few surviving isolated atolls today (Rowley Shoals, Scott Reef, Seringapatam Reef and Ashmore Reef). The distribution of these extant reefs therefore outlines the former presence of the mid-Miocene Great Barrier Reef of the Australian North West Shelf. This middle Miocene shallow-water rimmed-reefal shelf grew contemporaneously on a deeper-water heterozoan ramp, producing an unusual mixed heterozoan/photozoan carbonate system for most of its length. The initiation of reef growth appears related to Australia's northward drift into lower latitudes, combined with warm mid-Miocene climatic optimum conditions. However, the sudden and simultaneous initiation of reef growth in the mid-Miocene across the North West Shelf was probably also related to changes in paleoceanography (increased aragonite saturation and/or nutrient-depletion) perhaps influenced by changing climatic conditions (increased aridity). From the late Miocene (~10 Ma) to Holocene, high rates of subsidence across the North West Shelf probably set the scene for ultimate demise of this giant barrier reef system and led to widespread backstepping with the development of a series of isolated atolls and pinnacle reefs. It is likely that other paleoceanographic and climatic events (like nutrient supply, carbonate saturation, eustasy etc) combined with continued high subsidence rates acted to gradually extinguish the reef system in a series of steps over a period of 10 million years. The onset (~1 Ma) of a strong Leeuwin Current (with the delivery of warm and nutrient depleted water from the north) and its effect on the Quaternary reefs of the Western Australian coast is a good example of a paleoceanographic process that would be difficult to recognize in an ancient setting. It is likely that similar paleoceanographic events have controlled the rich and complex history of reef growth and drowning since the mid-Miocene on the North West Shelf.
Denuding a Craton: Thermochronology Record of Phanerozoic Unroofing from the Pilbara Craton, Australia
(American Geophysical Union (AGU), 2020)
Cratons are ancient regions of relatively stable continental fragments considered to have attained long-term tectonic and geomorphic stability. Low-temperature thermochronology data, however, suggest that some cratons have experienced discrete Phanerozoic heating and cooling episodes. We report apatite fission track, and apatite and zircon (U-Th)/He low-temperature thermochronology data from the Archean Pilbara craton and adjacent Paleoproterozoic basement, NW Australia. Inverse thermal history simulations of this spatially extensive data set reveal that the region has experienced ~50–70°C cooling, which is interpreted as a response to the unroofing of erodible strata overlying basement. The timing of cooling onset is variable, mainly ~420–350 Ma in the southern and central Pilbara-eastern Hamersley Basin and ~350–300 Ma in the northern Pilbara, while the westernmost Pilbara-central Hamersley Basin does not record a significant Paleozoic cooling event. These differences are attributed to variations in sedimentary thickness and proximity to adjacent rift basins, which lack Archean age zircons in their Paleozoic strata. The onset of Paleozoic cooling coincides with the timing of the episodic intraplate late Ordovician-Carboniferous Alice Springs Orogeny. This orogeny is thought to have resulted from far-field plate margin stresses, which in turn caused the opening of the adjacent Canning Basin, to the north and east of the craton. We propose that basin development triggered a change of base level, resulting in denudation and the crustal cooling event reported here. Our results provide further evidence for the transmission of far-field forces to cratons over hundreds of kilometers and support the view that cratons have experienced geomorphic changes during the Phanerozoic.