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Crystal and magnetic structure of (1− x) BiFeO3–xSrTiO3 (x= 0.2, 0.3, 0.4 and 0.8)
No full textThe effect of doping SrTiO3 into BiFeO3 on the magnetic and crystal structure has been explored using powder neutron diffraction for where x=0.2, 0.3, 0.4, 0.6 and 0.8. While the data are not sensitive to the cycloidal component of the magnetic ordering, the evolution of the collinear antiferromagnetic moment of the G-type antiferromagnetic component with T and x has been explored, as have structural parameters. It is found that for pure phase samples form in the R3c cell, and for x=0.8 a non-magnetic phase is obtained. The x=0.6 sample gives a mixed phase. Through the R3c phase the magnetic structure does not change appreciably apart from the reduction of magnetic moment magnitude with the increasing T and/or x. © 2013 Elsevier Inc
Comparison of in-situ water vapour isotope analysers
No full textRecently there have been a number of spectroscopic based in-situ water vapour isotope analysers developed. These analysers are capable of providing datasets that are useful for a range studies including interpreting rapid fluctuations associated with land atmosphere exchange processes, and validation of process based models that work on different spatial and temporal scales. Here we present a comparison of three spectroscopic analysers that provide in-situ analysis of water vapour isotopes. These include a Fourier Transform InfraRed (FTIR) spectroscopy based system (broad band technique), a system based on Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS), and a Wavelength-Scanned Cavity Ring-Down Spectroscopy (WS-CRDS) system. Using a continuous flow calibration system, liquid isotopic standards were vaporised and used to determine the response of the three analysers to changes isotopic composition and the water vapour mixing ratio. Based on these experiments it was shown that all three analysers required significant corrections to move the raw data onto the Standard Mean Ocean Water (SMOW) scale. We then deployed the three analysers at a coastal location near Sydney, Australia where diurnal temperature variations are relatively small and high mixing ratios are generally observed. The WS-CRDS and OA-ICOS were then deployed in central NSW, Australia where large diurnal temperature variations and relatively low mixing ratios were observed. The in-situ isotope data collected from the three analysers is then compared between these two locations
Sydney particle study: overview and motivations
No full textStudies of health impacts from atmospheric pollutants suggest that particles are currently one of the most significant pollutants with respect to human mortality and morbidity. However, reduction in particle concentrations through source regulation is challenging due to the large number particle sources (both natural and anthropogenic) present in an airshed, and the wide range of particle sizes and chemical species emitted. Additionally, secondary particles can also make a significant contribution to total particle exposure, particularly in the fine size fraction which is considered to have the largest impact on health. Being generated through photochemical processes (similar to ozone), a reduction in the concentration of secondary particles requires that source regulators also consider the relevant gas-phase precursors to these particles. Climate change projections for NSW suggest significant increases in the frequency of drought, increases in the frequency of hot days and increases in the frequency of high fire risk weather. This has important ramifications for air pollution and health, with atmospheric particle smog severity linked to the frequency of hot, sunny days, and with the highest particle pollution concentrations linked to the presence of bushfire plumes in the Sydney airshed. Particles and ozone are also coupled, with enhanced ozone concentrations often observed on bushfire days and with 50% or greater of fine particle mass potentially of photochemical origin. The development of a long term control strategy for particles in Sydney can be informed through the use of comprehensive three-dimensional simulations of the atmosphere, sources and multi-phase phase chemistry. However the development of such modelling capability requires a good understanding of the contribution made by local and remote particles sources to the total particle exposure within the region. Such understanding requires detailed and high quality data sets. We present here an overview of the Sydney Particle Study, a combined modelling and observation project which included an intensive field campaign of aerosol and aerosol precursor measurements carried out in Sydney during February 2011. We focus our discussion on the field campaign which combined sophisticated measurement techniques to produce a high quality data set of atmospheric composition observations. The campaign was a collaboration 43between CSIRO Marine and Atmospheric Research, NSW Office of Environment and Heritage, Queensland University of Technology and ANSTO. Data collected included criteria pollutant concentrations, aerosol microphysical properties, aerosol chemical composition (as a function of size, integrated over 4 hours and in real time), concentration of volatile organic compounds (integrated over 4 hours and in real time) and radon concentrations. Continuous aerosol size distributions indicated the occurrence of secondary aerosol formation occurring in the afternoons on approximately 50% of the days sampled. Data analysis continues in order to understand the processes driving this secondary formation. © 2011 CSIRO and the Bureau of Meteorology
Characterization of insoluble nanoparticles in Antarctic ice cores
No full textInsoluble nanoparticles in the form of aerosols have significant effects on climate and biogeochemical cycles. Records of these aerosols are essential for understanding paleoclimate forcing and future climate change. These particles and their precursors are emitted to the atmosphere from a variety of primary and secondary sources including biomass burning as well as biogenic, anthropogenic, volcanic, extraterrestrial, and terrestrial mineral emissions. While a large body of research exists with respect to mineral dust particles (on the micrometer scale) derived from ice and sediment cores, very little is known with regards to the history of insoluble particles on the nano scale. Ice core records are the only reliable way to study the past history of these particles. Here, we will present new data regarding the physical and chemical properties of nanoparticles found in ice cores from East Antarctica
26Al/10Be dating of an aeolian dust mantle soil in western New South Wales, Australia
No full textAeolian dust mantle soils are an important element of many landscapes in south-eastern Australia, though the age of these aeolian deposits has not been radiometrically determined. At Fowlers Gap in western New South Wales, surface cobbles of silcrete and quartz overlie a stone-free, aeolian dust mantle soil, which has a thickness of about 1.6m. The clay-rich aeolian dust deposit in turn lies upon a buried silcrete and quartz stone layer. Modelling in-situ cosmogenic 26Al and 10Be concentrations measured in both the surface quartz stones and in the buried quartz layer of rocks, reveals that each has experienced a complex exposure-burial history. Due to the absence of quartz stones or sand at intermediate depths, our cosmogenic 26Al and 10Be modelling was not able to determine a definitive mechanism of stone pavement formation and stone burial. Various scenarios of stone formation, transport, burial and exhumation were tested that constrain the age of the deposit to range from 0.9±0.2Ma to 1.8±0.2Ma, based largely on different assumptions taken for the time-dependency of the net sedimentation rate. This corresponds with the initiation of the Simpson Desert dune fields and the deflation of lakes in central Australia, which probably responded to the shift to longer-wavelength, larger-amplitude Quaternary glacial cycles at around 1Ma. Sensitivity analyses were carried out to identify those parameters which better constrained model outputs. Within model errors, which largely are the result of analytical errors in measured 26Al and 10Be concentrations, all three competing theories of colluvial wash, upward displacement of stones, and cumulic pedogenesis are possible mechanisms for the formation of the surface stone pavement. © 2020 Elsevier B.
Atmospheric carbondisulfide and dimethylsulfide measurements at Cape Grim Australia, Marine, Terrestrial and Anthropogenic Contributions
No full textHosted by CSIRO Marine and Atmospheric Researc
Drip hydrology monitoring in caves to inform stalagmite palaeoclimate records, Yarrangobilly, NSW.
No full textPalaeoclimate research using speleothems has significantly increased over the last decade, owing to their potential to provide multi-proxy high resolution (sub-annual) terrestrial records of past climate variability. A crucial step in using these archives as high resolution proxies is understanding the
connectivity between the surface climate and the signal transferred to the speleothem. This study investigates the modern karst hydrology at Yarrangobilly Caves, in the Snowy Mountains NSW. A
high-frequency, spatially-dense drip water monitoring campaign in Harrie Wood Cave, was conducted over a 13 month period to characterise the hydrology of 14 sites within the same cave. By utilising the
cave as a natural observatory we can determine 1) vadose-zone flow regimes, and 2) thresholds of
recharge at the site. Using a statistical approach (PCA and AHC) 5 main drip hydrological regimes
were established. Depth was found to have a moderate relationship (r2 = 0.4) with discharge, whereby increasing depth was associated with a dampening of flow and drip response. However,
depth could not account for all the variability observed in the drip hydrology, suggesting complex
controls unrelated to depth, such as unsaturated zone storage and mixing, appear to have a significant impact on vadose-zone flow regimes. As a speleothem is a function of the infiltrating drip
water, we suggest that stalagmites fed by different drip types may thus contain different parts of the climate record i.e. smoothed mean annual vs. an extreme event record. These findings will be used to
assess three suitable stalagmites for palaeoclimate reconstruction, fed by drip waters with different hydrological regimes and the preliminary results presented here. © Australasian Quaternary Association Inc
Trace elements: from sources to cave drip water, south-eastern Australia
No full textSpeleothem trace element time series are constructed from the infiltrating drip water geochemistry,
and hence are examined under contrasting rainfall conditions associated with El Niño and La Niña
phases of ENSO. The aim was to identify suitable inorganic element proxies for palaeoclimate
interpretation in speleothem records from Harrie Wood Cave, Yarrangobilly. The drip water chemical
composition at the stalactite tip reflects a contribution from different endmembers and processes;
therefore it is necessary to study the different sources, pathways and processes that occur as water
migrates through the atmosphere-soil-karst system. Here we present high resolution aerosol, rainfall
and drip water 18O and inorganic drip-water datasets. Analysis of aerosol samples above the caves
reveals the atmosphere supplies a suite of elements from automobile emissions, windblown soil,
smoke, secondary sulfate and aged sea salt sources. The bedrock and aerosols were identified as
contributory sources of solutes to the drip water. The clay-rich soil zone was recognised as a sink for
inorganic elements, and a secondary source for Zn. In soil, a number of processes were
demonstrated to modify the chemical composition of the resultant drip waters. The drip water
chemistry is driven by the long-term gradient in the cumulative water balance. The flow paths
feeding the drip sites were shown to be fracture flow, from a ventilated well-mixed pocket within
the epikarst storage reservoir. Dilution and reduced prior calcite precipitation (PCP) controlled the
drip-water chemistry during the La Niña/wet years whereas enhanced PCP was observed during the
El Niño and dry periods. Mg and Sr show particular promise as paleoclimate proxies for drought and
flood events, while with further research Na, K and Zn may also be reliably used. These findings will
be applied in a modern speleothem record. © Author(s