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Origin of high ammonium, arsenic and boron concentrations in the proximity of a mine: Natural vs. anthropogenic processes
No full textHigh ammonium (NH4), arsenic (As) and boron (B) concentrations are found in aquifers worldwide and are often related to human activities. However, natural processes can also lead to groundwater quality problems. High NH4, As and B concentrations have been identified in the confined, deep portion of the Niebla-Posadas aquifer, which is near the Cobre Las Cruces (CLC) mining complex. The mine has implemented a Drainage and Reinjection System comprising two rings of wells around the open pit mine, were the internal ring drains and the external ring is used for water reinjection into the aquifer. Differentiating geogenic and anthropogenic sources and processes is therefore crucial to ensuring good management of groundwater in this sensitive area where groundwater is extensively used for agriculture, industry, mining and human supply. No NH4, As and B are found in the recharge area, but their concentrations increase with depth, salinity and residence time of water in the aquifer. The increased salinity down-flow is interpreted as the result of natural mixing between infiltrated meteoric water and the remains of connate waters (up to 8%) trapped within the pores.
Ammonium and boron are interpreted as the result of marine solid organic matter degradation by the sulfate dissolved in the recharge water. The light δ15NNH4 values confirm that its origin is linked to marine organic matter.
High arsenic concentrations in groundwater are interpreted as being derived from reductive dissolution of As-bearing goethite by dissolved organic matter. The lack of correlation between dissolved Fe and As is explained by the massive precipitation of siderite, which is abundantly found in the mineralization. Therefore, the presence of high arsenic, ammonium and boron concentrations is attributed to natural processes. Ammonium, arsenic, boron and salinity define three zones of groundwater quality: the first zone is close to the recharge area and contains water of sufficient quality for human drinking; the second zone is downflow and contains groundwater suitable for continuous irrigation but not drinkable due to high ammonium concentrations; and the third zone contains groundwater of elevated salinity (up to 5940 μS cm− 1) and is not useable due to high ammonium, arsenic and boron concentrations. © 2015, Elsevier B.V
Investigation of the structure-property relationships in defect perovskite lithium ion conductors
No full textThe work presented in this PhD thesis explores the lithium mobility and lithium insertion behaviour of the defect perovskite material Li0.18Sr0.66Ti0.5Nb0.5O3.
The first part of the thesis focuses on the ex-situ characterisation of the structure before and after lithium insertion. Specifically, the lithium position within the structure was found to be dependent on thermal history, temperature, lithium content and the method by which lithium is inserted into the structure. This information was used to identify the position and nature of diffusion bottlenecks and determine that up to two lithium ions can fit per vacant site and lead to explorations of the deep discharge behaviour. Although a two phase reaction was predicted during deep discharge, a single phase was observed ex-situ.
The second part aimed to augment the ex-situ results with in-situ information. An in-situ electrochemical cell was designed for the powder diffraction beamline at the Australian Synchrotron enabling the real-time changes in the unit cell to be tracked during cycling. The influence of reduced lithium mobility within the structure was observed through the changing rate of unit cell expansion and the appearance of two phases below 1 V. Further, the presence of octahedral rotations was found to modulate the rate of unit cell expansion once the lithium content exceeds 0.16 lithium ions per formula unit.
The final chapter involves the design of a modified in-situ neutron diffraction cell for POLARIS at ISIS. Using data collected from this cell, the lithium position within the oxygen window after structural relaxation was confirmed and the response of oxygen ADPs to the insertion of lithium were able to be tracked during discharge. Finally, by reducing the particle size the limited lithium diffusion at high lithium contents, which resulted in the formation of two phases below 1 V, was overcome resulting in improved electrochemical performance
Single crystal and magnetic structures of maricite-type AgMnVO4
No full textSingle crystals of the ternary manganese vanadate AgMnVO4, were grown using AgVO3 flux. The structure was determined from single crystal X-ray diffraction data. The magnetic structure and properties of AgMnVO4 were characterized by magnetic susceptibility, specific heat, and low-temperature neutron powder diffraction measurements. AgMnVO4 crystallizes in the maricite-type structure with space group Pnma, a=9.5393(12), b=6.8132(9), c=5.3315(7) Å and Z=4. AgMnVO4 contains MnO4 chains made up of edge-sharing MnO6 octahedra, and these chains are interlinked by the VO4 and AgO4 tetrahedra. The specific heat measurements indicate a 3D-antiferromagnetic ordering at ~12.1 K and the neutron powder diffraction measurements at 5 K show that the Mn2+magnetic moments are antiferromagnetically coupled within the chains which are antiferromagnetically coupled to each other. © 2014, Elsevier Inc
Equatorial pacific coral ceochemical records show recent weakening of the Walker Circulation
No full textEquatorial Pacific ocean-atmosphere interactions affect climate globally, and a key component of the coupled system is the Walker Circulation, which is driven by sea surface temperature (SST) gradients across the equatorial Pacific. There is conflicting evidence as to whether the SST gradient and Walker Circulation have strengthened or weakened over the late twentieth century. We present new records of SST and sea surface salinity (SSS) spanning 1959–2010 based on paired measurements of Sr/Ca and δ18O in a massive Porites coral from Butaritari atoll in the Gilbert Islands, Republic of Kiribati, in the central western equatorial Pacific. The records show 2–7 year variability correlated with the El Niño–Southern Oscillation (ENSO) and corresponding shifts in the extent of the Indo-Pacific Warm Pool, and decadal-scale signals related to the Pacific Decadal Oscillation and the Pacific Warm Pool Index. In addition, the Butaritari coral records reveal a small but significant increase in SST (0.39°C) from 1959 to 2010 with no accompanying change in SSS, a trend that persists even when ENSO variability is removed. In contrast, larger increases in SST and SSS are evident in coral records from the equatorial Pacific Line Islands, located east of Butaritari. Taken together, the equatorial Pacific coral records suggest an overall reduction in the east-west SST and SSS gradient over the last several decades, and a recent weakening of the Walker Circulation.© 2014, American Geophysical Union
The comprehensive Australian Tsunami database – just when you thought it was safe to go back in the water
No full textThis new database incorporates peer-reviewed publications, critical reviews and searchable web-based datasets and
as such represents a complete re-organisation and restructuring of previous work. These new data take the number
of events from 57 (including two “erroneous events”) to 145. Several significant errors have been corrected, not the
least of which are mistaken run-up heights for the 19 August 1977 Sumba Island, Indonesia event that suggested it
was the largest historical tsunami in Australia’s history. This honour now goes to the 17 July 2006, Java, Indonesia
tsunami that had a run-up height of 7.90 m at Steep Point, Western Australia. Although estimated wave heights of
40 feet (~13 m) were noted for the 8 April 1911 event at Warrnambool, Victoria, no run-up data were provided and
so its full effects remain uncertain. One of the more interesting findings has been the occurrence of at least 11
deaths, albeit for events that are generally poorly defined.
Data gathered during the construction of this database were rigorously reviewed and as such several previous
paleotsunami entries have been removed and other potentially new ones discarded. The reasons for inclusion or
exclusion of data are discussed and it is acknowledged that while there has been an almost three-fold increase in the
number of entries, the database is still incomplete. With this in mind the database architecture has been brought in
line with others in the region with the ultimate goal of merging them all in order to provide a better understanding
of the national and regional tsunami hazard (and risk) and to move towards an open source Australasian database
Use of Accelerator Mass Spectrometry (AMS) to study the migration and bioaccumulation of actinides in the environment
Get PDFThe high sensitivity of AMS for actinides analysis can facilitate a range of studies aimed at
improving understanding of how actinides behave in the environment. Former nuclear sites,
which contain a range of levels of contamination with actinides, offer opportunities to study
the migration and bioaccumulation of actinides. In addition to the evaluation of the
radiological risk posed to potential human and non-human occupants of those specific sites,
such studies can contribute fundamental data to the understanding of the behaviour of
actinides in the environment.
The Little Forest Burial Ground, located on the edge of Sydney, was used by the Australian
Atomic Energy Commission to dispose of low level radioactive waste in shallow trenches in
the 1960s. The waste included small amounts of uranium and plutonium with various
isotopic compositions. α-spectrometry is being used as the primary method of radio-analysis
in current studies of this site [1]. In addition, AMS is being applied where higher sensitivity
is required, and to measure isotopes not easily measureable by α-spectrometry. 239Pu and
240Pu cannot be resolved by α-spectrometry, and 233U is poorly resolved from 234U. In both
cases we can apply AMS to define these isotopic signatures. In the case of plutonium, the
240Pu/239Pu ratio can be used to distinguish local contamination sources from global fallout.
The high sensitivity of AMS has enabled the detection of Pu and 233U in vegetation, providing
data on uptake and bioaccumulation.
The former nuclear weapons test site at Maralinga in South Australia was used in the 1950s and 1960s for seven nuclear weapon detonations and also numerous ‘safety trials’ which dispersed plutonium and uranium in the environment. By analysing plutonium in wildlife and
soil samples from around this site, we are able to evaluate the uptake of plutonium and its
mobility, and compare present-day results with earlier studies of the site [2]. Further work is
in progress examining the distribution of plutonium in the tissues of mammals and other
species inhabiting the site. By exploiting the high sensitivity of AMS, non-lethal methods for investigating actinide uptake and its effects on wildlife are being developed for this work
Low atmospheric CO2 levels during the Little Ice Age due to cooling-induced terrestrial uptake
No full textLow atmospheric carbon dioxide (CO2) concentration1 during the Little Ice Age has been used to derive the global carbon cycle sensitivity to temperature2. Recent evidence3 confirms earlier indications4 that the low CO2 was caused by increased terrestrial carbon storage. It remains unknown whether the terrestrial biosphere responded to temperature variations, or there was vegetation re-growth on abandoned farmland5. Here we present a global numerical simulation of atmospheric carbonyl sulfide concentrations in the pre-industrial period. Carbonyl sulfide concentration is linked to changes in gross primary production6 and shows a positive anomaly7 during the Little Ice Age. We show that a decrease in gross primary production and a larger decrease in ecosystem respiration is the most likely explanation for the decrease in atmospheric CO2 and increase in atmospheric carbonyl sulfide concentrations. Therefore, temperature change, not vegetation re-growth, was the main cause of the increased terrestrial carbon storage. We address the inconsistency between ice-core CO2 records from different sites8 measuring CO2 and δ13CO2 in ice from Dronning Maud Land (Antarctica). Our interpretation allows us to derive the temperature sensitivity of pre-industrial CO2 fluxes for the terrestrial biosphere (γL = −10 to −90 Pg C K−1), implying a positive climate feedback and providing a benchmark to reduce model uncertainties. © 2016, Nature Publishing Group
Ice core measurements of 14CH4 show no evidence of methane release to atmosphere from methane hydrates during a large warming event 11,600 years ago
No full textMarine methane hydrate destabilization has been proposed as a potentially large source of methane to the atmosphere in response to both past and future warming. We present new measurements of 14C of paleoatmospheric methane (CH4) over the Younger Dryas Preboreal (YD PB) abrupt warming event (11,600 years ago) from ancient ice outcropping at Taylor Glacier, Antarctica. The YD PB abrupt warming was centered in the North Atlantic, occurred partway through the global warming of last deglaciation and was associated with a 50% increase in atmospheric CH4 concentrations. 14C can unambiguously identify CH4 emissions from old carbon sources, such as CH4 hydrates. All samples from before, during and after the abrupt warming and associated CH4 increase yielded 14CH4 values that are consistent with 14C of atmospheric CO2 at that time, indicating a purely contemporaneous methane source. Our results show that neither the abrupt regional warming nor the gradual global warming that preceded it resulted in detectable CH4 release to the atmosphere from CH4 hydrates during the YD PB transition. Our results are thus consistent with the hypothesis that the vast majority of CH4 that is released from dissociating hydrates or other old-carbon seafloor CH4 sources is oxidized prior to reaching the atmosphere. © American Geophysical Unio
Modern and possible paleotsunami deposits in Samenoura, Sanriku Coast, and their relation to tsunami source mechanisms
Get PDFSamenoura is situated in the bay head of a small inlet on the Pacific coast of Oshika Peninsula, one of the nearest places to the epicenter of the 2011 Tohoku-oki Earthquake. According to the Joint Survey Group, wave heights were measured at more than 20 m near the coastline. This area was severely damaged as a result of both co-seismic subsidence and tsunami inundation. We carried out field surveys of the Tohoku-oki and paleotsunami deposits at Samenoura in March, May and October 2013. Sandy deposits laid down by the Tohoku-oki tsunami were up to 20 cm thick at locations with an elevation greater than 10 m, and were several cm thick within the forest higher up. The tsunami deposit also contained numerous shell fragments and foraminifera. Although some possible sources of the tsunami deposits can be attributed to narrow sandy beaches near the study area, the deposition of such a thick sandy deposit is more or less enigmatic, considering the steep Ria-type coastal topography.Using a gouge auger and geoslicer, we found at least two sand layers intercalated within muddy sediments. A volcanic ash layer, which corresponds to the AD 915 Towada-a tephra, was also identified from a horizon between these sand layers. The underlying sand layer was most probably laid down by the 869 Jogan earthquake tsunami, one of the large-scale events known to have affected the region. Previous studies of the Jogan tsunami have proposed several possible source models that involve an interplate thrust earthquake. Given that the local bathymetry and topography of Samenoura Bay may be sensitive to the waveform of a large-scale tsunami, paleotsunami deposits found from this area may be the key to determining the source mechanisms of events on the Sanriku Coast.In this presentation, the possible correlation of the sandy deposits with known paleotsunami events based on detailed radiocarbon dating is discussed. The hydrodynamic character and processes of tsunami sediment erosion and deposition in Samenoura Bay are analyzed using numerical modeling of both interplate and outer-rise earthquake scenarios.Copyright on Japan Geoscience Union Meeting, 2014
The search for geologic evidence of distant-source tsunamis using new field data in California
Get PDFA statewide assessment for geological evidence of tsunamis, primarily from distant-source events, found tsunami deposits at several locations, though evidence was absent at most locations evaluated. Several historical distant-source tsunamis, including the 1946 Aleutian, 1960 Chile, and 1964 Alaska events, caused inundation along portions of the northern and central California coast. Recent numerical tsunami modeling results identify the eastern Aleutian Islands subduction zone as the “worstcase” distant-source region, with the potential for causing tsunami runups of 7–10 m in northern and central California and 3–4 m in southern California. These model results, along with a review of historical topographic maps and past geotechnical evaluations, guided site selection for tsunami deposit surveys. A reconnaissance of 20 coastal marshlands was performed through site visits and coring of shallow surface sediments to determine if evidence for past tsunamis existed. Although conclusive evidence of tsunami deposits was not found at most of the sites evaluated, geologic evidence consistent with tsunami inundation was found at two locations: Three marshes in the Crescent City area and Pillar Point marsh near Half Moon Bay. Potential tsunami deposits were also evaluated at the Carpinteria Salt Marsh Reserve in Santa Barbara County. In Crescent City, deposits were ascribed to tsunamis on the basis of stratigraphic architecture, particle size, and microfossil content, and they were further assigned to the 1964 Alaska and 1700 Cascadia tsunamis on the basis of dating by cesium-137 and radiocarbon methods, respectively. The 1946 tsunami sand deposit was clearly identified throughout Pillar Point marsh, and one to two other similar but highly discontinuous sand layers were present within 0.5 m of the surface. A tsunami-origin interpretation for sand layers at Carpinteria is merely consistent with graded bedding and unsupported by diatom or foraminiferal assemblages. Additional studies, including age dating, grain-size, and microfossil analyses are underway for the deposits at Crescent City, Pillar Point marsh, and Carpinteria, which may help further identify if other tsunami deposits exist at those sites. The absence of evidence for tsunamis at other sites examined should not preclude further work beyond the reconnaissance-level investigations at those locations