Abstract Large Igneous Provinces (LIPs) are associated with global warming and carbon cycle perturbations during Oceanic Anoxic Event 2 (OAE2, ~94 Ma) and the Mid-Cenomanian Event (MCE, ~96.5 Ma). ...However, there is still no consensus on the role volcanism played as a trigger, or its source – previously ascribed to the Caribbean LIP or High Arctic LIP. Here, we use Mentelle Basin sedimentary mercury (Hg) concentrations to determine the timing of volcanism, and neodymium (Nd) and strontium (Sr) isotopes for sedimentary provenance. High Hg concentrations compared to Northern Hemisphere records, and a shift to radiogenic Nd isotopes, indicates Kerguelen LIP volcanic activity and plateau uplift occurred in the lead up to and within OAE2. Whilst we find limited evidence that a volcanic event caused the MCE, pulsed Hg spikes before and during OAE2 imply volcanic emissions were key in driving climate and carbon cycle changes and triggering OAE2.
ABSTRACT We present broadband observations and spectral modeling of PKS B0008-421 and identify it as an extreme gigahertz-peaked spectrum (GPS) source. PKS B0008-421 is characterized by the steepest ...known spectral slope below the turnover, close to the theoretical limit of synchrotron self-absorption, and the smallest known spectral width of any GPS source. Spectral coverage of the source spans from 0.118 to 22 GHz, which includes data from the Murchison Widefield Array and the wide bandpass receivers on the Australia Telescope Compact Array. We have implemented a Bayesian inference model fitting routine to fit the data with internal free-free absorption (FFA), single- and double-component FFA in an external homogeneous medium, FFA in an external inhomogeneous medium, or single- and double-component synchrotron self-absorption models, all with and without a high-frequency exponential break. We find that without the inclusion of a high-frequency break these models cannot accurately fit the data, with significant deviations above and below the peak in the radio spectrum. The addition of a high-frequency break provides acceptable spectral fits for the inhomogeneous FFA and double-component synchrotron self-absorption models, with the inhomogeneous FFA model statistically favored. The requirement of a high-frequency spectral break implies that the source has ceased injecting fresh particles. Additional support for the inhomogeneous FFA model as being responsible for the turnover in the spectrum is given by the consistency between the physical parameters derived from the model fit and the implications of the exponential spectral break, such as the necessity of the source being surrounded by a dense ambient medium to maintain the peak frequency near the gigahertz region. This implies that PKS B0008-421 should display an internal H i column density greater than 1020 cm−2. The discovery of PKS B0008-421 suggests that the next generation of low radio frequency surveys could reveal a large population of GPS sources that have ceased activity, and that a portion of the ultra-steep-spectrum source population could be composed of these GPS sources in a relic phase.
•BC sorbs hydrophobic organic compounds extremely strongly in soil.•Sorption of organic contaminants to BC reduces toxicity and biodegradability in soil.•BC has a significant impact on the ...bioavailability and bioaccessibility of contaminants to soil biota.•The application of BC to soil may reduce the risk associated with organic contaminants.
The ability of carbonaceous geosorbents (CGs) such as black carbon (BC) to extensively sorb many common environmental contaminants suggests that they potentially possesses qualities useful to the sequestration of harmful xenobiotics within contaminated land. Presently, however, there is limited understanding of the implications for the bioaccessibility, mobility and environmental risk of organic contaminants while sorbed to BC in soil and sediment, in addition to the inherent toxicity of BC itself to terrestrial flora and fauna. We review both the processes involved in and factors influencing BC sorption characteristics, and ultimately consider the impacts BC will have for bioavailability/bioaccessibility, toxicity and risk assessment/remediation of contaminated land. We conclude that while the application of BC is promising, additional work on both their toxicity effects and long-term stability is required before their full potential as a remediation agent can be safely exploited.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•The fate and behaviour of contaminants in soil are key to their risk assessment and remediation.•No single chemical assay can determine the bioavailability/accessibility of contaminants in ...soil.•Determination of bioaccessibility will improve the risk assessment of contaminated land.
Risk assessment and remediation of contaminated land is inherently dependent on the contaminants present and their availability for interaction with soil biota. An ever-growing body of evidence suggests that current regulatory procedures over-estimate the ‘true’ fraction available to biota. Thus, a procedure that predicts the ‘bioavailable fraction’ would be useful for predicting ‘actual’ exposure limits and provide a more relevant basis for risk assessment. The aim of this paper is to address several important questions: “How should bioavailability be defined?” “What factors affect bioavailability measurement?” “To what extent have existing protocols measured bioavailability?” “What is actually measured by chemical techniques purported to determine bioavailability?” We offer two definitions (namely ‘bioavailability’ and ‘bioaccessibility’) and review commonly employed chemical extraction techniques to measure putative bioavailability. Relative advantages and disadvantages of the techniques are highlighted to elucidate underlying factors for the wide range of conclusions observed in the literature. Although the concept of bioavailability is implicit to contaminated land risk assessment and remediation, explicit reference to and use of adjustment factors is rare amongst regulatory bodies and remediators. Use of chemical determinants for bioavailability, applicable within current legislation and due consideration to inherent variability, are proposed and barriers to their implementation discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
As the global population is expected to reach 9 billion by 2050, humanity needs to balance an ever increasing demand for food, energy and natural resources, with sustainable management of ecosystems ...and the vital services that they provide. The intensification of agriculture, including the use of fertilisers from finite sources, has resulted in extensive soil degradation, which has increased food production costs and CO2 emissions, threatening food security. The Bioenergy sector has significant potential to contribute to the formation of a circular economy. This paper presents the scientific, regulatory and socioeconomic barriers to the use of the nutrient waste streams from biomass thermal conversion (ash) and anaerobic digestion (digestate) as sustainable soil amendments for use in place of traditional fertilisers. It is argued that whilst the ability of combined ash and digestate to remedy many threats to ecosystems and provide a market to incentivise the renewable bio-energy schemes is promising, a step-change is required to alter perceptions of ‘waste’, from an expensive problem, to a product with environmental and economic value. This can only be achieved by well-informed interactions between scientists, regulators and end users, to improve the spread and speed of innovation with this sector.
•Demands for food and energy need meeting with sustainably managed ecosystems.•By-products from bioenergy have the potential to contribute to a circular economy.•Legislation prevents the use of bioenergy by-products to their maximum potential.•Perceptions of these by-products need changing from problems to products with value.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The exceptional sorptive ability of carbon nanomaterials (CNMs) for hydrophobic organic contaminants (HOCs) is driven by their characteristically large reactive surface areas and highly hydrophobic ...nature. Given these properties, it is possible for CNMs to impact on the persistence, mobility and bioavailability of contaminants within soils, either favourably through sorption and sequestration, hence reducing their bioavailability, or unfavourably through increasing contaminant dispersal. This review considers the complex and dynamic nature of both soil and CNM physicochemical properties to determine their fate and behaviour, together with their interaction with contaminants and the soil microflora. It is argued that assessment of CNMs within soil should be conducted on a case-by-case basis and further work to assess the long-term stability and toxicity of sorbed contaminants, as well as the toxicity of CNMs themselves, is required before their sorptive abilities can be applied to remedy environmental issues.
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