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Journal articleKumar P, Zavala-Reyes JC, Kalaiarasan G, et al., 2023,
Characteristics of fine and ultrafine aerosols in the London underground.
, Science of the Total Environment, Vol: 858, ISSN: 0048-9697Underground railway systems are recognised spaces of increased personal pollution exposure. We studied the number-size distribution and physico-chemical characteristics of ultrafine (PM0.1), fine (PM0.1-2.5) and coarse (PM2.5-10) particles collected on a London underground platform. Particle number concentrations gradually increased throughout the day, with a maximum concentration between 18:00 h and 21:00 h (local time). There was a maximum decrease in mass for the PM2.5, PM2.5-10 and black carbon of 3.9, 4.5 and ~ 21-times, respectively, between operable (OpHrs) and non-operable (N-OpHrs) hours. Average PM10 (52 μg m-3) and PM2.5 (34 μg m-3) concentrations over the full data showed levels above the World Health Organization Air Quality Guidelines. Respiratory deposition doses of particle number and mass concentrations were calculated and found to be two- and four-times higher during OpHrs compared with N-OpHrs, reflecting events such as train arrival/departure during OpHrs. Organic compounds were composed of aromatic hydrocarbons and polycyclic aromatic hydrocarbons (PAHs) which are known to be harmful to health. Specific ratios of PAHs were identified for underground transport that may reflect an interaction between PAHs and fine particles. Scanning transmission electron microscopy (STEM) chemical maps of fine and ultrafine fractions show they are composed of Fe and O in the form of magnetite and nanosized mixtures of metals including Cr, Al, Ni and Mn. These findings, and the low air change rate (0.17 to 0.46 h-1), highlight the need to improve the ventilation conditions.
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Journal articleRoyle SHH, Cropper L, Watson JSS, et al., 2023,
Solid-Phase Microextraction for Organic Contamination Control Throughout Assembly and Operational Phases of Space Missions
, ASTROBIOLOGY, Vol: 23, Pages: 127-143, ISSN: 1531-1074 -
Journal articleSalter TL, Watson J, Waite JH, et al., 2022,
Hydrothermal processing of microorganisms: Mass spectral signals of degraded biosignatures for life detection on icy moons
, ACS Earth and Space Chemistry, Vol: 6, Pages: 2508-2518, ISSN: 2472-3452Life detection missions to the outer solar system are concentrating on the icy moons of Jupiter and Saturn and their inferred sub-surface oceans. Access to evidence of habitability, and possibly even life, is facilitated by the ejection of subsurface material in plumes and outgassing fissures. Orbiting spacecraft can intersect the plume material or detect past sputtered remnants of outgassed products and analyse the contents using instruments such as mass spectrometers. Hydrothermalism has been proposed for the subsurface environments of icy moons and the organic remains of any associated life would be expected to suffer some degradation through hydrothermalism, radiolysis, or spacecraft flyby impact fragmentation. Hydrothermalism is treated here for the first time in the context of the Europa Clipper mission.To assess the influence of hydrothermalism on the ability of orbiting mass spectrometers to detect degrading signals of life, we have subjected Earth microorganisms to laboratory hydrothermal processing. The processed microorganism samples were then analysed using gas chromatography-mass spectrometry (GC-MS) and mass spectra were generated. Certain compound classes, such as carbohydrates and proteins are significantly altered by hydrothermal processing, resulting in small one-ring and two-ring aromatic compounds such as indoles and phenols. However, lipid fragments, such as fatty acids, retain their fidelity and their provenance is easily recognised as biological in origin. Our data indicate that mass spectrometry measurements in the plumes of icy moons, using instruments such as the MAss Spectrometer for Planetary Exploration (MASPEX) onboard the upcoming Europa Clipper mission, can reveal the presence of life even after significant degradation by hydrothermal processing has taken place.
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Journal articlePeers De Nieuwburgh C, Watson J, Weiss D, et al., 2022,
Environmental screening of water associated with shale gas extraction by fluorescence excitation emission matrix
, Environmental Science: Water Research & Technology, Vol: 8, Pages: 2196-2206, ISSN: 2053-1400The shale revolution has involved the production of oil and gas from shale reservoirs enabled by modern techniques such as horizontal drilling and hydraulic fracturing. Large volumes of water-based fluids are required for hydraulic fracturing, some of which return to the surface as produced water. The recycling and effective disposal of produced water reduces water demand and avoids environmental impacts, respectively. Yet risks of water quality degradation surrounding shale oil and gas extraction operations remain highest during produced water treatment and disposal. Risk assessments related to produced water use are difficult to generate due to a lack of standard monitoring methods to characterise produced water and a lack of baseline monitoring data of surrounding water resources. We have performed a study on laboratory shale leachates using fluorescence Excitation Emission Matrix (EEM) spectra and have demonstrated the utility of this spectroscopic technique as a standard method for environmental screening in which the chemical constitution of produced water is monitored. EEM spectra recorded in this work show that dissolved organic matter (DOM) in laboratory shale leachates contains chromophores such as humic acid-like and soluble microbial-like material. Short emission wavelengths (<380 nm) EEM spectra may indicate anthropogenic contamination incidents in future operations, especially as they correspond to fluorescence signatures of some injection fluid additives. Our simple fluorescence method requires little sample preparation and could be coupled with remote sensors for real time, in-situ monitoring of contamination incidents.
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Journal articleFarley KA, Stack KM, Shuster DL, et al., 2022,
Aqueously altered igneous rocks sampled on the floor of Jezero crater, Mars
, Science, Vol: 377, ISSN: 0036-8075<jats:p>The Perseverance rover landed in Jezero crater, Mars, to investigate ancient lake and river deposits. We report observations of the crater floor, below the crater’s sedimentary delta, finding that the floor consists of igneous rocks altered by water. The lowest exposed unit, informally named Séítah, is a coarsely crystalline olivine-rich rock, which accumulated at the base of a magma body. Magnesium-iron carbonates along grain boundaries indicate reactions with carbon dioxide–rich water under water-poor conditions. Overlying Séítah is a unit informally named Máaz, which we interpret as lava flows or the chemical complement to Séítah in a layered igneous body. Voids in these rocks contain sulfates and perchlorates, likely introduced by later near-surface brine evaporation. Core samples of these rocks have been stored aboard Perseverance for potential return to Earth.</jats:p>
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Journal articleKminek G, Benardini JN, Brenker FE, et al., 2022,
COSPAR Sample Safety Assessment Framework (SSAF).
, Astrobiology, Vol: 22, Pages: S186-S216, ISSN: 1531-1074The Committee on Space Research (COSPAR) Sample Safety Assessment Framework (SSAF) has been developed by a COSPAR appointed Working Group. The objective of the sample safety assessment would be to evaluate whether samples returned from Mars could be harmful for Earth's systems (e.g., environment, biosphere, geochemical cycles). During the Working Group's deliberations, it became clear that a comprehensive assessment to predict the effects of introducing life in new environments or ecologies is difficult and practically impossible, even for terrestrial life and certainly more so for unknown extraterrestrial life. To manage expectations, the scope of the SSAF was adjusted to evaluate only whether the presence of martian life can be excluded in samples returned from Mars. If the presence of martian life cannot be excluded, a Hold & Critical Review must be established to evaluate the risk management measures and decide on the next steps. The SSAF starts from a positive hypothesis (there is martian life in the samples), which is complementary to the null-hypothesis (there is no martian life in the samples) typically used for science. Testing the positive hypothesis includes four elements: (1) Bayesian statistics, (2) subsampling strategy, (3) test sequence, and (4) decision criteria. The test sequence capability covers self-replicating and non-self-replicating biology and biologically active molecules. Most of the investigations associated with the SSAF would need to be carried out within biological containment. The SSAF is described in sufficient detail to support planning activities for a Sample Receiving Facility (SRF) and for preparing science announcements, while at the same time acknowledging that further work is required before a detailed Sample Safety Assessment Protocol (SSAP) can be developed. The three major open issues to be addressed to optimize and implement the SSAF are (1) setting a value for the level of assurance to effectively exclude the presence
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Journal articleRoyle SH, Salter TL, Watson JS, et al., 2022,
Mineral matrix effects on pyrolysis products of kerogens infer difficulties in determining biological provenance of macromolecular organic matter at Mars
, Astrobiology, Vol: 22, Pages: 1-21, ISSN: 1531-1074Ancient martian organic matter is likely to take the form of kerogen-like recalcitrant macromolecular organic matter (MOM), existing in close association with reactive mineral surfaces, especially iron oxides. Detecting and identifying a biological origin for martian MOM will therefore be of utmost importance for life detection efforts at Mars. We show that Type I and Type IV kerogens provide effective analogues for putative martian MOM of biological and abiological (meteoric) provenances respectively. We analyse the pyrolytic breakdown products when these kerogens are mixed with mineral matrices highly relevant for the search for life on Mars. We demonstrate that, using traditional thermal techniques as generally used by the Sample Analysis at Mars and Mars Organic Molecule Analyser instruments, even the breakdown products of highly recalcitrant MOM are transformed during analysis in the presence of reactive mineral surfaces, particularly iron. Analytical transformation reduces the diagnostic ability of this technique, as detected transformation products of both biological and abiological MOM may be identical (low molecular weight gas phases and benzene) and indistinguishable. The severity of transformational effects increased through: calcite < kaolinite < haematite < nontronite < magnetite < goethite. Due to their representation of various habitable aqueous environments and the preservation potential of organic matter by iron, it is not advisable to completely avoid iron-rich strata. We conclude that haematite-rich localities, with evidence of extensive aqueous alteration of originally reducing phases, such as the Vera Rubin Ridge, may be relatively promising targets for identifying martian biologically-sourced MOM.
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Journal articleSalter TL, Magee BA, Waite JH, et al., 2022,
Mass spectrometric fingerprints of Bacteria and Archaea for life detection on icy moons
, Astrobiology, Vol: 22, Pages: 143-157, ISSN: 1531-1074The icy moons of the outer solar system display evidence of subsurface liquid water and therefore potential habitability for life. Flybys of Saturn’s moon Enceladus by the Cassini spacecraft have provided measurements of material from plumes that suggest hydrothermal activity and the presence of organic matter. Jupiter’s moon Europa may have similar plumes and is the target for the forthcoming Europa Clipper mission that carries a high mass resolution and high sensitivity mass spectrometer, called the MAss Spectrometer for Planetary EXploration (MASPEX), with the capability for providing detailed characterisation of any organic materials encountered. We have performed a series of experiments using pyrolysis-gas chromatography-mass spectrometry to characterise the mass spectrometric fingerprints of microbial life. A range of extremophile Archaea and Bacteria have been analysed and the laboratory data converted to MASPEX-type signals. Molecules characteristic of protein, carbohydrate and lipid structures were detected and the characteristic fragmentation patterns corresponding to these different biological structures were identified. Protein pyrolysis fragments included phenols, nitrogen heterocycles and cyclic dipeptides. Oxygen heterocycles, such as furans, were detected from carbohydrates. Our data reveal how mass spectrometry on Europa Clipper can aid in the identification of the presence of life, by looking for characteristic bacterial fingerprints that are similar to those from simple Earthly organisms.
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Journal articlePotiszil C, Montgomery W, Sephton M, 2021,
Heterogeneity within refractory organic matter from CM2 carbonaceous chondrites: evidence from Raman spectroscopy
, Earth and Planetary Science Letters, Vol: 574, Pages: 1-10, ISSN: 0012-821XCM2 chondrites experienced widespread aqueous and short term thermal alteration on their parent bodies. Whilst previous Raman spectroscopic investigations have investigated insoluble organic matter (IOM), they have not taken into account the binary nature of IOM. Studies employing mass spectrometry have indicated that IOM also known as macromolecular organic matter (MOM) is in fact composed of two distinct fractions: labile organic matter (LOM) and refractory organic matter (ROM). The ROM component represents the aromatic rich and heteroatom poor component of IOM/MOM, whilst the LOM fraction represents a more heteroatom and aliphatic rich component. Here we report Raman 2D maps and spectroscopic data for Murchison and Mighei, both before and after chemical degradation, which attacks and liberates LOM. The removal of LOM simulates the effects of aqueous alteration, where ester and ether bonds are broken and is thought to release some components to the soluble organic matter (SOM) fraction, also known as the free organic matter fraction (FOM). Raman spectroscopy can be used to reveal the nature of bonding (sp2 and sp3) within carbonaceous materials such as meteoritic organic matter, through evaluation of the D and G band peak centres and FWHM values from the recorded data. The presence of sp3 orbitals indicates that the organic materials contain aliphatic linkages and/or heteroatoms. Statistical analysis of the Raman parameters obtained here indicates that the organic matter originating the Raman response is indistinguishable between the bulk (chemically untreated) and chemically degraded (treated with KOH and HI) samples. Such an observation indicates that the ROM fraction is the major contributor to the Raman response of meteoritic organic matter and thus Raman spectroscopy is unlikely to record any aqueous alteration processes that have affected meteoritic organic matter. Therefore, studies which use Raman to probe the IOM are investigating just one of the compone
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Journal articleRoyle S, Watson JS, Sephton M, 2021,
Transformation of cyanobacterial biomolecules by iron oxides during flash pyrolysis: Implications for Mars life detection missions
, Astrobiology, Vol: 21, ISSN: 1531-1074Answering the question of whether life ever existed on Mars is a key goal of both NASA’s and ESA’s imminent Mars rover missions. The obfuscatory effects of oxidising salts, such as perchlorates and sulfates, on organic matter during thermal decomposition analysis techniques are well established. Less well studied are the transformative effects of iron oxides and (oxy)hydroxides, which are present in great abundances in the martian regolith. We examined the products of flash pyrolysis GC-MS, a technique analogous to the thermal techniques employed by past, current and future landed Mars missions, formed when the cyanobacteria Arthrospira platensis was heated in the presence of a variety of Mars-relevant 16iron bearing minerals. We found that iron oxides/(oxy)hydroxides have transformative effects on the pyrolytic products of cyanobacterial biomolecules. Both the abundance and variety of molecular species detected were decreased as iron substrates transformed biomolecules, by both oxidative and reductive processes, into lower fidelity alkanes, aromatic and aryl-bonded hydrocarbons. Despite the loss of fidelity, a suite containing mid-length alkanes and PAHs and/or aryl-bonded molecules in iron-rich samples subjected to pyrolysis, may allude to the transformation of cyanobacterially-derived mid-long chain length fatty acids (particularly unsaturated fatty acids) originally present in the sample. Haematite was found to be the iron-oxide with the lowest transformation potential and so, because this iron oxide has a high affinity forco-deposition of organic matter and preservation over geological timescales, sampling at Mars should target sediments/strata which have undergone a diagenetic history encouraging the dehydration, dehydroxylation and oxidation of more reactive iron-bearing phases to haematite by looking for (mineralogical) evidence of the activity of oxidising, acidic/neutral and either hot or long-lived fluids.
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Journal articleMontgomery W, Schofield E, Sephton MA, et al., 2021,
The Preservation of English Oak in Marine Environments
<jats:p><p>This study compares the chemical integrity of English Oak (Quercus robur) samples with an age range of four centuries by analysing the lignin degradation.The samples were collected from four historic British vessels and thusrepresent samples of diverse ages which have nonetheless experienced similar non-arborealenvironments. We conclude that the Mary Rose, the oldest vessel studied and therecipient of the most intensive conservation efforts, has been well-preserved throughtreatment with PEG, and we present a baseline for assessing whether a ship hasbeen biologically degraded.</p><p><br></p><p>The work combines quantitative analytic chemistry techniques (e.g., THM-GC-MS) with the conservation of large historic artifacts.</p></jats:p>
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Journal articleMontgomery W, Schofield E, Sephton MA, et al., 2021,
The Preservation of English Oak in Marine Environments
<jats:p>This study compares the chemical integrity of English Oak (Quercus robur) samples with an age range of four centuries by analysing the lignin degradation. The samples were collected from four historic British vessels and thus represent samples of diverse ages which have nonetheless experienced similar non-arboreal environments. We conclude that the Mary Rose, the oldest vessel studied and the recipient of the most intensive conservation efforts, has been well-preserved through treatment with PEG, and we present a baseline for assessing whether a ship has been biologically degraded.</jats:p><jats:p>The work combines quantitative analytic chemistry techniques (e.g., THM-GC-MS) with the conservation of large historic artifacts.</jats:p>
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Journal articleTan JSW, Sephton MA, 2021,
Quantifying preservation potential: lipid degradation in a Mars-analog circumneutral iron deposit
, Astrobiology, Vol: 21, Pages: 1-17, ISSN: 1531-1074Comparisons between the preservation potential of Mars-analog environments have historically been qualitative rather than quantitative. Recently, however, laboratory-based artificial maturation combined with kinetic modeling techniques have emerged as a potential means by which the preservation potential of solvent-soluble organic matter can be quantified in various Mars-analog environments. These methods consider how elevated temperatures, pressures, and organic–inorganic interactions influence the degradation of organic biomarkers post-burial. We used these techniques to investigate the preservation potential of deposits from a circumneutral iron-rich groundwater system. These deposits are composed of ferrihydrite (Fe5HO8 · 4H2O), an amorphous iron hydroxide mineral that is a common constituent of rocks found in ancient lacustrine environments on Mars, such as those observed in Gale Crater. Both natural and synthetic ferrihydrite samples were subjected to hydrous pyrolysis to observe the effects of long-term burial on the mineralogy and organic content of the samples. Our experiments revealed that organic–inorganic interactions in the samples are dominated by the transformation of iron minerals. As amorphous ferrihydrite transforms into more crystalline species, the decrease in surface area results in the desorption of organic matter, potentially rendering them more susceptible to degradation. We also find that circumneutral iron-rich deposits provide unfavorable conditions for the preservation of solvent-soluble organic matter. Quantitative comparisons between preservation potentials as calculated when using kinetic parameters show that circumneutral iron-rich deposits are ∼25 times less likely to preserve solvent-soluble organic matter compared with acidic, iron-rich environments. Our results suggest that circumneutral iron-rich deposits should be deprioritized in favor of acidic iron- and sulfur-rich deposits when searching for evidence o
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Journal articleRoyle SH, Tan J, Watson JS, et al., 2021,
Pyrolysis of carboxylic acids in the presence of iron oxides: implications for life detection on missions to Mars
, Astrobiology, Pages: 1-19, ISSN: 1531-1074The search for, and characterization of, organic matter on Mars is central to efforts in identifying habitable environments and detecting evidence of life in the martian surface and near surface. Iron oxides are ubiquitous in the martian regolith and are known to be associated with the deposition and preservation of organic matter in certain terrestrial environments, thus iron oxide-rich sediments are potential targets for life-detection missions. The most frequently used protocol for martian organic matter characterization (also planned for use on ExoMars) has been thermal extraction for the transfer of organic matter to gas chromatography-mass spectrometry (GC-MS) detectors. For the effective use of thermal extraction for martian samples, it is necessary to explore how potential biomarker organic molecules evolve during this process in the presence of iron oxides. We have thermally decomposed iron oxides simultaneously with (z)-octadec-9-enoic and n-octadecanoic acids and analyzed the products through pyrolysis-GC-MS. We found that the thermally driven dehydration, reduction, and recrystallization of iron oxides transformed fatty acids. Overall detectability of products greatly reduced, molecular diversity decreased, unsaturated products decreased, and aromatization increased. The severity of this effect increased as reduction potential of the iron oxide and inferred free radical formation increased. Of the iron oxides tested hematite showed the least transformative effects, followed by magnetite, goethite, then ferrihydrite. It was possible to identify the saturation state of the parent carboxylic acid at high (0.5 wt %) concentrations by the distribution of n-alkylbenzenes in the pyrolysis products. When selecting life-detection targets on Mars, localities where hematite is the dominant iron oxide could be targeted preferentially, otherwise thermal analysis of carboxylic acids, or similar biomarker molecules, will lead to enhanced polymerization, aromatiz
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Journal articleTan J, Royle S, Sephton M, 2021,
Artificial maturation of iron- and sulfur-rich Mars analogues: Implications for the diagenetic stability of biopolymers and their detection with pyrolysis gas chromatography–mass spectrometry
, Astrobiology, Vol: 21, Pages: 199-218, ISSN: 1531-1074Acidic iron- and sulfur-rich streams are appropriate analogues for the late Noachian and early Hesperian periods of martian history, when Mars exhibited extensive habitable environments. Any past life on Mars may have left behind diagnostic evidence of life that could be detected at the present day. For effective preservation, these remains must have avoided the harsh radiation flux at the martian surface, survived geological storage for billions of years, and remained detectable within their geochemical environment by analytical instrument suites used on Mars today, such as thermal extraction techniques.We investigated the detectability of organic matter within sulfur stream sediments that had been subjected to artificial maturation by hydrous pyrolysis. After maturation, the samples were analyzed by pyrolysis–gas chromatography–mass spectrometry (py-GC-MS) to determine whether organic matter could be detected with this commonly used technique. We find that macromolecular organic matter can survive the artificial maturation process in the presence of iron- and sulfur-rich minerals but cannot be unambiguously distinguished from abiotic organic matter. However, if jarosite and goethite are present in the sulfur stream environment, they interfere with the py-GC-MS detection of organic compounds in these samples. Clay reduces the obfuscating effect of the oxidizing minerals by providing nondeleterious adsorption sites. We also find that after a simple alkali and acid leaching process that removes oxidizing minerals such as iron sulfates, oxides, and oxyhydroxides, the sulfur stream samples exhibit much greater organic responses during py-GC-MS in terms of both abundance and diversity of organic compounds, such as the detection of hopanes in all leached samples.Our results suggest that insoluble organic matter can be preserved over billions of years of geological storage while still retaining diagnostic organic information, but sample selection strategies mu
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Journal articleBullen JC, Torres-Huerta A, Salaün P, et al., 2020,
Portable and rapid arsenic speciation in synthetic and natural waters by an As(V)-selective chemisorbent, validated against anodic stripping voltammetry
, Water Research, Vol: 175, Pages: 1-11, ISSN: 0043-1354Inorganic arsenic speciation, i.e. the differentiation between arsenite and arsenate, is an important step for any program aiming to address the global issue of arsenic contaminated groundwater, whether for monitoring purposes or the development of new water treatment regimes. Reliable speciation by easy-to-use, portable and cost-effective analytical techniques is still challenging for both synthetic and natural waters. Here we demonstrate the first application of an As(V)-selective chemisorbent material for simple and portable speciation of arsenic using handheld syringes, enabling high sample throughput with minimal set-up costs. We first show that ImpAs efficiently removes As(V) from a variety of synthetic groundwaters with a single treatment, whilst As(III) is not retained. We then exemplify the potential of ImpAs for simple and fast speciation by determining rate constants for the photooxidation of As(III) in presence of a TiO2 photocatalyst. Finally, we successfully speciate natural waters spiked with a mix of As(III) and As(V) in both Indian and UK groundwaters with less than 5 mg L−1 dissolved iron. Experimental results using ImpAs agreed with anodic stripping voltammetry (ASV), a benchmark portable technique, with analysis conditions optimised here for the groundwaters of South Asia. This new analytical tool is simple, portable and fast and should find applications within the overall multi-disciplinary remediation effort that is taking place to tackle this worldwide arsenic problem.
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Journal articleKirby ME, Watson JS, Najorka J, et al., 2020,
Experimental study of pH effect on uranium (UVI) particle formation and transport through quartz sand in alkaline 0.1 M sodium chloride solutions
, Colloids and Surfaces A: Physicochemical and Engineering Aspects, Vol: 592, Pages: 1-11, ISSN: 0927-7757A thorough understanding of the aqueous uranium VI (UVI) chemistry in alkaline, sodium containing solutions is imperative to address a wide range of critical challenges in environmental engineering, including nuclear waste management. The aim of the present study was to characterise experimentally in more detail the control of pH on the removal of UVI from aqueous alkaline solutions through particle formation and on subsequent transport through porous media. We conducted first static batch experiments in the pH range between 10.5 and 12.5 containing 10 ppm UVI in 0.1 M NaCl solutions and examined the particles formed using filtration, dynamic light scattering, transition electron microscopy and X-ray powder diffraction. We found that at pH 10.5 and 11.5, between 75 and 96 % of UVI was removed from the solutions as clarkeite and studtite over a period of 48 h, forming particles with hydrodynamic diameters of 640 ± 111 nm and 837 ± 142 nm, respectively and representing aggregates of 10′s nm sized crystals randomly orientated. At pH 12.5, the formation of particles >0.2 μm became insignificant and no UVI was removed from solution. The mobility of UVI in these solutions was further studied using column experiments through quartz sand. We found that at pH 10.5 and 11.5, UVI containing particles were immobilised near the column inlet, likely due physical immobilisation of the particles (particle straining). At pH 12.5, however, UVI quantitatively eluted from the columns in the filter fraction <0.2 μm. The findings of our study reinforce a strong control of solution pH on particle size and U removal in alkaline solutions and subsequently on mobility of U through quartz porous media.
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Journal articleTan J, Sephton M, 2020,
Organic records of early life on Mars: the role of iron, burial and kinetics on preservation
, Astrobiology, Vol: 20, Pages: 53-72, ISSN: 1531-1074Samples that are likely to contain evidence of past life on Mars must have been deposited when and where environments exhibited habitable conditions. Mars analogue sites provide the opportunity to study how life could have exploited such habitable conditions. Acidic iron- and sulfur-rich streams are good geochemical analogues for the late Noachian and early Hesperian, periods of Martian history where habitable conditions were widespread. Past life on Mars would have left behind fossilised microbial organic remains and these are often-sought diagnostic evidence, but must be shielded from the harsh radiation flux at the Martian surface and its deleterious effect on organic matter. One mechanism that promotes such preservation is burial, which raises questions about how organic biomarkers are influenced by the post-burial effects of diagenesis. We investigated the kinetics of organic degradation in the subsurface of Mars. Natural mixtures of acidic iron- and sulfur-rich stream sediments and their associated microbial populations and remains were subjected to hydrous pyrolysis, which simulated the increased temperatures and pressures of burial alongside any promoted organic-mineral interactions. Calculations were made to extrapolate the observed changes over Martian history. Our experiments indicate that low carbon contents, high water-to-rock ratios, and the presence of iron-rich minerals combine to provide unfavourable conditions for the preservation of organic matter over the billions of years necessary to produce present day organic records of late Noachian and early Hesperian life on Mars. Successful sample selection strategies must therefore consider the pre-, syn- and post-burial histories of sedimentary records on Mars and the balance between the production of biomass and the long-term preservation of organic biomarkers over geological time.
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Journal articleAbubakar R, Muxworthy A, Fraser A, et al., 2020,
Mapping hydrocarbon charge-points in the Wessex Basin using seismic, geochemistry and mineral magnetics
, Marine and Petroleum Geology, Vol: 111, Pages: 510-528, ISSN: 1873-4073This study reports a multidisciplinary approach to determining hydrocarbon charge-points and migration in the Wessex Basin, southern England. Geochemical analysis of reservoir core material (Bridport Sandstone and Inferior Oolite) using gas chromatography-mass spectrometry (GC-MS), suggests that the oil in the Wessex Basin is from a single source, and that small variations in environmentally sensitive biomarkers are likely due to small differences in maturity or depositional conditions during the formation of the oil over millions of years. Using seismic data, basin modelling revealed two potential hydrocarbon migration pathways from the hanging wall of the Purbeck fault into the Sherwood Sandstone reservoir at Wytch Farm. One of these potential pathways is represented by cores termed Creech and the other Bushey Farm. To try to distinguish between the two potential pathways, cores were studied using mineral magnetic techniques. The magnetic signature was characterised using low-temperature (<50 K) magnetic measurements; this is because much of the magnetic signature was dominated by nanoparticles < 30 nm, which are thermally activated at room temperature and magnetically “transparent”. Wells that contained considerable amounts of hydrocarbons were dominated by nanometric magnetite (<30 nm). Such particles are small enough to migrate with the oil, through pore spaces, which are of the order ~100 nm. Wells located at the fringes of large hydrocarbon accumulation had enhanced pyrrhotite-dominated magnetic signals. Of the two potential migration pathways, the mineral magnetic results suggest that the oil migrated through Creech rather than through Bushey Farm.
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Journal articleGeorgieva MN, Little CTS, Watson JS, et al., 2019,
Identification of fossil worm tubes from Phanerozoic hydrothermal vents and cold seeps
, Journal of Systematic Palaeontology, Vol: 17, Pages: 287-329, ISSN: 1477-2019One of the main limitations to understanding the evolutionary history of hydrothermal vent and cold seep communities is the identification of tube fossils from ancient deposits. Tube-dwelling annelids are some of the most conspicuous inhabitants of modern vent and seep ecosystems, and ancient vent and seep tubular fossils are usually considered to have been made by annelids. However, the taxonomic affinities of many tube fossils from vents and seeps are contentious, or have remained largely undetermined due to difficulties in identification. In this study, we make a detailed chemical (Fourier-transform infrared spectroscopy and pyrolysis gas-chromatography mass-spectrometry) and morphological assessment of modern annelid tubes from six families, and fossil tubes (seven tube types from the Cenozoic, 12 Mesozoic and four Palaeozoic) from hydrothermal vent and cold seep environments. Characters identified from these investigations were used to explore for the first time the systematics of ancient vent and seep tubes within a cladistic framework. Results reveal details of the compositions and ultrastructures of modern tubes, and also suggest that two types of tubes from ancient vent localities were made by the annelid family Siboglinidae, which often dominates modern vents and seeps. Our results also highlight that several vent and seep tube fossils formerly thought to have been made by annelids cannot be assigned an annelid affiliation with any certainty. The findings overall improve the level of quality control with regard to interpretations of fossil tubes, and, most importantly, suggest that siboglinids likely occupied Mesozoic vents and seeps, greatly increasing the minimum age of the clade relative to earlier molecular estimates.
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