Dr Wes Fraser
PhD, MSc, BSc(Hons), BSc, PCTHE
Reader in Physical Geography
School of Law and Social Sciences
Teaching and supervision
Courses
Modules taught
- GEOG4002: Introduction to Physical Geography
- GEOG4006: Investigating Geography
- GEOG4007: Introduction to Geographical Skills and Techniques
- GEOG5002: Global Change
- GEOG5003: Advanced Research Skills*
- GEOG5006: Earth Systems
- GEOG6002: Climate Change*
- GEOG6013: Oceans and the Marine Environment*
- GEOG6015: Sustainable Futures
- GEOG6012: Geography Dissertation
Key focus on delivering teaching in field and laboratory settings, as well as computer-based practical work.
Research
My primary interest is in Plant-Environment chemical interactions. Specifically the way in which plants alter their chemistry in relation to changes in environmental factors, eg changes in ultraviolet (UV) radiation as part of the spectrum of incoming solar radiation. I developed novel biogeochemical proxy for determining past levels of UV based on changes in chemistry locked in pollen and spores released from plants as part of their natural reproductive cycle. This proxy has been applied to variety of situations and timeframes, ranging from deep geological time to the present-day, and across different spatial scales. I am also interested in the way plants have played a part in shaping the world over geological time, including influencing rates of global chemical weathering at the time of plants invading the terrestrial realm approximately 470 million years ago.
Groups
Projects
Publications
Journal articles
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Jardine PE, Kent MS, Fraser WT, Knorr K-H, Lomax BH, 'Uncovering a phylogenetic signal in plant biopolymer chemistry: a comparison of sporopollenin isolation approaches for use in palynological research'
Palaeontology 66 (6) (2023)
ISSN: 0031-0239 eISSN: 1475-4983AbstractPublished here Open Access on RADARSporomorphs (pollen and spores) are a mainstay of research into past vegetation, and increasingly sporomorph chemistry is being used as a palaeoecological tool. To make extant sporomorphs directly comparable to fossil specimens, fresh material is processed to remove labile compounds and isolate the sporopollenin wall. A range of processing approaches are currently in use, but the chemistries produced by these different techniques have not yet been compared across a range of taxa. It is therefore not clear how they compare in terms of efficiently isolating sporopollenin without changing its chemical structure, and what impact they have on relative chemical similarities and differences among taxa (i.e. whether more closely related species will always appear chemically more similar, regardless of how they have been processed). Here, we test this by applying five different processing approaches to sporomorphs from 15 taxa from across the vascular plant phylogeny. We show that each approach has its own idiosyncrasies in terms of impacts on sporomorph chemistry. For the most part a common pattern of among-taxon chemical variability is uncovered, and a phylogenetic signal within sporopollenin chemistry is supported. Working with spectral derivatives generally increases agreement among the different processing approaches, but decreases the strength of the phylogenetic signal. No one processing approach is ideal, and the choice of which to use is likely to depend on the goal of the study, the type and quantity of material being processed, and the laboratory facilities available for processing.
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Li,u F, Peng H, Marshall JEA, Lomax BH, Bomfleur B, Kent MS, Fraser WT, Jardine PE, 'Dying in the Sun: direct evidence for elevated UV-B radiation at the end-Permian mass extinction'
Science Advances 9 (1) (2023)
ISSN: 2375-2548 eISSN: 2375-2548AbstractPublished here Open Access on RADARLand plants can adjust the concentration of protective UV-B-absorbing compounds (UACs) in the outer wall of their reproductive propagules in response to ambient UV-B flux. To infer changes in UV-B-radiation flux at the Earth’s surface during the end-Permian mass extinction, we analyze UAC abundances in ca. 800 pollen grains from an independently-dated Permian-Triassic boundary section in Tibet. Our data reveal an excursion in UACs that coincide with a spike in mercury concentration and a negative carbon-isotope excursion in the latest Permian deposits, suggesting a close temporal link between large-scale volcanic eruptions, global carbon- and mercury-cycle perturbations, and ozone-layer disruption. Because enhanced UV-B radiation can exacerbate the environmental deterioration induced by massive magmatism, ozone depletion is considered a compelling ecological driver for the terrestrial mass extinction.
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Pogge von Strandmann PAE, Liu X, Liu C-Y, Wilson DJ, Hammond SJ, Tarbuck G, Aristilde L, Krause AJ, Fraser WT, 'Lithium isotope behaviour during basalt weathering experiments amended with organic acids'
Geochimica et Cosmochimica Acta 328 (2022) pp.37-57
ISSN: 0016-7037 eISSN: 1872-9533AbstractPublished here Open Access on RADARLithium (Li) isotopes are a tracer of silicate weathering processes, but how they react to different components of organic and plant-assisted weathering is poorly known. To examine the effect of organic acids compared to a strong mineral acid (HCl) on Li isotope behaviour, basalt-water weathering experiments were amended with different organic acids (glycine, malic acid, cinnamic acid, and humic acid; 0.01 M). The presence of the different acids significantly affects the behaviour of dissolved elemental concentrations (such as Mg, Fe, and Al), both by increasing primary rock dissolution and hindering rates of secondary mineral formation. However, the behaviour of Li isotopes appears unaffected, with all experiments following an almost identical trend of δ7Li versus Li/Na. This observation was consistent with a single fractionation factor during the uptake of Li into secondary minerals, yet both calculated saturation states and leaching experiments on the reacted solids indicated that Li was removed into multiple phases, suggesting that the bulk combined fractionation factor barely varied. Of the Li lost from solution in the organic experiments, we estimated that on average 76% went into neoformed clays, 16% into oxides/oxyhydroxides, and 10% into the exchangeable fraction. The fractionations observed for each phase were Δ7Liexch-soln = −12.7 ± 1.7‰, Δ7Liox-soln = −26.7 ± 0.4‰, and Δ7Liclay-soln = −21.6 ± 3.3‰. These fractionations were identical, within error, to those from experiments with organic-free water, implying that the Li isotope behaviour was unaffected by the presence of organic acids in the weathering reaction. This result has interesting consequences for the interpretation of Li isotopes in terms of plant-assisted weathering and the geological record of terrestrialisation. In particular, it appears to imply that seawater Li isotope records can be expected to resolve the integrated effect of plants on weathering fluxes or weathering congruence, rather than being sensitive to specific organic-mediated weathering mechanisms.
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Jardine PE, Hoorn C, Beer MAM, Barbolini N, Woutersen A, Bogota-Angel G, Gosling WD, Fraser WT, Lomax BH, Huang H, Sciumbata M, He H, Dupont-Niven G , 'Sporopollenin chemistry and its durability in the geological record: an integration of extant and fossil chemical data across the seed plants. '
Palaeontology 64 (2) (2021) pp.285-305
ISSN: 0031-0239 eISSN: 1475-4983AbstractPublished here Open Access on RADARSporopollenin is a highly resistant biopolymer that forms the outer wall of pollen and spores (sporomorphs). Recent research into sporopollenin chemistry has opened up a range of new avenues for palynological research, including chemotaxonomic classification of morphologically cryptic taxa. However, there have been limited attempts to directly integrate extant and fossil sporopollenin chemical data. Of particular importance is the impact of sample processing to isolate sporopollenin from fresh sporomorphs, and the extent of chemical changes that occur once sporomorphs enter the geological record. Here, we explore these issues using Fourier transform infrared (FTIR) microspectroscopy data from extant and fossil grass, Nitraria (a steppe plant), and conifer pollen. We show a 98% classification success rate at subfamily level with extant grass pollen, demonstrating a strong taxonomic signature in isolated sporopollenin. However, we also reveal substantial chemical differences between extant and fossil sporopollenin, which can be tied to both early diagenetic changes acting on the sporomorphs and chemical derivates of sample processing. Our results demonstrate that directly integrating extant and late Quaternary chemical data should be tractable as long as comparable sample processing routines are maintained. Consistent differences between extant and deeper time sporomorphs, however, suggests that classifying fossil specimens using extant training sets will be challenging. Further work is therefore required to understand and simulate the effects of diagenetic processes on sporopollenin chemistry.
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Jardine PE, Fraser WT, Gosling WD, Roberts CN, Eastwood WJ, Lomax BH, 'Proxy reconstruction of ultraviolet-B irradiance at the Earth’s surface, and its relationship with solar activity and ozone
thickness'
Holocene 30 (1) (2020) pp.155-161
ISSN: 0959-6836 eISSN: 1477-0911AbstractPublished here Open Access on RADARSolar ultraviolet-B (UV-B) irradiance that reaches the Earth’s surface acts as a biotic stressor and has the potential to modify ecological and environmental functioning. The challenges of reconstructing ultraviolent (UV) irradiance prior to the satellite era mean that there is uncertainty over long-term surface UV-B patterns, especially in relation to variations in solar activity over centennial and millennial timescales. Here, we reconstruct surface UV-B irradiance over the last 650 years using a novel UV-B proxy based on the chemical signature of pollen grains. We demonstrate a statistically significant positive relationship between the abundance of UV-B absorbing compounds in Pinus pollen and modelled solar UV-B irradiance. These results show that trends in surface UV-B follow the overall solar activity pattern over centennial timescales, and that variations in solar output are the dominant control on surface level UV-B flux, rather than solar modulated changes in ozone thickness. The Pinus biochemical response demonstrated here confirms the potential for solar activity driven surface UV-B variations to impact upon terrestrial biotas and environments over long timescales.
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Jardine PE, Fraser WT, Gosling WD, Roberts CN, Eastwood WJ, Lomax BH, 'Proxy reconstruction of ultraviolet-B irradiance at the Earth's surface, and its relationship with solar acticity and ozone thickness.'
Holocene 30 (1) (2019) pp.155-161
ISSN: 0959-6836AbstractPublished here Open Access on RADARSolar ultraviolet-B (UV-B) irradiance that reaches the Earth’s surface acts as a biotic stressor and has the potential to modify ecological and environmental functioning. The challenges of reconstructing ultraviolent (UV) irradiance prior to the satellite era mean that there is uncertainty over long-term surface UV-B patterns, especially in relation to variations in solar activity over centennial and millennial timescales. Here, we reconstruct surface UV-B irradiance over the last 650 years using a novel UV-B proxy based on the chemical signature of pollen grains. We demonstrate a statistically significant positive relationship between the abundance of UV-B absorbing compounds in Pinus pollen and modelled solar UV-B irradiance. These results show that trends in surface UV-B follow the overall solar activity pattern over centennial timescales, and that variations in solar output are the dominant control on surface level UV-B flux, rather than solar modulated changes in ozone thickness. The Pinus biochemical response demonstrated here confirms the potential for solar activity driven surface UV-B variations to impact upon terrestrial biotas and environments over long timescales.
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Jardine PE, Kent M, Fraser WT, Lomax BH, 'Ginkgo leaf cuticle chemistry across changing pCO2 regimes.'
Paläontologische Zeitschrift 93 (3) (2019) pp.549-558
ISSN: 0031-0220 eISSN: 1867-6812AbstractPublished here Open Access on RADARCuticles have been a key part of palaeobotanical research since the mid-19th Century. Recently, cuticular research has moved beyond morphological traits to incorporate the chemical signature of modern and fossil cuticles, with the aim of using this as a taxonomic and classification tool. For this approach to work, cuticle chemistry would have to maintain a strong taxonomic signal, with a limited input from the ambient environment in which the plant grew. Here, we use attenuated total reflectance Fourier Transform infrared (ATR-FTIR) spectroscopy to analyse leaf cuticles from Ginkgo biloba plants grown in experimentally enhanced CO2 conditions, to test for the impact of changing CO2 regimes on cuticle chemistry. We find limited evidence for an impact of CO2 on the chemical signature of Ginkgo cuticles, with more pronounced differences demonstrated between the abaxial (lower leaf surface) and adaxial (upper leaf surface) cuticles. These findings support the use of chemotaxonomy for plant cuticular remains across geological timescales, and the concomitant large-scale variations in CO2 concentrations.
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Jardine PE, Gosling WD, Lomax BH, Julier ACM, Fraser WT, 'Chemotaxonomy of domesticated grasses: a pathway to understanding the origins of agriculture.'
Journal of Micropalaeontology 38 (1) (2019) pp.83-95
ISSN: 0262-821X eISSN: 2041-4978AbstractPublished here Open Access on RADARThe grass family (Poaceae) is one of the most economically important plant groups in the world today. In particular many major food crops, including rice, wheat, maize, rye, barley, oats and millet, are grasses that were 15 domesticated from wild progenitors during the Holocene. Archaeological evidence has provided key information on domestication pathways of different grass lineages through time and space. However, the most abundant empirical archive of floral change – the pollen record – has been underused for reconstructing grass domestication patterns, because of the challenges of classifying grass pollen grains based on their morphology alone. Here, we test the potential of a novel approach for pollen classification based on the chemical signature of the pollen grains, measured using Fourier Transform 20 infrared (FTIR) microspectroscopy. We use a dataset of eight domesticated and wild grass species, classified using k-nearest neighbour classification coupled with leave one out cross validation. We demonstrate a 95% classification success rate on training data, and an 82% classification success rate on validation data. This result shows that FTIR spectroscopy can provide enhanced taxonomic resolution enabling species level assignment from pollen. This will enable the full testing of the timing and drivers of domestication and agriculture through the Holocene.
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Pogge von Strandmann PAE, Fraser WT, Hammond SJ, Tarbuck G, Wood IG, Oelker EH, Murphy MJ, 'Experimental determination of Li isotope behaviour during basalt weathering.'
Chemical Geology 517 (2019) pp.34-43
ISSN: 0009-2541AbstractPublished here Open Access on RADARSilicate weathering is the primary control of atmospheric CO2 concentrations on multiple timescales. However, tracing this process has proven difficult. Lithium isotopes are a promising tracer of silicate weathering. This study has reacted basalt sand with natural river water for ~9 months in closed experiments, in order to examine the behaviour of Li isotopes during weathering. Aqueous Li concentrations decrease by a factor of ~10 with time, and δ7Li increases by ~19‰, implying that Li is being taken up into secondary phases that prefer 6Li. Mass balance using various selective leaches of the exchangeable and secondary mineral fractions suggest that ~12–16% of Li is adsorbed, and the remainder is removed into neoformed secondary minerals. The exchangeable fractionation factors have a Δ7Liexch-soln = −11.6 to −11.9‰, while the secondary minerals impose Δ7Lisecmin-soln = −22.5 to −23.9‰. Overall the experiment can be modelled with a Rayleigh fractionation factor of α = 0.991, similar to that found for natural basaltic rivers. The mobility of Li relative to the carbon-cycle-critical cations of Ca and Mg changes with time, but rapidly evolves within one month to remarkably similar mobilities amongst these three elements. This evolution shows a linear relationship with δ7Li (largely due to a co-variation between aqueous [Li] and δ7Li), suggesting that Li isotopes have the potential to be used as a tracer of Ca and Mg mobility during basaltic weathering, and ultimately CO2 drawdown.
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Julier ACM, Jardine PE, Adu-Bredu S, Coe AL, Fraser WT, Lomax BH, Malhi Y, Moore S, Gosliing WD, 'Variability in modern pollen rain from moist and wet tropical forest plots in Ghana, West Africa'
Grana 58 (1) (2019) pp.45-62
ISSN: 0017-3134 eISSN: 1651-2049AbstractPublished here Open Access on RADARHow pollen moves within and between ecosystems affects factors such as the genetic structure of populations, how resilient they are to environmental change, and the amount and nature of pollen preserved in the sedimentary record. We set artificial pollen traps in two 100 m by 100 m vegetation plots, one in a wet evergreen forest, and one in a moist semideciduous forest in Ghana, West Africa. Five traps from each plot were counted annually from 2011 to 2014, to examine spatial and temporal variation in the pollen rain of the most abundant taxa shared between pollen and vegetation assemblages. Samples from the wet evergreen plot exhibited high variability within years, with the dominant pollen types changing between samples, and many pollen taxa being over-represented relative to their parent plant abundance in some traps whilst being entirely absent from others. The most abundant plant taxa of the wet evergreen plot (Drypetes and Cynometra) do, however, constitute major components of the pollen rain. There is less variation between samples from the moist semi-deciduous plot spatially, as it is dominated by Celtis, which typically comprises >70% of the pollen assemblages. We conclude that pollen rain in these tropical ecosystems is highly heterogeneous, and suggest that pollen assemblages obtained by trapping are susceptible to small-scale variations in forest structure. Conversely, this may mean that current recommendations of more than three years of trapping in tropical systems may be too high, and that space could substitute for time in modern tropical pollen trapping.
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Kemp DB, Fraser WT, Izumi K, 'Stratigraphic completeness and resolution in an ancient mudrock succession'
Sedimentology 65 (6) (2018) pp.1875-1890
ISSN: 0037-0746 eISSN: 1365-3091AbstractMudrocks are the most common rock type at the Earth's surface, and they play a major role in informing current understanding of the palaeoenvironmental history of the planet. Their suitability for this purpose is at least partly underpinned by the assumed stratigraphic completeness of mudrock successions, and the ostensible fidelity with which they record temporal changes in palaeoenvironment. Mud does not necessarily accumulate, however, as a steady, near-continuous ‘rain’ under low energy conditions. Advective modes of mud transport and episodic, ephemeral accumulation have been shown to dominate in many ancient successions. This has implications for the completeness of these records and their suitability for high-resolution sampling and analysis. In this study, a numerical model of mud accumulation, parameterized with data from the Lower Jurassic of Yorkshire (United Kingdom) is presented to explore completeness and resolution constraints on ancient epicontinental mudrock successions. Using this model, stratigraphic completeness of the analysed Yorkshire succession is estimated to be ca 13% and ca 98% at centennial and millennial time scales, respectively. The findings indicate that sub-millennial scale processes and events are unlikely to be accurately resolved, despite the largely unbioturbated and well-laminated nature of the succession. Epicontinental mudrock successions are a crucial archive of ancient environmental changes, and the findings of this study help to define a plausible upper limit on the resolution achievable in these successions. Even with high-resolution sampling, sub-millennial scale records of palaeoenvironmental change may not be attainable in ancient epicontinental mudrocks.Published here Open Access on RADAR -
Gosling WD, Julier ACM, Adu-Bredu A, Djagbletey GD, Fraser WT, Jardine PE, Lomax BH, Malhi Y, Manu EA, Mayle FE, Moore S, 'Pollen-vegetation richness and diversity relationships in the tropics'
Vegetation History and Archaeobotany 27 (2) (2018) pp.411-418
ISSN: 0939-6314 eISSN: 1617-6278AbstractTracking changes in biodiversity through time requires an understanding of the relationship between modern diversity and how this diversity is preserved in the fossil record. Fossil pollen is one way in which past vegetation diversity can be reconstructed. However, there is limited understanding of modern pollen-vegetation diversity relationships from biodiverse tropical ecosystems. Here, pollen (palynological) richness and diversity (Hill N1) are compared with vegetation richness and diversity from forest and savannah ecosystems in the New World and Old World tropics (Neotropics and Palaeotropics). Modern pollen data were obtained from artificial pollen traps deployed in 1-ha vegetation study plots from which vegetation inventories had been completed in Bolivia and Ghana. Pollen counts were obtained from 15 to 22 traps per plot, and aggregated pollen sums for each plot were > 2,500. The palynological richness/diversity values from the Neotropics were moist evergreen forest = 86/6.8, semi-deciduous dry forest = 111/21.9, wooded savannah = 138/31.5, and from the Palaeotropics wet evergreen forest = 144/28.3, semi-deciduous moist forest = 104/4.4, forest-savannah transition = 121/14.1; the corresponding vegetation richness/diversity was 100/36.7, 80/38.7 and 71/39.4 (Neotropics), and 101/54.8, 87/45.5 and 71/34.5 (Palaeotropics). No consistent relationship was found between palynological richness/diversity, and plot vegetation richness/diversity, due to the differential influence of other factors such as landscape diversity, pollination strategy, and pollen source area. Palynological richness exceeded vegetation richness, while pollen diversity was lower than vegetation diversity. The relatively high global diversity of tropical vegetation was found to be reflected in the pollen rain.Published here Open Access on RADAR -
Julier ACM, Jardine PE, Adu-Bredu S, Coe AL, Duah-Gyamfi A, Fraser WT, Lomax BH, Malhi Y, Moore S, Owusu-Afriyie K, Gosling WD, 'The modern pollen-vegetation relationships of a tropical forest-savannah mosaic landscape, Ghana, West Africa'
Palynology 42 (3) (2017) pp.324-338
ISSN: 0191-6122 eISSN: 1558-9188AbstractTransitions between forest and savannah vegetation types in fossil pollen records are often poorlyPublished here Open Access on RADAR
understood due to over-production by taxa such as Poaceae and a lack of modern pollen-vegetation studies. Here, modern pollen assemblages from within a forest-savannah transition in West Africa are presented and compared, their characteristic taxa discussed, and implications for the fossil record considered. Fifteen artificial pollen traps were deployed for 1 year, to collect pollen rain from three vegetation plots within the forest-savannah transition in Ghana. High percentages of Poaceae and Melastomataceae/Combretaceae were recorded in all three plots. Erythrophleum suaveolens characterised the forest plot, Manilkara obovata the transition plot and Terminalia the savannah plot. The results indicate that Poaceae pollen influx rates provide the best representation of the forest-savannah gradient, and that a Poaceae abundance of >40% should be considered as indicative of savannah-type vegetation in the fossil record. -
Jardine PE, Abernethy AJ, Lomax BH, Gosling WD, Fraser WT, 'Shedding light on sporopollenin chemistry, with reference to UV reconstructions'
Review of Palaeobotany and Palynology 238 (2017) pp.1-6
ISSN: 0034-6667AbstractSporopollenin, which forms the outer wall of pollen and spores, contains a chemical signature of ultraviolet-B flux via concentrations of UV-B absorbing compounds (UACs), providing a proxy for reconstructing UV irradiance through time. Although Fourier transform infrared (FTIR) spectroscopy provides an efficient means of measuring UAC concentrations, nitrogen-containing compounds have the potential to bias the aromatic and hydroxyl bands used to quantify and standardise UAC abundances. Here, we explore the presence and possible influence of nitrogen in UV reconstruction via an FTIR study of Lycopodium spores from a natural shading gradient. We show that the UV-sensitive aromatic peak at 1510 cm− 1 is clearly distinguishable from the amide II peak at 1550 cm− 1, and the decrease in aromatic content with increased shading can be reconstructed using standardisation approaches that do not rely on the 3300 cm− 1 hydroxyl band. Isolation of the sporopollenin results in the loss of nitrogen-related peaks from the FTIR spectra, while the aromatic gradient remains. This confirms the lack of nitrogen in sporopollenin and its limited potential for impacting on palaeo-UV reconstructions. FTIR is therefore an appropriate tool for quantifying UACs in spores and pollen, and information on UV flux should be obtainable from fossil or processed samples.Published here Open Access on RADAR -
Jardine PE, Fraser WT, Lomax BH, Sephton MA, Shanahan TM, Miller CS, Gosling WD, 'Pollen and spores as biological recorders of past ultraviolet irradiance'
Scientific Reports 6 (2016)
ISSN: 2045-2322AbstractSolar ultraviolet (UV) irradiance is a key driver of climatic and biotic change. Ultraviolet irradiance modulates stratospheric warming and ozone production, and influences the biosphere from ecosystem-level processes through to the largest scale patterns of diversification and extinction. Yet our understanding of ultraviolet irradiance is limited because no method has been validated to reconstruct its flux over timescales relevant to climatic or biotic processes. Here, we show that a recently developed proxy for ultraviolet irradiance based on spore and pollen chemistry can be used over long (105 years) timescales. Firstly we demonstrate that spatial variations in spore and pollen chemistry correlate with known latitudinal solar irradiance gradients. Using this relationship we provide a reconstruction of past changes in solar irradiance based on the pollen record from Lake Bosumtwi in Ghana. As anticipated, variations in the chemistry of grass pollen from the Lake Bosumtwi record show a link to multiple orbital precessional cycles (19-21 thousand years). By providing a unique, local proxy for broad spectrum solar irradiance, the chemical analysis of spores and pollen offers unprecedented opportunities to decouple solar variability, climate and vegetation change through geologic time and a new proxy with which to probe the Earth system.Published here Open Access on RADAR -
Julier ACM, Jardine PE, Coe AL, Gosling WD, Lomax BH, Fraser WT, 'Chemotaxonomy as a tool for interpreting the cryptic diversity of Poaceae pollen'
Review of Palaeobotany and Palynology 235 (2016) pp.140-147
ISSN: 0034-6667AbstractThe uniform morphology of different species of Poaceae (grass) pollen means that identification to below family level using light microscopy is extremely challenging. Poor taxonomic resolution reduces recoverable information from the grass pollen record, for example, species diversity and environmental preferences cannot be extracted. Recent research suggests Fourier Transform Infra-red Spectroscopy (FTIR) can be used to identify pollen grains based on their chemical composition. Here, we present a study of twelve species from eight subfamilies of Poaceae, selected from across the phylogeny but from a relatively constrained geographical area (tropical West Africa) to assess the feasibility of using this chemical method for identification within the Poaceae family. We assess several spectral processing methods and use K-nearest neighbour (k-nn) analyses, with a leave-one-out cross-validation, to generate identification success rates at different taxonomic levels. We demonstrate we can identify grass pollen grains to subfamily level with an 80% success rate. Our success in identifying Poaceae to subfamily level using FTIR provides an opportunity to generate high taxonomic resolution datasets in research areas such as palaeoecology, forensics, and melissopalynology quickly and at a relatively low cost.Published here Open Access on RADAR -
Lomax BH, Fraser WT, 'Palaeoproxies: Botanical monitors and recorders of atmospheric change.'
Plant, Cell and Environment 58 (5) (2015) pp.759-768
ISSN: 0140-7791Published here -
Mangalassery S, Mooney SJ, Sparkes DL, Fraser WT, Sjögersten S, 'Impacts of zero tillage on soil enzyme activities, microbial characteristics and organic matter functional chemistry in temperate soils.'
European Journal of Soil Biology 68 (2015) pp.9-17
ISSN: 1164-5563AbstractPublished hereZero tillage management of agricultural soils has potential for enhancing soil carbon (C) storage and reducing greenhouse gas emissions. However, the mechanisms which control carbon (C) sequestration in soil in response to zero tillage are not well understood. The aim of this study was to investigate the links between zero tillage practices and the functioning of the soil microbial community with regards to C cycling, testing the hypothesis that zero tillage enhances biological functioning in soil with positive implications for C sequestration. Specifically, we determined microbial respiration rates, enzyme activities, carbon source utilization and the functional chemistry of the soil organic matter in temperate well drained soils that had been zero tilled for seven years against annually tilled soils. Zero tilled soils contained 9% more soil C, 30% higher microbial biomass C than tilled soil and an increased presence of aromatic functional groups indicating greater preservation of recalcitrant C. Greater CO2 emission and higher respirational quotients were observed from tilled soils compared to zero tilled soils while microbial biomass was 30% greater in zero tilled soils indicating a more efficient functioning of the microbial community under zero tillage practice. Furthermore, microbial enzyme activities of dehydrogenase, cellulase, xylanase, β-glucosidase, phenol oxidase and peroxidase were higher in zero tilled soils. Considering zero tillage enhanced both microbial functioning and C storage in soil, we suggest that it offers significant promise to improve soil health and support mitigation measures against climate change.
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Fraser WT, Blei E, Fry SC, Newman MK, Reay DS, Smith KA, McLeod AR, 'Emission of methane, carbon monoxide, carbon dioxide and short-chain hydrocarbons from vegetation foliage under ultraviolet irradiation.'
Plant, Cell and Environment 38 (5) (2015) pp.980-989
ISSN: 0140-7791AbstractPublished hereThe original report that plants emit methane (CH4) under aerobic conditions caused much debate and controversy. Critics questioned experimental techniques, possible mechanisms for CH4 production and the nature of estimating global emissions. Several studies have now confirmed that aerobic CH4 emissions can be detected from plant foliage but the extent of the phenomenon in plants and the precise mechanisms and precursors involved remain uncertain. In this study, we investigated the role of environmentally realistic levels of ultraviolet (UV) radiation in causing the emission of CH4 and other gases from foliage obtained from a wide variety of plant types. We related our measured emissions to the foliar content of methyl esters and lignin and to the epidermal UV absorbance of the species investigated. Our data demonstrate that the terrestrial vegetation foliage sampled did emit CH4, with a range in emissions of 0.6–31.8 ng CH4 g−1 leaf DW h−1, which compares favourably with the original reports of experimental work. In addition to CH4 emissions, our data show that carbon monoxide, ethene and propane are also emitted under UV stress but we detected no significant emissions of carbon dioxide or ethane.
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Fraser WT, Lomax BH, Jardine PE, Gosling WD, Sephton MA, 'Pollen and spores as a passive monitor of ultraviolet radiation'
Frontiers in Ecology and Evolution 2 (2014)
ISSN: 2296-701XAbstractPublished here Open Access on RADARThe nesting habits of ants play an important role in structuring ant populations. They vary from monodomy, a colony occupies a single nest, via polydomy, a colony occupies multiple adjacent nests, to supercoloniality, a colony spans over large territories comprising dozen to thousands nests without having any boundaries. The population structure of the desert ant Cataglyphis niger, previously considered to form supercolonies, was studied using genetic, chemical, and behavioral tools in plots of 50 × 50 m at two distinct populations. At the Palmahim site, the plot comprised 15 nests that according to the genetic analysis constituted three colonies. Likewise at the Rishon Leziyyon site 14 nests constituted 5 genetic colonies. In both sites, both chemical analysis and the behavioral (aggression) tests confirmed the colony genetic architecture. The behavioral tests also revealed that aggression between colonies within a population was higher than that exhibited between colonies of different populations, suggesting the occurrence of the “nasty neighbor” phenomenon. In contrast to supercolony structure previously reported in another population of this species, the presently studied populations were composed of polydomous colonies. However, both the genetic and chemical data revealed that the inter-colonial differences between sites were larger than those within site, suggesting some within-site population viscosity. Thus, C. niger exhibits flexible nesting characteristics, from polydomy to supercoloniality, and can be considered at the brink of supercoloniality. We attribute the differences in population structure among sites to the intensity of intraspecific competition.
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Jardine PE, Fraser WT, Lomax BH, Gosling WD, 'The impact of oxidation on spore and pollen chemistry'
Journal of Micropalaeontology 34 (2014) pp.139-149
ISSN: 0262-821XAbstractPublished hereSporomorphs (pollen and spores) have an outer wall composed of sporopollenin. Sporopollenin chemistry contains both a signature of ambient ultraviolet-B flux and taxonomic information, but it is currently unknown how sensitive this is to standard palynological processing techniques. Oxidation in particular is known to cause physical degradation to sporomorphs, and it is expected that this should have a concordant impact on sporopollenin chemistry. Here, we test this by experimentally oxidizing Lycopodium (clubmoss) spores using two common oxidation techniques: acetolysis and nitric acid. We also carry out acetolysis on eight angiosperm (flowering plant) taxa to test the generality of our results. Using Fourier Transform infrared (FTIR) spectroscopy, we find that acetolysis removes labile, non-fossilizable components of sporomorphs, but has a limited impact upon the chemistry of sporopollenin under normal processing durations. Nitric acid is more aggressive and does break down sporopollenin and reorganize its chemical structure, but when limited to short treatments (i.e. ≤10 min) at room temperature sporomorphs still contain most of the original chemical signal. These findings suggest that when used carefully oxidation does not adversely affect sporopollenin chemistry, and that palaeoclimatic and taxonomic signatures contained within the sporomorph wall are recoverable from standard palynological preparations.
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Fraser WT, Watson JS, Sephton MA, Lomax BH, Harrington G, Gosling WD, Self S, 'Changes in spore chemistry and appearance with increasing maturity'
Review of Palaeobotany and Palynology 201 (2013) pp.41-46
ISSN: 0034-6667AbstractSporopollenin is the primary biopolymer found in the walls of pollen and spores; during maturation sporopollenin undergoes a number of discrete chemical changes, despite maintaining identifiable morphological features which can be exploited for palynological study. Here we report the results of heating experiments performed using Lycopodium clavatum spores designed to investigate the changes that occur within sporopollenin across a wide range of temperatures (0–350 °C) to simulate different degrees of maturation. Changes in sporopollenin functionality were assessed using Fourier transform infrared (FTIR) microspectroscopy. Our analyses show that the chemical structure of sporopollenin remains relatively stable over a wide range of simulated maturation conditions, until a threshold of 250–300 °C is reached, at which point a reorganisation of chemical structure begins. Comparison of these artificially matured spores with fossil material obtained from a Carboniferous-age section in the United Kingdom shows a strong chemical resemblance, suggesting that our experimental procedure accurately reflects the process of maturation and provides an insight into the chemical stability of sporopollenin in the geosphere. -
Lomax, B H, Fraser W T, Harrington G J, Blackmore S, Sephton M A, Harris N B W, 'A novel palaeoaltimetry proxy based on spore and pollen wall chemistry'
Earth and Planetary Science Letters 353-354 (-) (2012) pp.22-28
ISSN: 0012-821XAbstractUnderstanding the uplift history and the evolution of high altitude plateaux is of major interest to a wide range of geoscientists and has implications for many disparate fields. Currently the majority of palaeoaltimetry proxies are based on detecting a physical change in climate in response to uplift, making the relationship between uplift and climate difficult to decipher. Furthermore, current palaeoaltimetry proxies have a low degree of precision with errors typically greater than 1km. This makes the calculation of uplift histories and the identification of the mechanisms responsible for uplift difficult to determine. Here we report on advances in both instrumentation and our understanding of the biogeochemical structure of sporopollenin that are leading to the establishment of a new proxy to track changes in the flux of UV-B radiation over geological time. The UV-B proxy is based on quantifying changes in the concentration of UV-B absorbing compounds (UACs) found in the spores and pollen grains of land plants, with the relative abundances of UACs increasing on exposure to elevated UV-B radiation. Given the physical relationship between altitude and UV-B radiation, we suggest that the analysis of sporopollenin chemistry, specifically changes in the concentration of UACs, may offer the basis for the first climate independent palaeoaltimetry proxy. Owing to the ubiquity of spores and pollen in the fossil record, our proposed proxy has the potential to enable the reconstruction of the uplift history of high altitude plateaux at unprecedented levels of fidelity, both spatially and temporally.Published here -
Fraser W T, Scott A C, Forbes A E S, Glasspool I J, Plotnick R E, Kenig F, Lomax B H, 'Evolutionary stasis of sporopollenin biochemistry revealed by unaltered carboniferous spores'
New Phytologist 196 (2) (2012) pp.397-401
ISSN: 0028-646XAbstractPublished hereThe biopolymer sporopollenin present in the spore/pollen walls of all land plants is regarded as one of the most recalcitrant biomacromolecules (biopolymers), providing protection against a range of abiotic stresses. This long-term stability is demonstrated by the near-ubiquitous presence of pollen and spores in the fossil record with spores providing the first evidence for the colonization of the land.Here, we report for the first time chemical analyses of geologically unaltered sporopollenin from Pennsylvanian (c. 310million yr before present (MyBP)) cave deposits.Our data show that Pennsylvanian Lycophyta megaspore sporopollenin has a strong chemical resemblance to extant relatives and indicates that a co-polymer model of sporopollenin formation is the most likely configuration.Broader comparison indicates that extant sporopollenin structure is similar across widely spaced phylogenetic groups and suggests land plant sporopollenin structure has remained stable since embryophytes invaded land.
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Watson J S, Fraser W T, Sephton M A, 'Formation of a polyalkyl macromolecule from the hydrolysable component within sporopollenin during heating/pyrolysis experiments with Lycopodium spores'
Journal of Analytical and Applied Pyrolysis 95 (May) (2012) pp.138-144
ISSN: 0165-2370AbstractThe most resistant component of Lycopodium spores is the macromolecule sporopollenin. The recent and fossil representatives of this material are structurally distinct and the transformations that bring about this chemical discord are poorly understood. To investigate the diagenesis of spores and their biopolymer, solvent extracted and saponified examples of Lycopodium clavatum underwent simulated diagenesis by heating (100-400°C) under vacuum for 48h. Following simulated maturation, spores were analysed by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and thermochemolysis-GC-MS. Py-GC-MS data clearly demonstrate that there is an increase in the polyalkyl hydrocarbon material in the pyrolysable component with increasing anhydrous maturation temperature. Hydrous pyrolysis of spores leads to similar changes but with an increased response from aliphatic relative to aromatic material. If the spores are hydrolysed prior to heating the generation of the polyalkyl portion of the macromolecule is markedly reduced. It appears, therefore, that the polyalkyl portion of fossil sporopollenin may be formed by maturation-induced polymerisation of the ‘labile' hydrolysable component to form a recalcitrant polyalkyl network.Published here -
Fraser W T, Sephton M A, Watson J S, Self S, Lomax B H, James D I, Wellman C H, Callaghan T V, Beerling D J, 'UV-B absorbing pigments in spores: Biochemical responses to shade in a high-latitude birch forest and implications for sporopollenin-based proxies of past environmental change'
Polar Research 30 (-) (2011) pp.8312-
ISSN: 0800-0395AbstractPublished here Open Access on RADARCurrent attempts to develop a proxy for Earth's surface ultraviolet-B (UV-B) flux focus on the organic chemistry of pollen and spores because their constituent biopolymer, sporopollenin, contains UV-B absorbing pigments whose relative abundance may respond to the ambient UV-B flux. Fourier transform infrared (FTIR) microspectroscopy provides a useful tool for rapidly determining the pigment content of spores. In this paper, we use FTIR to detect a chemical response of spore wall UV-B absorbing pigments that corresponds with levels of shade beneath the canopy of a high-latitude Swedish birch forest. A 27% reduction in UV-B flux beneath the canopy leads to a significant (p
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Lomax B H, Fraser W T, Sephton M A, Callaghan T V, Self S, Pyle J A, Wellman C H, Beerling D J, 'Plant spore walls as a record of long-term changes in ultraviolet-B radiation'
Nature Geoscience 1 (9) (2008) pp.592-596
ISSN: 1752-0894AbstractStratospheric ozone screens the Earth's surface from harmful ultraviolet-B radiation. Concentrations of stratospheric ozone are governed by a variety of natural and anthropogenic factors, including solar cycles1, volcanic aerosols2, ozone-depleting substances3 and climate change4. However, assessing this variability before instrumental records has proved difficult owing to the lack of a well-constrained proxy5. Here, we use microspectroscopy to analyse the chemical composition of herbarium samples of clubmoss (Lycophyta) spores originating from high- and low-latitude localities, where they were exposed to different ultraviolet-B histories. We show that the concentration of two ultraviolet-B-absorbing compounds in the walls of high-northern- and southern-latitude spores is strongly regulated by historical variations in ultraviolet-B radiation. Conversely, we find little change in the concentration of these compounds in spores originating from tropical Ecuador, where ultraviolet levels have remained relatively stable. Using spores from Greenland, we reconstruct past (1907-1993) changes in ozone concentration and ultraviolet-B flux; we reveal strong similarities between spore-wall reconstructions, and independent instrumental records6 and model results7. Our findings suggest that ultraviolet-B-absorbing compounds in plant spore walls have the potential to act as a proxy for past changes in terrestrial ultraviolet-B radiation and stratospheric ozone. The chemical signature of plant spore walls in herbaria, and possibly also in sedimentary and ice-core archives, may therefore prove valuable for reconstructing past variations in stratospheric ozone and their connections with changes in solar radiation and climate.Published here -
Lindgren P, Parnell J, Norman C, Mark DF, Baron M, Ormö J, Sturkell E, Conliffe J, Fraser WT, 'Formation of uranium-thorium-rich bitumen nodules in the Lockne impact structure, Sweden: A mechanism for carbon concentration at impact sites.'
Meteoritics & Planetary Science (2007)
ISSN: 1086-9379Published here -
Watson JS, Sephton MA, Sephton SV, Beerling DJ, Self S, Fraser WT, Lomax BH, Gilmour I, Wellman CH, 'Rapid determination of spore chemistry using thermochemolysis gas chromatography-mass spectrometry and micro-Fourier transform infrared spectroscopy.'
Photochemical & Photobiological Sciences 2007 (6) (2007) pp.689-694
ISSN: 1474-905XAbstractSpore chemistry is at the centre of investigations aimed at producing a proxy record of harmful ultraviolet radiation (UV-B) through time. A biochemical proxy is essential owing to an absence of long-term (century or more) instrumental records. Spore cell material contains UV-B absorbing compounds that appear to be synthesised in variable amounts dependent on the ambient UV-B flux. To facilitate these investigations we have developed a rapid method for detecting variations in spore chemistry using combined thermochemolysis gas chromatography-mass spectrometry and micro-Fourier transform infrared spectroscopy. Our method was tested using spores obtained from five populations of the tropical lycopsid Lycopodium cernuum growing across an altitudinal gradient (650–1981 m a.s.l.) in S.E. Asia with the assumption that they experienced a range of UV-B radiation doses. Thermochemolysis and subsequent pyrolysis liberated UV-B pigments (ferulic and para-coumaric acid) from the spores. All of the aromatic compounds liberated from spores by thermochemolysis and pyrolysis were active in UV-B protection. The various functional groups associated with UV-B protecting pigments were rapidly detected by micro-FTIR and included the aromatic C[double bond, length as m-dash]C absorption band which was exclusive to the pigments. We show increases in micro-FTIR aromatic absorption (1510 cm−1) with altitude that may reflect a chemical response to higher UV-B flux. Our results indicate that rapid chemical analyses of historical spore samples could provide a record ideally suited to investigations of a proxy for stratospheric O3 layer variability and UV-B flux over historical (century to millennia) timescales.Published here
Further details
Organic geochemist specialising in the reconstruction of past ultraviolet (UV) radiation regimes using chemical signatures locked within the walls of spores and pollen. Additional interests include greenhouse gas emissions from vegetation, the variation of UV within the environment and the micrometeorology of wall faces.