679 research outputs found
GEOFFREY EGLINTON - Publications from GEOFFREY EGLINTON. 1 November 1927 — 11 March 2016
No full textGeoffrey Eglinton trained as an organic chemist at the University of Manchester working on acetylene synthesis, and the Eglinton reaction signifies his discovery of an effective method for their oxidative coupling. At the University of Glasgow, he recognized the potential of analytical advances to open new frontiers for characterization of molecular constituents of complex mixtures and continued to adopt and adapt instrumental techniques throughout his career. Eglinton's exploration of plant leaf waxes, and their taxonomic profiles, prompted forays in organic geochemistry, seeking molecular evidence for ancient life. Thus, his focus shifted to studying ‘chemical fossils‘ preserved in the rock record and pioneering identification and interpretation of their compositions. At the University of Bristol, he established the Organic Geochemistry Unit and steered its rise to international prominence as a leading centre for research, a legacy that continues today. He served in planning the Apollo sampling programme and led research that explicated the carbon chemistry of the Moon. Major advances in using molecules as witnesses of the origins and fate of sedimentary organic matter bear the hallmarks of his insightful contributions and commitment to interdisciplinary, collaborative ventures. They include deciphering how environmental controls and thermal transformations govern the composition of petroleum hydrocarbons, and validating the ability for molecules to afford invaluable evidence of past climates. Eglinton's research accomplishments were recognized by many prestigious awards, including a Royal Gold Medal of the Royal Society, the V. M. Goldschmidt Medal of the Geochemical Society, the Wollaston Medal of the Geological Society, and the Dan David Prize
Alkenone concentration and sea surface temperature in surface sediments
No full textAlkenone concentration and radiocarbon age in 7 gobally-distributed surface sediment samples and their associated grain-size fractions. Total organic carbon (TOC) and fractional abundance of grain-size fractions from bulk sediments (Bulk%) are taken from Ausín et al. (2021). Analytical precision of Uk'37 is 0.003 units. Uk'37-SST propagated error is ±0.51℃. These parameters were measured to explore the influence of alkenone-mineral associations and hydrodynamic mineral sorting processes on alkenone proxy signals. Bulk sediment samples were fractionated into four grain-size fractions (sand (>300-63 µm); coarse silt (63-10 µm); fine silt (10-2 µm); and clay (< 2 µm) prior to lipid extraction and manual column chromatography to obtain a ketone fraction containing the alkenones. The concentration and distribution of C37 alkenones was analyzed using gas chromatography with flame ionization detection (GC-FID) at the Biogeoscience Group Laboratories, ETH Zürich in 2018. The ketone fractions used for determination of alkenone concentration and unsaturation were further purified for compound specific radiocarbon analysis following Ohkouchi et al. (2005). Samples, were measured as CO2 using an Elemental-Analyzer system interface coupled to a gas ion source (GIS)-equipped Minicarbon Dating System (MICADAS) at the Laboratory of Ion Beam Physics, ETH Zürich in 2018. References Ausín, B., Bruni, E., Haghipour, N., Welte, C., Bernasconi, S. M., & Eglinton, T. I. Controls on the abundance, provenance and age of organic carbon buried in continental margin sediments. Earth and Planetary Science Letters, 558, 116759, doi:10.1016/j.epsl.2021.116759, 2021. Ohkouchi, N., Xu, L., Reddy, C. M., Montluon, D., & linton, T. I. Radiocarbon dating of alkenones from marine sediments: I. Isolation Protocol Radiocarbon, 47, 401-412, doi:10.1017/S0033822200035189, 2005
Removal of the four c-terminal glycine-rich repeats enhances the thermostability and substrate binding affinity of barley b-amylase
No full textBarley beta-amylase undergoes proteolytic cleavage in the C-terminal region after germination. The implication of the cleavage in the enzyme's characteristics is unclear. With purified native beta-amylases from both mature barley grain and germinated barley, we found that the beta-amylase from germinated barley had significantly higher thermostability and substrate binding affinity for starch than that from mature barley grain. To better understand the effect of the proteolytic cleavage on the enzyme's thermostability and substrate binding affinity for starch, recombinant barley beta-amylases with specific deletions at the C-terminal tail were generated. The complete deletion of the four C-terminal glycine-rich repeats significantly increased the enzyme's thermostability, but an incomplete deletion with one repeat remaining did not change the thermostability. Although different C-terminal deletions affect the thermostability differently, they all increased the enzyme's affinity for starch. The possible reasons for the increased thermostability and substrate binding affinity, due to the removal of the four C-terminal glycine-rich repeats, are discussed in terms of the three-dimensional structure of beta-amylase.Yue F. Ma, Jason K. Eglinton, D. Evan Evans, Sue J. Logue, and Peter Langridg
Biomarker constraints on Mediterranean climate and ecosystem transitions during the Early-Middle Miocene
No full textWater uptake in barley grain: physiology; genetics and industrial applications
No full textAbstract not availableSuong Cu, Helen M. Collins, Natalie S. Betts, Timothy J. March, Agnieszka Janusz, Doug C. Stewart, Birgitte Skadhauge, Jason Eglinton, Bianca Kyriacou, Alan Little, Rachel A. Burton, Geoffrey B. Finche
The radiocarbon age of organic carbon in marine surface sediments
No full textAuthor Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 74 (2010): 6788-6800, doi:10.1016/j.gca.2010.09.001.Long-term carbon cycling and climate change are strongly dependent on organic carbon
(OC) burial in marine sediments. Radiocarbon (14C) has been widely used to constrain the
sources, sinks, and processing of sedimentary OC. To elucidate the dominant controls on the
radiocarbon content of total organic carbon (14CTOC) accumulating in surface sediments we
construct a box model that predicts 14CTOC in the sediment mixed layer (measured as fraction
modern, Fm). Our model defines three distinct OC pools (“degradable,” “semi-labile,” and
“refractory”) and assumes that 14CTOC flux to sediments is exclusively derived from surface
ocean primary productivity, and hence follows a “generic” surface ocean dissolved inorganic
carbon (DIC) bomb curve. Model predictions are compared to a set of 75 surface sediment
samples, which span a wide geographic range and reflect diverse water column and depositional
conditions, and for which sedimentation rate and mixed layer depth are well characterized. Our
model overestimates the Fm value for a majority (65%) of these sites, especially at shallow water
depths and for sites characterized by depleted δ13CTOC values. The model is most sensitive to
sedimentation rate and mixed-layer depth. Therefore, slight changes to these parameters can lead
to a match between modeled and measured Fm values at many sites. Because of model
sensitivity, slight changes in sedimentation rate and mixed layer depth can allow predictions to
match measured Fm at many sites. Yet, in some cases, we find that measured Fm values cannot
be simulated without large and unrealistic changes to sedimentation rate and mixed layer depth.
These results point to sources of pre-aged OC to surface sediments and implicate soil-derived
terrestrial OC, reworked marine OC, and/or anthropogenic carbon as important components of
the organic matter present in surface sediments. This approach provides a valuable framework within which to explore controls on sedimentary organic matter composition and carbon burial
over a range of spatial and temporal scales.This work was supported
by NSF grants OCE-0526389 (W. Martin), OCE-0851350 and OCE-0402533 (T. Eglinton), as
well as WHOI Senior Scientist Chair and Independent Study Award funds (T. Eglinton)
Compositional heterogeneity within oceanic particulate organic matter
No full textThesis (Ph. D.)--Joint Program in Oceanography, Massachusetts Institute of Technology/Woods Hole Oceanographic Institution, 1998.Includes bibliographical references.by Elizabeth C. Minor.Ph.D
Methane oxidation and emission in Lake Lugano (Southern Switzerland) : a lipid biomarker and isotopic approach
No full textMethane is an important greenhouse gas in Earth's atmosphere. The sources of atmospheric methane are largely biogenic, being produced under anoxic conditions by methanogenic Archaea. Wetlands, which include lakes, are important contributors to the atmospheric methane budget, since they commonly feature anoxic sediments or bottom water. Methane oxidising bacteria at the interface between oxic and anoxic sediments and water limit the efflux of methane. Furthermore, in the oceans, methane is oxidised anaerobically by Archaea, in a process coupled to sulfate reduction. In freshwater environments, where sulfate concentrations are orders of magnitude lower, this process is not thermodynamically favourable, and archaeal anaerobic oxidation of methane is often absent. It has been proposed in certain lake environments, however, that anaerobic oxidation of methane does take place.
One lake in which anaerobic oxidation of methane was proposed is the northern basin of Lake Lugano, southern Switzerland. Anaerobic oxidation of methane in this basin is explored in chapter 2 of this PhD thesis. Indeed we found methane concentration and carbon isotopic composition profiles characteristic of methane oxidation in the anoxic hypolimnion, more than 30 m below the interface between the oxic and anoxic waters. In addition, microbial biomass at these depths showed carbon isotope signatures of methane-derived carbon (d13C-values as low as -70‰ in C16:1 fatty acids), indicating that methane is used as a carbon source. However, no methane oxidation took place in incubation experiments under anoxic conditions. Addition of alternative potential electron acceptors did not stimulate methane oxidation, and methane oxidation was only observed in the presence of oxygen. Instead, we propose that episodic introduction of oxygenated water into the anoxic hypolimnion sustains a community of aerobic methanotrophs.
Carbon derived from methane oxidation has been shown in several studies to constitute an important carbon input to aquatic ecosystems. In the studies reported in chapters 2 and 3, compound specific stable carbon isotope analysis of lipid biomarkers was used to trace methane-derived carbon through the ecosystems at redox interfaces and in the anoxic hypolimnion of Lake Lugano. In the monomictic southern basin (chapter 3), an anoxic benthic nepheloid layer develops during the period of water column stratification. This layer was found to be derived from microbial production in the hypolimnion. Methane oxidising bacteria constituted up to 30% of total microbial cell numbers in the nepheloid layer, and 77% to 96% of the organic carbon in this layer was methane-derived. High rates of aerobic methane oxidation at the top of the anoxic nepheloid layer led to an oxygen consumption that was greater than the downward diffusion, causing the anoxic nepheloid layer to expand. Bacterial aerobic methanotrophs migrate upwards through the water column with the interface between the oxic hypolimnion and the anoxic nepheloid layer.
The extent of emission of methane to the atmosphere depends on the totality of sinks and sources in the lake basin. In both the northern and the southern basin of Lake Lugano, large amounts of methane are emitted from the sediments into the bottom water. However, consumption by aerobic methanotrophs at the oxic-anoxic redoxcline is near complete, and during stratified conditions, no methane escapes to the epilimnion. On the other hand, methane super-saturation in the surface water was observed throughout the year. Chapter 4 describes the results of three mapping campaigns of surface water methane concentrations in the northern basin of Lake Lugano, in spring and autumn. Additionally, methane concentration and carbon isotopic composition were measured on depth profiles down to 40 m depth in transects across the lake basin. Methane fluxes to the atmosphere were calculated from surface water concentration and wind speed. At a standardised wind speed of 1.6 m s-1 (average wind speed during the period from May until October) fluxes to the atmosphere were significantly higher in autumn (44 and 97 micromol m-2 d-1 in October 2011 and October 2012, respectively) than in spring (7 micromol m-2 d-1, May 2012). This difference is in part due to higher concentrations in autumn than in spring, and in part a result of a stronger dependence of the transfer velocity on buoyancy flux when the surface water cools. The source of methane in the surface water could not be determined with certainty. It is possible that internal waves at the thermocline induce friction at the sediment-water interface in the littoral zone, which leads to increased outgassing of sedimentary methane. However, the northern basin of Lake Lugano has steep shores along large parts of the basin, which offer little space for deposition of sediments, and the possibility of in situ production of methane in the water column must be considered
On the stratigraphic integrity of leaf-wax biomarkers in loess paleosols
No full textPaleoenvironmental and paleoclimate reconstructions based on molecular
proxies, such as those derived from leaf-wax biomarkers, in loess-paleosol
sequences represent a promising line of investigation in Quaternary research.
The main premise of such reconstructions is the synsedimentary deposition of
biomarkers and dust, which has become a debated subject in recent years. This
study uses two independent approaches to test the stratigraphic integrity of
leaf-wax biomarkers: (i) long-chain n-alkanes and fatty acids are
quantified in two sediment-depth profiles in glacial till on the Swiss
Plateau, consisting of a Holocene topsoil and the underlying B and C
horizons. Since glacial sediments are initially very poor in organic matter,
significant amounts of leaf-wax biomarkers in the B and C horizons of those
profiles would reflect postsedimentary root-derived or microbial
contributions. (ii) Compound-specific radiocarbon measurements are conducted
on n-alkanes and n-alkanoic (fatty) acids from several depth intervals in
the loess section "Crvenka", Serbia, and the results are compared to
independent estimates of sediment age.
We find extremely low concentrations
of plant-wax n-alkanes and fatty acids in the B and C horizons below the
topsoils in the sediment profiles. Moreover, compound-specific radiocarbon
analysis yields plant-wax 14C ages that agree well with published
luminescence ages and stratigraphy of the Serbian loess deposit. Both
approaches confirm that postsedimentary, root-derived or microbial
contributions are negligible in the two investigated systems. The good
agreement between the ages of odd and even homologues also indicates that
reworking and incorporation of fossil leaf waxes is not particularly relevant
either
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