Summons Roger E.

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Summons
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Roger E.
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  • Preprint
    Organic geochemistry of the early Toarcian oceanic anoxic event in Hawsker Bottoms, Yorkshire, England
    ( 2013-12) French, Katherine L. ; Sepulveda, Julio ; Trabucho-Alexandre, J. ; Grocke, Darren R. ; Summons, Roger E.
    A comprehensive organic geochemical investigation of the Hawsker Bottoms outcrop section in Yorkshire, England has provided new insights about environmental conditions leading into and during the Toarcian oceanic anoxic event (T-OAE; ~183 Ma). Rock-Eval and molecular analyses demonstrate that the section is uniformly within the early oil window. Hydrogen index (HI), organic petrography, polycyclic aromatic hydrocarbon (PAH) distributions, and tricyclic terpane ratios mark a shift to a lower relative abundance of terrigenous organic matter supplied to the sampling locality during the onset of the T-OAE and across a lithological transition. Unlike other ancient intervals of anoxia and extinction, biomarker indices of planktonic community structure do not display major changes or anomalous values. Depositional environment and redox indicators support a shift towards more reducing conditions in the sediment porewaters and the development of a seasonally stratified water column during the T-OAE. In addition to carotenoid biomarkers for green sulfur bacteria (GSB), we report the first occurrence of okenane, a marker of purple sulfur bacteria (PSB), in marine samples younger than ~1.64 Ga. Based on modern observations, a planktonic source of okenane’s precursor, okenone, would require extremely shallow photic zone euxinia (PZE) and a highly restricted depositional environment. However, due to coastal vertical mixing, the lack of planktonic okenone production in modern marine sulfidic environments, and building evidence of okenone production in mat-dwelling Chromatiaceae, we propose a sedimentary source of okenone as an alternative. Lastly, we report the first parallel compound-specific δ13C record in marine- and terrestrial-derived biomarkers across the T-OAE. The δ13C records of short-chain n-alkanes, acyclic isoprenoids, and long-chain n-alkanes all encode negative carbon isotope excursions (CIEs), and together, they support an injection of isotopically light carbon that impacted both the atmospheric and marine carbon reservoirs. To date, molecular δ13C records of the T-OAE display a negative CIE that is smaller in magnitude compared to the bulk organic δ13C excursion. Although multiple mechanisms could explain this observation, our molecular, petrographic, and Rock-Eval data suggest that variable mixing of terrigenous and marine organic matter is an important factor affecting the bulk organic δ13C records of the T-OAE.
  • Preprint
    Rapid, high-resolution C-14 chronology of ooids
    ( 2015-03) Beaupre, Steven R. ; Roberts, Mark L. ; Burton, Joshua R. ; Summons, Roger E.
    Ooids are small, spherical to ellipsoidal grains composed of concentric layers of CaCO3 that could potentially serve as biogeochemical records of the environments in which they grew. Such records, however, must be placed in the proper temporal context. Therefore, we developed a novel acidification system and employed an accelerator mass spectrometer (AMS) with a gas accepting ion source to obtain radiocarbon (14C) chronologies extending radially through ooids within one 8-hour workday. The method was applied to ooids from Highborne Cay, Bahamas and Shark Bay, Australia, yielding reproducible 14C chronologies, as well as constraints on the rates and durations of ooid growth and independent estimates of local 14C reservoir ages.
  • Preprint
    Insights into foraminiferal influences on microfabrics of microbialites at Highborne Cay, Bahamas
    ( 2013-03-15) Bernhard, Joan M. ; Edgcomb, Virginia P. ; Visscher, Pieter T. ; McIntyre-Wressnig, Anna ; Summons, Roger E. ; Bouxsein, Mary L. ; Louis, Leeann ; Jeglinski, Marleen
    Microbialites, which are organosedimentary structures formed by microbial communities through binding and trapping and/or in situ precipitation, have a wide array of distinctive morphologies and long geologic record. The origin of morphological variability is hotly debated; elucidating the cause or causes of microfabric differences could provide insights into ecosystem functioning and biogeochemistry during much of Earth’s history. Although rare today, morphologically distinct, co-occurring extant microbialites provide the opportunity to examine and compare microbial communities that may be responsible for establishing and modifying microbialite microfabrics. Highborne Cay, Bahamas, has extant laminated (i.e., stromatolites) and clotted (i.e., thrombolites) marine microbialites in close proximity, allowing focused questions about how community composition relates to physical attributes. Considerable knowledge exists about prokaryotic composition of microbialite mats (i.e., stromatolitic and thrombolitic mats) but little is known about their eukaryotic communities, especially regarding heterotrophic taxa. Thus, the heterotrophic eukaryotic communities of Highborne stromatolites and thrombolites were studied. Here, we show that diverse foraminiferal communities inhabit microbialite mat surfaces and subsurfaces, thecate foraminifera are relatively abundant in all microbialite types, especially thrombolitic mats, foraminifera stabilize grains in mats, and thecate reticulopod activities can impact stromatolitic mat lamination. Accordingly, and in light of foraminiferal impacts on modern microbialites, our results indicate that the microbialite fossil record may reflect the impact of the radiation of these protists.
  • Article
    Signature lipids and stable carbon isotope analyses of Octopus Spring hyperthermophilic communities compared with those of aquificales representatives
    (American Society for Microbiology, 2001-11) Jahnke, Linda L. ; Eder, Wolfgang ; Huber, Robert ; Hope, Janet M. ; Hinrichs, Kai-Uwe ; Hayes, John M. ; Des Marais, David J. ; Cady, Sherry L. ; Summons, Roger E.
    The molecular and isotopic compositions of lipid biomarkers of cultured Aquificales genera have been used to study the community and trophic structure of the hyperthermophilic pink streamers and vent biofilm from Octopus Spring. Thermocrinis ruber, Thermocrinis sp. strain HI 11/12, Hydrogenobacter thermophilus TK-6, Aquifex pyrophilus, and Aquifex aeolicus all contained glycerol-ether phospholipids as well as acyl glycerides. The n-C20:1 and cy-C21 fatty acids dominated all of the Aquificales, while the alkyl glycerol ethers were mainly C18:0. These Aquificales biomarkers were major constituents of the lipid extracts of two Octopus Spring samples, a biofilm associated with the siliceous vent walls, and the well-known pink streamer community (PSC). Both the biofilm and the PSC contained mono- and dialkyl glycerol ethers in which C18 and C20 alkyl groups were prevalent. Phospholipid fatty acids included both the Aquificales n-C20:1 and cy-C21, plus a series of iso-branched fatty acids (i-C15:0 to i-C21:0), indicating an additional bacterial component. Biomass and lipids from the PSC were depleted in 13C relative to source water CO2 by 10.9 and 17.2per thousand , respectively. The C20-21 fatty acids of the PSC were less depleted than the iso-branched fatty acids, 18.4 and 22.6per thousand , respectively. The biomass of T. ruber grown on CO2 was depleted in 13C by only 3.3per thousand relative to C source. In contrast, biomass was depleted by 19.7per thousand when formate was the C source. Independent of carbon source, T. ruber lipids were heavier than biomass (+1.3per thousand ). The depletion in the C20-21 fatty acids from the PSC indicates that Thermocrinis biomass must be similarly depleted and too light to be explained by growth on CO2. Accordingly, Thermocrinis in the PSC is likely to have utilized formate, presumably generated in the spring source region.
  • Preprint
    Diagenetic and detrital origin of moretane anomalies through the Permian–Triassic boundary
    ( 2011-11-22) French, Katherine L. ; Tosca, Nicholas J. ; Cao, Changqun ; Summons, Roger E.
    Many biogeochemical anomalies coincide with the Late 1 Permian Extinction (LPE; 252.28 Ma). Several mechanisms have been proposed to explain the moretane/hopane anomaly that has been identified in samples from Meishan GSSP section in southeastern China. Here, we report homohopane, 2α- and 3β- methylhomohopane and lithological data for a drill core from the Meishan section in southeastern China. Three intervals of elevated C30 moretane/hopane ratios are recorded in the Lungtan, Yinkeng and Helongshan Formations. Moretane/hopane ratios of C31-34 homohopanes and the 2α- and 3β-methylhomohopanes display the same stratigraphic patterns as the C30 moretane/hopane record. In light of the multiple and parallel moretane anomalies for the homohopane and 2α- and 3β-methylhomohopane series, enhanced input from higher plant organic matter, such as coal and peat, does not adequately explain the observed isomer patterns. Correlation of high moretane/hopane ratios with low C35 HHI and high hopane/sterane values suggest increased input of hopanoids from oxic soils. Additionally, moretane/hopane ratios show excellent correlations with total clay percentages and specific clay types, particularly chlorite, illite, and mixed layer illite/smectite. We conclude that a combination of episodic hopanoid input from soil bacteria and diagenetic effects related to redox and detrital clays generated the unique moretane/hopane patterns at Meishan. Similar relationships of Ts/(Ts+Tm) with redox and source indicators and lithology indicate that Ts/(Ts+Tm) is affected by the same factors controlling the moretane/hopane ratios. Berthierine, a clay that requires reducing conditions for formation, was detected in samples from the Lungtan Formation. We are unable to determine from our results whether the berthierine is authigenic or detrital, but future determination of the origin of berthierine at Meishan may offer additional environmental insight. No link between diasteranes and lithology was observed in this study suggesting that diasteranes are relatively unaffected by the detrital clay component of the Meishan sediments. In total, the results point toward the complex role of source input, lithology, and depositional redox conditions in the transformation of organic matter during maturation. Future work is required to elucidate the lithological effects on diagenetic processes, including biomarker genesis isomerization, and thermal degradation.
  • Article
    An interlaboratory study of TEX86 and BIT analysis of sediments, extracts, and standard mixtures
    (John Wiley & Sons, 2013-12-20) Schouten, Stefan ; Hopmans, Ellen C. ; Rosell-Mele, Antoni ; Pearson, Ann ; Adam, Pierre ; Bauersachs, Thorsten ; Bard, Edouard ; Bernasconi, Stefano M. ; Bianchi, Thomas S. ; Brocks, Jochen J. ; Carlson, Laura Truxal ; Castaneda, Isla S. ; Derenne, Sylvie ; Selver, Ayca Dogrul ; Dutta, Koushik ; Eglinton, Timothy I. ; Fosse, Celine ; Galy, Valier ; Grice, Kliti ; Hinrichs, Kai-Uwe ; Huang, Yongsong ; Huguet, Arnaud ; Huguet, Carme ; Hurley, Sarah ; Ingalls, Anitra ; Jia, Guodong ; Keely, Brendan ; Knappy, Chris ; Kondo, Miyuki ; Krishnan, Srinath ; Lincoln, Sara ; Lipp, Julius S. ; Mangelsdorf, Kai ; Martínez-Garcia, Alfredo ; Menot, Guillemette ; Mets, Anchelique ; Mollenhauer, Gesine ; Ohkouchi, Naohiko ; Ossebaar, Jort ; Pagani, Mark ; Pancost, Richard D. ; Pearson, Emma J. ; Peterse, Francien ; Reichart, Gert-Jan ; Schaeffer, Philippe ; Schmitt, Gaby ; Schwark, Lorenz ; Shah, Sunita R. ; Smith, Richard W. ; Smittenberg, Rienk H. ; Summons, Roger E. ; Takano, Yoshinori ; Talbot, Helen M. ; Taylor, Kyle W. R. ; Tarozo, Rafael ; Uchida, Masao ; van Dongen, Bart E. ; Van Mooy, Benjamin A. S. ; Wang, Jinxiang ; Warren, Courtney ; Weijers, Johan W. H. ; Werne, Josef P. ; Woltering, Martijn ; Xie, Shucheng ; Yamamoto, Masanobu ; Yang, Huan ; Zhang, Chuanlun L. ; Zhang, Yige ; Zhao, Meixun ; Sinninghe Damste, Jaap S.
    Two commonly used proxies based on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) are the TEX86 (TetraEther indeX of 86 carbon atoms) paleothermometer for sea surface temperature reconstructions and the BIT (Branched Isoprenoid Tetraether) index for reconstructing soil organic matter input to the ocean. An initial round-robin study of two sediment extracts, in which 15 laboratories participated, showed relatively consistent TEX86 values (reproducibility ±3–4°C when translated to temperature) but a large spread in BIT measurements (reproducibility ±0.41 on a scale of 0–1). Here we report results of a second round-robin study with 35 laboratories in which three sediments, one sediment extract, and two mixtures of pure, isolated GDGTs were analyzed. The results for TEX86 and BIT index showed improvement compared to the previous round-robin study. The reproducibility, indicating interlaboratory variation, of TEX86 values ranged from 1.3 to 3.0°C when translated to temperature. These results are similar to those of other temperature proxies used in paleoceanography. Comparison of the results obtained from one of the three sediments showed that TEX86 and BIT indices are not significantly affected by interlaboratory differences in sediment extraction techniques. BIT values of the sediments and extracts were at the extremes of the index with values close to 0 or 1, and showed good reproducibility (ranging from 0.013 to 0.042). However, the measured BIT values for the two GDGT mixtures, with known molar ratios of crenarchaeol and branched GDGTs, had intermediate BIT values and showed poor reproducibility and a large overestimation of the “true” (i.e., molar-based) BIT index. The latter is likely due to, among other factors, the higher mass spectrometric response of branched GDGTs compared to crenarchaeol, which also varies among mass spectrometers. Correction for this different mass spectrometric response showed a considerable improvement in the reproducibility of BIT index measurements among laboratories, as well as a substantially improved estimation of molar-based BIT values. This suggests that standard mixtures should be used in order to obtain consistent, and molar-based, BIT values.
  • Preprint
    Active eukaryotes in microbialites from Highborne Cay, Bahamas, and Hamelin Pool (Shark Bay), Australia
    ( 2013-06-26) Edgcomb, Virginia P. ; Bernhard, Joan M. ; Summons, Roger E. ; Orsi, William D. ; Beaudoin, David J. ; Visscher, Pieter T.
    Microbialites are organosedimentary structures that are formed through the interaction of benthic microbial communities and sediments and include mineral precipitation. These lithifying microbial mat structures include stromatolites and thrombolites. Exuma Sound in the Bahamas, and Hamelin Pool in Shark Bay, Western Australia are two locations where significant stands of modern microbialites exist. Although prokaryotic diversity in these structures is reasonably well documented, little is known about the eukaryotic component of these communities and their potential to influence sedimentary fabrics through grazing, binding and burrowing activities. Accordingly, comparisons of eukaryotic communities in modern stromatolitic and thrombolytic mats can potentially provide insight into the coexistence of both laminated and clotted mat structures in close proximity to one another. Here we examine this possibility by comparing eukaryotic diversity based on Sanger and high-throughput pyrosequencing of small subunit ribosomal RNA (18S rRNA) genes. Analyses were based on total RNA extracts as template to minimize input from inactive or deceased organisms. Results identified diverse eukaryotic communities particularly stramenopiles, Alveolata, Metazoa, Amoebozoa, and Rhizaria within different mat types at both locations, as well as abundant and diverse signatures of eukaryotes with <80% sequence similarity to sequences in GenBank. This suggests presence of significant novel eukaryotic diversity, particularly in hypersaline Hamelin Pool. There was evidence of vertical structuring of protist populations and foraminiferal diversity was highest in bioturbated/clotted thrombolite mats of Highborne Cay.