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  • 1
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    14C Blank Assessment in Small-Scale Compound-Specific Radiocarbon Analysis of Lipid Biomarkers and Lignin Phenols (2020)
    Cambridge Univ. Press
    In:  Radiocarbon, 62 (1). pp. 207-218.
    Details
    Publication Date: 2021-05-04
    Description: Compound-specific radiocarbon (14C) dating often requires working with small samples of 〈 100 µg carbon (µgC). This makes the radiocarbon dates of biomarker compounds very sensitive to biases caused by extraneous carbon of unknown composition, a procedural blank, which is introduced to the samples during the steps necessary to prepare a sample for radiocarbon analysis by accelerator mass spectrometry (i.e., isolating single compounds from a heterogeneous mixture, combustion, gas purification and graphitization). Reporting accurate radiocarbon dates thus requires a correction for the procedural blank. We present our approach to assess the fraction modern carbon (F14C) and the mass of the procedural blanks introduced during the preparation procedures of lipid biomarkers (i.e. n-alkanoic acids) and lignin phenols. We isolated differently sized aliquots (6–151 µgC) of n-alkanoic acids and lignin phenols obtained from standard materials with known F14C values. Each compound class was extracted from two standard materials (one fossil, one modern) and purified using the same procedures as for natural samples of unknown F14C. There is an inverse linear relationship between the measured F14C values of the processed aliquots and their mass, which suggests constant contamination during processing of individual samples. We use Bayesian methods to fit linear regression lines between F14C and 1/mass for the fossil and modern standards. The intersection points of these lines are used to infer F14Cblank and mblank and their associated uncertainties. We estimate 4.88 ± 0.69 μgC of procedural blank with F14C of 0.714 ± 0.077 for n-alkanoic acids, and 0.90 ± 0.23 μgC of procedural blank with F14C of 0.813 ± 0.155 for lignin phenols. These F14Cblank and mblank can be used to correct AMS results of lipid and lignin samples by isotopic mass balance. This method may serve as a standardized procedure for blank assessment in small-scale radiocarbon analysis.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1017/RDC.2019.108
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Relationships between grain size and organic carbon 14C heterogeneity in continental margin sediments (2019)
    Elsevier
    In:  Earth and Planetary Science Letters, 505 . pp. 76-85.
    Details
    Publication Date: 2022-01-31
    Description: Highlights • Continental margin-scale spatial variability in C values among grain size fractions is presented. • Two different hydrodynamic modes influencing in 14C heterogeneity are identified. • A new index (H14 index) is defined to describe overall 14C heterogeneity within marine surface sedimentary OC. Abstract The deposition and long-term burial of sedimentary organic matter (OM) on continental margins comprises a fundamental component of the global carbon cycle. A key unknown in interpretation of carbon isotope records of sedimentary OM is the extent to which OM accumulating in continental shelf and slope sediments is influenced by dispersal and redistribution processes. Here, we present results from an extensive survey of organic carbon (OC) characteristics of grain size fractions (ranging from 〈20 to 250 μm) retrieved from Chinese marginal sea surface sediments in order to assess the extent to which the abundance and isotope composition of OM in shallow shelf seas is influenced by hydrodynamic processes. Our findings show that contrasting relationships exist between 14C contents of OC and grain size in surface sediments associated with two different hydrodynamic modes, suggesting that transport pathways and mechanisms imparted by the different hydrodynamic conditions exert a strong influence on 14C contents of OM in continental shelf sediments. In deeper regions and erosional areas, we infer that bedload transport exerts the strongest influence on (decreases) OC 14C contents of the coarser fraction, while resuspension processes induce OC 14C depletion of intermediate grain size fractions in shallow inner-shelf settings. We use the inter-fraction spread in 14C values, defined here as 14H , to argue that the hydrodynamic processes amplify overall 14C heterogeneity within corresponding bulk sediment samples. The magnitude and footprint of this heterogeneity carries implications for our understanding of carbon cycling in shallow marginal seas.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.epsl.2018.10.013
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Understanding the role of the Biological Pump in the Global Carbon Cycle: An imperative for Ocean Science. (2014)
    Oceanography Society
    In:  EPIC3Oceanography, Oceanography Society, 27(3), pp. 10-16, ISSN: 1042-8275
    Details
    Publication Date: 2014-10-14
    Description: Anthropogenically driven climate change will rapidly become Earth's dominant transformative influence in the coming decades. The oceanic biological pump—the complex suite of processes that results in the transfer of particulate and dissolved organic carbon from the surface to the deep ocean—constitutes the main mechanism for removing CO2 from the atmosphere and sequestering carbon at depth on submillennium time scales. Variations in the efficacy of the biological pump and the strength of the deep ocean carbon sink, which is larger than all other bioactive carbon reservoirs, regulate Earth's climate and have been implicated in past glacial-​interglacial cycles. The numerous biological, chemical, and physical processes involved in the biological pump are inextricably linked and heterogeneous over a wide range of spatial and temporal scales, and they influence virtually the entire ocean ecosystem. Thus, the functioning of the oceanic biological pump is not only relevant to the modulation of Earth's climate but also constitutes the basis for marine biodiversity and key food resources that support the human population. Our understanding of the biological pump is far from complete. Moreover, how the biological pump and the deep ocean carbon sink will respond to the rapid and ongoing anthropogenic changes to our planet—including warming, acidification, and deoxygenation of ocean waters—remains highly uncertain. To understand and quantify present-day and future changes in biological pump processes requires sustained global observations coupled with extensive modeling studies supported by international scientific coordination and funding
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 4
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    Long-chain diols in rivers: distribution and potential biological sources (2018)
    In:  EPIC3Biogeosciences, 15(13), pp. 4147-4161, ISSN: 1726-4189
    Details
    Publication Date: 2018-09-10
    Description: Long-chain diols (LCDs) occur widespread in marine environments and also in lakes and rivers. Transport of LCDs from rivers may impact the distribution of LCDs in coastal environments, however relatively little is known about the distribution and biological sources of LCDs in river systems. In this study, we investigated the distribution of LCDs in suspended particulate matter (SPM) of three river systems (Godavari, Danube, and Rhine) in relation with precipitation, temperature, and source catchments. The dominant long-chain diol is the C32 1,15-diol followed by the C30 1,15-diol in all studied river systems. In regions influenced by marine waters, such as delta systems, the fractional abundance of the C30 1,15-diol is substantially higher than in the river itself, suggesting different LCD producers in marine and freshwater environments. A change in the LCD distribution along the downstream transects of the rivers studied was not observed. However, an effect of river flow is observed; i.e., the concentration of the C32 1,15-diol is higher in stagnant waters such as reservoirs and during seasons with river low stands. A seasonal change in the LCD distribution was observed in the Rhine, likely due to a change in the producers. Eukaryotic diversity analysis by 18S rRNA gene sequencing of SPM from the Rhine showed extremely low abundances of sequences (i.e., 〈0.32% of total reads) related to known algal LCD producers. Furthermore, incubation of the river water with 13C-labeled bicarbonate did not result in 13C incorporation into LCDs. This indicates that the LCDs present are mainly of fossil origin in the fast-flowing part of the Rhine. Overall, our results suggest that the LCD producers in rivers predominantly reside in lakes or side ponds that are part of the river system.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
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    14C Blank Assessment in Small-Scale Compound-Specific Radiocarbon Analysis of Lipid Biomarkers and Lignin Phenols (2020)
    In:  EPIC3Radiocarbon, 62(1), pp. 207-218, ISSN: 0033-8222
    Details
    Publication Date: 2021-06-21
    Description: Compound-specific radiocarbon (14C) dating often requires working with small samples of 〈 100 μg carbon (μgC). This makes the radiocarbon dates of biomarker compounds very sensitive to biases caused by extraneous carbon of unknown composition, a procedural blank, which is introduced to the samples during the steps necessary to prepare a sample for radiocarbon analysis by accelerator mass spectrometry (i.e., isolating single compounds from a heterogeneous mixture, combustion, gas purification and graphitization). Reporting accurate radiocarbon dates thus requires a correction for the procedural blank. We present our approach to assess the fraction modern carbon (F14C) and the mass of the procedural blanks introduced during the preparation procedures of lipid biomarkers (i.e. n-alkanoic acids) and lignin phenols. We isolated differently sized aliquots (6–151 μgC) of n-alkanoic acids and lignin phenols obtained from standard materials with known F14C values. Each compound class was extracted from two standard materials (one fossil, one modern) and purified using the same procedures as for natural samples of unknown F14C. There is an inverse linear relationship between the measured F14C values of the processed aliquots and their mass, which suggests constant contamination during processing of individual samples. We use Bayesian methods to fit linear regression lines between F14C and 1/mass for the fossil and modern standards. The intersection points of these lines are used to infer F14Cblank and mblank and their associated uncertainties. We estimate 4.88 ± 0.69 μgC of procedural blank with F14C of 0.714 ± 0.077 for n-alkanoic acids, and 0.90 ± 0.23 μgC of procedural blank with F14C of 0.813 ± 0.155 for lignin phenols. These F14Cblank and mblank can be used to correct AMS results of lipid and lignin samples by isotopic mass balance. This method may serve as a standardized procedure for blank assessment in small-scale radiocarbon analysis.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
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    Controls on the age of plant waxes in marine sediments – A global synthesis (2021)
    In:  EPIC3Organic Geochemistry, 157, pp. 104259, ISSN: 01466380
    Details
    Publication Date: 2021-06-21
    Description: Sedimentary high molecular weight (HMW) n-alkyl lipids derived from the waxes of terrestrial plants are common target compounds in biogeochemical and paleoenvironmental research. These plant waxes derive predominantly from the epicuticular cover of vascular plant leaves and their relative and absolute abundances and stable isotopic composition can be used as proxies to decipher, e.g., continental climate and land-ocean carbon transfer processes. In marine sediments, however, compound-specific radiocarbon analysis has revealed that plant waxes are often not syn-depositional, but instead are substantially 14C-depleted (‘pre-aged’) upon deposition. This 14C-depletion can be caused by various processes that either promote retention of plant waxes during transport from source to sink such as storage in soils or entrainment in deposition-resuspension loops in rivers and on continental shelves or, alternatively, by processes that add HMW n-alkyl lipids from other sources (e.g., petrogenic inputs). Here, we review the intrinsic and extrinsic processes affecting the sedimentary plant wax 14C composition (ranging from chemical processes to continental-scale environmental conditions), how plant wax 14C compositions translate into mean ages, and which processes control plant wax mean ages in marine sediments. Finally, we use a compilation of available and new compound-specific plant wax 14C data to provide a synthesis and evaluate the major controls on plant wax mean ages in marine sediments at the global scale.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 7
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    Tropical rainfall over the last two millennia: evidence for a low-latitude hydrologic seesaw (2017)
    In:  EPIC3Scientific Reports, 7, pp. 45809, ISSN: 2045-2322
    Details
    Publication Date: 2017-06-12
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 8
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    Compound-Specific Radiocarbon Measurements (2019)
    Elsevier
    In:  EPIC3Encyclopedia of Ocean Sciences, Encyclopedia of Ocean Sciences, Third Edition, Vol 1, Elsevier, 10 p., pp. 235-244, ISBN: 978-0-12-813081-0
    Details
    Publication Date: 2019-05-20
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , peerRev
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  • 9
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    High-sensitivity measurement of diverse vascular plant-derived biomarkers in high-altitude ice cores (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 36 (2009): L13501, doi:10.1029/2009GL037643.
    Description: Semi-volatile organic compounds derived from burned and fresh vascular plant sources and preserved in high-altitude ice fields were detected and identified through use of recently developed analytical tools. Specifically, stir bar sorptive extraction and thermal desorption coupled with gas chromatography/time-of-flight mass spectrometry allowed measurement of multiple biomarkers in small sample volumes (≤30 ml). Among other compounds of interest, several diterpenoids, which suggest inputs from conifers and conifer burning, were identified in post-industrial era and older Holocene ice from the Sajama site in the Bolivian Andes, but not in a glacial period sample, consistent with aridity changes. Differences in biomarker assemblages between sites support the use of these compounds as regionally constrained recorders of vegetation and climate change. This study represents the first application of these analytical techniques to ice core research and the first indication that records of vegetation fires may be reconstructed from diterpenoids in ice.
    Description: This project was supported in part by NSF-OCE (0402533), and NSF-EAR (0094475).
    Keywords: Biomass burning ; Molecular markers
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/postscript
    Format: application/pdf
    Format: text/plain
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  • 10
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    Blank assessment for ultra-small radiocarbon samples : chemical extraction and separation versus AMS (2011)
    Dept. of Geosciences, University of Arizona
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Arizona Board of Regents on behalf of the University of Arizona, 2010. This article is posted here by permission of Dept. of Geosciences, University of Arizona for personal use, not for redistribution. The definitive version was published in Radiocarbon 52 (2010): 1322-1335.
    Description: The Keck Carbon Cycle AMS facility at the University of California, Irvine (KCCAMS/UCI) has developed protocols for analyzing radiocarbon in samples as small as ~0.001 mg of carbon (C). Mass-balance background corrections for modern and 14C-dead carbon contamination (MC and DC, respectively) can be assessed by measuring 14C-free and modern standards, respectively, using the same sample processing techniques that are applied to unknown samples. This approach can be validated by measuring secondary standards of similar size and 14C composition to the unknown samples. Ordinary sample processing (such as ABA or leaching pretreatment, combustion/graphitization, and handling) introduces MC contamination of ~0.6 ± 0.3 μg C, while DC is ~0.3 ± 0.15 μg C. Today, the laboratory routinely analyzes graphite samples as small as 0.015 mg C for external submissions and ≅0.001 mg C for internal research activities with a precision of ~1% for ~0.010 mg C. However, when analyzing ultra-small samples isolated by a series of complex chemical and chromatographic methods (such as individual compounds), integrated procedural blanks may be far larger and more variable than those associated with combustion/graphitization alone. In some instances, the mass ratio of these blanks to the compounds of interest may be so high that the reported 14C results are meaningless. Thus, the abundance and variability of both MC and DC contamination encountered during ultra-small sample analysis must be carefully and thoroughly evaluated. Four case studies are presented to illustrate how extraction chemistry blanks are determined.
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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