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  • 2020-2024  (34)
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  • 1
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    In situ neutron diffraction for analysing complex coarse‐grained functional materials (2023)
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Details
    Publication Date: 2023-10-24
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Complex functional materials play a crucial role in a broad range of energy‐related applications and in general for materials science. Revealing the structural mechanisms is challenging due to highly correlated coexisting phases and microstructures, especially for 〈italic〉in situ〈/italic〉 or 〈italic〉operando〈/italic〉 investigations. Since the grain sizes influence the properties, these microstructural features further complicate investigations at synchrotrons due to the limitations of illuminated sample volumes. In this study, it is demonstrated that such complex functional materials with highly correlated coexisting phases can be investigated under 〈italic〉in situ〈/italic〉 conditions with neutron diffraction. For large grain sizes, these experiments are valuable methods to reveal the structural mechanisms. For an example of 〈italic〉in situ〈/italic〉 experiments on barium titanate with an applied electric field, details of the electric‐field‐induced phase transformation depending on grain size and frequency are revealed. The results uncover the strain mechanisms in barium titanate and elucidate the complex interplay of stresses in relation to grain sizes as well as domain‐wall densities and mobilities.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉This work reports 〈italic〉in situ〈/italic〉 neutron diffraction experiments on a broad range of grain sizes of barium titanate. The study reveals the grain‐size‐dependent strain mechanisms and shows the competitiveness of neutron diffraction with high‐resolution synchrotron diffraction.〈boxed-text position="anchor" content-type="graphic" xml:lang="en"〉〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:16005767:jcr2vb5054:jcr2vb5054-fig-0001"〉 〈alt-text〉image〈/alt-text〉 〈/graphic〉〈/boxed-text〉〈/p〉
    Keywords: ddc:550.724 ; ddc:548 ; neutron diffraction ; in situ ; applied electric fields ; barium titanate ; strain mechanisms ; grain sizes ; complex functional materials ; microstructures ; coexisting phases
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 2
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    Glacial heterogeneity in Southern Ocean carbon storage abated by fast South Indian deglacial carbon release (2020)
    Nature Research
    Details
    Publication Date: 2023-02-08
    Description: Past changes in ocean 14C disequilibria have been suggested to reflect the Southern Ocean control on global exogenic carbon cycling. Yet, the volumetric extent of the glacial carbon pool and the deglacial mechanisms contributing to release remineralized carbon, particularly from regions with enhanced mixing today, remain insufficiently constrained. Here, we reconstruct the deglacial ventilation history of the South Indian upwelling hotspot near Kerguelen Island, using high-resolution 14C-dating of smaller-than-conventional foraminiferal samples and multi-proxy deep-ocean oxygen estimates. We find marked regional differences in Southern Ocean overturning with distinct South Indian fingerprints on (early de-)glacial atmospheric CO2 change. The dissipation of this heterogeneity commenced 14.6 kyr ago, signaling the onset of modern-like, strong South Indian Ocean upwelling, likely promoted by rejuvenated Atlantic overturning. Our findings highlight the South Indian Ocean’s capacity to influence atmospheric CO2 levels and amplify the impacts of inter-hemispheric climate variability on global carbon cycling within centuries and millennia.
    Type: Article , PeerReviewed
    Format: text
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    PAPER (OCEANREP)
  • 3
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    The Southern Ocean during the ice ages: A review of the Antarctic surface isolation hypothesis, with comparison to the North Pacific (2021)
    Elsevier
    Details
    Publication Date: 2021-02-01
    Print ISSN: 0277-3791
    Electronic ISSN: 1873-457X
    Topics: Geography , Geosciences
    Published by Elsevier
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    PAPER CURRENT
  • 4
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    Foraminifera-bound nitrogen isotope data from eastern equatorial Pacific cores ME-24 and ME-27 back to the last ice age (2020)
    PANGAEA
    Details
    Publication Date: 2023-10-05
    Description: Previous paleoceanographic applications of the N isotopes in the eastern equatorial Pacific have used the N isotopic composition of the bulk sediment, which can be biased by diagenetic alteration or foreign N input. To avoid these biases, we measured foraminifera shell-bound d15N (FB-d15N) on the two species Neogloboquadrina dutertrei and Neogloboquadrina incompta in two sediment cores extending back to the last ice age. The datafile contains FB-d15N data measured on the two sediment cores ME0005-24JC (0°1.3' N, 86°27.8' W, 2941m) and ME0005-27JC (1°51.2' S, 82°47.2'W, 2203m) from the eastern equatorial Pacific, as well as updated age models for the two sediment cores. Moreover, it contains estimated changes in Pacific oxygen concentration from the LGM to the Holocene. The age models for both sediment cores have been updated by Dubois et al. (2014) and are based on (1) radiocarbon ages measured on the planktonic foraminifera N. dutertrei by accelerator mass spectrometry, (2) correlation of benthic foraminifera oxygen isotopes to the LR04 stack and (3) the identification of the Los Chocoyos Ash Layer in the sediment cores. In core ME0005-27JC, three additional 14C dates on N. dutertrei from Mekik (2014) were included. All radiocarbon ages were calibrated with Calib 7.1. and the marine calibration curve MARINE13, assuming a reservoir age of 467 years as given in Dubois et al. (2014). Ages were linearly interpolated between the stratigraphic tie points. Foraminifera-bound d15N (FB-d15N) was measured with the “persulfate-denitrifier” technique (Ren et al., 2009; Straub et al., 2013). In short, ~3-5 mg of foraminifera (N. dutertrei and N. incompta from the 300-600µm size fraction) were picked, cut open with a scalpel and underwent a chemical cleaning. The organic N bound within the calcite was then released by dissolution with HCl and converted to nitrate in a basic potassium persulfate solution. The nitrate concentration of the solution was determined by chemiluminescence, and an aliquot of the nitrate solution equivalent to 5nmol of N was converted to nitrous oxide (N2O) by denitrifying bacteria. The N isotopic composition of the N2O was measured with a custom continuous-flow system for N2O extraction and purification on-line to a Thermo MAT253 stable isotope mass spectrometer and referenced to air N2 using the international nitrate standards IAEA-N3 and USGS-34. The FB-d15N data were then corrected for the contribution of the oxidation procedural blank with an in-house aminocaproic acid standard of known isotopic composition. Changes in Pacific oxygen concentration from the LGM to the Holocene were calculated based on solubility changes as well as CYCLOPS box model results of Hain et al., (2010). Changes in oxygen saturation result from changes in temperature and salinity; changes in oxygen utilization result from a glacial shoaling of the Atlantic Meridional Overturning Circulation, enhanced nutrient consumption due to Subantarctic iron fertilization, reduced Antarctic surface-to-deep exchange and more complete Antarctic nutrient consumption. Oxygen utilization is calculated using O2:Pregenerated of -170:1 (Anderson and Sarmiento, 1994).
    Keywords: Eastern Equatorial Pacific; Foraminifera-bound nitrogen isotopes; Holocene; Last Glacial; suboxia; water column denitrification
    Type: Dataset
    Format: application/zip, 4 datasets
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    DATA PANGAEA
  • 5
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    Estimated changes in Pacific oxygen concentration (LGM-Holocene) (2020)
    PANGAEA
    Details
    Publication Date: 2023-10-05
    Keywords: Comment; Eastern Equatorial Pacific; Foraminifera-bound nitrogen isotopes; Holocene; Last Glacial; Oxygen, change; suboxia; water column denitrification
    Type: Dataset
    Format: text/tab-separated-values, 24 data points
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    DATA PANGAEA
  • 6
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    Age model tie points for sediment cores ME-24 and ME-27 (2020)
    PANGAEA
    Details
    Publication Date: 2023-10-05
    Keywords: Age, dated; Age, dated material; Age, dated standard deviation; Analytical method; Calendar age; Calendar age, maximum/old; Calendar age, minimum/young; Core; DEPTH, sediment/rock; Eastern Equatorial Pacific; Event label; Foraminifera-bound nitrogen isotopes; GC; Gravity corer; Holocene; Last Glacial; ME0005A; ME0005A-24JC; ME0005A-27JC; Melville; NEMO; Reference/source; Reservoir age; South Pacific Ocean; suboxia; water column denitrification
    Type: Dataset
    Format: text/tab-separated-values, 170 data points
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    DATA PANGAEA
  • 7
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    Foraminifera-bound nitrogen isotopes of sediment core ME0005-24JC (2020)
    PANGAEA
    Details
    Publication Date: 2023-11-25
    Keywords: AGE; Calculated; DEPTH, sediment/rock; Eastern Equatorial Pacific; Foraminifera-bound nitrogen isotopes; GC; Gravity corer; Holocene; interpolated; Last Glacial; ln-Nitrogen, total; ME0005A; ME0005A-24JC; Melville; NEMO; Neogloboquadrina dutertrei, δ15N, foraminifera-bound organic matter; Neogloboquadrina incompta, δ15N, foraminifera-bound organic matter; Nitrogen, total; South Pacific Ocean; suboxia; water column denitrification; δ15N; δ15N, bulk sediment; δ15N, foraminifera-bound organic matter
    Type: Dataset
    Format: text/tab-separated-values, 229 data points
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    DATA PANGAEA
  • 8
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    Foraminifera-bound nitrogen isotopes of sediment core ME0005-27JC (2020)
    PANGAEA
    Details
    Publication Date: 2023-11-25
    Keywords: AGE; Calculated; DEPTH, sediment/rock; Eastern Equatorial Pacific; Foraminifera-bound nitrogen isotopes; GC; Gravity corer; Holocene; interpolated; Last Glacial; ln-Nitrogen, total; ME0005A; ME0005A-27JC; Melville; NEMO; Neogloboquadrina dutertrei, δ15N, foraminifera-bound organic matter; Neogloboquadrina incompta, δ15N, foraminifera-bound organic matter; Nitrogen, total; South Pacific Ocean; suboxia; water column denitrification; δ15N; δ15N, bulk sediment; δ15N, foraminifera-bound organic matter
    Type: Dataset
    Format: text/tab-separated-values, 282 data points
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    DATA PANGAEA
  • 9
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    Radiocarbon and oxygen ventilation in the deep South Indian Ocean during the last deglaciation (2020)
    PANGAEA
    Details
    Publication Date: 2024-02-23
    Description: Past changes in ocean 14C disequilibria have been suggested to reflect the Southern Ocean control on global exogenic carbon cycling. Yet, the volumetric extent of the glacial carbon pool and the deglacial mechanisms contributing to release remineralized carbon, particularly from regions with enhanced mixing today, remain insufficiently constrained. Here, we reconstruct the deglacial ventilation history of the South Indian upwelling hotspot near Kerguelen Island, using high-resolution 14C-dating of smaller-than-conventional foraminiferal samples and multi-proxy deep-ocean oxygen estimates. We find marked regional differences in Southern Ocean overturning with distinct South Indian fingerprints on (early de-)glacial atmospheric CO2 change. The dissipation of this heterogeneity commenced 14.6 kyr ago, signaling the onset of modern-like, strong South Indian Ocean upwelling, likely promoted by rejuvenated Atlantic overturning. Our findings highlight the South Indian Ocean's capacity to influence atmospheric CO2 levels and amplify the impacts of inter-hemispheric climate variability on global carbon cycling within centuries and millennia.
    Keywords: Deglaciation; ocean circulation; radiocarbon; Termination; ventilation
    Type: Dataset
    Format: application/zip, 8 datasets
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    DATA PANGAEA
  • 10
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    Diatom-bound nitrogen isotope and TEX86L-SST records of MD12-3394 and MD11-3353 (2021)
    PANGAEA
    Details
    Publication Date: 2024-02-23
    Description: Previous studies suggest that, during the late Pleistocene ice ages, surface-deep exchange was somehow weakened in the Southern Ocean's Antarctic Zone (AZ), reducing the leakage of deeply sequestered CO2 and thus contributing to the lower atmospheric CO2 levels of the ice ages. To better understand the surface nutrient consumption in the Antarctic ocean during glacial intervals and its implication on atmospheric CO2 changes, we measured diatom-bound nitrogen isotopes (d15N_db) extending back to 150 thousand years ago (150ka) in two sediment cores in the Indian sector of the AZ. The data series include d15N_db, TEX86L-based SST, d18O of planktonic foraminifera Neogloboquadrina pachyderma (sin.), sediment Ba/Fe and the age model of MD12-3394 (48°23' S, 64°35' E, 2320m water depth), d15N_db and updated age model of MD11-3353 (50°34' S, 68°23' E, 1568m water depth), as well as the mean d15N_db of the two sediment cores, and the d15N_db offset calculated using the mean d15N_db and MD12-3394 d15N_db alone. The age model for MD12-3394 was based on 7 Holocene radiocarbon dates measured with planktonic foraminifera Neogloboquadrina pachyderma (sin.) and Globigerina bulloides hand-picked from the 〉 63µm fraction, and correlation of reconstructed SST by TEX86L to the Antarctic temperature stack (ATS) (adjusted to AICC2012 age scale) compiled from ice core data. Ages were linearly interpolated between the stratigraphic tie points. The age model of MD11-3353 is based on the age model published in Thöle et al. (2019), with modifications of the youngest age tie point and the tie point at Marine Isotope Stage (MIS) 5-6 transition, and two additional tie points during MIS 3 based on correlation of d15N_db to MD12-3394 d15N_db. Monte Carlo simulation and Kalman filter were combined to generate a mean d15N_db time series for the two sediment cores on a 500-year time grid, following the method in Wang et al. (2017). For the d15N_db offset, a linear fit was first applied to glacial (20-27 ka,140-155 ka) and interglacial (0-10 ka, 115-126 ka) extreme values of d15N_db (or calculated mean d15N_db) and ATS. Using this linear regression, we calculated the ATS-predicted d15N_db. The d15N_db offset was obtained by subtracting the ATS-predicted d15N_db from measured d15N_db (or calculated mean d15N_db).
    Keywords: Diatom; nitrogen isotope; Southern Ocean; TEX86
    Type: Dataset
    Format: application/zip, 9 datasets
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    DATA PANGAEA
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