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  • Radiocarbon  (3)
  • Seawater  (3)
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  • 1
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    Strontium isotopes in Chilean rivers : the flux of unradiogenic continental Sr to seawater (2009)
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2009. 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 Chemical Geology 268 (2009): 337-343, doi:10.1016/j.chemgeo.2009.09.013.
    Description: Analyses of Chilean river waters indicate that the average yield of unradiogenic Sr (~ 517 mol Sr km− 2 yr− 1, 87Sr/86Sr ~ 0.7057) from western South America (1,220,853 km2) into the southeastern Pacific Ocean is ~ 2–4 times higher than that from Iceland (~ 110 mol Sr km − 2 yr− 1, 87Sr/86Sr ~ 0.7025) and the Deccan traps, but lower than fluxes of unradiogenic Sr from ocean islands in the Lesser Antilles and Réunion. The Sr flux from western South America accounts for about 1.8% of the annual dissolved Sr delivered to the ocean via rivers. If Chilean rivers analyzed in this study accurately characterize runoff from western South America, active convergent continental margins release about as much unradiogenic Sr to seawater as a 0–1 Myr old mid-ocean ridge segment of equivalent length. Modulations of the flux of unradiogenic Sr from active margins over geologic time scales have to be considered as an additional driving force of change in the marine Sr isotope record, supplementing temporal variations in the submarine hydrothermal flux as a source of unradiogenic Sr to seawater. Such modulations can be driven by changes in the surface exposure of volcanic arc terrains, changes in climate, ocean currents and geographic latitude due to plate tectonics, as well as topographic changes that can affect local rainfall, runoff and erosion.
    Description: We acknowledge financial 302 support from NSF grant EAR-0519387, from WHOI’s Mary Sears Visitor Program, and thank the German DAAD for travel support for KF.
    Keywords: Strontium ; River ; Seawater ; Chile ; Andes ; Weathering
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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  • 2
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    Neodymium isotopes and concentrations in aragonitic scleractinian cold-water coral skeletons - modern calibration and evaluation of palaeo-applications (2017)
    Elsevier
    Details
    Publication Date: 2022-05-25
    Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Chemical Geology 453 (2017): 146–168, doi:10.1016/j.chemgeo.2017.01.022.
    Description: Cold-water corals (CWCs) are unique archives of mid-depth ocean chemistry and have been used successfully to reconstruct the neodymium (Nd) isotopic composition of seawater from a number of species. High and variable Nd concentrations in fossil corals however pose the question as to how Nd is incorporated into their skeletons. We here present new results on modern specimens of Desmophyllum dianthus, Balanophyllia malouinensis, and Flabellum curvatum, collected from the Drake Passage, and Madrepora oculata, collected from the North Atlantic. All modern individuals were either collected alive or uranium-series dated to be 〈 500 years old for comparison with local surface sediments and seawater profiles. Modern coral Nd isotopic compositions generally agree with ambient seawater values, which in turn are consistent with previously published seawater analyses, supporting small vertical and lateral Nd isotope gradients in modern Drake Passage waters. Two Balanophyllia malouinensis specimens collected live however deviate by up to 0.6 epsilon units from ambient seawater. We therefore recommend that this species should be treated with caution for the reconstruction of past seawater Nd isotopic compositions. Seventy fossil Drake Passage CWCs were furthermore analysed for their Nd concentrations, revealing a large range from 7.3 to 964.5 ng/g. Samples of the species D. dianthus and Caryophyllia spp. show minor covariation of Nd with 232Th content, utilised to monitor contaminant phases in cleaned coral aragonite. Strong covariations between Nd and Th concentrations are however observed in the species B. malouinensis and G. antarctica. In order to better constrain the source and nature of Nd in the cleaned aragonitic skeletons, a subset of sixteen corals was investigated for its rare earth element (REE) content, as well as major and trace element geochemistry. Our new data provide supporting evidence that the applied cleaning protocol efficiently removes contaminant lithogenic and ferromanganese oxyhydroxide phases. Mass balance calculations and seawater-like REE patterns rule out lithogenic and ferromanganese oxyhydroxide phases as a major contributor to elevated Nd concentrations in coral aragonite. Based on mass balance considerations, geochemical evidence, and previously published independent work by solid-state nuclear magnetic resonance (NMR) spectroscopy, we suggest authigenic phosphate phases as a significant carrier of skeletal Nd. Such a carrier phase could explain sporadic appearance of high Nd concentrations in corals and would be coupled with seawater-derived Nd isotopic compositions, lending further confidence to the application of Nd isotopes as a water mass proxy in CWCs.
    Description: TvdF and TS acknowledge financial support for a bursary by the Grantham Institute of Climate Change and the Environment and a Marie Curie Reintegration grant (IRG 230828), as well as funding from the Leverhulme Trust (RPG-398) and the NERC (NE/N001141/1). Additional financial support was provided to LFR by the USGS-WHOI Co-operative agreement, NSF-ANT grants 0636787 and 80295700, The European Research Council, the Leverhulme Trust and a Marie Curie Reintegration grant. LB was supported by a NOAA/UCAR Climate and Global Change Postdoctoral Fellowship and KJM acknowledges funding from a Marie Curie International Outgoing fellowship (IOF 236962).
    Keywords: Neodymium isotopes ; Rare earth elements ; Cold-water corals ; Seawater ; Sediments ; Drake Passage
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
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    Low reservoir ages for the surface ocean from mid-Holocene Florida corals (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 23 (2008): PA2209, doi:10.1029/2007PA001527.
    Description: The 14C reservoir age of the surface ocean was determined for two Holocene periods (4908–4955 and 3008–3066 calendar (cal) B.P.) using U/Th-dated corals from Biscayne National Park, Florida, United States. We found that the average reservoir ages for these two time periods (294 ± 33 and 291 ± 27 years, respectively) were lower than the average value between A.D. 1600 and 1900 (390 ± 60 years) from corals. It appears that the surface ocean was closer to isotopic equilibrium with CO2 in the atmosphere during these two time periods than it was during recent times. Seasonal δ 18O measurements from the younger coral are similar to modern values, suggesting that mixing with open ocean waters was indeed occurring during this coral's lifetime. Likely explanations for the lower reservoir age include increased stratification of the surface ocean or increased Δ14C values of subsurface waters that mix into the surface. Our results imply that a more correct reservoir age correction for radiocarbon measurements of marine samples in this location from the time periods ∼3040 and ∼4930 cal years B.P. is ∼292 ± 30 years, less than the canonical value of 404 ± 20 years.
    Description: NSF Chemical Oceanography program provided monetary support under grants OCE-9711326, OCE-0137207, and OCE-0551940 (to ERMD).
    Keywords: Reservoir age ; Radiocarbon ; Corals
    Repository Name: Woods Hole Open Access Server
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  • 4
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    Dynamic intermediate ocean circulation in the North Atlantic during Heinrich Stadial 1 : a radiocarbon and neodymium isotope perspective (2015)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 29 (2014): 1072–1093, doi:10.1002/2014PA002674.
    Description: The last deglaciation was characterized by a series of millennial-scale climate events that have been linked to deep ocean variability. While often implied in interpretations, few direct constraints exist on circulation changes at mid-depths. Here we provide new constraints on the variability of deglacial mid-depth circulation using combined radiocarbon and neodymium isotopes in 24 North Atlantic deep-sea corals. Their aragonite skeletons have been dated by uranium-series, providing absolute ages and the resolution to record centennial-scale changes, while transects spanning the lifetime of a single coral allow subcentennial tracer reconstruction. Our results reveal that rapid fluctuations of water mass sourcing and radiocarbon affected the mid-depth water column (1.7–2.5 km) on timescales of less than 100 years during the latter half of Heinrich Stadial 1. The neodymium isotopic variability (−14.5 to −11.0) ranges from the composition of the modern northern-sourced waters towards more radiogenic compositions, suggesting the presence of a greater southern-sourced component at some times. However, in detail, simple two-component mixing between well-ventilated northern-sourced and radiocarbon-depleted southern-sourced water masses cannot explain all our data. Instead, corals from ~15.0 ka and ~15.8 ka may record variability between southern-sourced intermediate waters and radiocarbon-depleted northern-sourced waters, unless there was a major shift in the neodymium isotopic composition of the northern end-member. In order to explain the rapid shift towards the most depleted radiocarbon values at ~15.4 ka, we suggest a different mixing scenario involving either radiocarbon-depleted deep water from the Greenland-Iceland-Norwegian Seas or a southern-sourced deep water mass. Since these mid-depth changes preceded the Bolling-Allerod warming and were apparently unaccompanied by changes in the deep Atlantic, they may indicate an important role for the intermediate ocean in the early deglacial climate evolution.
    Description: This study was supported by Natural Environment Research Council grant NE/F016751/1, Marie Curie International Reintegration grant IRG 230828, and Leverhulme Trust grant RPG-398 to TvdF, as well as a Phillip Leverhulme Prize, Marie Curie International Reintegration Grant, and European Research Council grant to L.F.R.
    Description: 2015-05-20
    Keywords: Heinrich stadial ; Deglaciation ; Atlantic meridional overturning circulation ; Neodymium isotopes ; Radiocarbon ; Deep sea corals
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 5
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    Neodymium isotope analyses after combined extraction of actinide and lanthanide elements from seawater and deep-sea coral aragonite (2016)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 17 (2016): 232–240, doi:10.1002/2015GC006130.
    Description: Isotopes of the actinide elements protactinium (Pa), thorium (Th), and uranium (U), and the lanthanide element neodymium (Nd) are often used as complementary tracers of modern and past oceanic processes. The extraction of such elements from low abundance matrices, such as seawater and carbonate, is however labor-intensive and requires significant amounts of sample material. We here present a combined method for the extraction of Pa, Th, and Nd from 5 to 10 L seawater samples, and of U, Th, and Nd from 〈1 g carbonate samples. Neodymium is collected in the respective wash fractions of Pa-Th and U-Th anion exchange chromatographies. Regardless of the original sample matrix, Nd is extracted during a two-stage ion chromatography, followed by thermal ionization mass spectrometry (TIMS) analysis as NdO+. Using this combined procedure, we obtained results for Nd isotopic compositions on two GEOTRACES consensus samples from Bermuda Atlantic Time Series (BATS), which are within error identical to results for separately sampled and processed dedicated Nd samples (εNd = −9.20 ± 0.21 and −13.11 ± 0.21 for 15 and 2000 m water depths, respectively; intercalibration results from 14 laboratories: εNd = −9.19 ± 0.57 and −13.14 ± 0.57). Furthermore, Nd isotope results for an in-house coral reference material are identical within analytical uncertainty for dedicated Nd chemistry and after collection of Nd from U-Th anion exchange chromatography. Our procedure does not require major adaptations to independently used ion exchange chromatographies for U-Pa-Th and Nd, and can hence be readily implemented for a wide range of applications.
    Description: Funding that supported this work was received from the National Science Foundation (NSF 0752402), the Leverhulme Trust (RPG-398), the Natural Environmental Research Council (NE/J021636/1 and NE/N003861/1), the European Research Council (278705), and the Grantham Institute for Climate Change.
    Description: 2016-07-09
    Keywords: Deep-sea corals ; Seawater ; GEOTRACES ; Extraction methods ; Neodymium isotopes
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  • 6
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    Rapid radiocarbon (14C) analysis of coral and carbonate samples using a continuous-flow accelerator mass spectrometry (CFAMS) system (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 26 (2011): PA4212, doi:10.1029/2011PA002174.
    Description: Radiocarbon analyses of carbonate materials provide critical information for understanding the last glacial cycle, recent climate history and paleoceanography. Methods that reduce the time and cost of radiocarbon (14C) analysis are highly desirable for large sample sets and reconnaissance type studies. We have developed a method for rapid radiocarbon analysis of carbonates using a novel continuous-flow accelerator mass spectrometry (CFAMS) system. We analyzed a suite of deep-sea coral samples and compared the results with those obtained using a conventional AMS system. Measurement uncertainty is 〈0.02 Fm or 160 Ryr for a modern sample and the mean background was 37,800 Ryr. Radiocarbon values were repeatable and in good agreement with those from the conventional AMS system. Sample handling and preparation is relatively simple and the method offered a significant increase in speed and cost effectiveness. We applied the method to coral samples from the Eastern Pacific Ocean to obtain an age distribution and identify samples for further analysis. This paper is intended to update the paleoceanographic community on the status of this new method and demonstrate its feasibility as a choice for rapid and affordable radiocarbon analysis.
    Description: This work was performed under NSF Cooperative Agreement OCE‐0753487, and also NSF‐OPP awards 0636787 and 0944474.
    Keywords: 14C ; CFAMS ; Carbonate ; Coral ; Paleoceanography ; Radiocarbon
    Repository Name: Woods Hole Open Access Server
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