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  • PANGAEA  (84)
  • Springer Nature  (4)
  • Copernicus  (1)
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  • 1
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    The Isotopx NGX and ATONA Faraday amplifiers (2020)
    Copernicus
    Details
    Publication Date: 2020-09-03
    Description: We installed the new Isotopx ATONA Faraday cup detector amplifiers on an Isotopx NGX mass spectrometer at Lamont-Doherty Earth Observatory in early 2018. The ATONA is a capacitive transimpedance amplifier, which differs from the traditional resistive transimpedance amplifier used on most Faraday detectors for mass spectrometry. Instead of a high-gain resistor, a capacitor is used to accumulate and measure charge. The advantages of this architecture are a very low noise floor, rapid response time, stable baselines, and very high dynamic range. We show baseline noise measurements and measurements of argon from air and cocktail gas standards to demonstrate the capabilities of these amplifiers. The ATONA exhibits a noise floor better than a traditional 1013 Ω amplifier in normal noble gas mass spectrometer usage, superior gain and baseline stability, and an unrivaled dynamic range that makes it practical to measure beams ranging in size from below 10−16 to above 10−9 A using a single amplifier.
    Print ISSN: 2628-3697
    Electronic ISSN: 2628-3719
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 2
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    Reduced North Atlantic Deep Water flux to the glacial Southern Ocean inferred from neodymium isotope ratios (2000)
    Springer Nature
    Details
    Publication Date: 2000-06-01
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Springer Nature
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  • 3
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    Abrupt changes in Antarctic Intermediate Water circulation over the past 25,000 years (2008)
    Springer Nature
    Details
    Publication Date: 2008-11-23
    Description: The circulation of Antarctic Intermediate Water is thought to make an important contribution to the global ocean-climate system, but the details of this interaction are not fully understood. Furthermore, the behaviour of Antarctic Intermediate Water under glacial and interglacial conditions is not well constrained. Here we present a 25,000-year-long record of neodymium isotopic variations a tracer of water-mass mixing from the middle depths of the tropical Atlantic Ocean. Our data reveal abruptly enhanced northward advection of Antarctic Intermediate Water during periods of reduced North Atlantic overturning circulation during the last deglaciation. These events coincide with an increase in the formation of Antarctic Intermediate Water and warming in the southwest Pacific Ocean, which suggests a tight link with Southern Hemisphere climate. In contrast, the initial incursion of southern source water into the North Atlantic 19,000 years ago coincided with weak Antarctic Intermediate Water formation in the Pacific and reduced overturning in the North Atlantic. We conclude that reduced competition at intermediate water depth at this time allowed expansion of Antarctic Intermediate Water into the North Atlantic. This early incursion of Antarctic Intermediate Water may have contributed to freshening of the North Atlantic, perhaps spurring the subsequent collapse of North Atlantic deep convection. © 2008 Macmillan Publishers Limited. All rights reserved.
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 4
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    Dynamic behaviour of the East Antarctic ice sheet during Pliocene warmth (2013)
    Springer Nature
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    Publication Date: 2013-07-21
    Description: Warm intervals within the Pliocene epoch (5.33-2.58 million years ago) were characterized by global temperatures comparable to those predicted for the end of this century and atmospheric CO 2 concentrations similar to today. Estimates for global sea level highstands during these times imply possible retreat of the East Antarctic ice sheet, but ice-proximal evidence from the Antarctic margin is scarce. Here we present new data from Pliocene marine sediments recovered offshore of Adélie Land, East Antarctica, that reveal dynamic behaviour of the East Antarctic ice sheet in the vicinity of the low-lying Wilkes Subglacial Basin during times of past climatic warmth. Sedimentary sequences deposited between 5.3 and 3.3 million years ago indicate increases in Southern Ocean surface water productivity, associated with elevated circum-Antarctic temperatures. The geochemical provenance of detrital material deposited during these warm intervals suggests active erosion of continental bedrock from within the Wilkes Subglacial Basin, an area today buried beneath the East Antarctic ice sheet. We interpret this erosion to be associated with retreat of the ice sheet margin several hundreds of kilometres inland and conclude that the East Antarctic ice sheet was sensitive to climatic warmth during the Pliocene. © 2013 Macmillan Publishers Limited. All rights reserved.
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 5
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    The contribution of glacial erosion to shaping the hidden landscape of East Antarctica (2013)
    Springer Nature
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    Publication Date: 2013-02-10
    Description: The subglacial topography in East Antarctica has been revealed by airborne radar surveys1-3. However, how this ice-hidden landscape has evolved over time is less well known2-12. Low pre-glacial erosion rates since the Permian period have been reported12, challenging arguments for enhanced erosion during the Cretaceous period4,6. Here we present a record of long-term East Antarctic erosion by applying multiple dating techniques to over 1,400 detrital mineral grains from onshore moraines and offshore sediments of Cretaceous to Quaternary age in the region of Lambert Glacier and Prydz Bay. Ages from pre-glacial sediments support overall low erosion rates before the expansion of the ice sheet, apart from a discrete interval of magmatic heating about 115 Myr ago that is inconsistent with widespread Cretaceous erosion. We find a shift towards younger and broader age distributions since ∼34 Myrago that necessitates spatially localized erosion of over 2 km in the Lambert Glacier catchment over this time. We infer that the trough containing Lambert Glacier was incised almost entirely by selective glacial erosion following initial expansion of the East Antarctic ice sheet. This implies that the early ice sheet was dynamic with ice flow concentrated along fixed ice streams. Copyright © 2013 Macmillan Publishers Limited.
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 6
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    Strontium isotopes, ages and carbonate content of sediments from the Agulhas Current
    PANGAEA
    In:  Supplement to: Franzese, Allison M; Hemming, Sidney R; Goldstein, Steven L (2009): Use of strontium isotopes in detrital sediments to constrain the glacial position of the Agulhas Retroflection. Paleoceanography, 24(2), PA2217, https://doi.org/10.1029/2008PA001706
    Details
    Publication Date: 2023-05-12
    Description: The Agulhas Leakage represents a significant portion of the warm, surface return flow of the global overturning circulation and thus may be an important feedback in the ocean climate system. Models indicate that reduced leakage could be caused by a stronger Agulhas Current and/or a more upstream (eastward) Agulhas Retroflection, while a weaker Agulhas Current would result in a more westward retroflection and increased leakage. However, data for the Last Glacial Maximum support both a weaker Agulhas Current and less leakage, implying a possible displacement of the retroflection. We present new 87Sr/86Sr results for modern sediments within this region, confirming that the modern pathway of the Agulhas Current, Retroflection, and Leakage can be traced by terrigenous sediment provenance using Sr isotopes. New 87Sr/86Sr data from sediments deposited during the Last Glacial Maximum suggest that the glacial Agulhas Current and Retroflection followed nearly their modern trajectory. The provenance data appear to rule out both a stronger Agulhas Current and a more upstream Agulhas Retroflection. We conclude that the reduced glacial leakage was caused by the weakened Agulhas Current, with no significant change in the retroflection position. This is inconsistent with the model predictions and thus emphasizes the need for further work in this region.
    Type: Dataset
    Format: application/zip, 27 datasets
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  • 7
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    (Table 2) Tie points and sedimentation rates of sediment core MD04-2829
    PANGAEA
    Details
    Publication Date: 2023-05-12
    Keywords: AGE; Age, comment; ALIENOR; Calculated; Calypso Square Core System; CASQS; DEPTH, sediment/rock; Marion Dufresne (1995); MD04-2829CQ; MD141; Northeast Atlantic; Sedimentation rate
    Type: Dataset
    Format: text/tab-separated-values, 33 data points
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  • 8
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    (Table S1) U-series ages of corals from the North Atlantic
    PANGAEA
    Details
    Publication Date: 2023-05-12
    Keywords: Age, dated; Age, dated standard deviation; Age, Uranium-Thorium; Corrected; Depth, bathymetric; DEPTH, sediment/rock; Gregg_Seamount; Identification; Laboratory code/label; Location; North Atlantic; Thorium-230; Thorium-230, standard deviation; Thorium-230/Uranium-238 activity ratio; Thorium-230/Uranium-238 activity ratio, standard deviation; Thorium-232; Thorium-232, standard deviation; Uranium-238; Uranium-238, standard deviation; δ234 Uranium; δ234 Uranium, standard deviation
    Type: Dataset
    Format: text/tab-separated-values, 200 data points
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  • 9
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    (Table S2) Nd isotope ratios for corals from the North Atlantic
    PANGAEA
    Details
    Publication Date: 2023-05-12
    Keywords: AGE; Age, standard deviation; Depth, bathymetric; DEPTH, sediment/rock; Gregg_Seamount; Identification; Laboratory code/label; Location; Neodymium-143/Neodymium-144 ratio; Neodymium-143/Neodymium-144 ratio, error; North Atlantic; ε-Neodymium; ε-Neodymium, standard deviation
    Type: Dataset
    Format: text/tab-separated-values, 108 data points
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  • 10
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    Neodymium isotope signature of Holocene corals
    PANGAEA
    In:  Supplement to: van de Flierdt, Tina; Robinson, Laura F; Adkins, Jess F; Hemming, Sidney R; Goldstein, Steven L (2006): Temporal stability of the neodymium isotope signature of the Holocene to glacial North Atlantic. Paleoceanography, 21, PA4102, https://doi.org/10.1029/2006PA001294
    Details
    Publication Date: 2023-05-12
    Description: The neodymium isotopic composition of marine precipitates is increasingly recognized as a powerful tool for identifying changes in ocean circulation and mixing on million year to millennial timescales. Unlike nutrient proxies such as d13C or Cd/Ca, Nd isotopes are not thought to be altered in any significant way by biological processes, and thus they can serve as a quasi-conservative water mass tracer. However, the application of Nd isotopes in understanding the role of thermohaline circulation in rapid climate change is currently hindered by the lack of direct constraints on the signature of the North Atlantic end-member through time. Here we present the first results of Nd isotopes measured in U-Th-dated deep-sea corals from the New England seamounts in the northwest Atlantic Ocean. Our data are consistent with the conclusion that the Nd isotopic composition of North Atlantic deep and intermediate water has remained nearly constant through the last glacial cycle. The results address long-standing concerns that there may have been significant changes in the Nd isotopic composition of the North Atlantic end-member during this interval and substantiate the applicability of this novel tracer on millennial timescales for paleoceanography research.
    Keywords: Gregg_Seamount; North Atlantic
    Type: Dataset
    Format: application/zip, 2 datasets
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