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  • 1
    Online Resource
    Online Resource
    Ocean Circulation : Mechanisms and Impacts -- Past and Future Changes of Meridional Overturning. (2007)
    Newark :American Geophysical Union,
    Details
    Keywords: Meridional overturning circulation. ; Electronic books.
    Type of Medium: Online Resource
    Pages: 1 online resource (401 pages)
    Edition: 1st ed.
    ISBN: 9781118671887
    Series Statement: Geophysical Monograph Series ; v.173
    URL: https://ebookcentral.proquest.com/lib/geomar/detail.action?docID=1184592
    Language: English
    Note: Intro -- Title Page -- Contents -- Preface -- Section 1. Introduction -- Introduction: The Ocean's Meridional Overturning Circulation -- Discovery and Quantification of the Atlantic Meridional Overturning Circulation: The Importance of 25°N -- Section 2. Theory and Perspectives -- A Simple Theory of the Pycnocline and Overturning Revisited -- Buoyancy-Driven Flow and Nature of Vertical Mixing in a Zonally Averaged Model -- The Past and Future Ocean Circulation From a Contemporary Perspective -- Section 3. Current State and Trend -- Present-Day Manifestation of the Nordic Seas Overflows -- Circulation and Deep Water Export of the Subpolar North Atlantic During the 1990's -- Strength and Variability of the Deep Limb of the North Atlantic Meridional Overturning Circulation From Chlorofluorocarbon Inventories -- Section 4. Decadal to Centennial Variability -- Decadal to Centennial Variability of the Atlantic From Observations and Models -- Decadal to Multidecadal Variability of the Atlantic MOC: Mechanisms and Predictability -- Section 5. Past States and Millennial Variability -- Is the Frequency of Abrupt Climate Change Modulated by the Orbital Insolation? -- 14C Reservoir Ages Show Deglacial Changes in Ocean Currents and Carbon Cycle -- Phasing of Millennial Climate Events and Northeast Atlantic Deep-Water Temperature Change Since 50 ka BP -- Mechanisms for an ~7-kyr Climate and Sea-Level Oscillation During Marine Isotope Stage 3 -- North Atlantic Intermediate Depth Variability During the Younger Dryas: Evidence From Benthic Foraminiferal Mg/Ca and the GFDL R30 Coupled Climate Model -- Section 6. Impact on Climate, Ecosystems, and Biogeochemical Cycles -- Musings About the Connection Between Thermohaline Circulation and Climate. , Millennial-Scale Interhemispheric Asymmetry of Low-Latitude Precipitation: Speleothem Evidence and Possible High-Latitude Forcing -- Adjustment of the Global Climate to an Abrupt Slowdown of the Atlantic Meridional Overturning Circulation -- Impact of the Ocean's Overturning Circulation on Atmospheric CO2 -- Antarctic Stratification, Atmospheric Water Vapor, and Heinrich Events: A Hypothesis for Late Pleistocene Deglaciations -- Section 7. Future Projections -- Response of the Meridional Overturning Circulation During Differing Pathways Toward Greenhouse Gas Stabilization -- Projected Strengthening of the Southern Ocean Winds: Some Implications for the Deep Ocean Circulation -- Effect of the Greenland Ice-Sheet Melting on the Response and Stability of the AMOC in the Next Centuries.
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  • 2
    Article
    Article
    Global neodymium-hafnium isotope systematics - revisited (2007)
    Associated volumes
    Details Availability
    In: Earth & planetary science letters, Amsterdam [u.a.] : Elsevier, 1966, 259(2007), 3/4, Seite 432-441, 0012-821X
    In: volume:259
    In: year:2007
    In: number:3/4
    In: pages:432-441
    Type of Medium: Article
    Pages: Graph. Darst.
    ISSN: 0012-821X
    Language: English
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    GEOMAR CATALOGUE
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  • 3
    Book
    Book
    Ocean circulation : mechanisms and impacts ; past and future changes of meridional overturning (2007)
    Washington, D.C : American Geophysical Union
    Details Availability
    Keywords: Meridional overturning circulation ; Aufsatzsammlung ; Meridionalzirkulation
    Type of Medium: Book
    Pages: VII, 392 S. , Ill., graph. Darst., Kt.
    ISBN: 9780875904382
    Series Statement: Geophysical monograph 173
    URL: http://www.loc.gov/catdir/toc/ecip0725/2007033751.html
    URL: http://www.loc.gov/catdir/enhancements/fy1309/2007033751-d.html
    DDC: 551.46/2
    RVK:
    RB 10414
    Language: English
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  • 4
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    Strong glacial-interglacial variability in upper ocean hydrodynamics, biogeochemistry, and productivity in the southern Indian Ocean (2021)
    Nature Publishing Group UK
    Details
    Publication Date: 2024-02-28
    Description: In the southern Indian Ocean, the position of the subtropical front – the boundary between colder, fresher waters to the south and warmer, saltier waters to the north – has a strong influence on the upper ocean hydrodynamics and biogeochemistry. Here we analyse a sedimentary record from the Agulhas Plateau, located close to the modern position of the subtropical front and use alkenones and coccolith assemblages to reconstruct oceanographic conditions over the past 300,000 years. We identify a strong glacial-interglacial variability in sea surface temperature and productivity associated with subtropical front migration over the Agulhas Plateau, as well as shorter-term high frequency variability aligned with variations in high latitude insolation. Alkenone and coccolith abundances, in combination with diatom and organic carbon records indicate high glacial export productivity. We conclude that the biological pump was more efficient and strengthened during glacial periods, which could partly account for the reported reduction in atmospheric carbon dioxide concentrations.
    Description: Migration of the Subtropical Front during glacial and interglacial periods resulted in variability in the strength of the biological pump in the Southern Ocean sector of the Indian Ocean, according to sedimentary records from the Agulhas Plateau.
    Description: https://doi.pangaea.de/10.1594/PANGAEA.912467
    Keywords: ddc:551.46 ; palaeoceanography ; southern Indian Ocean ; Agulhas Plateau ; upper ocean hydrodynamics ; biogeochemistry
    Language: English
    Type: doc-type:article
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  • 5
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    The Malpaisillo Formation: A sequence of explosive eruptions in the mid to late Pleistocene (Nicaragua, Central America) (2018)
    Elsevier
    In:  Journal of Volcanology and Geothermal Research, 359 . pp. 47-67.
    Details
    Publication Date: 2021-02-08
    Description: The subduction-related volcanic front in Nicaragua consists of the Tertiary “Coyol” member in the eastern highlands and the Quaternary to recent volcanic arc within the Nicaraguan depression. Although the Holocene to recent explosive volcanism has been studied extensively no detailed work has been done on the products of explosive volcanism from Quaternary volcanic complexes comprising also the Malpaisillo and Monte Galán Calderas, the focus of this study. The 11 km-wide Malpaisillo Caldera and ~3.5 km-wide Monte Galán Caldera, located ~50 km northwest of Managua, are surrounded by tens of meters of rhyolitic tephras. These pyroclastic flow and fall deposits extend proximally at least 11 km to the southeast and 23 km to the southwest, with observed depositional thicknesses of 〉16 m for a single ignimbrite unit (or 〉25 m for the entire section). Distal deposits are found as far as 350 km offshore in the Pacific. At least twelve highly explosive large-volume eruptive phases with corresponding tephra deposits (LPT = La Paz Centro Tephra, PPT = Punta de Plancha Tephra, LCbT = Lower Chibola Tephra, GT = Guacucal Tephra, UCbT = Upper Chibola Tephra, FeT = La Fuente Tephra, ST = Sabanettas Tephra, MgT = Miralago Tephra, ToT = Tolapa Tephra, LMT, MMT, UMT = Lower, Middle, and Upper Maderas Negras Tephras) are distinguished based on geochemical correlations and similar depositional characteristics. Radiometric 40Ar/39Ar ages indicate that most activity related to the large Malpaisillo Caldera occurred between ~570 and ~420 ka. The large Pleistocene Malpaisillo and Monte Galán Calderas are characterized by a long-lived history and, if evolved, a distinctly alkaline (K2O = 2.3–3.8 wt%; Na2O = 4.0–4.9 wt%) geochemical signature compared to the other Nicaraguan tephra deposits. As a result, the previously defined Malpaisillo Formation has been considerably extended and revised. Our findings contribute to fill a considerable gap in the long-term eruptive history of Nicaraguan volcanoes, with prominent implications for volcanic hazard evaluation for Nicaragua.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.jvolgeores.2018.06.015
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    GEOTRACES intercalibration of neodymium isotopes and rare earth element concentrations in seawater and suspended particles. Part 1: reproducibility of results for the international intercomparison (2012)
    American Society of Limnology and Oceanography
    In:  Limnology and Oceanography: Methods, 10 . pp. 234-251.
    Details
    Publication Date: 2018-08-15
    Description: One of the key activities during the initial phase of the international GEOTRACES program was an extensive international intercalibration effort, to ensure that results for a range of trace elements and isotopes (TEIs) from different cruises and from different laboratories can be compared in a meaningful way. Here we present the results from the intercalibration efforts on neodymium isotopes and rare earth elements in seawater and marine particles. Fifteen different laboratories reported results for dissolved 143Nd/144Nd ratios in seawater at three different locations (BATS 15 m, BATS 2000 m, SAFe 3000 m), with an overall agreement within 47 to 57 ppm (2σ standard deviation of the mean). A similar agreement was found for analyses of an unknown pure Nd standard solution carried out by 13 laboratories (56 ppm), indicating that mass spectrometry is the main variable in achieving accurate and precise Nd isotope ratios. Overall, this result is very satisfactory, as the achieved precision is a factor of 40 better than the range of Nd isotopic compositions observed in the global ocean. Intercalibration for dissolved rare earth element concentrations (REEs) by six laboratories for two water depths at BATS yielded a reproducibility of 15% or better for all REE except Ce, which seems to be the most blank-sensitive REE. Neodymium concentrations from 12 laboratories show an agreement within 9%, reflecting the best currently possible reproducibility. Results for Nd isotopic compositions and REE concentrations on marine particles are inconclusive, and should be revisited in the future.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.4319/lom.2012.10.234
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  • 7
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    Global neodymium-hafnium isotope systematics - revisited (2007)
    Elsevier
    In:  Earth and Planetary Science Letters, 259 . pp. 432-441.
    Details
    Publication Date: 2017-01-30
    Description: Global Nd–Hf isotope systematics can be mainly described with two linear arrays, the global silicate Earth array (“the terrestrial array”) and the global ferromanganese crust and nodule array (”the seawater array”). The offset between these two arrays provides evidence for the sources and mechanisms by which these elements are added to ocean water. However, the reason for this offset is under debate, with the two preferred hypotheses being (i) incongruent release of Hf during continental weathering and (ii) hydrothermal contribution of Hf to the seawater budget. Here we present new Nd and Hf isotope data on glacio-marine core-top sediments from around the perimeter of the Antarctic continent. The results range from εHf = − 30.0 to εHf = + 3.9 and εNd = − 21.3 to εNd = + 0.9, reflecting the large range of basement ages and lithologies around the Antarctic continent. In Nd–Hf isotope space, they confirm the systematic correlations found in rocks from other parts around the world and provide valuable insights into the previously underrepresented group of sediments with very old provenance. In this paper we revisit the cause for the offset of the seawater array from the terrestrial array using simple mass balance considerations. We use these calculations to test to what degree the seawater array could be a product of preferential weathering of “non-zircon portions” of the upper continental crust, implying retention of zircons in the solid residue of weathering. Lutetium–Hf and Sm–Nd evolution and mixing calculations show that the global seawater array can be generated with continental sources only. On the other hand, a predominantly hydrothermal origin of Hf in the ocean is not possible because the seawater Hf isotopic composition is significantly less radiogenic than hydrothermal sources, and requires a minimum fraction of 50% continental Hf. While hydrothermal sources may contribute some Hf to seawater, continental contributions are required to balance the budget.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.epsl.2007.05.003
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  • 8
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    Miocene to present oceanographic variability in the Scotia Sea and Antarctic ice sheets dynamics: Insight from revised seismic-stratigraphy following IODP Expedition 382 (2021)
    Elsevier
    Details
    Publication Date: 2024-02-07
    Description: Highlights • Core-log-seismic correlation allows to assign ages to the Scotia Sea seismic record. • Major implications are derived on the relation between regional and global events. • The main stratigraphic events are much younger than previously proposed. • Three major phases for the regional oceanography are observed from late Miocene. • These phases appear to be closely linked to the Antarctic Ice Sheet dynamics. Scotia Sea and the Drake Passage is key towards understanding the development of modern oceanic circulation patterns and their implications for ice sheet growth and decay. The sedimentary record of the southern Scotia Sea basins documents the regional tectonic, oceanographic and climatic evolution since the Eocene. However, a lack of accurate age estimations has prevented the calibration of the reconstructed history. The upper sedimentary record of the Scotia Sea was scientifically drilled for the first time in 2019 during International Ocean Discovery Program (IODP) Expedition 382, recovering sediments down to ∼643 and 676 m below sea floor in the Dove and Pirie basins respectively. Here, we report newly acquired high resolution physical properties data and the first accurate age constraints for the seismic sequences of the upper sedimentary record of the Scotia Sea to the late Miocene. The drilled record contains four basin-wide reflectors – Reflector-c, -b, -a and -a' previously estimated to be ∼12.6 Ma, ∼6.4 Ma, ∼3.8 Ma and ∼2.6 Ma, respectively. By extrapolating our new Scotia Sea age model to previous morpho-structural and seismic-stratigraphic analyses of the wider region we found, however, that the four discontinuities drilled are much younger than previously thought. Reflector-c actually formed before 8.4 Ma, Reflector-b at ∼4.5/3.7 Ma, Reflector-a at ∼1.7 Ma, and Reflector-a' at ∼0.4 Ma. Our updated age model of these discontinuities has major implications for their correlation with regional tectonic, oceanographic and cryospheric events. According to our results, the outflow of Antarctic Bottom Water to northern latitudes controlled the Antarctic Circumpolar Current flow from late Miocene. Subsequent variability of the Antarctic ice sheets has influenced the oceanic circulation pattern linked to major global climatic changes during early Pliocene, Mid-Pleistocene and the Marine Isotope Stage 11.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: other
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    New Magnetostratigraphic Insights From Iceberg Alley on the Rhythms of Antarctic Climate During the Plio‐Pleistocene (2021)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-02-07
    Description: International Ocean Discovery Program (IODP) Expedition 382 in the Scotia Sea’s Iceberg Alley recovered among the most continuous and highest resolution stratigraphic records in the Southern Ocean near Antarctica spanning the last 3.3 Myr. Sites drilled in Dove Basin (U1536/U1537) have well‐resolved magnetostratigraphy and a strong imprint of orbital forcing in their lithostratigraphy. All magnetic reversals of the last 3.3 Myr are identified, providing a robust age model independent of orbital tuning. During the Pleistocene, alternation of terrigenous versus diatomaceous facies shows power in the eccentricity and obliquity frequencies comparable to the amplitude modulation of benthic δ18O records. This suggests that variations in Dove Basin lithostratigraphy during the Pleistocene reflect a similar history as globally integrated ice volume at these frequencies. However, power in the precession frequencies over the entire ∼3.3 Myr record does not match the amplitude modulation of benthic δ18O records, suggesting Dove Basin contains a unique record at these frequencies. Comparing the position of magnetic reversals relative to local facies changes in Dove Basin and the same magnetic reversals relative to benthic δ18O at North Atlantic IODP Site U1308, we demonstrate Dove Basin facies change at different times than benthic δ18O during intervals between ∼3 and 1 Ma. These differences are consistent with precession phase shifts and suggest climate signals with a Southern Hemisphere summer insolation phase were recorded around Antarctica. If Dove Basin lithology reflects local Antarctic ice volume changes, these signals could represent ice sheet precession‐paced variations not captured in benthic δ18O during the 41‐kyr world.
    Type: Article , PeerReviewed
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    Format: other
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  • 10
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    Latitudinal Variance in the Drivers and Pacing of Warmth During Mid‐Pleistocene MIS 31 in the Antarctic Zone of the Southern Ocean (2022)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-02-07
    Description: Early Pleistocene Marine Isotope Stage (MIS)-31 (1.081–1.062 Ma) is a unique interval of extreme global warming, including evidence of a West Antarctic Ice Sheet (WAIS) collapse. Here we present a new 1,000-year resolution, spanning 1.110–1.030 Ma, diatom-based reconstruction of primary productivity, relative sea surface temperature changes, sea-ice proximity/open ocean conditions and diatom species absolute abundances during MIS-31, from the Scotia Sea (59°S) using deep-sea sediments collected during International Ocean Discovery Program (IODP) Expedition 382. The lower Jaramillo magnetic reversal (base of C1r.1n, 1.071 Ma) provides a robust and independent time-stratigraphic marker to correlate records from other drill cores in the Antarctic Zone of the Southern Ocean (AZSO). An increase in open ocean species Fragilariopsis kerguelensis in early MIS-31 at 53°S (Ocean Drilling Program Site 1,094) correlates with increased obliquity forcing, whereas at 59°S (IODP Site U1537; this study) three progressively increasing, successive peaks in the relative abundance of F. kerguelensis correlate with Southern Hemisphere-phased precession pacing. These observations reveal a complex pattern of ocean temperature change and sustained sea surface temperature increase lasting longer than a precession cycle within the Atlantic sector of the AZSO. Timing of an inferred WAIS collapse is consistent with delayed warmth (possibly driven by sea-ice dynamics) in the southern AZSO, supporting models that indicate WAIS sensitivity to local sub-ice shelf melting. Anthropogenically enhanced impingement of relatively warm water beneath the ice shelves today highlights the importance of understanding dynamic responses of the WAIS during MIS-31, a warmer than Holocene interglacia
    Type: Article , PeerReviewed
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    Format: other
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