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  • 1
    Publication Date: 2017-11-01
    Description: The Argentine margin contains important sedimentological, paleontological and chemical records of regional and local tectonic evolution, sea level, climate evolution and ocean circulation since the opening of the South Atlantic in the Late Jurassic–Early Cretaceous as well as the present-day results of post-depositional chemical and biological alteration. Despite its important location, which underlies the exchange of southern- and northern-sourced water masses, the Argentine margin has not been investigated in detail using scientific drilling techniques, perhaps because the margin has the reputation of being erosional. However, a number of papers published since 2009 have reported new high-resolution and/or multichannel seismic surveys, often combined with multi-beam bathymetric data, which show the common occurrence of layered sediments and prominent sediment drifts on the Argentine and adjacent Uruguayan margins. There has also been significant progress in studying the climatic records in surficial and near-surface sediments recovered in sediment cores from the Argentine margin. Encouraged by these recent results, our 3.5-day IODP (International Ocean Discovery Program) workshop in Buenos Aires (8–11 September 2015) focused on opportunities for scientific drilling on the Atlantic margin of Argentina, which lies beneath a key portion of the global ocean conveyor belt of thermohaline circulation. Significant opportunities exist to study the tectonic evolution, paleoceanography and stratigraphy, sedimentology, and biosphere and geochemistry of this margin.
    Type: Article , PeerReviewed
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  • 2
    Publication Date: 2017-07-27
    Description: Ten ODP sites drilled in a depth transect (2164–4775 m water depth) during Leg 172 recovered high-deposition rate (〉20 cm/kyr) sedimentary sections from sediment drifts in the western North Atlantic. For each site an age model covering the past 0.8–0.9 Ma has been developed. The time scales have a resolution of 10–20 kyr and are derived by tuning variations of estimated carbonate content to the orbital parameters precession and obliquity. Based on the similarity in the signature of proxy records and the spectral character of the time series, the sites are divided into two groups: precession cycles are better developed in carbonate records from a group of shallow sites (2164–2975 m water depth, Sites 1055–1058) while the deeper sites (2995–4775 m water depth, Sites 1060–1063) are characterized by higher spectral density in the obliquity band. The resulting time scales show excellent coherence with other dated carbonate and isotope records from low latitudes. Besides the typical Milankovitch cyclicity significant variance of the resulting carbonate time series is concentrated at millennial-scale changes with periods of about 12, 6, 4, 2.5, and 1.5 kyr. Comparisons of carbonate records from the Blake Bahama Outer Ridge and the Bermuda Rise reveal a remarkable similarity in the time and frequency domain indicating a basin-wide uniform sedimentation pattern during the last 0.9 Ma.
    Type: Article , PeerReviewed
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  • 3
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    In:  (PhD/ Doctoral thesis), Christian-Albrechts-Universität, Kiel, 107 pp . GEOMAR-Report, 046 . DOI 10.3289/GEOMAR-Report_46_1995 〈http://dx.doi.org/10.3289/GEOMAR-Report_46_1995〉.
    Publication Date: 2017-07-27
    Type: Thesis , NonPeerReviewed
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  • 4
    Publication Date: 2017-07-27
    Description: Changes in bulk sediment Fe(II)/Fe(III) ratio and in the distribution of iron among different minerals as a result of Ocean Drilling Program archive storage in the Bremen Core Repository were investigated using Mössbauer spectroscopy. Massive Fe(II) to Fe(III) oxidation, which involved between 24% and 45% of the initial Fe(II), occurred within only 6 months of refrigerated storage. Prior to archive storage, 〉95% of the Fe(II) in the sediment samples under investigation was structural iron in silicate minerals. Hence, virtually the entire oxidation process took place within silicate mineral lattices, and the sediment mineral assemblage was not changed in this case. Nevertheless, the observed oxidation of the comparatively shielded silicate lattice Fe(II) suggests that Fe(II) bound in authigenic carbonates, phosphates, or sulfides—such as that found in many marine sediments—would likely be oxidized at least as fast. Those minerals, however, would be replaced by Fe(III)-bearing oxides and oxyhydroxides, which implies a change of sediment composition, and thus, of various sediment properties, including the magnetic signal, within a few months of storage. Furthermore, changes in the silicate lattice Fe(II)/Fe(III) ratio during storage, such as those reported here, also signify loss of information. This is because oxidation of the structural Fe(II) upon contact with atmospheric oxygen may occur only inasmuch as the inverse Fe(III)–Fe(II) redox transition has taken place in the seabed. Therefore, the reversible shift, if it were measured under controlled reoxidation in the laboratory, may suggest the chemical stress that was suffered by the iron oxide minerals at the ocean bottom. Concerning Site 1062, this process might help to judge both the authenticity of magnetic field excursion records and the lithostratigraphic value of red lutites at given sediment depths. Although the nature and extent of information loss or alteration during storage depend on sediment type, the reported observations emphasize the need for special sample protection with respect to properties that might be affected.
    Type: Article , NonPeerReviewed
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  • 5
    Publication Date: 2019-09-23
    Description: Subtropical Gyres are an important constituent of the ocean–atmosphere system due to their capacity to store vast amounts of warm and saline waters. Here we decipher the sensitivity of the (sub)surface North Atlantic Subtropical Gyre with respect to orbital and millennial scale climate variability between ~ 140 and 70 ka, Marine Isotope Stage (MIS) 5. Using (isotope) geochemical proxy data from surface and thermocline dwelling foraminifers from Blake Ridge off the west coast of North America (ODP Site 1058) we show that the oceanographic development at subsurface (thermocline) level is substantially different from the surface ocean. Most notably, surface temperatures and salinities peak during the penultimate deglaciation (Termination II) and early MIS 5e, implying that subtropical surface ocean heat and salt accumulation might have resulted from a sluggish northward heat transport. In contrast, maximum thermocline temperatures are reached during late MIS 5e when surface temperatures are already declining. We argue that the subsurface warming originated from intensified Ekman downwelling in the Subtropical Gyre due to enhanced wind stress. During MIS 5a-d a tight interplay of the subtropical upper ocean hydrography to high latitude millennial-scale cold events can be observed. At Blake Ridge, the most pronounced of these high latitude cold events are related to surface warming and salt accumulation in the (sub)surface. Similar to Termination II, heat accumulated in the Subtropical Gyre probably due to a reduced Atlantic Meridional Overturning Circulation. Additionally, a southward shift and intensification of the subtropical wind belts lead to a decrease of on-site precipitation and enhanced evaporation, coupled to intensified gyre circulation. Subsequently, the northward advection of this warm and saline water likely contributed to the fast resumption of the overturning circulation at the end of these high latitude cold events.
    Type: Article , PeerReviewed
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  • 6
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    In:  [Talk] In: 4. International Conference on Paleoceanography (ICP IV), 21.09.-25.09.1992, Kiel .
    Publication Date: 2014-05-26
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 7
    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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