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  • ddc:551.7
  • 2020-2024  (2)
  • 1950-1954
  • 2023  (2)
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  • 2020-2024  (2)
  • 1950-1954
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  • 1
    Publication Date: 2024-02-28
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The ultimate demise of the Laurentide Ice Sheet (LIS) and the preceding and succeeding oceanographic changes along the western Labrador Sea offer insights critically important to improve climate predictions of expected future climate warming and further melting of the Greenland ice cap. However, while the final disappearance of the LIS during the Holocene is rather well constrained, the response of sea ice during the resulting meltwater events is not fully understood. Here, we present reconstructions of paleoceanographic changes over the past 9.3 Kyr BP on the northwestern Labrador Shelf, with a special focus on the interaction between the final meltwater event around 8.2 Kyr BP and sea ice and phytoplankton productivity (e.g., IP〈sub〉25〈/sub〉, HBI III (Z), brassicasterol, dinosterol, biogenic opal, total organic carbon). Our records indicate low sea‐ice cover and high phytoplankton productivity on the Labrador Shelf prior to 8.9 Kyr BP, sea‐ice formation was favored by decreased surface salinities due to the meltwater events from Lake Agassiz‐Ojibway and the Hudson Bay Ice Saddle from 8.55 Kyr BP onwards. For the past ca. 7.5 Kyr BP sea ice is mainly transported to the study area by local ocean currents such as the inner Labrador and Baffin Current. Our findings provide new insights into the response of sea ice to increased meltwater discharge as well as shifts in atmospheric and oceanic circulation.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Sea ice on the Labrador Shelf mainly follows the solar insolation and meltwater input from the decaying Laurentide Ice Sheet〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Sea ice increased following the Lake Agassiz outburst and Hudson Bay Ice Saddle Collapse between 8.5 and 8.2 Kyr BP〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Low sea ice conditions during the Holocene Thermal Maximum were replaced by an increase following the Neoglacial cooling trend〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Ocean Frontier Institute
    Description: NSERC
    Description: https://doi.org/10.4095/221564
    Description: https://doi.org/10.1594/PANGAEA.949244
    Description: https://doi.org/10.5281/zenodo.8247131
    Description: https://doi.org/10.1594/PANGAEA.949065
    Description: https://doi.org/10.1594/PANGAEA.949056
    Keywords: ddc:551.7 ; sea ice ; Atlantic Ocean ; IP25 ; 8.2 event
    Language: English
    Type: doc-type:article
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  • 2
    Publication Date: 2024-02-23
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉ABSTRACT〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The study examines bioclastic carbonate contourites that arise from the broad spectrum of bottom‐current related sedimentary processes ranging from deposition to erosion. The result of the intermittent accumulation of sediment are thin and condensed successions with abundant hiatuses. Such bottom‐current deposits are poorly known, since the broadly accepted contourite‐facies model, the bi‐gradational sequence, characterizes environments of contourite depositional systems as a continuous accretion of fine‐grained siliciclastic sediments. To increase current understanding of the carbonate facies within hiatal contourite records, the Eifelian–Frasnian of the Tafilalt Platform in Morocco was investigated. The succession is divided into five facies associations that are interpreted to reflect pelagic sedimentation and deposition from bottom currents on a contourite terrace, a gently inclined section of the upper slope of Gondwana shaped by a water‐mass interface. Contourite deposition was mainly controlled by oxic clear‐water currents (documented by moderately to completely bioturbated limestones with abundant hydrogenetic ferromanganese nodules, and low organic‐carbon contents), at times also by an anoxic water mass (featured by organic‐rich coquinas with absent to sparse bioturbation and predominantly syngenetic framboidal pyrites). Biostratigraphic data and the overall depositional architecture display palaeoceanographic hydrodynamic processes associated with a shifting water‐mass interface. The inner terrace was characterized by an alongslope contourite channel and a small mounded drift at its downslope margin. Energetic bottom currents furthermore caused abraded surfaces, i.e. plain areas of non‐deposition and localized erosion, and sandy condensation layers. The microfacies reflects repeated alternation between suspension deposition, winnowing of fines, bedload traction, dynamic sediment bypassing and reworking, together with concomitant seafloor cementation. Coquinas of mainly planktonic and nektonic organisms are identified as integral parts of bi‐gradational contourite sequences showing inverse and normal grading. Hiatal lag concentrations of carbonate intraclasts, ferromanganese nodules and conodonts often drape hardgrounds and erosional surfaces at the midpoint of these frequently incomplete sequences. This Devonian case provides the opportunity to investigate the spatial and temporal variability of the bed‐scale contourite sequence, also with regard to the drift‐scale depositional architecture. In addition, the identified high‐resolution record is a starting point for unravelling the pattern of oceanic circulation in the Devonian greenhouse world.〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:551.7 ; Anti‐Atlas ; bi‐gradational sequence ; bioclastic contourite ; carbonate contourite ; cephalopod limestone ; contourite channel ; contourite terrace
    Language: English
    Type: doc-type:article
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