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  • 1
    Call number: ZSP-168-243
    In: Berichte zur Polarforschung
    Type of Medium: Monograph available for loan
    Pages: 146 S. : Abb. ; 24 cm
    ISSN: 0176-5027
    Series Statement: Berichte zur Polarforschung 243
    Language: German
    Location: Reading room
    Branch Library: AWI Library
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  • 2
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Laminated glacimarine sediments are observed in visual core logs and x-radiographs from Scoresby Sund and Nansen Fjord, east Greenland. They are mostly underlain and overlain by massive or stratified glacimarine diamicton (Dmm or Dms), which is a product of iceberg delivery of heterogeneous debris and, in Scoresby Sund, reworking by deep-drafted iceberg keels. The laminated sediments are AMS radiocarbon dated to two cold periods since the last, Late Weichselian deglaciation: the Younger Dryas stadial (Milne Land Stadial in east Greenland) and the Little Ice Age. During cold climatic events, multiyear shorefast sea ice (‘sikussak’) formed in these fjords and trapped the icebergs. Fine-grained, laminated muds (Fl) were deposited in Scoresby Sund when the flux of icebergs was suppressed, but turbid meltwater continued to provide some sediment flux to the fjord systems, varying through time to produce laminations. In Nansen Fjord, thinner and often massive mud layers (Fm) resulted from shorter intervals of sea-ice cover with no ice rafting. Stratified diamicton layers (Dms), which alternate with mud deposition to produce a laminated unit, probably represent intervening times of more open conditions with iceberg rafting. In Scoresby Sund, foraminifera are either absent from the laminated unit or begin to appear towards the end of its deposition. The absence of both benthic and planktonic foraminifera also suggests that multiyear sea ice was covering the core sites. There is no evidence of macrofaunal activity, and bioturbation is absent from the laminated sediments. Satellite data show that multiyear shorefast sea ice is present in several areas of the high Arctic today, and this traps icebergs calved from interior ice-cap drainage basins. Thus, the process of laminated glacimarine sediment formation is likely to be applicable to a number of areas of the modern and Quaternary Arctic.
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  • 3
    Publication Date: 2018-07-09
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 4
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    In:  [Talk] In: 6. International Conference on "Palaeo-Arctic Spatial and Temporal (PAST) Gateways", 16.04.-20.04.2018, Durham, U.K. .
    Publication Date: 2018-07-09
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 5
    ISSN: 0014-5793
    Keywords: GM-CSF ; IL-6 receptor ; Neutrophil ; Receptor downregulation
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 6
    Publication Date: 2018-08-10
    Description: To test the pore density in benthic foraminifera as a potential proxy for bottom-water oxygenation, pore density analyses were carried out on tests of living (rose Bengal-stained) specimens of the deep-infaunal and anoxia-tolerant foraminiferal species Globobulimina turgida. Three stations within and two stations below the oxygen minimum zone (OMZ) off Namibia were investigated and compared to in situ-measured bottom-water oxygen content (BW-O2). Pore density was first conventionally assessed by rather time-consuming manual pore counting on SEM photographs and measurement of the analyzed test areas. To significantly shorten the measurement time we tested and evaluated an automation of the pore density measurement using the image analysis software package analySIS (version 5.0, Olympus Soft Imaging Solutions). Pore density data from automated analyses are compared to manually acquired data from G. turgida. Our study shows almost identical results for both manually and automatically acquired data. Consequently, we assume that the new technique provides an alternative and more rapid method to analyze the pore density of foraminifera. For both methods, our results show a distinct negative linear correlation (automatically analyzed pore density: τ = −0.50, p 〈 0.001; manually analyzed pore density: τ = −0.49, p 〈 0.001) between pore density and BW-O2, suggesting that G. turgida increases its pore density in response to decreasing oxygen. Thus, we suggest that, similar to other recently described low-oxygen-tolerant benthic foraminiferal species, G. turgida may improve its O2 uptake by increasing pore density to survive in low-oxic environments. This morphological adaption might be useful for future studies to establish an independent proxy for BW-O2. In addition, pore density has been compared to in situ-measured bottom-water nitrate concentration (BW-NO3−). Our investigation of the pore density-to-BW-NO3− relationship for G. turgida suggests that nitrate seems to be a minor factor influencing pore density in this species compared to BW-O2. Add to CiteULike
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 7
    Publication Date: 2016-12-09
    Description: The δ13C value measured on benthic foraminiferal tests is widely used by palaeoceanographers to reconstruct the distribution of past water masses. The biogeochemical processes involved in forming the benthic foraminiferal δ13C signal (δ13Cforam), however, are not fully understood and a sound mechanistic description is still lacking. We use a reaction–diffusion model for calcification developed by Wolf-Gladrow et al. (1999) and Zeebe et al. (1999) in order to quantify the effects of different physical, chemical, and biological processes on δ13Cforam of an idealised benthic foraminiferal shell. Changes in the δ13C value of dissolved inorganic carbon (δ13CDIC) cause equal changes in δ13Cforam in the model. The results further indicate that temperature, respiration rate, and pH have a significant impact on δ13Cforam. In contrast, salinity, pressure, the δ13C value of particulate organic carbon (δ13CPOC), total alkalinity, and calcification rate show only a limited influence. In sensitivity experiments we assess how combining these effects can influence δ13Cforam. We can potentially explain 33 to 47% of the interglacial-to-glacial decrease in δ13Cforam by changes in temperature and pH, without invoking changes in δ13CDIC. Furthermore, about a quarter of the − 0.4‰ change in δ13Cforam observed in phytodetritus layers can be accounted for by an increase in respiration rate and a reduction in pH.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 8
    Publication Date: 2017-05-08
    Description: Under modern conditions only North Pacific Intermediate Water is formed in the northwest Pacific Ocean. This situation might have changed in the past. Recent studies with general circulation models indicate a switch to deep-water formation in the northwest Pacific during Heinrich Stadial 1 (17.5–15.0 ka) of the last glacial termination. Reconstructions of past ventilation changes based on paleoceanographic proxy records are still insufficient to test whether a deglacial mode of deep-water formation in the North Pacific Ocean existed. Here we present deglacial ventilation records based on radiocarbon-derived ventilation ages in combination with epibenthic stable carbon isotopes from the northwest Pacific including the Okhotsk Sea and Bering Sea, the two potential source regions for past North Pacific ventilation changes. Evidence for most rigorous ventilation of the intermediate-depth North Pacific occurred during Heinrich Stadial 1 and the Younger Dryas, simultaneous to significant reductions in Atlantic Meridional Overturning Circulation. Concurrent changes in δ13C and ventilation ages point to the Okhotsk Sea as driver of millennial-scale changes in North Pacific Intermediate Water ventilation during the last deglaciation. Our records additionally indicate that changes in the δ13C intermediate-water (700–1750 m water depth) signature and radiocarbon-derived ventilation ages are in antiphase to those of the deep North Pacific Ocean (〉2100 m water depth) during the last glacial termination. Thus, intermediate- and deep-water masses of the northwest Pacific have a differing ventilation history during the last deglaciation.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 9
    Publication Date: 2018-08-10
    Description: The West Antarctic Ice Sheet (WAIS) is considered the most unstable part of the Antarctic Ice Sheet. As the WAIS is mostly grounded below sea level, its stability is of great concern. A collapse of large parts of the WAIS would result in a significant global sea-level rise. At present, the WAIS shows dramatic ice loss in its Amundsen Sea sector, especially in Pine Island Bay. Pine Island Glacier (PIG) is characterised by fast flow, major thinning and rapid grounding-line retreat. Its mass los over recent decades is generally attributed to melting caused by the inflow of warm Circumpolar Deep Water (CDW). Future melting of PIG may result in a sea level tipping point, because it could trigger widespread collapse of the WAIS, especially when considering ongoing climate change. Our research project aims to establish proxies (integration of foraminifera, sediment properties and oceanographic data) for modern environmental conditions by analysing seafloor surface sediments along a transect from the glacier proximal settings to the middle-outer shelf in the eastern Amundsen Sea Embayment. These proxies will then be applied on sediment records spanning the Holocene back to the Last Glacial Maximum for reconstructing spatial and temporal variations of CDW upwelling and ice-ocean interactions during the past c. 23,000 years. We will present preliminary results from the analyses of ten short marine sediment cores (multi and box cores) collected during expeditions JR179 (2008) and ANT-XXVI/3 (2010) along a transect from inner Pine Island Bay to the middle-outer shelf part of the Abbot Palaeo-Ice Stream Trough at water depths ranging from 458 m (middle shelf) to 1444 m (inner shelf). The sediment cores are currently investigated for distribution patterns of planktonic and benthic foraminifera and grain-size distribution at 1 cm resolution. Core tops (0-10 cm) were stained with Rose Bengal for living benthic foraminifera investigations. The chronology of the cores will be based on 210Pb and calibrated 14C dates. First results reveal the presence of living benthic foraminifera in surface sediments of all investigated cores suggesting that modern seabed surfaces were recovered. Moreover, a core retrieved from a water depth of 793 m in the Abbot Palaeo-Ice Stream Trough shows particularly high abundances of planktonic foraminifera Neogloboquadrina pachyderma.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 10
    Publication Date: 2016-02-09
    Description: We have evaluated the environmental and biological processes affecting the stable oxygen and carbon isotope composition of live (Rose Bengal stained) and dead (unstained) tests of different benthic foraminiferal species from the western Mediterranean Sea. Samples were retrieved from comparable water depths but contrasting trophic regimes, comprising the meso- to eutrophic Alboran Sea and the oligo- to mesotrophic Mallorca Channel. The recorded isotope signatures mirror the average microhabitat depth of each species and reflect the specific gradients in pore water δ13C of dissolved inorganic carbon (δ13CDIC) and oxygen. Maximum δ13CDIC pore water gradients of up to − 2.3‰ were estimated under the influence of meso- to eutrophic conditions in the Alboran Sea. The δ13C signal of Uvigerina mediterranea reflects the opportunistic behavior of this species as its δ13C is shifted to more negative values at higher organic matter fluxes. Accordingly, the δ13C signal of U. mediterranea appears particularly suitable as a proxy for quantitative reconstructions of past trophic conditions. Previously reported ontogenetic increase of stable isotope values is confirmed for buliminid taxa (genera Uvigerina and Globobulimina), while it is largely absent in rotaliid taxa (genera Cicidides, Cibicidoides, and Melonis). Particularly strong metabolic fractionation is observed in small specimens of Uvigerina peregrina overprinting the pore-water δ13CDIC signal and resulting in steep ontogenetic δ13C gradients. The δ18O values of epifaunal taxa, which thrive under high dissolved oxygen concentrations, and the shallow to intermediate infaunal Melonis barleeanum, are up to 1.2‰ lower relative to equilibrium calcite. In epifaunal taxa, this depletion can be attributed to enhanced fractionation at high concentrations of metabolically utilizable oxygen.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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