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  • 1
    Call number: ZSP-166-3
    Pages: 97 S. : Ill., graph. Darst.
    Series Statement: Berichte aus dem Fachbereich Geowissenschaften der Universität Bremen 3
    Branch Library: GFZ Library
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  • 2
    ISSN: 1432-1157
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Bulk δ15N values in surface sediment samples off the southwestern coast of Africa were measured to investigate the biogeochemical processes occurring in the water column. Nitrate concentrations and the degree of utilization of the nitrate pool are the predominant controls on sedimentary δ15N in the Benguela Current region. Denitrification does not appear to have had an important effect on the δ15N signal of these sediments and, based on δ15N and δ13C, there is little terrestrial input.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Corpora allata fromOncopeltus fasciatus incubated in vitro in medium containing 10−5.35 M (1 μg/ml) of precocene II lose their ability to secrete juvenile hormone when reimplanted into last instar larvae.
    Type of Medium: Electronic Resource
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  • 4
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    Academia Brasileira de Ciências
    In:  Anais da Academia Brasileira de Ciências = Annals of the Brazilian Academy of Sciences, 48 (Supplemento). pp. 287-296.
    Publication Date: 2015-03-03
    Description: Late Quaternary sediments on the West African continental margin between 24°N and 15°N were studied with RV METEOR (1971) and VALDIVIA (1975). Cores on the shelf were taken with a 6-m-vibrocorer, in deeper water mainly with a 12 m Kastenlot corer. During Holocene, and up to the present time, more or less and climatic conditions north of the Senegal River area reduced terrigenous supply. Therefore, the biogenic-carbonate content exceeds about 50%. Wüstenquarz numbers (red + yellow quartz : white quartz x 100) are high (20 to mmore than 200), indicating eolian input. The Senegal River supplied fine grained, green colored, terrigenous material with some plant debris. During Würm, the Mediterranean climatic zone with winter rains was shifted more than 5° to the South and was reaching Banc d'Arguin (at about 20°N). Therefore, the terrigenous supply was increased in this northern part and consequently the carbonate content and the Wüstenquartz numbers dropped below 50% and 10, respectively. The arid zone was also shifted to the south; as a consequence, the Senegal River did not reach the sea, eolian supply diluted the biogenic carbonates, and increased Wüstenquartz numbers to more than 200. Eolian dunes covered parts of the shelf. Ratios of radiolarians/plankonic foraminifera and planktonic/benthonic organisms and sedimentation rates of organic carbon indicate stronger upwelling in the northern region. Turbidity currents were more frequent, eroding as much as a third of the material supplied ba pelagic sedimentation.
    Type: Article , PeerReviewed
    Format: text
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  • 5
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: We present an approach for tracing the fate of anthropogenic CO2, compiling a large data set of stable organic carbon isotope ratios from surface sediments, plankton, and sinking matter in the Atlantic Ocean. The δ13C values of sinking matter are generally lower by 0.5–4.6‰ compared to the surface sediments. This difference increases with increasing latitude, which is explained by a stronger modern increase in surface water [CO2 (aq)] in the Southern Ocean relative to the Tropical/Subtropical Ocean. Preindustrial dissolved CO2 concentrations in Atlantic surface waters, estimated from the δ13Corg of surface sediments, are compared to recently measured surface water [CO2 (aq)] values taken from literature. We obtain only a slight increase in [CO2 (aq)] at lower latitudes but a significant change of about 7 ± 2 μm in high latitudinal surface waters which we attribute to anthropogenic perturbation. Our results suggest that CO2 released by human activities has been stored in Southern Ocean surface waters.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-2056
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A multi-cup sediment trap was deployed at 250m in the shelf area off Kapp Norvegia, Weddell Sea (630 m water depth) to determine the relative importance of water mass advection, sea ice movement, phytoplankton biomass and plankton feeding. Short-term fluctuations in sedimentation were determined using a sampling frequency of 2.7 days over 54 days during January and February 1988. Three periods of enhanced sedimentation were associated with water mass exchange, settling of diatoms following break-up of ice cover and release of fecal matter by krill feeding on particulate matter derived from phytoplankton and ice algae. An initial sedimentation pulse (28 Jan) was mainly due to sinking pelagic diatoms and krill fecal strings containing algae released from sea ice passing over the trap position. The δ13C-composition of the sedimented organic carbon was about-24‰. The isotope ratio decreased sharply by about 5.5‰ at the end of the first pulse indicating the source of sinking matter becoming pelagic diatoms of the retreating ice-edge. At this time the diatom Corethron criophilum contributed a very high proportion of the organic flux causing an increase of the opal/Corg ratios. The second pulse (6 Feb) was due to empty diatom frustules, minipellets and small planktonic aggregates. Much of the organic carbon was transported by round fecal pellets. During the third pulse (14 Feb), round fecal pellets transported even more; the percentage of C. criophilum to the diatom organic carbon flux was more than 80% (〉2mg C m−2 day−1).
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  • 7
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    CNRS
    In:  In: Biogéochimie de la matière organique à l'interface eau-sédiment marin. Colloques Internationaux du Centre National de la Recherche Scientifique, 293 . CNRS, Paris, pp. 17-29.
    Publication Date: 2016-07-12
    Description: The vertical flux of biogenous organic matter to the sediment surface is a function of water depth and primary productivity; this relationship can be expressed empirically as: (1) org-Cflux = 5.9 · depth-0 616 · productivity Upon descent through the water column and prior to burial, biogenous detrital organic matter undergoes strong elemental fractionation by preferential removal of nitrogenous and P-containing organic compounds. At the water-sediment interface, a portion of the detritus is converted into biomass by benthic organisms, which concentrate nitrogen and phosphorus relative to carbon. These two processes are reflected in the elemental composition of sedimentary organic matter. A third process concentrates organic matter in sediments by sorption onto clays. This sorbed material is high in organic-N and devoid of organic-P; its relative abundance is high only in pelagic clays. The concentrations of each of the three forms of organic matter -detrital, biomass, and sorbed- can be calculated from the following expressions: (2) org-Csorb = 0.005 · Al2O3 (3) org-Cdetr = org-Ctota1 – org-Csorb - e · org-Ntotal / 1-2/f (4) org-Cbiom = org-Ctotal - org-Cdetr - org-Csorb where e and f are the C/N elemental weight ratios of biomass and detritus respectively
    Type: Book chapter , NonPeerReviewed
    Format: text
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  • 8
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    In:  Geochemical Journal, 14 (3). pp. 129-137.
    Publication Date: 2016-03-01
    Description: Nutrient profiles in Southwest Pacific interstitial solutions suggest that in environments of oxic pelagic sedimentation microbially mediated nitrification is recognizable as a two-step process. During the first step partially oxidized nitrogenous intermediaries accumulate in distinctive ammonia and nitrite maxima along with nitrate. During the second step nitrification continues and all intermediate species are fully oxidized to nitrate. Both steps occur within a zone that corresponds in thickness to the biologically active surface layer. Similarly, experimental nitrogen regeneration from decomposition of plankton in seawater (VON BRAND and RAKESTRAW, 1941: VON BRAND et al., 1942) suggests that each step corresponds to a distinct reaction in the microbially mediated transformation of N-org → NH3 → NO2 → NO3. The resolution of distinct reaction zones in pore water nutrient profiles possibly depends on the nature and mode of supply of the organic matter undergoing nitrification or reflects the spatial succession downcore of microbial populations capable of deamination, ammonium oxidation and nitrite oxidation, respectively. Finally, stoichiometric ratios of nutrients in the free water column - here demonstrated on published data from Saanich Inlet - reflect the same two steps of nitrification as delineated by the dissolved pore water species. Future pore water studies should include dissolved oxygen measurements as well as accurate ∑CO2, PO4 and nitrogenous species profiles, to verify and better quantify these separate steps in nitrification mechanism of oxic pelagic sediments.
    Type: Article , PeerReviewed
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  • 9
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    American Association for the Advancement of Science (AAAS)
    In:  Science, 216 (4550). pp. 1128-1131.
    Publication Date: 2018-03-08
    Description: Large euhedral crystals of calcium carbonate hexahydrate were recovered from a shelf basin of the Bransfield Strait, Antarctic Peninsula, at a water depth of 1950 meters and sub-zero bottom water temperatures. The chemistry, mineralogy, and stable isotope composition of this hydrated calcium carbonate phase, its environment of formation, and its mode of precipitation confirm the properties variously attributed to hypothetical precursors of the glendonites and thereby greatly expand their use in paleoceanographic interpretation.
    Type: Article , PeerReviewed
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  • 10
    Publication Date: 2017-12-21
    Description: The presence of the cosmopolitan deep-sea coral Eguchipsammia fistula has recently been documented in the Red Sea, occurring in warm (〉20 °C), oxygen- and nutrient-limited habitats. We collected colonies of this species from the central Red Sea that successfully resided in aquaria for more than one year. During this period the corals were exposed to increased oxygen levels and nutrition ad libitum unlike in their natural habitat. Specimens of long-term reared E. fistula colonies were incubated for 24 h and calcification (G) as well as respiration rates (R) were measured. In comparison to on-board measurements of G and R rates on freshly collected specimens, we found that G was increased while R was decreased. E. fistula shows extensive tissue growth and polyp proliferation in aquaculture and can be kept at conditions that notably differ from its natural habitat. Its ability to cope with rapid and prolonged changes in regard to prevailing environmental conditions indicates a wide physiological plasticity. This may explain in part the cosmopolitan distribution of this species and emphasizes its value as a deep-sea coral model to study mechanisms of acclimation and adaptation.
    Type: Article , PeerReviewed
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