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  • 1
    Publikationsdatum: 2019-07-12
    Beschreibung: Observations of electron and ion distributions inside a fast neutral barium jet in the ionosphere show significant fluxes within 4 km of release, presumably related to beam plasma instability processes involved in the Critical Ionization Velocity (CIV) effect. Electron fluxes exceeding 5 x 10 exp 12/sq cm-str-sec-keV were responsible for ionizing both the streaming barium and ambient oxygen. Resulting ion fluxes seem to be consistent with 1-2 percent ionization of the fast barium, as reported by optical observations, although the extended spatial distribution of the optically observed ions is difficult to reconcile with the in situ observations. When the perpendicular velocity of the neutrals falls below critical values, these processes shut off. Although these observations resemble the earlier Porcupine experimental results (Haerendel, 1982), theoretical understanding of the differences between these data and that of earlier negative experiments is still lacking.
    Schlagwort(e): GEOPHYSICS
    Materialart: Geophysical Research Letters (ISSN 0094-8276); 19; 10 M
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Publikationsdatum: 2019-07-12
    Beschreibung: Unusually low delta N-15 found in early to middle Cretaceous beds rich in marine organic matter from two separate eastern Atlantic Ocean basins is reported. These findings constitute unambiguous evidence that the N contained in these strata is the end result of biogeochemical processes that differed substantially from those that operated on the N contained in intervening organic carbon-poor strata and younger marine sediments. The data indicate that the low N-15 relative abundance is the consequence of pelagic rather than postdepositional processes. Reduced ocean circulation, increased denitrification, and hence, reduced euphotic zone nitrate availability may have led to Cretaceous phytoplankton assemblages that were periodically dominated by N2-fixing blue-green algae, a possible source of the sedimentary N-15 depletion.
    Schlagwort(e): GEOPHYSICS
    Materialart: Earth and Planetary Science Letters (ISSN 0012-821X); 82; 3-4; 269-279
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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