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  • 1
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Zusammenfassung Es wird ein papierchromatographisches Verfahren zur quantitativen Bestimmung des von Oxydkathoden abdampfenden Bariums und Strontiums angegeben. Unter den bekannten Lösungsmittelgemischen eignet sich Salzsäure-Methanol-Wasser am besten für die papierchromatographische Trennung der Abdampfprodukte. Die günstigsten Bedingungen zur Anfärbung des Chromatogramms mit Natriumrhodizonat werden angegeben. Die Chromatogramme werden bei 510 mμ, d. h. im Absorptionsmaximum des Strontiumrhodizonats bzw. in der Nähe des Absorptionsmaximums des Bariumrhodizonats photometriert. Die Auswertung ergibt eine gute Proportionalität zwischen den Barium-bzw. Strontiumkonzentrationen und den Extinktionsflächenwerten.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2020-02-12
    Description: Terrestrial cosmogenic nuclide (TCN) concentrations in fluvial sediment, from which denudation rates are commonly inferred, can be affected by hillslope processes. TCN concentrations in gravel and sand may differ if localized, deep‐excavation processes (e.g. landslides, debris flows) affect the contributing catchment, whereas the TCN concentrations of sand and gravel tend to be more similar when diffusional processes like soil creep and sheetwash are dominant. To date, however, no study has systematically compared TCN concentrations in different detrital grain‐size fractions with a detailed inventory of hillslope processes from the entire catchment. Here we compare concentrations of the TCN 10Be in 20 detrital sand samples from the Quebrada del Toro (southern Central Andes, Argentina) to a hillslope‐process inventory from each contributing catchment. Our comparison reveals a shift from low‐slope gullying and scree production in slowly denuding, low‐slope areas to steep‐slope gullying and landsliding in fast‐denuding, steep areas. To investigate whether the nature of hillslope processes (locally excavating or more uniformly denuding) may be reflected in a comparison of the 10Be concentrations of sand and gravel, we define the normalized sand‐gravel index (NSGI) as the 10Be‐concentration difference between sand and gravel divided by their summed concentrations. We find a positive, linear relationship between the NSGI and median slope, such that our NSGI values broadly reflect the shift in hillslope processes from low‐slope gullying and scree production to steep‐slope gullying and landsliding. Higher NSGI values characterize regions affected by steep‐slope gullying or landsliding. We relate the large scatter in the relationship, which is exhibited particularly in low‐slope areas, to reduced hillslope‐channel connectivity and associated transient sediment storage within those catchments. While high NSGI values in well‐connected catchments are a reliable signal of deep‐excavation processes, hillslope excavation processes may not be reliably recorded by NSGI values where sediment experiences transient storage.
    Language: English
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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  • 4
    Publication Date: 2020-02-12
    Description: Advances in cosmogenic nuclide exposure dating have made moraines valuable terrestrial recorders of palaeoclimate. A growing number of moraine chronologies reported from the Central Andes show that tropical glaciers responded sensitively to past changes in precipitation and temperature over timescales ranging from 103 to 105 years. However, the causes of past glaciation in the Central Andes remain uncertain. Explanations have invoked insolation-modulated variability in the strength of the South American Summer Monsoon, teleconnections with the North Atlantic Ocean, and/or cooling in the Southern Hemisphere. The driver for these past climate changes is difficult to identify, partly due to a lack of dated moraine records, especially in climatically sensitive areas of the southern Central Andes. Moreover, new constraints are needed on precisely where and when glaciers advanced. We use cosmogenic 10Be produced in situ to determine exposure ages for three generations of moraines at the Sierra de Aconquija, situated at 27°S on the eastern flank of the southern Central Andes. These moraines record glacier advances at approximately 22 ka and 40 ka, coincident with summer insolation maxima in the sub-tropics of the Southern Hemisphere, as well as at 12.5 ka and 13.5 ka during the Younger Dryas and the Antarctic Cold Reversal, respectively. We also identify minor glaciation during Bond Event 5, also known as the 8.2 ka event. These moraines register past climate changes with high fidelity, and currently constitute the southernmost dated record of glaciation on the eastern flank of the Central Andes. To contextualise these results, we compile 10Be data reported from 144 moraines in the eastern Central Andes that represent past glacier advances. We re-calculate exposure ages from these data using an updated reference production rate, and we re-interpret the moraine ages by taking the oldest clustered boulder age (after the exclusion of outliers attributed to nuclide inheritance) as closest to the timing of glacier advance—an approach for which we provide empirical justification. This compilation reveals that Central Andean glaciers have responded to changes in temperature and precipitation. We identify cross-latitude advances in phase with insolation cycles, the last global glacial maximum, and episodes of strengthened monsoonal moisture transport including the Younger Dryas and Heinrich Stadials 1 and 2. Our results from the Sierra de Aconquija allow us to constrain the southerly limit of enhanced precipitation associated with Heinrich Stadials at ∼25°S. More broadly, our findings demonstrate at both local and regional scales that moraines record past climate variability with a fine spatial and temporal resolution.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 5
    Publication Date: 2020-04-30
    Type: info:eu-repo/semantics/article
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