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  • 1
    Digitale Medien
    Digitale Medien
    High-resolution210Pb dating of Lake Constance sediments: Stable lead in Lake Constance (1994)
    Springer
    Environmental geology 24 (1994), S. 267-274 
    Details
    ISSN: 1432-0495
    Schlagwort(e): 210Pb dating ; Lead ; Sediments
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: Abstract Two sediment cores (BO90/13b and BO90/17b) from Lake Constance were investigated byγ-spectrometry for210Pb,134Cs,137Cs,241Am,234Th, and other members of the238U decay chain. The sediments were dated using the constant-flux model for210Pb, and accumulation rates were determined. These range from 0.04 to 0.65g/cm 2/yr (BO90/13b) and 0.04 to 0.8g/cm 2/yr (BO90/17b), respectively. The mean accumulation rate amounts to 0.16g/cm 2/yr for both cores. The cores had already been dated by lamination counting and reconstruction of high-water events at the Limnological Institute at Constance, so that a very precise time scale was available. Both ages derived are in agreement within statistical error up to 1900, which means dating with the constant-flux model for210Pb was confirmed up to that age. The position of the maxima of bomb cesium and americium confirm the stratigraphic and210Pb datings. With241Am a further radioactive isotope is available, which can, due to the half-life of241Pu (t 1/2=14.4yr) be detected now byγ-spectrometry and can serve as an additional time indicator, the maximum being dated at 1963. By applying the various time scales, the depth profiles of stable lead and zinc of core BO90/13b were dated. Both heavy metals show a very significant maximum located beneath the layer of the maxima of bomb cesium and americium, showing that these maxima are older than those of the bomb isotopes. It is remarkable in this context that the maximum of zinc concentration occurs a little later than that of stable lead. Similar concentration profiles are observable in core BO90/17b and other, older sediment cores (CS6-CS10) on a transect across the lake. In contrast to a former assumption, the depth profile of stable lead in Lake Constance sediments does not reflect the anthropogenic gasoline lead emissions into the atmosphere for Germany, their maximum being dated at 1971.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00767087
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  • 2
    Digitale Medien
    Digitale Medien
    Geochemistry of a piston core from Ontong Java Plateau (western equatorial Pacific): evidence for sediment redistribution and changes in paleoproductivity (1996)
    Springer
    Geologische Rundschau 85 (1996), S. 536-545 
    Details
    ISSN: 0016-7835
    Schlagwort(e): Key words Ontong Java Plateau ; Thorium-230 ; Barium ; Productivity ; Lysocline ; Sediment focusing ; Vertical mass accumulation rate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: Abstract  We discuss geochemical proxies, reflecting processes of primary productivity, CaCO3 dissolution, and sediment redistribution in a piston core (RNDB 74P) from the Ontong Java Plateau. Due to the shallow water depth, biogenic carbonate is well preserved and a very good δ18O stratigraphy is available down to isotopic stage 11. 230Thex gives evidence that the sediment accumulation pattern is driven mainly by processes of sediment focusing or winnowing. Due to the constant production of 230Th in the water column, the bulk sediment accumulation rates could be corrected for the particle rain deriving from the water column above. The 230Thex 0/CaCO3 ratio reflects the well-known Pacific CaCO3 preservation pattern with ice growth dissolution spikes and deglacial preservation spikes. The record of the grain size fraction 〉63 μm supports these results. The downcore concentrations and accumulation rates of barium (Ba) are on a higher level during interglacials and show several peaks. Normalization of Ba with 230Thex 0 delivers a more uniform level of the Ba accumulation rates throughout the core. This pattern suggests a constantly higher biological productivity (nearly tenfold) in this area throughout the past 200 kyr compared with an open ocean environment. Barium peaks observed at the climatic transitions 2/1 and 6/5 and in stage 5 are in contrast to a predicted reduction of interglacial productivity at this location. A possible explanation might be the onset of the modern circulation pattern. The transition from Ba-enriched deep water to lower contents in the Atlantic might have resulted in an enhanced deposition of Ba in the Pacific.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s005310050094
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Geochemistry of a piston core from Ontong Java Plateau (western equatorial Pacific): evidence for sediment redistribution and changes in paleoproductivity (1996)
    Springer
    International journal of earth sciences 85 (1996), S. 536-545 
    Details
    ISSN: 1437-3262
    Schlagwort(e): Ontong Java Plateau ; Thorium-230 ; Barium ; Productivity ; Lysocline ; Sediment focusing ; Vertical mass accumulation rate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: Abstract We discuss geochemical proxies, reflecting processes of primary productivity, CaCO3 dissolution, and sediment redistribution in a piston core (RNDB 74P) from the Ontong Java Plateau. Due to the shallow water depth, biogenic carbonate is well preserved and a very goodδ 18O stratigraphy is available down to isotopic stage 11.230Thex gives evidence that the sediment accumulation pattern is driven mainly by processes of sediment focusing or winnowing. Due to the constant production of230Th in the water column, the bulk sediment accumulation rates could be corrected for the particle rain deriving from the water column above. The230Thex 0/CaCO3 ratio reflects the well-known Pacific CaCO3 preservation pattern with ice growth dissolution spikes and deglacial preservation spikes. The record of the grain size fraction 〉63 µm supports these results. The downcore concentrations and accumulation rates of barium (Ba) are on a higher level during interglacials and show several peaks. Normalization of Ba with230Thex 0 delivers a more uniform level of the Ba accumulation rates throughout the core. This pattern suggests a constantly higher biological productivity (nearly tenfold) in this area throughout the past 200 kyr compared with an open ocean environment. Barium peaks observed at the climatic transitions 2/1 and 6/5 and in stage 5 are in contrast to a predicted reduction of interglacial productivity at this location. A possible explanation might be the onset of the modern circulation pattern. The transition from Ba-enriched deep water to lower contents in the Atlantic might have resulted in an enhanced deposition of Ba in the Pacific.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02369008
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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    Artikel (Nationallizenzen)
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