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  • 1
    Electronic Resource
    Electronic Resource
    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
    Keywords: 210Pb dating ; Lead ; Sediments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00767087
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  • 2
    Electronic Resource
    Electronic Resource
    Thorium and uranium isotopes in a manganese nodule from the Peru basin determined by alpha spectrometry and thermal ionization mass spectrometry (TIMS): Are manganese supply and growth related to climate? (1996)
    Springer
    International journal of earth sciences 85 (1996), S. 577-585 
    Details
    ISSN: 1437-3262
    Keywords: Manganese nodules ; Thorium dating ; Uranium isotopes ; Peru basin ; TIMS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Thorium- and uranium isotopes were measured in a diagenetic manganese nodule from the Peru basin applying alpha- and thermal ionization mass spectrometry (TIMS). Alpha-counting of 62 samples was carried out with a depth resolution of 0.4 mm to gain a high-resolution230Thexcess profile. In addition, 17 samples were measured with TIMS to obtain precise isotope concentrations and isotope ratios. We got values of 0.06–0.59 ppb (230Th), 0.43–1.40 ppm (232Th), 0.09–0.49 ppb (234U) and 1.66–8.24 ppm (238U). The uranium activity ratio in the uppermost samples (1–6 mm) and in two further sections in the nodule at 12.5±1.0 mm and 27.3–33.5 mm comes close to the present ocean water value of 1.144±0.004. In two other sections of the nodule, this ratio is significantly higher, probably reflecting incorporation of diagenetic uranium. The upper 25 mm section of the Mn nodule shows a relatively smooth exponential decrease in the230Thexcess concentration (TIMS). The slope of the best fit yields a growth rate of 110 mm/Ma up to 24.5 mm depth. The section from 25 to 30.3 mm depth shows constant230Thexcess concentrations probably due to growth rates even faster than those in the top section of the nodule. From 33 to 50 mm depth, the growth rate is approximately 60 mm/Ma. Two layers in the nodule with distinct laminations (11–15 and 28–33 mm depth) probably formed during the transition from isotopic stage 8 to 7 and in stage 5e, respectively. The Mn/Fe ratio shows higher values during interglacials 5 and 7, and lower ones during glacials 4 and 6. A comparison of our data with data from adjacent sediment cores suggests (a) a variable supply of hydrothermal Mn to sediments and Mn nodules of the Peru basin or (b) suboxic conditions at the water sediment interface during periods with lower Mn/Fe ratios.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02369012
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  • 3
    Electronic Resource
    Electronic Resource
    Thorium and uranium isotopes in a manganese nodule from the Peru basin determined by alpha spectrometry and thermal ionization mass spectrometry (TIMS): Are manganese supply and growth related to climate? (1996)
    Springer
    Geologische Rundschau 85 (1996), S. 577-585 
    Details
    ISSN: 0016-7835
    Keywords: Key words Manganese nodules ; Thorium dating ; Uranium isotopes ; Peru basin ; TIMS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Thorium- and uranium isotopes were measured in a diagenetic manganese nodule from the Peru basin applying alpha- and thermal ionization mass spectrometry (TIMS). Alpha-counting of 62 samples was carried out with a depth resolution of 0.4 mm to gain a high-resolution 230Thexcess profile. In addition, 17 samples were measured with TIMS to obtain precise isotope concentrations and isotope ratios. We got values of 0.06–0.59 ppb (230Th), 0.43-1.40 ppm (232Th), 0.09–0.49 ppb (234U) and 1.66–8.24 ppm (238U). The uranium activity ratio in the uppermost samples (1–6 mm) and in two further sections in the nodule at 12.5±1.0 mm and 27.3–33.5 mm comes close to the present ocean water value of 1.144±0.004. In two other sections of the nodule, this ratio is significantly higher, probably reflecting incorporation of diagenetic uranium. The upper 25 mm section of the Mn nodule shows a relatively smooth exponential decrease in the 230Thexcess concentration (TIMS). The slope of the best fit yields a growth rate of 110 mm/Ma up to 24.5 mm depth. The section from 25 to 30.3 mm depth shows constant 230Thexcess concentrations probably due to growth rates even faster than those in the top section of the nodule. From 33 to 50 mm depth, the growth rate is approximately 60 mm/Ma. Two layers in the nodule with distinct laminations (11–15 and 28–33 mm depth) probably formed during the transition from isotopic stage 8 to 7 and in stage 5e, respectively. The Mn/Fe ratio shows higher values during interglacials 5 and 7, and lower ones during glacials 4 and 6. A comparison of our data with data from adjacent sediment cores suggests (a) a variable supply of hydrothermal Mn to sediments and Mn nodules of the Peru basin or (b) suboxic conditions at the water sediment interface during periods with lower Mn/Fe ratios.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005310050098
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