Die Bedeutung der Isotopenforschung für die Geologie

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Bildung von Kondensationskernen durch UV-Strahlung in verschiedenen Gasen

Zusammenfassung Die Erzeugung von Kondensationskernen durch UV-Licht wurde mittels eines automatischenPollakschen Kernzählers und einerWilsonkammer aus Glas untersucht. Da die UV-Kerne von einem Schwebstoffilter zurückgehalten werden, ließ sich durch Verwendung zweier Bestrahlungsgefäße mit dazwischengeschaltetem Filter die Spurengashypothese bestätigen. Bestrahlungsversuche in Luft, Stickstoff, Sauerstoff, Argon und Wasserstoff ergaben, daß durch längere Bestrahlung eines abgeschlossenen Gasvolumens die kernbildende Substanz allmählich verbraucht wird. Durch Zugabe definierter Mengen gasförmigen Ammoniaks in den Bestrahlungsraum zeigte sich, daß die von verschiedenen Autoren geäußerte Ansicht, gasförmiges Ammoniak sei die kernbildende Substanz, nicht haltbar ist. Die Untersuchung des Einflusses von Schwefelwasserstoff bzw. Schwefeldioxyd ergab, daß die atmosphärische Konzentration von H₂S zur Erklärung des UV-Effektes nicht ausreicht, während dies bei SO₂ der Fall ist. Das Ergebnis, daß SO₂ maßgebend an der Bildung der UV-Kerne in atmosphärischer Luft beteiligt ist, wird dadurch gestützt, daß der UV-Effekt einen ähnlichen Tagesgang zeigt wie das atmosphärische SO₂.

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Summary The production of condensation nuclei by UV light was investigated by means of an automaticPollak nucleus counter and aWilson glass-chamber. As the UV nuclei can be removed by an aerosol filter, the trace gas hypothesis could be confirmed by using two irradiation tubes separated by an aerosol filter. Irradiation experiments in air, nitrogen, oxygen, argon and hydrogen in a closed volume had the result that the nucleogenic substance gradually disappears after sufficiently long irradiation. By adding definite quantities of ammonia vapour into the irradiation tube it could be shown that ammonia is not the nucleogenic substance, as was supposed by some authors. The investigation of the influence of sulphur dioxide and hydrogen sulfide showed that the atmospheric concentration of H₂S is not sufficient to explain the UV effect in atmospheric air, whereas this is true with SO₂. The result that SO₂ takes part in the formation of the UV nuclei is supported by the fact that SO₂ and the UV effect show a similar diurnal variation.

     

Mean and Turbulent Flow Statistics in a Trellised Agricultural Canopy

Flow physics is investigated in a two-dimensional trellised agricultural canopy to examine that architecture’s unique signature on turbulent transport. Analysis of meteorological data from an Oregon vineyard demonstrates that the canopy strongly influences the flow by channelling the mean flow into the vine-row direction regardless of the above-canopy wind direction. Additionally, other flow statistics in the canopy sub-layer show a dependance on the difference between the above-canopy wind direction and the vine-row direction. This includes an increase in the canopy displacement height and a decrease in the canopy-top shear length scale as the above-canopy flow rotates from row-parallel towards row-orthogonal. Distinct wind-direction-based variations are also observed in the components of the stress tensor, turbulent kinetic energy budget, and the energy spectra. Although spectral results suggest that sonic anemometry is insufficient for resolving all of the important scales of motion within the canopy, the energy spectra peaks still exhibit dependencies on the canopy and the wind direction. These variations demonstrate that the trellised-canopy’s effect on the flow during periods when the flow is row-aligned is similar to that seen by sparse canopies, and during periods when the flow is row-orthogonal, the effect is similar to that seen by dense canopies.     

The carbon cycle and biogeochemical dynamics in lake sediments

The concentrations of organic carbon (OC) and CaCO3 in lake sediments are often inversely related. This relation occurs in surface sediments from different locations in the same lake, surface sediments from different lakes, and with depth in Holocene sediments. Where data on accumulation rates are available, the relation holds for organic carbon and CaCO3 accumulation rates as well. An increase of several percent OC is accompanied by a decrease of several tens of percent CaCO3 indicating that the inverse relation is not due to simple dilution of one component by another. It appears from core data that once the OC concentration in the sediments becomes greater than about 12%, the CO2 produced by decomposition of that OC and production of organic acids lowers the pH of anoxic pore waters enough to dissolve any CaCO3 that reaches the sediment-water interface. In a lake with a seasonally anoxic hypolimnion, processes in the water column also can produce an inverse relation between OC and CaCO3 over time. If productivity of the lake increases, the rain rate of OC from the epilimnion increases. Biogenic removal of CO2 and accompanying increase in pH also may increase the production of CaCO3. However, the decomposition of organic matter in the hypolimnion will decrease the pH of the hypolimnion causing greater dissolution of CaCO3 and therefore a decrease in the rain rate of CaCO3 to the sediment-water interface.     

40Ar/39Ar Thermochronology west of the Main Uralian fault, southern Urals, Russia

West of the Main Uralian fault, the main suture in the southern Urals, ⁴⁰Ar/³⁹Ar apparent ages of amphibole, muscovite and potassium feldspar are interpreted as cooling ages. A fast exhumation of the metamorphic complex of Kurtinsky during Upper Carboniferous time is indicated by the small age difference (15 Ma) between cogenetic amphibole and muscovite. Differentiated movement in the footwall of the Main Uralian fault along strike is indicated by the age difference of 70 Ma between the metamorphic complexes of Kurtinsky (north) and Maksyutov (south). No Upper Paleozoic (Uralian) medium- to high-temperature event is recorded in ⁴⁰Ar/³⁹Ar data from the metamorphic complex of Beloretzk (MCB). An amphibole age of 718±5 Ma and the occurrence of mafic intrusions might signal the break-up of Rodinia and therefore indicate the rifting period followed by the separate movement of the "Beloretzk terrane". Muscovite ages of approximately 550±5 Ma, the unique pre-Ordovician tectonometamorphic evolution of the MCB and the Late Vendian sedimentary history of the western Bashkirian Megaanticlinorium (BMA) imply the existence of a Neoproterozoic orogeny at the eastern margin of Baltica. This orogeny might have been initiated by the accretion of the "Beloretzk terrane". The metamorphic grade of the overlain Silurian shales and the K/Ar microcline ages from the "Beloretzk terrane" give evidence for a new thermal event at approximately 370 Ma. A microcline age of 530–550 Ma obtained for the Vendian conglomerate in the western BMA suggests that a maximum temperature of approximately 200°C was reached in Cambrian or Vendian times. An orthoclase age (590–630 Ma) of the Vendian Zigan flysch deposits might be inherited from the eastern source area, the Cadomian orogen. An orthoclase age (910–950 Ma) from the Riphean Zilmerdak conglomerate coincides with a documented decrease in the subsidence rate of the Upper Riphean basin.