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121.
David Etienne Bruno Wilhelm Pierre Sabatier Jean-Louis Reyss Fabien Arnaud 《Journal of Paleolimnology》2013,49(2):117-127
Spores of coprophilous fungi, especially Sporormiella, are often well preserved in lake sediment cores. It has been hypothesized that such spores can be used to quantify past livestock abundance. The quantitative relationship between fungal spore abundance and livestock populations, however, is not well established, nor are the mechanisms of spore transport and deposition in lacustrine systems. Multiple cores from Lake Allos, a large high-elevation lake in the French Alps, were used to map the modern abundance of Sordaria and Sporormiella spores throughout the lake. We observed high spatial heterogeneity with respect to spore numbers. No correlation with the distance from shoreline was found. There was, however, a relation with distance from the two main lake inlets. These results were used to select two fungi-rich sediment cores to investigate grazing pressure over the last two centuries. Comparisons were made between spore influx and historic data on livestock densities in the catchment. A sharp decrease in Sporormiella influx ca. 1894–1895 was associated with a reported reduction in sheep in the Allos catchment at that time. Mean influx of Sporormiella decreased by a factor of three between the nineteenth and twentieth centuries, reflecting a reduction in the reported number of animals in the Lake Allos catchment, from 6,000 to 2,000. This study confirmed that Sporormiella spore abundance in lake sediments can be used as a proxy for catchment herbivore numbers in paleoecological reconstructions. Nevertheless, our data indicate that before spore accumulation can be used to infer past domestic herbivore density, one must understand the processes of coprophilous spore transfer from the catchment to the lake and the influence of core location on spore numbers in the sediment. 相似文献
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123.
Observations of the quiet-Sun network in the UV emission line Siiv 1393 Å over a time period of two hours are presented. Bursts of explosive events, highly Doppler-shifted emission, seem to be sporadically emitted from the brighter regions of the network lanes. Individual events have typical lifetimes of ≈ 1–6 min and come in bursts of up to 30 min. The most spectacular burst in this dataset, shown in the accompanying movie, lasts ≈ 30 min and shows a wide variety of line profiles with both red and blue shifts ≈180 km s1. There appears to be no characteristic form or evolutionary pattern to the line profiles in either the individual events or series of events. There are about twice as many blue shifts as red shifts. 相似文献
124.
It is well known that sunspots are dark. This statement is not correct in the sunspot atmosphere between the chromosphere and the corona, where sunspots often are brighter than their surroundings. The brightest feature in the sunspot transition region is called a sunspot plume. Not all sunspots contain a plume. We find that 20 out of 21 sunspots show a plume when one magnetic polarity dominates the sunspot region out to a distance of 50 from the sunspot. Most sunspots show downflows that exceed 25 km s–1 in the sunspot plumes at temperatures close to 250000 K. This downflow is not maintained by inflow from the corona, but by gas at transition region temperatures, streaming in flow channels from locations well outside the sunspot. We suggest that this inflow is a necessary requirement for the sunspot plume to occur and present a working hypothesis for the origin of sunspot plumes. This paper is the first thorough spectral analysis of sunspot plumes. It is based on simultaneous observations of ten or six EUV emission lines in 42 sunspot regions with the Coronal Diagnostic Spectrometer – CDS on the Solar and Heliospheric Observatory – SOHO. The line profiles are studied in detail with another SOHO instrument, the Solar Ultraviolet Measurements of Emitted Radiation – SUMER. 相似文献
125.
Jurassic Ferrar rocks in Victoria Land (Antarctica) occur predominantly as basaltic or andesitic flows and sills. Both show
characteristic petrographical and chemical variations, which can be related to in-situ differentiation processes. Such characteristics
have been investigated at one flow (“Colonnade flow”) and one sill (“Thumb Point sill”) in the Prince Albert Mountains (Central
Victoria Land) based on a statistical grain size analysis and the application of the crystal size distribution theory. A third
magma body (“HiTi-unit”), which in previous literature was described as a flow, does not show clear similarities to either
the flow or sill. Sill and flow are in-situ differentiated with accumulation of silicic residual melt in the latest cooled
parts. For the flow this part is located in the lower half and for the sill in the upper third of their thickness. Thumb Point
sill additionally shows an accumulation zone of olivine in the lower third. The position of the residual melt accumulation
zone is an indicator for an origin as flow or sill. The HiTi-unit, by contrast, exhibits, only moderate petrographical and
chemical variations. Growth and nucleation rates have been determined using, with some modifications, the CSD theory introduced
by Marsh (1988). Growth rates of plagioclase for the flow vary from 10−11 to 10−10 cm/s and are comparable with literature values for basaltic lava lakes on Hawaii. Nucleation rates vary from 10−4 to 10−3 cm−3s−1, which are generally smaller than for Hawaiian basalts. Growth and nucleation rates for the sill cover a large range from
10−13 to 10−11 cm/s and 10−9 to 10−3 cm−3s−1, respectively. Systematic variations of these parameters with vertical position were obtained for the sill with its extensive
differentiation history. Nucleation and growth rates are dependant on the mode of cooling. Nevertheless, small but significant
differences between the flow and sill exist. Growth and nucleation rates of HiTi-unit (10−12 to 10−11 cm/s and 10−6 to 10−5 cm−3s−1) are intermediate between the flow and sill and thus do not allow a distinction of emplacement mode.
Received: 6 December 1995 / Accepted: 3 May 1996 相似文献
126.
127.
128.
Wilhelm Nümann 《Aquatic Sciences - Research Across Boundaries》1964,26(1):102-146
Ohne Zusammenfassung
Prof. Dr. Curt Kosswig zum 60. Geburtstag gewidmet 相似文献
129.
Prof. Dr. Wilhelm Vortisch 《International Journal of Earth Sciences》1964,53(2):650-679
Atectonic deformations of all scales are discussed and their knowledge is historically analyzed. 相似文献
130.
Wilhelm Wolff 《International Journal of Earth Sciences》1957,46(1):186-196
Zusammenfassung Magnetische Messungen zeigen im Bereich des Siegerländer Gewölbes und seiner SSW-lichen Verlängerung eine geringe Erniedrigung der Störungswerte gegenüber den Randgebieten. Diese magnetische Depression kann unter grö\eren Vorbehalten als Auswirkung sauerer Intrusionen gedeutet werden.Refraktionsseismische Untersuchungen erbrachten im Siegerland den Nachweis eines seismischen Horizontes mit hoher Geschwindigkeit unter dem devonischen Deckgebirge. Die wahre Geschwindigkeit der seismischen Welle in diesem Tiefenhorizont beträgt nach neueren Beobachtungen wahrscheinlich etwa 6,18 km/sec. Sie kann granitischem Material zugeordnet werden, das im Bereich des Siegen-Wieder-Sattels seine Höchstlage (etwa 1,5 km u. F.) aufweist und an seinen Flanken bis zu 4 km Tiefe hinabreicht. Bei dieser Deutung würden die magnetischen und seismischen Ergebnisse sich gegenseitig nicht ausschlie\en.Gravimetrische Messungen stellten über dem Siegerländer Gewölbe eine variszisch streichende positive Anomalie von etwa 4 mgl fest, deren geologische Deutung unsicher ist. Die Anomalie kann sowohl durch einen in der Tiefe lagernden Intrusivkörper als auch durch eine Höherlage des Basements und durch die bekannte Sedimenttektonik des Gebietes hervorgerufen sein.Nach einem Vortrag auf der Tagung der Geologischen Vereinigung am 11. März 1956 in Göttingen. 相似文献