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排序方式: 共有234条查询结果,搜索用时 15 毫秒
1.
Viability theory for an ecosystem approach to fisheries 总被引:1,自引:1,他引:1
2.
3.
Serge von Bubnoff 《International Journal of Earth Sciences》1949,37(1):60-71
Zusammenfassung Die epirogenetische Geschichte Osteuropas (Fennosarmatiens) läßt sich seit dem Kambrium in 11 Zyklen der Transgression und Regression gliedern, die vermutlich den PulsationenGrabaus entsprechen. Bei im allgemeinen gleichzeitigem und gleichsinnigem Verlauf zeigen sich regional gewisse Unterschiede oder Phasendifferenzen, indem einige stabilere Teile Sarmatiens die einzelnen Zyklen nur verzögert oder überhaupt nicht mitmachen. Diese Pulsationen sind nicht identisch mit den vom Verf. angenommenen Großzyklen Westeuropas, sondern werden von ihnen überlagert, allerdings in regelmäßiger Weise, derart, daß mehrere Pulsationen einen Großzyklus zusammensetzen. Durch diese Überlagerung entstehen Phasendivergenzen, welche den Gesamtvorgang komplizieren, ohne seine Gesetzmäßigkeit aufzuheben. Eine dritte Ursache für regionale Unterschiede besteht in dem vom Verf. schon früher betonten zyklischen Abdrehen der tektogenetischen Beanspruchung, welche zwischen alpidisch und uralisch wechselt. Da, entsprechend dem Großgefüge, im Westen die alpidische, im Osten die uralische Bewegungstendenz vorwiegt, entstehen zwangsläufig zeitliche Differenzen, die zu einer weiteren Komplikation des Bildes beitragen. Der Verf. legt aber Wert auf die Feststellung, daß diese Differenzen und Komplikationen in dem Wesen der zyklischen Prozesse begründet sind und ihre Gesetzmäßigkeit nicht nur nicht aufheben, sondern im Gegenteil dazu dienen können, die tieferen Ursachen des erdgeschichtlichen Rhythmus zu ergründen. 相似文献
4.
In this study, we documented the Holocene history of a peat plateau at the arctic tree line in northern Québec using stratigraphic and macrofossil analyses to highlight the effects of geomorphic setting in peatland development. Paludification of the site began about 6800 cal yr BP. From 6390 to 4120 cal yr BP, the peatland experienced a series of flooding events. The location of the peatland in a depression bounded by two small lakes likely explains its sensitivity to runoff. The proximity of a large hill bordering the peatland to the south possibly favored the inflow of mineral-laden water. The onset of permafrost aggradation in several parts of the peatland occurred after 3670 cal yr BP. Uplifting of the peatland surface caused by permafrost stopped the flooding. According to radiocarbon dating of the uppermost peat layers, permafrost distribution progressed from the east to the west of the peatland, indicating differential timing for the initiation of permafrost throughout the peatland. Most of the peatland was affected by permafrost growth during the Little Ice Age. Picea mariana macroremains at 6450 cal yr BP indicate that the species was present during the early stages of peatland development, which occurred soon after the sea regression. 相似文献
5.
Emmanouil Flaounas Serge Janicot Sophie Bastin Rémy Roca Elsa Mohino 《Climate Dynamics》2012,38(5-6):965-983
In spring the inland penetration of the West African Monsoon (WAM) is weak and the associated rainband is located over the Guinean coast. Then within a few days deep convection weakens considerably and the rainband reappears about 20?days after over the Sahel, where it remains until late September signalling the summer rainy season. Over the period 1989–2008 a teleconnection induced by the Indian monsoon onset is shown to have a significant impact on the WAM onset, by performing composite analyses on both observational data sets and atmospheric general circulation model simulations ensembles where the model is nudged to observations over the Indian monsoon sector. The initiation of convective activity over the Indian subcontinent north of 15°N at the time of the Indian monsoon onset results in a westward propagating Rossby wave establishing over North Africa 7–15?days after. A back-trajectory analysis shows that during this period, dry air originating from the westerly subtropical jet entrance is driven to subside and move southward over West Africa inhibiting convection there. At the same time the low-level pressure field over West Africa reinforces the moisture transport inland. After the passage of the wave, the dry air intrusions weaken drastically. Hence 20?days after the Indian monsoon onset, convection is released over the Sahel where thermodynamic conditions are more favourable. This scenario is very similar in the observations and in the nudged simulations, meaning that the Indian monsoon onset is instrumental in the WAM onset and its predictability at intraseasonal scale. 相似文献
6.
Bernard Fontaine Javier Garcia-Serrano Pascal Roucou Belen Rodriguez-Fonseca Teresa Losada Fabrice Chauvin Sébastien Gervois Sivarajan Sijikumar Paolo Ruti Serge Janicot 《Climate Dynamics》2010,35(1):95-114
Using both empirical and numerical ensemble approaches this study focuses on the Mediterranean/West African relationship in
northern summer. Statistical analyses utilize skin temperature, sea surface temperature, in situ and satellite rainfall, outgoing
longwave radiation (OLR) observations and reanalyzed data winds and specific humidity on isobaric surfaces. Numerical investigations
are based on a large set of sensitivity experiments performed on four atmospheric general circulation models (AGCM): ARPEGE-Climat3,
ECHAM4, LMDZ4 and UCLA7.3. Model outputs are compared to observations, discussed model by model and with an ensemble (multi-model)
approach. As in previous studies the anomalous Mediterranean warm events are associated with specific impacts over the African
monsoon region, i.e., a more intense monsoon, enhanced flux convergence and ascendances around the ITCZ, a strengthening of
low level moisture advection and a more northward location of ascending motion in West Africa. The results show also new features
(1) thermal variability observed in the two Mediterranean basins has unalike impacts, i.e. the western Mediterranean covaries
with convection in Gulf of Guinea, while the eastern Mediterranean can be interpreted as Sahelian thermal-forcing; (2) although
observations show symmetry between warming and cooling, modelling evidences only support the eastern warming influence; (3)
anomalous East warm situations are associated with a more northward migration of the monsoon system accompanied by enhanced
southwertely flow and weakened northeasterly climatological wind; (4) the multi-model response shows that anomalous East warm
surface temperatures generate an enhancement of the overturning circulation in low and high levels, an increase in TEJ (Tropical
Eeasterly Jet) and a decrease in AEJ (African Eeasterly Jet). 相似文献
7.
Xavier Le Pichon Jacques Angelier Jean Aubouin Nicolas Lyberis Serge Monti Vincent Renard Henri Got Ken Hsu¨ Yossi Mart Jean Mascle Drummond Matthews Dimitri Mitropoulos Pandelis Tsoflias Georges Chronis 《Earth and Planetary Science Letters》1979,44(3):441-450
Preliminary results of a multi-narrow beam survey of the Hellenic trench system, in the Eastern Mediterranean, are presented. The southwestern Ionian branch is divided in small basins, partly filled with Pleistocene sediments. The morphology suggests that the basins are deformed by a compressional stress acting roughly perpendicularly to the trench along N50°E. This direction is the direction of the regional slip vector of the shallow thrust-type earthquakes. The structure of the southeastern Pliny-Strabo branch is quite different. Narrow en-e´chelon slots, oriented N40°E, have been mapped within the main troughs oriented N60°E. The regional earthquake slip vector is also oriented along N40°E. We conclude that the Hellenic trench system is an active subduction system, dominated by thrust along the Ionian branch and by transform motion along the Pliny-Strabo branch. 相似文献
8.
Jean Louis Birck Serge Fourcade Claude J. Allegre 《Earth and Planetary Science Letters》1975,26(1):29-35
Internal isochrons for two Apollo 15 rocks give an age of(3.34 ± 0.09)and(3.46 ± 0.04) × 109 years with an identical87Sr/86Sr initial ratio of 0.69928. Considering the possibility for the line obtained in a87Sr/86Sr,87Rb/86Sr diagram to be a mixing line, the significance of these results are discussed. 相似文献
9.
The paper first recalls briefly a methodological framework to assess landslide hazard and risk analysis in terms of predisposition, triggering andrevealing factors. This framework, that reflects the mechanisms involved in the landslide, is based on the Geotechnical Characterisation of slope movements proposed by Vaunat et al. (1994) and Leroueil et al. (1996). The Geotechnical Characterisation can be schematized by a 3-D matrix having the following axes: types of movement; types ofmaterial; and the four stages of movement: pre-failure, failure, post-failure andreactivation. For each relevant element of this 3-D matrix, there is a characterisationsheet including: the controlling laws and parameters, the predisposition factors, thetriggering or aggravating factors, the revealing factors and the consequences of the movement. The paper focuses afterwards on the post-failure stage, which generallyis the most destructive, and on the mobility index. It is shown that this laterindex can be described as the product of sub-indices associated with failure, brittlenessof the material, ability of the soil to develop pore pressures, geometry of the moving soil mass and characteristics of the terrain. It is also shown how these aspectscan be incorporated into the Geotechnical characterisation of slope movements. This seems to provide a rational basis for examining slope movements at the post-failure stage and assessing associated risks. 相似文献
10.
Abdelkader Ouali Mehadji Serge Elmi Patrick Rachebœuf Larbi Mekahli 《Comptes Rendus Geoscience》2004,336(14):1283-1292
In the Saoura, the brachiopod shell beds, so-called niveau coralligène, correspond to a major shell deposit dated to the Late Emsian. Brachiopods and crinoids dominate the benthic assemblage that contains also corals, bryozoans, trilobites, goniatites, and orthocones. This major level has a large geographic distribution and it is characterized by a wide brachiopod diversity due to time-averaging, taphonomic feedback and alternate bottom conditions changing from soft to shelly and firm. This kind of brachiopod association is linked to a transgressive onlap system. At regional extent, we can correlate this major shell bed to similar shell deposits from the Ahnet-Mouydir, Tindouf, and Zemmour areas. It indicates an important transgressive event underlined by change in the sedimentation from detritic deposits to carbonate sediments. To cite this article: A. Ouali Mehadji et al., C. R. Geoscience 336 (2004). 相似文献