Fischwachstum bei Oligo-, Meso- und Eutrophie des Bodensees

Recent growth of 14 fish taxa of Lake Constance has been studied. In the mesotrophic basin summer-pelagic species opposite to the others appear to grow faster now than during earlier oligotrophic status. From trends of growth, feeding and yield (table) it is concluded that eutrophication has favoured planktivores.—In the eutrophic lower basin only coregonids grow slower than in the mesotrophic part of the lake. Factors that have caused growth differences are thought to be food density and water temperature (through changed fish distribution and different shape of basin).     

Weather and seasonal climate prediction for flood planning in the Yangtze River Basin

This paper describes the use of numerical weather and climate models for predicting severe rainfall anomalies over the Yangtze River Basin (YRB) from several days to several months in advance. Such predictions are extremely valuable, allowing time for proactive flood protection measures to be taken. Specifically, the dynamical climate prediction system (IAP DCP-II), developed by the Institute of Atmospheric Physics, Chinese Academy of Sciences (IAP), is applied to YRB rainfall prediction and flood planning. IAP DCP-II employs ensemble prediction with dynamically conditioned perturbations to reduce the uncertainty associated with seasonal climate prediction. IAP DCP-II was shown to successfully predict seasonal YRB summer flooding events based on a 15-year (1980–1994) hindcast experiment and the real-time prediction of two summer flooding events (1999 and 2001). Finally, challenges and opportunities for applying seasonal dynamical forecasting to flood management problems in the YRB are discussed.     

The manganese nodules of the Kane Gap (East Atlantic). Indicators of sedimentation — erosion changes

Manganese nodules from the Kane Gap (a deep sea channel connecting the Sierra Leone and Gambia Basins off West Africa) were investigated chemically and dated by¹⁰Be along cross-sections. Comparing the nodule structure with the stratigraphy of the related sediments, the following conclusions are drawn concerning the sedimentation processes during the last 4 to 6×10⁶ years: The growth of the nodules started about 4 to 4.5 Ma before present during or near to the end of a period of erosion on a fossil-free, probably Miocene sediment. During the first phase of only a few hundred thousandyears, the nodules grew very quickly (7 to >18 mm/Ma). Fe-rich hydrogenetic material formed the internal sections of the nodules during this time. Slowing down of the bottom currents, resulting in deposition of thin sediment covers for short intervals, caused the character of the nodules to change to a more diagenetic composition. The growth rates were reduced to about 1 to 2 mm/Ma. The time of slowing is roughly 3 to 4 Ma BP.Probable uncertainties of the dating and growth rates resulting from supposed changes of the¹⁰Be supply to the nodules due to variations of the near bottom environment are discussed.

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Zusammenfassung An Manganknollen aus der Kane-Lücke, dem Verbindungskanal zwischen Sierra Leone Becken und Gambia Becken (vor W-Afrika) wurden entlang Querprofilen durch mehrere Knollen chemische Untersuchungen und¹⁰Be Altersbestimmungen durchgeführt. Durch Vergleich des Aufbaus der Knollen mit der Stratigraphie des unterlagernden Sediments werden Rückschlüsse auf Veränderungen des Sedimentationsgeschehens während der letzten 4–6×10⁶ Jahre gezogen. Hiernach begann das Wachstum der Knollen vor maximal 4.5×10⁶ Jahren während oder gegen Ende einer Erosionsphase auf fossilfreiem, vermutlich miozänem Sediment. Während der ersten Phase wuchsen die Knollen über wenige 100000 Jahre sehr schnell (7 bis>18 mm/10⁶ Jahre). Hierbei schied sich Fe-reiche Knollensubstanz hydrogener Zusammensetzung ab. Nach Verringerung der Strömung und vermutlich zeitweiser Bildung von dünnen Sedimentschleiern änderte sich der Charakter der Knollen zu mehr diagnetischer Zusammensetzung bei wesentlich reduziertem Wachstum (ca. 1 bis 2 mm/10⁶ Jahre). Der Zeitpunkt der Umstellung ist nur sehr grob zu ermitteln, er dürfte etwa zwischen 3 und 4×10⁶ Jahren vor heute liegen.Eventuelle Unsicherheiten bei der Datierung und den Wachstumsraten, die möglicherweise aus milieubedingten Änderungen in der¹⁰Be Versorgung der Knollen resultieren, werden diskutiert.

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Résumé Le «Kana Gap» est un chenal sous-marin qui relie les bassins de Sierra Leone et de Gambie, au large de l'Afrique occidentale. Des nodules de manganèse, recueillis le long de profils transversaux dans ce chenal, ont fait l'objet d'une étude chimique et d'une détermination d'âge¹⁰Be. La comparaison entre la structure des nodules et la stratigraphie des sédiments sous-jacents permet de tirer les conclusions suivantes relatives au processus sédimentaire au cours des 4 à 6 derniers Ma. La croissance des nodules a commencé il y a environ 4 à 4,5 Ma pendant ou juste après un épisode d'érosion sous-marine sur des sédiments non fossilifères, probablement miocènes. Au cours d'une première phase d'une durée de quelques centaines de milliers d'années, la croissance a été très rapide (7 à > 18 mm par Ma) avec formation de la partie centrale du nodule, constituée de matière hydrogénée riche en Fe. Ensuite, après ralentissement des courants de fond et dépôt probable d'une mince couche de sédiment, le caractère des nodules a évolué vers une composition plus diagénétique, avec réduction du taux de croissance à 1 à 2 mm par Ma. Le moment de ce changement de régime doit se situer entre 3 et 4 Ma.Des changements dans les conditions de milieu sur le fond de la mer pourraient avoir provoqué une variation de la quantité de¹⁰Be apportée aux nodules, d'où résulterait une incertitude sur l'estimation des âges et du taux de croissance; cette question est discutée par les auteurs.

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P-T-X-controlled element transport through granulite-facies ternary feldspar from Lofoten,Norway

Fluid transport on the grain-scale controls many rock properties and governs chemical exchange. Charnockites from Lofoten indicate fluid penetration into ternary alkali feldspars controlled by their microtextures. In a process of fluid infiltration at granulite-facies conditions (∼600°C and 8–11 kbar), tiny pyroxenes enclosed in alkali feldspar reacted to amphiboles, which are always spatially connected to perthitic albite. Investigation of these microtextures by TEM imaging of Focused Ion Beam (FIB) prepared foils revealed that pyroxenes in contact with albite lamellae show dissolution features. An amorphous Fe- and Cl-bearing material interpreted to be a residuum of the percolating fluid was found within albite lamellae. Textures and mineral compositions indicate that a Cl-rich aqueous fluid attacked the lamellae, which then provided pathways for further fluid flow. A correspondence was found between feldspar compositions, their microtexture and their degree of alteration as a result of their permeability for fluids at specific temperatures. Hence, in addition to pressure and temperature, small variations of feldspar composition can strongly influence the fluid permeability of feldspathic rocks under lower crustal conditions.     

The geochemical composition of the terrestrial surface (without soils) and comparison with the upper continental crust

The terrestrial surface, the “skin of the earth”, is an important interface for global (geochemical) material fluxes between major reservoirs of the Earth system: continental and oceanic crust, ocean and atmosphere. Because of a lack in knowledge of the geochemical composition of the terrestrial surface, it is not well understood how the geochemical evolution of the Earth’s crust is impacted by its properties. Therefore, here a first estimate of the geochemical composition of the terrestrial surface is provided, which can be used for further analysis. The geochemical average compositions of distinct lithological classes are calculated based on a literature review and applied to a global lithological map. Comparison with the bulk composition of the upper continental crust shows that the geochemical composition of the terrestrial surface (below the soil horizons) is significantly different from the assumed average of the upper continental crust. Specifically, the elements Ca, S, C, Cl and Mg are enriched at the terrestrial surface, while Na is depleted (and probably K). Analysis of these results provide further evidence that chemical weathering, chemical alteration of minerals in marine settings, biogeochemical processes (e.g. sulphate reduction in sediments and biomineralization) and evaporite deposition are important for the geochemical composition of the terrestrial surface on geological time scales. The movement of significant amounts of carbonate to the terrestrial surface is identified as the major process for observed Ca-differences. Because abrupt and significant changes of the carbonate abundance on the terrestrial surface are likely influencing CO₂-consumption rates by chemical weathering on geological time scales and thus the carbon cycle, refined, spatially resolved analysis is suggested. This should include the recognition of the geochemical composition of the shelf areas, now being below sea level.     

Fischereiliche Veränderungen in kulturbedingt eutrophierenden Seen

Mainly from the trends of fish yield four stages of fish succession in European lakes under cultural eutrophication are described. Trends of transparency, phosphorus, weed, benthos, and plankton are included. Supplementary interrelated effects of eutrophication on fish biology (growth, fat content, condition, distribution, reproduction, parasites, fish kills, introgression, feeding) have been collected from literature. The effects, mainly observed on planktivores, are not specific for species or localities.     

Circumstellar envelopes and disks of pre-main sequence stars

The current state of knowledge about circumstellar matter of young stellar objects is briefly reviewed. It appears that some very young stars yet to accrete substantial amounts of mass may be seen through their dusty infalling envelopes even at optical wavelengths, because of the presence of holes or large departures from spherical symmetry in the envelopes. The evidence for this picture is summarized in the context of one wellstudied young star, HL Tau, indicating that much of the large-scale structure originally identified as a rotating disk is probably a flattened infalling envelope. Departures from spherical symmetry in protostellar clouds are likely to lead to quite flattened structures once collapse gets under way, further suggesting that infall in large-scale toroids may be a general feature of low-mass star formation. The best kinematic evidence for Keplerian disk rotation comes from optical and near-infrared high-resolution spectroscopy of the innermost regions of circumstellar disks. Disk masses are uncertain but are likely to be at least the order of minimum mass solar nebula models, if not much larger.     

Evolution and Fragmentation of Wide-Angle Wind Driven Molecular Outflows

We present two dimensional cylindrically symmetric hydrodynamic simulations and synthetic emission maps of a stellar wind propagating into an infalling, rotating environment. The resulting outflow morphology, collimation and stability observed in these simulations have relevance to the study of young stellar objects, Herbig-Haro jets and molecular outflows. Our code follows hydrogen gas with molecular, atomic and ionic components tracking the associated time dependent molecular chemistry and ionization dynamics with radiative cooling appropriate for a dense molecular gas. We present tests of the code as well as new simulations which indicate the presence of instabilities in the wind-blown bubble’s swept-up shell.