Glacial morphology and post-glacial contourites in northern Prince Gustav Channel (NW Weddell Sea,Antarctica)     

Camerlenghi  Angelo  Domack  Eugene  Rebesco  Michele  Gilbert  Robert  Ishman  Scott  Leventer  Amy  Brachfeld  Stefanie  Drake  Allison 《Marine Geophysical Researches》2001,22(5-6):417-443

We present the results of a marine geophysical investigation of the northern Prince Gustav Channel. By comparative analysis of multibeam bathymetric data, single channel seismic reflection profiles, underway chirp sonar data, ADCP current data and sediment coring, we define the main morphological elements of the area. In particular we define the glacial morphogenesis in relation to the excavation of inner shelf basins and troughs along structural discontinuities and lithologic boundaries. We identify streamlined surfaces that testify to the grounding of ice and past ice flow directions. These glacial forms are found only on glacial tills preserved in the deepest part of the basins, while net erosion to bedrock has occurred elsewhere. Since the Last Glacial Maximum (LGM), the relict glacial morphology has been draped by hemipelagic and diatomaceous mud, and bottom currents have played a major role in focusing sedimentation within small depocentres, that we define as contouritic drifts. Based on shallow sediment architecture and supported by direct measurements, we propose that the direction of bottom water flow is from the outer shelf into the Prince Gustav channel as a result of a combination of tidal currents and ice shelf-related thermohaline circulation.  相似文献   

Seismic Characterisation of Gas-rich Near Surface Sediments in the Arkona Basin, Baltic Sea     

M. Mathys  O. Thießen  F. Theilen  M. Schmidt 《Marine Geophysical Researches》2005,26(2-4):207-224

Gas in sediments has become an important subject of research for various reasons. It affects large areas of the sea floor where it is mainly produced. Gas and gas migration have a strong impact on the environmental situation as well as on sea floor stability. Furthermore, large research programs on gas hydrates have been initiated during the last 10 years in order to investigate their potential for future energy production and their climatic impact. These activities require the improvement of geophysical methods for reservoir investigations especially with respect to their physical properties and internal structures. Basic relationships between the physical properties and seismic parameters can be investigated in shallow marine areas as they are more easily accessible than hydrocarbon reservoirs. High-resolution seismic profiles from the Arkona Basin (SW Baltic Sea) show distinct ‘acoustic turbidity’ zones which indicate the presence of free gas in the near surface sediments. Total gas concentrations were determined from cores taken in the study area with mean concentrations of 46.5 ml/l wet sediment in non-acoustic turbidity zones and up to 106.1 ml/l in the basin centre with acoustic turbidity. The expression of gas bubbles on reflection seismic profiles has been investigated in two distinct frequency ranges using a boomer (600–2600 Hz) and an echosounder (38 kHz). A comparison of data from both seismic sources showed strong differences in displaying reflectors. Different compressional wave velocities were observed in acoustic turbidity zones between boomer and echosounder profiles. Furthermore, acoustic turbidity zones were differently characterised with respect to scattering and attenuation of seismic waves. This leads to the conclusion that seismic parameters become strongly frequency dependent due to the dynamic properties of gas bubbles.  相似文献   

Qualitätsziele für die Nordsee?- Pro und Kontra-Pro     

Dr. Maren Voß 《Ocean Dynamics》1991,44(5-6):283-288

Zusammenfassung Bereits im Oktober 1973 wurde von der EG ein Aktionsprogramm für den Umweltschutz verabschiedet, in dem die Definition von Qualitätszielen gefordert wird. Danach sollen Qualitätsziele für den Schutz des Menschen gegen Umweltverschmutzung, aber auch für den Schutz der Umwelt an sich formuliert werden. Die Vorstellungen bezogen das Meerwasser zwar ausdrücklich mit ein, waren jedoch stark funktionsbezogen (Badewasser, Fischzucht). 1986 fanden Qualitätsziele in die Leitlinien Umweltvorsorge Eingang. Die Dritte Internationale Nordseeschutzkonferenz 1991 forderte, Qualitätsziele international zu entwickeln. Im selben Jahr erhielt das Nationalparkamt vom Schleswig-Holsteinischen Umweltministerium den Auftrag, ein Diskussionspapier zu erarbeiten. Dieses Papier liegt inzwischen vor. Es beschreibt ökologische Schäden und schlägt auch Parameter für Qualitätsziele vor.In der aktuellen Diskussion wird z. T. bestritten, daß die Beschreibung ökologischer Ziele von Nutzen sein könnte. Sinnvolles Handeln zum Schutz der Umwelt ist aber nur möglich, wenn Klarheit über die Ziele besteht. Auch in der Umweltpolitik reichen vage Formulierungen nicht aus, zumal dann allzu leicht eine breite, aber folglose Zustimmung erfolgt. Präzise definierte Ziele ermöglichen dagegen eine Kontrolle über den Erfolg von eingeleiteten Maßnahmen.Aus diesen Gründen müssen ökologische Qualitätsziele für den Natur- und Umweltschutz definiert werden. Die dafür benötigten Begriffe sind eindeutig festzulegen und zu verwenden (z. B. Qualitätsstandards, Grenzwerte, Richtwerte). Erst dann ist es möglich, die Ziele von den anzuwendenden Methoden zu unterscheiden, die in der bisherigen Diskussion ständig verwechselt werden. Ohne Beteiligung der Naturwissenschaftler können Qualitätsziele nicht verständlich und präzise formuliert werden.

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For and against ecological quality objectives for the North Sea-for

Summary In October 1973 the EC approved environmental protection measures in which a demand was made for a definition of ecological quality objectives. These were to be formulated to ensure that humans were protected against environmental pollution, but aims to protect the environment itself were also to be drawn up. Sea water was included in the programme, but suggestions were strongly oriented towards its various uses (bathing, fish farming). Quality aims were included in the 1986 Leitlinien Umweltvorsorge (Guidelines for environmental precautions). The 3rd International North Sea conference in 1991 requested that ecological quality objectives should be developed internationally. Also in 1991, the Ministry of the Environment in Schleswig-Holstein instructed the Nationalpark agency to draw up a discussion document which has now been presented. It describes ecolgical damage and suggests parameters for ecological quality objectives.In the current discussion, it is partly disputed that describing ecological aims could be useful. But sensible action to protect the environment is only possible if there is no confusion about the aims. In ecological policy, too, vague formulations are not sufficient, particularly if what follows is broad but ineffective agreement. Precisely defined aims, on the other hand, mean that the success of measures taken can be checked.It is for these reasons that ecological quality objectives must be defined for conservation purposes. The terms to be used must be fixed and used unambiguously (e. g. quality standards, limit values, guide values). Only then it will be possible to distinguish between aims and the methods which in previous discussions have always been confused. Ecological quality objectives cannot be formulated intelligibly and precisely without the pariticipation of scientists.

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Veröffentlichung Nr. 32 des Projektes Ökosystemforschung Wattenmeer  相似文献   

The origin of rutile-ilmenite aggregates (“nigrine”) in alluvial-fluvial placers of the Hagendorf pegmatite province, NE Bavaria, Germany     

H. G. Dill  F. Melcher  M. Füßl  B. Weber 《Mineralogy and Petrology》2007,89(3-4):133-158

Summary Titanium placer deposits occur in alluvial-fluvial drainage systems which dissect Moldanubian gneisses intruded by Late Variscan pegmatites (Hagendorf province) in southern Germany. Based upon their texture (zonation, exsolution lamellae, intergrowth), microchemical data (Nb, Cr, Ta, V, Fe, W, Sn) and mineral inclusions, two major grain types of intergrown rutile and ilmenite have been established. Grains of type A are always zoned and consist of rutile cores enveloped by ilmenite containing small inclusions of wolframite. A core-rim transition zone is characterized by complex relations of rutile and ilmenite, with rutile lamellae being rich in Nb, V and Fe. Types B1 and B2 aggregates consist of ilmenite with lamellae of niobian rutile and/or ilmenorutile, and additionally have inclusions of ferrocolumbite, pyrochlore, betafite, sphalerite, pyrrhotite and Fe oxides. Such grain types featuring an intimate intergrowth of rutile and ilmenite were called nigrine. Type-C grains are quite similar in their morphological appearance but consist of W-enriched rutile devoid of mineral inclusions and reaction products. Pseudorutile and leucoxene replacing minerals of the nigrine aggregates are presumably caused by supergene alteration under fluctuating redox conditions. Phosphate and aluminum remobilized by supergene processes led to the formation of hydrous Ti-rich phases containing Al, P and Fe. High Nb and W concentrations in nigrine aggregates and in rutile type C may be taken as a marker for highly differentiated granites or pegmatites. This has implications for both, heavy-mineral-based provenance analysis and stream sediment exploration.  相似文献   

Multi-proxy Reconstruction of Trophic State,Hypolimnetic Anoxia and Phototrophic Sulphur Bacteria Abundance in a Dimictic Lake in Northern Germany over the past 80 Years     

Mirko Dreßler  Thomas Hübener  Solvig Görs  Petra Werner  Uwe Selig 《Journal of Paleolimnology》2007,37(2):205-219

During monthly investigations from 1996 to 2000, a hypolimnetic layer of phototrophic sulphur bacteria (Chromatium spp.) were observed in Lake Dudinghausen, a small dimictic lake in northern Germany. This paleolimnological study was initiated to detect if the occurrence of sulphur bacteria was related to cultural eutrophication or reflected natural conditions. Therefore, diatoms, algal pigments, okenone, geochemical proxies, and ²¹⁰Pb and ¹³⁷Cs were used in four sediment cores to investigate historical changes in trophic development, hypolimnetic redox conditions, anoxia and phototrophic sulphur bacteria abundances. Fossil diatoms, pigments, the ratio of chlorophyll derivatives to total carotenoids and the ratio of chlorophyll a to its derivatives suggest two phases of eutrophication coupled with hypolimnetic anoxia over the last ~80 years: a first phase from about 1923–1932 and a second from 1952 to 1982. In the first phase the ratios of Fe–Mn as well as Fe–Ca increased, suggesting seasonal anoxia. However, hypolimnetic anoxia was only weak because low levels of okenone suggest no mass development of sulphur bacteria. In contrast, sulphur bacteria increased during the early stages of the second eutrophication phase, suggesting increased temporal and spatial hypolimnetic anoxia. Surprisingly, the ratios of Fe–Mn as well as Fe–Ca decreased during this time. Possibly Fe, Mn and Ca were equally reduced through the intense anoxia. In the final stage, sulphur bacteria decreased again. As these bacteria need both anoxic conditions and a certain amount of light, the increased nutrient load probably led to low Secchi depth and therefore insufficient light conditions. In more recent years, diatoms and pigments suggest a decrease in nutrient levels. A second mass development of sulphur bacteria occurred, probably due to improved light conditions and continued anoxia in the upper hypolimnion. We conclude that the recent development of phototrophic sulphur bacteria do not represent natural conditions in Lake Dudinghausen. Furthermore, the upper sediments contain a completely new diatom flora that never occurred in older sediments of Lake Dudinghausen. Therefore, nutrient levels may eventually reach natural conditions, however they may not represent biological background reference conditions.  相似文献   

Stratospheric-tropospheric exchange influenced by solar activity. Results of a 5 years study     

Dr. R. Reiter  M. Littfaß 《Meteorology and Atmospheric Physics》1977,26(2-3):127-154

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Neuere Ergebnisse der Anwendung physikalischchemischer Methoden auf Probleme der Geologie     

B. Goßner 《International Journal of Earth Sciences》1915,6(4-6):218-241

Ohne Zusammenfassung  相似文献   

Über die Bewertung der Schneeverhältnisse alpiner Orte auf Grund der Abhängigkeit der Andauer der Schneedecke,der mittleren maximalen Schneehöhe und ihrer Eintrittszeit von der Seehöhe     

H. Steinhäußer 《Theoretical and Applied Climatology》1950,2(1-2):120-128

Zusammenfassung Für 64 Stationen wurde die mittlere Eintrittszeit der maximalen Schneehöhe ermittelt und ihre Abhängigkeit von verschiedenen Faktoren untersucht. In Abhängigkeit von der Seehöhe zeigt diese Eintrittszeit einen der mittleren maximalen Schneehöhe ähnlichen Gang: sie verschiebt sich mit zunehmender Seehöhe zum Sommer hin, oberhalb 1300 m fast linear; zwischen 900 und 1200 m Seehöhe jedoch verschiebt sich die Eintrittszeit nur wenig.Mittlere maximale Schneehöhe und ihre Eintrittszeit zeigen in ihren Einzelwerten guten stochastischen Zusammenhang mit dem Schneeanteil an der Jahresniederschlagsmenge. Weniger gut ist der Zusammenhang mit der Seehöhe, am schlechtesten mit der Jahresniederschlagsmenge.Aus den Normalkurven lassen sich für jede Station diejenigen Seehöhen ermitteln, in denen die Andauer der Schneedecke, die mittlere maximale Schneehöhe und ihre Eintrittszeit normal wären. Diese Normalhöhen sind wertvolle Größen zur Charakterisierung der Schneedeckenverhältnisse, z. B. von Wintersportplätzen. Da die Anomalien dieser drei Schneedeckengrößen in der Mehrzahl der Fälle von gleichem Vorzeichen sind, lassen sich die Schneeverhältnisse häufig durch ein Normalhöhenmittel aus den Normalhöhen bezüglich Andauer, Betrag und Eintrittszeit der größten Schneehöhe kennzeichnen.

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Summary The average date of the maximum of snow-depth has been calculated for 64 stations and its dependence on different factors investigated. As a function of the altitude this date shows a variation similar to that of the mean maximum of snow-depth: with increasing height it is moving towards summer, above 1300 m in an almost linear way, whereas between 900 and 1200 m there is no great variation at all. The values of the mean maximum of snow-depth and of its date have individually nearly the same probability as the snow fraction of the yearly precipitation. Not so good is the connection with the altitude and still worse that with the yearly precipitation. It is possible to deduce from the standard curves for every station the altitude at which the duration of snow-cover, the mean maximum of snow-depth and its date would be normal. These normal altitudes are valuable terms for the characterization of conditions of snow-cover, e. g. at places for winter sports. The anomalies of these three, terms of snow-cover having mostly the same sign, the snow conditions can be often described by the average value of the normal altitudes for duration, amount, and date of the maximum of snow-depth.

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Résumé L'auteur a établi pour 64 stations l'époque moyenne de la hauteur maximum de la couche de neige gisante et a étudié sa relation avec divers facteurs. En fonction de l'altitude, cette époque varie dans le même sens que la hauteur moyenne de la couche maximum de neige: elle recule vers l'été avec l'altitude, presque linéairement au-dessus de 1300 m; entre 900 et 1200 m, l'époque ne se déplace que peu. Les valeurs moyennes de la couche maximum de neige et leur époque présentent individuellement la même probabilité que la fraction neigeuse des précipitations annuelles; la relation est moins bonne avec l'altitude, et encore moins avec la quantité annuelle des précipitations. Des courbes établies, on peut déduire pour chaque station les altitudes auxquelles la durée de l'enneigement, la moyenne de la couche maximum et son époque seraient dites normales. Ces altitudes sont utiles pour caractériser les conditions de la neige, par exemple dans les stations de sports d'hiver. Comme les anomalies de ces trois facteurs ont en général le même signe, il est possible de décrire les conditions de l'enneigement (durée, hauteur et époque) à l'aide des valeurs normales ainsi calculées.

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Mit 2 Textabbildungen.  相似文献   

Study of the initiation and propagation of excavation damaged zones around openings in argillaceous rock     

Alain Millard  Jobst Maßmann  Amel Rejeb  Shin Uehara 《Environmental Geology》2009,57(6):1325-1335

The study of the creation and evolution of the excavation disturbed zone (EDZ) in argillaceous rocks is a major issue for the safety of nuclear wastes underground repositories. In this context, the argillaceous Tournemire site has provided a unique opportunity to study the evolution of the EDZ with time thanks to the existence of three openings of different ages. A thorough characterization of the EDZ has been conducted by different means such as visual observation, analysis of samples extracted from drilled boreholes, EDZ permeability measurements, etc. On the basis of these measurements, a conceptual model of the EDZ initiation and propagation at the Tournemire site has been proposed. In order to validate this model, numerical simulations of increasing complexity have been carried out. In a first attempt, the response of the rock mass to the excavation phase, followed by seasonal cyclic variations of temperature and relative humidity inside the opening, has been simulated by means of a purely mechanical analysis, using a simple elastic material model. The EDZ has been estimated by post-processing the calculated stress states, using a Mohr–Coulomb failure criterion. The results obtained show that no EDZ could be predicted unless adopting a low cohesion value for the rock mass. Moreover, the deferred nature of the EDZ formation in Tournemire could not be reproduced. These limitations have then been suppressed by using a coupled viscoplastic-damaging mechanical model, the parameters of which have been identified from different laboratory experiments. With this model, a time evolution of the EDZ could be predicted, but the EDZ pattern could not match the one observed in situ. Finally, in view of the importance of the hydraulic couplings, unsaturated hydro-mechanical calculations have been carried out to investigate the effect of the numerous seasonal variations cycles and the resulting shrinkage.  相似文献   

Remote Sensing of Biologically Reworked Sediments: A Laboratory Experiment     

Annelies De Backer  Stefanie Adam  Jaak Monbaliu  Erik Toorman  Magda Vincx  Steven Degraer 《Estuaries and Coasts》2009,32(6):1121-1129

The present study aims to test the application of remote sensing to address the impact of bioturbation on physical sediment properties. Therefore, a laboratory experiment was developed, using microcosms mimicking a marine intertidal water–sediment interface to test the influence of Corophium volutator densities on sediment properties. Three main variables (water content, clay content, and mean grain size) were measured in three treatments (no Corophium, 5,000 Corophium per square meter, and 20,000 Corophium per square meter) after 16 days of bioturbation. Results obtained with conventional—destructive—techniques showed a significant increase of water content and a significant, but small decrease of clay content in the presence of Corophium. The remote sensing technique detected the impact of Corophium on water content as an increase in absorption at 1,450 nm, but was not able to detect the animal impact on clay content. This study demonstrates that remote sensing data could be significantly modified by bioturbation activities and that remote sensing can be applied in the laboratory to address the impact of bioturbation on sediment properties. This possibly opens new perspectives for long-term experiments concerning the role of bioturbation on sedimentary processes.  相似文献