A SF6 tracer study of horizontal mixing in Lake Constance   总被引：1，自引：1，他引：0  

Manfred Maiss  Johann Ilmberger  Axel Zenger  Karl Otto Münnich 《Aquatic Sciences - Research Across Boundaries》1994,56(4):307-328

Horizontal mixing processes in the hypolimnion of the western part of Lake Constance are studied by measuring the dispersion of a sulfur hexafluoride (SF₆) tracer plume. Only 1 liter gaseous SF₆ (STP) was released at a central hypolimnic depth of 60 m in August 1990. Over a period of 3 months the horizontal dispersion of the tracer plume was measured by 19 surveys using a new, vertically integrating sampling device. The observed horizontal dispersion is marked by strong storm-induced stirring events. Nevertheless mean turbulent diffusion coefficients for the whole period can be computed. They rise about linear from 0.7 10⁵ cm²/s to 3.0 10⁵ cm²/s with the distance from the western end of the lake. For the hypolimnion of Überlingersee, a sill-separated basin in the western part of Lake Constance, a simple budget model gives an exchange time of 67 ± 6 days with the main basin (Obersee).  相似文献   

Greenhouse-gas versus aerosol forcing and African climate response     

Heiko Paeth  Johann Feichter 《Climate Dynamics》2006,26(1):35-54

There are many indicators that human activity may change climate conditions all around the globe through emissions of greenhouse gases. In addition, aerosol particles are emitted from various natural and anthropogenic sources. One important source of aerosols arises from biomass burning, particularly in low latitudes where shifting cultivation and land degradation lead to enhanced aerosol burden. In this study the counteracting effects of greenhouse gases and aerosols on African climate are compared using climate model experiments with fully interactive aerosols from different sources. The consideration of aerosol emissions induces a remarkable decrease in short-wave solar irradiation near the surface, especially in winter and autumn in tropical West Africa and the Congo Basin where biomass burning is mainly prevailing. This directly leads to a modification of the surface energy budget with reduced sensible heat fluxes. As a consequence, temperature decreases, compensating the strong warming signal due to enhanced trace gas concentrations. While precipitation in tropical Africa is less sensitive to the greenhouse warming, it tends to decrease, if the effect of aerosols from biomass burning is taken into account. This is partly due to the local impact of enhanced aerosol burden and partly to modifications of the large-scale monsoon circulation in the lower troposphere, usually lagging behind the season with maximum aerosol emissions. In the model equilibrium experiments, the greenhouse gas impact on temperature stands out from internal variability at various time scales from daily to decadaland the same holds for precipitation under the additional aerosol forcing. Greenhouse gases and aerosols exhibit an opposite effect on daily temperature extremes, resulting in an compensation of the individual responses under the combined forcing. In terms of precipitation, daily extreme events tend to be reduced under aerosol forcing, particularly over the tropical Atlantic and the Congo basin. These results suggest that the simulation of the multiple aerosol effects from anthropogenic sources represents an important factor in tropical climate change, hence, requiring more attention in climate modelling attempts.  相似文献   

Imaging distribution patterns of magnetic minerals by a novel high-T_c-SQUID-based field distribution measuring system: application to Permian sediments     

Norbert Nowaczyk  Horst-Ulrich Worm  rea Knecht  & Johann Hinken 《Geophysical Journal International》1998,132(3):721-724

A newly developed field distribution measuring system based on a high- T _c SQUID has been employed in the study of magnetic mineral distribution in several Permian sedimentary rocks. The instrument consists of a small, 1.4×1.4 mm sized YBaCu-oxide SQUID magnetic field sensor that is operated in a thin-walled dewar, so that the sample's surface, at room temperature, can be scanned at a distance of only ∼1.5 mm. The samples were subjected to a saturation remanence perpendicular to the surface and the scanning measurements in zero field reveal that the magnetization might be carried by only a small part of a sample, in one case associated with secondary oxide phases. High-resolution magnetic scans can aid in the interpretation of the magnetic remanence acquisition process.  相似文献   

Airborne measurements of savanna fire emissions and the regional distributio of pyrogenic pollutants over Western Africa     

Helas  Günter  Lobert  Jürgen  Scharffe  Dieter  Schäfer  Luise  Goldammer  Johann  Baudet  Jean  Ajavon  Ayité-Lô  Ahoua  Brou  Lacaux  Jean-Pierre  Delmas  Robert  Andreae  Meinrat O. 《Journal of Atmospheric Chemistry》1995,22(1-2):217-239

We measured CO₂, CO, CH₄, H₂, and NO₂ in air masses polluted by savanna fires over Côte d'Ivoire, western Africa. Elevated concentrations of these trace gases were found in fire plumes and also in extensive haze layers. Trace gas mixing ratios ranged as high as 605 ppmv for CO₂, 14.8 ppmv for CO, 2.7 ppmv for CH₄, 4.2 ppmv for H₂, and 25 ppbv for NO₂. We compare our emission ratios to those obtained in previous field and laboratory studies. The emission ratios, expressed as an average and as a range or as an average only, were: dCO/dCO₂ 5.3×10^–2 (3–18×10^–2); dCH₄/dCO 5.3×10^–2; dH₂/dCO 2.4×10^–1 and dNO₂/dCO₂ 1.8×10^–4 (1.5–2.2×10^–4). The values found match those found during similar measurements, though our results point to rather vigorous burning in the savanna of western Africa.  相似文献   

Upper bathyal trace fossils document palaeoclimate changes     

Johann Hohenegger  Peter Pervesler  Alfred Uchman  Michael Wagreich 《地学学报》2009,21(3):229-236

Marine trace fossils were investigated in a 102-m cored section that covers −14.379 to −14.142 Ma (Middle Miocene). Long-term climate trends are perfectly reflected by changing trace fossil communities of the upper bathyal (−200 to −300 m). The community structure is expressed in abundance of taxa based on probabilities of time concordance between the deposition of the sediment and the time, when the traces were produced. Changes in community structure precisely parallel the increasing δ¹³C isotopes during the Middle Miocene climate transition and perfectly mirror oscillations in solar insolation in both amplitudes and phase. Furthermore, the density stratification of the seawater caused by wind-induced currents is reflected in trace fossil communities. Additionally, the dependence of ichnotaxa abundance from threshold values in the sedimentation rate could be demonstrated.  相似文献   

Transforming management of tropical coastal seas to cope with challenges of the 21st century     

Peter F. Sale  Tundi Agardy  Cameron H. Ainsworth  Blake E. Feist  Johann D. Bell  Patrick Christie  Ove Hoegh-Guldberg  Peter J. Mumby  David A. Feary  Megan I. Saunders  Tim M. Daw  Simon J. Foale  Phillip S. Levin  Kenyon C. Lindeman  Kai Lorenzen  Robert S. Pomeroy  Edward H. Allison  R.H. Bradbury  Jennifer Corrin  Alasdair J. Edwards  David O. Obura  Yvonne J. Sadovy de Mitcheson  Melita A. Samoilys  Charles R.C. Sheppard 《Marine pollution bulletin》2014

Over 1.3 billion people live on tropical coasts, primarily in developing countries. Many depend on adjacent coastal seas for food, and livelihoods. We show how trends in demography and in several local and global anthropogenic stressors are progressively degrading capacity of coastal waters to sustain these people. Far more effective approaches to environmental management are needed if the loss in provision of ecosystem goods and services is to be stemmed. We propose expanded use of marine spatial planning as a framework for more effective, pragmatic management based on ocean zones to accommodate conflicting uses. This would force the holistic, regional-scale reconciliation of food security, livelihoods, and conservation that is needed. Transforming how countries manage coastal resources will require major change in policy and politics, implemented with sufficient flexibility to accommodate societal variations. Achieving this change is a major challenge – one that affects the lives of one fifth of humanity.  相似文献   

Neues über den Basalt von Kollnitz im Lavanttal Kärnten     

Erich Johann Zirkl  O. Braitsch  F. Hofer  Erentraud Kahler 《Mineralogy and Petrology》1962,8(1):96-139

  相似文献   

Possibilities and Limitations of Interdisciplinary, User-oriented Research: Experiences from the German Research Network Natural Disasters     

Bruno Merz  Jana Friedrich  Markus Disse  Jochen Schwarz  Johann G. Goldammer  Jochen Wächter 《Natural Hazards》2006,38(1-2):3-20

The German Research Network for Natural Disasters (DFNK) linked 15 partners with scientific expertise in the field of natural hazards. Main objectives were the development and provision of the scientific fundamentals for an advanced risk management of important natural disasters in Germany, i.e., floods, earthquakes, storms and wildland fires. This included risk analyses, the development of information systems for supporting disaster management, and recommendations for risk reduction measures. This paper gives an overview of DFNK and summarises its experiences concerning multidisciplinarity and user-orientation. It illustrates the concept of risk chains, causally linking the different processes from hazard to risk. The step from hazard to risk requires interdisciplinary research teams. The experiences show that integrative concepts allow results not achievable with mono-disciplinary approaches. Integrative approaches pave the way to harmonised safety considerations taking into account the different hazards in a region within a common framework. User-orientation, policy advice and development of operational tools are key issues of disaster research. The experiences of DFNK illustrate the limitations of a research network in bridging the gap between research and application within rather short-term projects. Successful cooperation with users could be established by those activities where, at the beginning of the project, a user was identified who had a strong interest in solving an urgent problem.  相似文献   

Modèle de formation du gisement d'argent d'Imiter (Anti-Atlas oriental,Maroc). Nouveaux apports de l'analyse structurale et minéralogique     

Johann Tuduri  Alain Chauvet  Aomar Ennaciri  Luc Barbanson 《Comptes Rendus Geoscience》2006,338(4):253-261

Based on a combined geometrical and mineralogical analysis, a three-stage model of formation of the mineralized veins of the giant Imiter silver deposit (Anti-Atlas, Morocco) is herein proposed. A first episode is characterized by the development of quartz, pink dolomite and Ag-rich minerals veins formed during a dextral transpressive event. The second episode is associated with a normal left-lateral motion that re-opens previous structures, filled by pink dolomite gangue. Alteration stages contribute to a local Ag enrichment. To cite this article: J. Tuduri et al., C. R. Geoscience 338 (2005).  相似文献   

Colloidally separated samples from Allende residues: Noble gases,carbon and an ESCA-study     

Ulrich Ott  Johann Kronenbitter  Jose Flores  Sherwood Chang 《Geochimica et cosmochimica acta》1984,48(2):267-280

A non-colloidal fraction separated by physical means from an $\text{HF}\text{HCl}$-resistant residue of the Allende carbonaceous meteorite exhibits a ratio of isotopically “normal” (Q-type) xenon to “anomalous” xenon (X-type) that is ~4 times larger than usually observed. Coincidentally this fraction contains carbon that is isotopically heavier by ~10%. than bulk Allende residue samples. ESCA analyses of companion colloidal separates show that the major portion of the S contained in our $\text{HF}\text{HCl}$-residues is elemental rather than a sulfide. They also confirm earlier observations that no elementally distinct surface coating is present, in accord with the absence of a surface-sited sulfur-bearing gas carrier, and that the oxygen content is increased after etching with nitric acid. For these separates noble gas data coupled with the ESCA data for nitrogen and the isotopic data for carbon point to the existence of heterogeneities among the noble gas-, carbon- and nitrogen-bearing phases and, thus, preservation of discrete components from the variety of source regions (or production mechanisms, or both) sampled by the Allende parent body. In sharp contrast to the success of physical and chemical methods in yielding samples in which one of the major noble gas components predominates to an extraordinary degree over the other, carbon isotopic compositions that have been inferred for the respective carrier phases in these same samples are strongly contradictory. Mass and isotope balance considerations lead us to conclude that a major fraction of the carbonaceous matter in Allende is noble-gas-poor, a result that could be confirmed by direct isolation of a sample, the carbon in which is dominated by this variety; and for that reason no simple relationship is discernable yet between observed isotopic compositions and either major noble gas component. Similar ambiguities may exist for nitrogen. The possible relationship between carbon-rich phases in ureilites and carbonaceous chondrites is considered.  相似文献