How Episodic Coral Breakage Can Determine Community Structure: A South African Coral Reef Example     

Bernhard  Riegl Andrea  Riegl 《Marine Ecology》1996,17(1-3):399-410

Abstract. Africa's southernmost coral reefs are situated in Natal Province, South Africa. The Natal coast is exposed to open Ocean swells and episodic storm swell conditions. Benthic communities on these reefs differentiated into three community types: shallow reefs (8–18 m) were dominated by alcyonacean corals and low-growing, massive Scleractinia; intermediate reefs (18–25 m) were dominated chiefly by branching and tabular Scleractinia of the genus Acropora (A. austera, A. clathrata); deep reefs were not dominated by corals but by sponges. Breakage and recovery experiments indicated that the difference in Acropora dominance between shallow and intermediate sites was caused by breakage in high swell conditions. Survival of experimentally produced A. austera fragments was significantly higher in intermediate than in shallow sites, where higher surge made re-attachment and regeneration unlikely. Also, colony morphology was adapted to differential surge conditions: colonies on the shallow reefs were smaller with shorter branches, while on intermediate reefs they were much bigger with long, widely spreading branches. Episodic breakage and low fragment survival due to high water-motion thus excluded branching corals from shallow reef sites.  相似文献   

Über die Berechnung sämtlicher Feldgrössen aus der Vertikalintensität und deren Anwendung auf die Auswertung von Schwerebildern     

Bernhard Kosbahn 《Pure and Applied Geophysics》1949,15(1-2):27-36

Zusammenfassung In nachstehender Untersuchung wird in umfassender Weise gezeigt, wie sich aus der Karte der Vertikalintensität einer lokalen, für sich allein betrachteten Schwerestörung sämtliche anderen Feldgrössen und Ableitungen berechnen lassen. Es ergibt sich dadurch die Möglichkeit, den Verlauf des störenden Kraftfeldes auch unter der Erdoberfläche zu berechnen und aus einem Kraftlinienbild unmittelbar den Aufbau der Inhomogenitäten im Untergrund zu erkennen.

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Summary It is shown that the picture of a local anomaly in gravity (U _z ) may give the basement of structural calculations to an extend that was not known till now. FromU _z all other terms and derivations of the field of gravity are obtainable such asU, U _x ,U _y ,U _zz ,U _zzz , etc. The knowledge of these terms enables us to pursue the lines of gravity under the surface and thus to recognise immediately the characterising features of the structure itself.

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Klima und Artbildung     

Rensch  Bernhard 《International Journal of Earth Sciences》1952,40(1):137-152

International Journal of Earth Sciences - Der kurze Vortrag bezweckt lediglich, durch einige generelle Betrachtungen dem Paläontologen Anregungen bei Diskussionen über das Thema...  相似文献   

Illuminated and shadowed contour lines: improving algorithms and evaluating effectiveness     

James D. Eynard  Bernhard Jenny 《International journal of geographical information science》2016,30(10):1923-1943

Shadowed contour lines vary line width. Illuminated contour lines additionally vary color based on an angle of illumination. Illuminated and shadowed contour lines date back to the mid-nineteenth century, but their effectiveness compared to conventional contour lines has not been fully examined. Currently, illuminated and shadowed contour lines are not widely used in computer-based cartography because they are not included in most GIS apmaking software. This article introduces improvements to existing algorithms for creating illuminated and shadowed contour lines from digital elevation data. A software package is made available to allow mapmakers to more easily make customized illuminated and shadowed contour maps. A user study comparing illuminated and shadowed contour lines to conventional contour lines and shaded relief with approximately 400 participants was conducted. Results indicate that map-readers can interpret relative height differences between points better and quicker with illuminated contour lines than regular contour lines or shaded relief. Study participants were able to select absolute maxima on an unlabeled illuminated contour map and a labeled regular contour map with equal accuracy and speed. These findings suggest that illuminated contour lines could be used more frequently for improved visualization of terrain and other surface data on maps.  相似文献   

Understanding the Interactions between Climate Change, Landscape Evolution, Surface Processes and Tectonics in the Earth System: What Can the Studies of Chinese Deserts Contribute?     

YANG Xiaoping  Bernhard EITEL 《《地质学报》英文版》2016,90(4):1444-1454

Due to large deserts on Earth surface a thorough understanding of climate change, landscape evolution and geomorphological processes having occurred in deserts is crucial for Earth System Science. The landscapes in deserts are, however, diverse and different over the globe with regard to their geomorphological nature, human activities and geological histories. In the last decades a great number of efforts have been put to the investigation of the initial timing of the occurrence of arid climate, e. g. in northwestern China. Silty sediments in the downwind directions have been used to deduce the histories of deserts. In general, there is a lack of knowledge about processes and landscapes in Chinese drylands between the initial Miocene silt sedimentation at desert margins and the late Quaternary multiple occurrences of wetter climate with assumed large lakes in many of the deserts in northern China. The geomorphological concept of three primary triggering factors, i.e., the sediment supply, sediment availability and transport capacity of wind, and additionally the underground geology need to be fully considered for a better understanding of the environmental histories of sand seas which should not be viewed as equivalent for deserts because sand seas cover between < 1% and ca. 45% of the desert areas in various continents dependent on a complex interaction between various processes of both exogenous and endogenous origins.  相似文献   

Mesozoic transpression,transtension, subduction and metallogenesis in northern and central California     

W. G. Ernst  Cameron A. Snow  Hannah H. Scherer 《地学学报》2008,20(5):394-413

Middle Paleozoic to Middle Jurassic terrane assemblies in the Klamaths and Sierran Foothills consist of mafic–ultramafic complexes + fine‐grained terrigenous strata derived from previously accreted continental‐margin belts. Sutured oceanic terranes reflect c. 230 Myr of margin‐parallel slip involving chiefly transtension and transpression. Quartzofeldspathic clastic rocks and blueschists ± eclogites are very rare. Little devolatilization occurred at magmagenic depths; hence, coeval hydrothermal ore deposits and granitoids are uncommon. In contrast, nearly head‐on Cretaceous subduction of the Farallon plate generated the massive Klamath–Sierra Nevada volcanic–plutonic arc, reflecting dewatering of the eastward descending oceanic lithosphere in the magmagenic zone. Immature Great Valley forearc and Franciscan trench deposits shed from the arc record c. 70 Myr. of rapid crustal growth. Au‐bearing solutions rising from magmagenic depths, exsolved from plutons, and expelled from heated wall rocks were mobilized attending arc construction. Precipitation of gold‐bearing quartz veins occurred where H₂O + CO₂‐bearing fluids encountered major geochemical discontinuities in the wall rocks.  相似文献   

From micron-sized needle-shaped hydrates to meter-sized shotcrete tunnel shells: micromechanical upscaling of stiffness and strength of hydrating shotcrete     

Bernhard Pichler  Stefan Scheiner  Christian Hellmich 《Acta Geotechnica》2008,3(4):273-294

Knowledge on the stresses in shotcrete tunnel shells is of great importance, as to assess their safety against severe cracking or failure. Estimation of these stresses from 3D optical displacement measurements requires shotcrete material models, which may preferentially consider variations in the water–cement and aggregate–cement ratios. Therefore, we employ two representative volume elements within a continuum micromechanics framework: the first one relates to cement paste (with a spherical material phase representing cement clinker grains, needle-shaped hydrate phases with isotropically distributed spatial orientations, a spherical water phase, and a spherical air phase; all being in mutual contact), and the second one relates to shotcrete (with phases representing cement paste and aggregates, whereby aggregate inclusions are embedded into a matrix made up by cement paste). Elasticity homogenization follows self-consistent schemes (at the cement paste level) and Mori–Tanaka estimates (at the shotcrete level), and stress peaks in the hydrates related to quasi-brittle material failure are estimated by second-order phase averages derived from the RVE-related elastic energy. The latter permits upscaling from the hydrate strength to the shotcrete strength. Experimental data from resonant frequency tests, ultrasonics tests, adiabatic tests, uniaxial compression tests, and nanoindentation tests suggest that shotcrete elasticity and strength can be reasonably predicted from mixture- and hydration-independent elastic properties of aggregates, clinker, hydrates, water, and air, and from strength properties of hydrates. At the structural level, the micromechanics model, when combined with 3D displacement measurements, predicts that a decrease of the water–cement ratio increases the safety of the shotcrete tunnel shell.  相似文献   

Heterozoan carbonates from the equatorial rocky reefs of the Galápagos Archipelago          下载免费PDF全文

Claire E. Reymond  Konny‐Sebastian Zihrul  Jochen Halfar  Bernhard Riegl  Alexander Humphreys  Hildegard Westphal 《Sedimentology》2016,63(4):940-958

Strongly influenced by seasonal and interannual (i.e. El Niño‐Southern Oscillation) upwelling, the equatorial setting of the Galápagos Archipelago is divided into well‐defined temperature, nutrient and calcium carbonate saturation (Ω_aragonite) regions. To understand the relationship between oceanographic properties and sediment grain associations, grain size, carbonate content and components from sea floor surface samples were analysed, representing the main geographical regions of the Galápagos Archipelago. The shallow‐water rocky reefs of the Galápagos Archipelago are characterized by mixed carbonate–siliciclastic slightly gravelly sands. Despite minor differences in carbonate content, major differences exist in the distribution and composition of key carbonate producing biota. Halimeda is absent and benthic foraminifera occur in extremely low abundance. The western side of the Galápagos Archipelago is strongly influenced by nutrient‐rich, low‐Ω_aragonite, subtropical water, which generates a heterozoan carbonate biofacies in a tropical realm resembling cold‐water counterparts (i.e. serpulid, echinoderm, gastropod, barnacle and bryozoan‐rich facies). The Central East region is composed of a transitional‐heterozoan biofacies. Biofacies observed in the northern region have an increased occurrence of tropical corals, albeit with a minor overall contribution to the carbonate components. Although the temperature gradient would allow for a broader distribution of photozoan biofacies, the increased nutrient concentration and related reduced light penetration from the upwelled waters favour heterozoan carbonate factories, mimicking cool‐water, deeper or higher latitude environments. The recent sedimentary record of the Galápagos Archipelago presents a range of tropical heterozoan carbonate communities, responding to more than simply latitude or temperature but a much more complex mixture of physical, evolutionary and geological processes.  相似文献   

Thermal history of the westernmost Eastern Alps (Penninic Rhenodanubian Flysch nappes,Helvetic nappes,and Subalpine Molasse thrust sheets)     

Michael Zerlauth  Audrey Bertrand  Gerd Rantitsch  Doris Groß  Hugo Ortner  Hannah Pomella  Bernhard Fügenschuh 《International Journal of Earth Sciences》2016,105(5):1525-1547

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Three generations of monazite in Austroalpine basement rocks to the south of the Tauern Window: evidence for Variscan, Permian and Eo-Alpine metamorphic events     

Erwin Krenn  Bernhard Schulz  Fritz Finger 《Swiss Journal of Geoscience》2012,105(3):343-360

Three monazite generations were observed in garnet-bearing micaschists from the Schobergruppe in the basement to the south of the Tauern Window, Eastern Alps. Low-Y monazite of Variscan age (321?±?14?Ma) and high-Y monazite of Permian age (261?±?18?Ma) are abundant in the mica-rich rock matrix and in the outer domains of large garnet crystals. Pre-Alpine monazite commonly occurs as polyphase grains with low-Y Variscan cores and high-Y Permian rims. Monazite of Eo-Alpine age (112?±?22?Ma) is rarer and was observed as small, partly Y-enriched grains (3?wt. %?Y₂O₃) in the rock matrix and within garnet. Based on monazite-xenotime thermometry, Y?+?HREE values in monazite indicate minimum crystallization conditions of 500?°C during the Variscan and 650?°C for the Permian and Alpine events, respectively. Garnet zoning and thermobarometric calculations with THERMOCALC 3.21 record an amphibolite facies, high-pressure stage of ~600?°C/13?C16?kbar, followed by a thermal maximum at 650?C700?°C and 6?C9?kbar. The Eo-Alpine age for these two events is supported by inclusions of Cretaceous monazite in the garnet domains used for thermobarometric constraints and through the high growth temperatures of Eo-Alpine monazite, which is consistent with that of the thermal maximum (~700?°C). The age and growth conditions of a few Mn-rich garnet cores, sporadically present within Eo-Alpine garnet, are unclear because inclusions of monazite, plagioclase and biotite necessary for thermobarometric- and age constraints are absent. However, based on monazite thermometry, Permian and Variscan metamorphic conditions were high enough for the growth of pre-Alpine garnet. The formation of Variscan garnet and its later resorption, plus Y-release, would also explain the high Y in Permian monazite, which cannot originate from preexisting Variscan monazite only. Monazite of Variscan, Permian and/or Eo-Alpine ages were also observed in other garnet-bearing micaschists from the Schobergruppe. This suggests that the basement of the Schobergruppe was overprinted by three discrete metamorphic events at conditions of at least lower amphibolite facies. While the Variscan event affected all parts of this basement, the younger events are more pronounced in its structurally lower units.  相似文献