Sand transport measurements in Chioggia inlet,Venice lagoon: Theory versus observations

This paper presents results of recent measurements of sand transport made in Chioggia inlet as part of an extensive monitoring programme in the Venetian inlets. Measurements were made in order: (1) to define a relationship between sand transport magnitude and tidal flow; (2) to derive the thresholds for sand transport; (3) to identify the dominant modes of transport; (4) to evaluate the concentration profiles of sand within the benthic boundary layer; (5) to compare bedload transport observations with model predictions using existent bedload formulae; and (6) to produce yearly estimates of bedload transport across the inlet. The vertical distribution of sand in the water column was sampled using modified Helley–Smith bedload samplers at three sites. Transport was found to vary according to the flow and bed grain size, with considerable temporal and spatial variability. A difference of up to three orders of magnitude in transport was observed through the inlet, with higher transport rates measured on the seaward part. The dominant mode of transport in the central inlet was suspension, while bedload was dominant in the mouths. The measured profiles of sand concentration varied with the tidal stage and seabed grain size according to the Rouse parameter (R). R was high at the inlet mouths (1<R<2), indicative of a well-developed bedload layer. The inverse movability number (W_s/U_*) was also higher at these sites and appeared to be grain size dependant. Formulae for bedload transport were tested against field data; stochastic methods such as Einstein–Brown, Engelund–Hansen and Van Rijn produce the best fits. The coupled model SHYFEM-Sedtrans05 appears to simulate well observed transport for most conditions of flow. Long-term bedload predictions indicate a dominant export of sand, with a yearly average of 4500 m³.     

Ecological stability during the LGM and the mid-Holocene in the Alpine Steppes of Tibet?

Arid and Alpine ecosystems are known for extreme environmental changes during the Late Quaternary. We hypothesize that the world's largest Alpine arid ecosystem however, the Alpine Steppes of the Tibetan highlands, remained ecologically stable during the LGM and the mid-Holocene. This hypothesis is tested by distributional range of plant species, plant life forms and rate of endemism. The set of character species has a precipitation gradient between 50 and 350 mm/a, testifying for resilience to precipitation changes. 83% of the species have a wider vertical range than 1000 m used as a proxy for resilience to temperature changes. 30% of the species are endemic with 10 endemic genera, including plate-shaped cushions as a unique plant life form. These findings are in line with palaeo-ecological proxies (δ¹⁸O, pollen) allowing the assumption that Alpine Steppes persisted during the LGM with 3 to 4 K lower summer temperatures.During the mid-Holocene, forests could have replaced Alpine Steppes in the upper catchments of the Huang He, Yangtze, Mekong, Salween and Yarlung Zhangbo, but not in the interior basins of the north-western highlands, because the basins were then flooded, suppressing forests and supporting the environmental stability of this arid Alpine grassland biome.     

Hydrostatic pressure tests for the permeability - formation factor relation on crystalline rocks from the KTB drilling project

Transport properties (permeability and electrical conductivity) have been measured at different hydrostatic pressure runs on 7 crystalline rocks (gneisses and amphibolites) sampled from the KTB drilling project. The decrease of permeability by pressure are compared with the pressure-dependent data of the electrical conductivity (formation factor) resulting from complex impedance measurements. According to the equivalent-channel model (ECM), there exists a linear relationship between these parameters by representing both properties on logarithmic scales. The results show that it is possible to extrapolate high-pressure permeability from low-pressure (< 60 MPa) permeability data by using the pressure-dependent electrical conductivity (up to 300 MPa).     

Silicon isotope fractionation during magmatic differentiation

The Si isotopic composition of Earth’s mantle is thought to be homogeneous (δ³⁰Si = −0.29 ± 0.08‰, 2 s.d.) and not greatly affected by partial melting and recycling. Previous analyses of evolved igneous material indicate that such rocks are isotopically heavy relative to the mantle. To understand this variation, it is necessary to investigate the degree of Si isotopic fractionation that takes place during magmatic differentiation. Here we report Si isotopic compositions of lavas from Hekla volcano, Iceland, which has formed in a region devoid of old, geochemically diverse crust. We show that Si isotopic composition varies linearly as a function of silica content, with more differentiated rocks possessing heavier isotopic compositions. Data for samples from the Afar Rift Zone, as well as various igneous USGS standards are collinear with the Hekla trend, providing evidence of a fundamental relationship between magmatic differentiation and Si isotopes. The effect of fractionation has been tested by studying cumulates from the Skaergaard Complex, which show that olivine and pyroxene are isotopically light, and plagioclase heavy, relative to the Si isotopic composition of the Earth’s mantle. Therefore, Si isotopes can be utilised to model the competing effects of mafic and felsic mineral fractionation in evolving silicate liquids and cumulates.At an average SiO₂ content of ∼60 wt.%, the predicted δ³⁰Si value of the continental crust that should result from magmatic fractionation alone is −0.23 ± 0.05‰ (2 s.e.), barely heavier than the mantle. This is, at most, a maximum estimate, as this does not take into account weathered material whose formation drives the products toward lighter δ³⁰Si values. Mass balance calculations suggest that removal of continental crust of this composition from the upper mantle will not affect the Si isotopic composition of the mantle.     

Time-scale and state dependence of the carbon-cycle feedback to climate

Climate and atmospheric CO₂ concentration are intimately coupled in the Earth system: CO₂ influences climate through the greenhouse effect, but climate also affects CO₂ through its impact on the amount of carbon stored on land and in the ocean. The change in atmospheric CO₂ as a response to a change in temperature ( $\varDelta CO_{2}/\varDelta T$ ) is a useful measure to quantify the feedback between the carbon cycle and climate. Using an ensemble of experiments with an Earth system model of intermediate complexity we show a pronounced time-scale dependence of $\varDelta CO_{2}/\varDelta T$ . A maximum is found on centennial scales with $\varDelta CO_{2}/\varDelta T$ values for the model ensemble in the range 5–12 ppm °C^?1, while lower values are found on shorter and longer time scales. These results are consistent with estimates derived from past observations. Up to centennial scales, the land carbon response to climate dominates the CO₂ signal in the atmosphere, while on longer time scales the ocean becomes important and eventually dominates on multi-millennial scales. In addition to the time-scale dependence, modeled $\varDelta CO_{2}/\varDelta T$ show a distinct dependence on the initial state of the system. In particular, on centennial time-scales, high $\varDelta CO_{2}/\varDelta T$ values are correlated with high initial land carbon content. A similar relation holds also for the CMIP5 models, although for $\varDelta CO_{2}/\varDelta T$ computed from a very different experimental setup. The emergence of common patterns like this could prove to usefully constrain the climate–carbon cycle feedback.     

Effect of grossular-content in garnet on the partitioning of Fe and Mg between garnet and biotite

In contrast to Ferry (1980) (X _Ca)-values in garnet even lower than 0.1 have a significant effect on the calculated equilibrium temperature using the experimental calibration of the Fe and Mg paritioning between garnet and biotite. Garnet compositions and Mg/Fe — distribution coefficients from samples of the Eoalpine staurolite — in zone in the southern Ötztal are related by the quadratic regression equation: InK _D= -1.7500 (±0.0226) + 2.978 (±0.5317)X _Ca ^Gt -5.906(±2.359)(X _Ca ^Gt )² Temperatures derived by the Ferry and Spear (1978) calibration using chemistry — correctedK _D values are petrologically realistic.Analysis of our data supports non ideal mixing of grossular with almandine — pyrope solid solution. The derived excess mixing energies are quite small for the almandine — pyrope solution (W _FeMg= –133 cal/mole) and about +2775 cal/mole for the difference between pyrope-grossular and almandine-grossular solutions (W _MgCa —W _FeCa) at metamorphic conditions of 570° C and 5,000 bar. The mixing parameters proposed by Ganguly and Saxena (1984) are not confirmed by our data as they would result in significantly lower temperatures.     

Effects of seed particle size and composition on heterogeneous nucleation of n-nonane

Heterogeneous nucleation of supersaturated n-nonane vapour on seed particles of different size and composition has been investigated using a fast expansion chamber. Monodisperse seed particle sizes were ranging from about 4 nm up to about 24 nm in diameter. By using different types of particle generators WO_x, Ag and (NH₄)₂SO₄ particles were generated. For direct comparison between different particle compositions overlapping sizes have been generated for WO_x and Ag at about 7 nm particle diameter as well as for Ag and (NH₄)₂SO₄ at about 15 nm. Nucleation temperature was kept constant at about 278 K. Experimental data were compared to Kelvin equation and Fletcher theory including the effect of line tension. It was found that heterogeneous nucleation of n-nonane seems to be independent of seed particle composition and starts well below the Kelvin curve. Good agreement was achieved with Fletcher theory including the effect of line tension.     

Die Temperaturinversion im Tiefenwasser des Südatlantischen Ozeans

Zusammenfassung Die südatlantische Temperaturinversion wurde 1873–1876 zwischen 5° N und 40° S in 1000–2400 m Tiefe von Challenger und Gazelle mittels Minimumthermometer entdeckt, wie von A. Merz 1922 dargelegt ist. Es wird gezeigt, daß die Fehlerquellen der alten Reihenmessungen in der Regel kleiner sind als das Ausmaß der Inversion und daß sich bereits die ersten Bearbeiter in der Deutung dieses Phänomens auf dem richtigen Wege befanden. Doch finden diese Ergebnisse wegen der (nur z. T. berechtigten) Skepsis gegenüber der Meßgenauigkeit der Extremthermometer keinen Eingang in die Ozeanographie. Erst 1911 wird die südatlantische Temperaturinversion von Brennecke auf Deutschland mittels exakter Kippthermometer auf der Westseite wiederentdeckt und 1925–27 von den Ozeanographen des Meteor bis zu den letzten Spuren im ganzen Ozeanraum verfolgt. Eine Darstellung dieses Phänomens bot der Verfasser bei der Bearbeitung der ozeanischen Stratosphäre im Meteor-Werk 1936. In Abb. 1 und 2 der folgenden Arbeit werden nunmehr neue Karten über die regionale Verbreitung des Inversionsausmaßes auf Grund der Reihenmessungen von Challenger-Gazelle und von Meteor vorgelegt, die in großen Zügen übereinstimmen, jedoch abweichend von Merz lehren, daß weite Gebiete der Osthälfte keine Inversion (bzw. Isothermie) aufweisen. Aus den engabständigen Meteor-Serien ergibt sich eine unerwartet enge Beziehung der Inversion zum Relief des Tiefseebodens. In ihrem Ausmaß spiegelt sich ferner die bevorzugte Tiefenzirkulation der Westseite mit ihren schwächeren Ausläufern nach Osten, wodurch die von Defant und vom Verfasser im Meteor-Werk erzielten Ergebnisse bestätigt werden. Das räumliche Bild der Inversion wird durch Karten der Temperatur und Topographie ihrer Grenzschichten ergänzt (Abb. 4 u. 5). An Wiederholungsserien des Meteor (Stat. 197 u. 241) wird gezeigt, daß sich die Tiefenlage der Inversion im Rhythmus der halbtägigen inneren Gezeitenwelle hebt und senkt und daß die Amplitude dieser vertikalen Verlagerung mit ±60 bzw. ±25 m bemerkenswert groß ist (Abb. 7 u. 8). Neben diesen kurzperiodischen Änderungen deuten gewisse Anzeichen auf langperiodische (jahreszeitliche) und unperiodische Pulsationen im Ausmaß der Inversion.

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The temperature inversion in the deep water of the South Atlantic

Summary The temperature inversion in the South Atlantic has been discovered in 1000–2400 m depth between 5° N and 40° S by means of minimum thermometers in the years 1873–1876 by the research ships Challenger and Gazelle, as A. Merz has pointed out in 1922. In the present paper it is shown that the inaccuracies of the old temperature series are usually smaller than the amount of inversion and that the first interpreters have already been on the right way in explaining this phenomenon. However these results were not acknowledged on account of general (but only partly justified) doubts in the measuring accuracy of maximum and minimum thermometers. Only in 1911 the South Atlantic temperature inversion has been rediscovered in the western part of the ocean by Brennecke on board the polar ship Deutschland by means of exact reversing therm ometers, and its extension has been pursued to its utmost ends throughout the southern and tropic Atlantic by the oceanographers of Meteor in 1925–27. In 1936 the author has discussed the phenomenon in his treatise on the oceanic stratosphere in the Meteor work. In Fig. 1 and 2 of the following paper new charts of the regional distribution of the amount of inversion are given as based on the serial observations of Challenger — Gazelle and Meteor, which on the whole agree with each other and — divergently from Merz — show that in vast regions of the eastern part of the South Atlantic there is no inversion (or isothermal layer). From the Meteor series which are arranged very close together a remarkably close relation between inversion and bottom relief is derived. Moreover in the amount of the inversion the greater intensity of deep sea circulation in the western South Atlantic with its slight extensions towards the east is recognized, another verification of the results obtained by Defant and the author in the Meteor work. The spatial representation of the inversion is completed by charts of the temperature and topography of its boundary layers (Fig. 4 and 5). By aid of repeat series of the Meteor expedition (Station 197 and 241) it is pointed out that the depth of the inversion is rising and sinking in accordance with the semi-diurnal internal tide and that the amplitude of this vertical wave, amounting to ±60 or ±25 m, is remarkably great (Fig. 7 and 8). Besides these short-period variations there is some indication that the inversion is also undergoing long-period (seasonal) and aperiodic pulsations.

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Hierzu Tafel 6 mit Abbildung 2

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Herrn Prof. Dr. Dr. h. c. Georg Tischler (Universität Kiel) zum 70. Geburtstag.     

An SVG-based method to support spatial analysis in XML/GML/SVG-based WebGIS

XML/GML/SVG-based approaches are promising for building Web-based geographic information systems (WebGIS). However, current XML/GML/SVG-based WebGISs are lacking in spatial analysis. Some of them are designed for web mapping only. Others adopt a server-side solution for spatial analysis, which suffers from the ‘bottleneck’ problem and results in a high network transmission load. Load-balancing spatial analysis between server side and browser side can be used to solve the above problems. This article focuses on one of the key building blocks of load-balancing spatial analysis, that is, SVG-based spatial analysis which enables spatial querying and analysis directly on SVG (on the browser side). After analyzing the workflow of spatial analysis, we identify and focus on two key issues in providing spatial analysis on SVG: SVG-based spatial information representation and SVG-based spatial extended structured query language (SSESQL). For the first issue, a theoretical foundation is set up to develop an SVG-based spatial information representation model. Some spatial operators are designed and integrated into an SSESQL to support spatial querying on SVG. Finally, we design and implement two case studies. The results of these case studies show that the proposed method is feasible and operable in supporting spatial analysis directly on SVG on the browser side. The proposed method can be easily incorporated with some existing methods (e.g., GML-based spatial analysis on the server side) to provide load-balancing spatial analysis (load balancing between server side and browser side) in XML/GML/SVG-based WebGIS. As a result, users can access high-performance spatial analysis simply via a web browser (such as Internet Explorer and Firefox).