Turbulent exchange above a pine forest II. Organized structures

Data from two 100-min runs on the turbulent atmospheric wind, temperature and humidity fields above a pine forest have been analysed using conditional sampling techniques. With the aid of the temperature time series, ramp events were identified and all fields were averaged in order to remove smaller scale turbulence and random low-frequency turbulence, and to map the organized structures revealed in this way. It is shown that the turbulent fluxes of momentum, heat and humidity, determined from these ramp-events, in fact constitute a large part of the total fluxes, about 90% during the actual events.On average, the duration of and the time between ramps were found to be about 35 s and 100 s, respectively. These periods were also found in the uw-, wT- and wq-cospectra, not only in the data analysed in this paper, but in the major part of all day-time data from this forest site (about 80 runs of 60 or 100 min). This indicates that the ramp events described arc a rather common phenomenon. The organized structures also have remarkable resemblance to near-wall structures observed in the laboratory.     

Compactional behavior of fine-grained sediments — examples from Deep Sea Drilling Project cores

Laboratory experiments, statistical analysis of field data and theoretical models are combined in the attempt to derive standard compaction curves for various deep-sea sediments which are in compaction equilibrium with the overburden. A revised and generalized version of Athy's law together with laboratory experiments allows the classification of sediments in terms of the amount of porewater structurally bound to the particles' surfaces. Especially suction pressure experiments are useful in quantifying the forces that bind water on the particle surfaces. The sediments analyzed almost range from systems of »suspended grains« to nearly perfect »colloidal systems«. The methods and equations required to derive the relevant parameters are given for both, downhole porosity/density measurements and laboratory experiments.

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Zusammenfassung Die Synthese experimenteller Labordaten, statistischer Analysen von Messungen an Kernen und theoretischer Modellierung der Kompaktion im Gleichgewicht mit der Auflast ermöglicht die Definition von Typ-Kurven für das Kompaktionsverhalten von verschiedenen Tiefsee-Sedimenten. Eine erweiterte und verbesserte Form der Athy'schen Gleichung erlaubt zusammen mit Laborexperimenten, Sedimente entsprechend des Anteils an strukturell gebundenem Porenwasser zu klassifizieren. Anhand von Saugspannungsexperimenten können die Bindungskräfte zwischen Wasser und Partikeloberflächen abgeschätzt werden. Die untersuchten Sedimente reichen von »suspendierten Körnern« bis zu einem »kolloidalen System«. Die notwendigen Methoden und Gleichungen zur Bestimmung der relevanten Parameter aus Bohrlochdaten und Laborexperimenten werden diskutiert.

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Résumé A partir d'une synthèse de résultats d'expériences de laboratoires, d'analyses statistiques de données de terrain et d'une modélisation théorique, il est possible d'établir des courbes standard du processus de compaction pour divers types de sédiments de mer profonde, pour lesquels la compaction est en équilibre avec la charge. Une version revue et généralisée de la loi d'Athy permet, en accord avec les résultats expérimentaux, de classer les sédiments selon la quantité d'eau intersticielle liée structuralement à la surface des particules. Les sédiments analysés correspondent à des systèmes qui vont du type à «grains suspendus» à des colloïdes presque parfaits. Les auteurs présentent une discussion détaillée des méthodes et des équations néssaires à l'obtention des paramètres significatifs tant à partir des expériences de laboratoire qu'à partir des mesures de porosité/densité effectuées dans les forages.

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Turbulent characteristics of a shallow convective internal boundary layer

Turbulent characteristics of a 50 to 100 m deep convective internal boundary layer (I.B.L.) have been studied. The data were gathered at a flat coastal site (Näsudden on the island of Gotland, Sweden) during three consecutive days in May 1980 which were characterized by a steady, very stable stratified marine approach flow. The site is situated on a flat area ca. 1500 m from the shoreline. Only daytime runs have been analysed in the present paper. The sensible heat flux at the ground was typically 200 W m^-2 and was found to decrease more or less linearly with height throughout the I.B.L., being slightly negative at greater heights. The momentum flux was also found to decrease with height, but nevertheless shear production of turbulent kinetic energy was found to be large throughout the entire I.B.L. The analysis shows that the turbulent regime has a mixed character. Certain characteristics, such as the rate of growth of the I.B.L., appear to be almost entirely controlled by mechanical turbulence, while others, notably temperature variance and the spectrum of vertical velocity, scale remarkably well with w _* and z _i, in accordance with the results found in fully convective conditions during the experiments at Minnesota and Aschurch. Other turbulent characteristics, such as spectra of the horizontal wind components measured near the top of the I.B.L. tend to adhere to mixed-layer scaling in the high frequency range, exhibiting much increased energy in the lower (reduced) frequency range. Spectra of the velocity components from 10 m are shown to be in general agreement with findings from ‘ideal’, homogeneous sites (Kansas) when properly normalized, although the low frequency part of u- and v-spectra are slightly reduced compared to the case with deep convection.     

Sm–Nd and Sr isotope systematics of scheelite from the giant Au(–W) deposit Muruntau (Uzbekistan): implications for the age and sources of Au mineralization

The application of the Sm-Nd isotope system of scheelite to dating of low-sulfide, quartz-vein hosted Au mineralization is still under discussion. In the present work, new Sm-Nd and Rb-Sr data for scheelite from the giant Muruntau/Myutenbai Au deposit (Kyzylkum, Western Uzbekistan) are discussed. Based on the geological relationship, mineralogical properties, and trace element characteristics, two types of scheelite can be distinguished within the deposit. The first one is represented by early bluish luminescent and weakly coloured scheelite (generation 1) found within strongly deformed flat quartz veins. The apparent isochron defined by this scheelite (351ᆪ Ma) is interpreted as a mixing line. Typically brownish to orange and yellowish luminescent scheelite from steeply dipping veins (generation 2) defines a Sm-Nd isochron age of 279ᆦ Ma ()_Nd=-9.5ǂ.3; MSWD: 1.5). No evidence for mixing or disturbance by late alteration were found for these scheelites. This Sm-Nd isochron age agrees with the Rb-Sr and K-Ar age range for wall rock alteration in this deposit reported previously. The age of 280 Ma is interpreted to date the high-grade ore formation in the Muruntau deposit. There are currently no reliable age data available on the magmatic events in the Muruntau region. Probably, there is some overlap in time of the Hercynian gold deposition with the intrusion of lamprophyric dykes. The Nd and Sr isotopic signatures of scheelite define the wall rocks (mainly metasiltstones and metasandstones) as the most probable sources for these elements in scheelite.     

Antagonistic structures in border areas: Local milieux and local politics in the Polish-German twin city Gubin/Guben

Cross-border communication and co-operation at the Eastern fringe of the European Union seems so far to have been a matter of political initiative and a lot of good will at the levels of national, regional and local governance. This article maintains that everyday culture must be given more notice when cross-border activities are regarded at the local level, especially in twin cities. The case of the German-Polish twin city Guben/Gubin reveals a strong tendency towards a new divergence of thought and action between formal and informal levels of action, namely the level of local politics and governance and the level of local everyday milieux. While the politics of Euroregions, local administrations and local governments is very often directed towards establishing symbolic gestures of border-crossing and mutual understanding, social milieux at the ‘base’ of local societies are rather driven by a paradoxical mixture of hope, anxiety, resentments and prejudice, thus producing contradictions and even conflict with official political initiative. This revised version was published online in July 2006 with corrections to the Cover Date.     

Zircon ages of high-grade gneisses in the Eastern Erzgebirge (Central European Variscides)—constraints on origin of the rocks and Precambrian to Ordovician magmatic events in the Variscan foldbelt

This study is an attempt to unravel the tectono-metamorphic history of high-grade metamorphic rocks in the Eastern Erzgebirge region. Metamorphism has strongly disturbed the primary petrological genetic characteristics of the rocks. We compare geological, geochemical, and petrological data, and zircon populations as well as isotope and geochronological data for the major gneiss units of the Eastern Erzgebirge; (1) coarse- to medium-grained “Inner Grey Gneiss”, (2) fine-grained “Outer Grey Gneiss”, and (3) “Red Gneiss”. The Inner and Outer Grey Gneiss units (MP–MT overprinted) have very similar geochemical and mineralogical compositions, but they contain different zircon populations. The Inner Grey Gneiss is found to be of primary igneous origin as documented by the presence of long-prismatic, oscillatory zoned zircons (540 Ma) and relics of granitic textures. Geochemical and isotope data classify the igneous precursor as a S-type granite. In contrast, Outer Grey Gneiss samples are free of long-prismatic zircons and contain zircons with signs of mechanical rounding through sedimentary transport. Geochemical data indicate greywackes as main previous precursor. The most euhedral zircons are zoned and document Neoproterozoic (ca. 575 Ma) source rocks eroded to form these greywackes. U–Pb-SHRIMP measurements revealed three further ancient sources, which zircons survived in both the Inner and Outer Grey Gneiss: Neoproterozoic (600–700 Ma), Paleoproterozoic (2100–2200 Ma), and Archaean (2700–2800 Ma). These results point to absence of Grenvillian type sources and derivation of the crust from the West African Craton. The granite magma of the Inner Grey Gneiss was probably derived through in situ melting of the Outer Grey Gneiss sedimentary protolith as indicated by geological relationships, similar geochemical composition, similar Nd model ages, and inherited zircon ages. Red Gneiss occurs as separate bodies within fine- and medium-grained grey gneisses of the gneiss–eclogite zone (HP–HT overprinted). In comparison to Grey Gneisses, the Red Gneiss clearly differs in geochemical composition by lower contents of refractory elements. Rocks contain long-prismatic zircons (480–500 Ma) with oscillatory zonation indicating an igneous precursor for Red Gneiss protoliths. Geochemical data display obvious characteristics of S-type granites derived through partial melting from deeper crustal source rocks. The obtained time marks of magmatic activity (ca. 575 Ma, ca. 540 Ma, ca. 500–480 Ma) of the Eastern Erzgebirge are compared with adjacent units of the Saxothuringian zone. In all these units, similar time marks and geochemical pattern of igneous rocks prove a similar tectono-metamorphic evolution during Neoproterozoic–Ordovician time.     

Stoßwellenmetamorphose des Anorthosits vom Manicouagan Krater,Québec,Canada

The central anorthosite peak of the Maniconagan crater displays characteristic shock deformation and transition phenomena in plagioclase feldspars, scapolithe, apatite and other maphitic minerals. The optical orientation of plagioclases is determined. With increasing shock, a trend to a highly disordered structure of the plagioclase lattice can be observed. Rock fracturing occurs at low pressures. At higher pressures different kinds of isotropisation features and planar deformation structures in plagioclase, scapolithe and apatite can be distinguished. These planar elements can be interpreted as glide planes of low crystallographic indices, set in motion during shock compression by plastic deformation. Their optical orientation is measured. At very high pressures a completely isotropic phase, the s. c. diaplectic glass is formed. The physical properties of diaplectic plagioclase crystals and diaplectic glass are determined which are different from those of an unshocked crystal and its molten plagioclase glass of the same chemical composition. The diaplectic plagioclase phases are apparently mixed phases of molten glass and normal crystal. This can be proved by x-ray and infrared absorption studies. These results are correlated to shock recovery experiments and hugoniot states of plagioclase. All shock effects of plagioclases are classified into three groups according to the low pressure regime, mixed phase regime and high pressure regime. The low pressure regime is characterised by strong fracturing, the mixed phase regime by the development of planar elements, which were transformed during shock compression into the high pressure plagioclase phase with hollandite structure. The latter is converted into diaplectic glass after pressure release. The high pressure regime is characterised by complete transformation of plagioclase into the high pressure phase, which is unstable and reverts completely to the amorphous phase (diaplectic glass or maskelynite) at zero pressure density.

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Meinem verehrten Lehrer, Herrn Prof. Dr. W. v. Engelhardt, danke ich für die Unterstützung bei der Bearbeitung des Themas. Herrn Dr. D. Stöffler danke ich für klärende Diskussionen und Ratschläge. Dem Ministère des Richesses Naturelles, Québec, Canada, sowie Herrn M.S. J. Murtaugh sei für die großzügige Unterstützung bei den Geländearbeiten im Manicouagan-Krater gedankt. Die Deutsche Forschungsgemeinschaft hat die Arbeit finanziell unterstützt.     

Carbon isotopic fractionation during a mesocosm bloom experiment dominated by Emiliania huxleyi: Effects of CO2 concentration and primary production

We investigated the effect of CO₂ and primary production on the carbon isotopic fractionation of alkenones and particulate organic matter (POC) during a natural phytoplankton bloom dominated by the coccolithophore Emiliania huxleyi. In nine semi-closed mesocosms (∼11 m³ each), three different CO₂ partial pressures (pCO₂) in triplicate represented glacial (∼180 ppmv CO₂), present (∼380 ppmv CO₂), and year 2100 (∼710 ppmv CO₂) CO₂ conditions. The largest shift in alkenone isotopic composition (4-5‰) occurred during the exponential growth phase, regardless of the CO₂ concentration in the respective treatment. Despite the difference of ∼500 ppmv, the influence of pCO₂ on isotopic fractionation was marginal (1-2‰). During the stationary phase, E. huxleyi continued to produce alkenones, accumulating cellular concentrations almost four times higher than those of exponentially dividing cells. Our isotope data indicate that, while alkenone production was maintained, the interaction of carbon source and cellular uptake dynamics by E. huxleyi reached a steady state. During stationary phase, we further observed a remarkable increase in the difference between δ¹³C of bulk organic matter and of alkenones spanning 7-12‰. We suggest that this phenomenon is caused mainly by a combination of extracellular release of ¹³C-enriched polysaccharides and subsequent particle aggregation induced by the production of transparent exopolymer particles (TEP).     

Calcium isotope fractionation in coccoliths of cultured Calcidiscus leptoporus, Helicosphaera carteri, Syracosphaera pulchra and Umbilicosphaera foliosa

Four species of marine calcifying algae, the coccolithophores Calcidiscus leptoporus, Helicosphaera carteri, Syracosphaera pulchra and Umbilicosphaera foliosa were grown in laboratory cultures under temperatures varying between 14 and 23 °C, and one species, C. leptoporus, under varying [CO₃²⁻], ranging from 105 to 219 μmol/kg. Calcium isotope compositions of the coccoliths resemble in both absolute fractionation and temperature sensitivity previous calibrations of marine calcifying species e.g. Emiliania huxleyi (coccolithophores) and Orbulina universa (planktonic foraminifera) as well as inorganically precipitated CaCO₃, but also reveal small species specific differences. In contrast to inorganically precipitated calcite, but similar to E. huxleyi and O. universa, the carbonate ion concentration of the medium has no statistically significant influence on the Ca isotope fractionation of C. leptoporus coccoliths; however, combined data of E. huxleyi and C. leptoporus indicate that the observed trends might be related to changes of the calcite saturation state of the medium. Since coccoliths constitute a significant portion of the global oceanic CaCO₃ export production, the Ca isotope fractionation in these biogenic structures is important for defining the isotopic composition of the Ca sink of the ocean, one of the key parameters for modelling changes to the marine Ca budget over time. For the present ocean our results are in general agreement with the previously postulated and applied mean value of the oceanic Ca sink (Δ_sed) of about − 1.3‰, but the observed inter- and intra-species differences point to possible changes in Δ_sed through earth history, due to changing physico-chemical conditions of the ocean and shifts in floral and faunal assemblages.     

Pétrographie des „Permoskyth“ der Jaggl-Plawen-Einheit (Südtirol) und Diskussion der Detritusherkunft mit Hilfe von Kathoden-Lumineszenz-Untersuchungen

The Permo-Scythian deposits E of Lake Reschen (North-Italy) are composed of a sequence of terrestrial sediments in Verrucanofacies and of a series of detrital carbonate and lagoonal-evaporitic rocks (“Wechselschichten”) overlaid by Anisian fossiliferous dolomites. Examinations by cathodo-luminescence give reference to the source area of the detrius and to the diagenesis of the sediments. Further statements can be made by X-ray (triclinity of K-feldspars; inclusions in authigenic minerals) and chemical examinations (composition of dolomites). The detritus of the slightly metamorphic rocks, indicated by the crystallinity of illite, does not originate from the underlying “Plawenkristallin” and from the adjacent “ötztalkristallin”, respectively, but by 70% from a porphyritic source area that is supposed to be located in the region of Lugano.