Ein Brief von C. F. Gauβ

Ohne Zusammenfassung     

The geology of the Morro Velho gold deposit in the Archean Rio das Velhas greenstone belt, Quadrilátero Ferrífero, Brazil

The Morro Velho gold deposit, Quadrilátero Ferrífero region, Minas Gerais, Brazil, is hosted by rocks at the base of the Archean Rio das Velhas greenstone belt. The deposit occurs within a thick carbonaceous phyllite package, containing intercalations of felsic and intermediate volcaniclastic rocks and dolomites. Considering the temporal and spatial association of the deposit with the Rio das Velhas orogeny, and location in close proximity to a major NNW-trending fault zone, it can be classified as an orogenic gold deposit. Hydrothermal activity was characterized by intense enrichment in alteration zones of carbonates, sulfides, chlorite, white mica±biotite, albite and quartz, as described in other Archean lode-type gold ores. Two types of ore occur in the deposit: dark gray quartz veins and sulfide-rich gold orebodies. The sulfide-rich orebodies range from disseminated concentrations of sulfide minerals to massive sulfide bodies. The sulfide assemblage comprises (by volume), on average, 74% pyrrhotite, 17% arsenopyrite, 8% pyrite and 1% chalcopyrite. The orebodies have a long axis parallel to the local stretching lineation, with continuity down the plunge of fold axis for at least 4.8 km. The group of rocks hosting the Morro Velho gold mineralization is locally referred to as lapa seca. These were isoclinally folded and metamorphosed prior to gold mineralization. The lapa seca and the orebodies it hosts are distributed in five main tight folds related to F1 (the best examples are the X, Main and South orebodies, in level 25), which are disrupted by NE- to E-striking shear zones. Textural features indicate that the sulfide mineralization postdated regional peak metamorphism, and that the massive sulfide ore has subsequently been neither metamorphosed nor deformed. Lead isotope ratios indicate a model age of 2.82 ± 0.05 Ga for both sulfide and gold mineralization. The lapa seca are interpreted as the results of a pre-gold alteration process and may be divided into carbonatic, micaceous and quartzose types. The carbonatic lapa seca is subdivided into gray and brown subtypes. Non-mineralized, gray carbonatic lapa seca forms the hanging wall to the orebodies, and is interpreted as the product of extreme CO₂ metasomatism during hydrothermal alteration. This dolomitic lapa seca ranges in composition from relatively pure limestone and dolomite to silty limestone and dolomite. The brown carbonatic and micaceous lapa secas are the host rocks to gold. These units are interpreted to correspond to the sheared and hydrothermal products of metamorphosed volcaniclastic and/or volcanic rocks of varying composition from dacitic to andesitic, forming various types of schists and phyllites. The high-grade, massive sulfide orebodies occur at the base of the gray carbonatic lapa seca. Both disseminated mineralization and quartz veins are hosted by micaceous lapa seca. The data are consistent with a model of epigenetic mineralization for the lapa seca, from a hydrothermal fluid derived in part from the Archean basement or older crust material.     

Intercomparison of Tropospheric OH Measurements by Different Laser Techniques during the POPCORN Campaign 1994

In-situ OH measurements by laser-induced fluorescence (LIF) spectroscopy and folded long-path differential optical absorption spectroscopy (DOAS) were carried out in a rural environment in North-East Germany as part of the field experiment POPCORN in August 1994. The large set of OH data obtained allowed an intercomparison of both techniques based on relative diurnal profiles and simultaneously measured absolute concentrations. Most of the time the two OH instruments encountered the same air and agreed well in the measured relative diurnal variations. Only on a few occasions the measurements significantly disagreed due to a perturbation of the DOAS measurements by a local OH source in the north-western wind sector. Excluding data from this wind direction, the statistical analysis of 137 data pairs yields a correlation coefficient of r = 0.90 and a weighted linear fit with a slope of 1.09 ± 0.12. The correlations are carefully analyzed. The comparison of both instruments is discussed in the light of newly published effective absorption cross-sections for H2O and O2 that affect the calibration of LIF.     

Hydrologic characteristics of lake‐ and stream‐side riparian wetted margins in the McMurdo Dry Valleys,Antarctica

Water is a limiting factor for life in the McMurdo Dry Valleys (MDV), Antarctica. The active layer (seasonally thawed soil overlying permafrost) accommodates dynamic hydrological and biological processes for 10–16 weeks per year. Wetted margins (visually wetted areas with high moisture content) adjacent to lakes and streams are potential locations of great importance in the MDV because of the regular presence of liquid water, compared with the rest of the landscape where liquid water is rare. At 11 plots (four adjacent to lakes, seven adjacent to streams), soil particle size distribution, soil electrical conductivity, soil water content and isotopic signature, width of the wetted margin, and active layer thaw depth were characterised to determine how these gradients influence physicochemical properties that determine microbial habitat and biogeochemical cycling. Sediments were generally coarse‐grained in wetted margins adjacent to both lakes and streams. Wetted margins ranged from 1·04 to 11·01 m in average length and were found to be longer at lakeside sites than streamside. Average thaw depths ranged from 0·12 to 0·85 m, and were found to be deepest under lake margins. Lake margins also had much higher soil electrical conductivity, steeper topographic gradients, but more gradual soil moisture gradients than stream margins. Patterns of soil water δ¹⁸O and δD distribution indicate capillary action and evaporation from wetted margins; margin pore waters generally demonstrated isotopic enrichment with distance from the shore, indicating evaporation of soil water. Lake margin pore waters were significantly more negative in D_XS (D_XS = δD‐8δ¹⁸O) than streamside pore waters, indicating a longer history of evaporation there. Differences between lake and stream margins can be explained by the more consistent availability of water to lake margins than stream margins. Differences in margin characteristics between lakes and streams have important consequences for the microbial habitat of these margins and their functional role in biogeochemical cycling at these terrestrial–aquatic interfaces. Copyright © 2009 John Wiley & Sons, Ltd.     

Reducing the draconitic errors in GNSS geodetic products

Systematic errors at harmonics of the GPS draconitic year have been found in diverse GPS-derived geodetic products like the geocenter $Z$ -component, station coordinates, $Y$ -pole rate and orbits (i.e. orbit overlaps). The GPS draconitic year is the repeat period of the GPS constellation w.r.t. the Sun which is about 351 days. Different error sources have been proposed which could generate these spurious signals at the draconitic harmonics. In this study, we focus on one of these error sources, namely the radiation pressure orbit modeling deficiencies. For this purpose, three GPS+GLONASS solutions of 8 years (2004–2011) were computed which differ only in the solar radiation pressure (SRP) and satellite attitude models. The models employed in the solutions are: (1) the CODE (5-parameter) radiation pressure model widely used within the International GNSS Service community, (2) the adjustable box-wing model for SRP impacting GPS (and GLONASS) satellites, and (3) the adjustable box-wing model upgraded to use non-nominal yaw attitude, specially for satellites in eclipse seasons. When comparing the first solution with the third one we achieved the following in the GNSS geodetic products. Orbits: the draconitic errors in the orbit overlaps are reduced for the GPS satellites in all the harmonics on average 46, 38 and 57 % for the radial, along-track and cross-track components, while for GLONASS satellites they are mainly reduced in the cross-track component by 39 %. Geocenter $Z$ -component: all the odd draconitic harmonics found when the CODE model is used show a very important reduction (almost disappearing with a 92 % average reduction) with the new radiation pressure models. Earth orientation parameters: the draconitic errors are reduced for the $X$ -pole rate and especially for the $Y$ -pole rate by 24 and 50 % respectively. Station coordinates: all the draconitic harmonics (except the 2nd harmonic in the North component) are reduced in the North, East and Height components, with average reductions of 41, 39 and 35 % respectively. This shows, that part of the draconitic errors currently found in GNSS geodetic products are definitely induced by the CODE radiation pressure orbit modeling deficiencies.     

Semantically Enriching an Open Source Sensor Observation Service Implementation for Accessing Heterogeneous Environmental Data Sources

Many kinds of environmental data are nowadays publicly available, but spread over the web. This article discusses using the Sensor Observation Service (SOS) standard of the Open Geospatial Consortium (OGC) as a common interface for providing data from heterogeneous sources which can be integrated to a user tailored environmental information system. In order to allow for providing user‐tailored and problem‐specific information the adjusted SOS is augmented by a semantic layer which maps the environmental information to ontology concepts. The necessary information fusion from different domains and data types lead to several specific requirements for the SOS. Addressing these requirements we have implemented a SOS which still conforms to the OGC SOS 1.0.0 standard specification. The developed SOS has been integrated in a publicly available demonstrator of our personalized environmental information system. Additionally this article discusses future consequences for the SOS, caused by the recently published SOS 2.0 specification.     

Consistent realization of Celestial and Terrestrial Reference Frames

The Celestial Reference System (CRS) is currently realized only by Very Long Baseline Interferometry (VLBI) because it is the space geodetic technique that enables observations in that frame. In contrast, the Terrestrial Reference System (TRS) is realized by means of the combination of four space geodetic techniques: Global Navigation Satellite System (GNSS), VLBI, Satellite Laser Ranging (SLR), and Doppler Orbitography and Radiopositioning Integrated by Satellite. The Earth orientation parameters (EOP) are the link between the two types of systems, CRS and TRS. The EOP series of the International Earth Rotation and Reference Systems Service were combined of specifically selected series from various analysis centers. Other EOP series were generated by a simultaneous estimation together with the TRF while the CRF was fixed. Those computation approaches entail inherent inconsistencies between TRF, EOP, and CRF, also because the input data sets are different. A combined normal equation (NEQ) system, which consists of all the parameters, i.e., TRF, EOP, and CRF, would overcome such an inconsistency. In this paper, we simultaneously estimate TRF, EOP, and CRF from an inter-technique combined NEQ using the latest GNSS, VLBI, and SLR data (2005–2015). The results show that the selection of local ties is most critical to the TRF. The combination of pole coordinates is beneficial for the CRF, whereas the combination of \(\varDelta \hbox {UT1}\) results in clear rotations of the estimated CRF. However, the standard deviations of the EOP and the CRF improve by the inter-technique combination which indicates the benefits of a common estimation of all parameters. It became evident that the common determination of TRF, EOP, and CRF systematically influences future ICRF computations at the level of several \(\upmu \)as. Moreover, the CRF is influenced by up to \(50~\upmu \)as if the station coordinates and EOP are dominated by the satellite techniques.     

Ionospheric Joule dissipation as a damping mechanism for high latitude ULF pulsations: Observational evidence

On 9 January 1979 an SI-excited pulsation event was observed by the Scandinavian Magnetometer Array. The pulsation period shows a clear variation with latitude which suggests decoupled oscillations of individual magnetic field shells. The pulsation amplitudes exhibit an e-fold decay with the damping rate γ varying both in longitudinal and latitudinal directions. Assuming Joule heating in the ionosphere as the dominant damping mechanism (and thus γ ～ Σ^?1_p) approximate height-integrated Pedersen conductivity profiles were calculated which fit well with previously observed Σ_p distributions. This is interpreted as observational evidence for ionosopheric Joule dissipation as the major damping mechanism for high-latitude ULF-pulsations.     

Theorie des Triftstromes und der virtuellen Reibung im Meer

Zusammenfassung Entsprechend der Reynoldsschen Konzeption werden die virtuellen Reibungskr?fte berechnet. Die Orbitalbewegungen der Oberfl?chen- und internen Wellen stellen die st?rksten Abweichungen vom mittleren Strom dar. Der auf diesen Bewegungen basierende Reynoldssche Spannungstensor wird aus dem Gleichungssystem (12) bis (14) ermittelt. Formale L?sungen sind (25) bis (28), wennW(z) aus (24) für beliebigeū(z) bekannt ist. Für Oberfl?chenwellen reduziert sich (24) auf (29) mit der N?herungsl?sung (34). Hieraus folgen (37) und (38). Absch?tzung der Integrale führt für Wellen endlicher Kamml?nge auf (55), woraus die Reibungskr?fte (56) bis (58) folgen. Station?re mittlere Str?mungen sind dann durch (61) beschreibbar. μ, gegeben durch (62), wird in Anlehnung an die bestehende Nomenklatur als “virtueller Reibungskoeffizient” bezeichnet. Er ist durch die Parameter des Seeganges bestimmt. Im Gegensatz zu V. W. Ekman werden Triftstr?me durch (67) bis (69) mit den L?sungen (71), (72) bzw. (73), (74) beschrieben. Aus dem sinusoidalen Verlauf der Reibungskoeffizienten (62) folgt eine Streifenstruktur des Triftstromes, wie sie Abb. 3 in Zuordnung zum Seegang zeigt. Die Geschwindigkeitsverteilung eines Streifens ist in Abb. 2 wiedergegeben. Eine Rechtsablenkung analog zur Ekman-Spirale tritt nicht auf; der Strom setzt stets in Richtung des Windes. Durch Messungen in der Ostsee mit Rhodamin wurde die theoretisch zu erwartende Streifenbildung für verschiedene Windgeschwindigkeiten qualitativ nachgewiesen (Abb. 4 und Tafeln 8 und 9).

---

The theory of the drift current and the virtual friction in the sea

Summary According to the Reynolds' procedure, the “turbulent” stresses due to surface and internal waves are computed. Starting from Eqs. (12) to (14) for linear internal and surface waves we get the solutions (25) to (28) withW(z) as a solution of (24) for arbitrary mean currents. For surface waves, (24) reduces to (29) with the approximate solution (34). From this follow (37) and (38). Estimating the integrals, we get (55) for waves of finite crests. From this follow (56) to (58) for the frictional forces due to waves. Stationary mean currents are then described by (61). The coefficient (62) is called “eddy viscosity”. It depends on the wave parameters. In contrast to Ekman's theory, drift currents are described by (67) to (69) with the solutions (71), (72) or (73), (74). Due to the sinusoidal shape of the eddy viscosity coefficients (62) the drift current has a band structure. This structure is shown in Fig. 3. The current distribution within a band is shown in Fig. 2. The current runs always in the direction of the wind, a deflection to the right due to Coriolis force is not observed. The forming of bands has been tested by Rhodamin. The results are in qualitative agreement with the theory (Fig. 4 and Plates 8 and 9).

---

La théorie du courant de dérive et du frottement virtuel en mer

Résumé Les forces de frottement virtuelles sont calculées d'après la conception de Reynolds. Les mouvements périodiques dans la couche de surface et les ondes internes constituent les écarts les plus importants par rapport au courant moyen. Le tenseur de Reynolds qui prend pour base ces mouvements, est obtenu au moyen du système d'équations (12) à (14). Les solutions obtenues sont (25) à (28) lorsqu'on conna?tW(z) au moyen de (24) pour desū(z) quelconques. Pour les ondes de surface, (24) se réduit à (29) avec la solution approchée (34); les solutions (37) et (38) s'en déduisent. De l'évaluation de l'intégrale on déduit (55) pour des ondes d'une longueur de crête finie et on en tire les forces de frottement (56) à (58). Des courants moyens stationnaires peuvent alors être décrits au moyen de (61). μ, donné par (62) est appelé ?coefficient de frottement virtuel? suivant les dénominations admises et il est déterminé par les paramètres des vagues. Contrairement à V. W. Ekman les courants de dérive sont décrits par (67) à (69) avec les solutions (71), (72) ou encore (73), (74). Du fait de la forme sinuso?dale prise par les coefficients de frottement (62) le courant de dérive se présente sous forme de bandes comme le montre la fig. 3 d'après l'état de la mer. La fig. 2 indique la distribution des vitesses dans une bande. On ne constate pas de déviation vers la droite analogue à celle de la spirale d'Ekman: le courant suit toujours la direction du vent. Des mesures effectuées en mer Baltique avec de la rhodamine ont confirmé quantitativement la formation des bandes théoriquement prévisibles pour différentes vitesses de vent (fig. 4 et planches 8 et 9).

---

Hierzu Tafeln 8 und 9     

Interngefüge der Kalifeldspate in einem Ötztaler Gneis

Ohne ZusammenfassungMit 18 Gefügediagrammen.