Aluminium species distribution during mixing of acid coal and slate mine drainage with neutral stream waters

We measured the spatial variation of aluminium concentrations and computed its species distribution before and during mixing of acid mine drainage containing waters with near neutral receiving waters. Acid mine drainage was collected from the Loquitz Creek, Thuringia, Germany, and Garvey Creek, Westland, New Zealand, which drain slate mine workings and coal mine workings, resp. The acidneutralizing capacity (ANC) of the receiving streams and the mixing with waters having low Al-concentrations cause a decrease of aluminium concentrations below the confluence. Depending on volumes and ANCs involved, the content of free Al and sulphate bound Al decreases after mixing in favour of organic and hydroxide bound Al. In addition, below the junction of the Loquitz Creek and the Aue Creek with its high ANC, we observe the precipitation of aluminium hydroxides and Al hydroxysulphates.

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Zusammenfassung Wir haben die räumliche Änderung der Aluminiumkonzentrationen vor und nach der Mischung von Flußwasser, versauert durch Bergwerksabwässer, mit nahezu neutralem Wasser der Vorfluter gemessen und haben dazu die Speziesverteilung berechnet. Saure Bergwerksabwässer sickern aus Halden eines Schiefertagebaus in Thüringen in die Loquitz ebenso wie aus Halden eines Kohletagebaus in den Garvey Creek, Westland, Neuseeland. Die Säuren-Neutralisierungskapazität der Vorfluter und die Mischung mit Al-armem Wasser bewirken eine Abnahme der Aluminiumkonzentrationen nach dem Zusammenfluß. In Abhängigkeit von beteiligten Abflüssen und Säuren-Neutralisierungskapazitäten nimmt der Gehalt an freiem Aluminium und sulfatgebundenem Aluminium nach der Mischung zugunsten von organisch- und hydroxy-gebundenem Aluminium ab. Ferner beobachten wir unterhalb des Zusammenflusses von Loquitz und Aue, der eine hohe Säuren-Neutralisierungskapazität eigen ist, eine Ausfällung von Aluminiumhydroxyden und Aluminiumhydroxysulfaten.

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Résumé Nous avons mesuré la variation spatiale de la teneur en Al et calculé la distribution de ses différentes formes dans deux cours d'eau différents, qui reçoivent des eaux acides venant de mines situées sur leur cours. Ces mesures ont été faites d'une part sur le cours du Loquitz (Thuringe-Allemagne) qui reçoit des aux acides venant d'une mine d'ardoise et d'autre part sur le cours du Garvey (Westland - Nouvelle Zélande) qui reçoit les eaux d'une mine de charbon. Pour chaque cours d'eau, les mesures ont été faites en amont de la source d'apport, puis en aval, c'est-à-dire après le mélange avec les eaux acides. La capacité de neutralisation des acides (ANC) des eaux des cours d'eau récepteurs et la basse teneur en Al des eaux d'apport provoquent une diminution de la teneur en Al après le mélange. Dans une mesure liée aux volumes en jeu et à l'ANC, la teneur en Al libre et en Al lié au sulfate diminue près le mélange au profit de l'Al lié soit à des substances organiques, soit à des hydroxydes. De plus, en aval du confluent du Loquitz et de l'Aue, rivière à ANC élevé, nous observons la précipitation d'hydroxydes d'Al et d'hydroxisulfates d'Al.

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Rapid orbit determination of LEO satellites using IGS clock and ephemeris products

Different types of GPS clock and orbit data provided by the International GPS Service (IGS) have been used to assess the accuracy of rapid orbit determination for satellites in low Earth orbit (LEO) using spaceborne GPS measurements. To avoid the need for reference measurements from ground-based reference receivers, the analysis is based on an undifferenced processing of GPS code and carrier-phase measurements. Special attention is therefore given to the quality of GPS clock data that directly affects the resulting orbit determination accuracy. Interpolation of clock data from the available 15 min grid points is identified as a limiting factor in the use of IGS ultra-rapid ephemerides. Despite this restriction, a 10-cm orbit determination accuracy can be obtained with these products data as demonstrated for the GRACE-B spacecraft during selected data arcs between 2002 and 2004. This performance may be compared with a 5-cm orbit determination accuracy achievable with IGS rapid and final products using 5 min clock samples. For improved accuracy, high-rate (30 s) clock solutions are recommended that are presently only available from individual IGS centers. Likewise, a reduced latency and more frequent updates of IGS ultra-rapid ephemerides are desirable to meet the requirements of upcoming satellite missions for near real-time and precise orbit determination.     

Metamorphic evolution and geochemistry of kyanite eclogites in central Rhodope,northern Greece

In central Rhodope of northern Greece, kyanite eclogites were discovered in the area of Thermes. They are strongly overprinted and exhibit a multi-stage development of minerals and mineral assemblages formed during successive stages of the exhumation. The initial high-pressure assemblage was garnet+omphacite+kyanite+zoisite+phengite+rutile+quartz. Corundum, Fe-Mg-spinel, sapphirine and högbomite occur as products of a first, high-temperature overprint, still at high pressures, whereas various symplectites [corundum-plagioclase (pl), spinel-pl, sapphirine-pl, clinopyroxene-pl, biotite-pl, amphibole-pl] grew during subsequent stages of the exhumation. Diablastic amphibole+plagioclase formed as end-products of the amphibolitization. According to geochemical data, the protoliths of the kyanite eclogites were basalts to basaltic andesites with “volcanic arc” affinities. For the high-pressure stage of metamorphism, minimum PT conditions were around 19 kbar, 700°C, while for the initial stages of the overprint, high-pressure granulite-facies conditions prevailed (T>800°C, at P>15 kbar). The PT conditions of the amphibolite facies were 8–11 kbar, 580–690°C. The kyanite eclogites of Thermes record the highest temperatures of metamorphism within the whole of Rhodope.     

On the determination of the closure parameters in higher-order closure models

In higher-order closure models at least the pressure redistribution and the dissipation of the turbulent kinetic energy and the temperature variance have to be parameterized. Due to this, the introduction of proportionality coefficients — the so-called closure parameters — is forced, which have to be determined before the model is used. We compare a group of models which use the return-to-isotropy hypothesis (Rotta, 1951) to describe the pressure redistribution and assume local isotropy for the smallest eddies in order to parameterize the dissipation. Special concern is given to the method of Mellor and Yamada (1982). Some of the closure parameters are re-derived on the basis of sensitivity studies requiring that both shear production and buoyancy behave in a realistic way if pressure redistribution or dissipation is changed by varying the closure parameters. This set of parameters is compared with those obtained by fitting to experimental data, by use of the Monin-Obukhov similarity theory and by considering ratios of variances, covariances and mean flow gradients, respectively. It is shown that the various sets of closure parameters are at least of the same order. The differences give some insight into the advantages and disadvantages of the various determination procedures. However, the general accordance of the different parameter sets supports the assumption of universal constants.     

Direct measurements of volume transports through Fram Strait

Heat and freshwater transports through Fram Strait are understood to have a significant influence on the hydrographic conditions in the Arctic Ocean and on water mass modifications in the Nordic seas. To determine these transports and their variability reliable estimates of the volume transport through the strait are required. Current meter moorings were deployed in Fram Strait from September 1997 to September 1999 in the framework of the EU MAST III Variability of Exchanges in the Northern Seas programme. The monthly mean velocity fields reveal marked velocity variations over seasonal and annual time scales, and the spatial structure of the northward flowing West Spitsbergen Current and the southward East Greenland Current with a maximum in spring and a minimum in summer. The volume transport obtained by averaging the monthly means over two years amounts to 9.5 ± 1.4 Sv to the north and 11.1 ± 1.7 Sv to the south (1 Sv = 10⁶ m³s⁻¹). The West Spitsbergen Current has a strong barotropic and a weaker baroclinic component; in the East Greenland Current barotropic and baroclinic components are of similar magnitude. The net transport through the strait is 4.2 ± 2.3 Sv to the south. The obtained northward and southward transports are significantly larger than earlier estimates in the literature; however, within its range of uncertainty the balance obtained from a two year average is consistent with earlier estimates.