Chemistry, small-scale inhomogeneity, and formation of moldavites as condensates from sands vaporized by the Ries impact

The formation of the Ries impact and the moldavites have identical radiogenic ages of 14.3 Ma. According to this conformity in age moldavites are generally regarded as products of the Ries impact. This paper, which is divided into two sections, deals with two aspects of the moldavite-forming process: the formation of moldavite bodies by accretion of small precursors, and the physical and chemical conditions under which these primary units originated from sands which covered the Ries impact site.First, the chemical inhomogeneity of moldavite glasses is investigated in sections of 11 moldavites, using back scattered electron (BSE) images and electron microprobe analyses on 0.4-2.7 mm long traverses. Schlieren and lechatelierite particles are interpreted as relics of small, chemically different precursors, which accumulated to larger moldavite bodies at temperatures too low to be efficient for mixing. The patterns of schlieren and lechatelierite inclusions represent two successive rheological regimes: Small agglomerating primary melt units were extended into thin lamellae and threads under conditions of laminar flow. As evidenced by folded textures, these fluidal arrays were later plastically deformed under conditions of compressional stress.To elucidate the production of the primary melt units by the Ries impact, in the second section the geologic situation of the Ries area is considered with regard to possible source materials. The site of the Ries impact, situated at the northern border of the pre-Alpine Molasse basin, was covered at the time of the impact by fluviatile sediments of the lower sequence of the Obere Süßwasser-Molasse (OSM) Formation of Middle Miocene age, consisting of sands, marly sands and clays. Chemical analyses for major and trace elements of 38 moldavites from Bohemia and Moravia, and of 28 samples of the OSM Formation, collected from outcrops and drill holes, immediately south of the Ries crater and south of the Danube, show chemical conformity of moldavites and sand samples with regard to the major parameters SiO_2,Al₂O₃+ FeO, and MgO + CaO, indicating that these sands were the essential source material of moldavites. But, differences in contents of individual major and trace elements between moldavites and sands show that the formation of moldavites from sands involved a specific chemical differentiation which can not be explained by selective vaporization or melting, nor by selective condensation from melt or vapeur. Because large ions were enriched and small ones depleted in moldavites, the ionic radius has controlled the distribution of elements between sands and moldavites. We assume that moldavites originated from a plasma that the impact produced at its encounter with the surficial sand formation at the impact site, and that the primary units formed as early condensates in which large ions were preferentially trapped.     

A progressive line simplification algorithm

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Reconstructing the iron cycle from the horizontal distribution of metals in the sediment of Baldeggersee

In Baldeggersee, the distributions of solid phase Fe, Mn, V, Cr, As and Mo were determined in different sediment strata, deposited under various deep-water oxygen conditions. Iron concentrations are correlated with water depth when an anoxic sediment is in contact with an oxic water column. Benthic redox gradients trigger iron transport towards the deepest site (geochemical focusing) and loss of iron from the shallower parts through the outflow. Fe cycling in the lake is inhibited by oxygen penetration into the sediment. Vanadium and arsenic can be used as tracers for the internal Fe cycle. Their distribution patterns are highly correlated with iron. In case of a stable oxycline in the deep water, Mo is enriched in the sediment and correlates with Mn. The horizontal distribution patterns of Fe, V, As and the correlation of Fe and Mn with trace metals are promising proxy indicators for the reconstruction of deep-water oxygen conditions during deposition.     

Quasi-geostrophic stratified flow over isolated finite amplitude topography

The quasi-geostrophic response of a stratified stream incident upon isolated finite amplitude topography on a f-plane is examined in the limit of a Boussinesq, incompressible, inviscid fluid. Compact solutions are derived subject to the following stipulations: uniform upstream velocity and stratification, a circular obstacle and an entirely isentropic/isopycnic lower surface.It is shown that for a semi-infinite flow domain the criterion for Taylor cap formation (i.e., a region of closed streamlines) is . However, for the isentropic lower boundary condition the solutions exist (i.e., have physical validity) only if R₀F⁻¹ < 0.5. (Here R₀ and F refer to the Rossby and Froude numbers defined respectively in terms of the mountain half-width and height.) Also considered are the modifications both to the flow response and to the foregoing existence criterion that are induced by the introduction of an upstream profile comprising two layers of uniform but different stratification. In addition, the relationship of the derived solutions to the results obtained in previous studies is explored, and in particular an outline is given of the impact of adopting the ‘traditional’ simplified lower boundary condition.     

Elasticity of a beryllium silicate (phenacite: Be2SiO4)

The adiabatic single-crystal elastic moduli of a beryllium silicate (phenacite: Be₂SiO₄, trigonal, have been determined at atmospheric pressure and 22° C by Brillouin spectroscopy. The elastic stiffness moduli in gigapascals are: C ₁₁=341.9 C ₃₃=391.0 C ₄₄=91.4 C ₆₆= 96.9 C ₁₂=148.0 C ₁₃=136.0 C ₁₄= 0.1 C ₁₅= 3.5Overall, the elastic stiffness moduli for phenacite parallel and perpendicular to the c axis are comparable (i.e., it is almost cubic in its elastic signature). The elastic moduli can be rationalized in terms of division of the structure into two types of coordination polyhedra (1Si+2Be) with slightly different stiffnesses, which are linked to form a three dimensional framework. Values of the isothermal bulk modulus and the linear compressibilities, as determined from hydrostatic compression experiments of Hazen and Au (1986), are in good agreement with those obtained here. Combining the two studies indicates a low pressure derivative of the bulk modulus for phenacite.     

Long-term precipitation variability in Morocco and the link to the large-scale circulation in recent and future climates

Summary ?Monthly precipitation data from the Global Historical Climatology Network for 42 stations in Morocco and its vicinity are investigated with respect to baroclinicity, storm track and cyclone activity, moisture transports, North Atlantic Oscillation (NAO) variations, and different circulation types by means of correlation and composite studies. The results are related to a climate change scenario from an ECHAM4/OPYC3 transient greenhouse gas only (GHG) simulation. Precipitation in northwestern Morocco shows a clear link to the baroclinic activity over the North Atlantic during boreal winter (DJF). In large precipitation months the North Atlantic storm track is shifted southward, more westerly and northwesterly circulation situations occur and moisture transports from the Atlantic are enhanced. The occurrence of local cyclones and upper-level troughs is more frequent than in low precipitation months. The negative correlation to the NAO is relatively strong, especially with Gibraltar as a southern pole (−0.71). The northward shift of the storm track and eastward shift of the Azores High predicted by the ECHAM model for increasing GHG concentrations would therefore be associated with decreasing precipitation and potentially serious impacts for the future water supply for parts of Morocco. In the region south of the Atlas mountains, moisture transports from the Atlantic along the southern flank of the Atlas Mountains associated with cyclones west of Morocco and the Iberian Peninsula can be identified as a decisive factor for precipitation. Northeastern Morocco and Northwestern Algeria, however, is rather dominated by the influence of cyclones over the Western Mediterranean that are associated with a strong northwesterly moisture transport. As both regions appear to be less dependent on the North Atlantic storm track and more on local processes, a straight forward interpretation of the large-scale changes predicted by the ECHAM4/OPYC3 cannot be done without the application of down-scaling methods in the future. Received July 19, 2001; revised May 31, 2002     

Partial integer decorrelation: optimum trade-off between variance reduction and bias amplification

Different techniques have been developed for determining carrier phase ambiguities, ranging from float approximations to the efficient solution of the integer least square problem by the LAMBDA method. The focus so far was on double-differenced measurements. Practical implementations of the LAMBDA method lead to a residual probability of wrong fixing of the order one percent. For safety critical applications, this probability had to be reduced by eight orders of magnitude, which could be achieved by linear multi-frequency code–carrier combinations. Scenarios with single or no differences include biases due to orbit errors, satellite clock offsets, as well as residual code and phase biases. For this case, a linear combination of Galileo E1 and E5 code and carrier phase measurements with a wavelength of 3.285 m and a noise level of a few centimeters is derived. This ionosphere-free combination preserves the orbit and clock errors, and suppresses the E1 code multipath by 12.6 dB. Since integer decorrelation transformations, as used in the LAMBDA method, inflate biases, the number of such transformations must be limited, and applied in a judicious order. With a Galileo type constellation, this leads to a vertical standard deviation of ca. 20 cm, while keeping the probability of wrong fixing extremely low for code biases of 10 cm, and phase biases of 0.1 cycle, combined in a worst case.     

Emerging organic contaminants (EOCs) in freshwaters in Dunedin,New Zealand

Emerging organic contaminants (EOCs) in New Zealand freshwaters are not well documented for regulatory assessments. We collected water and sediment samples for measurement of 26 EOC compound concentrations at four waterways within the city of Dunedin (Otago province). Compounds measured ranged from stimulants and depressants to pain-killers and insect repellants. Sampling was conducted before and after the student ‘Orientation Week’ at the University of Otago. Most compounds were below detection limits in all samples. However, caffeine, carbamazepine, cotinine and DEET were all measured at concentrations above detection limits. In general, concentrations of EOC compounds were ～20% higher following the influx of students to the University though student effects varied by site and additional sampling is needed to better assess temporal variation in concentrations. These data indicate that some EOCs are present in New Zealand freshwater ecosystems.     

The planet formation imager

The Planet Formation Imager (PFI, www.planetformationimager.org) is a next-generation infrared interferometer array with the primary goal of imaging the active phases of planet formation in nearby star forming regions. PFI will be sensitive to warm dust emission using mid-infrared capabilities made possible by precise fringe tracking in the near-infrared. An L/M band combiner will be especially sensitive to thermal emission from young exoplanets (and their disks) with a high spectral resolution mode to probe the kinematics of CO and H₂O gas. In this paper, we give an overview of the main science goals of PFI, define a baseline PFI architecture that can achieve those goals, point at remaining technical challenges, and suggest activities today that will help make the Planet Formation Imager facility a reality.