Tabulated statistics for some ion dispersion experiments in turbulent air

In July 1977 dispersion experiments with air ions as tracer were carried out at Porton in southern England. Each trial lasted about 40 min. The source height was 5 m. Continuous ion production took place in eight trials for source-sensor distances between 10 and 100m. Ion production in 1 s pulses took place in another four trials for source-sensor distances between 10 and 50 m. Two sensors were positioned at a height of 5 m and one sensor at 4 m. The experimental set-up and the weather conditions are described. Tabulated results comprise concentration frequency distributions, as well as auto- and cross-correlations, both for 0.01 and 0.1 s resolution.     

Petrogenesis of the Kirkpatrick Basalt,Solo Nunatak,northern Victoria Land,Antarctica, based on isotopic compositions of strontium,oxygen and sulfur

Chemical and isotopic compositions of Jurassic tholeiites of the Kirkpatrick Basalt Group from Solo Nunatak, northern Victoria Land, indicate that these rocks are contaminated with crustal material. The basalts are fine grained and contain phenocrysts of augite, pigeonite, hypersthene and plagioclase. The flows on Solo Nunatak are chemically more similar to average tholeiite than flows from Mt. Falla and Storm Peak in the Central Transantarctic Mountains (TAM) which appear to be more highly differentiated. Initial ⁸⁷Sr/⁸⁶Sr ratios of the flows on Solo Nunatak are high (>0.710) and are similar to those reported for the Kirkpatrick Basalt in the Central TAM. Whole-rock δ¹⁸O values are also high, ranging from +6.0 to +9.3‰ and correlate positively with initial ⁸⁷Sr/⁸⁶Sr ratios, similar to the Kirkpatrick Basalt in the Central TAM. The correlation between initial ⁸⁷Sr/⁸⁶Sr ratios and δ¹⁸O values is explained as the result of simultaneous fractional crystallization and assimilation of a crustal contaminant. Sulfur isotope compositions vary between limits of δ³⁴S= -4.01 to +3.41‰ Variations in (δ³⁴S probably resulted from outgassing of SO₂ under varying oxygen fugacities. Laboratory for Isotope Geology and Geochemistry (Isotopia), Contribution No. 71     

Biomechanical conflicts between adaptations for diving and aerial flight in estuarine birds

Diving and aerial flight place conflicting physiological constraints on diving birds depending on their typical dive depths. The amount by which air volumes in the respiratory system and plumage are reduced by hydrostatic pressure decreases rapidly with depth. Thus, birds diving shallowly, and ascending passively by means of positive buoyancy, content with greater work against buoyancy as well as more unstable buoyancy as they move vertically in the water column. The buoyancy of air far exceeds that of tissues or blood, whose buoyancy does not change appreciably with depth. Accordingly, experiments on ducks suggest that birds adapt to shallow diving by increasing blood volume and thus blood oxygen stores while decreasing respiratory volume. During dives, increased inertia from greater mass of blood and associated muscle lowers the costs of foraging at the bottom by resisting the upward buoyant force, but raises the costs of descent because of higher inertial work in accelerating the body with each stroke. Thus, average dive depth (compression of buoyant air spaces), stroke kinematics (inertial effects), and the relative time spent descending versus bottom foraging will determine the appropriate balance between buoyancy and inertia for diving. Greater blood volume also increases wing loading, so elements of dive costs must be balanced against flight costs in optimizing allocation of oxygen stores to blood versus the respiratory system. For example, biomechanical models for ducks suggest that increasing blood volume while decreasing respiratory volume lowers dive costs only for dives to depths <5 m or for dives with extended time at constant depth. If flight costs are also considered, these anti-buoyancy mechanisms reduce daily energy expenditure only if average dive depth is <2 m. High wing-loading in many foot-propelled divers is probably not an adaptation to diving but rather a result of modifications in wing size and shape for high flight-speed. These wing modifications appear possible because competing demands on wing morphology (maneuverability, takeoff ability) are relaxed in open aquatic environments.     

Platinum-group-mineral inclusions in chromite from the bird river sill,Manitoba

Platinum-group minerals (PGM) have been identified as inclusions in chromite from the Bird River Sill, Manitoba. The inclusions are small (<20 microns) and are commonly euhedral. The PGM inclusions are (Ru, Os, Ir) S₂, laurite, and (Os, Ir, Ru alloy), rutheniridosmine: Laurites contain up to 2.99 wt. % palladium. Arsenic content is negligible and no platinum or rhodium has been detected. One platinum-group element alloy contains 0.96 wt. % rhodium but neither platinum nor palladium has been detected. Laurite inclusions in chromite from the ultramafic zone record two compositional trends; first increasing and then decreasing Ru/(Ru+Os+Ir) up section. PGM inclusions and other solid inclusions occur as discrete phases in chromite and are part of the chromite precipitation event. Increasing oxygen fugacity by wall rock assimilation or new magma injection initiates chromite precipitation, locally increasing the sulphur content of the magma to convert PGE alloys to sulphides.     

Isostatic geoid anomalies over trenches and island arcs

Altimeter geoid profiles crossing trenches and island arcs typically exhibit a long-wavelength increase in geoidal height approaching the trench which, in many cases, reaches a maximum over the back-arc area. Bathymetry profiles across trenches show a similar regional increase in the mean depth of the ocean floor behind the trench. Filters corresponding to Airy and Pratt models of isostatic compensation were applied to bathymetry profiles crossing seven different trench systems in order to estimate how much of the observed geoid variation in these regions could be attributed to isostatically-compensated ocean-floor topography. The results indicate that short-wavelength, high-amplitude variations in the geoid, which in some cases account for over 50% of the total observed amplitude variation, can be reasonably reproduced assuming a Pratt model of isostatic compensation. An additional component of the geoid arises from the uncompensated outer rise seaward of the trench. It is therefore concluded that a large part of the geoid signal over trenches and island arcs may be related to variations in sea-floor topography. This topographic component should be removed from altimeter geoid profiles before using the data to infer details of the deeper structure of subduction zones.     

87Sr/86Sr in kimberlitic carbonates by ion microprobe: Hydrothermal alteration,crustal contamination and relation to carbonatite

Carbonates in a 30 cm wide zoned kimberlite dyke from the De Beers Mine, Kimberley, S. Africa were studied by cathodoluminescence and electron microprobe techniques and their ⁸⁷Sr/⁸⁶Sr ratios were measured using an AEI-IM20 ion microprobe. Primary carbonates (including calcite dendrites, rhombohedral calcites in segregation vesicles and mosaic dolomite) have high Sr (0.69–1.35 wt.% SrO) and Ba (0.24–0.44% BaO) and ⁸⁷Sr/⁸⁶Sr ratios in the range 0.7046 to 0.7056. Secondary sparry calcite in amygdales and veins is characterised by low Ba (<0.05% BaO) and ⁸⁷Sr/⁸⁶Sr near 0.72. Rhombohedral calcite 0.5 cm from a contact with 2,900 my. old biotite-gneiss has minor element chemistry like that of primary carbonate, but an elevated ⁸⁷Sr/⁸⁶Sr ratio of 0.7103, possibly indicating crustal contamination in a boundary layer of the kimberlite magma. Amygdale-like segregations of carbonate and/or serpentine originated as gas-cavities and were not formed by liquid immiscibility. They are now filled either by secondary calcite or by minerals precipitated from residual kimberlite liquid. However, dendritic calcite and primary dolomite and calcite with high Sr, Ba and low ⁸⁷Sr/⁸⁶Sr demonstrate shared chemical characteristics between these carbonates and carbonatite. The primary kimberlite magma had initial ⁸⁷Sr/⁸⁶Sr close to 0.7046.     

Atmospheric chemistry of carbon disulphide

The oxidation of carbon disulphide has been studied under conditions which are likely to pertain in the atmosphere. The quantum yield for direct photo-oxidation of CS₂ in air at 1 atm pressure, using near UV radiation was 0.012, with OCS as a major product. The rate coefficient (k ₁) for the reaction of OH with CS₂, was determined from measurements of OCS formation in the near UV photolysis of HONO?CS₂?O₂?N₂ mixtures. k ₁ was dependent on oxygen concentration rising from ≤4×10^-14 cm³ molecule^-1 s^-1 at O₂≤15 Torr to (2.0±1.0)×10^-12 cm³ molecule^-1 s^-1 at 1 atm air and 300 K. Equimolar amounts of carbonyl sulphide and sulphur dioxide were the major reaction products. The concentration of carbon disulphide in the ambient atmosphere was measured and the concentration to be expected in the background atmosphere was estimated. Rate and concentration data were used to show that carbon disulphide oxidation represents a major source for atmospheric carbonyl sulphide. It can also serve as an alternate source for atmospheric sulphur dioxide in addition to that produced from hydrogen sulphide and dimethyl sulphide. A consideration of atmospheric concentrations and rate data for these trace sulphur gases suggests that the natural sulphur budget is much smaller than the yearly amounts of sulphur dioxide emitted from anthropogenic sources.     

Bayesian Mixture Modelling in Geochronology via Markov Chain Monte Carlo

In this paper we develop a generalized statistical methodology for characterizing geochronological data, represented by a distribution of single mineral ages. The main characteristics of such data are the heterogeneity and error associated with its collection. The former property means that mixture models are often appropriate for their analysis, in order to identify discrete age components in the overall distribution. We demonstrate that current methods (e.g., Sambridge and Compston, 1994) for analyzing such problems are not always suitable due to the restriction of the class of component densities that may be fitted to the data. This is of importance, when modelling geochronological data, as it is often the case that skewed and heavy tailed distributions will fit the data well. We concentrate on developing (Bayesian) mixture models with flexibility in the class of component densities, using Markov chain Monte Carlo (MCMC) methods to fit the models. Our method allows us to use any component density to fit the data, as well as returning a probability distribution for the number of components. Furthermore, rather than dealing with the observed ages, as in previous approaches, we make the inferences of components from the “true” ages, i.e., the ages had we been able to observe them without measurement error. We demonstrate our approach on two data sets: uranium-lead (U-Pb) zircon ages from the Khorat basin of northern Thailand and the Carrickalinga Head formation of southern Australia.     

The influence of carbon on trace element partitioning behavior

Carbon has been proposed as a potential light element in planetary cores, included in models of planetary core formation, and found in meteoritic samples and minerals. To better understand the effect of C on the partitioning behavior of elements, solid/liquid partition coefficients (D = (solid metal)/(liquid metal)) were determined for 17 elements (As, Au, Co, Cr, Cu, Ga, Ge, Ir, Ni, Os, Pd, Pt, Re, Ru, Sb, Sn, and W) over a range of C contents in the Fe-Ni-C system at 1 atm. The partition coefficients for the majority of the elements increased as the C content of the liquid increased, an effect analogous to that of S for many of the elements. In contrast, three of the elements, Cr, Re, and W, were found to have anthracophile (C-loving) preferences, partitioning more strongly into the metallic liquid as the C content increased, resulting in decreases to their partition coefficients. For half of the elements examined, the prediction that partitioning in the Fe-Ni-S and Fe-Ni-C systems could be parameterized using a single set of variables was not supported. The effects of S and C on elemental partitioning behavior can be quite different; consequently, the presence of different non-metals can result in different fractionation patterns, and that uniqueness offers the opportunity to gain insight into the evolution of planetary bodies.