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.     

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.     

北京PM10的生物活性与微量元素的相关性研究

在使用质粒DNA评价法对北京PM₁₀的生物活性进行研究的基础上, 结合PM₁₀中微量元素分析结果, 探讨了PM₁₀对质粒DNA产生损伤的原因. 研究表明北京不同季节、不同地区PM₁₀对DNA的氧化性损伤有明显的差别. 冬季市区和对照点PM₁₀(全样)的TM50分别是900和74 μg·mL^-1, 水溶组分的TM50分别是540和86 μg·mL^-1; 夏季市区和对照点PM₁₀(全样)的TM50分别是116和210 μg·mL^-1, 水溶组分的TM50分别是180和306 μg·mL^-1; 北京PM₁₀的生物活性的差别主要来自PM₁₀中微量元素含量的不同. PM₁₀(全样)中Pb, Zn和As三种元素对质粒DNA氧化性损伤能力较强; 而PM₁₀水溶组分中Mn, V, Zn同TM50的相关性较高; Zn元素可能是导致PM10具有氧化性损伤能力的主要微量重金属元素.     

Quantifying climatic change through the last glacial–interglacial transition based on lake isotope palaeohydrology from central Turkey

Questions remain as to the nature of climatic change through the last glacial–interglacial transition in the eastern Mediterranean region, particularly the relative contribution of evaporation and precipitation to regional water balance. Here changes in oxygen isotope values through this time period from Eski Acıgöl, a crater lake in central Turkey, are investigated using hydrological and isotope mass balance models. These allow changes in evaporation and precipitation to be quantified and their relative importance evaluated. We show that it is the volumetric flux rate of water passing through the lake system and not the precipitation-to-evaporation ratio per se which controlled the stable isotope record in Eski Acıgöl. Early Holocene precipitation is shown to be much greater than that during both the latter part of the last glaciation and the present day. We test these calculated values against other records in the same region, firstly with other lake records in Anatolia, the Konya basin and Lake Van, and secondly with isotope-inferred palaeo-precipitation data from Soreq cave in Israel. This reveals a contrast between pre- and post-LGM precipitation values in Turkey (wetter and drier, respectively) and also suggests that during the last glacial–interglacial transition there was a more marked precipitation gradient than at present between northern/interior and southern/coastal parts of the eastern Mediterranean region.