Mineralogy and petrogenesis of lunar magnesian granulitic meteorite Northwest Africa 5744

Lunar meteorite Northwest Africa (NWA) 5744 is a granulitic breccia with an anorthositic troctolite composition that may represent a distinct crustal lithology not previously described. This meteorite is the namesake and first‐discovered stone of its pairing group. Bulk rock major element abundances show the greatest affinity to Mg‐suite rocks, yet trace element abundances are more consistent with those of ferroan anorthosites. The relatively low abundances of incompatible trace elements (including K, P, Th, U, and rare earth elements) in NWA 5744 could indicate derivation from a highlands crustal lithology or mixture of lithologies that are distinct from the Procellarum KREEP terrane on the lunar nearside. Impact‐related thermal and shock metamorphism of NWA 5744 was intense enough to recrystallize mafic minerals in the matrix, but not intense enough to chemically equilibrate the constituent minerals. Thus, we infer that NWA 5744 was likely metamorphosed near the lunar surface, either as a lithic component within an impact melt sheet or from impact‐induced shock.     

Canonical Modelling of Relative Spacecraft Motion Via Epicyclic Orbital Elements

This paper presents a Hamiltonian approach to modelling spacecraft motion relative to a circular reference orbit based on a derivation of canonical coordinates for the relative state-space dynamics. The Hamiltonian formulation facilitates the modelling of high-order terms and orbital perturbations within the context of the Clohessy–Wiltshire solution. First, the Hamiltonian is partitioned into a linear term and a high-order term. The Hamilton–Jacobi equations are solved for the linear part by separation, and new constants for the relative motions are obtained, called epicyclic elements. The influence of higher order terms and perturbations, such as Earth’s oblateness, are incorporated into the analysis by a variation of parameters procedure. As an example, closed-form solutions for J₂-invariant orbits are obtained.     

The distribution of carbon monoxide in the lower atmosphere of Venus

We have obtained spatially resolved near-infrared spectroscopy of the Venus nightside on 15 nights over three observing seasons. We use the depth of the CO absorption band at 2.3 μm to map the two-dimensional distribution of CO across both hemispheres. Radiative transfer models are used to relate the measured CO band depth to the volume mixing ratio of CO. The results confirm previous investigations in showing a general trend of increased CO abundances at around 60° latitude north and south as compared with the equatorial regions. Observations taken over a few nights generally show very similar CO distributions, but significant changes are apparent over longer periods. In past studies it has been assumed that the CO latitudinal variation occurs near 35 km altitude, at which K-band sensitivity to CO is greatest. By modeling the detailed spectrum of the excess CO at high latitudes we show that it occurs at altitudes around 45 km, much higher than has previously been assumed, and that there cannot be significant contribution from levels of 36 km or lower. We suggest that this is most likely due to downwelling of CO-rich gas from the upper atmosphere at these latitudes, with the CO being removed by around 40 km through chemical processes such as the reaction with SO₃.     

Age and tectonomagmatic setting of the Eocene Çöpler–Kabataş magmatic complex and porphyry-epithermal Au deposit, East Central Anatolia, Turkey

The Çöpler epithermal Au deposit and related subeconomic porphyry Cu–Au deposit is hosted by the middle Eocene Çöpler–Kabata? magmatic complex in central eastern Anatolia. The intrusive rocks of the complex were emplaced into Late Paleozoic–Mesozoic metamorphosed sedimentary basement rocks near the northeastern margin of the Tauride-Anatolide Block. Igneous biotite from two samples of the magmatic complex yielded ⁴⁰Ar/³⁹Ar plateau ages of 43.75?±?0.26 Ma and 44.19?±?0.23, whereas igneous hornblende from a third sample yielded a plateau age of 44.13?±?0.38. These ages closely overlap with ⁴⁰Ar/³⁹Ar ages of hydrothermal sericite (44.44?±?0.28 Ma) and biotite (43.84?±?0.26 Ma), and Re–Os ages from two molybdenite samples (44.6?±?0.2 and 43.9?±?0.2 Ma) suggesting a short-lived (<1 my) magmatic and hydrothermal history at Çöpler. No suitable minerals were found that could be used to date the epithermal system, but it is inferred to be close in age to the precursor porphyry system. The Çöpler–Kabata? intrusive rocks show I-type calc-alkaline affinities. Their normalized trace element patterns show enrichments in large ion lithophile and light rare earth elements and relative depletions in middle and heavy rare earth elements, resembling magmas generated in convergent margins. However, given its distance from the coeval Eocene Maden–Helete volcanic arc, the complex is interpreted to be formed in a back-arc setting, in response to Paleocene slab roll-back and upper-plate extension. The tectonomagmatic environment of porphyry-epithermal mineralization at Çöpler is comparable to some other isolated back-arc porphyry systems such as Bajo de la Alumbrera (Argentina) or Bingham Canyon (USA).     

Enthalpies and entropies of proton and cadmium adsorption onto Bacillus subtilis bacterial cells from calorimetric measurements

We used titration calorimetry to measure the bulk heats of proton and Cd adsorption onto a common Gram positive soil bacterium Bacillus subtilis at 25.0 °C. Using the 4-site non-electrostatic model of Fein et al. [Fein, J.B., Boily, J.-F., Yee, N., Gorman-Lewis, D., Turner, B.F., 2005. Potentiometric titrations of Bacillus subtilis cells to low pH and a comparison of modeling approaches. Geochim. Cosmochim. Acta69 (5), 1123-1132.] to describe the bacterial surface reactivity to protons, our bulk enthalpy measurements can be used to determine the following site-specific enthalpies of proton adsorption for Sites 1-4, respectively: −3.5 ± 0.2, −4.2 ± 0.2, −15.4 ± 0.9, and −35 ± 2 kJ/mol, and these values yield the following third law entropies of proton adsorption onto Sites 1-4, respectively: +51 ± 4, +78 ± 4, +79 ± 5, and +60 ± 20 J/mol K. An alternative data analysis using a 2-site Langmuir-Freundlich model to describe proton binding to the bacterial surface (Fein et al., 2005) resulted in the following site-specific enthalpies of proton adsorption for Sites 1 and 2, respectively: −3.6 ± 0.2 and −35.1 ± 0.3 kJ/mol. The thermodynamic values for Sites 1-3 for the non-electrostatic model and Site 1 of the Langmuir-Freundlich model of proton adsorption onto the bacterial surface are similar to those associated with multifunctional organic acid anions, such as citrate, suggesting that the protonation state of a bacterial surface site can influence the energetics of protonation of neighboring sites. Our bulk Cd enthalpy data, interpreted using the 2-site non-electrostatic Cd adsorption model of Borrok et al. [Borrok, D., Fein, J.B., Tischler, M., O’Loughlin, E., Meyer, H., Liss, M., Kemner, K.M., 2004b. The effect of acidic solutions and growth conditions on the adsorptive properties of bacterial surfaces. Chem. Geol.209 (1-2), 107-119.] to account for Cd adsorption onto B. subtilis, yield the following site-specific enthalpies of Cd adsorption onto bacterial surface Sites 2 and 3, respectively: −0.2 ± 0.4 and +14.4 ± 0.9 kJ/mol, and the following third law entropies of Cd adsorption onto Sites 2 and 3, respectively: +57 ± 4 and +128 ± 5 J/mol K. The calculated enthalpies of Cd adsorption are typical of those associated with Cd complexation with anionic oxygen ligands, and the entropies are indicative of inner sphere complexation by multiple ligands. The experimental approach described in this study not only yields constraints on the molecular-scale mechanisms involved in proton and Cd adsorption reactions, but also provides new thermodynamic data that enable quantitative estimates of the temperature dependence of proton and Cd adsorption reactions.     

The impact of natural hazards on the health sector in the Caribbean: Implications for health sector planning

In the last decade significant initiatives have been taken in the health sector with the view to better manage and respond to natural disaster emergencies. However, the recent hurricane disasters related to Hugo and Gilbert have highlighted many areas of health sector emergency planning still to be adressed. This paper briefly summarises the impact of recent natural disaster on the health sector in the Caribbean and comments on the performance of the sector during the emergencies. An effort is then made to detail what are the policy and programming issues to be tackled, if desired improvements are to be achieved.The reader may like to see GeoJournal vol. 23, no. 4 (April 1991) on Caribbean Hurricanes     

Recent progress on combining geomorphological and geochronological data with ice sheet modelling,demonstrated using the last British–Irish Ice Sheet

Palaeo-ice sheets are important analogues for understanding contemporary ice sheets, offering a record of ice sheet behaviour that spans millennia. There are two main approaches to reconstructing palaeo-ice sheets. Empirical reconstructions use the available glacial geological and chronological evidence to estimate ice sheet extent and dynamics but lack direct consideration of ice physics. In contrast, numerically modelled simulations implement ice physics, but often lack direct quantitative comparison with empirical evidence. Despite being long identified as a fruitful scientific endeavour, few ice sheet reconstructions attempt to reconcile the empirical and model-based approaches. To achieve this goal, model-data comparison procedures are required. Here, we compare three numerically modelled simulations of the former British–Irish Ice Sheet with the following lines of evidence: (a) position and shape of former margin positions, recorded by moraines; (b) former ice-flow direction and flow-switching, recorded by flowsets of subglacial bedforms; and (c) the timing of ice-free conditions, recorded by geochronological data. These model–data comparisons provide a useful framework for quantifying the degree of fit between numerical model simulations and empirical constraints. Such tools are vital for reconciling numerical modelling and empirical evidence, the combination of which will lead to more robust palaeo-ice sheet reconstructions with greater explicative and ultimately predictive power.     

Decadal Changes in Water Quality and Net Productivity of a Shallow Danish Estuary Following Significant Nutrient Reductions

We utilized an extensive data set (1977–2013) from a water quality monitoring program to investigate the recovery of a Danish estuary following large reductions in total phosphorus (TP) and total nitrogen (TN) loading. Monthly rates of net transport and biogeochemical transformation of dissolved inorganic nitrogen (DIN) and phosphorus (DIP) were computed in two basins of the estuary using a box model approach, and oxygen-based rates of net ecosystem production (NEP) were determined. Since 1990, nutrient loading was reduced by 58 % for nitrogen and 80 % for phosphorus, causing significant decreases in DIN (60 %) and DIP (85 %) concentrations. Reductions in nutrient loadings and concentrations reduced annual chlorophyll levels by 50 % in the inner estuary and improved Secchi depth by approximately 1 m during the same period, particularly in the summer period. In the outer, deeper region of the estuary trends in water quality was less evident. Improvements in the inner estuary were strongly coupled to declines in DIN. Thresholds of DIN and DIP concentrations limiting phytoplankton growth indicated that both regions of the estuary were nitrogen limited. NEP rates indicated the development of more net autotrophic conditions over time that were likely associated with higher benthic primary production stimulated by improved light conditions. Box model computations revealed a modest reduction in summer net production of DIP over time, despite the persistence of elevated fluxes for several years after external loads were reduced. Since the mid-1990s, nutrient loading and transformation were stable while nutrient concentrations continued to decline and water quality improved in the inner estuary. The oligotrophication trajectory involved an initial fast transformation and modest retention of nutrients followed by a gradual decline in the rate of improvement towards a new stable condition.     

Potentiometric titrations of Bacillus subtilis cells to low pH and a comparison of modeling approaches

To provide constraints on the speciation of bacterial surface functional groups, we have conducted potentiometric titrations using the gram-positive aerobic species Bacillus subtilis, covering the pH range 2.1 to 9.8. Titration experiments were conducted using an auto-titrator assembly, with the bacteria suspended in fixed ionic strength (0.01 to 0.3 M) NaClO₄ solutions. We observed significant adsorption of protons over the entire pH range of this study, including to the lowest pH values examined, indicating that proton saturation of the cell wall did not occur under any of the conditions of the experiments. Ionic strength, over the range studied here, did not have a significant effect on the observed buffering behavior relative to experimental uncertainty. Electrophoretic mobility measurements indicate that the cell wall is negatively charged, even under the lowest pH conditions studied. These experimental results necessitate a definition of the zero proton condition such that the total proton concentration at the pH of suspension is offset to account for the negative bacterial surface charge that tends towards neutrality at pH <2.The buffering intensity of the bacterial suspensions reveals a wide spread of apparent pKa values. This spread was modeled using three significantly different approaches: a Non-Electrostatic Model, a Constant Capacitance Model, and a Langmuir-Freundlich Model. The approaches differ in the manner in which they treat the surface electric field effects, and in whether they treat the proton-active sites as discrete functional groups or as continuous distributions of related sites. Each type of model tested, however, provides an excellent fit to the experimental data, indicating that titration data alone are insufficient for characterizing the molecular-scale reactions that occur on the bacterial surface. Spectroscopic data on the molecular-scale properties of the bacterial surface are required to differentiate between the underlying mechanisms of proton adsorption inherent in these models. The applicability and underlying conceptual foundation of each model is discussed in the context of our current knowledge of the structure of bacterial cell walls.     

Formation by silicate–fluoride + phosphate melt immiscibility of REE-rich globular segregations within aplite dikes

Aplite dikes intruding the Proterozoic 1.42(±?3) Ga Longs Peak-St. Vrain Silver Plume-type peraluminous granite near Jamestown, Colorado, contain F, P, and rare earth element (REE)-rich globular segregations, with 40–46% REE, 3.7–4.8 wt% P₂O₅, and 5–8 wt% F. A combination of textural features and geochemical data suggest that the aplite and REE-rich globular segregations co-existed as two co-genetic liquids prior to their crystallization, and we propose that they are formed by silicate–fluoride?+?phosphate (+?S?+?CO₂) melt immiscibility following ascent, cooling, and decompression of what was initially a single homogeneous magma that intruded the granite. The REE distribution coefficients between the silica-rich aplites and REE-rich segregations are in good agreement with experimentally determined distribution coefficients for immiscible silicate–fluoride?+?phosphate melts. Although monazite-(Ce) and uraninite U–Th–Pb microprobe ages for the segregations yield 1.420(±?25) and 1.442(±?8) Ga, respectively, thus suggesting a co-genetic relationship with their host granite, ε_Nd1.42Ga values for the granites and related granitic pegmatites range from ??3.3 to ??4.7 (average ??3.9), and differ from the values for both the aplites and REE-rich segregations, which range from ??1.0 to ??2.2 (average ??1.6). Furthermore, the granites and pegmatites have (La/Yb)_N <50 with significant negative Eu anomalies, which contrast with higher (La/Yb)_N >100 and absence of an Eu anomaly in both the aplites and segregations. These data are consistent with the aplite dikes and the REE-rich segregations they contain being co-genetic, but derived from a source different from that of the granite. The higher ε_Nd1.42Ga values for the aplites and REE-rich segregations suggest that the magma from which they separated had a more mafic and deeper, dryer and hotter source in the lower crust or upper mantle compared to the quartzo-feldspathic upper crustal source proposed for the Longs Peak-St. Vrain granite.