The first known natural occurrence of calcium monoaluminate,in a calcium‐aluminum‐rich inclusion from the CH chondrite Northwest Africa 470

Abstract— Natural calcium monoaluminate, CaAl₂O₄, has been found in a grossite‐rich calcium‐aluminum‐rich inclusion (CAI) from the CH chondrite Northwest Africa 470. The calcium monoaluminate occurs as colorless ～10 μm subhedral grains intergrown with grossite, perovskite, and melilite. Nebular condensation is the most likely origin for the precursor materials of this CAI, but calculations suggest that dust/gas ratios substantially enhanced over solar are required to stabilize CaAl₂O₄.     

Lateral inhomogeneities in the Venus atmosphere: Analysis of thermal infrared maps

The thermal infrared maps of Venus published by Murray, Wildey, and Westphal (1963) and Westphal, Wildey, and Murray (1965) have been analyzed systematically in order to separate the observed intensity into a limb-darkening component and a solar-associated component representing fixed patterns of intensity corotating with the earth and sun, respectively. Interesting new results are obtained for the solar-associated component. Regions near the subsolar point and the poles are not covered in the original maps or in the analysis.The solar-associated pattern of intensity is very nearly symmetric about the equator. In both northern and southern hemispheres, an intensity minimum seems to occur near the morning terminator at middle to high latitudes, slightly beyond the limit of the maps. An intensity maximum occurs on the equator slightly to the east of the antisolar point. Three broad ridges of relatively high intensity radiate away from this point, one pointing to the west along the equator, the others pointing to the northeast and southeast, respectively. The eastward tilt of the latter two ridges may indicate that horizontal exchange is important in maintaining the equatorial maximum of zonal momentum which is associated with the 4-day circulation of the Venus atmosphere.     

Photometry of 433 Eros from 0.65 to 2.2 μm

Lightcurves of 433 Eros are reported for 11 bandpasses ranging from 0.65 to 2.2 μm in wavelength. The relative spectral reflectance, R(λ), was not seen to vary during our observations. Eros has R(1.6 μm) = 1.5 ± 0.1 and R(2.2 μm) = 1.7 ± 0.1, where R(λ) is the spectral reflectance scaled to unity at λ = 0.56 μm. This spectral reflectance is suggestive of a mixture of silicates and material with high infrared reflectance, perhaps a metallic phase such as meteoritic “iron”.     

Investigating the micro mechanics of cemented sand using DEM

The discrete element method has been used to investigate the micro mechanics of cemented sand. High‐pressure drained triaxial tests are modelled in 3D using a flexible membrane that allows the correct deformation to develop. Simulations with up to 12 MPa confining pressure are presented, which are compared with laboratory experiments on a sand with a range of cement contents. Cementation is modelled using ‘parallel bonds’, and various parameters and strength distributions are investigated. Varying levels of cementation are successfully modelled, with the correct qualitative behaviour observed and the separate effects of cementation and confining pressures demonstrated. The triaxial behaviour is found to be highly influenced by the distribution of bond strengths. Copyright © 2014 John Wiley & Sons, Ltd.     

Surmounting luminescence age overestimation in Alaska-margin Arctic Ocean sediments by use of ‘micro-hole’ quartz dating

Because of several difficulties with the application of radiocarbon (¹⁴C) dating to Arctic Ocean sediments, numeric dating techniques are needed that can complement, supplant and reach beyond the ¹⁴C method. However, large age overestimates (often >7 kyr) for near-sediment-water-interface horizons from Arctic Ocean cores have been almost universal when luminescence dating has been applied to multigrain aliquots of fine silt (4–11 μm) quartz and feldspar grains. Here micro-hole quartz-grain photon-stimulated-luminescence (PSL) dating is applied to the 0.5–2.0 cm horizons of multicores from high-sedimentation-rate sites spanning depths from 87 m to 1140 m at the Alaska margin of the Arctic Ocean. Expected near zero ages (0–200 a) result when grains larger than ～11 μm are used, demonstrating that fine-silt age overestimations here and perhaps elsewhere in the Arctic Ocean are a function of grain and aliquot size. At the 87 m site, the micro-hole PSL approach revealed no significant gradient in age estimates over the 1–26 cm horizon range, implying that bioturbation reached to at least 26 cm. Micro-hole PSL dating of 25–62 μm quartz grains from trans-ocean sea-ice sediment also produced expected near zero ages, in contrast to earlier reported long-bleach multigrain PSL results from 4–11 μm fractions of the same samples. The micro-hole PSL approach thus surmounts the age overestimation problem associated with the use of multigrain silt fractions, and overcomes limitations of the ¹⁴C method in this region. Finally, results unexpectedly suggest the potential of micro-hole quartz PSL for use in provenance studies of Arctic Ocean sea-ice sediment.     

The effect of ammonia ice on the outgoing thermal radiance from the atmosphere of Jupiter

We examine the effects of NH₃ ice particle clouds in the atmosphere of Jupiter on outgoing thermal radiances. The cloud models are characterized by a number density at the cloud base, by the ratio of the scale height of the vertical distribution of particles (H_p) to the gas scale height (H_g), and by an effective particle radius. NH₃ ice particle-scattering properties are scaled from laboratory measurements. The number density for the various particle radius and scale height models is inferred from the observed disk average radiance at 246 cm^?1, and preliminary lower limits on particle sizes are inferred from the lack of apparent NH₃ absorption features in the observed spectral radiances as well as the observed minimum flux near 2100 cm^?1. We find lower limits on the particle size of 3 μm if H_p/H_g = 0.15, or 10μmif H_p/H_g = 0.50 or 0.05. NH₃ ice particles are relatively dark near the far-infrared and 8.5-μm atmospheric windows, and the outgoing thermal radiances are not very sensitive to various assumptions about the particle-scattering function as opposed to radiances at 5 μm, where particles are relatively brighter. We examined observations in these three different spectral window regions which provide, in principle, complementary constraints on cloud parameters. Characterization of the cloud scale height is difficult, but a promising approach is the examination of radiances and their center-to-limb variation in spectral regions where there is significant opacity provided by gases of known vertical distribution. A blackbody cloud top model can reduce systematic errors due to clouds in temperature sounding to the level of 1K or less. The NH₃ clouds provide a substantial influence on the internal infrared flux field near the 600-mbar level.     

Development of a Multimetric Index for Integrated Assessment of Salt Marsh Ecosystem Condition

Tools for assessing and communicating salt marsh condition are essential to guide decisions aimed at maintaining or restoring ecosystem integrity and services. Multimetric indices (MMIs) are increasingly used to provide integrated assessments of ecosystem condition. We employed a theory-based approach that considers the multivariate relationship of metrics with human disturbance to construct a salt marsh MMI for five National Parks in the northeastern USA. We quantified the degree of human disturbance for each marsh using the first principal component score from a principal components analysis of physical, chemical, and land use stressors. We then applied a metric selection algorithm to different combinations of about 45 vegetation and nekton metrics (e.g., species abundance, species richness, and ecological and functional classifications) derived from multi-year monitoring data. While MMIs derived from nekton or vegetation metrics alone were strongly correlated with human disturbance (r values from ?0.80 to ?0.93), an MMI derived from both vegetation and nekton metrics yielded an exceptionally strong correlation with disturbance (r = ?0.96). Individual MMIs included from one to five metrics. The metric-assembly algorithm yielded parsimonious MMIs that exhibit the greatest possible correlations with disturbance in a way that is objective, efficient, and reproducible.