Magnetic Characterization of Amphibolites from the Fomopéa Pluton (West Cameroon): Their Implication in the Pan-African Deformation of the Central African Fold Belt

The Fomopea granitic pluton is emplaced in gnessic and amphibolitic basement.These gneissic and amphibolitic basement rocks are represented in the pluton's body as sub-rounded,elongated or stretched xe...     

Quantifying the effects of environmental change on an oyster population: A modeling study

Three models are combined to investigate the effects of changes in environmental conditions on the population structure of the Eastern oyster,Crassostrea virginica. The first model, a time-dependent model of the oyster population as described in Powell et al. (1992, 1994, 1995a,b, 1996, 1997) and Hofmann et al. (1992, 1994, 1995), tracks the distribution, development, spawning, and mortality of sessile oyster populations. The second model, a time-dependent larval growth model as described in Dekshenieks et al. (1993), simulates larval growth and mortality. The final model, a finite element hydrodynamic model, simulates the circulation in Galveston Bay, Texas. The coupled post-settlement-larval model (the oyster model) runs within the finite element grid at locations that include known oyster reef habitats. The oyster model was first forced with 5 yr of mean environmental conditions to provide a reference simulation for Galveston Bay. Additional simulations considered the effects of long-term increases and decreases in freshwater inflow and temperature, as well as decreases in food concentration and total seston on Galveston Bay oyster populations. In general, the simulations show that salinity is the primary environmental factor controling the spatial extent of oyster distribution within the estuary. Results also indicate a need to consider all environmental factors when attempting to predict the response of oyster populations; it is the superposition of a combination of these factors that determines the state of the population. The results from this study allow predictions to be made concerning the effects of environmental change on the status of oyster populations, both within Galveston Bay and within other estuarine systems supporting oyster populations.     

Major-element vapor fractionation on the lunar surface: An unusual lithic fragment from the Luna 20 fines

A 250-μm fragment in the Luna 20 fines has a very fine-grained “igneous” texture and has the composition (wt.%): SiO₂, 41.1; TiO₂, 0.35; Al₂O₃, 27.2; Cr₂O₃, 0.14; FeO, 4.2; MnO, 0.06; MgO, 8.5; CaO, 17.8; Na₂O, 0.05; and K₂O < 0.02. It contains ～ 65% plagioclase An_99–100, ～ 15% olivine Fo₉₀, ～ 2% Mg-Al spinel and the remainder an unusual interstitial phase with composition SiO₂, 34.8; TiO₂, 1.78; Al₂O₃, 18.3; Cr₂O₃, 0.04; FeO, 14.1; MnO, 0.22; MgO, 5.0; CaO, 24.1; Na₂O, 0.34; K₂O < 0.02. This fragment probably represents a portion of a normal highland rock (anorthositic norite) which was heated to a very high temperature by impact, lost volatiles including SiO₂, and then partially crystallized. The observed phases and their inferred crystallization sequence are consistent with experimental results in the system CaOMgOAl₂O₃SiO₂ (Schairer and Yoder, 1969), assuming the unusual phase to be a residual glass. This type of internal fractionation, leading to silica depletion in the residuum, is different from that normally observed in lunar rocks and is attributed to slightly lower bulk SiO₂ resulting from vapor fractionation due to impact (which also results in lower Na₂O and other volatiles). Because differentiation of the type shown by this fragment is rare in lunar materials, we infer that such major-element vapor fractionation is uncommon on the surface of the moon. The experimental CaOMgOAl₂O₃SiO₂ phase relations also have a bearing on the lunar model proposed by D.L. Anderson in 1973: his “refractory” original lunar composition would differentiate to produce silica deficient liquids, like the unusual phase in our fragment, rather than the normal lunar crustal rocks.     

Examining the Use of USEPA's Generic Attenuation Factor in Determining Groundwater Screening Levels for Vapor Intrusion

A value of 0.001 is recommended by the United States Environmental Protection Agency (USEPA) for its groundwater‐to‐indoor air Generic Attenuation Factor (GAFG), used in assessing potential vapor intrusion (VI) impacts to indoor air, given measured groundwater concentrations of volatile chemicals of concern (e.g., chlorinated solvents). The GAFG can, in turn, be used for developing groundwater screening levels for VI given target indoor air quality screening levels. In this study, we examine the validity and applicability of the GAFG both for predicting indoor air impacts and for determining groundwater screening levels. This is done using both analysis of published data and screening model calculations. Among the 774 total paired groundwater‐indoor air measurements in the USEPA's VI database (which were used by that agency to generate the GAFG) we found that there are 427 pairs for which a single groundwater measurement or interpolated value was applied to multiple buildings. In one case, up to 73 buildings were associated with a single interpolated groundwater value and in another case up to 15 buildings were associated with a single groundwater measurement (i.e., that the indoor air contaminant concentrations in all of the associated buildings were influenced by the concentration determined at a single point). In more than 70% of the cases (390 of 536 paired measurements in which horizontal building‐monitoring well distance was recorded) the monitoring wells were located more than 30 m (and one up to over 200 m) from the associated buildings. In a few cases, the measurements in the database even improbably implied that soil gas contaminant concentrations increased, rather than decreased, in an upward direction from a contaminant source to a foundation slab. Such observations indicate problematic source characterization within the data set used to generate the GAFG, and some indicate the possibility of a significant influence of a preferential contaminant pathway. While the inherent value of the USEPA database itself is not being questioned here, the above facts raise the very real possibility that the recommended groundwater attenuation factors are being influenced by variables or conditions that have not thus far been fully accounted for. In addition, the predicted groundwater attenuation factors often fall far beyond the upper limits of predictions from mathematical models of VI, ranging from screening models to detailed computational fluid dynamic models. All these models are based on the same fundamental conceptual site model, involving a vadose zone vapor transport pathway starting at an underlying uniform groundwater source and leading to the foundation of a building of concern. According to the analysis presented here, we believe that for scenarios for which such a “traditional” VI pathway is appropriate, 10^?4 is a more appropriately conservative generic groundwater to indoor air attenuation factor than is the EPA‐recommended 10^?3. This is based both on the statistical analysis of USEPA's VI database, as well as the traditional mathematical models of VI. This result has been validated by comparison with results from some well‐documented field studies.     

Asteroid 21 Lutetia at 3 μm: Observations with IRTF SpeX

We present observations of Asteroid 21 Lutetia collected 2003–2008 using the SpeX instrument on the NASA Infrared Telescope Facility (IRTF) covering 2–4 μm. We also reevaluate NSFCam observations obtained in 1996 (Rivkin, A.S., Lebofsky, L.A., Clark, B.E., Howell, E.S., Britt, D.T. [2000]. Icarus 145, 351–368). Taken together, these show deeper 3-μm band depths (of order 3–5%) in the southern hemisphere of Lutetia, and shallower band depths (of order 2% or less) in the north. Such variation is consistent with observations at shorter wavelength by previous workers (Nedelcu, D.A. et al. [2007]. Astron. Astrophys. 470, 1157–1164; Lazzarin, M. et al. [2010]. Mon. Not. R. Astron. Soc. 408, 1433–1437), who observed hemispheric-level variations from C-like spectra to X-like spectra.While the shallowness of absorption bands on Lutetia hinders identification of its surface composition, goethite appears plausible as a constituent in its southern hemisphere (Beck, P., Quirico, E., Sevestre, D., Montes-Hernandez, G., Pommerol, A., Schmitt, B. [2011]. Astron. Astrophys. 526, A85–A89). Mathematical models of space weathered goethite are most consistent with Lutetia’s southern hemisphere spectrum, but more work and further observations are necessary to confirm this suggestion.     

Future climate in the Pacific Northwest

Climate models used in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) on the whole reproduce the observed seasonal cycle and twentieth century warming trend of 0.8°C (1.5°F) in the Pacific Northwest, and point to much greater warming for the next century. These models project increases in annual temperature of, on average, 1.1°C (2.0°F) by the 2020s, 1.8°C (3.2°F) by the 2040s, and 3.0°C (5.3°F) by the 2080s, compared with the average from 1970 to 1999, averaged across all climate models. Rates of warming range from 0.1°C to 0.6°C (0.2°F to 1.0°F) per decade. Projected changes in annual precipitation, averaged over all models, are small (+1% to +2%), but some models project an enhanced seasonal cycle with changes toward wetter autumns and winters and drier summers. Changes in nearshore sea surface temperatures, though smaller than on land, are likely to substantially exceed interannual variability, but coastal upwelling changes little. Rates of twenty-first century sea level rise will depend on poorly known factors like ice sheet instability in Greenland and Antarctica, and could be as low as twentieth century values (20 cm, 8^″) or as large as 1.3 m (50^″).     

Carbonyl products of the gas phase reaction of ozone with 1,1-disubstituted alkenes

Carbonyl products have been identified and their formation yields measured in experiments involving the gas phase reaction of ozone with 1,1-disubstituted alkenes at ambient T and p=1 atm. of air. Sufficient cyclohexane was added to scavenge the hydroxyl radical in order to minimize OH-alkene and OH-carbonyl reactions. Formation yields (carbonyl formed/ozone reacted) of primary carbonyls were close to the value of 1.0 that is consistent with the mechanism: O₃+R₁R₂C=CH₂ (HCHO+R₁R₂COO)+(1–)(R₁COR₂+H₂COO) where formaldehyde and the ketone R₁ COR₂ are the primary carbonyls and R₁R₂COO and H₂COO are the corresponding biradicals. Measured values of were 0.58–0.82 and indicate modest preferential formation of formaldehyde and the disubstituted biradical as compared to the ketone and the biradical H₂COO. Carbonyls other than the primary carbonyls were identified. Their formation is discussed in terms of subsequent reactions of the disubstituted biradicals R₁R₂COO. Similarities and differences between disubstituted and monosubstituted biradicals are outlined.     

Diffusion-limited REE uptake by eclogite garnets and its consequences for Lu–Hf and Sm–Nd geochronology

Garnets from the Zermatt-Saas Fee eclogites contain narrow central peaks for Lu + Yb + Tm ± Er and at least one additional small peak towards the rim. The REE Sm + Eu + Gd + Tb ± Dy are depleted in the cores but show one prominent peak close to the rim. These patterns cannot be modeled using Rayleigh fractionation accompanied by mineral breakdown reactions. Instead, the patterns are well explained using a transient matrix diffusion model where REE uptake is limited by diffusion in the matrix surrounding the porphyroblast. Observed profiles are well matched if a roughly linear radius growth rate is used. The secondary peaks in the garnet profiles are interpreted to reflect thermally activated diffusion due to temperature increase during prograde metamorphism. The model predicts anomalously low ¹⁷⁶Lu/¹⁷⁷Hf and ¹⁴⁷Sm/¹⁴⁴Nd ratios in garnets where growth rates are fast compared to diffusion of the REE, and these results have important implications for Lu–Hf and Sm–Nd geochronology using garnet.     

Using GPS multipath to measure soil moisture fluctuations: initial results

Measurements of soil moisture are important for studies of climate and weather forecasting, flood prediction, and aquifer recharge studies. Although soil moisture measurement networks exist, most are sparsely distributed and lack standardized instrumentation. Measurements of soil moisture from satellites have extremely large spatial footprints (40–60 km). A methodology is described here that uses existing networks of continuously-operating GPS receivers to measure soil moisture fluctuations. In this technique, incoming signals are reflected off and attenuated by the ground before reception by the GPS receiver. These multipath reflections directly affect signal-to-noise ratio (SNR) data routinely collected by GPS receivers, creating amplitude variations that are a function of ground reflectivity and therefore soil moisture content. After describing this technique, multipath reflection amplitudes at a GPS site in Tashkent, Uzbekistan are compared to estimates of soil moisture from the Noah land surface model. Although the GPS multipath amplitudes and the land surface model are uncalibrated, over the 70-day period studied, they both rise sharply following each rainfall event and slowly decrease over a period of ∼10 days.