Weathering of the black limestone of historical monuments (Ljubljana,Slovenia): Oxygen and sulfur isotope composition of sulfate salts

The black limestone widely used in Slovenian monuments, particularly in the baroque architecture, is deteriorating extensively due to salt crystallization. Samples of soluble salts from two important historical monuments (in Ljubljana, Slovenia) were investigated in terms of their mineral and isotopic (S and O) compositions. Results revealed the presence of gypsum and soluble salts of the MgSO₄·nH₂O series, such as starkeyite (MgSO₄·4H₂O), pentahydrite (MgSO₄·5H₂O) and hexahydrite (MgSO₄·6H₂O). Whereas black crusts and subflorescences consisted of gypsum, efflorescences appeared to be an assemblage of gypsum and MgSO₄ hydrates. Sample δ¹⁸O_sulfate values varied from ?1.9‰ to +5.5‰ vs. V-SMOW and δ³⁴S_sulfate values from ?19.8‰ to +3.2‰ vs. V-CDT. The respective isotopic composition of analysed outdoor and indoor monument samples indicated different sources of contamination.     

Chemical treatments for mobilizing arsenic from contaminated aquifer solids to accelerate remediation

Arsenic is a prevalent contaminant at US Superfund sites where remediation by pump and treat systems is often complicated by slow desorption of As from Fe and Al (hydr)oxides in aquifer solids. Chemical amendments that either compete with As for sorption sites or dissolve Fe and Al (hydr)oxides can increase As mobility and improve pump and treat remediation efficiency. The goal of this work was to determine optimal amendments for improving pump and treat at As contaminated sites such as the Vineland Chemical Co. Superfund site in southern New Jersey. Extraction and column experiments were performed using As contaminated aquifer solids (81 ± 1 mg/kg), site groundwater, and either phosphate (NaH₂PO₄·H₂O) or oxalic acid (C₂H₂O₄·2H₂O). In extraction experiments, phosphate mobilized between 11% and 94% of As from the aquifer solids depending on phosphate concentration and extraction time (1 mM–1 M; 1–24 h) and oxalic acid mobilized between 38% and 102% depending on oxalic acid concentration and extraction time (1–400 mM; 1–24 h). In column experiments, phosphate additions induced more As mobilization in the first few pore volumes but oxalic acid was more effective at mobilizing As overall and at lower amendment concentrations. At the end of the laboratory column experiments, 48% of As had been mobilized from the aquifer sediments with 100 mM phosphate and 88% had been mobilized with 10 mM oxalic acid compared with 5% with ambient groundwater alone. Furthermore, simple extrapolations based on pore volumes suggest that chemical treatments could lower the time necessary for clean up at the Vineland site from 600 a with ambient groundwater alone to potentially as little as 4 a with 10 mM oxalic acid.     

Tectonic implications of garnet-bearing mantle xenoliths exhumed by Quaternary magmatism in the Hangay dome, central Mongolia

Garnet-bearing mantle xenoliths have been recovered from Quaternary alkali basalts, both within and peripheral to the Hangay dome of central Mongolia. Microfabric analysis and thermobaromery, combining empirical thermobarometers and the self-consistent dataset of THERMOCALC, indicate that garnet websterites from the Shavaryn-Tsaram volcanic centre at the dome core were formed in the spinel-lherzolite upper mantle at pressures of 17–18 kbars and temperatures of 1,070–1,090°C, whereas garnet lherzolites were derived from greater depths (18–20 kbars). Garnet lherzolites from the Baga Togo Uul vents near the dome edge were formed at 18–22 kbars under significantly cooler conditions (960–1,000°C). These xenoliths reveal reaction coronas of (1) orthopyroxene, clinopyroxene, plagioclase and spinel mantling garnets; (2) spongy rims of olivine replacing orthopyroxene and (3) low-Na, low-Al clinopyroxene replacing primary clinopyroxene. Trace-element abundances indicate that clinopyroxene from these coronas is in chemical equilibrium with the host magma. The thermobarometric and textural data suggest that lherzolite xenoliths from both sites were derived from depths of 60–70 km and entrained in magma at 1,200–1,300°C. The average rate of ascent, as determined by olivine zoning, lies in the range 0.2–0.3 m s⁻¹. The contrast in thermal profiles of the upper mantle between the two sites is consistent with a mantle plume beneath the Hangay dome with elevated thermal conditions beneath the core of the dome being comparable to estimates of the Pleistocene geotherm beneath the Baikal rift.     

Successful Eelgrass (<Emphasis Type="Italic">Zostera marina</Emphasis>) Restoration in a Formerly Eutrophic Estuary (Boston Harbor) Supports the Use of a Multifaceted Watershed Approach to Mitigating Eelgrass Loss

From a watershed perspective, Boston Harbor, MA, USA is an ideal site for eelgrass restoration due to major wastewater improvements. Therefore, by focusing on site selection and transplant methods, high survival and expansion rates were recorded at four large eelgrass-restoration sites planted in Boston Harbor as partial mitigation for a pipeline construction project. Transplanted sites met and exceeded reference and donor bed habitat function after 2 years. Hand planting and seeding in checkerboard-patterned transplant plots were efficient and effective methods for jump-starting eelgrass growth over large areas. Although restoration through planting can be successful, it is highly site specific. Even using a published site-selection model, intensive fieldwork was required to identify sites at fine enough scale to ensure successful planting. Given the effort required to identify scarce potential sites, we recommend that future focus includes alternative mitigation strategies that can more adequately prevent eelgrass loss and address water quality degradation which is the leading cause of dieback, site unsuitability for planting, and lack of natural re-colonization.     

How much oxygen is too much? Constraining Saturn's ring atmosphere

The discovery of a molecular oxygen atmosphere around Saturn's rings has important implications for the electrodynamics of the ring system. Its existence was inferred from the Cassini in situ detection of molecular oxygen ions above the rings during Saturn Orbit Insertion in 2004. Molecular oxygen is difficult to observe remotely, and theoretical estimates have yielded only a lower limit (Nn?¹⁰¹³ cm⁻²) to the O₂ column density. Comparison with observations has previously concerned matching ion densities at spacecraft altitudes far larger than the scale height of the neutral atmosphere. This is further complicated by charged particle propagation effects in Saturn's offset magnetic field. In this study we adopt a complementary approach, by focusing on bulk atmospheric properties and using additional aspects of the Cassini observations to place an upper limit on the column density. We develop a simple analytic model of the molecular atmosphere and its photo-ionization and dissociation products, with Nn a free parameter. Heating of the neutrals by viscous stirring, cooling by collisions with the rings, and torquing by collisions with pickup ions are all included in the model. We limit the neutral scale height to h?3000 km using the INMS neutral density nondetection over the A ring. A first upper limit to the neutral column is derived by using our model to reassess O₂ production and loss rates. Two further limits are then obtained from Cassini observations: corotation of the observed ions with the planet implies that the height-integrated conductivity of the ring atmosphere is less than that of Saturn's ionosphere; and the nondetection of fluorescent atomic oxygen over the rings constrains the molecular column from which it is produced via photo-dissociation. These latter limits are independent of production and loss rates and are only weakly dependent on temperature. From the three independent methods described, we obtain similar limits: Nn?2×¹⁰¹⁵ cm⁻². The mean free path for collisions between neutrals thus cannot be very much smaller than the scale height.     

High-resolution simulations of stellar collisions between equal-mass main-sequence stars in globular clusters

We performed high-resolution simulations of two stellar collisions relevant for stars in globular clusters. We considered one head-on collision and one off-axis collision between two 0.6-M_⊙ main-sequence stars. We show that a resolution of about 100 000 particles is sufficient for most studies of the structure and evolution of blue stragglers. We demonstrate conclusively that collision products between main-sequence stars in globular clusters do not have surface convection zones larger than 0.004 M_⊙ after the collision, nor do they develop convection zones during the 'pre-main-sequence' thermal relaxation phase of their post-collision evolution. Therefore, any mechanism which requires a surface convection zone (i.e. chemical mixing or angular momentum loss via a magnetic wind) cannot operate in these stars. We show that no disc of material surrounding the collision product is produced in off-axis collisions. The lack of both a convection zone and a disc proves a continuing problem for the angular momentum evolution of blue stragglers in globular clusters.     

COUNCIL MEETING,SEATTLE April 26-27, 1974

Since the U.S. Embassy in Beijing placed an air quality sensor on its roof and began publishing the results on Twitter in 2008, air quality has gained widespread attention on Chinese microblogs. When the Chinese government introduced new air quality standards in 2012, some hailed this as a victory for Chinese microbloggers, signifying the emergence of social media as a democratizing force leading to greater citizen power. Using a representative sample of microblog posts collected from October 2012 to June 2013 on the topic of air pollution, as well as contextual information from a variety of sources, we examine how the government, companies, nongovernmental organizations, and individuals approach the Chinese social media landscape. We find that although microblogs are capable of empowering citizens to advance an environmental cause, social media have also been increasingly employed by the government as a tool for social monitoring and control and by companies as a platform for profiting from air pollution.