The westward thermospheric jet-stream of the evening auroral oval

One of the most consistent and often dramatic interactions between the high latitude ionosphere and the thermosphere occurs in the vicinity of the auroral oval in the afternoon and evening period. Ionospheric ions, convected sunward by the influence of the magnetospheric electric field, create a sunward jet-stream in the thermosphere, where wind speeds of up to 1 km s^?1 can occur. This jet-stream is nearly always present in the middle and upper thermosphere (above 200 km altitude), even during periods of very low geomagnetic activity. However, the magnitude of the winds in the jet-stream, as well as its location and range in latitude, each depend on geomagnetic activity. On two occasions, jet-streams of extreme magnitude have been studied using simultaneous ground-based and satellite observations, probing both the latitudinal structure and the local time dependence. The observations have then been evaluated with the aid of simulations using a global, three-dimensional, time-dependent model of thermospheric dynamics including the effects of magnetospheric convection and particle precipitation. The extreme events, where sunward winds of above 800 ms^?1 are generated at relatively low geomagnetic latitudes (60–70°) require a greatly expanded auroral oval and large cross-polar cap electric field ( ~ 150 kV). These in turn are generated by a persistent strong Interplanetary Magnetic Field, with a large southward component. Global indices such as K_p are a relatively poor indicator of the magnitude and extent of the jet-stream winds.     

Tenerife – the big pyramid

There is nothing like a good controversy in geology, when vehemently held conflicting opinions set the adrenaline running. The debate over hot spots or mantle plumes is developing in this way; as such it is pertinent to look at the Canary Islands archipelago where hot spot ideas have been in place for some time.     

The X-ray emission in post-merger ellipticals

The evolution in X-ray properties of early-type galaxies is largely unconstrained. In particular, little is known about how, and if, remnants of mergers generate hot gas haloes. Here we examine the relationship between X-ray luminosity and galaxy age for a sample of early-type galaxies. Comparing normalized X-ray luminosity to three different age indicators, we find that L _X L _B increases with age, suggesting an increase in X-ray halo mass with time after the last major star formation episode of a galaxy. The long-term nature of this trend, which appears to continue across the full age range of our sample, poses a challenge for many models of hot halo formation. We conclude that models involving a declining rate of type Ia supernovae, and a transition from outflow to inflow of the gas originally lost by galactic stars, offer the most promising explanation for the observed evolution in X-ray luminosity.     

Control of As and Ni releases from a uranium mill tailings neutralization circuit: Solution chemistry, mineralogy and geochemical modeling of laboratory study results

Processing U ores in the JEB Mill of the McClean Lake Operation in northern Saskatchewan produces spent leaching solutions (raffinates) with pH  1.5, and As and Ni concentrations up to 6800 and 5200 mg L⁻¹, respectively. Bench-scale neutralization experiments (pH 2–8) were performed to help optimize the design of mill processes for reducing As and Ni concentrations in tailings and raffinates to 1 mg L⁻¹ prior to their disposal. Precipitate mineralogy determined by chemical analysis, XRD, SEM, EM, XM and EXAFS methods, included gypsum (the dominant precipitate), poorly crystalline scorodite (precipitated esp. from pH 2–4), annabergite, hydrobasaluminite, ferrihydrite, green rust II and theophrastite. The As was mostly in scorodite with smaller amounts in annabergite and trace As adsorbed and/or co-precipitated, probably by ferrihydrite. Geochemical modeling indicated that above pH 2, the ion activity product (IAP) of scorodite lies between the solubility products of amorphous and crystalline phases (log K_sp = −23.0 and −25.83, respectively). The IAP decreases with increasing pH, suggesting that the crystallinity of the scorodite increases with pH. Forward geochemical models support the assumption that during neutralization, particles of added base produce sharp local pH gradients and disequilibrium with bulk solutions, facilitating annabergite and theophrastite precipitation.     

Experimental constraints on hydrogen diffusion in garnet

The incorporation mechanisms and diffusional loss of hydrogen in garnet have been experimentally investigated. A suite of gem-quality hydrous spessartine- and grossular-rich garnets were analysed by Fourier transform infrared spectroscopy (FTIR) and by ion microprobe (SHRIMP-SI) to determine the calibration coefficients for quantification of FTIR data. The excellent agreement between measured absorption and OH/O indicates that the same molar extinction coefficient can be used for spessartine and grossular. The coefficient of 14400 l mol^??1 cm^??2 proposed by Maldener et al. (Phys Chem Miner 30:337–344, 2003) seems the most appropriate for both minerals. A grossular with 6.4% andradite and 1.6% almandine containing 834 ppm H₂O, and an almost pure spessartine with 282 ppm H₂O, were selected for diffusion experiments. 1.5-mm cubes of garnets were heated between 12 h and 10 days at 1 atm under various temperature (750–1050 °C) and oxygen fugacity (\({f_{{{\text{O}}_2}}}\)) conditions, (ΔQFM +?15.2 to ??3.0). Diffusion profiles were acquired from sections through the cubes using FTIR, with a deconvolution algorithm developed to assess peak-specific behaviour. Different families of peaks have been identified based on their diffusive behaviour, representing hydrogen incorporated in different H-bearing defects. A dominant, fast, strongly \({f_{{{\text{O}}_2}}}\)-dependent oxidation-related diffusion mechanism is proposed \(\left( {\{ {{\text{M}}^{2+}}+{{\text{H}}^+}\} +\frac{1}{4}{{\text{O}}_2}={{\text{M}}^{3+}}+\frac{1}{2}{{\text{H}}_2}{\text{O}}} \right)\) (M=Fe, Mn) with a relatively low activation energy (158?±?19 kJ mol^??1). This diffusion mechanism is likely restricted by availability of ferrous iron in grossular. At low oxygen fugacity, this diffusion mechanism is shut off and the diffusivity decreased by more than three orders of magnitude. A second, slower hydrogen diffusion mechanism has been observed in minor bands, where charge balance might be maintained by diffusion of cation vacancies, with much higher activation energy (≈?200–270 kJ mol^??1). Spessartine shows clear differences in peak retentivity suggesting that up to four different H sites might exist. This opens exciting opportunities to use hydrogen diffusion in garnet as speedometer. However, it is essential to constrain the main diffusion mechanisms and the oxygen fugacity in the rocks investigated to obtain timescales for metamorphic or igneous processes.     

Chemical speciation and fate of tripolyphosphate after application to a calcareous soil

Adsorption and precipitation reactions often dictate the availability of phosphorus in soil environments. Tripolyphosphate (TPP) is considered a form of slow release P fertilizer in P limited soils, however, investigations of the chemical fate of TPP in soils are limited. It has been proposed that TPP rapidly hydrolyzes in the soil solution before adsorbing or precipitating with soil surfaces, but in model systems, TPP also adsorbs rapidly onto mineral surfaces. To study the adsorption behavior of TPP in calcareous soils, a short-term (48 h) TPP spike was performed under laboratory conditions. To determine the fate of TPP under field conditions, two different liquid TPP amendments were applied to a P limited subsurface field site via an in-ground injection system. Phosphorus speciation was assessed using X-ray absorption spectroscopy, total and labile extractable P, and X-ray diffraction. Adsorption of TPP to soil mineral surfaces was rapid (< 48 h) and persisted without fully hydrolyzing to ortho-P. Linear combination fitting of XAS data indicated that the distribution of adsorbed P was highest (~ 30–40%) throughout the site after the first TPP amendment application (high water volume and low TPP concentrations). In contrast, lower water volumes with more concentrated TPP resulted in lower relative fractions of adsorbed P (15–25%), but a significant increase in total P concentrations (~ 3000 mg P kg soil) and adsorbed P (60%) directly adjacent to the injection system. This demonstrates that TPP application increases the adsorbed P fraction of calcareous soils through rapid adsorption reactions with soil mineral surfaces.     

The Impact Of Extreme Summer Melt on Net Accumulation of an Avalanche Fed Glacier,as Determined by Ground‐Penetrating Radar

Glacier mass balance is more sensitive to warming than cooling, but feedbacks related to the exposure of previously buried firn and ice in very warm years is not generally considered in sensitivity studies. A ground‐penetrating radar survey in the accumulation area of Rolleston Glacier, New Zealand shows that five years of previous net accumulation was removed by melt from parts of the glacier above the long‐term equilibrium line altitude during a single negative mass balance year. Rolleston Glacier receives a large amount of accumulation from snow avalanches, which may temporarily buffer it from climate warming by providing additional mass that has accumulated at higher elevations, effectively increasing the elevation range of the glacier. However, glaciers reliant on avalanche input may have high sensitivity to climatic variations because the extra mass is concentrated on a small part of the glacier, and small variations in avalanche input could have a large impact on overall glacier accumulation. Further research is needed to better estimate the amount and spatial distribution of accumulation by avalanche in order to quantify the climate sensitivity of small avalanche‐fed glaciers.     

Detrital zircon U–Pb reconnaissance of the Franciscan subduction complex in northwestern California

In northwestern California, the Franciscan subduction complex has been subdivided into seven major tectonostratigraphic units. We report U-Pb ages of ≈2400 detrital zircon grains from 26 sandstone samples from 5 of these units. Here, we tabulate each unit’s interpreted predominant sediment source areas and depositional age range, ordered from the oldest to the youngest unit. (1) Yolla Bolly terrane: nearby Sierra Nevada batholith (SNB); ca. 118 to 98 Ma. Rare fossils had indicated that this unit was mostly 151–137 Ma, but it is mostly much younger. (2) Central Belt: SNB; ca. 103 to 53 Ma (but poorly constrained), again mostly younger than previously thought. (3) Yager terrane: distant Idaho batholith (IB); ca. 52 to 50 Ma. Much of the Yager’s detritus was shed during major core complex extension and erosion in Idaho that started 53 Ma. An Eocene Princeton River–Princeton submarine canyon system transported this detritus to the Great Valley forearc basin and thence to the Franciscan trench. (4) Coastal terrane: mostly IB, ±SNB, ±nearby Cascade arc, ±Nevada Cenozoic ignimbrite belt; 52 to <32 Ma. (5) King Range terrane: dominated by IB and SNB zircons; parts 16–14 Ma based on microfossils. Overall, some Franciscan units are younger than previously thought, making them more compatible with models for the growth of subduction complexes by progressive accretion. From ca. 118 to 70 Ma, Franciscan sediments were sourced mainly from the nearby Sierra Nevada region and were isolated from southwestern US and Mexican sources. From 53 to 49 Ma, the Franciscan was sourced from both Idaho and the Sierra Nevada. By 37–32 Ma, input from Idaho had ceased. The influx from Idaho probably reflects major tectonism in Idaho, Oregon, and Washington, plus development of a through-going Princeton River to California, rather than radical changes in the subduction system at the Franciscan trench itself.