A new high‐precision 40Ar/39Ar age for the Rochechouart impact structure: At least 5 Ma older than the Triassic–Jurassic boundary

The Rochechourt impact structure in south‐central France, with maximum diameter of 40–50 km, has previously been dated to within 1% uncertainty of the Triassic–Jurassic boundary, at which time ~30% of global genera became extinct. To evaluate the temporal relationship between the impact and the Triassic–Jurassic boundary at high precision, we have re‐examined the structure's age using multicollector ARGUS‐V ⁴⁰Ar/³⁹Ar mass spectrometry. Results from four aliquots of impact melt are highly reproducible, and yield an age of 206.92 ± 0.20/0.32 Ma (2σ, full analytical/external uncertainties). Thus, the Rochechouart impact structure predates the Triassic–Jurassic boundary by 5.6 ± 0.4 Ma and so is not temporally linked to the mass extinction. Rochechouart has formerly been proposed to be part of a multiple impact event, but when compared with new ages from the other purported “paired” structures, the results provide no evidence for synchronous impacts in the Late Triassic. The widespread Central Atlantic Magmatic Province flood basalts remain the most likely cause of the Triassic–Jurassic mass extinction.     

The defining characteristics of intermediate polars – the case of three-candidate systems

Intermediate polars (IPs) are a group of cataclysmic variables (CVs) which are thought to contain white dwarfs which have a magnetic field strength in the range ∼0.1–10 MG. A significant fraction of the X-ray sources detected in recent deep surveys has been postulated to consist of IPs. Until now two of the defining characteristics of IPs have been the presence of high (and complex) absorption in their X-ray spectra and the presence of a stable modulation in the X-ray light curve which is a signature of the spin period, or the beat period, of the accreting white dwarf. Three CVs, V426 Oph, EI UMa and LS Peg, have characteristics which are similar to IPs. However, there has been only tentative evidence for a coherent period in their X-ray light curve. We present the results of a search for coherent periods in XMM–Newton data of these sources using an autoregressive analysis which models the effects of red noise. We confirm the detection of a ∼760 s period in the soft X-ray light curve of EI UMa reported by Reimer et al. and agree that this represents the spin period. We also find evidence for peaks in the power spectrum of each source in the range 100–200 s which are just above the 3σ confidence level. We do not believe that they represent genuine coherent modulations. However, their X-ray spectra are very similar to those of known IPs. We believe that all three CVs are bona fide IPs. We speculate that V426 Oph and LS Peg do not show evidence for a spin period since they have closely aligned magnetic and spin axes. We discuss the implications that this has for the defining characteristics of IPs.     

Dry separation of respirable lunar dust: Providing samples for the lunar airborne dust toxicity advisory group

In order to study the toxicity of lunar dust, the respirable size fraction of lunar soil needed to be separated with an apparatus that possesses the following capabilities: no use of liquid; fully recoverable sample; and use of only small sample quantities (<1 gm). We report the design of a simple apparatus that meets these requirements and implements an inertial-impaction mechanism established in aerosol science. Lunar soil was agitated at a frequency of 100 Hz using a vibration table with a containment chamber under a constant air flow. The air flow carried the lofted lunar dust particles past four impactors (four T-junction connectors), upon which a fraction of large particles were captured during the impaction. The fine particles in the air flow were then collected by an end-of-the line membrane filter. Detailed examination of particles on the filter showed that the majority (∼80-90 wt%) are <3 μm (geometric diameter), suggesting a high level of effectiveness for the apparatus.     

A comparative analysis of the loss of life during two recent floods in France: the sea surge caused by the storm Xynthia and the flash flood in Var

This paper aims to analyse and compare the loss of life that occurred during two recent floods in France. The first flood was due to a sea surge triggered by the storm called Xynthia that hit the Atlantic coast on 28 February 2010 (41 flood-related deaths). The second was a flash flood that struck the Var Department in the French Mediterranean region on 15 June 2010 (26 fatalities). After detailing the assumptions and expected outcomes of the study of disaster-related fatalities, the paper focuses on the characteristics of the victims and the circumstances of their deaths. In the first case, 71% of the victims were people aged over 60 (mainly women) who were surprised while they were sleeping and who died in or near their homes. In the case of the flash flood, the profiles of the victims were diverse as the flooding occurred in the afternoon and many people were trapped in open. The paper also highlights the factors that explain mortality. Physical factors such as water depth were determined. The relationship between the water depth and the age of victims was found to be relevant. In the case of the storm surge Xynthia, the correlation between age and water depth is positive. For the flash flood, the correlation between age and water depth was negative as male adults died in open. In the first case, the vulnerability of people was closely linked to human features such as type of housing and age that people are not directly responsible for. During flash floods, dangerous behaviour by people highlighted the role of risk-taking in loss of life. We also examined the particular case of the deaths of the children. The paper concludes by discussing the factors of vulnerability on frail population such as elderly people or marginalized. The lack of risk awareness and crisis preparedness were clearly a major factor of vulnerability.     

Choosing an arbitrary calibration period for hydrologic models: How much does it influence water balance simulations?

The selection of calibration and validation time periods in hydrologic modelling is often done arbitrarily. Nonstationarity can lead to an optimal parameter set for one period which may not accurately simulate another. However, there is still much to be learned about the responses of hydrologic models to nonstationary conditions. We investigated how the selection of calibration and validation periods can influence water balance simulations. We calibrated Soil and Water Assessment Tool hydrologic models with observed streamflow for three United States watersheds (St. Joseph River of Indiana/Michigan, Escambia River of Florida/Alabama, and Cottonwood Creek of California), using time period splits for calibration/validation. We found that the choice of calibration period (with different patterns of observed streamflow, precipitation, and air temperature) influenced the parameter sets, leading to dissimilar simulations of water balance components. In the Cottonwood Creek watershed, simulations of 50-year mean January streamflow varied by 32%, because of lower winter precipitation and air temperature in earlier calibration periods on calibrated parameters, which impaired the ability for models calibrated to earlier periods to simulate later periods. Peaks of actual evapotranspiration for this watershed also shifted from April to May due to different parameter values depending on the calibration period's winter air temperatures. In the St. Joseph and Escambia River watersheds, adjustments of the runoff curve number parameter could vary by 10.7% and 20.8%, respectively, while 50-year mean monthly surface runoff simulations could vary by 23%–37% and 169%–209%, depending on the observed streamflow and precipitation of the chosen calibration period. It is imperative that calibration and validation time periods are chosen selectively instead of arbitrarily, for instance using change point detection methods, and that the calibration periods are appropriate for the goals of the study, considering possible broad effects of nonstationary time series on water balance simulations. It is also crucial that the hydrologic modelling community improves existing calibration and validation practices to better include nonstationary processes.     

Phase-equilibrium geobarometers for silicic rocks based on rhyolite-MELTS. Part 2: application to Taupo Volcanic Zone rhyolites

Constraining the pressure of crystallisation of large silicic magma bodies gives important insight into the depth and vertical extent of magmatic plumbing systems; however, it is notably difficult to constrain pressure at the level of detail necessary to understand shallow magmatic systems. In this study, we use the recently developed rhyolite-MELTS geobarometer to constrain the crystallisation pressures of rhyolites from the Taupo Volcanic Zone (TVZ). As sanidine is absent from the studied deposits, we calculate the pressures at which quartz and feldspar are found to be in equilibrium with melt now preserved as glass (the quartz +1 feldspar constraint of Gualda and Ghiorso, Contrib Mineral Petrol 168:1033. doi: 10.1007/s00410-014-1033-3. 2014). We use glass compositions (matrix glass and melt inclusions) from seven eruptive deposits dated between ~320 and 0.7 ka from four distinct calderas in the central TVZ, and we discuss advantages and limitations of the rhyolite-MELTS geobarometer in comparison with other geobarometers applied to the same eruptive deposits. Overall, there is good agreement with other pressure estimates from the literature (amphibole geobarometry and H₂O–CO₂ solubility models). One of the main advantages of this new geobarometer is that it can be applied to both matrix glass and melt inclusions—regardless of volatile saturation. The examples presented also emphasise the utility of this method to filter out spurious glass compositions. Pressure estimates obtained with the new rhyolite-MELTS geobarometer range between ~250 to ~50 MPa, with a large majority at ~100 MPa. These results confirm that the TVZ hosts some of the shallowest rhyolitic magma bodies on the planet, resulting from the extensional tectonic regime and thinning of the crust. Distinct populations with different equilibration pressures are also recognised, which is consistent with the idea that multiple batches of eruptible magma can be present in the crust at the same time and can be tapped simultaneously by large eruptive events.     

Mechanical Heating in Disk-Driven Winds – Thermal Structure & Observational Predictions

Following the work of Garcia et al. (2001a) (GFCB), we compute the thermal properties and ionization structure of magnetically-driven disk winds. The original model's dominant heating function along the jet, ambipolar diffusion, is augmented by a mechanical heating term supposed to arise from weak shocks, as used by (Shang et al., 2002). We add this mechanical heating function to a cold disk wind model and calculate its effect on the jet as a whole. The temperature and ionization of the flow are calculated in the case of cold jet solutions consistent with the underlying accretion disk (Ferreira, 1997). These solutions are compared to those of (GFCB) in order to quantitatively determine the effect of the mechanical heating on the flow. We then use the computed thermal and ionization structures to calculate jet synthetic observations. We find that the addition of mechanical heating leads to higher electron fractions, in turn leading to increased line fluxes and line ratios approaching observed values.