Numerical modelling of circulation and dispersion processes in Boulogne-sur-Mer harbour (Eastern English Channel): sensitivity to physical forcing and harbour design

The MARS-3D model in conjunction with the particle tracking module Ichthyop is used to study circulation and tracer dynamics under a variety of forcing conditions in the eastern English Channel, and in the Boulogne-sur-Mer harbour (referred to hereafter as BLH). Results of hydrodynamic modelling are validated against the tidal gauge data, VHF radar surface velocities and ADCP measurements. Lagrangian tracking experiments are performed with passive particles to study tracer dispersal along the northern French coast, with special emphasis on the BLH. Simulations revealed an anticyclonic eddy generated in the harbour at rising tide. Tracers, released during flood tide at the Liane river mouth, move northward with powerful clockwise rotating current. After the high water, the current direction changes to westward, and tracers leave the harbour through the open boundary. During ebb tide, currents convergence along the western open boundary but no eddy is formed, surface currents inside the harbour are much weaker and the tracer excursion length is small. After the current reversal at low water, particles are advected shoreward resulting in a significant increase of the residence time of tracers released during ebb tide. The effect of wind on particle dispersion was found to be particularly strong. Under strong SW wind, the residence time of particles released during flood tide increases from 1.5 to 6 days. For release during ebb tide, SW wind weakens the southward tidally induced drift and thus the residence time decreases. Similar effects are observed when the freshwater inflow to the harbour is increased from 2 to 10 m³/s during the ebb tide flow. For flood tide conditions, the effect of freshwater inflow is less significant. We also demonstrate an example of innovative coastal management targeted at the reduction of the residence time of the pathogenic material accidentally released in the harbour.

     

Formation of the first oxidized iron in the solar system

For fayalite formation times of several thousand years, and systems enriched in water by a factor of ten relative to solar composition, 1 μm radius olivine grains could reach 2 mole% fayalite and 0.1 μm grains 5 mole% by nebular condensation, well short of the values appropriate for precursors of most chondrules and the values found in the matrices of unequilibrated ordinary chondrites. Even 10 μm olivine crystals could reach 30 mole% fayalite above 1100 K in solar gas if condensation of metallic nickel‐iron were delayed sufficiently by supersaturation. Consideration of the surface tensions of several phases with equilibrium condensation temperatures above that of metallic iron shows that, even if they were supersaturated, they would still nucleate homogeneously above the equilibrium condensation temperature of metallic iron. This phenomenon would have provided nuclei for heterogeneous nucleation of metallic nickel‐iron, thus preventing the latter from supersaturating significantly and preventing olivine from becoming fayalitic. Unless a way is found to make nebular regions far more oxidizing than in existing models, it is unlikely that chondrule precursors or the matrix olivine grains of unequilibrated ordinary chondrites obtained their fayalite contents by condensation processes. Perhaps stabilization of FeO occurred after condensation of water ice and accretion of icy planetesimals, during heating of the planetesimals and/or in hot, dense, water‐rich vapor plumes generated by impacts on them. This would imply that FeO is a relatively young feature of nebular materials.     

Second generation of a rotational electrochemical seismometer using magnetohydrodynamic technology

Rotational seismometers have many applications. Some require a low self noise with a lower clip specification. Others require many different bandpass specifications, from very low to higher frequencies. The principles of the eentec second-generation R-2 electrochemical triaxial rotational seismometer can achieve many features for various applications. Combining the use of the sophisticated magnetohydrodynamic (MHD) technology increases the current and future features. Principles of the MHD technology used and the many advantages it has in a rotational seismometers are described.     

A method of comparison of exact and asymptotic wave field computations

Summary. A method of comparison of exact numerical computations with an asymptotic ray series expansion consisting of the two first terms is proposed. The method makes it unnecessary to derive complicated explicit expressions for the second leading term of the ray series.
As a practical example we consider the anomalous PS arrival generated in the case of a near-vertical incidence of a spherical P wave on a solid/solid boundary. The areas in which the PS wave may be described by two leading terms of the ray series expansion are marked and deviations from the ray theory are analysed.     

40Ar/39Ar age of the onset of high-Ti phase of the Emeishan volcanism strengthens the link with the end-Guadalupian mass extinction

Precise time constraints of the main extrusive phase of the Emeishan large igneous province (ELIP) remain unresolved because basalts commonly do not contain suitable minerals for U–Pb dating, whereas previous ⁴⁰Ar/³⁹Ar studies on basalts yielded tectonothermal overprint ages. The timing for the ELIP was deduced from indirect dating of minor intrusions of ultramafic/mafic and felsic compositions by geochronological methods and geological correlations. The extrusive part of the ELIP consists of an older low-Ti and younger high-Ti basalt phases. We have found fresh samples of plagioclase-phyric rocks at the lower Qiaojia extrusive section (the Yunnan province of China), which belong to the ELIP unit of the high-Ti basalt series. ⁴⁰Ar/³⁹Ar dating on plagioclase from two samples conducted at two different laboratories using different age standards yielded statistically indistinguishable results with the weighted mean age of 260.1 ± 1.2 Ma for five individual measurements. This provides the direct constraints on the onset of the ELIP high-Ti basalt extrusive phase. The obtained age is within the error or slightly older than the age of the Guadalupian–Lopingian boundary and felsic ignimbrite capping the ELIP lava succession (both dated at 259.1 ± 0.5 Ma). Our new data are strengthening the short duration of the, at least, high-Ti phase of the ELIP volcanism and its temporal link with the end-Guadalupian mass extinction. Estimation of the total duration of the ELIP volcanism awaits finding of suitable for dating low-Ti basalts.     

Effects of dust enrichment on oxygen fugacity of cosmic gases

The degree to which dust enrichment enhances the oxygen fugacity (fO₂) of a system otherwise solar in composition depends on the dust composition. Equilibrium calculations were performed at 10^?3 bar in systems enriched by a factor of 10⁴ in two fundamentally different types of dust to investigate the iron oxidation state in both cases. One type of dust, called SC for solar condensate, stopped equilibrating with solar gas at too high a temperature for FeO or condensed water to be stabilized in any form, and thus has the composition expected of a nebular condensate. The other has CI chondrite composition, appropriate for a parent body that accreted from SC dust and low‐temperature ice. Upon total vaporization at 2300 K, both systems have high fO₂, >IW. In the SC dust‐enriched system, FeO of the bulk silicate reaches ~10 wt% at 1970 K but decreases to <1 wt% below 1500 K. The FeO undergoes reduction because consumption of gaseous oxygen by silicate recondensation causes a precipitous drop in fO₂. Thus, enrichment in dust having the composition of likely nebular condensates cannot yield a sufficiently oxidizing environment to account for the FeO contents of chondrules. The fO₂ of the system enriched in water‐rich, CI dust, however, remains high throughout condensation, as gaseous water remains uncondensed until very low temperatures. This allows silicate condensates to achieve and maintain FeO contents of 27–35 wt%. Water‐rich parent bodies are thus excellent candidate sources of chondrule precursors. Impacts on such bodies may have created the combination of high dust enrichment, total pressure, and fO₂ necessary for chondrule formation.     

Maser Action in Methanol Transitions

We report the detection with the ATCA of 6.7 GHz methanol emission towards OMC-1. The source has a size between 40 and 90, is located to the south-east of Ori-KL and may coincide in position with the 25 GHz masers. The source may be an example of an interesting case recently predicted in theory where the transitions of traditionally different methanol maser classes show maser activity simultaneously. In addition, results of recent search for methanol masers from the 25 and 104.3 GHz transitions are reported.     

Machine Learning Can Assign Geologic Basin to Produced Water Samples Using Major Ion Geochemistry

Natural Resources Research - Understanding the geochemistry of waters produced during petroleum extraction is essential to informing the best treatment and reuse options, which can potentially be...     

Phase equilibria modeling in igneous petrology: use of COMAGMAT model for simulating fractionation of ferro-basaltic magmas and the genesis of high-alumina basalt

A new version of COMAGMAT-3.5 model designed for computer simulations of equilibrium and fractional crystallization of basaltic magmas at low to high pressures is presented. The most important modifications of COMAGMAT include an ability to calculate more accurately the crystallization of magnetite and ilmenite, allowing the user to study numerically the effect of oxygen fugacity on basalt magma fractionation trends. Methodological principles of the use of COMAGMAT were discussed based on its thermodynamical and empirical basis, including specific details of the model calibration. Using COMAGMAT-3.5 a set of phase equilibria calculations (called Geochemical Thermometry) has been conducted for six cumulative rocks from the Marginal Border Series of the Skaergaard intrusion. As a result, initial magma temperature (1165±10°C) and trapped melt composition proposed to be parental magma to the Skaergaard intrusion were determined. Computer simulations of perfect fractionation of this composition as well as another proposed parent produced petrochemical trends opposite to those followed from natural observations. This is interpreted as evidence for an initial Skaergaard magma containing a large amount of olivine and plagioclase crystals (about 40–45%), so that the proposed and calculated parents are related through the melt trapped in the crystal–liquid mixture. This promotes the conclusion that the Skaergaard magma fractionation process was intermediate between equilibrium and fractional crystallization. In this case the classic Wager's trend should be considered an exception rather than a rule for the differentiation of ferro-basaltic magmas. A polybaric version of COMAGMAT has been applied for the genetic interpretation of a volcanic suite from the Klyuchevskoi volcano, Kamchatka, Russia. To identify petrological processes responsible for the observed suite ranging from high-magnesia to high-alumina basalts, we used the model to simulate the Klyuchevskoi suite assuming isobaric crystallization of a parental HMB magma at a variety of pressures and a separate set of simulations assuming fractionation during continuous magma ascent from a depth of 60 km. These results indicate that the Klyuchevskoi trend can be produced by 40% fractionation of Ol–Aug–Sp±Opx assemblages during ascent of the parental HMB magma over the pressure range 19–7 kbar with the rate of decompression being 0.33 kbar/% crystallized (at 1350–1110°C), with 2 wt.% of H₂O in the initial melt and 3 wt.% of H₂O in the resultant high-Al basalt.