A secondary resonance in Mercury’s rotation

The resonant rotation of Mercury can be modelised by a kernel model on which we can add perturbations. Our kernel model is a two-degree of freedom one written in Hamiltonian formalism. For this kernel, we consider that Mercury is solid and rotates on a Keplerian orbit. By introducing the perturbations due to the other planets of the Solar System, it appears that, in a particular case, our slow degree of freedom may enter into a 1:1 resonance with the Great Inequality of Jupiter and Saturn. Actually, as the moments of inertia of Mercury are still poorly known, this phenomenon cannot be excluded.     

Lithostratigraphic and structural controls of ‘tsavorite’ deposits at Lemshuku,Merelani area,Tanzania

The first study of the Lemshuku ‘tsavorite’ mining district is presented. From bottom to top, the lithostratigraphic column corresponds to a metasedimentary sequence composed of quartzite, fine-grained graphitic gneiss, kyanite-graphite gneiss, biotite-almandine gneiss, metasomatized graphitic gneiss and dolomitic marble. ‘Tsavorite’ occurs in quartz veins and rarely as nodular concretions. Two factors control mineralization: (1) lithostratigraphy, with ‘tsavorite’ in association with pyrite and graphite confined to quartz veins within the metasomatized graphitic gneiss; and (2) structure, with the mineralized veins characteristically controlled by tight isoclinal folds associated with shearing.     

A TEM study of four particles extracted from the Stardust track 80

Abstract— Four particles extracted from track 80 at different penetration depths have been studied by analytical transmission electron microscopy (ATEM). Regardless of their positions within the track, the samples present a comparable microstructure made of a silica rich glassy matrix embedding a large number of small Fe‐Ni‐S inclusions and vesicles. This microstructure is typical of strongly thermally modified particles that were heated and melted during the hypervelocity impact into the aerogel. X‐ray intensity maps show that the particles were made of Mg‐rich silicates (typically 200 nm in diameter) cemented by a fine‐grained matrix enriched in iron sulfide. Bulk compositions of the four particles suggest that the captured dust particle was an aggregate of grains with various iron sulfide fraction and that no extending chemical mixing in the bulb occurred during the deceleration. The bulk S/Fe ratios of the four samples are close to CI and far from the chondritic meteorites from the asteroidal belt, suggesting that the studied particles are compatible with chondritic‐porous interplanetary dust particles or with material coming from a large heliocentric distance for escaping the S depletion.     

K–Ar dating and δO–δD tracing of illitization within and outside the Shea Creek uranium prospect,Athabasca Basin,Canada

Isotope analyses (K–Ar, δ¹⁸O and δD) were performed on illite from both the sandstone cover and the underlying basement, close to and distant from Shea Creek, an unconformity-type U deposit (Athabasca Basin, Canada); the illite had previously been characterized crystallographically. In the barren areas away from deposit, illite is mainly of the cis-vacant 1M polytype occurring as relatively coarse-grained lath-shaped particles, while it occurs as fine-grained particles of the trans-vacant 1M type next to and in the U mineralized strata. The tectonic-induced hydrothermal system that favored illite crystallization was multi-episodic 1453 ± 2, 1330 ± 20 and probably about 1235 Ma ago. These illite-forming episodes appear to have occurred contemporaneously to those favoring the concentration of the associated U oxides, which were dated independently by the U–Pb method in the Shea Creek deposits and elsewhere in the Athabasca Basin.     

Micro-scale flood risk analysis based on detailed 2D hydraulic modelling and high resolution geographic data

The paper presents a consistent micro-scale flood risk analysis procedure, relying on detailed 2D inundation modelling as well as on high resolution topographic and land use database. The flow model is based on the shallow-water equations, solved by means of a finite volume scheme on multi-block structured grids. Using highly accurate laser altimetry, the simulations are performed with a typical grid spacing of 2 m, which is fine enough to represent the flow at the scale of individual buildings. Consequently, the outcomes of hydraulic modelling constitute suitable inputs for the subsequent exposure analysis, performed at a micro-scale using detailed land use maps and geographic database. Eventually, the procedure incorporates social flood impact analysis and evaluation of direct economic damage to residential buildings. Besides detailing the characteristics and performance of the hydraulic model, the paper describes the flow of data within the overall flood risk analysis procedure and demonstrates its applicability by means of a case study, for which two different flood protection measures were evaluated.     

Long term high frequency sediment observatory in an alpine catchment: The Arc-Isère rivers,France

We present a dataset on to the Arc-Isère long-term environmental research observatory, which is part of the Rhône Basin Long Term Environmental Research Observatory. This alpine catchment located in the French Alps is characterized by high Suspended Particulate Matter (SPM) in anthropogenized valleys. Suspended Sediment Concentrations (SSC) naturally observed in the river are very high, ranging from a few tens of milligrams per litre at low flow to tens of grams per litre during major natural hydrological events (floods, debris flows) or river dam hydraulic flushes. One research objective related to this site is to better understanding the SSC dynamics along the river using a system of nested catchments (Arvan, Arc, and Isère) in order to assess both temporal and spatial dynamics. The data allow the quantification of fine sediment yields and also the evaluation of possible morphological changes due to fine sediment deposition or resuspension. Additionally, the observatory database support studies on contaminants (either dissolved or particulate contaminants). Our monitoring includes six stations with high frequency (2–30 min) streamflow, SSC measurement using turbidity sensors, and associated automatic sampling. Discharge is measured via water level measurements and a rating curve. The oldest station (Grenoble-campus) started recording discharge and concentration data from April 2006 while others stations were built between 2009 and 2011. Data are available in an online data website called ‘Base de Données des Observatoires en Hydrologie’ (Hydrological observatory database, https://bdoh.irstea.fr/ARC-ISERE/ ) with a DOI reference for the dataset. The hydrological and sediment transport time series are stored, managed and made available to a wide community with unfettered access in order to be used at their full extent. This database is used as a data exchange tool for both scientists and operational end-users and there is an associated online tool to compute integrated fluxes.     

What shapes mesoscale wind anomalies in coastal upwelling zones?

Observational studies have shown that mesoscale variations in sea surface temperature may induce mesoscale variations in wind. In eastern subtropical upwelling regions such as the California coast, this mechanism could be of great importance for the mean state and variability of the climate system. In coastal regions orography also creates mesoscale variations in wind, and the orographic effect may extend more than 100?km offshore. The respective roles of SST/wind links and coastal orography in shaping mesoscale wind variations in nearshore regions is not clear. We address this question in the context of the California Upwelling System, using a high-resolution regional numerical modeling system coupling the WRF atmospheric model to the ROMS oceanic model, as well as additional uncoupled experiments to quantify and separate the effects of SST/wind links and coastal orography on mesoscale wind variations. After taking into account potential biases in the representation of the strength of SST/wind links by the model, our results suggest that the magnitude of mesoscale wind variations arising from the orographic effects is roughly twice that of wind variations associated with mesoscale SST anomalies. This indicates that even in this region where coastal orography is complex and leaves a strong imprint on coastal winds, the role of SST/winds links in shaping coastal circulation and climate cannot be neglected.     

Combining suspended sediment monitoring and fingerprinting to determine the spatial origin of fine sediment in a mountainous river catchment

An excess of fine sediment (grain size <2 mm) supply to rivers leads to reservoir siltation, water contamination and operational problems for hydroelectric power plants in many catchments of the world, such as in the French Alps. These problems are exacerbated in mountainous environments characterized by large sediment exports during very short periods. This study combined river flow records, sediment geochemistry and associated radionuclide concentrations as input properties to a Monte Carlo mixing model to quantify the contribution of different geologic sources to river sediment. Overall, between 2007 and 2009, erosion rates reached 249 ± 75 t km^?2 yr^?1 at the outlet of the Bléone catchment, but this mean value masked important spatial variations of erosion intensity within the catchment (85–5000 t km^?2 yr^?1). Quantifying the contribution of different potential sources to river sediment required the application of sediment fingerprinting using a Monte Carlo mixing model. This model allowed the specific contributions of different geological sub‐types (i.e. black marls, marly limestones, conglomerates and Quaternary deposits) to be determined. Even though they generate locally very high erosion rates, black marls supplied only a minor fraction (5–20%) of the fine sediment collected on the riverbed in the vicinity of the 907 km² catchment outlet. The bulk of sediment was provided by Quaternary deposits (21–66%), conglomerates (3–44%) and limestones (9–27%). Even though bioengineering works conducted currently to stabilize gullies in black marl terrains are undoubtedly useful to limit sediment supply to the Bléone river, erosion generated by other substrate sources dominated between 2007 and 2009 in this catchment. Copyright © 2011 John Wiley & Sons, Ltd.     

<Superscript>18</Superscript>O/<Superscript>16</Superscript>O and V/Cr ratios in gem tsavorites from the Neoproterozoic Mozambique metamorphic belt: a clue towards their origins?

The combination of oxygen isotope composition with V–Cr–Mn trace element concentrations of V-bearing garnets (tsavorites) originating from the main deposits of the Neoproterozoic Mozambique Metamorphic Belt is reported for the first time. The database enables the identification of the geological and geographical sources of the main productive areas from northern and southern Tanzania, Kenya, and Madagascar. Three consistent sets of δ¹⁸O values between 9.5‰ and 11.0‰, 11.6‰ and 14.5‰, and 15.5‰ and 21.1‰ have been recognized for primary deposits hosted in graphitic gneisses related to the Neoproterozic metasedimentary series. The δ¹⁸O value of tsavorite is a good tracer of the environment of its formation; the δ¹⁸O of the fluid in equilibrium with tsavorite was buffered by the host rock during metamorphism and fluid-rock interaction. This study is a first step in characterizing the geochemistry of gem tsavorite from most of the deposits and occurrences worldwide.     

Characterization of ocean surface current properties from single site HF/VHF radar

Surface current mapping from HF/VHF coastal radars traditionally requires at least two distant sites. Vector velocities are estimated by combining the radial velocity components measured by the radars. In many circumstances (e.g., failures, interferences, logistics constraints), such a combination is not possible by lack of data from one station. Two methods are evaluated to get information on surface circulation from a single site radar: the Vectorial Reconstruction Method (VRM) for current vector mapping and the Vortex Identification Method (VIM) for detecting eddy-like structures. The VRM assumes a non-divergent horizontal surface current, and the VIM analyzes radial velocities and their radial and orthoradial gradients. These two methods are tested on modeled and measured data sets in the Northwestern Mediterranean Sea where both high-resolution ocean circulation model and radar campaigns are available. The VRM performance is strongly limited by the divergence-free hypothesis which was not satisfied in our real data. The VIM succeeded in detection of vortex in the Gulf of Lions and from an operating single site radar located on the Provence coasts in summer.