Microscopy and rock magnetism of fine grain-size titanomagnetite from the Jacupiranga Alkaline Complex,Brazil: unearthing Ti-magnesioferrite nanoparticles

Very fine samples from the mineralized zones of the Jacupiranga complex at the Cajati mine were selected for crystallographic identification of Ti-magnesioferrite (TMf) nanostructures embedded in titanomagnetite (TM) using high-resolution transmission electron microscopy (TEM). A magnetic concentrate obtained of pyroxenite samples (sites 4 to 7) was reduced and divided into fractions of distinct range sizes: 26±2 μm, 19±1 μm, 13±1 μm, 9±1 μm, 6±1 μm and 6-0.1 μm. The mineralized samples of carbonatite and pyroxenite were characterized by X-ray diffraction, transmitted and reflected light microscope, and scanning electron microscope with multielemental analysis. The finest magnetic concentrate sample (MC₆) was analyzed under high-resolution transmitted electron microscopy (TEM) and high angle annular dark field and Raman spectroscopy. Magnetic properties were measured for the distinct granulometric fractions, showing drastic changes when grain sizes go beyond the frontier from micro to nanometer sizes. Frequency-dependent magnetic susceptibility percentage (÷_fd%) report higher values (10.2%) for the finer fractions (6±1 μm and 6-0.1 μm) attributed to dominant fractions of superparamagnetic particles. Nanometer and < 6 μm grain size TMf in TM particles require a magnetic field up to 249 mT to reach saturation during the isothermal remanent magnetization experiment. Coercivity and remanent magnetization of these samples increase when the particle size decreases, probably due to parallel coupling effects. Magnetic susceptibility versus temperature experiments were conducted two times on the same (< 35 nm) sample, showing that the repetition during the second heating is probably due to the formation of new TMf nanoparticles and growth of those already present during the first heating process.     

Génération stochastique d'averses et de leurs index d'érosivité pour la simulation de la dynamique érosive en Tunisie centrale

Résumé

Le modèle proposé est un générateur stochastique d'averses couplé à un modèle empirique de calcul de leurs érosivités, calé à une série pluviographique de 15 ans d'observations. Notre objectif est de développer une démarche probabiliste, qui permettrait d'étudier les conséquences érosives des pluies dans le temps, en cumulant l'érosivité consécutive des pluies simulées durant plusieurs années, supposée proportionnelle à la dégradation des sols, ou au transport solide en suspension sur la même période. Cette génération peut en effet se faire sur plusieurs années calendaires, et nous permettrait de ce fait d'éviter d'être limité par la taille des échantillons. L'ensemble pouvant être utilisé en mode opérationnel, pour reconstituer de très longus séries d'épisodes pluvieux dans l'objectif d'étudier le cumul de leur érosivité dans le temps. Cette démarche ne contredit pas les approches expérimentales, qui ont une réalité concrète de terrain, bien au contraire elle les conforte et permet d'avancer davantage dans la réflexion posée par la problématique de l'érosion hydrique.     

Dynamique et modélisation des crues dans le bassin du Mono à Nangbéto (Togo/Bénin)

Résumé

Les inondations des dernières années en Afrique de l’Ouest rendent nécessaire la prévision hydrologique pour réduire la vulnérabilité des populations. Nous avons étudié la dynamique des crues dans le bassin du Mono en amont du barrage de Nangbéto (Togo et Bénin) par des méthodes statistiques et déterministes. L’augmentation des précipitations au cours de la décennie 1990 et la mise en eau du barrage de Nangbéto en 1988 ont modifié le régime du Mono, dont les débits d’étiages ont augmenté. Les débits entrants et sortants du barrage sont équivalents, même lors des crues. Les maximums annuels des débits entrants peuvent être modélisés par une distribution des valeurs extrêmes (GEV) de type Fréchet, tandis que ceux des débits sortants, suivent une loi GEV de type Weibull (bornée). Le mécanisme dominant de génération des crues dans le bassin est la montée progressive des eaux associée à l’augmentation de la saturation des sols. L’analyse des débits de crue entre 1988 et 2010 n’a pas montré d’augmentation de la magnitude ou de la fréquence des crues. Le modèle GR4J reproduit bien les débits de crues en période calage, mais ces critères de performance se dégradent lorsque l’on s’en éloigne. Dans ces conditions, l’utilisation de ce modèle pour évaluer les risques futurs de crues serait hasardeuse et il est nécessaire d’envisager d’autres types d’approches.     

Development and utilization of a national web-based chronology of hydrological events/Développement et utilisation sur internet d’une chronologie nationale d’événements hydrologiques

Abstract

Abstract The Chronology of British Hydrological Events (CBHE) has been created as an on-line information resource (http://www.dundee.ac.uk/geography/cbhe/) in order to enhance access to and use of historical facts pertaining to British hydrological phenomena. Its scope covers floods, droughts and all other notable historical phenomena of hydrological interest. This paper sets out the technical means by which the CBHE has been created, explains the benefits to hydrologists in creating such a facility, and illustrates its utility with a number of examples. Benefits include hydrological risk assessments, historical studies of individual events and objectives in environmental education. The scope for establishing comparable national chronologies for other countries is identified, along with prospects for enhancing the utility of such systems with additional functionality such as links to on-line gazetteers and maps.     

Statistics of extremes and estimation of extreme rainfall: II. Empirical investigation of long rainfall records / Statistiques de valeurs extrêmes et estimation de précipitations extrêmes: II. Recherche empirique sur de longues séries de précipitations

Abstract

Abstract In the first part of this study, theoretical analyses showed that the Gumbel distribution is quite unlikely to apply to hydrological extremes and that the extreme value distribution of type II (EV2) is a more consistent choice. Based on these theoretical analyses, an extensive empirical investigation is performed using a collection of 169 of the longest available rainfall records worldwide, each having 100–154 years of data. This verifies the theoretical results. In addition, it shows that the shape parameter of the EV2 distribution is constant for all examined geographical zones (Europe and North America), with value κ = 0.15. This simplifies the fitting and the general mathematical handling of the distribution, which become as simple as those of the Gumbel distribution.     

The topographic record of The Netherlands 1800–1992 for sale

Abstract

At the end of the eighteenth century, a large-scale map of the Austrian Netherlands and the Prince-Bishopric of Liège was manufactured, covering more or less the current territory of Belgium. The work for this Carte de Cabinet was carried out by artillerists under the guidance of count Joseph de Ferraris, who was commissioned for the task by the Habsburg government. At the time that the map was designed, no modern legend was included. This paper tries to fill that gap by presenting a legend that was constructed more systematically than any of its predecessors. It is based on the structure of the legend of the Topographic Map of Belgium and the CORINE land cover map, making it an easy-to-use tool for modern researchers. The problems encountered during the development of the legend are described, and the link between the Carte de Cabinet and eighteenth-century French cartography as well as with cartographic manuals is also discussed.     

Quantitative morphometric analysis of lakes using GIS: rectangularity R,ellipticity E,orientation O,and the rectangularity vs. ellipticity index,REi

Quantitative measures of polygon shapes and orientation are important elements of geospatial analysis. These kinds of measures are particularly valuable in the case of lakes, where shape and orientation patterns can help identifying the geomorphological agents behind lake formation and evolution. However, the lack of built-in tools in commercial geographic information system (GIS) software packages designed for this kind of analysis has meant that many researchers often must rely on tools and workarounds that are not always accurate. Here, an easy-to-use method to measure rectangularity R, ellipticity E, and orientation O is developed. In addition, a new rectangularity vs. ellipticity index, REi, is defined. Following a step-by-step process, it is shown how these measures and index can be easily calculated using a combination of GIS built-in functions. The identification of shapes and estimation of orientations performed by this method is applied to the case study of the geometric and oriented lakes of the Llanos de Moxos, in the Bolivian Amazon, where shape and orientation have been the two most important elements studied to infer possible formation mechanisms. It is shown that, thanks to these new indexes, shape and orientation patterns are unveiled, which would have been hard to identify otherwise.     

In Situ Determination of Au and Cu in Natural Pyrite by Near‐Infrared Femtosecond Laser Ablation‐Inductively Coupled Plasma‐Quadrupole Mass Spectrometry: No Evidence for Matrix Effects

Gold and copper concentrations were determined in natural pyrite by near‐infrared femtosecond LA‐ICP‐QMS, using both sulfide reference materials (pyrrhotite Po‐726 and in‐house natural chalcopyrite Cpy‐RM) and NIST SRM 610 as external calibrators. Firstly, using NIST SRM 610 as the external calibrator, we calculated the Au concentration in Po‐726 and the Cu concentration in Cpy‐RM. The calculated concentration averages for Au and Cu were similar to the values published for Po‐726 and Cpy‐RM, respectively. Secondly, we calculated Au and Cu concentrations taking NIST SRM 610 as an unknown sample and using Po‐726 and Cpy‐RM as external calibrators. Again, the average values obtained closely reflected the preferred concentrations for NIST SRM 610. Finally, we calculated Au and Cu concentrations in natural pyrite using sulfide and silicate reference materials as external calibrators. In both cases, calculated concentrations were very similar, independent of the external calibrator used. The aforementioned data, plus the fact that we obtained very small differences in relative sensitivity values (percentage differences are between 5% and 17% for ⁵⁷Fe, ⁶³Cu and ¹⁹⁷Au) on analyses of silicate and sulfide RMs, indicate that there were no matrix effects related to the differences in material composition. Thus, it is possible to determine Au and Cu in natural sulfides using NIST silicate glasses as an external calibrator.     

A buoyant plume adjacent to a headland—Observations of the Elwha River plume

Small rivers commonly discharge into coastal settings with topographic complexities - such as headlands and islands - but these settings are underrepresented in river plume studies compared to more simplified, straight coasts. The Elwha River provides a unique opportunity to study the effects of coastal topography on a buoyant plume, because it discharges into the Strait of Juan de Fuca on the western side of its deltaic headland. Here we show that this headland induces flow separation and transient eddies in the tidally dominated currents (O(100 cm/s)), consistent with other headlands in oscillatory flow. These flow conditions are observed to strongly influence the buoyant river plume, as predicted by the “small-scale” or “narrow” dynamical classification using Garvine's (1995) system. Because of the transient eddies and the location of the river mouth on the headland, flow immediately offshore of the river mouth is directed eastward twice as frequently as it is westward. This results in a buoyant plume that is much more frequently “bent over” toward the east than the west. During bent over plume conditions, the plume was attached to the eastern shoreline while having a distinct, cuspate front along its westernmost boundary. The location of the front was found to be related to the magnitude and direction of local flow during the preceding O(1 h), and increases in alongshore flow resulted in deeper freshwater mixing, stronger baroclinic anomalies, and stronger hugging of the coast. During bent over plume conditions, we observed significant convergence of river plume water toward the frontal boundary within 1 km of the river mouth. These results show how coastal topography can strongly influence buoyant plume behavior, and they should assist with understanding of initial coastal sediment dispersal pathways from the Elwha River during a pending dam removal project.     

Local sea level change scenarios for the end of the 21st century and potential physical impacts in the lower Ria de Aveiro (Portugal)

Sea level change is an important consequence of climate change due to its impact on society and ecosystems. Analyses of tide-gauge data have indicated that the global sea level has risen during the 20th century and several studies predict that the mean sea level will continue to rise during the 21st century, intensifying coastal hazards worldwide. In Portugal, the Ria de Aveiro is expected to be one of the regions most affected by sea level change.The main aim of this study is to evaluate the potential impacts of the mean sea level change on the hydrodynamics and morphodynamics of the Ria de Aveiro. With this purpose, local mean sea level change was projected for the period 2091-2100 relative to 1980-1999, for different Special Report on Emission Scenarios (SRES) scenarios developed by the Intergovernmental Panel on Climate Change (IPCC). These projections revealed an increase in the mean sea level between 0.28 m under scenario B1 and 0.42 m under scenario A2.The results obtained for sea level rise scenario A2 projection were used to force the morphodynamic model MORSYS2D, previously implemented for the Ria de Aveiro. The modelling results were compared with model forecasts for the present sea level. The residual sediment transport and its balance at the lagoon inlet were computed and analysed for both situations. While the residual sediment transport is generally seaward, sediments tend to deposit inside the inlet due to the weak sediment transport at its mouth. The direction of the residual flux will not change with the sea level rise, but sediment fluxes will intensify, and accretion inside the inlet will increase.The rise in mean sea level will also affect the lagoon hydrodynamics. The tidal prism at the lagoon mouth will increase by about 28% in spring tide. In the lower lagoon only a slight increase of the tidal asymmetry is predicted.