Modified Technique for Calculating the Parameters of Climatic Variability of Upwelling by Thermal Index

Izvestiya, Atmospheric and Oceanic Physics - A modified technique for calculating the amplitude-phase characteristics of the seasonal cycle and long-term trends in the intensity of upwelling is...     

Wind-driven upwelling and surface chlorophyll blooms in Greater Cook Strait

We present the results of a combined observational and numerical study to investigate cool plumes of nutrient-rich upwelled water that emanate near the Kahurangi Shoals and extend into Greater Cook Strait. Surface temperature and chlorophyll are mapped using satellite observations to produce surface climatologies, to validate a numerical simulation and to show the utility of using spatial temperature differences as a measure of upwelling. We find upwelling near the Kahurangi Shoals is strongly wind-driven in the weather band. Upwelling occurs at all times of the year, but its surface signature is only visible in summer months. The upwelled nutrient-rich water supports increased primary production compared to surrounding waters, particularly in summer when the water column is more stratified and surrounding surface waters are presumably nutrient depleted.     

Modellversuche zur Hangtektonik

Zusammenfassung Das Verformungsverhalten von Felshängen wird einmal durch die geologische Entwicklungsgeschichte, zum anderen durch die zum Zeitpunkt der Beobachtung herrschenden Randbedingungen (Höhe, Neigung des Hanges, eingeprägte Kräfte) und Gebirgseigenschaften bestimmt. Diese Gebirgseigenschaften sind einerseits von den Gesteinseigenschaften (Verformbarkeit und Festigkeit) und andererseits von der Klüftung abhängig.Mit Hilfe zweidimensionaler großmaßstäblicher Modelle, die in einer ersten Serie aus starren Kluftkörpern (Strukturmodelle) und in einer zweiten Serie aus äquivalentem Modellmaterial aufgebaut waren, wird der Versuch unternommen, die innere Kinematik eines ganzen Hangquerschnittes zu studieren. Während im ersten Fall der Einfluß des Trennflächengefüges allein untersucht werden kann, überlagern sich im zweiten Fall Material- und Gefügeparameter.Anhand der Strukturmodelle wird eine Einteilung in verschiedene typische Verformungsverhalten von Hängen in Abhängigkeit von der Kluftstellung und vom Kluftreibungswinkel vorgenommen.Der besonders interessante Fall eines Kluftkörperverbandes mit bergeinwärtsfallender Bankung — hier überlagern sich Rotations- und Translationsbewegungen — wird in seinem gesamten Verformungsablauf beschrieben und nach charakteristischen Verformungsstadien unterteilt. Dabei wird die Entwicklung der Verformungen vom Hakenwerfen der Böschungsfront bis zu einem tiefgreifenden Talzuschub mit der Ausbildung ausgeprägter Schwächezonen erfaßt.Die an den Versuchen durchgeführten Beobachtungen gestatten eine bessere Bewertung des Trennflächeneinflusses auf das Verformungsverhalten von Felsmassen mit regelmäßigem Gefügemuster (H-Typ) und geben Hinweise zur besseren Abschätzung des Verformungsablaufes im Inneren eines Hanges sowie der zu erwartenden Form des Böschungsbruchkörpers.

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The deformation behaviour of rock slopes is influenced by the geological history, by the boundary conditions (height, inclination of the slope, additional forces) acting at the time of observation and the material properties of the rock mass. The properties depend on the rock parameters (deformability and strength) and on the joint patterns.With two-dimensional large scale models which consisted of rigid blocks in the first series of tests (structural models) and of equivalent model material in a second one, it was tried to study the kinematics of a whole slope section.In the first of those cases joint fabric is the only parameter to be investigated while in the second, series of test material and structural parameters have to be considered simultaneously. The structural models allow a classification into different types of deformation behaviour of the slopes. Criteria of classifications are the inclination of the strata and the friction angle.The especially interesting case of a jointed rock system with strata dipping into the mountain (in this case rotational and translational displacements are superposed) is described in its whole deformation history which is divided into characteristic stages of deformation. The development of displacements is studied from a first Hakenwerfen at the front of the slope to a deep Talzuschub with the formation of zones of weakness (latent sliding surfaces).Conclusions drawn from these tests allow a better assessment of the influence of joint sets on the deformation behaviour of a rock mass, the development of displacements in the interior of a slope and the shape of sliding surfaces.

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Résumé Le processus de déformation des versants rocheux est déterminé d'abord par l'histoire géologique, ensuite par les conditions immédiates du milieu régnant au moment de l'observation (hauteur, inclinaison de la pente, forces emmagasinées) et par les propriétés à l'échelle de l'ensemble rocheux. Ces dernières dépendent d'une part des propriétés du matériau rocheux lui-même (déformabilité et résistance) et d'autre part de la fissuration.A l'aide de maquettes bidimensionelles à grande échelle composées, lors d'une première série, de blocs rigides (modèle structural) et lors d'une seconde série, de blocs faits d'un matériau équivalent, on a assayé d'étudier la cinématique interne d'une coupe transversale faite dans un versant. Tandis que dans le premier cas, c'est seulement l'influence de la disposition des plans de division qui a pu être recherchée, dans le second il y a eu superposition des paramètres propres à cette disposition et au matériau.En partant de ces modèles structuraux, on a pu classer les différents types de comportements à la déformation des versants en fonction de la position de fissures et de leur angle de frottement.Le cas particulièrement intéressant d'un complexe fissuré à stratification inclinant vers l'intérieur du versant (ici se superposent en effet les mouvements de rotation et de translation) est décrit intégralement dans le déroulement de sa déformation et subdivisé en stades caractéristiques de déformation. On a pu ainsi saisir le développement des déformations depuis le «Hakenwerfen» du front du talus jusqu'à la poussée en profondeur vers la vallée, avec formation de zones de faiblesse bien marquées.Les observations faites lors des essais permettent de mieux évaluer l'influence des plans de division sur le processus de déformation des masses rocheuses qui ont une structure régulière (type H). Elles donnent des indications pour apprécier plus justement le développement de la déformation dans un versant, et de la forme de la zone de rupture à laquelle il faut s'attendre.

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Trace elements in organic- and iron-rich surficial fluids of the boreal zone: Assessing colloidal forms via dialysis and ultrafiltration

On-site size fractionation of about 40 major and trace elements (TE) was performed on waters from boreal small rivers and their estuaries in the Karelia region of North-West Russia around the “Vetreny Belt” mountain range and in Paanajärvi National Park (Northern Karelia). Samples were filtered in the field using a progressively decreasing pore size (5 μm, 2.5 (3) μm, 0.22 (0.45) μm, 100 kDa, 10 and 1 kDa) by means of frontal filtration and ultrafiltration (UF) techniques and employing in-situ dialysis with 10 and 1 kDa membranes followed by ICP-MS analysis. For most samples, dialysis yields a systematically higher (factor of 2-3) proportion of colloidal forms compared to UF. Nevertheless, dialysis is able to provide a fast and artefact-free in-situ separation of colloidal and dissolved components.Similar to previous studies in European subarctic zones, poor correlation of iron concentration with that of organic carbon (OC) in (ultra)filtrates and dialysates reflect the presence of two pools of colloids composed of organic-rich and Fe-rich particles. All major anions and silica are present as dissolved species (or solutes) passing through the 1-kDa membrane. Size-separation ultrafiltration experiments show the existence of larger or smaller pools of colloidal particles different for each of the considered elements.The effect of rock lithology (acidic versus basic) on the colloidal speciation of TE is seen solely in the increase of Fe and some accompanying TE concentrations in catchment areas dominated by basic rocks compared to granitic catchments. Neither the ultrafiltration pattern nor the relative proportions of colloidal versus truly dissolved TE are affected by the lithology of the underlying rocks: within ±10% uncertainty, the two colloidal (10 kDa-0.22 μm and 1-10 kDa) and the truly dissolved (<1 kDa) pools show no difference in percentage of TE distribution between two types of bedrock lithology. The same conclusion is held for organic- and Fe-rich waters. In contrast, landscape context analysis demonstrated slight dominance, for most TE affected by UF, of large-size colloids (10 kDa-0.22 μm) in rivers and streams and small-size colloids and truly dissolved fractions in swamp stagnant surface waters. This supports the existence of two pathways of colloids formation: during the plant litter degradation in wetland zones and at the redox front in river riparian zone.     

Frictional Properties and Microstructure of Calcite-Rich Fault Gouges Sheared at Sub-Seismic Sliding Velocities

We report an experimental and microstructural study of the frictional properties of simulated fault gouges prepared from natural limestone (96 % CaCO₃) and pure calcite. Our experiments consisted of direct shear tests performed, under dry and wet conditions, at an effective normal stress of 50 MPa, at 18–150 °C and sliding velocities of 0.1–10 μm/s. Wet experiments used a pore water pressure of 10 MPa. Wet gouges typically showed a lower steady-state frictional strength (μ = 0.6) than dry gouges (μ = 0.7–0.8), particularly in the case of the pure calcite samples. All runs showed a transition from stable velocity strengthening to (potentially) unstable velocity weakening slip above 80–100 °C. All recovered samples showed patchy, mirror-like surfaces marking boundary shear planes. Optical study of sections cut normal to the shear plane and parallel to the shear direction showed both boundary and inclined shear bands, characterized by extreme grain comminution and a crystallographic preferred orientation. Cross-sections of boundary shears, cut normal to the shear direction using focused ion beam—SEM, from pure calcite gouges sheared at 18 and 150 °C, revealed dense arrays of rounded, ~0.3 μm-sized particles in the shear band core. Transmission electron microscopy showed that these particles consist of 5–20 nm sized calcite nanocrystals. All samples showed evidence for cataclasis and crystal plasticity. Comparing our results with previous models for gouge friction, we suggest that frictional behaviour was controlled by competition between crystal plastic and granular flow processes active in the shear bands, with water facilitating pressure solution, subcritical cracking and intergranular lubrication. Our data have important implications for the depth of the seismogenic zone in tectonically active limestone terrains. Contrary to recent claims, our data also demonstrate that nanocrystalline mirror-like slip surfaces in calcite(-rich) faults are not necessarily indicative of seismic slip rates.     

Low-salinity plumes in the oceanic region of the Basque Country

Low-salinity waters, within the upper layers of the water column, have been observed in the oceanic region of the southeastern limit of the Bay of Biscay (in March, 2007). This contribution assesses the potential role of large surface freshwater discharges from the Adour (France), Nervión, Oria, Deba, Urola, Urumea and Bidasoa (Basque Country) rivers, to explain the presence of these low-salinity waters. Such discharges, within the offshore waters, reached to at least 50 m in depth; likewise, extending over 15–20 km, in the horizontal. This pattern is confirmed by field data collected by offshore buoys, model results, and the analysis of satellite images. The presence of the low-salinity waters is corroborated by numerical simulations, performed by the ROMS (Regional Ocean Modeling System) hydrodynamic model, with the incorporation of river discharges. In order to simulate the freshwater movements and to identify their origin, particles were released at the river mouths and dispersed (by a Lagrangian particle-tracking model, LPTM), supplied by 3-hourly current fields derived from the ROMS model. The plumes of the Nervión, Oria, Urola and Urumea rivers appear to be the main factors contributing to the low-salinity field, at the offshore locations of the buoys. This pattern is related mainly to the prevailing oceano-meteorological conditions, over the period of analysis.     

Application of connectivity theory to model the impact of terrace failure on runoff in semi‐arid catchments

Terraces are a common feature of Mediterranean landscapes. In many places they are no longer maintained so that the number of intact terraces is in prolonged decline. The aim of this paper is to examine the effect of terrace removal and failure on hydrological connectivity and peak discharge in an agricultural catchment (475 ha) in south‐east Spain. The situation of 2006 is compared to that in 1956 and to a scenario without terraces (S2). The spatial distribution of concentrated flow was mapped after four storms in 2006. The degree of connectivity was quantified by means of connectivity functions and related to storm characteristics, land use and topography. For 1956, 2006 and scenario S2, connectivity functions and peak discharge to the river were determined for a storm with a return period of 8·2 years. The results show that the decrease in intact terraces has led to a strong increase in connectivity and discharge. The contributing area to the river system has increased by a factor 3·2 between 1956 and 2006. If all terraces were to be removed (scenario S2), the contributing area may further increase by a factor 6·0 compared to 2006. The spatial extent of concentrated flow and the degree of connectivity are related to storm magnitude as expressed by the erosivity index (EI₃₀). Although a large part of the concentrated flow (25–50%) occurs on dirt roads, it appears that croplands become a major source of runoff with increasing rainfall. The results suggest that connectivity theory can be used to improve rainfall–runoff models in semi‐arid areas. Copyright © 2009 John Wiley & Sons, Ltd.