Fabrication and test of sol–gel based planar oxygen optodes for use in aquatic sediments

We describe the fabrication of organically modified sol–gel (ORMOSIL) planar optodes for mapping the two-dimensional oxygen distribution in sediments. All sensor foils were based on the use of ruthenium(II)-tris-(4,7-diphenyl-1,10-phenantrolin)-perchlorate, which is a fluorescent dye quenched dynamically by oxygen. Sensors made with different sol–gel immobilisation matrices, different concentrations of precursors and indicator dye, as well as different types of scattering particles co-immobilised in the sensor foil were investigated systematically. Optimal sensor performance was obtained with dye concentrations of 2–10 mmol/kg in an immobilisation matrix made of diphenyldiethoxy-silan and phenyltriethoxy-silan precursors with addition of organically coated TiO₂ particles. The sensors exhibited a good mechanical stability and a high sensitivity from 0% to 100% oxygen, which remained constant over at least 36 days. The planar optodes were used with a fluorescent lifetime imaging system for direct mapping of the spatio-temporal variation in oxygen distribution within marine sediment inhabited by the polychaete Hediste diversicolor. The measurements demonstrated the spatio-temporal heterogeneity of the oxygen distribution in bioturbated sediments due to burrow structures and non-constant irrigation activity of the polychaete, which is difficult to resolve with microsensors or with traditional biogeochemical techniques.     

The rhombohedral framework of the Scandinavian Caledonides and their foreland

The Baltic Shield of northern Europe is transsected by approximately N-S and NW-SE striking Proterozoic fault and fracture zones that were remobilized during the Late Precambrian opening of the Iapetus ocean and the SE-directed thrusting of the Caledonian nappes in Mid-Paleozoic time. Remobilizations of these older structures account for a distinct subsidence history and sedimentological evolution over each fault-bounded basement segment during opening of the Iapetus and for a distinct metamorphic and structural development found within each block during overthrusting of the Caledonian nappes and the exhumation of the orogen. The two fault sets define basement blocks with rhombus-like plan sections which had individual subsidence histories during Iapetus rifting as is expressed by their Late Precambrian (Riphean and Vendian) to Silurian sedimentary cover of contrasting thickness and facies. This contrasting subsidence history of the various basement blocks may have contributed to differences in thrusting level, thrust excision (nappe size), and tectonic style. Correlative Caledonian nappes from adjacent faultbounded basement blocks were thrust diachronously resulting in transport transverse to the general thrusting direction. Thrusting oblique to the NW-SE fault zones and orogen parallel extension resulted in lateral-ramp folds in the cover and reactivation along the NW-SE faults imbricated the overlying nappes. The extent of basement imbrication and duplex formation is variable in the different segments. Within single segments, the basement imbrication and duplex-formation defined basement highs that roughly align in two parallel zones within the orogen. The site of the basement duplexes is probably controlled by older N-S fracture zones while the pinch- and-swell structure parallel to the orogen is caused by the individual deformation and thrusting behavior of the basement and cover sequences that are bound by the NW-SE fault zones. Thus the Caledonian orogen appears to have inherited the Precambrian structural grain of the underlying, Baltic Shield.

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Zusammenfassung Der Baltische Schild Nordeuropas ist von im Proterozoikum angelegten Verwerfungen und Scherzonen mit nördlichem sowie und nordwestlichem Streichen durchzogen, welche während der spätpräkambrischen Öffnung des Iapetus-Ozeanes und der anschließenden, südöstlich gerichteten Überschiebung der kaledonischen Decken im ausgehenden Alt-Paläozoikum reaktiviert worden sind. Die Wiederbelebung dieses ererbten, durch steilstehende Störungen gekennzeichneten, rhombenförmigen Strukturmusters führte zu unterschiedlichen Absenkungsraten der Störungsbegrenzten Grundgebirgsblöcke und steuerte somit die Ablagerungsbedingungen in entstehenden Sedimentationströgen während der Öffnungsphase des Iapetus-Ozeans. Durch diesen Prozeß lassen sich latterale Unterschiede in Mächtigkeit und Fazies der jungpräkambrischen bis altpaläozoischen Deckensedimente entlang dem Nordwestrande des damaligen Kontinentes Baltica, sowie Differenzen in der metamorphen und strukturellen Entwicklung der durch Störungen begrenzten Blöcke während der Überschiebung der kaledonischen Decken und der Hebung des Gebirges erklären. Vertikale Blockverschiebungen und Kippungen von Blöcken relativ zueinander können beobachtete Unterschiede in den Abscherungs- und Überschiebungsniveaus, sowie unterschiedliche tektonische Baustile auf und vor (vor allem) zwischen Blöcken erklären helfen. Untereinander korrelierbare kaledonische Deckensegmente haben, in Bezug auf Transportrichtung und Strecke, voneinander unterschiedliche Wege oberhalb ihrer Untergrundsegmente zurückgelegt. Während dieser Überschiebung auf ein sich simultan veränderndes Relief ist es dabei zu Teilbewegungen schräg zur Hauptüberschiebungsrichtung gekommen, was seinerseits zu seitlichen Verzahnungen benachbarter Deckensegmente geführt hat. Die NWSE streichenden Blockgrenzen haben während lokaler Überschiebungen leicht schräg zu dieser Hauptrichtung als Widerlager und Rampen (lateral ramps) für die darübergleitenden Decken gewirkt, welche sich ihrerseits bei diesem Prozeß in orogentransversale Falten gelegt haben. Je nach ihrer Lage und Neigung sind die verschiedenen Segmente während der Kollisionsphase des kaledonischen Orogens in unterschiedlichem Grade von internen Störungen betroffen worden. Die durch intensive Internscherung hervorgerufenen Krustenverdickungen zeigen eine perlschnurartige Anordnung in zwei orogenparallele zonen, deren Anlage sich auf unterliegende und mitverfrachtete N-S Störungszonen zurückführen lassen kann. Das Anschwellen und Ausdünnen (pinch- and-swell) von tektonischen Einheiten entlang der Längsrichtung des Orogens läßt sich durch unterschiedliche Deformationsverhalten innerhalb der durch NW-SE Störungen begrenzten Segmente erklären. Die Kaledoniden Skandinaviens haben offensichtlich das strukturelle Gepräge ihrer präkaledonischen Unterlage ererbt.

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Résumé Le bouclier baltique est traversé par des fractures protérozoïques orientées approximativement N-S et NW-SE. Ces failles furent réactivées d'abord au Précambrien tardif lors de l'extension correspondant à l'ouverture de l'Océan lapétus, ensuite au Protérozoïque moyen lors du charríage des nappes calédoniennes vers le SE. La réactivation de ces vieilles structures explique qu'on observe pour chaque bloc du socle faillé une subsidence et une sédimentation différente pendant la phase d'extension (ouverture du lapétus), ainsi qu'une évolution métamorphique et structurale distincte pendant le charriage des nappes calédoniennes et l'exhumation de l'orogène. Les deux groupes de failles définissent dans le socle des blocs à sections rhombiques qui présentaíent chacun une subsidence particulière pendant l'ouverture du lapétus, comme l'indiquent les variations d'épaisseur et de facies de leur couverture sédimentaire tardi-précambrienne (vendienne) à silurienne. Cette subsidence variable selon les blocs pourrait avoir contribué à induire des différences dans les niveaux de décollement et de charriage des nappes, ainsi que dans le style tectonique. Les unités tectonostratigraphiques des blocs adjacents furent charriées de façon diachronique avec comme résultat un transport transverse par rapport à la direction dominante du charriage. Ce déplacement oblique vers les zones de failles NW-SE et l'extension parallèle de l'orogène ont produit des plis transversaux dans la couverture; la réactivation des failles NW-SE s'est traduite par l'imbrication des nappes surincombantes. L'importance de cette imbrication et de la formation de duplex est variable selon les différents segments du socle. Pour chaque segment particulier, l'imbrication du socle et la formation de duplex ont engendré des culminations de socle alignés selon deux zones parallèles dans l'orogène. La position des duplex est probablement régie par de vieilles failles N-S alors que la structure en «pinch- and-swell» le long de l'orogène est causée par le caractère individuel de la déformation et du charriage du socle et de sa couverture, propre à chaque bloc limité par des failles NW-SE. L'orogenèse calédonienne a été ainsi fortement afffectée par les structures précambriennes du bouclier baltique sous-jacent.

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, lapetus - . , , , , , lapetus. - - , , . , , , . , , . , . NW-SE (»side-wall ramps«) , . . , , , ; , , , - . (pinck- and-swell) , , NW-S . , - .

     

A multilaminate constitutive model accounting for anisotropic small strain stiffness

In this paper an extension of existing multilaminate soil models is presented, which can account for inherent and stress‐induced cross‐anisotropic elasticity in the small strain range and its dependency on the load history. In the multilaminate framework, material behaviour is formulated on a number of local planes in each stress point, and the macroscopic response of the material is obtained by integration of the local contributions. Strain‐induced anisotropy, which adds to the stiffness anisotropy inherently present in the material, is therefore intrinsically taken into account. Micro–macro relations between local parameters on plane level and global parameters on macroscopic level are obtained by the spectral decomposition of the global elastic compliance matrix. The model is implemented into a finite‐element code, and model predictions are compared with experimental data of triaxial tests on different soils involving small and large load cycles. The importance of cross‐anisotropic elasticity within the small strain range for predicting ground deformations in geotechnical boundary value problems is discussed at the example of an excavation problem. Copyright © 2012 John Wiley & Sons, Ltd.     

Radar observations of snow formation in a warm pre‐frontal snowband

Abstract

Radar reflectivity measurements and sounding data were analyzed to investigate snowfall production in a long‐lasting snowband that formed in advance of a warm surface front moving across Alberta. The sounding data indicated that the band could have been forced by slantwise overturning during the release of moist symmetric instability combined with frontogenesis. The stability analysis presented here is novel in that it includes ice phase thermodynamics, neglected in previous studies of slantwise convection.

Radar reflectivity fields were analyzed to determine the total snow content and the mass outflow rate as factors of time. The peak value of total snow content was 17 kilotons per km of snowband, and the peak mass outflow rate was 10 tons s^‐1 km^‐1. The snowfall rate averaged across the cloud base was about 0.8 cm h^‐1, and the average snow content remained close to 0.2 g m^‐1. The characteristic time (defined as the ratio of total snow content over mass outflow rate) was about 30 minutes, which is approximately the time needed for the growth of snowflakes by aggregation in the observed temperature range. The precipitation efficiency of the snowband, defined as the ratio of snow mass outflow to water vapour inflow was estimated to be 14%. The precipitation production values observed in the Alberta snowband are compared with previous estimates reported for frontal rainbands and Alberta thunderstorms.     

Public climate-change skepticism,energy preferences and political participation

Many studies have shown a general decline of public concern about climate change or vice versa a rise in public climate-change skepticism, in particular in the U.S. and other Anglo-Saxon countries. There is a vivid debate on whether this is a global phenomenon, on which factors explain the decline, and on the broader societal implications of these trends in the context of the transformation toward a low-carbon society. We add to this literature by presenting the results of a recent general population survey in Germany in which we looked for systematic linkages between public climate-change skepticism on one hand, and energy preferences and political participation on the other. Germany is an interesting testbed as it is currently involved in a large-scale restructuring of its system of energy supply toward renewable energy sources (the “Energiewende”). Our results indicate that climate-change skepticism has not diffused widely in Germany, but that it correlates with less support of renewable energy sources. However, skepticism correlates negatively with political participation, and there is no strong political outlet for public climate-change skepticism in Germany. Alternative potential barriers for the successful implementation of the “Energiewende” are also discussed.     

The significance of chemical,isotopic, and detrital components in three coeval stalagmites from the superhumid southernmost Andes (53°S) as high-resolution palaeo-climate proxies

Stalagmites are important palaeo-climatic archives since their chemical and isotopic signatures have the potential to record high-resolution changes in temperature and precipitation over thousands of years. We present three U/Th-dated records of stalagmites (MA1–MA3) in the superhumid southern Andes, Chile (53°S). They grew simultaneously during the last five thousand years (ka BP) in a cave that developed in schist and granodiorite. Major and trace elements as well as the C and O isotope compositions of the stalagmites were analysed at high spatial and temporal resolution as proxies for palaeo-temperature and palaeo-precipitation. Calibrations are based on data from five years of monitoring the climate and hydrology inside and outside the cave and on data from 100 years of regional weather station records.Water-insoluble elements such as Y and HREE in the stalagmites indicate the amount of incorporated siliciclastic detritus. Monitoring shows that the quantity of detritus is controlled by the drip water rate once a threshold level has been exceeded. In general, drip rate variations of the stalagmites depend on the amount of rainfall. However, different drip-water pathways above each drip location gave rise to individual drip rate levels. Only one of the three stalagmites (MA1) had sufficiently high drip rates to record detrital proxies over its complete length. Carbonate-compatible element contents (e.g. U, Sr, Mg), which were measured up to sub-annual resolution, document changes in meteoric precipitation and related drip-water dilution. In addition, these soluble elements are controlled by leaching during weathering of the host rock and soils depending on the pH of acidic pore waters in the peaty soils of the cave’s catchment area. In general, higher rainfall resulted in a lower concentration of these elements and vice versa. The Mg/Ca record of stalagmite MA1 was calibrated against meteoric precipitation records for the last 100 years from two regional weather stations. Carbonate-compatible soluble elements show similar patterns in the three stalagmites with generally high values when drip rates and detrital tracers were low and vice versa. δ¹³C and δ¹⁸O values are highly correlated in each stalagmite suggesting a predominantly drip rate dependent kinetic control by evaporation and/or outgassing. Only C and O isotopes from stalagmite MA1 that received the highest drip rates show a good correlation between detrital proxy elements and carbonate-compatible elements. A temperature-related change in rainwater isotope values modified the MA1 record during the Little Ice Age (～0.7–0.1 ka BP) that was ～1.5 °C colder than today. The isotopic composition of the stalagmites MA2 and MA3 that formed at lower drip rates shows a poor correlation with stalagmite MA1 and all other chemical proxies of MA1. ‘Hendy tests’ indicate that the degassing-controlled isotope fractionation of MA2 and MA3 had already started at the cave roof, especially when drip rates were low. Changing pathways and residence times of the seepage water caused a non-climatically controlled isotope fractionation, which may be generally important in ventilated caves during phases of low drip rates. Our proxies indicate that the Neoglacial cold phases from ～3.5 to 2.5 and from ～0.7 to 0.1 ka BP were characterised by 30% lower precipitation compared with the Medieval Warm Period from 1.2 to 0.8 ka BP, which was extremely humid in this region.     

Surface roughness and geological mapping at subhectometer scale from the High Resolution Stereo Camera onboard Mars Express

The quantitative measurement of surface roughness of planetary surfaces at all scales provides insights into geological processes. A characterization of roughness variations at the scale of a few tens of meters is proposed that complements the analysis of local topographic data of the martian surface at kilometer scale, as achieved from the Mars Orbiter Laser Altimeter (MOLA) data, and at the subcentimeter scale using photometric properties derived from multi-angular observations. Relying on a Gabor filtering process, an algorithm developed in the context of image classification for the purpose of texture analysis has been adapted to handle data from the High Resolution Stereo Camera (HRSC). The derivation of roughness within a wavelength range of tens of meters, combined with analyses at even longer wavelengths, gives an original view of the martian surface. The potential of this approach is evaluated for different examples for which the geological processes are identified and the geological units are mapped and characterized in terms of roughness.     

Synthesis of refractory metal nuggets and constraints on the thermal histories of nugget‐bearing Ca,Al‐rich inclusions

Tiny refractory metal nuggets are mainly observed inside Ca, Al‐rich inclusions (CAIs) from chondritic meteorites and are commonly assumed to be condensates from a solar composition gas. However, recent detailed studies of metal nugget compositions and their comparison with predictions from condensation show that the observed abundance patterns are extremely difficult to achieve in this way. As a test for the proposed alternative, precipitation from a silicate liquid, we conducted melting experiments, in which nine different refractory metals (nugget components) were equilibrated with each other along with a CAI‐like liquid at reducing conditions. When quenched, minerals similar to those in CAIs formed from such liquids including refractory metal nuggets exhibiting compositions and appearances similar to those of the meteoritic nuggets. The run products and their comparison with a meteoritic nugget‐bearing CAI is evidence for formation of refractory metal nuggets during cooling of Ca, Al‐rich liquids at rates about 1000°/40 s (in the interval from 1900 to 900 °C). To achieve the formation of refractory metal nuggets and the textures observed in the host inclusions, during cooling the rate probably changed. Refractory metal nuggets apparently formed during quenching before spinel crystallized.