Hydrological trends and the evolution of catchment research in the Alptal valley,central Switzerland

When the observation of small headwater catchments in the pre-Alpine Alptal valley (central Switzerland) started in the late 1960s, the researchers were mainly interested in questions related to floods and forest management. Investigations of geomorphological processes in the steep torrent channels followed in the 1980s, along with detailed observations of biogeochemical and ecohydrological processes in individual forest stands. More recently, research in the Alptal has addressed the impacts of climate change on water supply and runoff generation. In this article, we describe, for the first time, the evolution of catchment research at Alptal, and present new analyses of long-term trends and short-term hydrologic behaviour. Hydrometeorological time series from the past 50 years show substantial interannual variability, but only minimal long-term trends, except for the ~2°C increase in mean annual air temperature over the 50-year period, and a corresponding shift towards earlier snowmelt. Similar to previous studies in larger Alpine catchments, the decadal variations in mean annual runoff in Alptal's small research catchments reflect the long-term variability in annual precipitation. In the Alptal valley, the most evident hydrological trends were observed in late spring and are related to the substantial change in the duration of the snow cover. Streamflow and water quality are highly variable within and between hydrological events, suggesting rapid shifts in flow pathways and mixing, as well as changing connectivity of runoff-generating areas. This overview illustrates how catchment research in the Alptal has evolved in response to changing societal concerns and emerging scientific questions.     

Sensitivity analysis of a deterministic water temperature model to forest canopy and soil temperature in Catamaran Brook (New Brunswick,Canada)

A coupled deterministic hydrological and water temperature model, CEQUEAU, was modified to include soil temperature and crown closure in its calculation of local advective terms in the heat budget. The modified model was than tested to verify its sensitivity to these modifications. An analysis of the heat budget of a small forested catchment in eastern Canada revealed that the advective term related to interflow plays a significant role in the daily water heat budget, providing on average 28% of the local advective budget (which also includes advective heat terms from surface runoff and groundwater) and nearly 14% of the total heat budget (which includes all radiative terms at the water surface, convection and evaporation, as well as the local advective terms). Relative sensitivity indices (RSIs) were used to verify the impact of the newly introduced parameters and variables. Among them, parameters related to the forest cover (crown closure and leaf area index) have a maximum RSI of ?0·6; i.e. a 100% increase in value produces a 60% decrease in the local advective term. Parameters with the greatest influence are the volume of water contributing to interflow and the amplitude of the net radiative flux at the soil surface, which, if doubled, would double the contribution of the local interflow advective term to the heat budget. Copyright © 2003 John Wiley & Sons, Ltd.     

The Relationship of Green-Line Transients to White-Light Coronal Mass Ejections

We report observations by the Large Angle Spectrometric Coronagraph (LASCO) on the SOHO spacecraft of three coronal green-line transients that could be clearly associated with coronal mass ejections (CMEs) detected in Thomson-scattered white light. Two of these events, with speeds >25 km s^-1, may be classified as ‘whip-like’ transients. They are associated with the core of the white-light CMEs, identified with erupting prominence material, rather than with the leading edge of the CMEs. The third green-line transient has a markedly different appearance and is more gradual than the other two, with a projected outward speed <10 km s^-1. This event corresponds to the leading edge of a ‘streamer blowout’ type of CME. A dark void is left behind in the emission-line corona following each of the fast eruptions. Both fast emission-line transients start off as a loop structure rising up from close to the solar surface. We suggest that the driving mechanism for these events may be the emergence of new bipolar magnetic regions on the surface of the Sun, which destabilize the ambient corona and cause an eruption. The possible relationship of these events to recent X-ray observations of CMEs is briefly discussed. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004981125702     

Exploring the gap of the digital divide

While much of the literature related to the digital divide focuses on either technology penetration in developed countries or the introduction of new technology to the poor and disadvantaged in the developing world, this paper pays attention to the middle-classes in a developing country which is connected to the Internet but under poor conditions. The digital divide is examined by investigating how the uneven distribution of Internet connection influences distance education students’ participation in higher education. Empirically, the paper is informed by a qualitative study of distance education in Indonesia. The main conclusion is that while in more peripheral areas students may not gain much from the use of new technology, the use of this technology may be useful for the further development of such regions. In central areas the new technology seems to contribute to students’ study situations more effectively and the daily environment empowers the students’ study activities, rather than vice versa.     

Aspects of Deep Ocean Mixing

The turbulent motions responsible for ocean mixing occur on scales much smaller than those resolved in numerical simulations of oceanic flows. Great progress has been made in understanding the sources of energy for mixing, the mechanisms, and the rates. On the other hand, we still do not have adequate answers to first order questions such as the extent to which the thermohaline circulation of the ocean, and hence the earth's climate, is sensitive to the present mixing rates in the ocean interior. Internal waves, generated by either wind or flow over topography, appear to be the principle cause of mixing. Mean and eddy flows over topography generate internal lee waves, while tidal flows over topography generate internal tides. The relative importance of these different internal wave sources is unknown. There are also great uncertainties about the spatial and temporal variation of mixing. Calculations of internal tide generation are becoming increasingly robust, but we do not know enough about the subsequent behavior of internal tides and their eventual breakdown into turbulence. It does seem, however, that most internal tide energy flux is radiated away from generation sites as low modes that propagate over basin scales. The mechanisms of wave-wave interaction and topographic scattering both act to transfer wave energy from low modes to smaller dissipative scales. This revised version was published online in August 2006 with corrections to the Cover Date.     

New age constraints on emplacement of the Cévenol granitoids, South French Massif Central

During the development of the Variscan orogeny, large amounts of granitic melt were produced, giving rise to the intrusion of granitoids at different structural levels. Despite numerous studies, ages available from previous work on the Cévennes granites remain largely imprecise. In order to better constrain the age and emplacement mode of these granites, we have combined U–Pb dating on monazites and zircons and ⁴⁰Ar/³⁹Ar dating on biotites with petrological observations, major element chemical analysis and SEM zircon imaging on five samples from the Aigoual–St Guiral–Liron and Mont Lozère granitic massifs. The results revealed that granitic intrusions and cooling in Southern Cévennes occurred in a short time span at ∼306 Ma after the main episode of regional metamorphism. Petrological and chemical data suggest that they result from a mixing between mantle-derived basic magmas (lamprophyres) and lower crust acid magmas. At a regional scale the production of these melts occurred at the end of crustal thickening induced by nappe stacking, at the same time as the late anatectic events recorded further north in the Velay dome and the granulite facies metamorphism recorded in metasedimentary granulite enclaves brought up by Tertiary volcanoes of the Velay area (Bournac).     

The qualitative zoning record of minerals. A method for determining the duration of metamorphic events?

Summary The efficacy of ion exchange in petrological systems, for example the Fe-Mg exchange between garnet and biotite, is a function of grainsize, temperature, rates of temperature change and diffusion parameters. The combination of these variables determines the final zoning profile of minerals. Therefore, zoning profiles may be used to derive one of these variables if the others are known. For example, a mineral grain that experienced a short thermal event may still preserve a zoning profile characteristic of the heating path. In contrast, if that grain experienced a long thermal event it may develop a zoning profile typical of the cooling path. Conversely, for the same temperature-time cycle, large grains may not completely equilibrate at the metamorphic peak, and in smaller grains any previous record may have been erased. This is commonly observed in natural rocks where different grains within one thin section preserve often qualitatively different zoning profiles. Thus, a critical grainsize,l _crit, may exist that separates grains with qualitatively different zoning profiles so that grains of sizel > l _crit still retain zoning information about the heating path and grains of sizel <l _crit contain only information about the cooling path. If the critical grainsize can be measured and an independent estimate for the peak metamorphic temperature exists, the duration of the thermal event may, in principle, be estimated.The applicability of this method to natural garnets is hampered by a range of uncertainties. However, a parameterisation of the critical grain size may be used to illustrate the relative importance of grain size, temperature and event duration to the equilibration of minerals. In this paper, the critical grainsize is parameterized for various temperature-time cycles and its dependence on diffusion parameters is discussed. It is shown that, for Barrovian conditions,l _crit between 0.1 and 1 mm separates garnets retaining prograde information from garnets retaining cooling path information. For illustration, we compare the results with the critical grainsize of garnets from two metamorphic terranes, the Prydz Bay region (Antarctica) and the Koralm complex (Eastern Alps). Despite the large range of uncertainties attached to the method, it is shown that the critical grainsize of garnets in both terranes is consistent with a very short duration of the last thermal event that affected the two regions.

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Die qualitative Form von Zonierungsprofilen in Mineralen. Information über die Dauer metamorpher Ereignisse?

Zusammenfassung Zonierungsprofile von Paragenesen im Ionenaustausch, zum Beispiel das Fe-Mg Austauschsgleichgewicht zwischen Granat und Biotit, sind eine Funktion von (i) Korngröße, (ii) Temperatur, (iii) Kühl- und Heizgeschwindigkeit sowie (iv) den Diffusionskonstanen. Es sollte daher möglich sein, Zonierungsprofile dazu zu verwenden, einen dieser Parameter zu bestimmen, wenn die anderen bekannt sind. Zonierungsprofile von Kristallen die ein kurzes thermisches Ereignis erfahren haben, mögen daher prograde Information beinhalten, wogegen derselbe Kristall ein retrogrades Profil aufweisen mag, wenn er einem langlebigen thermischen Ereignis unterlag (prograd und retrograd ist hier als: bei ansteigender Temperatur und bei abfallender Temperatur definiert). In Kristallen die dem gleichen Temperatur-Zeitpfad unterworfen waren, könnten kleine Körner nur die Kühlgeschichte dokumentieren, wogegen große noch Zonierungsinformation vom Heizpfad aufweisen. In natürlichen Gesteinen wird das oft dadurch beobachtet, daß verschiedene Körner auseinem Dünnschliff qualitativ verschiedene Zonierungsprofile aufweisen. Es ist daher möglich eine kritische Korngöße,l _crit, zu definieren, die Korngrößen mit qualitativ verschiedenen Zonierungsprofilen voneinander trennt. Körner mit einem Durchmesserl > l _crit haben, zumindest teilweise, noch prograde Profile, wogegen Körner mitl <l _crit nur retrograde Information dokumentieren. Wenn man diese kritische Korngröße messen kann, sollte sie dazu benutzt werden können, etwas über die Dauer des thermischen Ereignisses auszusagen.Die Anwendbarkeit dieser Methode ist durch eine Reihe von Fehlern limitiert. Nichtsdestotrotz, ist eine Parameterisierung der kritischen Korngröße nützlich um die relative Wichtigkeit von Korngröße, Temperatur und Zeit, für die Entwicklung von Zonierungsprofilen, zu illustrieren. Unser Modell kann dazu benutzt werden, um die Größenordnung von Granaten abzuschätzen, die noch prograde Information dokumentieren können. Die Abhängigkeit der kritischen Korngröße von Diffusionsparametern und der Form des Temperatur-Zeit Pfades wird ebenfalls diskutiert. Es wird gezeigt, daß für Metamorphose in der mittleren Grünschiefer und Amphibolit fazies,l _crit zwischen 0.1 and 1 mm prograd zonierte von retrograd zonierten Granaten trennt. Um das Modell zu illustrieren, werden die Ergebnisse auf die Prydz Bay Region (Antarktis) und den Koralm Komplex (Ostalpen) angewendet. Trotz der großen Fehlergrenzen der Methode glauben wir zeigen zu können, daß die kritische Korngröße beider Terrains andeutet, daß das letzte thermische Ereignis in beiden Gebieten kurzlebig war.

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With 5 Figures     

A window to the operation of microplate tectonics in the Tethys Ocean: the geochemistry of the Samothrace granite,Aegean Sea

Summary The island of Samothrace, northeastern Aegean Sea, consists of five main geological units: (i) A basement unit consisting of low grade metamorphic rocks (metapelites, marbles, metavolcanic rocks, and a metaconglomerate); (ii) an ophiolitic complex with K-Ar hornblende date of 154 ± 7 and 155 ± 7 Ma; (iii) A granite intrusion with biotite K-Ar dates of 14.5 ± 0.3 and 14.5 ± 0.5 Ma, and a contact metamorphic event dated at 40.9 + 2.2 Ma; (iv) a unit of Cenozoic volcanic rocks: orogenic volcanism apparently occurred in two cycles with Upper Eocene tholeiitic to calc-alkaline volcanic rocks and post-Eocene high-K andesites to trachytes. (v) Quaternary clastic sedimentary rocks which occur around the peripheral parts of the island. The granitic intrusion is predominantly a hornblende-biotite granite, granodiorite or quartz monzonite, with porphyritic variants and mafic enclaves. The pluton is cut by granophyre, aplite and rare granodioritic veins. All lithological units of the Samothrace intrusion show smooth and continuous major element trends and similar chondrite- and Ocean Ridge Granite-normalized incompatible element profiles. ORG-normalized incompatible element contents of Hf, Zr, Sm are explained with fractionation close to the normalizing values Y and Yb contents combined with high K/Yb ratios; Rb and Th are significantly enriched relative to Nb and Ta. In Y-Nb and Rb-SiO₂ space most samples of the Samothrace granite, plot in the volcanic arc and the syn-collisional granite fields. In Y + Nb-Rb space they are equally distributed within and transgress these two domains. The geochemical and regional data suggest a subduction or collision environment but biotite mineral data do not support a collisional setting for magma genesis. The Samothrace granite was probaby associated with a post-collisional domain after the closure of the Axios section of the Tethys Ocean.

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Ein Einblick in das Wirken von Mikroplattentektonik in der Tethys—Die Geochemie des Samothrake Granites, Agäisches Meer

Zusammenfassung Die Insel Samothrake in der nordöstlichen Ägäis besteht aus fünf geologischen Haupteinheiten: (i) einem schwach metamorphen Basement (Metapelite, Marmore, Metavulkanite und Metakonglomerate); (ii) einem ophiolithischem Komplex, der mit K-Ar Datierungen an Hornblende ein Alter von 154 ± 7 und 155 ± 7 Ma ergab; (iii) ein granitischer Intrusionskörper mit K-Ar Altern an Biotit von 14.0 ± 0.3 und 14.5 ± 0.5 Ma und einem kontaktmetamorphen Ereignis, das mit 40.9 ± 2.2 Ma datiert ist; (iv) eine Abfolge känozoischer Vulkanite, wobei der orogene Vulkanismus offensichtlich in zwei Zyklen ablief mit tholeiitischen bis kalkalkalischen Vulkaniten im oberen Eozän und high-K Andesiten bis Trachyten im post-Eozän; (v) quartären klastischen Sedimentgesteinen, die im Randbereich der Insel auftreten. Die Granitintrusion setzt sich hauptsächlich aus Hornblende-Biotitgraniten, Granodioriten oder Quarzmonzoniten mit teilweise porphyrischen und mafischen Enklaven enthaltenden Varietäten zusammen. Der Pluton wird von Granophyren, Apliten und seltener von granodioritischen Gängen durchschlagen. Alle lithologischen Einheiten der Samothrake Intrusion zeigen kontinuierliche Hauptelementtrends und ähnliche Chondrit und ORG-normalisierte inkompatible Elementprofile. Die Gehalte an den inkompatiblen Elementen Hf, Zr, Sm sind sehr ähnlich denen von ozeanischen Graniten (ORG). Die niedrigen Y und Yb-Gehalte und die hohen K/Yb Verhältnisse werden durch Fraktionierung erklärt. Rb und Th sind signifikant angereichert im Vergleich zu Nb und Ta. In Y-Nb und Rb-SiO₂ Diagrammen plotten die meisten Proben des Samothrake Granites im Feld der vulkanischen Inselbogen- und Synkollisionsgranite. Im Y + Nb-Rb Diagramm zeigt sich eine gleichmäßige und überlappende Verteilung. Die geochemischen und regionalen Daten weisen auf einen Subduktions- oder Kollisionsbereich hin, obwohl die Biotitzusammensetzungen nicht für eine Bildung der Magmen in einem Kollisionsbereich sprechen. Die Bildung des Samothrake Granites steht möglicherweise mit post-Kollisionstektonik nach dem Schließen der Axioszone in der Tethys in Zusammenhang.

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With 7 Figures     

Thermodynamic data from redox reactions at high temperatures. II. The MnO-0Mn3O4 oxygen buffer,and implications for the thermodynamic properties of MnO and Mn3O4

The \(\mu _{O_2 } \) defined by the reaction 6 MnO+O₂ =2 Mn₃O₄ has been determined from 917 to 1,433 K using electrochemical cells (with calcia-stabilized zirconta, CSZ) of the type: Steady emfs were achieved rapidly at all temperatures on both increasing and decreasing temperature, indicating that the MnO-Mn₃O₄ oxygen buffer equilibrates relatively easily. It therefore makes a useful alternative choice in experimental petrology to Fe₂O₃-Fe₃O₄ for buffering oxygen potentials at oxidized values. The results are (in J/mol, temperature in K, reference pressure 1 bar); \(\mu _{O_2 } \) (±200)=-563,241+1,761.758T-220.490T inT+0.101819T ² with an uncertainty of ±200 J/mol. Third law analysis of these data, including a correction for the deviations in stoichiometry of MnO, impliesS _298.15 for Mn₃O₄ of 166.6 J/K · mol, which is 2.5 J/K · mol higher than the calorimetric determination of Robie and Hemingway (1985). The low value of the calorimetric entropy may be due to incomplete ordering of the magnetic spins. The third law value of Δ _r H _298.15 ⁰ is-450.09 kJ/mol, which is significantly different from the calorimetric value of-457.5±3.4 kJ/mol, calculated from Δ _f H _298.15 ⁰ of MnO and Mn₃O₄, implying a small error in one or both of these latter.     

Initiation and development of pull-apart basins with Riedel shear mechanism: insights from scaled clay experiments

Typical pull-apart structures were created in scaled clay experiments with a pure strike-slip geometry (Riedel type experiments). A clay slab represents the sedimentary cover above a strike-slip fault in the rigid basement. At an early stage of the development of the deformation zone, synthetic shear fractures (Riedel shears) within the clay slab display dilatational behaviour. With increasing basal displacement the Riedel shears rotate and open further, developing into long, narrow and deep troughs. The shear displacement and the low angle with the prescribed principal basal fault set them apart from tension gashes. At a more evolved stage, synthetic segments (Y-shears) parallel to the basal principal fault develop and accommodate progressive strike-slip deformation. The Y-shears connect the tips of adjacent troughs developed from the earlier Riedel shears, resulting in the typical rhomb-shaped structures characteristic for pull-apart basins. The Strait of Sicily rift zone, with major strike-slip systems being active from the Miocene to the Present, comprises pull-apart basins at different length scales, for which the structural record suggests development by a mechanism similar to that observed in our experiments.