Fluvial suspended sediment yields over hours to millennia in the High Arctic at proglacial Lake Linnévatnet,Svalbard

Sediment yield can be a sensitive indicator of catchment dynamics and environmental change. For a glacierized catchment in the High Arctic, we compiled and analyzed diverse sediment transfer data, spanning a wide range of temporal scales, to quantify catchment yields and explore landscape response to past and ongoing hydroclimatic variability. The dataset integrates rates of lake sedimentation from correlated varve records and repeated annual and seasonal sediment traps, augmented by multi‐year lake and fluvial monitoring. Consistent spatial patterns of deposition enabled reconstruction of catchment yields from varve‐ and trap‐based fluxes. We used hydroclimatic data and multivariate modeling to examine annual controls of sediment delivery over almost a century, and to examine shorter‐term controls of sediment transfer during peak glacier melt. Particle‐size analyses, especially for annual sediment traps, were used to further infer sediment transfer mechanisms and timing. Through the Medieval Warm Period and Little Ice Age, there were no apparent multi‐century trends in lake sedimentation rates, which were over three times greater than those during the mid‐Holocene when glaciers were diminished. Twentieth‐century sedimentation rates were greater than those of previous millennia, with a mid‐century step increase in mean yield from 240 to 425 Mg km^?2 yr^?1. Annual yields through the twentieth century showed significant positive relations with spring/summer temperature, rainfall, and peak discharge conditions. This finding is significant for the future of sediment transfer at Linnévatnet, and perhaps more broadly in the Arctic, where continued increases in temperature and rainfall are projected. For 2004–2010, annual yields ranged from 294 to 1330 Mg km^?2 yr^?1. Sediment trap volumes and particle‐size variations indicate that recent annual yields were largely dominated by spring to early summer transfer of relatively coarse‐grained sediment. Fluvial monitoring showed daily to hourly sediment transfer to be related to current and prior discharge, diurnal hysteresis, air temperature, and precipitation. Copyright © 2017 John Wiley & Sons, Ltd.     

Determination of the mixing properties of molten silicates by Knudsen cell mass spectrometry—II. The systems (NaK)AlSi4O10, and (Na-K)AlSi5O12

The mixing properties of aluminosilicate melts in the systems NaAlSi₄O₁₀-KAlSi₄O₁₀ and NaAlSi₅O₁₂-KAlSi₅O₁₂ have been determined by measuring the compositions of their saturated vapours by Knudsen cell mass spectrometry. The melts mix very close to ideally over the whole composition range in agreement with theoretical models and the predictions of our previous work.     

Elemental abundances in Green River oil shale

Spark-source mass spectrometric analysis of pyrolyzed Green River oil shale for trace element distribution showed enhanced concentrations for only lithium and beryllium. In general, trace elemental concentrations were found to be below anticipated crustal amounts. There appears to be no promise of any substantial accumulation of any trace elements within the organic matrix of Green River oil shale.     

The Simulation of the Opposing Fluxes of Latent Heat and CO<Subscript>2</Subscript> over Various Land-Use Types: Coupling a Gas Exchange Model to a Mesoscale Atmospheric Model

A mesoscale meteorological model (FOOT3DK) is coupled with a gas exchange model to simulate surface fluxes of CO₂ and H₂O under field conditions. The gas exchange model consists of a C3 single leaf photosynthesis sub-model and an extended big leaf (sun/shade) sub-model that divides the canopy into sunlit and shaded fractions. Simulated CO₂ fluxes of the stand-alone version of the gas exchange model correspond well to eddy-covariance measurements at a test site in a rural area in the west of Germany. The coupled FOOT3DK/gas exchange model is validated for the diurnal cycle at singular grid points, and delivers realistic fluxes with respect to their order of magnitude and to the general daily course. Compared to the Jarvis-based big leaf scheme, simulations of latent heat fluxes with a photosynthesis-based scheme for stomatal conductance are more realistic. As expected, flux averages are strongly influenced by the underlying land cover. While the simulated net ecosystem exchange is highly correlated with leaf area index, this correlation is much weaker for the latent heat flux. Photosynthetic CO₂ uptake is associated with transpirational water loss via the stomata, and the resulting opposing surface fluxes of CO₂ and H₂O are reproduced with the model approach. Over vegetated surfaces it is shown that the coupling of a photosynthesis-based gas exchange model with the land-surface scheme of a mesoscale model results in more realistic simulated latent heat fluxes.     

Aridic crusts and vein mineralisations in the playa Areg el Makrzene, South Tunisia

The playa Areg el Makrzene is situated in the north of the escarpment of the Djebel Rehach in southern Tunisia. It is characterised by more than 70 spring mounds which are bound to faults in the Triassic sandstone, and by (sub-) recent calcareous and iron hydroxide precipitations. The artesian spring water contains high amounts of Na⁺, Ca²⁺, Mg²⁺ and Cl⁻, SO₄²⁻, and HCO₃, shows slightly alkaline character and a temperature of 25 °C. The spring mounds consist of porous travertine (calcite), goethite, gypsum and of Na–Mg evaporites and are up to 10 m high. Few metres away from the springs the amorphous iron hydroxides have altered to badly ordered goethite and ferrihydrite and finally to well ordered goethite. The muddy precipitate has altered to hard crusts (calcrete, ferricrete). The source of the precipitated material is discussed.

The faults in the sandstone are filled with (hydr-)oxides of iron and manganese, e.g. with goethite, hollandite and pyrolusite. The amount of Mn-oxides may reach 60 mass%.     

Geologisches Profil durch den mittleren Abschnitt der Anden (Chile-Bolivia)

Zusammenfassung Mit Hilfe neuer Arbeiten wird ein geologischer Schnitt durch den über 900 km breiten mittleren Abschnitt der Anden von der pazifischen Küste Chiles bis in die subandine Zone Boliviens gegeben. Die Profile zeigen folgende Tatsachen: die Anden sind ein Falten-, aber kein Deckengebirge; die Vergenzen der Strukturen sind vorwiegend nach Osten gerichtet, der Anteil von Magmatiten seit dem Beginn der Trias ist bedeutend; die Anden werden von tiefgreifenden, jungen Gräben durchzogen, mit deren Einbruch eine enorme vulkanische Tätigkeit im Zusammenhang steht.Die Küstenkordillere Chiles hat eine andere tektonische Geschichte als die Hochkordilleren.Aus dem tektonischen Bild der mittleren Anden können unmittelbar keine Beweise für eine Westdrift Südamerikas abgeleitet werden.

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By aid of recent studies a geological section is made through the central part of the Andes (900 km large), from the pacific coast of Chile up to the subandine zone of Bolivia. The profiles show the following facts: the Andes are mountains with folds and not with nappes; the overturns of the structures are mainly turned eastward; the part of the ignecus rocks since the beginning of the Triassic is considerable; the Andes are interlaced by thorough-going trenches of younger date, whose appearance an enormous volcanic activity is connected.The tectonic history of the coastal Cordillera is different from that of the High Cordillera.A western drift of South America cannot be directly proved from the tectonic picture of the central Andes.

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Résumé A l'aide de nouvelles recherches on fait une coupe géologique à travers le secteur central des Andes (large de 900 km) de la côte pacifique de Chile jusque dans la zone subandienne de la Bolivie. Les profils montrent les faits suivants: les Andes sont des montagnes à plis, non pas à nappes; les déversements en sens inverse des structures vont principalement vers l'est; la part des roches éruptives depuis le commencement du Triassique est considérable; les Andes sont sillonnées par des fossés profondes et d'un origine récent; leur apparition est en rapport avec une énorme activité volcanique.La Cordillère à la côte de Chile a une histoire tectonique différente de celle de la Haute Cordillère.On ne peut pas dériver du tableau tectonique des Andes centrales la preuve d'une drift vers l'ouest de l'Amérique du Sud.

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The metamorphic evolution of migmatites from the Ötztal Complex (Tyrol,Austria) and constraints on the timing of the pre-Variscan high-T event in the Eastern Alps

Within the Ötztal Complex (ÖC), migmatites are the only geological evidence of the pre-Variscan metamorphic evolution, which led to the occurrence of partial anatexis in different areas of the complex. We investigated migmatites from three localities in the ÖC, the Winnebach migmatite in the central part and the Verpeil- and Nauderer Gaisloch migmatite in the western part. We determined metamorphic stages using textural relations and electron microprobe analyses. Furthermore, chemical microprobe ages of monazites were obtained in order to associate the inferred stages of mineral growth to metamorphic events. All three migmatites show evidence for a polymetamorphic evolution (pre-Variscan, Variscan) and only the Winnebach migmatite shows evidence for a P-accentuated Eo-Alpine metamorphic overprint in the central ÖC. The P-T data range from 670–750 °C and < 2.8 kbar for the pre-Variscan event, 550–650 °C and 4–7 kbar for the Variscan event and 430–490 °C and ca. 8.5 kbar for the P-accentuated Eo-Alpine metamorphic overprint. U-Th-Pb electron microprobe dating of monazites from the leucosomes from all three migmatites provides an average age of 441 ± 18 Ma, thus indicating a pervasive Ordovician-Silurian metamorphic event in the ÖC.     

Tonminerale in normalsedimenten,hydrothermal beeinflu\ten sedimenten und Erzschlämmen des Roten Meeres

From 14 deeps and other regions of the Red Sea totally 226 samples from 28 cores recovered during the VALDIVIA cruises (1971, 1972) were investigated according to their clay mineral content (<2μm resp. < 6.3 μm) after carbonate dissolution. Three facies groups are to distinguish:

1. normal sediments: dominance of chlorite, kaolinite, illite, small amounts of smectite and sepiolite. Two palygorskite types are present only in a few samples.
2. normal sediments with hydrothermal influence: clay mineral paragenesis similar like that of normal sediments; but increase of smectite and presence of goethite in each sample; partly small contents of talc.
3. heavy metal deposits: dominance of iron-bearing smectite, partly with amorphous components resp. pure ore mineral assemblages with authigenic silicates (talc, quartz, opal, chrysotile, sepiolite, palygorskite, chlorite).

Crystallinity of the clay and ore minerals is independent from sedimentary overburden. Sepiolite shows in small amounts a wide distribution; palygorskite₂ (d₁₁₀=11.3 Å) yields locally an increased concentration in the range of pteropod layers cemented by aragonite. The environment of ore deposits is characterized by iron-bearing smectite besides the ore minerals.