Paleostress field reconstruction in the Oslo region

The geodynamic history of a region is archived in its geologic record which, in turn, may reflect deformation patterns that causally can be related to certain configurations of paleostresses. In the Oslo Region, the exposed geological record ranges from Precambrian high-grade metamorphic rocks through Cambro-Silurian sedimentary rocks to Permo-Carboniferous sedimentary and magmatic rocks, the latter being related to the development of the Oslo rift system. We investigate the kinematics of outcrop-scale faults to derive the diversity of paleostress states responsible for the observed strain. For this purpose, we combine different graphical and numerical approaches to separate heterogeneous fault-slip data sets and estimate the associated reduced stress tensors. A reduced stress tensor consists of the directions of the three principal stress axes with σ₁ ≥ σ₂ ≥ σ₃ and the ratio of principal stress differences, R = (σ₂ − σ₃)/(σ₁ − σ₃).     

Colloidal Control on the Distribution of Rare Earth Elements in Shallow Groundwaters

A 7-year monitoring period of rare earth element (REE) concentrations and REE pattern shapes was carried out in well water samples from a 450 m long transect setup in the Kervidy/Coët-Dan experimental catchment, France. The new dataset confirms systematic, topography-related REE signatures and REE concentrations variability but challenges the validity of a groundwater mixing hypothesis. Most likely, this is due to REE preferential adsorption upon mixing. However, the coupled mixing–adsorption mechanism still fails to explain the strong spatial variation in negative Ce anomaly amplitude. A third mechanism—namely, the input into the aquifer of REE-rich, Ce anomaly free, organic colloids—is required to account for this variation. Ultrafiltration results and speciation calculations made using Model VI agree with this interpretation. Indeed, the data reveal that Ce anomaly amplitude downslope decrease corresponds to REE speciation change, downhill groundwaters REE being mainly bound to organic colloids. Water table depth monitoring shows that the colloid source is located in the uppermost, organic-rich soil horizons, and that the colloid input occurs mainly when water table rises in response to rainfall events. It appears that the colloids amount that reaches groundwater increases downhill as the distance between soil organic-rich horizons and water table decreases. Topography is, therefore, the ultimate key factor that controls Ce anomaly spatial variability in these shallow groundwaters. Finally, the <0.2 μm REE fraction ultimately comes from two solid sources in these groundwaters: one located in the deep basement schist; another located in the upper, organic-rich soil horizon.     

Early detection of large eruptions at Piton de La Fournaise volcano (La Réunion Island): Contribution of a distant tiltmeter station

We report a compilation of data recorded at a distant tiltmeter station (RER) during recent episodes of dyke emplacement and eruption (2003–2007) at Piton de La Fournaise volcano (La Réunion Island). This sensitive station provides useful information for evaluating the extent of deformation. Distinct responses of this station were recorded based on the eruption type. Dykes feeding summit eruptions did not significantly influence the RER tiltmeter signals, whereas dykes feeding large distal eruptions (with vents located more than 4 km from the summit) generated up to 1.4 μrad of tilt, an amplitude 2 to 4 times greater than for proximal eruptions (0.3–0.7 μrad) on the flanks of the summit cone. The distinct tilt amplitude is directly linked to the location, depth, and volume of the dyke. Comparison with summit tiltmeters reveals that up to one-third to half of the RER tilt signal associated to dyke propagation is recorded when the dyke is still below the summit crater. Thus, before large distal eruptions, more than 0.5 μrad of tilt is recorded in less than 20 min when the dyke is below the summit crater (i.e. a few minutes/hours before the beginning of the eruption). We can thus propose for the RER station a threshold value of 0.5 μrad which, when reached as a dyke rises beneath the summit crater, suggests a high likelihood of a large distal eruption. The distant RER tiltmeter station thus appears to be a powerful tool for forecasting the type of eruption that is likely to occur, and can contribute to the early detection of large distal eruptions at Piton de La Fournaise, which are the most dangerous to inhabitants. For volcano monitoring, installation of high precision distant tiltmeters along the lower slopes of a volcano may provide warnings of large eruptions with enough lead time to allow for short-term hazards mitigation efforts.     

Adsorption of Cationic Dyes from Aqueous Solution by Termite Feces,a Non‐Conventional Adsorbent

The adsorption of three cationic dyes (rhodamine B, RB; crystal violet, CV; and malachite green, MG) onto termite feces, a low‐cost adsorbent, was investigated. The adsorbent was characterized by IR spectroscopy, point of zero charge measurement, and the Boehm titration method. The adsorption follows the pseudo‐second‐order kinetic model and the Langmuir–Freundlich isotherm with maximum adsorption capacities of 95.53 mg g^?1 (RB), 75.71 mg g^?1 (CV), and 44.78 mg g^?1 (MG). The study of thermodynamics showed that the adsorption is a spontaneous and endothermic process. This works suggest that termite feces can be used as a new low‐cost adsorbent for cationic dye removal.     

Jellyfish diversity and distribution patterns in the tropical Southwestern Atlantic

Jellyfish are often the most prominent components of plankton, with severe consequences for fisheries and tourism. However, in tropical regions, there is much uncertainty about these consequences due to the lack of basic data. Our objective was to improve the knowledge about jellyfish in the Western Atlantic, with an emphasis on understanding diversity, abundance, and distribution patterns. Samples were collected at 34 stations in 1995 using a 300‐μm‐mesh Bongo net. The 21 species identified belonged to Hydromedusae (11), Siphonophora (nine), and Scyphomedusae (one). The overall mean density was low (5.2 ± 5.3 ind. m^?3). Total Hydromedusae biomass was 130.86 mg C m^?3, and total Siphonophora biomass was 19.04 mg C m^?3. Chelophyes appendiculata (Eschscholtz, 1829) was the most frequent species captured in the oceanic samples, and Aglaura hemistoma (Péron & Lesueur, 1810) was the most common in the neritic region. The latter species is sometimes characterized as a bloom associated with the most polluted and eutrophic river plumes. The main role of jellyfish species in the area is as a higher‐order carnivore. A cross‐shelf significant difference (P < 0.05) was registered, with higher species numbers in oceanic regions and higher densities and biomass in neritic regions.     

Analysis of Different Solar Spectral Irradiance Reconstructions and Their Impact on Solar Heating Rates

Proper numerical simulation of the Earth’s climate change requires reliable knowledge of solar irradiance and its variability on different time scales, as well as the wavelength dependence of this variability. As new measurements of the solar spectral irradiance have become available, so too have new reconstructions of historical solar irradiance variations, based on different approaches. However, these various solar spectral irradiance reconstructions have not yet been compared in detail to quantify differences in their absolute values, variability, and implications for climate and atmospheric studies. In this paper we quantitatively compare five different reconstructions of solar spectral irradiance changes during the past four centuries, in order to document and analyze their differences. The impact on atmosphere and climate studies is discussed in terms of the calculation of short wave solar heating rates.     

Interpretation in terms of gravity waves of structures observed at the mesopause level by photogrammetry and lidar

Experiment data of the vertical distribution of sodium density measured by lidar are compared with the horizontal structures observed by photogrammetry on the sodium emissive layer. The gravity wave induced variations seen in the vertical distribution are used to define a 2-dimensional model of the layer, which is shown to explain the observed horizontal patterns. It is strongly suggested that the structures currently seen on OH can be also related to gravity waves and that their sporadic occurrence in specific angular directions is explained by the wave characteristic and by wave or wind induced chemistry.     

The Solar Spectral Irradiance as a Function of the Mg <Emphasis Type="SmallCaps">ii</Emphasis> Index for Atmosphere and Climate Modelling

We present a new method to reconstruct the solar spectrum irradiance in the Ly α – 400 nm region, and its variability, based on the Mg ii index and neutron-monitor measurements. Measurements of the solar spectral irradiance available in the literature have been made with different instruments at different times and different spectral ranges. However, climate studies require harmonised data sets. This new approach has the advantage of being independent of the absolute calibration and aging of the instruments. First, the Mg ii index is derived using solar spectra from Ly α (121 nm) to 410 nm measured from 1978 to 2010 by several space missions. The variability of the spectra with respect to a chosen reference spectrum as a function of time and wavelength is scaled to the derived Mg ii index. The set of coefficients expressing the spectral variability can be applied to the chosen reference spectrum to reconstruct the solar spectra within a given time frame or Mg ii index values. The accuracy of this method is estimated using two approaches: direct comparison with particular cases where solar spectra are available from independent measurements, and calculating the standard deviation between the measured spectra and their reconstruction. From direct comparisons with measurements we obtain an accuracy of about 1 to 2%, which degrades towards Ly α. In a further step, we extend our solar spectral-irradiance reconstruction back to the Maunder Minimum introducing the relationship between the Mg ii index and the neutron-monitor data. Consistent measurements of the Mg ii index are not available prior to 1978. However, we remark that over the last three solar cycles, the Mg ii index shows strong correlation with the modulation potential determined from the neutron-monitor data. Assuming that this correlation can be applied to the past, we reconstruct the Mg ii index from the modulation potential back to the Maunder Minimum, and obtain the corresponding solar spectral-irradiance reconstruction back to that period. As there is no direct measurement of the spectral irradiance for this period we discuss this methodology in light of the other proposed approaches available in the literature. The use of the cosmogenic-isotope data provides a major advantage: it provides information about solar activity over several thousands years. Using technology of today, we can calibrate the solar irradiance against activity and thus reconstruct it for the times when cosmogenic-isotope data are available. This calibration can be re-assessed at any time, if necessary.     

Petrogenesis of A-type Granitoids from the Alto Moxoto and Alto Pajeu Terranes of the Borborema Province, ne Brazil: Constraints from Geochemistry and Isotopic Composition

A-type granitoids (512 Ma) either intruded into Paleoproterozoic gneiss of the Alto Moxoto Terrane (Prata Complex and Serra da Engabelada Pluton) or into Early Neoproterozoic metavolcanic metasedimentary sequence of the Alto Pajeu Terrane (Serrote Santo Antonio Pluton), constitute a small proportion of Brasiliano (= Pan-African) granitoids in the Central Tectonic Domain of the Borborema Province, northeastern Brazil. The Prata Complex consists of syenogranites, monzogranites, mafic enclaves of diorites and norites. The felsic and mafic members are not genetically related through fractionation. Mingling and mixing were extensive processes within the Prata Complex. The granites evolution appears to have involved fractionation of alkali feldspar, biotite, apatite and sphene without significant wall-rock assimilation. The Serra da Engabelada and Serrote Santo Antonio plutons consist of biotite syenogranites, with rare mafic enclaves. The studied granitoids are dominantly metaluminous, characterized by Fe-rich biotite and Fe-hornblende. High total alkalis, Y, Nb and REE and low CaO, MgO and Sr abundances and high FeO/(FeO+MgO) ratios characterize these granitoids. Chondrite-normalized REE patterns show enriched LREE, moderate to strong negative Eu anomalies and more or less flat heavy REE.The studied granitoids and diabase from dykes and enclaves show negative eNd _(512Ma) values (-14 to -10), high incompatible elements such as LILE, HFSE and REE, suggesting important contribution of Paleoproterozoic crust. The origin of the granites is thought to have involved partial melting of granodioritic or tonalitic lower crust. Such isotopic signature of the diabase from the dykes also reflects a Paleoproterozoic enriched lithospheric mantle in the area. The intrusion of the studied granitoids contemporary with sub-volcanic bimodal magmatism and deposition of many Cambrian "pull-apart" basins in the north and central tectonic Domain of the Borborema Province, suggest intrusion during post-tectonic relaxation of the Brasiliano orogeny following the assembly of West Gondwana.