Tracing clinothem geometry and sediment pathways in the prograding Holocene Po Delta system through integrated core stratigraphy

Though clinothem geometry represents a key control on fluid flow in reservoir modelling, tracing clinothem boundaries accurately is commonly limited by the lack of sufficiently precise outcrop or subsurface data. This study shows that in basin systems with strongly heterogeneous compositional signatures, the combination of bulk-sediment geochemistry and benthic foraminiferal distribution can help identify clinothem architecture and generate realistic models of 3D deltaic upbuilding and evolution. Middle-late Holocene deposits in the Po Delta area form an aggradational to progradational parasequence set that reveals the complex interaction of W–E Po Delta progradation, S-directed longshore currents (from Alpine rivers) and Apennines rivers supply. Unique catchment lithologies (ophiolite rocks and dolostones) were used to delineate basin-wide geochemical markers of sediment provenance (Cr and Mg) and to assess distinctive detrital signatures. The geochemical characterization of cored intervals across different components of the sediment routing system enabled a direct linkage between clinothem growth, transport pathways and provenance mixing to be established. On the other hand, abrupt microfaunal variations at clinothem boundaries were observed to reflect the palaeoenvironmental response to sharp changes in sediment flux and fluvial influence. This study documents the ability of an integrated geochemical and palaeoecological approach to delineate three distinct sources (Po, Alps and Apennines) that contributed to coastal progradation and to outline the otherwise lithologically cryptic geometries of clinothems that using conventional sedimentological methods it would be virtually impossible to restore.     

TIMS measurements of Ra and Ra in the Gulf of Lion, an attempt to quantify submarine groundwater discharge

Submarine groundwater discharge (SGD) is now recognized as an important pathway for water and chemical species fluxes to the coastal ocean. In order to determinate SGD to the Gulf of Lion (France), we measured the activities of ²²⁶Ra and ²²⁸Ra by thermal ionization mass spectrometry (TIMS) in coastal waters and in the deep aquifer waters of the Rhone deltaic plain after pre-concentration of radium by MnO₂. Compared to conventional counting techniques, TIMS requires lower quantities of water for the analyses, and leads to higher analytical precision. Radium isotopes were thus measured on 0.25–2 L water samples containing as little as 20 fg of ²²⁶Ra and 0.2–0.4 fg of ²²⁸Ra with precision equal to 2%. We demonstrate that coastal surface waters samples are enriched in ²²⁶Ra and ²²⁸Ra compared to the samples further offshore. The high precision radium measurements display a small but significant ²²⁶Ra and ²²⁸Ra enrichment within a strip of circa 30 km from the coast. Radium activities decrease beyond this region, entrained in the northern current along the shelf break or controlled by eddy diffusion. The radium excess in the first 30 km cannot be accounted for by the river nor by the early diagenesis. The primary source of the radium enrichment must therefore be ascribed to the discharge of submarine groundwater. Using a mass-balance model, we estimated the advective fluxes of ²²⁶Ra and ²²⁸Ra through SGD to be 5.2 × 10¹⁰ and 21 × 10¹⁰ dpm/d respectively. The ²²⁶Ra activities measured in the groundwater from the Rhone deltaic plain aquifer are comparable to those from other coastal groundwater studies throughout the world. By contrast, ²²⁸Ra activities are higher by up to one order of magnitude. Taking those groundwater radium activities as typical of the submarine groundwater end-member, a minimum volume of 0.24–4.5 × 10¹⁰ l/d is required to support the excess radium isotopes on the inner shelf. This has to be compared with the average rivers water runoff of 15.4 × 10¹⁰ l/d during the study period (1.6 to 29% of the river flow).     

Reduction of Multiphase Atmospheric Chemistry

The aim of this article is to investigate the dynamical behaviour ofmultiphase atmospheric chemical mechanisms. Reducing procedures areapplied to a multiphase chemical box model including gas-phasereactions, aqueous-phase reactions and interfacial mass transfer. The lumping of species is computed in an automatic wayusing an efficient algorithm (apla). The computed lumped species arerelated to the fast behaviour of chemical and microphysical processessuch as Chapman cycle, ionic dissociations within the cloud drops andinterfacial Henry's equilibria. Depending on some parameters (liquidwater content, droplet radius) mixed lumped species (including both phases) may also becomputed. We show the existence of hierarchical reduced models due to the existence ofmultiple timescales. We use a special algorithm (dan2) in order tosolve the reduced models. Such models are accurate and the relative errorremains under the threshold of 1%. The speed-up is up to a factor 5comparedwith a fully implicit method (Gear) for the same accuracy. The key pointis that it provides a good qualitative understanding for the behaviourof the kinetic scheme.     

Magnetic fabric of Late Miocene clay-rich sediments from the southern Pannonian basin

The magnetic fabric of Late Miocene sediments from the southern Pannonian basin was studied on oriented samples collected from 19 geographically distributed localities. All of them are characterized by near-horizontal magnetic foliation plane after tilt correction, indicating weak deformation. Well-developed lineations were observed for 16 localities, which are interpreted as due to compressional/transpressional deformation, except from three localities, where the fabric must have been formed in an extensional setting. Comparison between the orientation of the map-scale folds and faults and magnetic lineation directions shows that magnetic lineation is either related to NNE-SSW directed compression, leading to the formation of folds or it can be connected to NW–SE or NNE-SSW trending dextral faults.     

Complete Trace Elemental Characterisation of Granitoid (USGS G-2, GSP-2) Reference Materials by High Resolution Inductively Coupled Plasma-Mass Spectrometry

The United States Geological Survey granitic and granodioritic reference materials G‐2 and GSP‐2 were decomposed in high‐pressure bombs using both HF‐HNO₃ and HF‐HNO₃‐HClO₄ in order to evaluate the feasibility of characterising the entire suite of geologically relevant trace elements through direct analysis with a high‐resolution inductively coupled plasma‐mass spectrometer (HR‐ICP‐MS). The digested samples were diluted to the appropriate levels and analysed at low, medium and high resolution depending on the required sensitivity and potential interferences for each element. Memory effects during analysis of the high field strength elements (HFSE) were negligible when analysed using an all‐Teflon, uncooled sample introduction system and combined with adequate wash times with 4% v/v aqua regia + 0.5% v/v HF between samples. The concentration of the remaining lithophile elements was determined with a conventional, cooled, Scott‐type spray chamber using a wash solution of 1% v/v HNO₃. Total procedural blanks contributed between 0.01 to 0.5% to final sample concentrations and blank subtractions were typically unnecessary. Abundances for Li, Hf, Ba, Zr, Ga, Rb, Sr, La, Ce, Th and U were systematically higher, while those for the heavy rare earth elements (HREEs), Cu and Y were systematically lower in this study compared to USGS values for G‐2 and GSP‐2. This is likely to be related to, respectively, higher recoveries from more efficient digestion of refractory phases (i.e., zircon, tourmaline), and better resolution of interferences when using a HR‐ICP‐MS. Sample digestion experiments also showed that perchloric acid digestion in high pressure bombs resulted in superior recoveries and better precision for the bulk of the trace elements analysed. The concentration of the remaining elements overlapped within uncertainty with recommended reference values and with values determined in other studies using isotope‐dilution TIMS, ICP‐MS and XRF. Concentrations for the elements Cd, Sn, Sb, Ta, Bi, Tb, Ni and Mo are also reported for G‐2 and GSP‐2 reference materials. Our study shows therefore that it is feasible to determine thirty‐nine geologically relevant trace elements accurately and directly in granitoid sample digests when using a HR‐ICP‐MS, thereby negating the need for ion exchange or isotopic spiking.     

After the peak water: the increasing influence of rock glaciers on alpine river systems

Human‐accelerated climate change is quickly leading to glacier‐free mountains, with consequences for the ecology and hydrology of alpine river systems. Water origin (i.e., glacier, snowmelt, precipitation, and groundwater) is a key control on multiple facets of alpine stream ecosystems, because it drives the physico‐chemical template of the habitat in which ecological communities reside and interact and ecosystem processes occur. Accordingly, distinct alpine stream types and associated communities have been identified. However, unlike streams fed by glaciers (i.e., kryal), groundwater (i.e., krenal), and snowmelt/precipitation (i.e., rhithral), those fed by rock glaciers are still poorly documented. We characterized the physical and chemical features of these streams and investigated the influence of rock glaciers on the habitat template of alpine river networks. We analysed two subcatchments in a deglaciating area of the Central European Alps, where rock glacier‐fed, groundwater‐fed, and glacier‐fed streams are all present. We monitored the spatial, seasonal, and diel variability of physical conditions (i.e., water temperature, turbidity, channel stability, and discharge) and chemical variables (electrical conductivity, major ions, and trace element concentrations) during the snowmelt, glacier ablation, and flow recession periods of two consecutive years. We observed distinct physical and chemical conditions and seasonal responses for the different stream types. Rock glacial streams were characterized by very low and constant water temperatures, stable channels, clear waters, and high concentrations of ions and trace elements that increased as summer progressed. Furthermore, one rock glacier strongly influenced the habitat template of downstream waters due to high solute export, especially in late summer under increased permafrost thaw. Given their unique set of environmental conditions, we suggest that streams fed by thawing rock glaciers are distinct river habitats that differ from those normally classified for alpine streams. Rock glaciers may become increasingly important in shaping the hydroecology of alpine river systems under continued deglaciation.     

Exploration of the Outer Solar System by Stellar Occultations

Stellar occultations are a powerful method for exploring the outer solar system, where faintness and small angular diameters prevent us from exploring in details objects like satellites, rings, or Kuiper Belt Objects. Unique kilometric spatial resolutions or better can be reached through that method. Occultations usually observe identified objects whose trajectory is known, though the occultation events might be difficult to predict. It is also possible to explore populations of small objects populations whose density in the sky plane is large enough to search for serendipitous occultations. Various instrumental methods exist for both predicted and serendipitous occultation, both needing fast photometric recordings of target stars.     

High Spectral Resolution Observation of Decimetric Radio Spikes Emitted by Solar Flares – First Results of the Phoenix-3 Spectrometer

A new multichannel spectrometer, Phoenix-3, is in operation having capabilities to observe solar flare radio emissions in the 0.1?–?5 GHz range at an unprecedented spectral resolution of 61.0 kHz with high sensitivity. The present setup for routine observations allows measuring circular polarization, but requires a data compression to 4096 frequency channels in the 1?–?5 GHz range and to a temporal resolution of 200 ms. First results are presented by means of a well observed event that included narrowband spikes at 350?–?850 MHz. Spike bandwidths are found to have a power?–?law distribution, dropping off below a value of 2 MHz for full width at half maximum (FWHM). The narrowest spikes have a FWHM bandwidth less than 0.3 MHz or 0.04% of the central frequency. The smallest half-power increase occurs within 0.104 MHz at 443.5 MHz, which is close to the predicted natural width of maser emission. The spectrum of spikes is found to be asymmetric, having an enhanced low-frequency tail. The distribution of the total spike flux is approximately an exponential.     

Monitoring the Dynamics of the Ionosphere–Plasmasphere System by Ground-Based ULF Wave Observations

Cross-spectral analysis of ULF wave measurements recorded at ground magnetometer stations closely spaced in latitude allows accurate determinations of magnetospheric field line resonance (FLR) frequencies. This is a useful tool for remote sensing temporal and spatial variations of the magnetospheric plasma mass density. The spatial configuration of the South European GeoMagnetic Array (SEGMA, 1.56 <  L <  1.89) offers the possibility to perform such studies at low latitudes allowing to monitor the dynamical coupling between the ionosphere and the inner plasmasphere. As an example of this capability we present the results of a cross-correlation analysis between FLR frequencies and solar EUV irradiance (as monitored by the 10.7-cm solar radio flux F10.7) suggesting that changes in the inner plasmasphere density follow the short-term (27-day) variations of the solar irradiance with a time delay of 1–2 days. As an additional example we present the results of a comparative analysis of FLR measurements, ionospheric vertical soundings and vertical TEC measurements during the development of a geomagnetic storm.