A review of undulated sediment features on Mediterranean prodeltas: distinguishing sediment transport structures from sediment deformation

Most Mediterranean prodeltas show undulated sediment features on the foresets of their Holocene wedges. These features have been described all along the Mediterranean for the last 30 years and interpreted as either soft sediment deformation and incipient landsliding, and more recently, as sediment transport structures. We perform a review and detailed analysis of these undulated sediment features using ultrahigh-resolution seismic and bathymetric data as well as geotechnical information and hydrodynamic time series and hydrographic transects. In this study we show that the characteristics of the sediment undulations (configuration of the reflections down section and between adjacent undulations and overall morphologic characteristics) are incompatible with a genesis by sediment deformation alone and do not show evidence of sediment deformation in most cases. Various processes in the benthic boundary layer can be invoked to explain the variety of features observed in the numerous areas displaying sediment undulations.     

Contrasting interactions of sodium and potassium with H<Subscript>2</Subscript>O in haplogranitic liquids and glasses at 200 MPa from hydration–diffusion experiments

This study examines hydration–diffusion in the metaluminous haplogranite system at 200 MPa H₂O and 800–300°C. At 800°C hydration is accompanied by melting and uphill diffusion of sodium from anhydrous glass toward the region of hydration and melting, whereas potassium diffuses away from the hydration front and into anhydrous glass. Silicon and aluminum are simply diluted upon hydration. There is no change in molecular Al/(Na + K) throughout the entire hydration-diffusion aureole and, therefore, (1) there is no loss of alkalis to the vapor, and (2) K migrates to replace Na in order to maintain local charge balance required by ^IVAl. Alkali diffusion occurs over a viscosity contrast from 10^4.1 Pa s in hydrous liquid to 10^11.8–10^13.5 Pa s in anhydrous glass. From these results, we interpret that: (1) Na is structurally or energetically favored over K as a charge-balancing cation for ^IVAl in hydrous granitic liquids, whereas the opposite behavior has been observed for anhydrous melts, and (2) the diffusion of alkalis through silicate melts is largely independent of viscosity. Results from 600°C are similar to those at 800°C, but hydration at 300°C involves a loss of Na and concomitant increase in molar Al/(Na + K) in the hydration zone due to hydrogen-alkali exchange between fluid and glass. Hydration behavior at 400°C is transitional between those at 300°C and 600°C, suggesting that the change in hydration mechanism occurs near the glass transition.     

Diet of Phycis blennoides (Gadidae) in Relation to Fish Size and Season in the Western Mediterranean (Spain)

Abstract. Despite its commercial value, little is known about the feeding ecology of the greater forkbeard, Phycis blennoides (Brünnich 1768). The stomach contents of 2631 greater forkbeard were taken at monthly intervals off the coast of the Gulf of Valencia (western Mediterranean). They were examined in order to assess the diet and to determine the fish size- and season-related dietary variation of the species. Prey items were identified to the lowest taxonomic level possible. The basic food consisted of epibenthic species, mostly Decapoda, Mysidacea and Teleostei. A change in food composition based on fish size was observed and seasonal variation in diet was also recorded. The food overlap analysis indicated a high convergence in diet among similar size groups.     

The impact of dredge-fill on Posidonia oceanica seagrass meadows: regression and patterns of recovery

Posidonia oceanica meadows can be severely damaged by dredge-fill operations. We report on the construction of gas pipelines that occurred between 1981 and 1993 in SW Sicily, Italy. A large portion of the meadow was mechanically removed, and the excavated trench was filled with a mosaic of substrates, ranging from sand to consolidated rock debris. Meadow loss and recovery were quantified over 7 years after the end of operations. We recorded an overall loss of 81.20 ha of meadow. Substrate strongly affected recovery as the percent cover by P. oceanica consistently increased on calcareous rubble, reaching values of 44.37 ± 3.05% in shallow sites after 7 years, whereas no significant increase occurred on other substrates. As in the Mediterranean Sea exploitation of coastal areas continues to grow with consequent impacts on P. oceanica meadows, this case study illustrates how artificial rubble-like materials could be employed to support the restoration of damaged meadows.     

Cotton Fiber/ZrO2, A New Material for Adsorption of Cr(VI) Ions in Water

The natural cotton fiber was used to synthesize an anion exchange, containing ZrO₂ film on its surface, NCFZC (natural cotton fiber/ZrO₂ composite). This anion exchanger was produced by the reaction of the zirconium oxychloride and hydroxyl groups on surface of the natural cotton fiber. The material was used for Cr(VI) ions adsorption studies. Adsorption equilibrium time and optimum pH for Cr(VI) adsorption were found to be 6 h and 4.0, respectively. The Langmuir and Temkin isotherms were used to models adsorption equilibrium data. The adsorption capacity of NCFZC was found to be 1.33 mmol/g. Kinetic studies showed that the rate of adsorption of Cr(VI) on NCFZC obeyed a pseudo‐second‐order kinetic model.     

POLARIX: a pathfinder mission of X-ray polarimetry

Since the birth of X-ray astronomy, spectral, spatial and timing observation improved dramatically, procuring a wealth of information on the majority of the classes of the celestial sources. Polarimetry, instead, remained basically unprobed. X-ray polarimetry promises to provide additional information procuring two new observable quantities, the degree and the angle of polarization. Polarization from celestial X-ray sources may derive from emission mechanisms themselves such as cyclotron, synchrotron and non-thermal bremsstrahlung, from scattering in aspheric accreting plasmas, such as disks, blobs and columns and from the presence of extreme magnetic field by means of vacuum polarization and birefringence. Matter in strong gravity fields and Quantum Gravity effects can be studied by X-ray polarimetry, too. POLARIX is a mission dedicated to X-ray polarimetry. It exploits the polarimetric response of a Gas Pixel Detector, combined with position sensitivity, that, at the focus of a telescope, results in a huge increase of sensitivity. The heart of the detector is an Application-Specific Integrated Circuit (ASIC) chip with 105,600 pixels each one containing a full complete electronic chain to image the track produced by the photoelectron. Three Gas Pixel Detectors are coupled with three X-ray optics which are the heritage of JET-X mission. A filter wheel hosting calibration sources unpolarized and polarized is dedicated to each detector for periodic on-ground and in-flight calibration. POLARIX will measure time resolved X-ray polarization with an angular resolution of about 20 arcsec in a field of view of 15 × 15 arcmin and with an energy resolution of 20% at 6 keV. The Minimum Detectable Polarization is 12% for a source having a flux of 1 mCrab and 10⁵ s of observing time. The satellite will be placed in an equatorial orbit of 505 km of altitude by a Vega launcher. The telemetry down-link station will be Malindi. The pointing of POLARIX satellite will be gyroless and it will perform a double pointing during the earth occultation of one source, so maximizing the scientific return. POLARIX data are for 75% open to the community while 25% + SVP (Science Verification Phase, 1 month of operation) is dedicated to a core program activity open to the contribution of associated scientists. The planned duration of the mission is one year plus three months of commissioning and SVP, suitable to perform most of the basic science within the reach of this instrument. A nice to have idea is to use the same existing mandrels to build two additional telescopes of iridium with carbon coating plus two more detectors. The effective area in this case would be almost doubled.     

Magnetic and structural study of the Eaux-Chaudes intrusion: understanding the Variscan deformation in the Western Axial Zone (Pyrenees)

The present study provides new magnetic and microstructural data for the Eaux-Chaudes granodioritic massif (Western Axial Zone, Pyrenees) and contributes to the understanding of its geometry, internal structure and emplacement mechanism. Moreover, the geological cross-sections and field data allow to reconstruct the evolution of the whole area from Variscan to Alpine times and to integrate the emplacement of the igneous body in the context of the Variscan orogeny. The Eaux-Chaudes pluton (301?±?9?Ma) is mainly composed by granodiorite, describing a normal compositional zoning and an approximately concentric arrangement that is consistent with the zonation of the low-field magnetic susceptibility. Magnetic foliation is subhorizontal in the inner part of the intrusion and becomes parallel to the petrographical contacts along pluton margins, roughly describing the geometry of the intrusion. Magnetic lineations are dominantly subhorizontal, with E–W to ENE–WSW directional maximum. The general parallelism between Variscan structures of the host rock and the geometry and magmatic fabric of the intrusion reveals a late syn-Variscan emplacement. The tectonic regime registered during magma emplacement is in agreement with an N–S shortening and an E–W stretching direction, consistent with the transpressive regime deduced for other Pyrenean intrusions. Alpine overprint produced a slight tilting in the southern part of the intrusion, but it can be considered that the original Variscan structure is basically unchanged.     

High-pressure melting relations in Fe-C-S systems: Implications for formation, evolution, and structure of metallic cores in planetary bodies

We present new high-pressure temperature experiments on melting phase relations of Fe-C-S systems with applications to metallic core formation in planetary interiors. Experiments were performed on Fe-5 wt% C-5 wt% S and Fe-5 wt% C-15 wt% S at 2-6 GPa and 1050-2000 °C in MgO capsules and on Fe-13 wt% S, Fe-5 wt% S, and Fe-1.4 wt% S at 2 GPa and 1600 °C in graphite capsules. Our experiments show that: (a) At a given P-T, the solubility of carbon in iron-rich metallic melt decreases modestly with increasing sulfur content and at sufficiently high concentration, the interaction between carbon and sulfur can cause formation of two immiscible melts, one rich in Fe-carbide and the other rich in Fe-sulfide. (b) The mutual solubility of carbon and sulfur increases with increasing pressure and no super-liquidus immiscibility in Fe-rich compositions is likely expected at pressures greater than 5-6 GPa even for bulk compositions that are volatile-rich. (c) The liquidus temperature in the Fe-C-S ternary is significantly different compared to the binary liquidus in the Fe-C and Fe-S systems. At 6 GPa, the liquidus of Fe-5 wt% C-5 wt% S is 150-200 °C lower than the Fe-5 wt% S. (d) For Fe-C-S bulk compositions with modest concentration of carbon, the sole liquidus phase is iron carbide, Fe₃C at 2 GPa and Fe₇C₃ at 6 GPa and metallic iron crystallizes only with further cooling as sulfur is concentrated in the late crystallizing liquid. Our results suggest that for carbon and sulfur-rich core compositions, immiscibility induced core stratification can be expected for planets with core pressure less than ∼6 GPa. Thus planetary bodies in the outer solar system such as Ganymede, Europa, and Io with present day core-mantle boundary (CMB) pressures of ∼8, ∼5, and 7 GPa, respectively, if sufficiently volatile-rich, may either have a stratified core or may have experienced core stratification owing to liquid immiscibility at some stage of their accretion. A similar argument can be made for terrestrial planetary bodies such as Mercury and Earth’s Moon, but no such stratification is predicted for cores of terrestrial planets such as Earth, Venus, and Mars with the present day core pressure in the order ?136 GPa, ?100 GPa, and ?23 GPa. (e) Owing to different expected densities of Fe-rich (and carbon-bearing) and sulfur-rich metallic melts, their settling velocities are likely different; thus core formation in terrestrial planets may involve rain of more than one metallic melt through silicate magma ocean. (f) For small planetary bodies that have core pressures <6 GPa and have a molten core or outer core, settling of denser carbide-rich liquid or flotation of lighter, sulfide-rich melt may contribute to an early, short-lived geodynamo.     

Late Pleistocene highstand and recession of a small, high-altitude pluvial lake, Jakes Valley, central Great Basin, USA

Models of factors controlling late Pleistocene pluvial lake-level fluctuations in the Great Basin are evaluated by dating lake levels in Jakes Valley. “Jakes Lake” rose to a highstand at 13,870 ± 50 ¹⁴C Yr B.P., receded to a stillstand at 12,440 ± 50 ¹⁴C yr B.P., and receded steadily to desiccation thereafter. The Jakes Lake highstand is roughly coincident with highstands of lakes Bonneville, Lahontan and Russell. The rise to highstand and recession of Jakes Lake were most likely controlled by a storm track steered by the polar jet stream. The final stillstand of Jakes Lake helps constrain timing of northward retreat of the polar jet stream during the Pleistocene-Holocene transition.     

The Cabo Frio upwelling overrides geographical patterns in the population dynamics of the shrimp Artemesia longinaris Spence Bate, 1888 (Decapoda: Penaeidae)

Upwelling areas are among the most productive ecosystems on the planet, influencing the biology of marine organisms. This study investigated the population dynamics of the shrimp Artemesia longinaris in two regions in southeastern Brazil, one inside (Macaé—Rio de Janeiro State) and one outside (Ubatuba—State of São Paulo) the Cabo Frio upwelling area. The aim was to verify the influence of the upwelling phenomenon on the abundance, growth, longevity, size of sexual maturity, and reproductive period of the species. In total, 188,902 individuals were captured at Macaé and 3,461 at Ubatuba. Individuals captured at Macaé showed larger maximum size, higher longevity, and slower growth rate, besides reaching sexual maturity at larger sizes than at Ubatuba. Continuous reproduction was observed in both regions, with juvenile recruitment peaks in spring and summer. Local conditions observed at Macaé were influenced by the Cabo Frio upwelling zone, characterized by productive and cooler waters that are around 20°C during most of the year. The upwelling phenomenon is probably the main factor influencing the population parameters studied here, changing the geographic patterns previously observed for the variation of these parameters in A. longinaris.