Structure formation in the rift zones and in the tranvers offset of the spreading axes: Results of physical modeling

The paper presents the results of experimental modeling of the specific features in the structure formation within the rift zones and also within lateral displacements of the spreading axes such as transform faults and nontransform displacements. The experiments were conducted on materials consisting of liquid and solid hydrocarbons; the similarity conditions were taken into account.     

Field-aligned currents and parallel electric field potential drops at Mars. Scaling from the Earth’ aurora

The observations of electron inverted ‘V’ structures by the MGS and MEX spacecraft, their resemblance to similar events in the auroral regions of the Earth, and the discovery of strong localized magnetic field sources of the crustal origin on Mars, raised hypotheses on the existence of Martian aurora produced by electron acceleration in parallel electric fields. Following the theory of this type of structures on Earth we perform a scaling analysis to the Martian conditions. Similar to the Earth, upward field-aligned currents necessary for the generation of parallel potential drops and peaked electron distributions can arise, for example, on the boundary between ‘closed’ and ‘open’ crustal field lines due to shears of the flow velocity of the magnetosheath or magnetospheric plasmas. A steady-state configuration assumes a closure of these currents in the Martian ionosphere. Due to much smaller magnetic fields as compared to the Earth case, the ionospheric Pedersen conductivity is much higher on Mars and auroral field tubes with parallel potential drops and relatively small cross scales to be adjusted to the scales of the localized crustal patches may appear only if the magnetosphere and ionosphere are decoupled by a zone with a strong E_∥. Another scenario suggests a periodic short-circuit of the magnetospheric electric fields by a coupling with the conducting ionosphere.     

Suprathermal electron fluxes on the nightside of Mars: ASPERA-3 observations

Recently aurora-type UV emissions were discovered on the nightside of Mars [Bertaux, J.-L., Leblanc, F., Witasse, O., et al., 2005. Discovery of an aurora on Mars. Nature 439, doi:10.1038/nature03603]. It was suggested that these emissions are produced by suprathermal electrons with energies of tens of eV, rather than by the electrons with spectra peaked above 100 eV [Leblanc, F., Witasse, O., Winningham J., et al., 2006. Origin of the martian aurora observed by spectroscopy for investigation of characteristics of the atmosphere of Mars (SPICAM) onboard Mars Express. J. Geophys. Res. 111, A09313, doi:10.1029/2006JA011763]. In this paper we present observations of fluxes of suprathermal electrons (E_e≈30-100 eV) on the Martian nightside by the ASPERA-3 experiment onboard the Mars Express spacecraft. Narrow spikes of suprathermal electrons are often observed in energy-time spectrograms of electron fluxes at altitudes between 250 and 600 km. These spikes are spatially organized and form narrow strips in regions with strong upward or downward crustal magnetic field. The values of electron fluxes in such events generally could explain the observed auroral UV emissions although a question of their origin (transport from the dayside or local precipitation) remains open.     

Determination of the reduced sulfur species in the anoxic zone of the Black Sea: A comparison of the spectrophotometry and iodometry techniques

The report presents the results of the studies of the reduced sulfur species in the water of the anoxic zone of the Black Sea. The content of hydrogen sulfide was determined by means of spectrophotometry using dilution with oxygen-free distilled water. The detection limit of the H₂S amounted to 0.3 μM with the method’s precision below 3%. The accuracy of the spectrophotometric determination was verified by iodometry after the fixation of the hydrogen sulfide in zinc acetate under the distillation with argon from the acidified seawater sample.     

Structure and Evolution of the Eastern Part of the Southwest Indian Ridge

Geotectonics - The structure and evolution of the eastern part of the Southwest Indian Ridge are discussed. Based on geological-geophysical data and cartographic materials, analysis of spatial and...     

Determination of Platinum‐Group Elements and Gold in Ferromanganese Nodule Reference Samples

A measurement procedure for determining of Ru, Pd, Ir, Pt and Au mass fractions in ferromanganese deposits by inductively coupled plasma‐mass spectrometry after acid digestion and anion exchange preconcentration is presented. To eliminate incomplete recovery after sorption preconcentration of the platinum‐group elements (PGE) and Au, a standard addition method was used. Detection limits ranged from 0.02 ng (Pd, Ir) to 0.19 ng (Ru). The measurement results for ferromanganese nodule reference material NOD‐A‐1 and NOD‐P‐1 agree with earlier reported values. Intermediate precision of PGE concentration data for nodule reference materials in this work was 5–24% (1s) and could reflect sample heterogeneity.     

Evolution of the Kerguelen plume and its impact upon the continental and oceanic magmatism of East Antarctica

Petrological–geochemical study showed that the alkaline-ultramafics of the Jetty Oasis (rift zone of the Lambert glacier, East Antarctica) are similar in the age (117–110 Ma) and geochemistry to the ultrapotassic alkali basalts of eastern India (Jharia and Raniganj intrusions). Alkaline magmatism in India and Antarctica is related to the activity of the Kerguelen plume, which significantly affected the evolution of the entire eastern Indian Ocean, in particular, determined geodynamic peculiarities of the ocean opening (existence of non-spreading blocks, fragments of the Gondwana lithosphere in oceanic areas) and geochemical characteristics of erupted tholeiitic magmas. Enriched magma sources related to the Kerguelen plume were formed by melting of ancient Gondwana-derived continental fragments, which experienced multiple transformations during its evolution up to the formation of metasomatized mantle under the impact of the Kerguelen plume on the Antarctic and India margins.     

Determination of the platinum-group elements and gold in ferromanganese nodule reference material NOD-A-1

The concentrations of Ru, Pd, Ir, Pt, and Au were determined in a ferromanganese nodule reference sample NOD-A-1 by inductively coupled plasma mass-spectrometry. Sample preparation procedures include acid digestion and anion exchange preconcentration. Standard addition method was used to eliminate losses of the analyte during the chromatographic separation. The results are in agreement with previously published data. The low level of intermediate precision for Au between different subsamples of the same sample probably originates from the heterogeneous distribution of Au in ferromanganese nodules. The accumulation of PGE in ferromanganese nodules was studied using international reference samples.     

Convection and field-aligned currents, related to polar cap arcs, during strongly northward IMF (11 January 1983)

Electric and magnetic fields and auroral emissions have been measured by the Intercosmos-Bulgaria-1300 satellite on 10–11 January 1983. The measured distributions of the plasma drift velocity show that viscous convection is diminished in the evening sector under IMF B_y < 0 and in the morning sector if IMF B_y > 0. A number of sun-aligned polar cap arcs were observed at the beginning of the period of strongly northward IMF and after a few hours a θ-aurora appeared. The intensity of ionized oxygen emission [O⁺(²P), 7320 Å] increased significantly reaching up to several kilo-Rayleighs in the polar cap arc. A complicated pattern of convection and field-aligned currents existed in the nightside polar cap which differed from the four-cell model of convection and NBZ field-aligned current system. This pattern was observed during 12 h and could be interpreted as six large scale field-aligned current sheets and three convective vortices inside the polar cap. Sun-aligned polar cap arcs may be located in regions both of sunward and anti-sunward convection. Structures of smaller spatial scale correspond to the boundaries of hot plasma regions related to polar cap arcs. Obviously these structures are due to S-shaped distributions of electric potential. Parallel electric fields in these S-structures provide electron acceleration up to 1 keV at the boundaries of polar cap arcs. The pairs of field-aligned currents correspond to those S-structures: a downward current at the external side of the boundary and an upward current at the internal side of it.