Mud volcano gas hydrates in the Gulf of Cadiz

ABSTRACT This paper presents new geochemical data on gas-hydrate-bearing mud volcanoes discovered for the first time in the Gulf of Cadiz during cruises TTR9 and TTR10 of the R/V Professor Logachev in 1999–2000. The estimated gas hydrate content is 3–16% of sediment volume and 5–31% of pore space volume. Estimated values of the water isotopic composition for the Ginsburg mud volcano are very heavy for δ¹⁸O (up to +53‰) and light for δD (up to − 210‰). Gas released from the hydrates contains 81% of C₁ and 19% of C₂₊. The inferred source of the gas in the hydrates is enriched in C₂–C₆ (≤ 5%), indicating that the gas has a thermogenic origin. Gas hydrate of cubic structure II should be formed from a gas of such composition. It is interpreted that the composition of the mud volcano fluid corresponds to deep oil basins below the Gulf of Cadiz.     

On the Sudden Depression of Radio Emission From Plasma Above a Fast-Moving Sunspot

We present a very rare case of unexpected depression of radio emission above a sunspot using solar observations from RATAN-600. The sunspot had a very high proper motion on the solar surface. The depression lasted for 5 days without significant changes in area or magnitude of magnetic field of the associated sunspot. The observations show that the depression cannot be explained by the absorption of the emission during its propagation through the overlying magnetosphere of the AR or through the cold and opaque matter of a prominence. The theoretical interpretation of the phenomenon is based on the hypothesis that the motion of the sunspot on the photosphere leads to the significant expanding of the magnetic loop originated at this sunspot. The extension of the twisted magnetic rope results in the loss of equilibrium of the system: the closed magnetic structure (the twisted magnetic loop) seems destined to transform into an open one. The only mechanism of plasma heating which would be `switched off' in such a non-equilibrium configuration is that based on the quasi-static topological relaxation of a force-free magnetic field towards a configuration of minimum energy. Relaxation of magnetic fields does not occur in a non-equilibrium state. As a consequence, the energy release in the twisted magnetic rope and the temperature of the plasma of the local radio source have to fall down abruptly. Thus, the discussed phenomenon argues in favor of the relaxation model of plasma heating.     

Modeling the dynamics of the block structure and seismicity of the Caucasus

Based on the morphostructural zoning scheme of the Caucasus, the block structure reflecting the real fault geometry and the block formation of the region is constructed. Several dozens of numerical experiments are conducted for simulating the dynamics of the block structure and the arising seismicity. The modeling relies on the following principles. It is assumed that the structure is composed of perfectly rigid blocks separated by infinitely thin fault planes. On the fault planes and on the blocks' bottoms, the blocks viscoelastically interact with each other and with the underlying medium. At each time instant, the translational displacements and rotations of the blocks are calculated from the condition of the quasi-static equilibrium of the entire block structure. The earthquakes occur in accordance with the dry friction model at the time instants when within a certain segment of the fault the stress-to-pressure ratio exceeds the given threshold. The modeling yields the synthetic catalog of the Caucasian earthquakes the spatial distribution of which reflects a set of characteristic features of the real seismicity. The similarity is observed in the magnitude–frequency diagrams of the synthetic and real seismicity. The comparison of the positions of the epicenters of the strong synthetic earthquakes with the results of recognizing the highly seismically active areas in the Caucasus demonstrates the presence of such epicenters in a few highly active areas where, according to the observations, strong earthquakes have not occurred to date.     

Identification of Vortex Currents in the Ionosphere and Estimation of Their Parameters Based on Ground Magnetic Data

Geomagnetism and Aeronomy - A system to process data from a 2D network of magnetic stations is proposed for the identification of eddy currents in the ionosphere and the estimation of their...     

Application of the SP algorithm to the INTERMAGNET magnetograms of the disturbed geomagnetic field

The algorithmic system developed in the Laboratory of Geoinformatics at the Geophysical Center, Russian Academy of Sciences, which is intended for recognizing spikes on the magnetograms from the global network INTERMAGNET provides the possibility to carry out retrospective analysis of the magnetograms from the World Data Centers. Application of this system to the analysis of the magnetograms allows automating the job of the experts-interpreters on identifying the artificial spikes in the INTERMAGNET data. The present paper is focused on the SP algorithm (abbreviated from SPIKE) which recognizes artificial spikes on the records of the geomagnetic field. Initially, this algorithm was trained on the magnetograms of 2007 and 2008, which recorded the quiet geomagnetic field. The results of training and testing showed that the algorithm is quite efficient. Applying this method to the problem of recognizing spikes on the data for periods of enhanced geomagnetic activity is a separate task. In this short communication, we present the results of applying the SP algorithm trained on the data of 2007 to the INTERMAGNET magnetograms for 2003 and 2005 sampled every minute. This analysis shows that the SP algorithm does not exhibit a worse performance if applied to the records of a disturbed geomagnetic field.     

Recognition of the Cambrian Timan–Severnaya Zemlya orogen and timing of geological evolution of the North Kara sedimentary basin based on detrital zircon dating

New data on the ages of detrital zircons from folded basement rocks and cover sediments of the Severnaya Zemlya archipelago and Izvestiy TSIK islands have been obtained. The basement age is defined as Cambrian (pre-Ordovician). The Ordovician and Silurian sandstones were mainly formed by erosion of the basement rocks. The Devonian sandstones were formed by debris sourced from the Caledonian orogen. The Carboniferous–Early Permian molasse was formed simultaneously with the erosion of the Carboniferous granitoids and weathering of the Ordovician volcanic arc rocks and the Cambrian basement. The North Kara basin was formed in the Ordovician as a back-arc basin. It experienced its main compression deformations at the boundary of the Devonian and Carboniferous and in the Carboniferous.     

Petrochemistry of rocks in the Chorukh-Dairon monzonite-syenite-granite pluton,Northern Tajikistan

The Chorukh-Dairon monzonite-syenite-granite pluton is part of the Chorukh-Dairon volcano-plutonic complex consisting of a number of multiphase plutons and comagmatic volcanic and subvolcanic suites. The rocks of the Chorukh-Dairon pluton affiliate with the shoshonite-latite type generated by deep (mantle) magma; they correspond to the continental marginal variety and were related to chambers generated in metasomatically enriched mantle material. The evolution of the melts during their crystallization differentiation proceeded via the predominant fractionation of, first, mafic and accessory minerals and then feldspars. The drastic decrease in W concentration by minerals that crystallized during the late evolution of the pluton was associated with the enhancement of the emanational differentiation and the development of aureoles of postmagmatic ore-bearing metasomatic rocks.     

COOL AND FRESHWATER SKIN OF THE OCEAN DURING RAINFALL

Rainfall over the sea modifies the molecular boundary layers of the upper ocean through a variety of different effects. These cover the freshwater flux stabilizing the near-surface layer, additional heat flux established due to rain versus surface temperature differences, modification of physical parameters by temperature and salinity changes, enhancement of the surface roughness, damping of short gravity waves, surface mixing by rain, and transfer of additional momentum from air to sea. They are separately described and included in our surface renewal model to investigate the rain's influence on the cool skin of the ocean and the creation of a haline molecular diffusion layer. Simulations with the upgraded model show that the most important effect on the conductive layer is that of reduced renewal periods followed by additional surface cooling due to rain on the order of 0.1 K. At rain rates below 50 mm h-1 rainfall is not able to completely destroy the mean temperature difference across the cool skin. A freshwater skin is created that exhibits a salinity difference exceeding 4 under strong rainfall. Comparisons with field data of the cool skin taken during the Coupled Ocean Atmosphere Response Experiment confirm the upgraded renewal model. Surface salinity measurements taken during the same field campaign are consistent with the calculated salinity differences across the freshwater skin. The enhancement of surface roughness by natural rain is less pronounced than described in earlier laboratory studies of rain with large drop sizes only.