Geochemistry of polycyclic aromatic hydrocarbons in the bottom sediments of the eastern Arctic shelf

Sources and pathways of supply of polycyclic aromatic hydrocarbons (PAH) in the surface sediments of the Laptev and East Siberian seas were identified based on an analysis of the lithological-geochemical characteristics and distribution of organic matter (OM). The distribution of organic carbon, humic acids, bitumoids, and hydrocarbons demonstrates the determining role of the riverine runoff in the formation of the recent sediments. The total average content of PAH in the sediments of this region approximates 37 ng/g, not exceeding 80 ng/g of dry sediment. The biogenic components of the PAH (alkylphenanthrenes, alkylchrysenes, perylene) dominate in the estuarine-shelf and coastal-shelf sediments enriched with plant detritus and significantly decrease in the pelagic zone. The anthropogenic influence is observed in sediments of the port of Tiksi, where the total content of PAH with dominant pyrogenic components is two orders of magnitude higher as compared with the background values in the study region.     

Siderite layers in the fresh-water Neogene sediments of Vietnam

Siderites forming beds and lenses in the Neogene lacustrine—swampy sediments of the Rinh Chua Formation (northern Vietnam) are considered in detail. Results of the mineralogical and chemical study of siderites and host terrigenous–clayey siltstones are reported. New analytical data characterize the composition and structure of microbiomorphic (bacterial) bodies in the siderites and terrigenous sediments. Microstructures (porosity) and compositional peculiarities (up to 18% P₂O₅) of individual horizons of the sediments testify to their lacustrine-swampy genesis. It is established that the siderites in association with the layer silicates were formed during the microbiochemogenic decomposition of terrigenous components, including quartz.     

Oscillations of the Earth with periods of 9–57 min in the background seismic process and the energy flux direction in the range of the free oscillation 0 S 2

Retrospective data of monitoring under conditions of low seismic activity are used to identify free oscillations of the Earth, including the fundamental mode, the oscillation with a central period of 54 min (₀ S ₂ ^m multiplet), split into five lines with azimuthal numbers m = ?2, ?1, 0, 1, 2. It is shown that some lines of this oscillation are also recorded in atmospheric pressure variation spectra and group in ensembles of observations around frequencies predicted by the ₀ S ₂ ^m splitting theory. This phenomenon is discovered in data recorded both synchronously and in different time intervals. A causal relationship involved in the oscillation under study is determined on the basis of the examination of the direction of the acoustic energy flux. The energy flux in the region of the ₀ S ₂ ^m multiplet is shown to be directed from the Earth toward the atmosphere. This suggests that deep processes in the Earth are capable of exciting its upper shells.     

Natural experiment “Thermal Front in Lake Ladoga, 2010”

The subsatellite experiment ??Thermal Front in Lake Ladoga, 2010?? and its results are described. The experiment was performed at the initial stages of thermal bar existence at the end of May 2010. We estimated the horizontal gradients of water temperature and the front motion rate by two successive surveys carried out with a discreteness of four days. Cumulative heat flows coming to the lake surface were different on different front sides. The hydrochemical and hydrobiological parameters of the front zone were not characterized by any significant horizontal differences.     

Origin of submarine volcanism at the eastern margin of the central atlantic: Investigation of the alkaline volcanic rocks of the carter seamount (Grimaldi Seamounts)

This paper addresses the composition, geochemistry, isotopic characteristics, and age of rocks from the Carter Seamount of the Grimaldi seamount group at the eastern margin of the Central Atlantic. The age of the seamount was estimated as 57–58 Ma. Together with other seamounts of the Grimaldi system and the Nadir Seamount, it forms a “hot line” related to the Guinea Fracture Zone, which was formed during the late Paleocene pulse of volcanism. The Carter Seamount is made up of olivine melilitites, ankaramites, and analcime-bearing nepheline tephrites, which are differentiated products of the fractional crystallization of melts similar to an alkaline ultramafic magma. The volcanics contain xenoliths entrained by melt at different depths from the mantle, layer 3 of the oceanic crust, which was formed at 113–115 Ma, and earlier magma chambers. The rocks were altered by low-temperature hydrothermal solutions. The parental melts of the volcanics of the Carter Seamount were derived at very low degrees of mantle melting in the stability field of garnet lherzolite at depths of no less than 105 km. Anomalously high Th, Nb, Ta, and La contents in the volcanics indicate that a metasomatized mantle reservoir contributed to the formation of their primary melts. The Sr, Pb, and Nd isotopic systematics of the rocks show that the composition of the mantle source lies on the mixing line between two mantle components. One of them is a mixture of prevailing HIMU and the depleted mantle, and the other is an enriched EM2-type mantle reservoir. These data suggest that the formation of the Carter Seamount volcanics was caused by extension-related decompression melting in the Guinea Fracture Zone of either (1) hot mantle plume material (HIMU component) affected by carbonate metasomatism or (2) carbonated basic enclaves (eclogites) ubiquitous in the asthenosphere, whose isotopic characteristics corresponded to the HIMU and EM2 components. In the former case, it is assumed that the melt assimilated during ascent the material of the metasomatized subcontinental mantle (EM2 component), which was incorporated into the oceanic lithospheric mantle during rifting and the breakup of Pangea.     

New data on the composition of stable isotopes in glendonites of the White Sea and their genesis

Several samples including host sediments, recent molluscan shells, glendonites, and associated carbonate concretions were subjected to the thorough investigation. The obtained analytical data characterize the unique locality of Holocene and Recent carbonate structures in the White Sea basin. The microscopic examination of glendonites revealed several microtextural types of calcite and the succession of their formation. It is established that they are composed of carbonate material, which was discretely formed due to biochemical destruction of terrigenous sedimentary material. The revealed differences in the carbon isotope composition in different glendonites are likely explained by local geochemical properties, which existed within host sediments, or the asynchronous formation of carbonate structures due to changes in the chemical composition of waters that saturated sediments.     

New data on the rock composition of the Bahia Seamounts (Brazil Basin,South Atlantic Ocean)

During the 28th cruise of R/V Akademik Sergei Vavilov in 2009, five different mountains belonging to the northern chain of the Baia Seamounts, located in the Brazil Basin, were dredged. Igneous rocks, limestones, and Fe-Mn crusts were collected. Igneous rocks are greatly altered resulting from halmyrolithic and/or low-temperature hydrothermal processes; the main secondary minerals are smectite, iron hydroxide, and phillipsite. Igneous rocks are subdivided into two groups, namely, trachybasalts and trachyandesites. Trachybasalts are aphyric rocks, consisting of basal plagioclase microlites, Fe-Ti ore mineral, olivine, and clinopyroxene. Trachyandesites are rarely porphyre rocks. Inclusions in trachyandesite are represented by acidic plagioclase, olivine, biotite, and zircon. The main mass is formed by acidic plagioclase and a small quantity of clinopyroxene.