Diurnal Variations in the Hydrochemical Indices in Amur Bay

A study was conducted to assess the diurnal variations in water temperature, in-situ density, and salinity; major components of the salt composition; ion–chlorine relationships; elements of the carbonate system and their chlorine ratios; major nutrient compounds; total organic carbon content; suspended matter; dissolved oxygen and its percentage in the coastal waters of Amur Bay. The notions of zero, very small, small, medium, high, and very high relative variability are introduced.     

Climate induced temperature effects on growth performance, fecundity and recruitment in marine fish: developing a hypothesis for cause and effect relationships in Atlantic cod (Gadus morhua) and common eelpout (Zoarces viviparus)

Effects of global warming on animal distribution and performance become visible in many marine ecosystems. The present study was designed to develop a concept for a cause and effect understanding with respect to temperature changes and to explain ecological findings based on physiological processes. The concept is based on a wide comparison of invertebrate and fish species with a special focus on recent data obtained in two model species of fish. These fish species are both characterized by northern and southern distribution limits in the North Atlantic: eelpout (Zoarces viviparus), as a typical non-migrating inhabitant of the coastal zone and the cod (Gadus morhua), as a typical inhabitant of the continental shelf with a high importance for fisheries.Mathematical modelling demonstrates a clear significant correlation between climate induced temperature fluctuations and the recruitment of cod stocks. Growth performance in cod is optimal at temperatures close to 10°C, regardless of the population investigated in a latitudinal cline. However, temperature specific growth rates decrease at higher latitudes. Also, fecundity is less in White Sea than in North and Baltic Sea cod or eelpout populations. These findings suggest that a cold-induced shift in energy budget occurs which is unfavorable for growth performance and fecundity. Thermal tolerance limits shift depending on latitude and are characterized by oxygen limitation at both low or high temperatures. Oxygen supply to tissues is optimized at low temperature by a shift in hemoglobin isoforms and oxygen binding properties to lower affinities and higher unloading potential. Protective stimulation of heat shock protein synthesis was not observed.According to a recent model of thermal tolerance the downward shift of tolerance limits during cold adaptation is associated with rising mitochondrial densities and, thus, aerobic capacity and performance in the cold, especially in eurythermal species. At the same time the costs of mitochondrial maintenance reflected by mitochondrial proton leakage should rise leaving a lower energy fraction for growth and reproduction. The preliminary conclusion can be drawn that warming will cause a northern shift of distribution limits for both species with a rise in growth performance and fecundity larger than expected from the Q₁₀ effect in the north and lower growth or even extinction of the species in the south. Such a shift may heavily affect fishing activities in the North Sea.     

The dust envelope of the symbiotic nova V1016 Cyg

Brightness and color variations of V1016 Cyg are studied using many years of UBVRJHKLM photometric observations and information about its spectral energy distribution in the intermediate IR (7.7 to 22.7 µm) obtained with the IRAS and ISO low-resolution spectrometers. Models for its stationary, spherically symmetrical, extended dust envelope are computed for two cases of heating: by the radiation of the cool component only and by the combined radiation from both components. Model fitting of the IRAS and ISO observations shows that the model with a single central source—the Mira star—provides a better fit to the data, indicating that the hot component’s radiation is appreciably reprocessed by the ambient gas medium and has almost no direct influence on the IR spectrum of the symbiotic nova. The mean spectral energy distributions measured by IRAS in 1983 and ISO on October 1, 1996, differ considerably. The observed evolution of the envelope’s spectrum probably reflects an increasing grain concentration and decreasing grain temperature at the inner edge of the envelope, associated with decreased luminosity and increased temperature of the hot component. The total mass-loss rate, gas-expansion velocity at the outer edge of the envelope, and upper limit to the mass of the central radiation source are estimated.     

A possible manifestation of spiral shock waves in the accretion disks of cataclysmic variables

We present the results of three-dimensional numerical simulations of flow structures in binary systems with spiral shock waves. Variations of the mass-transfer rate perturb the equilibrium state of the accretion disk; consequently, a condensation (blob) behind the shock breaks away from the shock front and moves through the disk with variable speed. Our computations indicate that the blob is a long-lived formation, whose mean parameters do not vary substantially on timescales of several tens of orbital periods of the system. The presence of the spiral shocks maintains the compact blob in the disk: it prevents the blob from spreading due to the differential motion of matter in the disk, and dissipative spreading on this timescale is negligible. A number of cataclysmic variables display periodic or quasi-periodic photometric variations in their light curves with characteristic periods ～0.1–0.2P _orb, where P _orb is the orbital period. The blobs formed in systems with spiral shock waves are examined as a possible origin for these variations. The qualitative (and, in part, quantitative) agreement between our computations and observations of IP Peg and EX Dra provides evidence for the efficacy of the proposed model.     

Investigations on the Quaternary Glaciation in the Khumbu Himal (Nepal, East-Himalaya)

Based on geomorphological field work the mapping of former lateral/terminal moraines in the middle segment of the Bhotekoshi Nadi is quite similar to the geomorphological findings of Heuberger (1956: Fig. 2). The deductive calculation of the equilibrium line altitudes is oriented on the reconstructed types of former glaciers. Based on the geomorphological findings of this valley segment the relation of Neoglacial and Late Glacial ice margins of the glaciers of the tributary valleys of the Bhotekoshi Nadi is not conclusive. A post-late glacial maximum snow-line depression of at least 950 m has not obligatory caused an ice fill of the Bhotekoshi Nadi below 3200 m. This revised version was published online in July 2006 with corrections to the Cover Date.     

Some Problems of Clastogenic Mica Transformation during Anchimetamorphism (Metagenesis)

The transformation of clastogenic muscovite and biotite from the Tyumen superdeep well was studied with the SEM and microprobe techniques. It was shown that under conditions of anchimetamorphism (metagenesis), the white mica becomes unstable and may be replaced by several newly formed minerals. In particular, the brammallite, a sodic analogue of illite, is formed at the expense of sodic component of muscovite. The chloritization of mica provokes the removal of excess silica, which is present in the anchizone as a readily soluble in water modification rather than quartz. The release of excess silica as a result of clastogenic mica destruction may be a source of rock silification. As follows from the review of experimental data on silica solubility, the replacement of many silicate minerals leads to the formation of excess silica. This process can be highly extensive during the breakdown of clastogenic minerals.     

Parameters of the dust envelope of the symbiotic star CH Cygni

The brightness and color variations of the symbiotic star CH Cygni are studied, and its stationary, spherically symmetric, extended dust envelope is modeled based on long-term UBVRJHKLM photometry, the mid-IR spectral energy distribution (7–23 µm), and far-IR fluxes measured by IRAS and ISO. The existence of a hot dust envelope, detected earlier in the near IR, is confirmed; the optical depth of the envelope has probably increased with time. Model fits to the IRAS and ISO data indicate that the V-band optical depth increased from 0.22 to 0.41 due to dust density enhancement during the 14 years between the observations by the two spacecraft. The mass-loss rate, gas-expansion velocity at the outer boundary of the envelope, and upper limit of the mass of the central source of emission are estimated assuming that the stellar wind of the system is driven by the pressure of the red giant's radiation on the dust, with subsequent momentum transfer to the gaseous medium.     

Microbial–silica interactions in Icelandic hot spring sinter: possible analogues for some Precambrian siliceous stromatolites

Silicified deposits, such as sinters, occur in several modern geothermal environments, but the mechanisms of silicification (and crucially the role of microorganisms in their construction) are still largely unresolved. Detailed examination of siliceous sinter, in particular sections of microstromatolites growing at the Krisuvik hot spring, Iceland, reveals that biomineralization contributes a major component to the overall structure, with approximately half the sinter thickness attributed to silicified microorganisms. Almost all microorganisms observed under the scanning electron microscope (SEM) are mineralized, with epicellular silica ranging in thickness from < 5 μm coatings on individual cells, to regions where entire colonies are cemented together in an amorphous silica matrix tens of micrometres thick. Within the overall profile, there appears to be two very distinct types of laminae that alternate repeatedly throughout the microstromatolite: ‘microbial’ layers are predominantly consisting of filamentous, intact, vertically aligned, biomineralized cyanobacteria, identified as Calothrix and Fischerella sp.; and weakly laminated silica layers which appear to be devoid of any microbial component. The microbial layers commonly have a sharply defined base, overlying the weakly laminated silica, and a gradational upper surface merging into the weakly laminated silica. These cyclic laminations are probably explained by variations in microbial activity. Active growth during spring/summer allows the microorganisms to keep pace with silicification, with the cell surfaces facilitating silicification, while during their natural slow growth phase in the dark autumn/winter months silicification exceeds the bacteria’s ability to compensate (i.e. grow upwards). At this stage, the microbial colony is probably not essential to microstromatolite formation, with silicification presumably occurring abiogenically. When conditions once again become favourable for growth, recolonization of the solid silica surface by free‐living bacteria occurs: cell motility is not responsible for the laminations. We have also observed that microbial populations within the microstromatolite, some several mm in depth, appear viable, i.e. they still have their pigmentation, the trichomes are not collapsed, cell walls are unbroken, cytoplasm is still present and they proved culturable. This suggests that the bulk of silicification occurred rapidly, probably while the cells were still alive. Surprisingly, however, measurements of light transmittance through sections of the microstromatolite revealed that photosynthetically active light (PAL) only transmitted through the uppermost 2 mm. Therefore the ‘deeper’ microbial populations must have either: (i) altered their metabolic pathways; (ii) become metabolically inactive; or (iii) the deeper populations may be dominated by different microbial assemblages from that of the surface. From these collective observations, it now seems unequivocal that microstromatolite formation is intimately linked to microbial activity and that the sinter fabric results from a combination of biomineralization, cell growth and recolonization. Furthermore, the similarities in morphology and microbial component to some Precambrian stromatolites, preserved in primary chert, suggests that we may be witnessing contemporaneous biomineralization processes and growth patterns analogous to those of the early Earth.     

Onset of seafloor spreading in the Iapetus Ocean at 608 Ma: precise age of the Sarek Dyke Swarm, northern Swedish Caledonides

The Sarek Dyke Swarm (SDS) crops out in the Sarektjåkkå Nappe (SN) of the Seve-Kalak Superterrane in the northern Swedish Caledonides. The SN has two main components: (1) a 4–5 km thick succession of rift-related sedimentary rocks, which is intruded by (2) a suite of tholeiitic dykes (the SDS) constituting 70–80% of the nappe. The nappe was deformed during Caledonian thrusting, but dykes and sedimentary rocks in the interior of the eastern parts of the SN are preserved in a pristine state. The tholeiitic dykes of the SDS commonly occur in sheeted dyke complexes, and up to 11 successive generations can be identified from crosscutting relations. The SN represents the fossil continent–ocean transition between the Baltic craton and the Iapetus Ocean, marking the initiation of seafloor spreading. Bubble-shaped pods and veinlets of diorite are present in the SDS sheeted dyke complexes. The pods are absent in the oldest dykes, but the younger a dyke, the more frequent the pods. The diorite pods are the equivalent of gabbro pegmatites, and both cogenetic and coeval with the dykes. The rapid successive emplacement of tholeiitic magma raised the ambient temperature in the dyke complex, so that crystallization in the youngest dykes mimicked similar processes in gabbro plutons. Six zircon fractions, from the diorite pods including two single grains, were analysed geochronologically by the U–Pb thermal ionization mass spectrometry method. The data yield a linear array of points that are 0.4–0.8% normally discordant, indicating a crystallization age of 608±1 Ma (²⁰⁷Pb/²⁰⁶Pb=607.9±0.7 Ma, MSWD=0.33). This age is inferred to date the onset of seafloor spreading in the Iapetus Ocean along the Baltoscandian margin.     

On the origin of inhomogeneity of anomalous birefringence in mixed crystals: an example of alums

 Optical anomalies (deviations of the symmetry of optical properties from the ideal symmetry of the crystal) occur in many minerals and synthetic compounds and have been under investigation since the last century. An important feature of optically anomalous mixed crystals is a high degree of optical inhomogeneity, whereas the optical patterns of mixed crystals without anomalies are usually rather uniform. This work is devoted to the study of this phenomenon. As a model object we have chosen mixed alum crystals, which were known for their anomalous birefringence and which revealed the following types of optical inhomogeneities: (1) sector zoning; (2) concentric zoning; (3) subsector zoning; (4) stripes normal to growth front. The inhomogeneity of anomalous birefringence of mixed crystals of alums can be explained by superposition of several effects: mismatch strain, strain along dislocations and growth ordering of isomorphous components. Optical inhomogeneities due to the sector zoning of crystals and their dislocation structure arise even under stationary growth conditions and stationary micromorphology of the growing face. Both variable growth conditions and the relief of the growing face strongly intensify the optical inhomogeneity due to three interrelated factors: (1) a significantly inhomogeneous mismatch strain; (2) a variable degree of ordering of isomorphous components due to the compositional inhomogeneities; (3) different degrees of ordering of isomorphous atoms caused by different orientations, heights and velocities of growth steps. These effects lead to the formation of subsector zoning and zoning superimposed on the optical sector zoning. These optical structures are crossed by birefringent stripes arising from dislocations. Received: 29 March 2000 / Accepted: 11 March 2001