Diatom record from Lake Hovsgol, Mongolia, during the last 1 Ma: The results from the HDP-04 drill core     

Galina K. Khursevich  Alexander A. Prokopenko   《Quaternary International》2009,205(1-2):84

Quantitative diatom abundance and species composition was studied in the longest 81-m Lake Hovsgol drill core, HDP-04. Lake Hovsgol diatom biostratigraphy of the past 1 Ma includes 14 local diatom assemblage zones (LDAZ). Planktonic diatom flora of Lake Hovsgol is dominated by members of Stephanodiscus and Cyclotella. A large-scale shift from Stephanodiscus-dominated to Cyclotella-dominated flora occurred in the mid-Brunhes chron. Significant morphological variability of Cyclotella ocellata complex and Cyclotella cf. minuta, as well as the presence of new extinct endemic taxa of genus Stephanodiscus, suggest long speciation and/or adaptation history of diatom flora. The recognition of taxa morphologically similar to the extinct endemic species of Lake Baikal suggests potential correlation ties between Lake Hovsgol and Lake Baikal diatom biostratigraphies around the MIS 17, MIS 25, and, possibly, MIS 15 interglacial intervals. Narrow peaks of diatom abundance in the Lake Hovsgol sedimentary record are episodic and short-lived. These peaks may represent humid optima of past interglacials and/or interstadials, characterized by elevated surface runoff in the Hovsgol basin and relative highstands of the lake.  相似文献   

Cenozoic history of the Bering Sea and its northwestern margin     

Vadim Chekhovich  Dmitry Kovalenko  & Galina Ledneva 《Island Arc》1999,8(2):168-180

Tectonic reconstructions based on the geodynamic analysis of geologic, paleomagnetic, structural and kinematic data of Cenozoic age from the western Bering Sea region are proposed in the present paper. The most active tectonic and magmatic processes took place in the Komandorsky segment of the Bering Sea, exemplified by the Late Cretaceous–Early Eocene Olutorsky Arc and Eocene–Oligocene Govena–Karaginsky Arc, which was built on the structures of the Olutorsky Arc. A model of the complex collision of these two arcs with the paleocontinental margin, which considers rotations of the geological blocks from the various structural zones of the western margin of the Bering Sea in the horizontal plane (paleomagnetic data), was proposed by the authors. According to this model the collision of the flanks of the Olutorsky and Govena–Karaginsky arcs took place in the Eocene, before the collision of the central parts in the Miocene.  相似文献   

Trophic relations of capelin Mallotus villosus and polar cod Boreogadus saida in the Barents Sea as a factor of impact on the ecosystem     

Emma L. Orlova  Andrey V. Dolgov  Galina B. Rudneva  Ivan A. Oganin  Ludmila L. Konstantinova 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(21-22):2054

The purpose of the study is to assess the role of trophic relations of the dominant pelagic fishes capelin and polar cod in the Barents Sea with regard to distribution and accessibility as prey for the Atlantic cod in warm years (2004–2005). Unlike in the previous period, during these warm years a dramatic increase of the polar cod population resulted in a northwards expansion of the feeding grounds where overlapping of polar cod and capelin concentrations was observed. This caused an increased competition for copepods, which are the main food item for young fish. In the areas dominated by polar cod the shortage of copepods forced immature capelin to switch to the chaetognath Sagitta, which affected their fatness negatively.During the warm years the feeding grounds of Atlantic cod also expanded, to a large degree caused by the shortage of their main food, the capelin. In 2004–2005 the cod formed feeding concentrations in the north and northeast Barents Sea where they fed on the capelin. In this area the consumption of polar cod by cod increased, and in some local areas the polar cod practically replaced the capelin in the diet of cod. In general polar cod in the diet of Atlantic cod were more important in the northern than in the southern part of the Barents Sea. The fatness of cod was extremely low during the whole spring–summer period (until August), and after the feeding period the fatness index of the Atlantic cod became lower than the average long-term autumn value.  相似文献   

Finite-difference algorithm with local time-space grid refinement for simulation of waves     

Vadim Lisitsa  Galina Reshetova  Vladimir Tcheverda 《Computational Geosciences》2012,16(1):39-54

This paper presents a new approach to a local time-space grid refinement for a staggered-grid finite-difference simulation of waves. The approach is based on approximation of a wave equation at the interface where two grids are coupled. As no interpolation or projection techniques are used, the finite-difference scheme preserves second order of convergence. We have proved that this approach is low-reflecting, the artificial reflections are about 10^− 4 of an incident wave. We have also shown that if a successive refinement is applied, i.e. temporal and spatial steps are refined at different interfaces, this approach is stable.  相似文献   

Non-Integrability and Structure of the Resonance Zones in a Class of Galactic Potentials     

Efi Meletlidou  Galina Stagika  Simos Ichtiaroglou 《Celestial Mechanics and Dynamical Astronomy》2005,91(3-4):323-335

The structure of the resonance zone in nearly integrable Hamiltonian systems is studied by a more general method than the pendulum approximation. This method applies to the case of a non-degenerate integrable part in the Hamiltonian. This problem may be overcome in a class of galactic-type polynomial potentials, in the case where the higher-order term is by itself integrable. An illustrative example is worked out.  相似文献   

Permo-Triassic hypabyssal mafic intrusions and associated tholeiitic basalts of the Kolyuchinskaya Bay,Chukotka (NE Russia): Links to the Siberian LIP     

Galina V. Ledneva  Victoria L. Pease  Sergey D. Sokolov 《Journal of Asian Earth Sciences》2011,40(3):737-745

In order to test tectonic hypotheses regarding the evolution of the Arctic Alaska–Chukotka microplate prior to the opening of the Amerasian basin, we investigated rocks exposed near Kolyuchinskaya Bay, eastern Chukotka. Hypabyssal mafic rocks and associated basaltic flows enclose terrigenous sediments, minor cherts and limestones in pillow interstices. The hypabyssal mafic rock yields a U–Pb zircon age of 252 ± 4 Ma and indicates intrusion of basic magma at the Permo-Triassic boundary, contemporaneous with voluminous magmatism of the Siberian large igneous province (LIP). The lava flows and hypabyssal mafic rocks of the Kolyuchinskaya Bay region have trace elements, Sm–Nd and Rb–Sr isotope compositions identical to the tholeiitic flood basalts of the main plateau stage of the Siberian LIP, but differ from the latter in the major-element variations. We conclude that compositional variations in the hypabyssal rocks studied reflect their generation in an extensional environment that might be related to the Siberian super-plume activity at the time. Although the genetic and temporal links between intrusive mafic rocks and lavas are not well proved, compositional variations of the eruptive rocks still indicate their generation in an extensional environment.  相似文献   

Atmospheric circulation and storm events in the Black Sea and Caspian Sea     

Galina V. Surkova  Victor S. Arkhipkin  Alexander V. Kislov 《Central European Journal of Geosciences》2013,5(4):548-559

Extreme sea storms are dangerous and a potential source of damage. In this study, we examine storm events in the Black Sea and Caspian Sea, the atmosphere circulation patterns associated with the sea storm events, and their changes in the present (1961–2000) and future (2046–2065) climates. A calendar of storms for the present climate is derived from results of wave model SWAN (Simulating WAves Nearshore) experiments. On the basis of this calendar, a catalog of atmospheric sea level pressure (SLP) fields was prepared from the NCEP/NCAR reanalysis dataset for 1961–2000. The SLP fields were subjected to a pattern recognition algorithm which employed empirical orthogonal decomposition followed by cluster analysis. The NCEP/NCAR reanalysis data is used to evaluate the occurring circulation types (CTs) within the ECHAM5-MPI/OM Atmosphere and Ocean Global Circulation Model (AOGCM) for the period 1961–2000. Our analysis shows that the ECHAM5-MPI/OM model is capable of reproducing circulation patterns for the storm events. The occurrence of present and future ECHAM5-MPI/OM CTs is investigated. It is shown that storm CTs are expected to occur noticeably less frequently in the middle of the 21^st century.  相似文献   

Determination of grid size for digital terrain modelling in landscape investigations—exemplified by soil moisture distribution at a micro-scale     

Igor V. Florinsky  Galina A. Kuryakova 《International journal of geographical information science》2013,27(8):815-832

The central problem of a combined analysis of digital terrain models (DTMs) and other landscape data is determination of a DTM grid size (w) providing a correct study of relationships between topographic variables and landscape properties. Generally, an adequate w is determined by an expert estimate, and solutions are largely subjective. We developed an experimental statistical method to determine an adequate w for DTMs applied to landscape studies. The method includes the following steps: (a) derivation of a DTM set using a series of w_i , (b) performance of a correlation analysis of data on a landscape property and a topographic variable estimated with various w_i , (c) plotting of correlation coefficients obtained versus w, and (d) determination of smoothed plot portions indicating intervals of an adequate w. We applied the method developed to study the ifluence of topography on the spatial distribution of soil moisture (M) at a micro-scale. We investigated the dependence of M on gradient (G), horizontal (k_h ), vertical (k_v ), and mean (H) landsurface curvatures. For DTM derivation, we used 13 values of w_i from 1 to 7m. An interval of adequate w_i for M falls between 2.25 and 3.25m in the given terrain conditions. In absolute magnitudes, correlation coefficients are largest within this interval; correlation coefficients of M with G, k_h , k_v and H are 0.28, 0.52, 0.50 and 0.60, respectively, for w = 3m. The results obtained demonstrate that the method actually works to identify an adequate w at a micro-scale. The method developed allows estimation of an adequate area of landform which realise a topographic control of landscape properties.  相似文献   

Modeling crustal structure of the south-eastern Fennoscandia     

Ninel I. Pavlenkova  Galina A. Pavlenkova 《Studia Geophysica et Geodaetica》2012,56(2):567-583

We present new seismic velocity models of the crust and uppermost mantle along two refraction and wide-angle reflection profiles in the southern Fennoscandia: the Pribalt and 1-EB profiles. Some new results obtained along the Coast and the Baltic Sea profiles are also presented. The intercept time method and ray tracing are used for the modeling. The study shows that the lateral variations are small in the velocity structure of?? the crust up to the depth of 20?C25 km. The most significant lateral variations are observed in the Moho discontinuity topography and in the seismic velocities in the lower crust. In Paleoproterosoic Svekofennian domain, besides the well-known Moho depression in southern Finland, another Moho depression is revealed in the region from the Gotland Island to the Gulf of Riga. We suggest that this depression can correspond to the unknown crustal unit (we call it the Gotland-Riga belt). The Moho depth increases from the average of 40?C45 km to 55 km in this belt. The Moho depression is filled by the matter with velocities of 6.8?C7.1 km/s. Deep faults inclined to the north and strong variations of the mantle velocities are typical for the uppermost mantle of the Gotland-Riga belt.  相似文献   

Physics of seasonally ice-covered lakes: a review   总被引：2，自引：0，他引：2  

Georgiy Kirillin  Matti Lepp?ranta  Arkady Terzhevik  Nikolai Granin  Juliane Bernhardt  Christof Engelhardt  Tatyana Efremova  Sergey Golosov  Nikolai Palshin  Pavel Sherstyankin  Galina Zdorovennova  Roman Zdorovennov 《Aquatic Sciences - Research Across Boundaries》2012,74(4):659-682

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