The characteristic pattern of multiple colored layers in coastal stratified lakes in the process of separation from the White Sea   总被引：1，自引：1，他引：0  

Krasnova  Elena D.  Matorin  Dmitry N.  Belevich  Tatiana A.  Efimova  Ludmila E.  Kharcheva  Anastasiia V.  Kokryatskaya  Natalia M.  Losyuk  Galina N.  Todorenko  Daria A.  Voronov  Dmitry A.  Patsaeva  Svetlana V. 《中国海洋湖沼学报》2018,36(6):1962-1977

An unusual feature of the saline stratified lakes that were formed due to ongoing postglacial uplift on the White Sea coast is the presence of several differently colored thin layers in the zone with sharp gradients. Colored layers in five lakes at various stages of separation from the sea were investigated using optical microscopy, spectrophotometry, spectrofluorimetry, and photobiology. The upper greenish colored layer located in the aerobic strata of all lakes near the compensation depth of 1% light penetration contains green algae. In the chemocline, another layer, brightly green, red or pink, is dominated by mixotrophic flagellates. Despite the very low light intensities and the presence of H 2 S, active photosynthesis by these algae appears to be occurring, as indicated by high values of the maximum quantum yield of primary photochemistry, electron transport activity, photosynthetic activity of photosystem II, the fraction of active centers, and low values of heat dissipation. In the reduced zone of the chemocline, a dense green or brown suspension of anoxygenic phototrophs(green sulfur bacteria) is located.  相似文献   

Energetics of a galactic fountain     

I. G. Kovalenko  Yu. A. Shchekinov 《Astrophysics》1985,23(2):578-584

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Natrocarbonatitic melts of the Bol’shaya Tagna Massif, the Eastern Sayan region     

I. A. Andreeva  V. I. Kovalenko  N. N. Kononkova 《Doklady Earth Sciences》2006,408(1):542-546

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Variability and climate sensitivity of fast ice extent in the north-eastern Kara Sea   总被引：1，自引：0，他引：1  

Dmitry Divine  Reinert Korsnes  Alexander Makshtas 《Polar research》2003,22(1):27-34

This work investigates the temporal and spatial variation of shore-fast ice extent in the north-eastern part of the Kara Sea during 1953-1990 and its sensitivity to interannual variability of the regional climate. The area of fast ice in spring months shows a bimodal distribution. This indicates the existence of two different regimes of fast ice formation driven by the system of prevailing winds. The westward wind transport during the cold season gives larger fast ice extent while the eastward wind transport suppresses the expansion of fast ice. There is a significant correlation (ca. −0.55) between the average winter temperature and the area of fast ice. Linear trends for time records of shore-fast ice area in spring show a decrease during 1953-1990. This decrease is most pronounced in April: the mean fast ice area in April is 12% lower in 1988-1990 compared to 1953-55. A comparison of fast ice regimes for two particular years–1979 and 1985–revealed a significant influence of cyclone activity on fast ice development over the course of the cold season. It is shown that partial break-ups of fast ice in spring 1985 are associated with the passage of cyclones across the area of fast ice.  相似文献   

Isotope provinces, mechanisms of generation and sources of the continental crust in the Central Asian mobile belt: geological and isotopic evidence   总被引：17，自引：0，他引：17  

V. I. Kovalenko  V. V. Yarmolyuk  V. P. Kovach  A. B. Kotov  I. K. Kozakov  E. B. Salnikova  A. M. Larin 《Journal of Asian Earth Sciences》2004,23(5):605-627

The available geological, geochronological and isotopic data on the felsic magmatic and related rocks from South Siberia, Transbaikalia and Mongolia are summarized to improve our understanding of the mechanisms and processes of the Phanerozoic crustal growth in the Central Asian mobile belt (CAMB). The following isotope provinces have been recognised: ‘Precambrian’ (T_DM=3.3–2.9 and 2.5–0.9 Ga) at the microcontinental blocks, ‘Caledonian’ (T_DM=1.1–0.55 Ga), ‘Hercynian’ (T_DM=0.8–0.5 Ma) and ‘Indosinian’ (T_DM=0.3 Ga) that coincide with coeval tectonic zones and formed at 570–475, 420–320 and 310–220 Ma. Continental crust of the microcontinents is underlain by, or intermixed with, ‘juvenile’ crust as evidenced by its isotopic heterogeneity. The continental crust of the Caledonian, Hercynian and Indosinian provinces is isotopically homogeneous and was produced from respective juvenile sources with addition of old crustal material in the island arcs or active continental margin environments. The crustal growth in the CAMB had episodic character and important crust-forming events took place in the Phanerozoic. Formation of the CAMB was connected with break up of the Rodinia supercontinent in consequence of creation of the South-Pacific hot superplume. Intraplate magmatism preceding and accompanying permanently other magmatic activity in the CAMB was caused by influence of the long-term South-Pacific plume or the Asian plume damping since the Devonian.  相似文献   

3-D modelling and analysis of Dst C-responses in the North Pacific Ocean region, revisited     

Alexei Kuvshinov  Hisashi Utada  Dmitry Avdeev  Takao Koyama 《Geophysical Journal International》2005,160(2):505-526

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Evolution of occlusal shape of the first and second upper molars of Middle–Late Pleistocene collared lemmings (Dicrostonyx,Arvicolinae, Rodentia) in northeast European Russia          下载免费PDF全文

Dmitry Ponomarev  Andrey Puzachenko 《Boreas: An International Journal of Quaternary Research》2015,44(4):741-759

An approach combining traditional morphotypical methods, multivariate analysis and informational‐statistical methods was used to study evolutionary changes in the occlusal shape of the first and second upper molars of Recent and Middle–Late Pleistocene Dicrostonyx (32 samples) from localities in northeast European Russia (northeastern Russian Plain, the Timan Ridge and the northern part of the Urals). The evolutionary history is described in terms of morphological evolutionary levels of teeth suggested by Smirnov et al. (1997, Materialy Po Istorii I Sovremennomu Sostojaniju Fauny Severa Zapadnoj Sibiri: Sbornik Nauchnyh Trudov, Chelyabinsk, slightly modified). Based on ¹⁴C‐dated samples, levels of molar evolution did not always successively replace each other in time, but rather there were often synchronous populations at any given level. This finding supports the notion of a mosaic pattern of morphotypical diversity and relatively independent, parallel evolution of lemming teeth amongst different populations. Six relatively distinct stages in the evolutionary history of Dicrostonyx from the Pechora (Dnieper) to Recent time have been described, but estimations of their relative ages are often debatable. The rates of change in the M1 and M2 morphotypes and morphological diversity in collared lemmings varied over the entire time interval. The fastest replacement of morphotypes and the highest level of morphological diversity in the study area occurred approximately during the Lateglacial (16–10 cal. ka BP). In the present study, we suggest a new version of evolutionary history of collared lemmings in northeast European Russia, taking into consideration the morphological variability of molars, radiocarbon dates and geological data. Our results provide a more detailed pattern of species evolution in the studied region and specific ages of some localities.  相似文献   

Vegetation and climate changes in northwestern Russia during the Lateglacial and Holocene inferred from the Lake Ladoga pollen record     

Larisa A. Savelieva  Andrei A. Andreev  Raphael Gromig  Dmitry A. Subetto  Grigory B. Fedorov  Volker Wennrich  Bernd Wagner  Martin Melles 《Boreas: An International Journal of Quaternary Research》2019,48(2):349-360

The new pollen record from the upper 12.75 m of a sediment core obtained in Lake Ladoga documents regional vegetation and climate changes in northwestern Russia over the last 13.9 cal. ka. The Lateglacial chronostratigraphy is based on varve chronology, while the Holocene stratigraphy is based on AMS ¹⁴C and OSL dates, supported by comparison with regional pollen records. During the Lateglacial (c. 13.9–11.2 cal. ka BP), the Lake Ladoga region experienced several climatic fluctuations as reflected in vegetation changes. Shrub and grass communities dominated between c. 13.9 and 13.2 cal. ka BP. The increase in Picea pollen at c. 13.2 cal. ka BP probably reflects the appearance of spruce in the southern Ladoga region at the beginning of the Allerød interstadial. After c. 12.6 cal. ka BP, the Younger Dryas cooling caused a significant decrease in spruce and increase in Artemisia with other herbs, indicative of tundra‐ and steppe‐like vegetation. A sharp transition from tundra‐steppe habitats to sparse birch forests characterizes the onset of Holocene warming c. 11.2 cal. ka BP. Pine forests dominated in the region from c. 9.0 to 8.1 cal. ka BP. The most favourable climatic conditions for deciduous broad‐leaved taxa existed between c. 8.1 and 5.5 cal. ka BP. Alder experiences an abrupt increase in the local vegetation c. 7.8 cal. ka BP. The decrease in tree pollen taxa (especially Picea) and the increase in herbs (mainly Poaceae) probably reflect human activity during the last 2.2 cal. ka. Pine forests have dominated the region since that time. Secale and other Cerealia pollen as well as ruderal herbs are permanently recorded since c. 0.8 cal. ka BP.  相似文献   

Database of molecular masers and variable stars     

Andrej M.Sobolev  Dmitry A.Ladeyschikov  Jun-ichi Nakashima 《天文和天体物理学研究(英文版)》2019,(3)

We present the database of maser sources in H2 O, OH and Si O lines that can be used to identify and study variable stars at evolved stages. Detecting the maser emission in H2 O, OH and Si O molecules toward infrared-excess objects is one of the methods for identifing long-period variables(LPVs, including miras and semiregulars), because these stars exhibit maser activity in their circumstellar shells. Our sample contains 1803 known LPV objects. Forty-six percent of these stars(832 objects) manifest maser emission in the line of at least one molecule: H2 O, OH or Si O. We use the database of circumstellar masers in order to search for LPVs which are not included in the General Catalogue of Variable Stars(GCVS). Our database contains 4806 objects(3866 objects without associations in GCVS) with maser detection in at least one molecule. Therefore it is possible to use the database in order to locate and study the large sample of LPV stars. The database can be accessed at http://maserdb.net.  相似文献   

Basin evolution and palaeoenvironmental variability of the thermokarst lake El'gene‐Kyuele,Arctic Siberia          下载免费PDF全文

Philipp Schleusner  Boris K. Biskaborn  Frank Kienast  Juliane Wolter  Dmitry Subetto  Bernhard Diekmann 《Boreas: An International Journal of Quaternary Research》2015,44(1):216-229

Thermokarst lakes are a widespread feature of the Arctic tundra, in which highly dynamic processes are closely connected with current and past climate changes. We investigated late Quaternary sediment dynamics, basin and shoreline evolution, and environmental interrelations of Lake El'gene‐Kyuele in the NE Siberian Arctic (latitude 71°17′N, longitude 125°34′E). The water‐body displays thaw‐lake characteristics cutting into both Pleistocene Ice Complex and Holocene alas sediments. Our methods are based on grain size distribution, mineralogical composition, TOC/N ratio, stable carbon isotopes and the analysis of plant macrofossils from a 3.5‐m sediment profile at the modern eastern lake shore. Our results show two main sources for sediments in the lake basin: terrigenous diamicton supplied from thermokarst slopes and the lake shore, and lacustrine detritus that has mainly settled in the deep lake basin. The lake and its adjacent thermokarst basin rapidly expanded during the early Holocene. This climatically warmer than today period was characterized by forest or forest tundra vegetation composed of larches, birch trees and shrubs. Woodlands of both the HTM and the Late Pleistocene were affected by fire, which potentially triggered the initiation of thermokarst processes resulting later in lake formation and expansion. The maximum lake depth at the study site and the lowest limnic bioproductivity occurred during the longest time interval of ～7 ka starting in the Holocene Thermal Maximum and lasting throughout the progressively cooler Neoglacial, whereas partial drainage and an extensive shift of the lake shoreline occurred ～0.9 cal. ka BP. Correspondingly, this study discusses different climatic and environmental drivers for the dynamics of a thermokarst basin.  相似文献