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EILIV LARSEN KURT H. KJæR MARIA JENSEN IGOR N. DEMIDOV LENA HAKANSSON AAGE PAUS 《Boreas: An International Journal of Quaternary Research》2006,35(3):476-492
A section, almost 20 km long and up to 80 m high, through alternating layers of diamict and sorted sediments is superbly exposed on the north coast of the Kanin Peninsula, northwestern Russia. The diamicts represent multiple glacial advances by the Barents Sea and the Kara Sea ice sheets during the Weichselian. The diamicts and stratigraphically older lacustrine, fluvial and shallow marine sediments have been thrust as nappes by the Barents Sea and Kara Sea ice sheets. Based on stratigraphic position, OSL dating, sea level information and pollen, it is evident that the sorted sediments were deposited in the Late Eemian-Early Weichselian. Sedimentation started in lake basins and continued in shallow marine embayments when the lakes opened to the sea. The observed transition from lacustrine to shallow marine sedimentation could represent coastal retreat during stable or rising sea level. 相似文献
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Diagnostic computations of density-driven circulation for seven winters from 1973 through 1979 were carried out. The only forcing was provided by observed temperature and salinity data collected during onsite Russian winter surveys in 1973–79. Computed circulations from 1973 through 1978 were close to the mean circulation obtained earlier by averaging observed 1973–79 temperature and salinity (Polyakov & Timokhov 1994). The computed 1979 density-driven circulation flowed counter-clockwise to the north of the Laptev Sea. This circulation pattern was caused by an anomalous salinity distribution associated with changes in the atmospheric circulation regime in 1979. Prevailing offshore winds blew fresh water from the Laptev and East Siberian shelves toward Fram Strait. Fresh water was exchanged for saltier intermediate water that upwelled to the surface along the slope. The observed surface salinity anomalies at the continental slope of the Laptev Sea in 1979 increased by several salinity units. One may speculate that the same process may have caused the observed salinification of the Eurasian Basin in the 1990s. 相似文献
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Interdecadal changes in the links between European precipitation and atmospheric circulation during boreal spring and fall 总被引：2，自引：0，他引：2
IGOR I. ZVERYAEV 《地球，A辑:动力气象学与海洋学》2009,61(1):50-56
A gridded monthly terrestrial precipitation from the Climatic Research Unit (CRU), University of East Anglia data set and the UK Met Office Northern Hemisphere mean sea level pressure data are used to investigate interdecadal changes in the relationships between precipitation variability over Europe and atmospheric circulation in the Atlantic–European sector during boreal spring and fall.
Singular value decomposition (SVD) analysis, performed for the climatic periods of strong/weak links to the North Atlantic Oscillation (NAO) during spring and fall, revealed considerable interdecadal changes both in the strength and the structure of the links between European precipitation and regional atmospheric circulation. During periods of strong links to the NAO, the leading SVD mode is characterized by the NAO-like meridional dipole in sea level pressure (SLP) fields and associated opposite precipitation variations over northern/southern Europe. When the links to the NAO are weak, the leading SVD mode is represented by the tripole pattern in SLP fields over the North Atlantic–European region, driving regional precipitation variability both in spring and fall. Further correlation analysis has shown that this mode is associated with the Scandinavian teleconnection pattern (SCA). Thus, for the considered seasons during periods of weak NAO influence, the SCA plays a role of major driver of the regional precipitation variability. 相似文献
Singular value decomposition (SVD) analysis, performed for the climatic periods of strong/weak links to the North Atlantic Oscillation (NAO) during spring and fall, revealed considerable interdecadal changes both in the strength and the structure of the links between European precipitation and regional atmospheric circulation. During periods of strong links to the NAO, the leading SVD mode is characterized by the NAO-like meridional dipole in sea level pressure (SLP) fields and associated opposite precipitation variations over northern/southern Europe. When the links to the NAO are weak, the leading SVD mode is represented by the tripole pattern in SLP fields over the North Atlantic–European region, driving regional precipitation variability both in spring and fall. Further correlation analysis has shown that this mode is associated with the Scandinavian teleconnection pattern (SCA). Thus, for the considered seasons during periods of weak NAO influence, the SCA plays a role of major driver of the regional precipitation variability. 相似文献
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The intensity of sea-ice interaction in the Fram Strait is estimated from hydrographic data by use of three different methods. Preliminary results concerning fresh water formation rate are reported. 相似文献
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Conditions of Formation and Crystallization Kinetics of Highly Oxidized Pseudotachylytes from the High Tatras (Slovakia) 总被引：2，自引：0，他引：2
PETRIK IGOR; NABELEK PETER I.; JANAK MARIAN; PLASIENKA DUSAN 《Journal of Petrology》2003,44(5):901-927
Tectonic activity during the Miocene exhumation of the Tatragranitoid basement resulted in frictional melting of granite.The activity marks the early stages of the faulting that isresponsible for uplift of the High Tatras. As indicated by pre-existingcataclasite metamorphic mineral assemblages, the ambient pressurewas about 250–300 MPa, corresponding to depths between10 and 12 km. The pseudotachylytes are Fe rich, highly oxidizedand crystalline. The matrix composition suggests disequilibriumpartial melting of a biotite-dominated assemblage. Oxygen isotopiccompositions of a pseudotachylyte sample and its constituentminerals show equilibration with the host granodiorite and allowfor the introduction of oxidizing external water rather thanoxidation as a result of the dissociation of free water liberatedduring melting. The kinetic information extracted from hematitecrystal-size distributions (CSDs) that are preserved in feldspathicmatrices shows that crystals in most places were accumulatedwhile the system was open. The melt was highly mobile and proneto strong differentiation. The hematite crystals reach a maximumof 26 vol. % (45 wt % Fe2O3). In rare places where the flowceased, the system became closed and produced distinct CSDs.The longest apparent crystallization times (90 s) are recordedmostly in pools in the central parts of the pseudotachylyteswhereas the shortest times (10 s) come from rims and tips offractures. The estimated hematite growth rate was about fiveorders of magnitude higher than that of ilmenite in lava lakes.Such extreme crystallization rates result from high undercoolingsassociated with high cooling rates. Very high cooling ratesare promoted by the extremely high surface/volume ratios ofthe pseudotachylyte sheets. KEY WORDS: pseudotachylyte; hematite; kinetics; High Tatra; Slovakia 相似文献
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Peculiarities in the intra-annual variations of 03 , N2 0 and CH4 in the middle and upper stratosphere are analysed by different methods for the middle and polar latitudes of the Northern and the Southern hemispheres. In the middle stratosphere the phase of the O, annual harmonic shifts in the Northern Hemisphere from polar to lower latitudes, while in the Southern Hemisphere the downward shift is exhibited. The phase of the NiO annual harmonic shifts to the poles both in the Northern and Southern hemispheres, but in the Northern Hemisphere it is almost vertical with the horizontal spreading, while in the Southern Hemisphere the phase propagation has a remarkable downward component. The most similar shifts of the phase of the annual harmonic in the middle stratosphere of both hemispheres are exhibited for the CII" content in the middle and high latitudes. Remarkable differences are noted between the intervals with the increase of mixing ratios in the annual cycle at different latitudinal belts. In particular, these intervals are large in subtropical stratosphere, with a shorter and steeper decrease of the mixing ratios. The general decrease of these intervals is exhibited from middle to polar latitudes. The striking difference in temporal variations of the species exists between the northern polar and middle latitudes, where the month-to-month changes of the species are often opposite each to other. These peculiarities and interhemispheric differences are associated with the different stratospheric dynamics of the Northern and Southern hemispheres, particularly with different regimes of planetary wave activity in the northern and southern extratropical latitudes. 相似文献
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ELBURG MARLINA; KAMENETSKY VADIM S.; NIKOGOSIAN IGOR; FODEN JOHN; SOBOLEV ALEXANDER V. 《Journal of Petrology》2006,47(12):2433-2462
Mineral and melt inclusions in olivines from the most Mg-richmagma from the southern West Sulawesi Volcanic Province indicatethat two distinct melts contributed to its petrogenesis. Thecontribution that dominates the whole-rock composition comesfrom a liquid with high CaO (up to 16 wt %) and low Al2O3 contents(CaO/Al2O3 up to 1), in equilibrium with spinel, olivine (Fo85–91;CaO 0·35–0·5 wt %; NiO 0·2–0·30wt %) and clinopyroxene. The other component is richer in SiO2(>50 wt %) and Al2O3 (19–21 wt %), but contains significantlyless CaO (<4 wt %); it is in equilibrium with Cr-rich spinelwith a low TiO2 content, olivine with low CaO and high NiO content(Fo90–94; CaO 0·05–0·20 wt %; NiO0·35–0·5 wt %), and orthopyroxene. Boththe high- and low-CaO melts are potassium-rich (>3 wt % K2O).The high-CaO melt has a normalized trace element pattern thatis typical for subduction-related volcanic rocks, with negativeTa–Nb and Ti anomalies, positive K, Pb and Sr anomalies,and a relatively flat heavy rare earth element (HREE) pattern.The low-CaO melt shows Y and HREE depletion (Gdn/Ybn 41), butits trace element pattern resembles that of the whole-rock andhigh-CaO melt in other respects, suggesting only small distinctionsin source areas between the two components. We propose thatthe depth of melting and the dominance of H2O- or CO2-bearingfluids were the main controls on generating these contrastingmagmas in a syn-collisional environment. The composition ofthe low-CaO magma does not have any obvious rock equivalent,and it is possible that this type of magma does not easily reachthe Earth's surface without the assistance of a water-poor carriermagma. KEY WORDS: melt inclusions; mineral chemistry; olivine; syn-collisional magmatism; ankaramites; low-Ca magma 相似文献
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ASTRID LYSÅ MARIA A. JENSEN EILIV LARSEN OLA FREDIN IGOR N. DEMIDOV 《Boreas: An International Journal of Quaternary Research》2011,40(3):481-497
Lyså, A., Jensen, M. A., Larsen, E., Fredin, O. & Demidov, I. N.* 2010: Ice‐distal landscape and sediment signatures evidencing damming and drainage of large pro‐glacial lakes, northwest Russia. Boreas, Vol. 40, pp. 481–497. 10.1111/j.1502‐3885.2010.00197.x. ISSN 0300‐9483. Sediments from river sections and the morphology of the upper reaches of Severnaya Dvina and Vychegda in northwest Russia show evidence of the existence of large ice‐dammed lakes in the area twice during the Weichselian. During the Late Weichselian, three separate ice‐dammed lakes (LGM lake(s)) existed, the largest one at about 135 m a.s.l. having a volume of about 1510 km3. Stepwise and rapid lake drainage is suggested to have taken place within less than 1000 years. The locations of various passpoints controlled the drainage, and when the lake was at its maximum level water spilled southeastwards into the Volga basin. Later, but before the lake water finally drained into the White Sea, water was routed northeastwards into the southeastern part of the Barents Sea. The oldest lake, the White Sea lake, existed around 67–57 ka ago, slightly in conflict with earlier palaeogeographic reconstructions regarding the chronology. The extent of the lake was constrained by, in addition to the Barents Sea ice‐sheet margin in the north, thresholds in the drainage basin. Later, one threshold was eroded and lowered during the LGM lake drainage. Given a lake level of about 115 m a.s.l., a lake area of about 2.5 × 104 km3 and a water volume of about 4800 km3, the lake drainage northwards and into the ocean probably impacted the ocean circulation. 相似文献
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KURT H. KJæR EILIV LARSEN SVEND FUNDER IGOR N. DEMIDOV MARIA JENSEN LENA HAKANSSON REW MURRAY 《Boreas: An International Journal of Quaternary Research》2006,35(3):444-475
Sediment successions from the Kanin Peninsula and Chyoshskaya Bay in northwestern Russia contain information on the marginal behaviour of all major ice sheets centred in Scandinavia, the Barents Sea and the Kara Sea during the Eemian-Weichselian. Extensive luminescence dating of regional lithostratigraphical units, supported by biostratigraphical evidence, identifies four major ice advances at 100-90, 70-65, 55-45 and 20-18 kyr ago interbedded with lacustrine, glaciolacustrine and marine sediments. The widespread occurrence of marine tidal sediments deposited c. 65-60 kyr ago allows a stratigraphical division of the Middle Weichselian Barents Sea and Kara Sea ice sheets into two shelf-based glaciations separated by almost complete deglaciation. The first ice dispersal centre was in the Barents Sea and thereafter in the Kara Sea. It is possible to extract both flow patterns from ice marginal landforms inside the southward termination. Accordingly, it is proposed that the Markhida line and its western continuation are asynchronous and originate from two separate glaciations before and after the marine transgression. The marine sedimentation occurred during a eustatic sea-level rise of up to 20 m/1000 yr, i.e. the Mezen Transgression. We speculate that the rapid eustatic sea-level rise triggered a collapse of the Barents Sea Ice Sheet at the MIS (Marine Isotope Stage) 4 to 3 transition. This is motivated by lack of an early marine highstand, the timing of events, and the marginal position of Arkhangelsk relative to open marine conditions. 相似文献