Vegetation and climate history in the Laptev Sea region (Arctic Siberia) during Late Quaternary inferred from pollen records     

Andrei A. Andreev  Lutz Schirrmeister  Pavel E. Tarasov  Andrey Ganopolski  Viktor Brovkin  Christine Siegert  Sebastian Wetterich  Hans-Wolfgang Hubberten 《Quaternary Science Reviews》2011,30(17-18):2182-2199

Paleoenvironmental records from a number of permafrost sections and lacustrine cores from the Laptev Sea region dated by several methods (¹⁴C-AMS, TL, IRSL, OSL and ²³⁰Th/U) were analyzed for pollen and palynomorphs. The records reveal the environmental history for the last ca 200 kyr. For interglacial pollen spectra, quantitative temperature values were estimated using the best modern analogue method. Sparse grass-sedge vegetation indicating arctic desert environmental conditions existed prior to 200 kyr ago. Dense, wet grass-sedge tundra habitats dominated during an interstadial ca 200–190 kyr ago, reflecting warmer and wetter summers than before. Sparser vegetation communities point to much more severe stadial conditions ca 190–130 kyr ago. Open grass and Artemisia communities with shrub stands (Alnus fruticosa, Salix, Betula nana) in more protected and moister places characterized the beginning of the Last Interglacial indicate climate conditions similar to present. Shrub tundra (Alnus fruticosa and Betula nana) dominated during the middle Eemian climatic optimum, when summer temperatures were 4–5 °C higher than today. Early-Weichselian sparse grass-sedge dominated vegetation indicates climate conditions colder and dryer than in the previous interval. Middle Weichselian Interstadial records indicate moister and warmer climate conditions, for example, in the interval 40–32 kyr BP Salix was present within dense, grass-sedge dominated vegetation. Sedge-grass-Artemisia-communities indicate that climate became cooler and drier after 30 kyr BP, and cold, dry conditions characterized the Late Weichselian, ca 26–16 kyr BP, when grass-dominated communities with Caryophyllaceae, Asteraceae, Cichoriaceae, Selaginella rupestris were present. From 16 to 12 kyr BP, grass-sedge communities with Caryophyllaceae, Asteraceae, and Cichoriaceae indicate climate was significantly warmer and moister than during the previous interval. The presence of Salix and Betula reflect temperatures about 4 °C higher than present at about 12–11 kyr BP, during the Allerød interval, but shrubs were absent in the Younger Dryas interval, pointing to a deterioration of climate conditions. Alnus fruticosa, Betula nana, Poaceae, and Cyperaceae dominate early Holocene spectra. Reconstructed absolute temperature values were substantially warmer than present (up to 12 °C). Shrubs gradually disappeared from coastal areas after 7.6 kyr BP when vegetation cover became similar to modern. A comparison of proxy-based paleoenvironmental reconstructions with the simulations performed by an Earth system model of intermediate complexity (CLIMBER-2) show good accordance between the regional paleodata and model simulations, especially for the warmer intervals.  相似文献   

Some pressure test phenomena of worden and CG-2 (sharpe) gravimeters     

Karel Diviš  Viktor Höschl  Stanislav Hrách  Reviewer M. Pick 《Studia Geophysica et Geodaetica》1981,25(1):14-23

Summary The results of pressure tests of gravimeters Worden No. 961, CG-2 Nos 174 G, 323 and 374 in a pressure chamber are presented. Apart from deriving the barometric correction, the authors have also studied accompanying phenomena, which occur during pressure tests of gravimeters — the barometric after-effect and hysteresis. The processing of the results in two ways differing in the method of eliminating the drift of the gravimeter, yields nearly identical results. The hysteresis was investigated for atmospheric pressures of 720±150 Torr (1 Torr=0.133322 kPa), a rate of change of 30 Torr/min and a temperature of 22°C. The barometric after-effect was investigated in greater detail for the CG-2 gravimeter No. 174 G at a pressure difference of 225 Torr, rate of change of 30, 15 and 7.5 Torr/min and a gravimeter heating temperature of 35 °C. It was also found that the barometric correction can be determined, using the method given, with sufficient accuracy. As a result of the existence of hysteresis, however, the derived results must be applied carefully in field gravity measurements with some gravimeters.  相似文献   

Computation of gravity anomalies caused by three-dimensional bodies of arbitrary shape and arbitrary varying density     

Viktor Höschl  Reviewer M. Burda 《Studia Geophysica et Geodaetica》1981,25(4):315-320

Summary A numerical method is proposed which enables a direct computation of the vertical gravity anomaly due to three-dimensional bodies of arbitrary shape and with an inhomogeneous density distribution. The bodies are approximated by an assembly of appropriate curved finite elements. Gravity effects of such elements are calculated using the Gaussian quadrature formula. The integration domain is simply a cube, into which all the finite elements are transformed. The accuracy of the method is tested on a numerical example.  相似文献   

云母的命名   总被引：3，自引：1，他引：3  

MilanRieder  GiancarloCavazzini 《矿物学报》2001,21(2):119-128

根据容许的化学成分范围，给出了纯云母类（true micas)，脆云母类（brittle micas)和层间阳离子亏损的云母类（interlayer-cation-deficient micas)的端元矿物和矿物种，概括介绍了利用现有的各种化学分析数据计算云母晶体化学式的方法，以及描述不常见化学元素代换或多型堆积的一系列修饰词和后缀，列出了云母的同义词和变种、定名有误的物质，以及过去使用或误用的云母名称。  相似文献   

Multi-Element Reference Samples of Black Shale     

Lev L. Petrov  Yuri N. Kornakov  Irina la. Korotaeva  Elena A. Anchutina  Luidmila A. Persikova  Vera E. Susloparova  Irina N. Fedorova  Viktor A. Shibanov 《Geostandards and Geoanalytical Research》2004,28(1):89-102

This paper describes the creation of two new reference samples of black shale, SCHS-1 and SLg-1, collected in the Bodaibo Region of Irkutsk District (Siberia, Russia). These samples have been developed as State Standard Samples to meet the requirements of Russia's Normative Documents, so that they can be recognised by the Russian State Certification Agency and included on the State Register of certified reference materials. SCHS-1 was produced from shale of the Khomolkho suite; SLg-1 represents the average composition of the Sukhoy Log gold deposit (within Au mineralisation). The homogeneity was assessed by applying the concept of potential inhomogeneity, and the inhomogeneity uncertainties (σ_inhom) for the indicator elements that were estimated experimentally by silicate XRF analysis. It was found that a majority of the indicator elements was characterised by σ_inhom/Δ_p < 1/8 (Δ_p is the permissible certification uncertainty), and so σ_inhom was neglected for the indicator elements and all other elements that were included in their respective group. The value of σ_inhom calculated for Fe (σ_inhom,Fe/Δ_p > 1 /8) was taken into consideration for the noble metals and their associated elements (e.g., Ag, As, Au, etc.). More than fifty laboratories (thirty-seven from Russia) were involved in the interlaboratory experiment (ILE) to analyse these reference samples. The data obtained from the ILE allowed SCHS-1 and SLg-1 to be certified for, fifty-one and forty-three elements, respectively, as State Standard Samples.  相似文献   

Periglacial landscape evolution and environmental changes of Arctic lowland areas for the last 60 000 years (western Laptev Sea coast, Cape Mamontov Klyk)     

Lutz Schirrmeister  Guido Grosse  Viktor Kunitsky  Diana Magens  Hanno Meyer  Alexander Dereviagin  Tatyana Kuznetsova  rei Andreev  Olga Babiy  Frank Kienast  Mikhael Grigoriev  Pier Paul Overduin  & Frank Preusser 《Polar research》2008,27(2):249-272

Non-glaciated Arctic lowlands in north-east Siberia were subjected to extensive landscape and environmental changes during the Late Quaternary. Coastal cliffs along the Arctic shelf seas expose terrestrial archives containing numerous palaeoenvironmental indicators (e.g., pollen, plant macro-fossils and mammal fossils) preserved in the permafrost. The presented sedimentological (grain size, magnetic susceptibility and biogeochemical parameters), cryolithological, geochronological (radiocarbon, accelerator mass spectrometry and infrared-stimulated luminescence), heavy mineral and palaeoecological records from Cape Mamontov Klyk record the environmental dynamics of an Arctic shelf lowland east of the Taymyr Peninsula, and thus, near the eastern edge of the Eurasian ice sheet, over the last 60 Ky. This region is also considered to be the westernmost part of Beringia, the non-glaciated landmass that lay between the Eurasian and the Laurentian ice caps during the Late Pleistocene. Several units and subunits of sand deposits, peat–sand alternations, ice-rich palaeocryosol sequences (Ice Complex) and peaty fillings of thermokarst depressions and valleys were presented. The recorded proxy data sets reflect cold stadial climate conditions between 60 and 50 Kya, moderate inderstadial conditions between 50 and 25 Kya and cold stadial conditions from 25 to 15 Kya. The Late Pleistocene to Holocene transition, including the Allerød warm period, the early to middle Holocene thermal optimum and the late Holocene cooling, are also recorded. Three phases of landscape dynamic (fluvial/alluvial, irregular slope run-off and thermokarst) were presented in a schematic model, and were subsequently correlated with the supraregional environmental history between the Early Weichselian and the Holocene.  相似文献   

A thermodynamic model of Fe–Cr spinels     

Viktor?A.?KurepinEmail author 《Contributions to Mineralogy and Petrology》2005,149(5):591-599

A new thermodynamic model for multi-component spinel solid solutions has been developed which takes into account thermodynamic consequences of cation mixing in spinel sublattices. It has been applied to the evaluation of thermodynamic functions of cation mixing and thermodynamic properties of Fe₃O₄–FeCr₂O₄ spinels using intracrystalline cation distribution in magnetite, lattice parameters and activity-composition relations of magnetite–chromite solid solutions. According to the model, cation distribution in binary spinels, (Fe_1-x²⁺ Fe_x³⁺)[Fe_x²⁺Fe_2-2y-x³⁺Cr_2y]O₄, and their thermodynamic properties depend strongly on Fe²⁺–Cr³⁺ cation mixing. Mixing of Fe²⁺–Fe³⁺ and Fe³⁺–Cr³⁺ can be accepted as ideal. If Fe²⁺, Fe³⁺ and Cr are denoted as 1, 3 and 4 respectively, the equation of cation distribution is –RT ln(x²/((1–x)(2–2y–x)))= G₁₃^* + (1–2x)W₁₃+y(W₁₄–W₁₃–W₃₄) where G₁₃^* is the difference between the Gibbs energy of inverse and normal magnetite, W_ij is a Margules parameter of cation mixing and G₁₃^*, J/mol =–23,000+13.4 T, W₁₄=36 kJ/mol, W₁₃=W₃₄=0. The positive nonconfigurational Gibbs energy of mixing is the main reason for changing activity–composition relations with temperature. According to the model, the solvus in Fe₃O₄–FeCr₂O₄ spinel has a critical temperature close to 500°C, which is consistent with mineralogical data.  相似文献   

Pollution law — the way forward     

Viktor Sebek 《Marine Policy》1980,4(3):158

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