| 1. |
- Campbell, PJ, et al.
(författare)
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Pan-cancer analysis of whole genomes
- 2020
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 1476-4687 .- 0028-0836. ; 578:7793, s. 82-
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Tidskriftsartikel (refereegranskat)abstract
- Cancer is driven by genetic change, and the advent of massively parallel sequencing has enabled systematic documentation of this variation at the whole-genome scale1–3. Here we report the integrative analysis of 2,658 whole-cancer genomes and their matching normal tissues across 38 tumour types from the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium of the International Cancer Genome Consortium (ICGC) and The Cancer Genome Atlas (TCGA). We describe the generation of the PCAWG resource, facilitated by international data sharing using compute clouds. On average, cancer genomes contained 4–5 driver mutations when combining coding and non-coding genomic elements; however, in around 5% of cases no drivers were identified, suggesting that cancer driver discovery is not yet complete. Chromothripsis, in which many clustered structural variants arise in a single catastrophic event, is frequently an early event in tumour evolution; in acral melanoma, for example, these events precede most somatic point mutations and affect several cancer-associated genes simultaneously. Cancers with abnormal telomere maintenance often originate from tissues with low replicative activity and show several mechanisms of preventing telomere attrition to critical levels. Common and rare germline variants affect patterns of somatic mutation, including point mutations, structural variants and somatic retrotransposition. A collection of papers from the PCAWG Consortium describes non-coding mutations that drive cancer beyond those in the TERT promoter4; identifies new signatures of mutational processes that cause base substitutions, small insertions and deletions and structural variation5,6; analyses timings and patterns of tumour evolution7; describes the diverse transcriptional consequences of somatic mutation on splicing, expression levels, fusion genes and promoter activity8,9; and evaluates a range of more-specialized features of cancer genomes8,10–18.
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| 2. |
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| 3. |
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| 4. |
- Demidov, V. I., et al.
(författare)
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Electric probes for plasmas : The link between theory and instrument
- 2002
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 73:10, s. 3409-3439
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Forskningsöversikt (refereegranskat)abstract
- Electric probe methods for diagnostics of plasmas are reviewed with emphasis on the link between the appropriate probe theories and the instrumental design. The starting point is an elementary discussion of the working principles and a discussion of the physical quantities that can be measured by the probe method. This is followed by a systematic classification of the various regimes of probe operation and a summary of theories and methods for measurements of charged particle distributions. Application of a single probe and probe clusters for measurements of fluid observables is discussed. Probe clusters permit both instantaneous and time-averaged measurements without sweeping the probe voltage. Two classes of applications are presented as illustrations of the methods reviewed. These are measurements of cross sections and collision frequencies (plasma electron spectroscopy), and measurements of fluctuations and anomalous transport in magnetized plasma.
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| 5. |
- Demidov, V. I., et al.
(författare)
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Reducing influence of ion current on measurements of electron energy distributions in collisional plasmas
- 2001
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 72:11, s. 4106-4109
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Tidskriftsartikel (refereegranskat)abstract
- A method for reducing the influence of ion current on probe measurements of electron velocity distributions in plasmas has been developed and tested in noble gas afterglow plasmas. It is valid for diffusive transport of ions to the probe. Experiments have demonstrated high accuracy of the proposed method.
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| 6. |
- Demidov, V. I., et al.
(författare)
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The analysis of probe I-V characteristics in a magnetized low-temperature plasma
- 2001
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Ingår i: Contributions to Plasma Physics. - 0863-1042 .- 1521-3986. ; 41:5, s. 443-448
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Tidskriftsartikel (refereegranskat)abstract
- The validity of probe theories based on the classical electron transport to probes in low-temperature magnetized plasma of the toroidal device `Blaamann has been demonstrated. The analysis was carried out for the conditions when global transport of charged particles in the device is anomalous, namely for magnetic field up to 0.3 T and pressure range 0.1 - 1 Pa. It was shown also that for the magnetic field larger than 0.1 T probes longer than 15 mm provide electron saturation current practically independent of probe potential, hence more accurate measurements of the plasma parameters. The experiments have revealed that application of long probes oriented parallel to the magnetic field may cause an anomaly of the I-V characteristics in the sense that a local increase of the electron current appears near the plasma potential.
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| 7. |
- Demidov, V. V., et al.
(författare)
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Magnetic anisotropy in strained manganite films and bicrystal junctions
- 2013
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 113:16
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Tidskriftsartikel (refereegranskat)abstract
- Transport and magnetic properties of La0.67Sr0.33MnO3 (LSMO) manganite thin films and bicrystal junctions were investigated. Epitaxial manganite films were grown on SrTiO3, LaAlO3, NdGaO3 (NGO), and (LaAlO3)(0.3) + (Sr2AlTaO6)(0.7) substrates, and their magnetic anisotropy were determined by two independent techniques of magnetic resonance spectroscopy. It was demonstrated that by using these techniques, a small (0.3%) anisotropy of crystal structure at the (110) surface plane of the orthorhombic NGO substrate leads to uniaxial magnetic anisotropy of the films in the plane of the substrate at least at the room temperature. It was found that on vicinal NGO substrates, the value of magnetic anisotropy strength can be varied in the range 100-200 Oe at T = 295 K by changing the substrate vicinal angle from 0 degrees to 25 degrees. Measurement of the magnetic anisotropy of manganite bicrystal junction demonstrated the presence of two ferromagnetic spin subsystems for both types of bicrystal boundaries with tilting of basal plane of manganite tilted bicrystal (TB-junction) and with rotation of crystallographic axes (RB-junction) used for comparison. The magnetoresistance of TB-junctions increases with decreasing temperature and the misorientation angle. Variation of bicrystal misorientation angle does not lead to change of misorientation of easy magnetic axes in the film parts forming TB-junction. Analysis of the voltage dependencies of bicrystal junction conductivity show that the low value of the magnetoresistance for the LSMO bicrystal junctions can be caused by two scattering mechanisms. The first one is the spin-flip of spin-polarized carriers due to the strong electron-electron interactions in a disordered layer at the bicrystal boundary at low temperatures and the second one is spin-flip by antiferromagnetic magnons at high temperatures.
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| 8. |
- Demidov, V. V., et al.
(författare)
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Magnetic Anisotropy of Strained Epitaxial Manganite Films
- 2011
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Ingår i: Journal of Experimental and Theoretical Physics. - : Pleiades Publishing Ltd. - 1090-6509 .- 1063-7761. ; 112:5, s. 825-832
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Tidskriftsartikel (refereegranskat)abstract
- The in-plane magnetic anisotropy of epitaxial La(0.7)Sr(0.3)MnO(3) (LSMO) films is studied at room temperature by the following three independent techniques: magnetooptical Kerr effect, ferromagnetic resonance at a frequency of 9.61 GHz, and recording of absorption spectra of electromagnetic radiation at a frequency of 290.6 MHz. The films are deposited onto NdGaO(3) (NGO) substrates in which the (110) NGO plane is tilted at an angle of 0-25.7 degrees to the substrate plane. The uniaxial magnetic anisotropy induced by the strain of the film is found to increase with the tilt angle of the (110) NGO plane. A model is proposed to describe the change in the magnetic anisotropy energy with the tilt angle. A sharp increase in the radio-frequency absorption in a narrow angular range of a dc magnetic field near a hard magnetization axis is detected The anisotropy parameters of the LSMO films grown on (110) NGO, (001) SrTiO(3), and (001)[(LaAlO(3))(0.3) + (Sr(2)AlTaO(6))(0.7)] substrates are compared.
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| 9. |
- Hubberten, HW, et al.
(författare)
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The periglacial climate and environment in northern Eurasia during the Last Glaciation
- 2004
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 23:11-13, s. 1333-1357
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Forskningsöversikt (refereegranskat)abstract
- This paper summarizes the results of studies of the Late Weichselian periglacial environments carried out in key areas of northern Eurasia by several QUEEN teams (European Science Foundation (ESF) programme: "Quaternary Environment of the Eurasian North"). The palaeoglaciological boundary conditions are defined by geological data on timing and extent of the last glaciation obtained in the course of the EU funded project "Eurasian Ice Sheets". These data prove beyond any doubt, that with the exception of the northwestern fringe of the Taymyr Peninsula, the rest of the Eurasian mainland and Severnaya Zemlya were not affected by the Barents-Kara Sea fee Sheet during the Last Glacial Maximum (LGM). Inversed modelling based on these results shows that a progressive cooling which started around 30 ka BP, caused ice growth in Scandinavia and the northwestern areas of the Barents-Kara Sea shelf, due to a maritime climate with relatively high precipitation along the western flank of the developing ice sheets. In the rest of the Eurasian Arctic extremely low precipitation rates (less than 50 mm yr(-1)), did not allow ice sheet growth in spite of the very cold temperatures. Palaeoclimatic and palaeoenvironmental conditions for the time prior to, during, and after the LGM have been reconstructed for the non-glaciated areas around the LGM ice sheet with the use of faunal and vegetation records, permafrost, eolian sediments, alluvial deposits and other evidences. The changing environment, from interstadial conditions around 30 ka BP to a much colder and drier environment at the culmination of the LGM at 20-15 ka BP, and the beginning of warming around 15 ka BP have been elaborated from the field data, which fits well with the modelling results. (C) 2003 Elsevier Ltd. All rights reserved.
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| 10. |
- Ovsyannikov, Gennady, 1948, et al.
(författare)
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Magnetotransport characteristics of strained La0.7Sr0.3MnO3 epitaxial manganite films
- 2009
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Ingår i: Journal of Experimental and Theoretical Physics. - 1090-6509 .- 1063-7761. ; 108:1, s. 48-55
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Tidskriftsartikel (refereegranskat)abstract
- The electrical and magnetic characteristics of La0.7Sr0.3MnO3 (LSMO) epitaxial manganite films are investigated by different methods under conditions when the crystal structure is strongly strained as a result of mismatch between the lattice parameters of the LSMO crystal and the substrate. Substrates with lattice parameters larger and smaller than the nominal lattice parameter of the LSMO crystal are used in experiments. It is shown that the behavior of the temperature dependence of the electrical resistance for the films in the low-temperature range does not depend on the strain of the film and agrees well with the results obtained from the calculations with allowance made for the interaction of electrons with magnetic excitations in the framework of the double-exchange model for systems with strongly correlated electronic states. Investigations of the magneto- optical Kerr effect have revealed that an insignificant (0.3%) orthorhombic distortion of the cubic lattice in the plane of the NdGaO3(110) substrate leads to uniaxial anisotropy of the magnetization of the film, with the easy-magnetization axis lying in the substrate plane. However, LSMO films on substrates (((LaAlO3)(0.3)+(Sr2AlTaO6)(0.7))(001)) ensuring minimum strain of the films exhibit a biaxial anisotropy typical of cubic crystals. The study of the ferromagnetic resonance lines at a frequency of 9.76 GHz confirms the results of magnetooptical investigations and indicates that the ferromagnetic phase in the LSMO films is weakly inhomogeneous.
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| 11. |
- Ovsyannikov, Gennady, 1948, et al.
(författare)
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Proximity effect and electron transport in oxide hybrid heterostructures with superconducting/magnetic interfaces
- 2011
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Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 24:5, s. Art. no. 055012-
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Tidskriftsartikel (refereegranskat)abstract
- We report on electron transport in oxide heterostructures with superconducting/magnetic (S/M) thin film interfaces. The investigated hybrid mesa-heterostructures consist of a cuprate superconductor, a nonsuperconducting cuprate (antiferromagnetic) or manganite (ferromagnetic) interlayer with thickness d(M) = 5-50 nm and a conventional superconductor (Nb). The superconducting critical current (I-C) with a critical current density j(c) = 10(3) A cm(-2) (for d(M) = 10 nm) and a characteristic voltage ICRN = 100-200 mu V (RN is normal resistance) are observed at liquid helium temperature for a CaXSr1-XCuO2 antiferromagnetic cuprate interlayer with a thickness of d(M) = 10-50 nm. The superconducting current-phase relation of heterostructures deviates from the regular sine type, demonstrating a second harmonic component. These hybrid heterostructures with S/M interfaces show unusually high sensitivity to external magnetic fields. When substituting the cuprate interlayer by a manganite film, no critical current was observed although the manganite interlayer was made several times thinner (down to d(M)
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| 12. |
- Petrzhik, A. M., et al.
(författare)
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Electron transport in hybrid superconductor heterostructures with manganite interlayers
- 2011
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Ingår i: Journal of Experimental and Theoretical Physics. - : Pleiades Publishing Ltd. - 1090-6509 .- 1063-7761. ; 112:6, s. 1042-1050
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Tidskriftsartikel (refereegranskat)abstract
- Hybrid herostructures comprising an YBa(2)Cu(3)O (x) (YBCO) high-temperature superconductor (HTS) layer and Nb/Au low-temperature superconductor (LTS) bilayer (with critical HTS and LTS temperatures T (c) and T'(c), respectively), separated by a thin (d (M) = 5-20 nm) interlayer of LaMnO(3), La(0.7)Ca(0.3)MnO(3), or La(0.7)Sr(0.3)MnO(3) manganite have been studied. The electric resistance and magnetic properties of individual (evaporated directly onto the substrate) manganite films and related hybrid herostructures have been measured. Based on quasi-classical equations, analytical expressions for the conductivity of herostructures at T a parts per thousand currency sign T'(c) are obtained in the case of a low-transparency superconductor/manganite interface. It is established that the conductivity of heterostructures is determined by the proximity effect (related to the penetration of a condensate wavefunction from the Nb/Au bilayer to manganite) and depends strongly on interface transparency. At low temperatures (T a parts per thousand(a) T (c)'), the conductivity peaks are found at voltages determined by the exchange field of the manganite interlayer. At T (c)'
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| 13. |
- Petrzhik, A. M., et al.
(författare)
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Electron Transport in Manganite Bicrystal Junctions
- 2013
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Ingår i: Physics of the Solid State. - : Pleiades Publishing Ltd. - 1063-7834 .- 1090-6460. ; 55:4, s. 759-764
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Tidskriftsartikel (refereegranskat)abstract
- The transport and magnetic properties of junctions created in La0.67Sr0.33MnO3 thin films epitaxially grown on substrates with a bicrystal boundary have been investigated. In tilted neodymium gallate bicrystal substrates, the NdGaO3(110) planes are inclined at angles of 12 degrees and 38 degrees. The temperature dependences of the electrical resistance, magnetoresistance, and differential conductance of the junctions at different voltages have been measured and analyzed. It has been found that the magnetoresistance and electrical resistance of the junction significantly increase with an increase in the misorientation angle, even though the misorientation of the easy magnetization axes remains nearly unchanged. The ratio of the spin-dependent and spin-independent contributions to the conductance of the bicrystal junction increases by almost an order of magnitude with an increase in the misorientation angle from 12 degrees to 38 degrees. The magnetoresistance of the junction increases with decreasing temperature, which is most likely associated with an increase of the magnetic polarization of the electrons. It has been shown that, at low (liquid-helium) temperatures, the conductance depends on the voltage V according to the law V-1/2, which indicates the dominant contribution from the electron-electron interaction to the electrical resistance of the junction. An increase in the temperature leads to a decrease in this contribution and an increase in the contribution proportional to V-3/2, which is characteristic of the mechanism involving inelastic spin scattering by surface antiferromagnetic magnons.
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| 14. |
- Petrzhik, A. M., et al.
(författare)
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Spin-dependent electron transport in manganite bicrystal junctions
- 2012
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Ingår i: Journal of Experimental and Theoretical Physics. - 1090-6509 .- 1063-7761. ; 115:5, s. 876-884
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic bicrystal films and junctions of magnetic La0.67Sr0.33MnO3 (LSMO) and La0.67Ca0.33MnO3 (LCMO) films epitaxially grown on NdGaO3 substrates with the (110) planes of their two parts misoriented (tilted) at angles of 12A degrees, 22A degrees, 28A degrees, and 38A degrees are investigated. For comparison, bicrystal boundaries with a 90A degrees misorientation of the axes of the NdGaO3 (110) planes were fabricated. The directions of the axes and the magnetic anisotropy constants of the films on both sides of the boundary are determined by two independent techniques of magnetic resonance spectroscopy. The magnetic misorientation of the axes in the substrate plane has been found to be much smaller than the crystallographic misorientation for tilted bicrystal boundaries, while the crystallographic and magnetic misorientation angles coincide for boundaries with rotation of the axes. An increase in the magnetoresistance and characteristic resistance of bicrystal junctions with increasing misorientation angle was observed experimentally. The magnetoresistance of bicrystal junctions has been calculated by taking into account the uniaxial anisotropy, which has allowed the contributions from the tunneling and anisotropic magnetoresistances to be separated. The largest tunneling magnetoresistance was observed on LCMO bicrystal junctions, in which the characteristic resistance of the boundary is higher than that in LSMO boundaries.
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| 15. |
- Ratynskaia, Svetlana V., et al.
(författare)
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A probe for measurements of electrostatic fluctuations in a low-temperature magnetized plasma
- 2000
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 71:3, s. 1367-1369
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Tidskriftsartikel (refereegranskat)abstract
- A cylindrical probe with insulating end plugs for investigations of fluctuations of electron temperature and plasma potential is proposed. The radii of the metallic rod and plugs are chosen to optimize the ratio of ion saturation current to electron saturation current (> 1) for the probe oriented parallel to the magnetic field. This probe is applicable when the electron temperature is much larger than the ion temperature.
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| 16. |
- Ratynskaia, Svetlana V., et al.
(författare)
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Measurements of anomalous particle and energy fluxes in a magnetized plasma
- 2002
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1063-651X .- 1095-3787. ; 65:6
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Tidskriftsartikel (refereegranskat)abstract
- Electrostatic probe measurements of low frequency plasma fluctuations and anomalous particle and energy flux densities in a magnetized plasma are presented. A method allowing the simultaneous recording of instantaneous electric field, electron density, and temperature is invoked. The method is applied to flux density measurements in a weakly ionized, low beta plasma created in a toroidal device without magnetic rotational transform. It is also used to identify modes belonging to different dispersion branches and to obtain the dispersion relations for these modes. For the plasma states studied, the phase velocities and the cross phase between the electron density and electric field agree with those predicted from a local, linear stability analysis for electrostatic flute modes and drift waves. The instability threshold, however, is one order of magnitude higher than predicted by theory for unsheared flow. The fluxes measured are consistent with the estimated ionization rate.
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| 17. |
- Ratynskaia, Svetlana V., et al.
(författare)
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Measurements of plasma potential and electron temperature fluctuation in a low-temperature magnetized plasma
- 2001
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Ingår i: Contributions to Plasma Physics. - 0863-1042 .- 1521-3986. ; 41:5, s. 449-454
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of fluctuations of plasma potential and electron temperature in a toroidal magnetized plasma is carried out by applying a cylindrical probe with insulating end plugs oriented parallel to the B-field in conjunction with another cylindrical probe oriented perpendicularly. Coherency and cross-phase between (V) over tilde (f) and (T) over tilde (e) are estimated, and typically have values close to 0.6 and pi respectively. Power-law spectra are found for frequencies well above the poloidal rotation frequency with spectral index typically around 4.0 for (V) over tilde (f) and around 2.5 for (T) over tilde (e). The density gradient is above the threshold for flute interchange instability, and the results are consistent with theory and global numerical simulations of this plasma.
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| 18. |
- Ratynskaia, Svetlana V., et al.
(författare)
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Probe measurements of electron temperature and density in strongly magnetized plasma
- 2000
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 71:9, s. 3382-3384
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Tidskriftsartikel (refereegranskat)abstract
- It was demonstrated that with increasing probe length the electron saturation current becomes more independent of the probe potential. This provides higher accuracy of measurements of the electron density and plasma potential in a strongly magnetized plasma (B > 0.1 T). Long probes oriented parallel to the magnetic field yield better spatial resolution in the perpendicular direction. Parallel probes, however, are very sensitive to alignment errors. To avoid this problem, a cylindrical probe with a side surface coated by a thin insulating layer is proposed.
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| 19. |
- Ratynskaia, Svetlana V., et al.
(författare)
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Probe measurements of ion energy distribution in magnetized plasmas
- 2002
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 73:12, s. 4232-4236
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Tidskriftsartikel (refereegranskat)abstract
- A probe method for measurement of the ion energy distribution in magnetized plasmas is proposed. A cylindrical probe with end plugs is oriented parallel to the magnetic field and used to reduce the electron contribution to the total probe current. The contribution of ions to the second derivative of the total current is identified by experiments with different probe orientation and strength of the magnetic field. The ion density obtained from the measured ion energy distribution is in good agreement with the electron density obtained from measured electron energy distribution.
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| 20. |
- Ratynskaia, Svetlana V., et al.
(författare)
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Probe measurements of low-frequency plasma potential and electric field fluctuations in a magnetized plasma
- 2002
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 9:10, s. 4135-4143
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Tidskriftsartikel (refereegranskat)abstract
- A system of two cylindrical probes aligned along the magnetic field, and equipped with insulating end plugs, is proposed for measurement of low-frequency fluctuations of the electrostatic field in a magnetized plasma. It is demonstrated by modeling and experiments that the plug probe floats close to the plasma potential. The electric field component in a given direction is obtained by subtracting the plasma potentials obtained on two spatially separated plug probes. The probe system is applied to low-frequency electrostatic fluctuations in a simple magnetized torus, and reveals the presence of global oscillations, large scale propagating structures (m=1 modes), and developed turbulence with power-law spectra. Two different mode branches for the fluctuations are identified by comparing results from plug probes with results from conventional probes. Sources of errors arising from applying floating potential of conventional probes for electric field measurements are pointed out and discussed.
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| 21. |
- Rypdal, K., et al.
(författare)
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Non-equilibrium quasi-stationary states in a magnetized plasma
- 2003
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Ingår i: Nonlinear processes in geophysics. - : Copernicus GmbH. - 1023-5809 .- 1607-7946. ; 10:02-jan, s. 139-149
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Tidskriftsartikel (refereegranskat)abstract
- Non-equilibrium quasi-stationary states resulting from curvature driven interchange instabilities and driftwave instabilities in a low beta, weakly ionized, magnetized plasma are investigated in the context of laboratory experiments in a toroidal configuration. Analytic modelling, numerical simulations and experimental results are discussed with emphasis on identifying the unstable modes and understanding the physics of anomalous particle and energy fluxes and their linkage to self-organized pressure profiles.
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| 22. |
- Svendsen, John Inge, et al.
(författare)
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Maximum extent of the Eurasian ice sheets in the Barents and Kara Sea region during the Weichselian
- 1999
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Ingår i: Boreas. - : Wiley. - 1502-3885 .- 0300-9483. ; 28:1, s. 92-114
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Tidskriftsartikel (refereegranskat)abstract
- Based on field investigations in northern Russia and interpretation of offshore seismic data, we have made a preliminary reconstruction of the maximum ice-sheet extent in the Barents and Kara Sea region during the Early/Middle Weichselian and the Late Weichselian. Our investigations indicate that the Barents and Kara ice sheets attained their maximum Weichselian positions in northern Russia prior to 50 000 yr BP, whereas the northeastern flank of the Scandinavian Ice Sheet advanced to a maximum position shortly after 17000 calendar years ago. During the Late Weichselian (25 000–10000 yr BP), much of the Russian Arctic remained ice-free. According to our reconstruction, the extent of the ice sheets in the Barents and Kara Sea region during the Late Weichselian glacial maximum was less than half that of the maximum model which, up to now, has been widely used as a boundary condition for testing and refining General Circulation Models (GCMs). Preliminary numerical-modelling experiments predict Late Weichselian ice sheets which are larger than the ice extent implied for the Kara Sea region from dated geological evidence, suggesting very low precipitation.
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| 23. |
- Svendsen, JI, et al.
(författare)
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Late quaternary ice sheet history of northern Eurasia
- 2004
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 23:11-13, s. 1229-1271
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Forskningsöversikt (refereegranskat)abstract
- The maximum limits of the Eurasian ice sheets during four glaciations have been reconstructed: (1) the Late Saalian (> 140 ka), (2) the Early Weichselian (100-80 ka), (3) the Middle Weichselian (60-50 ka) and (4) the Late Weichselian (25-15 ka). The reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in Russia and Siberia, and with marine seismic- and sediment core data. The Barents-Kara Ice Sheet got progressively smaller during each glaciation, whereas the dimensions of the Scandinavian Ice Sheet increased. During the last Ice Age the Barents-Kara Ice Sheet attained its maximum size as early as 90-80,000 years ago when the ice front reached far onto the continent. A regrowth of the ice sheets occurred during the early Middle Weichselian, culminating about 60-50,000 years ago. During the Late Weichselian the Barents-Kara Ice Sheet did not reach the mainland east of the Kanin Peninsula, with the exception of the NW fringe of Taimyr. A numerical ice-sheet model, forced by global sea level and solar changes, was run through the full Weichselian glacial cycle. The modeling results are roughly compatible with the geological record of ice growth, but the model underpredicts the glaciations in the Eurasian Arctic during the Early and Middle Weichselian. One reason for this is that the climate in the Eurasian Arctic was not as dry then as during the Late Weichselian glacial maximum.
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| 24. |
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| 25. |
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| 26. |
- Wohlfarth, B, et al.
(författare)
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Unstable early-Holocene climatic and environmental conditions in northwestern Russia derived from a multidisciplinary study of a lake-sediment sequence from Pichozero, southeastern Russian Karelia
- 2004
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Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 14:5, s. 732-746
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Tidskriftsartikel (refereegranskat)abstract
- A sediment core from Lake Pichozero (61degrees46'; N, 37degrees25'; E 118 m a.s.l.) provides information on the environmental and climatic conditions in southeastern Russian Karelia during the Lateglacial and early Holocene (12800-9300 cal. BP). The chronology of the sequence is constrained by varve counting and AMS C-14 measurement of terrestrial plant macrofossils. Multiproxy analyses (magnetic susceptibility, grain size, TOC, TN, TS, Rock Eval, pollen and macrofossils) imply that cold and dry regional climatic conditions with sparse Arctic vegetation prevailed prior to 11500 cal. BP. Coincident with the transition to the Holocene at 11500 cal. BP, air temperatures and lake productivity increased and Betula pubescens and Populus tremula started to migrate into the area, followed by Picea abies at 10750 cal. BP. Although lake productivity decreased at around 11000 cal. BP and remained low until 9600 cal. BP, pollen-based climate reconstructions imply variable climatic conditions in the region over time. Drier and colder summers prevailed from similar to11200 to 10900 cal. BP, followed by an interval of higher annual temperatures and precipitation from 10900 to 10750 cal. BP. Lower annual temperatures and drier conditions existed from 10750 to 10200 cal. BP, and higher temperatures and precipitation are inferred between 10200 and 10000 cal. BP. Finally, declining temperatures and precipitation occurred from 10000 cal. BP onwards, with a minimum at around 9600 cal. BP. These climatic shifts are temporally coincident with those recorded in North Atlantic terrestrial, marine and ice-core archives and indicate that relatively minor climate signals were transmitted further to the east.
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