Recursos de colección

Hokkaido University Collection of Scholarly and Academic Papers (130.615 recursos)

HUSCAP (Hokkaido University Collection of Scholarly and Academic Papers) contains peer-reviewed journal articles, proceedings, educational resources and any kind of scholarly works of Hokkaido University.

vol. 68, Supplement Issue

Mostrando recursos 1 - 20 de 23

  1. Combined Analysis of Water Stable Isotopes (H_[2]^[16]O, H_[2]^[17]O, H_[2]^[18]O, HD^[16]O) in Ice Cores

    Landais, Amaelle; Barkan, Eugeni; Vimeux, Françoise; Masson-Delmotte, Valérie; Luz, Boaz
    Water stable isotopes are currently measured in polar ice cores. The long records of δ18O and δD provide unique information on the past polar temperature while the combination of δ18O and δD constrains the evolution of the oceanic evaporative regions. Recently, new analytical developments have made it possible to measure with high precision a new isotopic ratio in water, δ170. As for δD and δ180, the combination of δ170 and δ180 shows a high dependence with the climatic conditions during evaporation. Based on measurements of the different isotopic ratios in Antarctica surface snow, we show that while the combination of...

  2. Formation of the Ice Core Isotopic Composition

    Ekaykin, Alexey A.; Lipenkov, Vladimir Ya.
    Main processes of the ice core isotopic composition formation are overviewed. Theory of isotope-temperature relationship is discussed and confirmed by a number of experimental data. The factors related to wind-driven spatial snow redistribution and post-depositional isotopic changes that may alter or weaken this relationship, are also considered. For high-resolution isotopic time-series obtained at sites with low accumulation of snow, the signal-to-noise ratio is shown to be as low as 0.25, which means that noise accounts for about 80 % of the total variance. It is demonstrated that "classical isotopic method" (based on the present-day geographical isotope-temperature slope) underestimates the amplitude...

  3. Ion Fractionation and Percolation in Ice Cores with Seasonal Melting

    Moore, John C.; Grinsted, Aslak
    We examine the impact that post-depositional change has on ion concentrations in ice cores that suffer limited seasonal melting. We show that the impact in the case of at least one Svalbard ice core is limited to decreasing resolution of signals to about 3 years - a similar accuracy as the best dating can usually provide. We model various effects such as percolation and washout of ions, and show how they can be used to construct useful ice core proxies. The sulfate profile shows how post depositional effects lead to magnesium and nitrate being excellent predictors under normal conditions for...

  4. Chemical Compounds of Water-Soluble Impurities in Dome Fuji Ice Core

    Iizuka, Yoshinori; Ohno, Hiroshi; Sakurai, Toshimitsu; Horikawa, Shinichiro; Hondoh, Takeo
    The amounts of water-soluble impurities in ice cores have been widely discussed in past research on prehistoric climates; in those studies, the analysis of the soluble-aerosol signals of several ion concentrations took place after the ice cores were melted. However, the chemical compounds of the impurities being studied were unclear, due to the ionization of the impurities being caused by the melting of the ice cores. In this paper, the chemical compounds of water-soluble impurities in Dome Fuji ice core are discussed and analyzed using micro-Raman spectroscopy and ion chromatography. Raman spectroscopy helped identify micro-inclusions within ice grains as water-soluble...

  5. Seasonal Variations of Isotope Ratios and CO2 Concentrations in Firn Air

    Weiler, Karin; Schwander, Jakob; Leuenberger, Markus; Blunier, Thomas; Mulvaney, Robert; Anderson, Philip S.; Salmon, Rhian; Sturges, William T.
    A first year-round firn air sampling carried out at the British Antarctic station Halley in 2003 shows isotope and CO2 changes owing to diffusive mixing driven by seasonal variations of surface temperature, and gas composition of the atmosphere. Seasonal firn temperatures are well reproduced from the atmospheric temperature history. Based on these profiles thermal diffusion is forced with thermal diffusion factors αT with respect to air. Application of the available literature data for αT (15N14 / N2) leads to a proper prediction of the seasonal thermal amplitude during the entire year. By forcing thermal fractionation with αT as derived from...

  6. A Probabilistic Method to Construct an Optimal Ice Chronology for Ice Cores

    Lemieux-Dudon, Benedicte; Frederic, Parrenin; Blayo, Eric
    Accurate ice chronologies are needed for the interpretation of paleoclimate reconstructions inferred from ice cores. Several methods are used to provide chronological information: identification of dated horizons along the cores, synchronization to other dated paleoclimatic records, counting of annual layers or modelling of the ice flow. These methods are relevant for different parts of the core and enable to reach various levels of accuracy. We present a probabilistic approach based on inverse techniques which aims at building an optimal ice core chronology by using all the available chronological information. It consists in identifying the accumulation rate and the thinning function...

  7. Impact of Local Insolation on Snow Metamorphism and Ice Core Records

    Hutterli, Manuel A.; Schneebeli, Martin; Freitag, Johannes; Kipfstuhl, Josef; Röthlisberger, Regine
    Local insolation is a major component of the energy balance at the surface of an ice sheet and causes temperature gradient metamorphism (TGM) of snow and firn. TGM is one of the dominant processes changing the structure of dry snow. We present a physically based model that calculates insolation-induced relative changes in TGM in the past. The results indicate that TGM at Dome Fuji varied by up to a factor of 2 over the past 350ka, and is driven predominately by the precession-band variability in local summer solstice insolation. At Dome Fuji, the impact of glacial-interglacial temperature changes on TGM...

  8. Snow/Firn Densification in Polar Ice Sheets

    Salamatin, Andrey N.; Lipenkov, Vladimir Ya.; Barnola, Jean Marc; Hori, Akira; Duval, Paul; Hondoh, Takeo
    A sophisticated physical model of the dry snow/firn densification process in ice sheets is proposed. Macroscopically, snow and firn undergo vertical uniaxial compression with non-zero deviatoric stresses and strain rates. The present mathematical description of densificntion includes dilatancy and "force-chain" effects in snow and develops previous concepts of ice-particle rearrangement by grain-boundary sliding and sintering by power-law creep under overburden pressure. Both densification mechanisms work together during the first snow stage until the closest packing of ice grains is reached at critical densities of 0.7-0.76 and the firn stage controlled only by the dislocation creep sets on. In addition to...

  9. Ice Flow Line Modeling and Ice Core Data Interpretation : Vostok Station (East Antarctica)

    Salamatin, Andrey N.; Tsyganova, Elena A.; Popov, Sergey V.; Lipenkov, Vladimir Ya.
    This work, originally based on a series of the authors' publications [101 , 102, 104, 112, 130, 131], considers general questions of ice-sheet flow modeling as related to ice core records interpretation. It reviews the previous results and, using new geographical, geophysical and glaciological data, continues the study aimed at solving the twofold problem of ice core age dating and paleoclimatic reconstructions from the isotopic content measurements in the deep ice cores from Vostok Station located in central East Antarctica, above the vast subglacial lake. The principal idea of the paper is to develop a general approach to past climate...

  10. A Review of Anisotropic Polar Ice Models : from Crystal to Ice-Sheet Flow Models

    Gagliardini, Olivier; Gillel-Chaulet, Fabien; Montagnat, Maurine
    The ice single crystal is one of the most anisotropic natural materials and the resulting viscous behaviour of polycrystalline ice can also be strongly anisotropic and is a function of the distribution of the crystal c-axis orientations, i.e. its fabric. Such a strong and strain-dependant anisotropy of the ice polycrystal certainly affects the general flow of polar ice. The aim of this paper is to present an exhaustive overview of most of the glaciological efforts made from more than two decades to account for polar ice anisotropy in ice flow modelling, from the crystal to the ice-sheets scale. We first...

  11. A Continuum-Mechanical Model for the Flow of Anisotropic Polar Ice

    Greve, Ralf; Placidi, Luca; Seddik, Hakime
    In order to study the mechanical behaviour of polar ice masses, the method of continuum mechanics is used. The newly developed CAFFE model (Continuum-mechanical, Anisotropic Flow model, based on an anisotropic Flow Enhancement faclor) is described, which comprises an anisotropic flow law as well as a fabric evolution equation. The flow law is an extension of the isotropic Glen's flow law, in which anisotropy enters via an enhancement factor that depends on the deformability of the polycrystal. The fabric evolution equation results from an orientational mass balance and includes constitutive relations for grain rotation and recrystallization. The CAFFE model fulfills...

  12. The Stress Pattern within the Law Dome Summit to Cape Folger Ice Flow Line, Inferred from Measurements of Crystal Fabric

    Donoghue, Shavawn; Jacka, Tim H.
    Crystal fabric and texture data are presented from ten ice cores that have previously been drilled along an approximate flow line extending from the summit of Law Dome ice cap to Cape Folger, East Antarctica. Our interest in these data is their interpretation in terms of stress patterns within the ice cap, and in particular the detection of the depths at which the stress changes from predominantly near-vertical compression to predominantly near-horizontal simple shear zones. This transition potentially marks an increase in flow rate, from a factor of ~3 in the compression zone to ~10 in the shear zone, compared...

  13. Deformation Microstructures in an Antarctic Ice Core (EDML) and in Experimentally Deformed Artificial Ice

    Weikusat, Ilka; Kipfstuhl, Sepp; Azuma, Nobuhiko; Faria, Sérgio H.; Miyamoto, Atsushi
    Deformation microstructures in an Antarctic ice core (EDML) and in experimentally deformed artificial ice, which together comprise a great variety of conditions and parameters, are reconsidered and compared. Data presented here cover grain substructure and shape. Despite the different flow conditions surprising similarities in these observations indicate intracrystalline slip as the deformation carrier in natural as well as in experimentally deformed ice. Similar subgrain-boundary shapes and arrangements in both cases indicate characteristic types, which suggest that non-basal dislocations may play a significant role in the deformation of ice. Subgrain-boundary density and grain-boundary shapes show that a difference between processes in...

  14. Texture of the Upper 1000 m in the GRIP and NorthGRIP Ice Cores

    Svensson, Anders; Durand, Gaël; Mathiesen, Joachim; Persson, Asbjørn; Dahl-Jensen, Dorthe
    In this study we discuss new and published profiles of c-axis fabric and size distributions of a large number of crystals in the upper 1000 m of the Greenland GRIP and NorthGRIP ice cores as obtained with an automatic c-axis fabric analyzer. We show that in both cores the fabric is strongly anisotropic already just below the firn (about 110 m depth) with a degree of orientation around 30%. We determine the mean crystal area profiles which are somewhat contrasting to earlier findings based on manual measurements. The crystal size distributions are compared to a simple ID model which takes...

  15. Evolution of the Texture along the EPICA Dome C Ice Core

    Durand, Gaël; Svensson, Anders; Persson, Asbjørn; Gagliardini, Olivier; Gillet-Chaulet, Fabien; Sjolte, Jesper; Montagnat, Maurine; Dahl-Jensen, Dorthe
    New measurements of ice texture made along the EPICA Dome C ice core, together with a review of previous studies of fabric and microstructure, are presented. Mean grain size increases steadily with age, and so depth. However, sharp decreases are observed contemporary with each climatic termination. These sharp decreases are believed to be mainly driven by the change in dust content between glacial and interglacial periods. C-axes steadily clustered with depth toward a vertical single maximum. However, a sharp clustering of the fabric is observed during termination II (≈ 1750 m), suggesting the presence of shear in the upper part...

  16. Recrystallization Processes in Granular Ice

    Montagnat, Maurine; Durand, Gaël; Duval, Paul
    Recrystallization mechanisms are known to accommodate the deformation as observed along ice cores. The three main processes are classically described as being, successively from the top of the cores, normal grain growth, rotation dynamic recrystallization and migration dynamic recrystallization. Recent observations on local mechanisms at the grain scale tend to question this description. This paper aims at presenting the basic knowledge about dynamic recrystallization processes in materials, with focus on the corresponding mechanisms occuring during deformation of granular ice, more particularly along ice cores. We stress the significance of the scale to consider when analysing the mechanisms, depending on the...

  17. Visual Observation of Volume Relaxation under Different Storage Temperatures in the Dome Fuji Ice Core, Antarctica

    Miyamoto, Atsushi; Saito, Takeshi; Hondoh, Takeo
    We are keeping Dome Fuji ice core samples at two storage temperatures (-50 and -20℃) after deep ice core drilling reached 2503 m at the Dome Fuji station, Antarctica. Since we aimed to develop new methods for studying physical properties of ice cores, cold storage down to -50℃ was necessary to avoid volume relaxation of ice cores during storage. To compare the volume relaxation process of an ice core under different storage temperatures, we captured images using a digital camera. Many tiny bubbles and plate-like inclusions (cleavage cracks) were observed in the ice core kept at the high storage temperature...

  18. The Multiscale Structure of Antarctica Part II : Ice Shelves

    Kirchner, Nina; Faria, Sérgio H.
    Polar ice masses, including grounded (inland) ice, ice shelves, icebergs and sea ice, constitute an essential part of the global climate system. They interact with the hydrosphere and the atmosphere, and, if persisting through millennia, serve as archives of the past climate of Earth. Currently. significant efforts in climate reconstructions are being undertaken, serving as a basis for climate predictions into the future. It has been argued in Part I of this work that more attention should be given to interactions between structures on distinct scales (multiscale structural interactions), which seem to play a decisive role in the structure-form-environment interplay...

  19. The Multiscale Structure of Antarctica Part I : Inland Ice

    Faria, Sérgio H.; Kipfstuhl, Sepp; Azuma, Nobuhiko; Freitag, Johannes; Weikusat, Ilka; Murshed, M. Mangir; Kuhs, Werner F.
    The dynamics of polar ice sheets is strongly influenced by a complex coupling of intrinsic structures. Some of these structures are extremely small, like dislocation walls and micro-inclusions; others occur in a wide range of scales, like stratigraphic features; and there are also those collossal structures as large as megadunes and subglacial lakes. Their significance results from their interactions with the ice-sheet flow and the environment through an intricate Structure-Form-Environment Interplay (SFEI). Glaciologists are not unaware of the SFEI issue, as particular details of the problem are well documented in the literature. Nevertheless, many aspects of the SFEI remain unclear...

  20. The Multidisciplinary Ice Core

    Faria, Sérgio H.
    Ice-core physics and climate research undoubtedly form a very successful partnership. Nevertheless, even the best union may sometimes suffer under the wearing of time. Multidisciplinarity may support the stability of this partnership, by helping ice-core physics to become more independent and dynamic, as well as a better partner to other disciplines - including climate research.

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