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Mass loss from ice sheets contributes to global sea level rise, and accelerated ice flow to the oceans is one of the major causes of rapid ice sheet mass loss. To understand flow dynamics of polar ice sheets, we need to understand deformation mechanisms of the polycrystalline ice in ice sheets. Laboratory experiments have shown that deformation of polycrystalline ice occurs largely by dislocation glide, which mainly depends on crystal orientation distribution. Grain size and impurities are also important factors that determine ice deformation mechanisms. Compared with ice formed during interglacial periods, ice formed during glacial periods, especially ice that forms cloudy bands, exhibits finer grain sizes and higher impurity concentrations. A previous report suggests the deformation rate of ice containing cloudy bands is higher than that of ice without cloudy bands. To examine the microstructures and deformation histories of ice in cloudy bands, we applied the electron backscatter diffraction (EBSD) technique to samples from the Greenland Ice Sheet using an environmental scanning electron microscope (ESEM) equipped with cold stages. Prior to the EBSD analysis, we optimised our ESEM/EBSD system and performed angular error assessment using artificial ice. In terms of c-and a-axis orientation distributions and grain orientation spread, we found little difference between samples taken from a cloudy band and those taken from an adjacent layer of clear ice. However, subgrain boundary density and orientation gradients were higher in the cloudy band, suggesting that there are more dislocations in the cloudy band than in the clear ice layer.

Here we present the ice microstructure and CPO (c-axes fabric) data from the upper 2121 m of the EastGRIP ice core, an on-going deep drilling project on the North East Greenland Ice Stream. Understanding ice flow behaviour of fast flowing ice streams is crucial for accurate projections of future global sea level rise, but is still poorly understood due to e.g. missing observational fabric data from ice streams. The presented CPO patterns found at EastGRIP show (1) a rapid evolution of c-axes anisotropy compared to deep ice cores from less dynamic sites, (2) a CPO evolution towards a strong vertical girdle and (3) CPO patterns that have not previously been directly observed in ice. Furthermore, data regarding grain properties (e.g. grain size) and indications of dynamic recrystallization, already at shallow depths, are presented. The ice CPO shows a clear evolution with depth. In the first measurements at 111 m depth a broad single maximum distribution is observed, which transforms into a crossed girdle CPO (196-294 m). With increasing depth, an evolution towards a vertical girdle c-axes distribution occurs. Below 1150 m the CPO evolves into a vertical girdle with a higher density of c-axes oriented horizontally, a novel CPO in ice. These CPO patterns indicate a depth-related change in deformation modes, from vertical compression to extensional deformation along flow. Grain size values are similar to results from other Greenlandic deep ice cores. Grain size evolution is characterized by an increase until 500 m depth, a decrease until 1360 m depth and mainly constant values in the Glacial. These findings are accompanied by indications of an early onset of dynamic recrystallisation e.g. irregular grain shapes, protruding grains and island grains. The presented high-resolution data enable, for the very first time, a detailed and data- based look into a fast-flowing ice stream and are an important step towards a better understanding of the rheology of ice and its flow behaviour.

The Tenth Symposium on Polar Science/Ordinary sessions: [OM] Polar Meteorology and Glaciology, Thu. 5 Dec. / 2F Auditorium , National Institute of Polar Research

The Tenth Symposium on Polar Science/Ordinary sessions: [OM] Polar Meteorology and Glaciology, Wed. 4 Dec. / Entrance Hall (1st floor) , National Institute of Polar Research

The thermoelectric transport properties of the van der Waals-type layered rhombohedral SnAs-based compound, EuSn2As2, have been investigated. A densified polycrystalline sample of EuSn2As2 with porosity (ϕ) of 2.4(9) vol.% exhibited a weak orientation to the c-axis for hexagonal coordination system; the weak orientation is parallel (P ∥) to the pressing direction of hot pressing. Measurements of electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) were conducted perpendicular (P ⊥) to the pressing direction. The experimental values of ρ and S exhibit metallic temperature dependence and p-type carrier polarity. The power factor (P) was 0.51(8) mW m−1 K−2 at 673(4) K. Using the Wiedemann–Franz–Lorenz law, the phonon thermal conductivity (κ ph) was estimated to be 0.4(6) W m−1 K−1 at 673(6) K. The dimensionless figure of merit, ZT, was 0.092(17) at 673(3) K.

The Ninth Symposium on Polar Science/Ordinary sessions: [OM] Polar meteorology and glaciology, Wed. 5 Dec. / 3F Multipurpose Conference room, National Institute of Polar Research

The orientations of individual crystals within a polycrystalline aggregate subjected to stress have a strong influence on its bulk strain rate and flow behavior. The ability to include the effect of crystal fabric and recrystallization processes in an ice flow law, especially at the bottom of glaciers and ice sheets where temperature is close to the pressure-melting point, is important because the stratigraphy of the ice body may be affected and the paleoclimate reconstruction hampered. We present herein three newly developed deformation apparatuses offering the possibility, from single experiments, of investigating different finite strain stages and their corresponding c-axis fabric and grain texture patterns in various confined, shear flow configurations (simple shear, pure shear and compression/extension bending). The technical set-ups and major advantages compared to classical methods are explained, and results from experiments are discussed in order to illustrate the functioning and purposes of the methods. In all experiments, significant variations in the microstructural development have been observed that reflect the varying orientations of the anisotropy and its relationship to the stress pattern. In monocrystalline ice-bending experiments, the pre-existing c-axis fabric is shown to have a profound influence on the response to stress and possibly to the type of slip system activated.

Normal grain growth experiments were performed using polycrystalline ice samples with and without air bubbles. The bubble-free polycrystalline ice was prepared by a special sample preparation technique that employed a phase change method. The ice samples with air bubbles were prepared from a mixture of ice powder and pure distilled water using conventional methods. The temperature dependencies of the rate of grain growth were measured in artificial polycrystalline ice samples with and without air bubbles. The average grain growth exponent n of the ice with bubbles was much greater than the theoretical value of 2, while that of bubble-free ice was close to 2. The activation energy for the grain boundary migration of bubble-free ice was 110–120 kJ mol −1 , whereas that of the ice with bubbles was between 40 and 70 kJ mol −1 . The observation of the microscopic images of samples and analyses of the evolution of bubble size distribution and location during grain growth revealed that small air bubbles are caught and swept by moving grain boundaries and a coalescence of bubbles occurs. This indicates that the slow grain boundary migration of ice with bubbles is controlled by the migration of air bubbles dragged by grain boundary migration.

Climatic variabilities on millennial and longer time scales with a bipolar seesaw pattern have been documented in paleoclimatic records, but their frequencies, relationships with mean climatic state, and mechanisms remain unclear. Understanding the processes and sensitivities that underlie these changes will underpin better understanding of the climate system and projections of its future change. We investigate the long-term characteristics of climatic variability using a new ice-core record from Dome Fuji, East Antarctica, combined with an existing long record from the Dome C ice core. Antarctic warming events over the past 720,000 years are most frequent when the Antarctic temperature is slightly below average on orbital time scales, equivalent to an intermediate climate during glacial periods, whereas interglacial and fully glaciated climates are unfavourable for a millennial-scale bipolar seesaw. Numerical experiments using a fully coupled atmosphere-ocean general circulation model with freshwater hosing in the northern North Atlantic showed that climate becomes most unstable in intermediate glacial conditions associated with large changes in sea ice and the Atlantic Meridional Overturning Circulation. Model sensitivity experiments suggest that the prerequisite for the most frequent climate instability with bipolar seesaw pattern during the late Pleistocene era is associated with reduced atmospheric CO2 concentration via global cooling and sea ice formation in the North Atlantic, in addition to extended Northern Hemisphere ice sheets., SCOPUS: ar.j, info:eu-repo/semantics/published

Results of laboratory uniaxial compression tests over the stress range 0.18–0.52 MPa and the strain range 0.5–8.6% at approximately –5 and –20°C are presented. Grain-size analysis and comparisons with annealing tests confirm that grain-growth reducing processes are active during deformation. Microstructural observations reveal that subgrain-rotation recrystallization and grain-shape changes due to strain-induced grain-boundary migration are the causes of the grain-growth deceleration. Further results from microstructural observations show that obstacle formation by dislocation walls and subgrain boundaries is the reason for isotropic hardening during creep. Subgrainboundary types that are likely to be relevant for studies on the activity of different dislocation types are described.

In order to understand and solve the ‘warm-ice problem’ in deep ice-core drilling, we applied the metal-cutting theory to ice and estimated the heat generated during ice coring taking into account the mechanical and thermal properties of the ice and cutters. We found that (1) most of the heat in cutting is generated by shear deformation at the shear plane of ice, and the heat could increase the chip temperature by several degrees; (2) the rake angle of the cutter has more influence on the temperature increase in chips than the barrel rotation speed and penetration pitch; (3) if the cutter is made of a material with larger thermal conductivity, the temperature increase in the chips can be reduced; and (4) if the density of the liquid is less than the density of ice, the cutting chips sink to the bottom and the friction heat generated by the drill head and slush can raise the ambient temperature of the drill head by several degrees.

第6回極域科学シンポジウム[OM] 極域気水圏11月16日（月） 国立極地研究所１階交流アトリウム

Oxgen isotope ratio and chemistry profiles were compared to find the corresponding interstadials during the Wisconsin Ice Age between the GRIP (Greenland) and Dome Fuji (Antarctica) deep ice core data for the past one hundred and sixty thousand years. Eight interstadials in GRIPδ18O profile were found to correspond to those in Dome Fuji δ18O profile. Eleven interstadials in GRIPδ18O profile were found to correspond to those in Dome Fuji chemistry (calcium, nitrate and sulfate) profile, which is better suited for the purpose of interstadial search than the δ18O profile at Dome Fuji. The Eemian interglacial period at Dome Fuji seems to be much shorter and more stable than that in the GRIP profile. Three major periods having higher contents of calcium, nitrate and sulfate appear at Dome Fuji, ranging (1) between interstadials number 1 and 8, (2) between interstadials number 17 and 19, and (3) before the Eemian, which correspond to relatively cold and stable periods in the GRIP δ18O profile. These findings promise a favorable outcome from more detailed bipolar comparison in the future for an understanding of climatic linkage conditions and the driving forces between northern and southern hemispheres.

Recent results of physical analyses of the Dome Fuji ice core are summarized with special attention to new methods introduced in the present studies. Microphysical processes which affect the ice core records are reviewed to better understand the paleoclimatic and paleoenvironmental signals stored.

Dating of ice cores is of important but is difficult for an ice core where there is low snow accumulation, and also for the deep part because seasonal chemical and isotopic signals are not easily preserved due to vapor migration after snow deposition and molecular diffusion in the deep part of ice sheet. In this paper, an attempt to reveal annual layer thickness is conducted on the basis of precise number density measurement of air bubbles and air hydrates. The annual layer thickness from air bubbles and hydrates agrees well with a calculated value within 10-15% at all depths of the 2500 m deep core. The obtained thickness in the interglacial period according to Eemian period in the Greenland ice core was half of the calculated value.

A study of c-axis orientations in the upper 1500m of the Dome C (East Antarctica) deep ice core has been carried out using an automatic ice-fabric analyzer (AIFA). Twenty-nine vertical and a few horizontal thin sections from different depths in the core have been analyzed. Several statistical parameters describing fabric strength and fabric shapes have been calculated from the c-axis orientation data. The fabric diagrams display a near-random c-axis orientation distribution in the uppermost parts of the ice sheet. A tendency of c-axis rotation towards a broad single-maximum fabric is observed in the lowest part of the studied interval. The fabric development at Dome C thus appears typical for ice-sheet summit and dome sites. The fabric development at Dome C is compared with the fabric evolution in the Dome F and GRIP ice cores, and data on crystal size obtained with image-analysis techniques are presented. Studies of misorientation angles between the c axes of neighbouring crystals reveal little evidence for polygonization, but microscopic observations show that sub-grain boundaries are present in half of the grains at any depth.

The second phase of the deep ice core drilling at Dome Fuji, Antarctica is planned to be carried out in three successive summer seasons starting from 2003/2004 with an improved JARE deep ice core drill. On the basis of tests, major improvements were made including extension of the core barrel to 4m, addition of a more powerful chip-collecting pump, addition of a check valve to avoid loss of collected chips while hoisting the drill in borehole liquid, and a more powerful drill motor. This report describes the improvements and results of the tests as of December 2000.

Deep ice core drilling was carried out at Dome Fuji, Antarctica in 1995 and 1996 from the bottom of the casing installed in 1993 and reached 2503.52m in December 1996. We used a JARE type electromechanical drill with a core barrel of 2.2m length. Total numbers of ice corings and chip collections were 1369 and 837 respectively. The mean coring depths per run and per day were 1.75m and 8.21m, respectively. Quality of ice cores was perfect throughout the whole depth, even in the brittle zone. We report the outline of the system, coring performance, and troubles encountered.

From 1993 to 1998,members of the Dome F project group carried out ice coring at Dome F station. They recovered a 2503-m-long ice core. Specific tasks for the ice core processing included (1) core storage, (2) cutting and packing the ice samples for transportation from the station to Japan, and (3) performing initial ice analyses that can be done at the station. In this report we outline the operation and describe our experiences related to the ice core processing to aid similar processing in the future.

Two ice cores were extracted from Rikha Samba Glacier located in the central Nepal Himalayas in 1994 and 1998. Ice core quality in 1994 was poor due to cutter problems and samples were melted in situ. In 1998,a better ice core was successfully extracted and brought to Japan in frozen condition. The logistics of drilling, the transportation and preservation of ice, and problems of ice core drilling in Nepal are presented in this paper.

Laboratory experiments were done to better understand the electrical conduction mechanisms of impure, polycrystalline ice as represented by the 2503 m Dome Fuji (Antarctica) ice core. Also, two electrical measurement techniques for ice cores were compared and their usefulness for determining the acidity of ice cores was studied. We measured the electrical conductivity and complex permittivity of 167 slab-ice samples at frequencies from 20 Hz to 1 MHz. Measurements were performed at –21˚C for all samples, and at –110˚ to –20˚C for several samples, to examine the effects of temperature. We found linear relations between the AC loss factor and the molarity of sulfuric acid, and between the high-frequency-limit conductivity and the AC loss factor. Thus, the acidity levels can be determined from the AC loss factor. In contrast, the electrical conductivity measurement (ECM) current correlated weakly with the other parameters; furthermore, the correlation worsens at larger signal. In several samples containing high acidity, the dielectric properties had distinct changes near –81˚C. We argue that these changes were caused by a change from a liquid-vein-mediated conduction mechanism above the eutectic point of the solute/water/ ice system to a solid-phase conduction mechanism at lower temperatures.

1996年に米国により打ち上げられた火星探査機によって火星両極冠の表面地形が詳細に明らかになった.これにより火星極地雪氷に関する研究が急速に進展しだした.これまでドライアイスと考えられていた火星南極氷床もH2O氷でできた氷床である可能性が強いことや,氷床の涵養消耗機構に関する新しい観測結果が続々と発表されている.これらの最新の研究を紹介するとともに問題点や今後の研究の方向性などについて述べる.

The 320 kyr climatic record from the 2503 m Dome Fuji (Antarctica) ice core was analyzed using two electrical methods: AC-ECM and ECM (electrical conductivity measurements). AC-ECM is a method to detect the complex admittance between electrodes dragged on the ice surface with mm-scale resolution and uses 1V and 1 MHz. the ratio of the real to imaginary part of the admittance is the AC loss factor, which responds linearly to the amount of sulfuric acid and hydrogen ions. Both the AC loss factor and the ECM current respond to acid, but the ECM signal tends to saturate at high acidities. Dome Fuji ice was measured to be highly acidic, with background values of 2–7 μM, and had 4500 major peaks with acidities of up to 90 μM. This ice-core evidence and earlier snow-chemistry survey around the dome region indicates that Dome F may have a better connection to the stratosphere than have sites at lower altitude, which allows more stratospheric aerosol and gases to reach the snow surface. Acidity tends to be high in interglacial periods, but correlation between acidity and δ18O is not straightforward. Electrical signals decreased and smoothed out with increasing depth; the diffusion coefficients deduced from this smoothing were 10–102 times greater than in solid ice. the ice core exhibited electromechanical effects and expelling effects from sulfate peaks.

An important feature of natural ice, in addition to the obvious relevance of glaciers and ice sheets for climate-related issues, is its ability to creep on geological time scales and low deviatoric stresses at temperatures very close to its melting point, without losing its polycrystalline character. This fact, together with its strong mechanical anisotropy and other notable properties, makes natural ice an interesting model material for studying the high-temperature creep and recrystallization of rocks in Earth’s interior. After having reviewed the major contributions of deep ice coring to the research on natural ice microstructures in Part I of this work (Faria et al., 2014), here in Part II we present an up-todate view of the modern understanding of natural ice microstructures and the deformation processes that may produce them. In particular, we analyze a large body of evidence that reveals fundamental flaws in the widely accepted tripartite paradigm of polar ice microstructure (also known as the “three-stage model,” cf. Part I). These results prove that grain growth in ice sheets is dynamic, in the sense that it occurs during deformation and is markedly affected by the stored strain energy, as well as by air inclusions and other impurities. The strong plastic anisotropy of the ice lattice gives rise to high internal stresses and concentrated strain heterogeneities in the polycrystal, which demand large amounts of strain accommodation. From the microstructural analyses of ice cores, we conclude that the formation of many and diverse subgrain boundaries and the splitting of grains by rotation recrystallization are the most fundamental mechanisms of dynamic recovery and strain accommodation in polar ice. Additionally, in fine-grained, high-impurity ice layers (e.g. cloudy bands), strain may sometimes be accommodated by diffusional flow (at low temperatures and stresses) or microscopic grain boundary sliding via microshear (in anisotropic ice sheared at high temperatures). Grain boundaries bulged by migration recrystallization and subgrain boundaries are endemic and very frequent at almost all depths in ice sheets. Evidence of nucleation of new grains is also observed at various depths, provided that the local concentration of strain energy is high enough (which is not seldom the case). As a substitute for the tripartite paradigm, we propose a novel dynamic recrystallization diagram in the three-dimensional state space of strain rate, temperature, and mean grain size, which summarizes the various competing recrystallization processes that contribute to the evolution of the polar ice microstructure. Dedicated to Sepp Kipfstuhl on occasion of his 60th birthday.

Fresh snow samples were collected at Dome Fuji Station, Antarctica, from October 1995 to November 1996,and were analyzed for dicarboxylic acids by capillary gas chromatography and mass spectrometry. Concentrations of oxalic acid (C_2,the most abundant diacid) ranged from 2.07 to 17.4μg/kg-snow. C_2-C_8 dicarboxylic acids showed clear seasonal changes with higher concentration in summer than in winter. This suggested that low molecular weight dicarboxylic acids were produced by photochemical reactions. Concentrations of dicarboxylic acids at Dome Fuji Station were about 20 times higher than the snow samples collected on the route from Syowa Station to Dome Fuji Station. The concentrations of maleic acid and phthalic acid (derived from photochemical oxidation of anthropogenic aromatic hydrocarbons) at Dome Fuji Station was about 40 times higher than the route samples. In contrast, the concentrations of C_8 and C_9 diacids (derived from photochemical oxidation of biogenic unsaturated fatty acids) at Dome Fuji Station were only 3-5 times higher than the route samples. This comparison suggests that surface snow samples at Dome Fuji Station contained photooxidation products of anthropogenic organic matter, suggesting that the diacids are emitted from incomplete combustion of fossil fuel used at the Station and/or produced in the atmosphere by photooxidation of exhaust gases. On the other hand, concentration ratios of fumaric acid (trans-C_4 unsaturated diacid) to maleic acid (cis-C_4 unsaturated diacid) showed higher values in summer than in winter, suggesting that cis to trans isomerization occurs photochemically in the atmosphere and possibly in the snow surface. Although the atmosphere over Dome Fuji Station is contaminated by diesel exhaust from the station, seasonal distribution of dicarboxylic acids in fresh snow samples provide useful information on photochemical reactions occurring in the polar atmosphere.

Physical analyses of the Dome Fuji ice core have been carried out to reveal fundamental properties of the core : (1) Stratigraphy, (2) Bulk density by a volumetric method, (3) Bulk density by an x-ray transmission method, (4) Total gas content, (5) Permeability and bubble volume, (6) Distribution of air-bubbles, (7) Distribution of clathrate hydrates, (8) Raman spectral N_2/O_2 ratios of air-bubbles and clathrate hydrates, (9) Ice fabrics, (10) Ice grain size, (11) Laser scattering tomography, (12) DC-ECM and AC-ECM, (13) Mechanical test, and (14) Crystalline structures of ice and clathrate hydrate. In the present paper the main results obtained so far are summarized.

Air bubbles trapped near the surface of an ice sheet are transformed into air hydrates below a certain depth Their volume and number varies partly with environment and climate. Air bubbles and hydrates at 120-2200 m depth in the Dome Fuji (Dome F) ice core were examined with a microscope. This depth range covers the Holocene/Last Glacial/Last Interglacial/Previous Glacial periods. No air bubbles were seen below about 1100 m depth, and air hydrates began to appear from about 600 m. The observed number of air bubbles and hydrates was similar to that found in the Vostok ice core. For the ice covering the Last Glacial Maximum period, however the hydrate concentration in the Dome F core is about half that of the Vostok core. Reference to snow metamorphism and packing does not explain this finding.

多結晶氷薄片の個々の結晶粒の主軸(C軸)方位を画像解析によって自動解析する方法の開発を行った.氷薄片は,交差偏光板の間に置かれ,その垂直上方に設置されたカメラと,このカメラを中心,として左右にそれぞれ20°ずつ傾け設置された2台のカメラ,あわせて3台のCCD(Charge Coupled Device)カメラによって撮影される.交差偏光板を回転させ,取り込んだ画像から個々の結晶の消光位角を,それぞれのカメラ座標系に対して求め,これら複数の消光位角とC軸方位の幾何学的関係から,個々のC軸の方位角と天頂角が算出される.氷と同じ六方晶である石英薄片を用いて検証実験した結果,C軸の方位によっては方位角が90°ずれたり,あるいは全くの誤答となるケースが頻発した.これを解決するため,斜めの2台のCCDカメラを鉛直軸のまわりに90°回転させ,新たな撮影方向からそれぞれの消光位角を求めた.こうして得られた合計4セットの消光位角の大小関係から,あらかじめC軸のおおよその方位角を定める方法(象限判定法)を取り入れた.これにより,誤答が少なくなり,C軸天頂角が約10°以内の結晶と消光位角が0°または90°近傍にある結晶を除けば,C軸方位を決定することができた.

An automatic ice-fabric analyzer has been developed, which can determine individual ,-axis orientations by image-analysis techniques. The analyzer consists of four major components: a sample stage, a pair of crossed polaroids, a charge coupled device (CCD) camera and a light source. Both the sample stage and the crossed polaroids can be rotated independently of each other by the stepping motors controlled by a personal computer (PC). Measurements are conducted as follows. An ice thin section is set on the sample stage and then the crossed polaroids are rotated. Thin-section images are recorded by the PC at intervals of 2° of rotation. From the image-intensity (gray value) dataset of each crystal in the thin section the extinction angles of individual crystals can be determined. Similarly, eight other extinction angles of individual crystals are obtained from eight other CCD camera positions with respect to the thin section: Finally, the .-axis orientation of individual crystals is calculated by using these extinction angles. With this technique, all crystals within the view of the CCD camera can be analyzed at the same time. In addition, with image-processing techniques the individual crystals are recognized automatically and other parameters, such as grain-size and grain shape, can be measured simultaneously. Textural studies of Dome Fuji (Antarctica) ice cores have been conducted with this analyzer.

An X-ray transmission method has been developed to obtain a continuous profile of bulk densities of ice cores. Intensities of X-rays transmitted through an ice-core sample were continuously measured by an X-ray detector during translation of the sample across the X-ray beam. A thick section of an ice core with a constant thickness was prepared by band-sawing followed by microtome planing. The X-ray intensity profile obtained was converted to a density profile using a calibration curve for X-ray absorption vs ice thickness. Using this method, spatial resolution of the density profile was down to 1 mm. X-ray radiographs were also taken on a two-dimensional detector imaging plate, in order to observe layer structures of the ice cores.The method was applied to Dome Fuji (Antarctica) ice cores from the surface to 110 m depth. From the density profile obtained we calculated the power spectrum of the density variation by the discrete Fourier transform, and obtained several peaks at different frequencies. The center period in the spectrum was close to the annual accumulation thickness at the drill site.

A comprehensive study of ice-crystal fabrics and textures was conducted on the Dome F (Antarctica) ice core. Crystal ,-axis orientations, crystal sizes and crystal shape were measured on thin sections with an automatic ice-fabric analyzer. The general feature of textural and fabric development through a 2500 m long core was obtained by a 20 m interval study. Crystal size steadily increases with depth except for depths of about 500,1800, 2000, 2200 and 2300 m, at which depths crystal size decreases suddenly. There is a clear correlation between crystal-size and ´18O values. Crystals tend to elongate horizontally with depth, and the aspect ratio (long axis vs short axis of a grain) increases twofold at 1600 m depth and fluctuates below that depth. The .-axis orientation fabrics gradually change with depth from a random orientation pattern near the surface to a strong vertical single maximum at 2500 m. These are very similar to those from the GRIP (Greenland) core The observations of crystal shape and the fabric measurements indicate that nucleation-recrystallization does not take place at Dome F.

An ice core to 2503.52 m depth was drilled during 1995 and 1996 at 77°19′01″S, 39°42′12″ E (3810 m a.s.l.), at the summit of Dome Fuji, East Antarctica. Climatic and environmental conditions were observed at the coring site throughout the 2 years of wintering operation. Meteorological and glaciological observations made clear the present surface processes of mass balance. The chemistry of the surface snow layers was observed for investigation of the atmospheric environment reflected in snow deposits. Core analyses have been carried out in Japan. Permeability and density measurements show that air bubbles are completely closed off by densification processes at about 98 m depth. The vertical profile of δ 18O suggests that the core covers two warm stages and one cold stage from the surface down to 1800 m depth. The transition from the cold to the warm period affects the vertical distribution of ice-crystal size. The chemical constituents in the ice core show large differences between warm and cold periods. A depth–age relationship is presented and a study made of palaeoclimatic and core signals.

Fabric (distribution of crystallographic orientations) profile along the full NEEM ice core, Greenland, is presented in this work. Data were measured in the field by an Automatic Ice Texture Analyzer every 10 m, from 33 m down to 2461 m depth. The fabric evolves from a slightly anisotropic fabric at the top, toward a strong single maximum at about 2300 m, which is typical of a deformation pattern mostly driven by uniaxial compression and simple shearing. A sharp increase in the fabric strengthening is observed at the Holocene to Wisconsin climatic transition. A similar strengthening, toward an anisotropic single maximum-type fabric, has been observed in several ice cores from Greenland and Antarctica, and can be attributed to a positive feedback between changes in ice viscosity at the climatic transition, and the impact of a shear component of stress. Centimeter scale abrupt texture (fabric and microstructure) variations are observed in the bottom part of the core. Their positions are in good agreement with the folding hypothesis used for a climatic reconstruction by Dahl-Jensen and co authors (2013). Comparison is made to two others ice cores drilled along the same ridge; the GRIP ice core drilled at the summit of the ice sheet, and the NorthGRIP ice core, drilled 325 km to the NNW of the summit along the ridge, and 365 km upstream from NEEM. The fabric profile clearly reflects the increase in shear deformation when moving NW along the ridge from GRIP to NorthGRIP and NEEM. The difference in fabric profiles between NEEM and NorthGRIP also evidences a stronger lateral extension associated with a sharper ridge at NorthGRIP. References: Dahl-Jensen, D. and 120 co-authors. Eemian interglacial reconstructed from a Greenland folded ice core, Nature, 493, 489–493, 2013.

Fabric (distribution of crystallographic orientations) along the full NEEM ice core, Greenland was measured in the field by an automatic ice texture analyzer every 10 m, from 33 m down to 2461 m depth. The fabric evolves from a slightly anisotropic fabric at the top, toward a strong single maximum at about 2300 m, which is typical of a deformation pattern mostly driven by uniaxial compression and simple shearing. A sharp increase in the fabric strengthening rate is observed at the Holocene to Wisconsin (HW) climatic transition. From a simple model we estimate that this depth is located at a transition from a state dominated by vertical compression to a state dominated by vertical shear. Comparisons are made to two others ice cores drilled along the same ridge; the GRIP ice core, drilled at the summit of the ice sheet, and the NGRIP ice core, drilled 325 km to the NNW of the summit along the ridge, and 365 km upstream from NEEM. This comparison tends to demonstrate that the ice viscosity change with the HW climatic transition must be associated with the shear-dominated state to induce the abrupt fabric strengthening observed at NEEM. This comparison therefore reflects the increasing role of shear deformation on the coring site when moving NW along the ridge from GRIP to NGRIP and NEEM. The difference in fabric profiles between NEEM and NGRIP also evidences a stronger lateral extension associated with a sharper ridge at NGRIP. Further along the core, centimeter scale abrupt texture (fabric and microstructure) variations are observed in the bottom part of the core. Their positions are in good agreement with the observed folding layers in Dahl-Jensen et al. (2013).