scholarly journals Crystalline Texture of the 2083 m Ice Core at Vostok Station, Antarctica

1989 ◽  
Vol 35 (121) ◽  
pp. 392-398 ◽  
Author(s):  
V.Ya. Lipenkov ◽  
N.I. Barkov ◽  
P. Duval ◽  
P. Pimienta
Keyword(s):  
Enhancement Factor ◽  
Crystal Size ◽  
Gradual Increase ◽  
Ice Core ◽  
Impurity Content ◽  
Mean Value ◽  
Axis Orientation ◽  
Vostok Station ◽  
The Mean ◽  
Convergent Flow

AbstractCrystalline texture and c-axis orientation of the 2083 m ice core at Vostok Station, covering more than 150kyear, reveal the existence of strong anisotropics. Changes in crystal size with depth are compatible with the growth of grains driven by the free energy of grain boundaries. A smaller growth rate appears to be associated with cold periods. A gradual increase in the horizontal elongation of grains was observed between 350 and 680 m. But, the mean value of the coefficient of the linear dimensional orientation of grains does not change below 700 m.The c-axis orientation of ice grains tends to orientate perpendicular to the direction of the elongation of grains, forming a vertical girdle pattern. This characteristic fabric has been interpreted as resulting from the gradual rotation of grains by basal glide under uniaxial longitudinal tension. The rotation of grains was calculated with respect to the total strain, simulating the formation of the girdle fabric pattern. The fabric-enhancement factor was calculated at various depths. It appears that Vostok ice hardens gradually with depth when considering the transverse convergent flow. No significant variation of the enhancement factor was observed with changes in climate and impurity content.

scholarly journals Crystalline Texture of the 2083 m Ice Core at Vostok Station, Antarctica

1989 ◽  
Vol 35 (121) ◽  
pp. 392-398 ◽  
Author(s):  
V.Ya. Lipenkov ◽  
N.I. Barkov ◽  
P. Duval ◽  
P. Pimienta
Keyword(s):  
Enhancement Factor ◽  
Crystal Size ◽  
Gradual Increase ◽  
Ice Core ◽  
Impurity Content ◽  
Mean Value ◽  
Axis Orientation ◽  
Vostok Station ◽  
The Mean ◽  
Convergent Flow

AbstractCrystalline texture andc-axis orientation of the 2083 m ice core at Vostok Station, covering more than 150kyear, reveal the existence of strong anisotropics. Changes in crystal size with depth are compatible with the growth of grains driven by the free energy of grain boundaries. A smaller growth rate appears to be associated with cold periods. A gradual increase in the horizontal elongation of grains was observed between 350 and 680 m. But, the mean value of the coefficient of the linear dimensional orientation of grains does not change below 700 m.Thec-axis orientation of ice grains tends to orientate perpendicular to the direction of the elongation of grains, forming a vertical girdle pattern. This characteristic fabric has been interpreted as resulting from the gradual rotation of grains by basal glide under uniaxial longitudinal tension. The rotation of grains was calculated with respect to the total strain, simulating the formation of the girdle fabric pattern. The fabric-enhancement factor was calculated at various depths. It appears that Vostok ice hardens gradually with depth when considering the transverse convergent flow. No significant variation of the enhancement factor was observed with changes in climate and impurity content.

scholarly journals Air-hydrate crystals in deep ice-core samples from Vostok Station, Antarctica

1994 ◽  
Vol 40 (134) ◽  
pp. 79-86 ◽  
Author(s):  
T. Uchida ◽  
T. Hondoh ◽  
S. Mae ◽  
V.YA. Lipenkov ◽  
P. Duval
Keyword(s):  
Volume Concentration ◽  
Ice Core ◽  
Site Occupancy ◽  
Mean Value ◽  
Gas Content ◽  
Glacial Ice ◽  
Core Samples ◽  
Vostok Station ◽  
The Mean ◽  
Geometrical Equation

AbstractMicroscopic observation of air-hydrate crystals was carried out using 34 deep ice-core samples retrieved at Vostok Station, Antarctica. Samples were obtained from depths between 1050 and 2542 m, which correspond to Wisconsin/Sangamon/Illinoian ice. It was found that the volume and number of air-hydrate varied with the climatic changes. The volume concentration of air-hydrate in the interglacial ice was about 30% larger than that in the glacial ice. In the interglacial ice, the number concentration of air-hydrate was about a half and the mean volume of air-hydrate was nearly three times larger than that in the glacial-age ice. The air-hydrate crystals were found to grow in the ice sheet, about 6.7 × 10−12cm3year-1, in compensation for the disappearance of smaller ones. The volume concentration of air-hydrate was related to the total gas content by a geometrical equation with a proportional parameter α. The mean value of α below 1250 m, where no air bubbles were found, was about 0.79. This coincided with an experimentally determined value of the crystalline site occupancy of the air-hydrate in a 1500 m core obtained at Dye 3, Greenland (Hondoh and others, 1990). In the depth profile of calculated α for many samples, α in the interglacial ice was about 30% smaller than that in the glacial-age ice.

scholarly journals Air-hydrate crystals in deep ice-core samples from Vostok Station, Antarctica

1994 ◽  
Vol 40 (134) ◽  
pp. 79-86 ◽  
Author(s):  
T. Uchida ◽  
T. Hondoh ◽  
S. Mae ◽  
V.YA. Lipenkov ◽  
P. Duval
Keyword(s):  
Volume Concentration ◽  
Ice Core ◽  
Site Occupancy ◽  
Mean Value ◽  
Gas Content ◽  
Glacial Ice ◽  
Core Samples ◽  
Vostok Station ◽  
The Mean ◽  
Geometrical Equation

AbstractMicroscopic observation of air-hydrate crystals was carried out using 34 deep ice-core samples retrieved at Vostok Station, Antarctica. Samples were obtained from depths between 1050 and 2542 m, which correspond to Wisconsin/Sangamon/Illinoian ice. It was found that the volume and number of air-hydrate varied with the climatic changes. The volume concentration of air-hydrate in the interglacial ice was about 30% larger than that in the glacial ice. In the interglacial ice, the number concentration of air-hydrate was about a half and the mean volume of air-hydrate was nearly three times larger than that in the glacial-age ice. The air-hydrate crystals were found to grow in the ice sheet, about 6.7 × 10−12 cm3 year-1, in compensation for the disappearance of smaller ones. The volume concentration of air-hydrate was related to the total gas content by a geometrical equation with a proportional parameter α. The mean value of α below 1250 m, where no air bubbles were found, was about 0.79. This coincided with an experimentally determined value of the crystalline site occupancy of the air-hydrate in a 1500 m core obtained at Dye 3, Greenland (Hondoh and others, 1990). In the depth profile of calculated α for many samples, α in the interglacial ice was about 30% smaller than that in the glacial-age ice.

scholarly journals Spatial and temporal variability in isotope composition of recent snow in the vicinity of Vostok station, Antarctica: implications for ice-core record interpretation

2002 ◽  
Vol 35 ◽  
pp. 181-186 ◽  
Author(s):  
Alexey A. Ekaykin ◽  
Vladimir Ya. Lipenkov ◽  
Narcisse I. Barkov ◽  
Jean Robert Petit ◽  
Valerie Masson-Delmotte
Keyword(s):  
Isotope Composition ◽  
Ice Core ◽  
Snow Accumulation ◽  
Spatial And Temporal Variability ◽  
Weak Correlation ◽  
Ice Core Record ◽  
Vostok Station ◽  
The Mean ◽  
Mean Annual Air Temperature ◽  
Snow Samples

AbstractContinuous, detailed isotope (δD and δ18O) profiles were obtained from eight snow pits dug in the vicinity of Vostok station, Antarctica, during the period 1984– 2000. In addition, snow samples taken along the 1km long accumulation-stake profile were measured to determine spatial variability in isotope composition of recent snow. the stacked δD time series spanning the last 55 years shows only weak correlation with the mean annual air temperature recorded at Vostok station. Significant oscillations of both snow accumulation and snow isotope composition with the periods 2.5, 5, 20 and, possibly, ~102 years observed at single points are interpreted in terms of drift of snow-accumulation waves of various scales on the surface of the ice sheet.

scholarly journals A model of crystal-size evolution in polar ice masses

2014 ◽  
Vol 60 (221) ◽  
pp. 463-477 ◽  
Author(s):  
Felix NG ◽  
T.H. Jacka
Keyword(s):  
Crystal Growth ◽  
Dislocation Density ◽  
Grain Boundary ◽  
Crystal Size ◽  
Boundary Migration ◽  
Ice Core ◽  
Ice Cores ◽  
Grain Boundary Migration ◽  
Shallow Subsurface ◽  
The Mean

AbstractIn the deep ice cores drilled at the GRIP, NGRIP and GISP2 sites in Greenland and at Byrd Station and the summit of Law Dome in Antarctica, the mean crystal size increases with depth in the shallow subsurface and reaches steady values at intermediate depth. This behaviour has been attributed to the competition between grain-boundary migration driven crystal growth and crystal polygonization, but the effects of changing crystal dislocation density and non-equiaxed crystal shape in this competition are uncertain. We study these effects with a simple model. It describes how the mean height and width of crystals evolve as they flatten under vertical compression, and as crystal growth and polygonization compete. The polygonization rate is assumed to be proportional to the mean dislocation density across crystals. Migration recrystallization, which can affect crystal growth via strain-induced grain boundary migration but whose impact on the mean crystal size is difficult to quantify for ice at present, is not accounted for. When applied to the five ice-core sites, the model simulates the observed crystal-size profiles well down to the bottom of their steady regions, although the match for Law Dome is less satisfactory. Polygonization rate factors retrieved for the sites range from 10–5 to 10–2 a–1. We conclude that since crystal size and dislocation density evolve in a strongly coupled manner, consistent modelling requires multiple differential equations to track both of these variables. Future ice-core analysis should also determine crystal size in all three principal directions.

scholarly journals Crystal Size and Orientation Patterns in the Wisconsin-Age Ice from Dye 3, Greenland

1988 ◽  
Vol 10 ◽  
pp. 109-115 ◽  
Author(s):  
C.C. Langway ◽  
H. Shoji ◽  
N. Azuma
Keyword(s):  
Crystal Size ◽  
Ice Core ◽  
Ice Crystal ◽  
Axis Orientation ◽  
Measuring Device ◽  
Thin Sections ◽  
Core Samples ◽  
Physical Measurements ◽  
Ice Crystal Size ◽  
Velocity Measuring

Crystal size and c-axis orientation patterns were measured on the Dye 3, Greenland, deep ice core in order to investigate time-dependent changes or alterations in the physical character of the core as a function of time after recovery. The physical measurements were expanded to include depth intervals not previously studied in the field. The recent study focused on core samples located between 1786 m and the bottom of the ice sheet at 2037 m.Manual c-axis measurements were made on 23 new thin sections using a Rigsby-type universal stage. A new semi-automatic ultrasonic wave-velocity measuring device was developed in order to compare the results with the earlier manual measurements and to study an additional 114 ice-core samples in the Wisconsin-age ice. Crystal-size measurements were made on specimen surfaces by inducing evaporation grooves at crystal boundaries and measuring linear intercepts. The ultrasonically measured test samples were subsequently cleaned and analyzed by ion chromatography in order to measure impurity concentration levels of Cl−, NO3− and SO42− and study their effects on crystal growth and c-axis orientation.

scholarly journals Textures and fabrics in the Dome F (Antarctica) ice core

1999 ◽  
Vol 29 ◽  
pp. 163-168 ◽  
Author(s):  
N. Azuma ◽  
Y. Wang ◽  
K. Mori ◽  
H. Narita ◽  
T. Hondoh ◽  
...  
Keyword(s):  
Crystal Size ◽  
Ice Core ◽  
Clear Correlation ◽  
Crystal Shape ◽  
Ice Crystal ◽  
Axis Orientation ◽  
Thin Sections ◽  
Crystal Axis ◽  
Orientation Pattern ◽  
Comprehensive Study

AbstractA 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.

scholarly journals Shallow-ice microstructure at Dome Concordia, Antarctica

2000 ◽  
Vol 30 ◽  
pp. 8-12 ◽  
Author(s):  
Laurent Arnaud ◽  
Jérôme Weiss ◽  
Michel Gay ◽  
Paul Duval
Keyword(s):  
Crystal Size ◽  
Accumulation Rate ◽  
Ice Core ◽  
Processing Technique ◽  
Image Processing Technique ◽  
Size Distributions ◽  
Thin Sections ◽  
Crystal Size Distributions ◽  
Size Profile ◽  
The Mean

AbstractThe shallow-ice microstructure at Dome Concordia, Antarctica, has been studied between 100 m and 580 m. An original digital-image-processing technique has been specially developed to extract ice microstructure (grain boundaries) from thin sections prepared during the two first scientific EPICA field seasons (1997/98 and 1998/99). Using this, not only the mean crystal size, but also crystal-size distributions and shape anisotropy were determined. The mean crystal-size profile as well as crystal-size distributions reveal normal grain growth up to 430 m. Between 430 m and 500 m, a marked decrease of crystal size is observed and compared with a similar trend obtained in the "old" Dome C ice core formerly associated with the Holocene/Last Glacial transition (Duval and Lorius, 1980). This seems to indicate a slightly lower accumulation rate (by <10%) at Dome C. The shapes of the crystal-size distributions, though very similar, do evolve with depth and seem to be sensitive to climatic changes. An increasing flattening of crystal shape is observed with depth. This allowed estimation of the vertical strain rate in the shallow part of the ice sheet.

scholarly journals Ice Structure and Crystal Fabrics of the 2200 M Ice Core at Vostok Station, Antarctica

1988 ◽  
Vol 10 ◽  
pp. 223-223
Author(s):  
N.I. Barkov ◽  
V.Ya. Lipenkov ◽  
V.N. Petrov
Keyword(s):  
Ice Core ◽  
Three Dimensional ◽  
Air Bubbles ◽  
The Core ◽  
Polycrystalline Ice ◽  
Vostok Station ◽  
Dimensional Parameters ◽  
The Mean ◽  
Ice Fabrics

Both the ice structure and the ice fabric along the 2200 m ice core at Vostok Station were investigated during the 25th, 29th and 30th Soviet Antarctic Expeditions.Several kinds of three-dimensional parameters of polycrystalline ice were measured, e.g. the mean diameter and size distribution of ice crystals and air bubbles, and specific volumeThe variation in most of these parameters along the core reflects not only the process of metamorphism in ice but also changes in the environmental conditions at the surface. The causes of these variations are discussed, in order to estimate the possibility of a paleoclimatic interpretation.The evolution of c-axis fabrics with depth is discussed in relation to the ice-deformation conditions.A comparison of ice fabrics at Vostok, Byrd Station and Camp Century shows that similar mechanisms cause the reorientation of crystals. The role of temperature in fabric development is discussed.

scholarly journals Ice Structure and Crystal Fabrics of the 2200 M Ice Core at Vostok Station, Antarctica

1988 ◽  
Vol 10 ◽  
pp. 223 ◽  
Author(s):  
N.I. Barkov ◽  
V.Ya. Lipenkov ◽  
V.N. Petrov
Keyword(s):  
Ice Core ◽  
Three Dimensional ◽  
Air Bubbles ◽  
The Core ◽  
Polycrystalline Ice ◽  
Vostok Station ◽  
Dimensional Parameters ◽  
The Mean ◽  
Ice Fabrics

Both the ice structure and the ice fabric along the 2200 m ice core at Vostok Station were investigated during the 25th, 29th and 30th Soviet Antarctic Expeditions. Several kinds of three-dimensional parameters of polycrystalline ice were measured, e.g. the mean diameter and size distribution of ice crystals and air bubbles, and specific volume The variation in most of these parameters along the core reflects not only the process of metamorphism in ice but also changes in the environmental conditions at the surface. The causes of these variations are discussed, in order to estimate the possibility of a paleoclimatic interpretation. The evolution of c-axis fabrics with depth is discussed in relation to the ice-deformation conditions. A comparison of ice fabrics at Vostok, Byrd Station and Camp Century shows that similar mechanisms cause the reorientation of crystals. The role of temperature in fabric development is discussed.

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