scholarly journals Characteristics of bubble volumes in firn-ice transition layers of ice cores from polar ice sheets

1994 ◽  
Vol 20 ◽  
pp. 95-100
Author(s):  
Takao Kameda ◽  
Renji Naruse
Keyword(s):  
Bulk Density ◽  
Classical Method ◽  
Accumulation Rate ◽  
Bubble Formation ◽  
Ice Sheets ◽  
Ice Cores ◽  
Ideal Gas ◽  
Polar Ice ◽  
Polar Ice Sheets ◽  
Glacier Ice

The air-bubble formation process has been studied experimentally by using five ice cores from the Greenland and Antarctic ice sheets. Bubble volumes in firn-ice samples were measured by a classical method based on Boyle Mariotte's law for an ideal gas. It was found that the bubble volume varies with depth as a function of bulk density in the firn-ice transition layer, which is represented by an exponential function of firn density. Air bubbles start to form rapidly at a bulk density of 0.763–0.797 Mg m-3. This density (ρib) seems to be correlated with the ice temperature in the ice sheets; ρib increases with a decrease in the ice temperature. Vb shows the maximum value in the density range 0.819–0.832 Mg m-3. The corresponding porosity of the density ranges between 0.110 and 0.097. This porosity does not seem to correlate with ice temperature or accumulation rate at the coring site. These characteristics of firn densities probably affect the amount of entrapped air in glacier ice (total air content) in polar ice sheets.

scholarly journals Characteristics of bubble volumes in firn-ice transition layers of ice cores from polar ice sheets

1994 ◽  
Vol 20 ◽  
pp. 95-100
Author(s):  
Takao Kameda ◽  
Renji Naruse
Keyword(s):  
Bulk Density ◽  
Classical Method ◽  
Accumulation Rate ◽  
Bubble Formation ◽  
Ice Sheets ◽  
Ice Cores ◽  
Ideal Gas ◽  
Polar Ice ◽  
Polar Ice Sheets ◽  
Glacier Ice

The air-bubble formation process has been studied experimentally by using five ice cores from the Greenland and Antarctic ice sheets. Bubble volumes in firn-ice samples were measured by a classical method based on Boyle Mariotte's law for an ideal gas. It was found that the bubble volume varies with depth as a function of bulk density in the firn-ice transition layer, which is represented by an exponential function of firn density. Air bubbles start to form rapidly at a bulk density of 0.763–0.797 Mg m-3. This density (ρib) seems to be correlated with the ice temperature in the ice sheets; ρibincreases with a decrease in the ice temperature. Vbshows the maximum value in the density range 0.819–0.832 Mg m-3. The corresponding porosity of the density ranges between 0.110 and 0.097. This porosity does not seem to correlate with ice temperature or accumulation rate at the coring site. These characteristics of firn densities probably affect the amount of entrapped air in glacier ice (total air content) in polar ice sheets.

scholarly journals δD – δ18O Relationships in Ice Formed by Subglacial Freezing: Paleoclimatic Implications

1985 ◽  
Vol 31 (109) ◽  
pp. 229-232 ◽  
Author(s):  
R. A. Souchez ◽  
J. M. de Groote
Keyword(s):  
Computer Simulation ◽  
Isotopic Composition ◽  
Ice Sheets ◽  
Ice Cores ◽  
System Model ◽  
Polar Ice ◽  
Bottom Part ◽  
Basal Ice ◽  
Polar Ice Sheets ◽  
Glacier Ice

AbstractA freezing slope, distinct from that of precipitation, is displayed on a δD–δ18O diagram by basal ice in different circumstances. However, if the subglacial reservoir allowed to freeze is mixed in the course of time with an input having a lighter isotopic composition, basal ice cannot be distinguished from glacier ice in terms of slope. Such a situation is encountered at the base of Grubengletscher and is indicated by a computer simulation using the open-system model of Souchez and Jouzel (1984). Suggested implications for the paleoclimatic interpretation of deep ice cores recovered from the bottom part of polar ice sheets are given.

scholarly journals How well can we parameterize past accumulation rates in polar ice sheets?

1997 ◽  
Vol 25 ◽  
pp. 418-422 ◽  
Author(s):  
Eric J. Steig
Keyword(s):  
Accumulation Rate ◽  
Order Approximation ◽  
Ice Core ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Cores ◽  
Accumulation Rates ◽  
Polar Ice ◽  
Polar Ice Sheets ◽  
First Order Approximation

An important component of models of the cryosphere is the calculation of accumulation rates over polar ice sheets. As a first-order approximation, many models rely on the assumption that temperature is the main controlling factor for precipitation. However, compilation of available ice-core data, including a new core from Taylor Dome, East Antarctica, suggests that precipitation is significantly decoupled from temperature for a large proportion of both the Greenland and Antarctic ice sheets. While the estimated glacial-to-interglacial change in temperature does not differ greatly among ice cores from each ice sheet, the estimated change in accumulation rate varies by more than a factor of 2. A simple vapor-pressure parameterization gives reasonable estimates of accumulation in the ice-sheet interior, but this is not necessarily the case close to the ice-sheet margin, where synoptic weather systems are important.

δD – δ18O Relationships in Ice Formed by Subglacial Freezing: Paleoclimatic Implications

1985 ◽  
Vol 31 (109) ◽  
pp. 229-232 ◽  
Author(s):  
R. A. Souchez ◽  
J. M. de Groote
Keyword(s):  
Computer Simulation ◽  
Isotopic Composition ◽  
Ice Sheets ◽  
Ice Cores ◽  
System Model ◽  
Polar Ice ◽  
Bottom Part ◽  
Basal Ice ◽  
Polar Ice Sheets ◽  
Glacier Ice

AbstractA freezing slope, distinct from that of precipitation, is displayed on a δD–δ18O diagram by basal ice in different circumstances. However, if the subglacial reservoir allowed to freeze is mixed in the course of time with an input having a lighter isotopic composition, basal ice cannot be distinguished from glacier ice in terms of slope. Such a situation is encountered at the base of Grubengletscher and is indicated by a computer simulation using the open-system model of Souchez and Jouzel (1984). Suggested implications for the paleoclimatic interpretation of deep ice cores recovered from the bottom part of polar ice sheets are given.

scholarly journals How well can we parameterize past accumulation rates in polar ice sheets?

1997 ◽  
Vol 25 ◽  
pp. 418-422 ◽  
Author(s):  
Eric J. Steig
Keyword(s):  
Accumulation Rate ◽  
Order Approximation ◽  
Ice Core ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Cores ◽  
Accumulation Rates ◽  
Polar Ice ◽  
Polar Ice Sheets ◽  
First Order Approximation

An important component of models of the cryosphere is the calculation of accumulation rates over polar ice sheets. As a first-order approximation, many models rely on the assumption that temperature is the main controlling factor for precipitation. However, compilation of available ice-core data, including a new core from Taylor Dome, East Antarctica, suggests that precipitation is significantly decoupled from temperature for a large proportion of both the Greenland and Antarctic ice sheets. While the estimated glacial-to-interglacial change in temperature does not differ greatly among ice cores from each ice sheet, the estimated change in accumulation rate varies by more than a factor of 2. A simple vapor-pressure parameterization gives reasonable estimates of accumulation in the ice-sheet interior, but this is not necessarily the case close to the ice-sheet margin, where synoptic weather systems are important.

scholarly journals Deformation and recrystallization processes of ice from polar ice sheets

2000 ◽  
Vol 30 ◽  
pp. 83-87 ◽  
Author(s):  
Paul Duval ◽  
Laurent Arnaud ◽  
Olivier Brissaud ◽  
Maureen Montagnat ◽  
Sophie de la Chapelle
Keyword(s):  
Grain Boundary ◽  
Grain Growth ◽  
Boundary Migration ◽  
Ice Sheets ◽  
Ice Cores ◽  
Grain Boundary Sliding ◽  
Tertiary Creep ◽  
Dislocation Slip ◽  
Polar Ice ◽  
Polar Ice Sheets

AbstractInformation on deformation modes, fabric development and recrystallization processes was obtained by study of deep ice cores from polar ice sheets. It is shown that intracrystalline slip is the main deformation mechanism in polar ice sheets. Grain-boundary sliding does not appear to be a significant deformation mode. Special emphasis was laid on the occurrence of "laboratory" tertiary creep in ice sheets. The creep behavior is directly related to recrystallization processes. Grain-boundary migration associated with grain growth and rotation recrystallization accommodates dislocation slip and counteracts strain hardening. The fabric pattern is similar to that induced only by slip, even if rotation recrystallization slows down fabric development. Fabrics which develop during tertiary creep, and are associated with migration recrystallization, are typical recrystallization fabrics. They are associated with the fast boundary migration regime as observed in temperate glaciers. A decrease of the stress exponent is expected from 3, when migration recrystallization occurs, to a value ≤ 2 when normal grain growth occurs.

scholarly journals Snow Stratigraphic Studies At Dome C, East Antarctica: An Investigation Of Depositional and Diagenetic Processes

1982 ◽  
Vol 3 ◽  
pp. 239-242 ◽  
Author(s):  
J. M. Palais ◽  
I. M. Whillans ◽  
C. Bull
Keyword(s):  
Ice Sheets ◽  
Ice Cores ◽  
Snow Accumulation ◽  
East Antarctica ◽  
Polar Ice ◽  
Depositional Processes ◽  
Diagenetic Processes ◽  
Snow Stratigraphy ◽  
Stratigraphic Record ◽  
Polar Ice Sheets

The increased interest in past climatic changes, as revealed by studies of long ice cores from polar ice sheets, has stressed the need for a better understanding of the development of the stratigraphic record preserved in these cores. This paper presents some results of surface investigations at Dome C (74°30'S, 123°10'E), East Antarctica, carried out in austral summers 1978-79 and 1979-80. An explanation is presented of the snow stratigraphy, in terms of depositional and post-depositional processes, that is supported by detailed accumulation measurements at stakes and by snow-pit studies. Temporal and areal variability of snow accumulation are investigated to determine how representative the results interpreted from a single core might be for the Dome C region. Finally, the reliability of several stratigraphic methods for defining annual layers is assessed.Snow-pit studies show that major depositional features are preserved with depth. Visible annual strata at Dome C are composed of thin, hard crusts overlying thicker layers of soft to medium-hard snow. Low density depth-hoar layers, when they occur, are usually found below the thin, hard crusts. Depth profiles of gross 8-radioactivity and of microparticles concentration exhibit annual cyclicity which, together with the detailed visible stratigraphy, can be used to assign dates to the layers.

scholarly journals Post-drilling recrystallization of the Byrd Station deep ice core and its relevance to current and future deep-core drilling on polar ice sheets

1994 ◽  
Vol 20 ◽  
pp. 231-236
Author(s):  
A.J. Gow
Keyword(s):  
Ice Core ◽  
Ice Sheets ◽  
Ice Cores ◽  
The United States ◽  
Polar Ice ◽  
Thin Sections ◽  
Full Extent ◽  
Drill Site ◽  
Polar Ice Sheets ◽  
Highly Strained

Cores of highly strained ice recovered from depths of 1200–1800 m at Byrd Station in 1967–68 have been found to have recrystallized while in storage in the United States. Such recrystallization, inferred to have occurred when temperatures in the storage facility rose above about – 14°C, would not have been discovered if thin sections of the cores had not been prepared and photographed at the drill site within hours of pulling the cores to the surface. It was only after new sections of the long stored cores were compared with the original sections that the full extent of recrystallization was revealed. The recrystallized structure emulates in both texture and fabric those observed in naturally annealed ice in the bottom 350 m at Byrd Station. It is concluded that polar ice cores should be stored at temperatures of –20°C or colder in order to inhibit or minimize post-drilling recrystallization.

scholarly journals A Review of the Microstructural Location of Impurities in Polar Ice and Their Impacts on Deformation

2021 ◽  
Vol 8 ◽  
Author(s):  
Nicolas Stoll ◽  
Jan Eichler ◽  
Maria Hörhold ◽  
Wataru Shigeyama ◽  
Ilka Weikusat
Keyword(s):  
Deformation Behaviour ◽  
Ice Core ◽  
Measurement Techniques ◽  
Ice Sheets ◽  
Ice Cores ◽  
Holistic Approach ◽  
Triple Junctions ◽  
Polar Ice ◽  
Theoretical Approaches ◽  
Polar Ice Sheets

Insoluble and soluble impurities, enclosed in polar ice sheets, have a major impact on the deformation behaviour of the ice. Macro- and Micro-scale deformation observed in ice sheets and ice cores has been retraced to chemical loads in the ice, even though the absolute concentration is negligible. And therefore the exact location of the impurities matters: Allocating impurities to specific locations inside the ice microstructure inherently determines the physical explanation of the observed interaction between chemical load and the deformational behaviour. Both, soluble and non-soluble impurities were located in grain boundaries, triple junctions or in the grain interior, using different methods, samples and theoretical approaches. While each of the observations is adding to the growing understanding of the effect of impurities in polar ice, the growing number of ambiguous results calls for a dedicated and holistic approach in assessing the findings. Thus, we here aim to give a state of the art overview of the development in microstructural impurity research over the last 20 years. We evaluate the used methods, discuss proposed deformation mechanisms and identify two main reasons for the observed ambiguity: 1) limitations and biases of measurement techniques and 2) the physical state of the analysed impurity. To overcome these obstacles we suggest possible approaches, such as the continuous analysis of impurities in deep ice cores with complementary methods, the implementation of these analyses into established in-situ ice core processing routines, a more holistic analysis of the microstructural location of impurities, and an enhanced knowledge-transfer via an open access data base.

scholarly journals The Influence On Atmospheric Composition of Volcanic Eruptions as Derived From Ice-Core Analysis

1985 ◽  
Vol 7 ◽  
pp. 125-129 ◽  
Author(s):  
C.U. Hammer
Keyword(s):  
Ice Core ◽  
Ice Sheets ◽  
Ice Cores ◽  
Volcanic Eruptions ◽  
Atmospheric Composition ◽  
Core Analysis ◽  
Polar Ice ◽  
Ice Caps ◽  
The Past ◽  
Polar Ice Sheets

Polar ice cores offer datable past snow deposits in the form of annual ice layers, which reflect the past atmospheric composition. Trace substances in the cores are related to the past mid-tropospheric impurity load, this being due to the vast extent of the polar ice sheets (or ice caps), their surface elevations and remoteness from most aerosol sources. Volcanic eruptions add to the rather low background impurity load via their eruptive products. This paper concentrates on the widespread influence on atmospheric impurity loads caused by the acid gas products from volcanic eruptions. In particular the following subjects are discussed: acid volcanic signals in ice cores, latitude of eruptions as derived by ice-core analysis, inter-hemispheric dating of the two polar ice sheets by equatorial eruptions, volcanic deposits in ice cores during the last glacial period and climatic implications.

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