scholarly journals Simulated features of the air-hydrate formation process in the Antarctic ice sheet at Vostok

1999 ◽  
Vol 29 ◽  
pp. 191-201 ◽  
Author(s):  
Andrey N. Salamatin ◽  
Vladimir Ya. Lipenkov ◽  
Takeo Hondoh ◽  
Tomoko Ikeda
Keyword(s):  
Ice Core ◽  
Hydrate Formation ◽  
Ice Cores ◽  
Air Bubbles ◽  
Air Bubble ◽  
Self Diffusion ◽  
Rate Limiting Step ◽  
Typical Time ◽  
Polar Ice Sheets ◽  
Selective Diffusion

AbstractA recently developed theory of post-nucleation conversion of an air bubble to air-hydrate crystal in ice is applied to simulate two different types of air-hydrate formation in polar ice sheets. The work is focused on interpretation of the Vostok (Antarctica) ice-core data. The hydrostatic compression of bubbles is the rate-limiting step of the phase transformation which is additionally influenced by selective diffusion of the gas components from neighboring air bubbles. The latter process leads to the gas fractionation resulting in lower (higher) N2/O2 ratios in air hydrates (coexisting bubbles) with respect to atmospheric air. The typical time of the post-nucleation conversion decreases at Vostok from 1300-200 a at the beginning to 50-3 a at the end of the transition zone. The model of the diffusive transport of the air constituents from air bubbles to hydrate crystals is constrained by the data of Raman spectra measurements. The oxygen and nitrogen self-diffusion (permeation) coefficients in ice are determined at 220 K as 4.5 × 10−8 and 9.5 × 10−8 mm2 a−1, respectively while the activation energy is estimated to be about 50 kJ mol−1. The gas-fractionation time-scale at Vostok, τF ∼300 a, appears to be two orders of magnitude less than the typical time of the air-hydrate nucleation, τz ∼30-35 ka, and thus the condition for the extreme gas fractionation, τF ≪ τz is satisfied. Application of the theory to the GRIP and GISP2 ice cores shows that on average, a significant gas fractionation cannot be expected for air hydrates in central Greenland. However, a noticeable (statistically valid) nitrogen enrichment might be observed in the last air bubbles at the end of the transition.

scholarly journals New constraints on the gas age-ice age difference along the EPICA ice cores, 0–50 kyr

2007 ◽  
Vol 3 (3) ◽  
pp. 527-540 ◽  
Author(s):  
L. Loulergue ◽  
F. Parrenin ◽  
T. Blunier ◽  
J.-M. Barnola ◽  
R. Spahni ◽  
...  
Keyword(s):  
Ice Core ◽  
Phase Relationship ◽  
Ice Cores ◽  
Climatic Conditions ◽  
Ice Age ◽  
Age Difference ◽  
Last Deglaciation ◽  
Last Glacial Period ◽  
Polar Ice Sheets ◽  
Dronning Maud Land

Abstract. Gas is trapped in polar ice sheets at ~50–120 m below the surface and is therefore younger than the surrounding ice. Firn densification models are used to evaluate this ice age-gas age difference (Δage) in the past. However, such models need to be validated by data, in particular for periods colder than present day on the East Antarctic plateau. Here we bring new constraints to test a firn densification model applied to the EPICA Dome C (EDC) site for the last 50 kyr, by linking the EDC ice core to the EPICA Dronning Maud Land (EDML) ice core, both in the ice phase (using volcanic horizons) and in the gas phase (using rapid methane variations). We also use the structured 10Be peak, occurring 41 kyr before present (BP) and due to the low geomagnetic field associated with the Laschamp event, to experimentally estimate the Δage during this event. Our results seem to reveal an overestimate of the Δage by the firn densification model during the last glacial period at EDC. Tests with different accumulation rates and temperature scenarios do not entirely resolve this discrepancy. Although the exact reasons for the Δage overestimate at the two EPICA sites remain unknown at this stage, we conclude that current densification model simulations have deficits under glacial climatic conditions. Whatever the cause of the Δage overestimate, our finding suggests that the phase relationship between CO2 and EDC temperature previously inferred for the start of the last deglaciation (lag of CO2 by 800±600 yr) seems to be overestimated.

scholarly journals Tracer transport in an isochronal ice-sheet model

2016 ◽  
Vol 63 (237) ◽  
pp. 22-38 ◽  
Author(s):  
ANDREAS BORN
Keyword(s):  
Ice Core ◽  
Ice Sheet ◽  
Vertical Motion ◽  
Greenland Ice Sheet ◽  
Ice Cores ◽  
Model Parameters ◽  
Tracer Transport ◽  
Geochemical Tracers ◽  
Tuning Method ◽  
Polar Ice Sheets

ABSTRACTThe full history of ice sheet and climate interactions is recorded in the vertical profiles of geochemical tracers in polar ice sheets. Numerical simulations of these archives promise great advances both in the interpretation of these reconstructions and the validation of the models themselves. However, fundamental mathematical shortcomings of existing models subject tracers to spurious diffusion, thwarting straightforward solutions. Here, I propose a new vertical discretization for ice-sheet models that eliminates numerical diffusion entirely. Vertical motion through the model mesh is avoided by mimicking the real-world flow of ice as a thinning of underlying layers. A new layer is added to the surface at equidistant time intervals, isochronally, thus identifying each layer uniquely by its time of deposition and age. This new approach is implemented for a two-dimensional section through the summit of the Greenland ice sheet. The ability to directly compare simulations of vertical ice cores with reconstructed data is used to find optimal model parameters from a large ensemble of simulations. It is shown that because this tuning method uses information from all times included in the ice core, it constrains ice-sheet sensitivity more robustly than a realistic reproduction of the modern ice-sheet surface.

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.

scholarly journals Formation of air clathrate hydrates in polar ice sheets: heterogeneous nucleation induced by micro-inclusions

2010 ◽  
Vol 56 (199) ◽  
pp. 917-921 ◽  
Author(s):  
Hiroshi Ohno ◽  
Vladimir Ya. Lipenkov ◽  
Takeo Hondoh
Keyword(s):  
High Resolution ◽  
Ice Sheets ◽  
Ice Cores ◽  
Transformation Process ◽  
Clathrate Hydrates ◽  
Air Bubbles ◽  
Polar Ice ◽  
High Resolution Mapping ◽  
Polar Ice Sheets ◽  
Resolution Mapping

AbstractTo investigate factors influencing nucleation of air clathrate hydrates in polar ice sheets, we have performed high-resolution mapping of the distributions of soluble impurities, air bubbles and air- hydrate crystals versus depth in the Dome Fuji Antarctic ice. Significant correlation observed between the concentrations of air inclusions and impurities in ice along with frequent occurrence of impurities inside hydrate crystals suggest that micro-inclusions promote hydrate nucleation in the ice matrix. Our observations also show that the diffusive macroscopic-scale redistribution of air constituents in ice in the bubble-hydrate transition zone is controlled by the original sedimentary layering of soluble impurities acting as nucleation helpers. The results of this study are important for the correct interpretation of high-resolution gas analyses of ice cores and for better understanding the global bubble-to-hydrate transformation process in polar ice sheets.

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.

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 Distribution of air bubbles in the EDML and EDC (Antarctica) ice cores, using a new method of automatic image analysis

2010 ◽  
Vol 56 (196) ◽  
pp. 339-348 ◽  
Author(s):  
Kai J. Ueltzhöffer ◽  
Verena Bendel ◽  
Johannes Freitag ◽  
Sepp Kipfstuhl ◽  
Dietmar Wagenbach ◽  
...  
Keyword(s):  
Ice Core ◽  
User Interaction ◽  
Ice Cores ◽  
Software Framework ◽  
Air Bubbles ◽  
Climate Research ◽  
The Past ◽  
Bubble Sizes ◽  
Bubble Number ◽  
Processing Framework

AbstractAir bubbles in ice cores play an essential role in climate research, not only because they contain samples of the palaeoatmosphere, but also because their shape, size and distribution provide information about the past firn structure and the embedding of climate records into deep ice cores. In this context, we present profiles of average bubble size and bubble number for the entire EDML (Antarctica) core and the top 600 m of the EDC (Antarctica) core, and distributions of bubble sizes from selected depths. The data are generated with an image-processing framework which automatically extracts position, orientation, size and shape of an elliptical approximation of each bubble from thick-section micrographs, without user interaction. The presented software framework allows for registration of overlapping photomicrographs to yield accurate locations of bubble-like features. A comparison is made between the bubble parameterizations in the EDML and EDC cores and data published on the Vostok (Antarctica) ice core. The porosity at the firn/ice transition is inferred to lie between 8.62% and 10.48% for the EDC core and between 10.56% and 12.61 % for the EDML core.

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