scholarly journals The Vertical Structure of the Antarctic Ice Sheet and Palaeoclimatic Interpretation of the Data (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 344
Author(s):  
Ye. Korotkevich ◽  
V.N. Petrov ◽  
N.I. Barkov ◽  
V.Ya. Lipenkov
Keyword(s):  
Grain Size ◽  
Ice Core ◽  
Isotope Analysis ◽  
Ice Sheet ◽  
Air Content ◽  
Cross Section Area ◽  
Section Area ◽  
Vostok Station ◽  
The Antarctic ◽  
Gradient Change

The ice core from the 1 415 m Vostok bore hole has been studied. It was found that the ice-grain size increases with depth in the upper 700 m, a sharp gradient change occurring in the 300 to 400 m range. The grain cross-section area at depths of 100, 200, 300, 400, 500, 600, and 700 m was 1.1, 2.0, 1.5, 1.9, 2.6, and 3.3 mm2 respectively. Since grain size is a function of age, and is determined by initial size and growth rate, the latter being exponentially related to ice temperature, an attempt was made to interpret the obtained data in terms of palaeoclimatology. Calculations show that the upper part of the ice sheet (down to 300 m depth) formed during the past 12 ka, and grew under temperatures higher than those at which the lower part of the ice formed, that is ice at 300 to 700 m depth. This conclusion was confirmed by the results of oxygen isotope analysis. The air content of ice at depths 100 to 650, 650 to 850, 850 to 1 100, and 1 100 to 1 400 m reduced to normal conditions was 65, 70, 75, and 70 mm3 g−1 respectively. Calculations suggest that 3 to 30 ka BP the ice-sheet elevation at Vostok station was close to the present one, while 30 to 40, 40 to 55, and 55 to 75 ka BP it was 500, 1 000, and 500 m lower than at present, respectively.

scholarly journals The Vertical Structure of the Antarctic Ice Sheet and Palaeoclimatic Interpretation of the Data (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 344-344
Author(s):  
Ye. Korotkevich ◽  
V.N. Petrov ◽  
N.I. Barkov ◽  
V.Ya. Lipenkov
Keyword(s):  
Grain Size ◽  
Ice Core ◽  
Isotope Analysis ◽  
Ice Sheet ◽  
Air Content ◽  
Cross Section Area ◽  
Section Area ◽  
Vostok Station ◽  
The Antarctic ◽  
Gradient Change

The ice core from the 1 415 m Vostok bore hole has been studied. It was found that the ice-grain size increases with depth in the upper 700 m, a sharp gradient change occurring in the 300 to 400 m range. The grain cross-section area at depths of 100, 200, 300, 400, 500, 600, and 700 m was 1.1, 2.0, 1.5, 1.9, 2.6, and 3.3 mm2 respectively. Since grain size is a function of age, and is determined by initial size and growth rate, the latter being exponentially related to ice temperature, an attempt was made to interpret the obtained data in terms of palaeoclimatology.Calculations show that the upper part of the ice sheet (down to 300 m depth) formed during the past 12 ka, and grew under temperatures higher than those at which the lower part of the ice formed, that is ice at 300 to 700 m depth. This conclusion was confirmed by the results of oxygen isotope analysis.The air content of ice at depths 100 to 650, 650 to 850, 850 to 1 100, and 1 100 to 1 400 m reduced to normal conditions was 65, 70, 75, and 70 mm3 g−1 respectively. Calculations suggest that 3 to 30 ka BP the ice-sheet elevation at Vostok station was close to the present one, while 30 to 40, 40 to 55, and 55 to 75 ka BP it was 500, 1 000, and 500 m lower than at present, respectively.

scholarly journals Evolution of the East Antarctic Ice Sheet: A Numerical Study of Thermo-Mechanical Response Patterns With Changing Climate

1988 ◽  
Vol 11 ◽  
pp. 52-59 ◽  
Author(s):  
P. Huybrechts ◽  
J. Oerlemans
Keyword(s):  
Mechanical Response ◽  
Flow Line ◽  
Numerical Study ◽  
Ice Core ◽  
Ice Sheet ◽  
Antarctic Ice Sheet ◽  
Mechanical Coupling ◽  
Vostok Station ◽  
Basal Melting ◽  
East Antarctic Ice Sheet

An efficient numerical ice-sheet model, including time dependence and full thermo-mechanical coupling, has been developed in order to investigate the thermal regime and overall configuration of a polar ice sheet with respect to changing environmental conditions. From basic sensitivity experiments, in which a schematic East Antarctic ice sheet is forced with a typical glacial–interglacial climatic shift, it is found that: (i) the mutual interaction of temperature and deformation has a stabilizing effect on its steady-state configuration; (ii) in the transient mode, this climatic transition initially leads to increased ice thickness due to enhanced accumulation, after which this trend is reversed due to a warmer base. Time-scales for this reversal are of the order of 103 years in marginal zones and of 104 years in interior regions; (iii) horizontal heat advection plays a major role in damping possible runaway behaviour due to the dissipation – strain-rate feed-back, suggesting that creep instability is a rather unlikely candidate to initiate surging of the East Antarctic ice sheet. The model is then applied to four East Antarctic flow lines. Only the flow line passing through Wilkes Land appears to be vulnerable to widespread basal melting, due to enhanced basal warming following climatic warming. Time-dependent modelling of the Vostok flow line indicates that the Vostok Station area has risen about 95 m since the beginning of the present interglacial due to thermo-mechanical effects, which is of particular interest in interpreting the palaeoclimatic signal of the ice core obtained there.

scholarly journals The SUBGLACIOR drilling probe: concept and design

2014 ◽  
Vol 55 (68) ◽  
pp. 233-242 ◽  
Author(s):  
O. Alemany ◽  
J. Chappellaz ◽  
J. Triest ◽  
M. Calzas ◽  
O. Cattani ◽  
...  
Keyword(s):  
Methane Concentration ◽  
Ice Core ◽  
Ice Sheet ◽  
General Concept ◽  
International Partnerships ◽  
Trapped Gases ◽  
Glacier Ice ◽  
Suitable Site ◽  
The Antarctic

AbstractIn response to the ‘oldest ice’ challenge initiated by the International Partnerships in Ice Core Sciences (IPICS), new rapid-access drilling technologies through glacier ice need to be developed. These will provide the information needed to qualify potential sites on the Antarctic ice sheet where the deepest section could include ice that is >1Ma old and still in good stratigraphic order. Identifying a suitable site will be a prerequisite for deploying a multi-year deep ice-core drilling operation to elucidate the cause and mechanisms of the mid-Pleistocene transition from 40 ka glacial–interglacial cycles to 100 ka cycles. As part of the ICE&LASERS/SUBGLACIOR projects, we have designed an innovative probe, SUBGLACIOR, with the aim of perforating the ice sheet down to the bedrock in a single season and continuously measuring in situ the isotopic composition of the melted water and the methane concentration in trapped gases. Here we present the general concept of the probe, as well as the various technological solutions that we have favored so far to reach this goal.

scholarly journals The Heat Regime of the Central Parts of the Antarctic Ice Sheet with Changing Climate (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 343
Author(s):  
V.R. Barbash ◽  
I.A. Zotikov
Keyword(s):  
Numerical Modelling ◽  
Surface Temperature ◽  
Greenhouse Effect ◽  
Ice Sheet ◽  
Heat Regime ◽  
Antarctic Ice Sheet ◽  
Temperature Changes ◽  
Dissipation Term ◽  
Vostok Station ◽  
The Antarctic

The heat regime and dynamics of the Antarctic ice sheet are studied using numerical modelling for two flow lines, one of which passes Vostok station and the other Byrd station. A two-dimensional non-steady heat-transfer equation with an energy dissipation term was used. The study consists of two parts. The first is a study of velocity and temperature distributions within the glacier under steady-state conditions. The second study was performed assuming surface temperature changes intended to model palaeoclimatic changes for the last 100 ka and also to model future climate changes due to a possible "greenhouse" effect. Computer numerical modelling shows that the Antarctic ice sheet retains a record of the climatic temperature minimum 18 ka BP. Numerical modelling of the greenhouse effect assumes a temperature increasing by 10 deg within the next 100 a; its influence increases after this even if the surface temperature then remains the same for the next 20 ka. It is shown that for the next 1 ka the temperature wave will penetrate only a thin surface layer of the ice. Even in 20 ka the bottom temperature of the ice sheet will still be unchanged. Small increases of ice velocity can produce ice-sheet thinning of the order of 10 mm a−1.

scholarly journals Simulation of the Antarctic ice sheet with a three-dimensional polythermal ice-sheet model, in support of the EPICA project

1998 ◽  
Vol 27 ◽  
pp. 201-206 ◽  
Author(s):  
R. Calov ◽  
A. Savvin ◽  
R. Greve ◽  
I. Hansen ◽  
K. Hutter
Keyword(s):  
Shear Deformation ◽  
Ice Core ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Climate Forcing ◽  
Drilling Process ◽  
Antarctic Ice Sheet ◽  
Atlantic Sector ◽  
Dronning Maud Land ◽  
The Antarctic

The three-dimensional polythermal ice-sheet model SICOPOLIS is applied to the entire Antarctic ice sheet in support of the European Project for Ice Coring in Antartica (EPICA). in this study, we focus on the deep ice core to be drilled in Dronning Maud Land (Atlantic sector of East Antarctica) as part of EPICA. It has not yel been decided where the exact drill-site will be situated. Our objective is to support EPICA during its planning phase as well as during the actual drilling process. We discuss a transient simulation with a climate forcing derived from the Vostok ice core and the SPECMAP sea-level record. This simulation shows the range of accumulation, basal temperature, age and shear deformation to be expected in the region of Dronning Maud Land. Based on these results, a possible coring position is proposed, and the distribution of temperature, age, horizontal velocity and shear deformation is shown for this column.

scholarly journals Evolution of the East Antarctic Ice Sheet: A Numerical Study of Thermo-Mechanical Response Patterns With Changing Climate

1988 ◽  
Vol 11 ◽  
pp. 52-59 ◽  
Author(s):  
P. Huybrechts ◽  
J. Oerlemans
Keyword(s):  
Mechanical Response ◽  
Flow Line ◽  
Numerical Study ◽  
Ice Core ◽  
Ice Sheet ◽  
Antarctic Ice Sheet ◽  
Mechanical Coupling ◽  
Vostok Station ◽  
Basal Melting ◽  
East Antarctic Ice Sheet

An efficient numerical ice-sheet model, including time dependence and full thermo-mechanical coupling, has been developed in order to investigate the thermal regime and overall configuration of a polar ice sheet with respect to changing environmental conditions.From basic sensitivity experiments, in which a schematic East Antarctic ice sheet is forced with a typical glacial–interglacial climatic shift, it is found that: (i) the mutual interaction of temperature and deformation has a stabilizing effect on its steady-state configuration; (ii) in the transient mode, this climatic transition initially leads to increased ice thickness due to enhanced accumulation, after which this trend is reversed due to a warmer base. Time-scales for this reversal are of the order of 103 years in marginal zones and of 104 years in interior regions; (iii) horizontal heat advection plays a major role in damping possible runaway behaviour due to the dissipation – strain-rate feed-back, suggesting that creep instability is a rather unlikely candidate to initiate surging of the East Antarctic ice sheet.The model is then applied to four East Antarctic flow lines. Only the flow line passing through Wilkes Land appears to be vulnerable to widespread basal melting, due to enhanced basal warming following climatic warming. Time-dependent modelling of the Vostok flow line indicates that the Vostok Station area has risen about 95 m since the beginning of the present interglacial due to thermo-mechanical effects, which is of particular interest in interpreting the palaeoclimatic signal of the ice core obtained there.

scholarly journals Issues with fracturing ice during an ice drilling project in Greenland (EastGRIP)

2020 ◽  
Author(s):  
Ilka Weikusat ◽  
David Wallis ◽  
Steven Franke ◽  
Nicolas Stoll ◽  
Julien Westhoff ◽  
...  
Keyword(s):  
Grain Size ◽  
Standard Procedure ◽  
Ice Core ◽  
Ice Sheet ◽  
Ice Cores ◽  
Orientation Distribution ◽  
Geothermal Heat ◽  
Ice Dynamics ◽  
The Core ◽  
Pulling Forces

<p>Drilling an ice core through an ice sheet (typically 2000 to 3000 m thick) is a technical challenge that nonetheless generates valuable and unique information on palaeo-climate and ice dynamics. As technically the drilling cannot be done in one run, the core has to be fractured approximately every 3 m to retrieve core sections from the bore hole. This fracture process is initiated by breaking the core with core-catchers which also clamp the engaged core in the drill head while the whole drill is then pulled up with the winch motor.</p><p> </p><p>This standard procedure is known to become difficult and requires extremely high pulling forces (Wilhelms et al. 2007), in the very deep part of the drill procedure, close to the bedrock of the ice sheet, especially when the ice material becomes warm (approximately -2°C) due to the geothermal heat released from the bedrock. Recently, during the EastGRIP (East Greenland Ice coring Project) drilling we observed a similar issue with breaking off cored sections only with extremely high pulling forces, but started from approximately 1800 m of depth, where the temperature is still very cold (approximately -20°C). This has not been observed at other ice drilling sites. As dependencies of fracture behaviour on crystal orientation and grain size are known (Schulson & Duval 2009) for ice, we thus examined the microstructure in the ice samples close to and at the core breaks.</p><p> </p><p>First preliminary results suggest that these so far unexperienced difficulties are due to the profoundly different c-axes orientation distribution (CPO) in the EastGRIP ice core. In contrast to other deep ice cores which have been drilled on ice domes or ice divides, EastGRIP is located in an ice stream. This location means that the deformation geometry (kinematics) is completely different, resulting in a different CPO (girdle pattern instead of single maximum pattern). Evidence regarding additional grain-size dependence will hopefully help to refine the fracturing procedure, which is possible due to a rather strong grain size layering observed in natural ice formed by snow precipitation.</p><p> </p><p>---------------------</p><p>Wilhelms, F.; Sheldon, S. G.; Hamann, I. & Kipfstuhl, S. Implications for and findings from deep ice core drillings - An example: The ultimate tensile strength of ice at high strain rates. Physics and Chemistry of Ice (The proceedings of the International Conference on the Physics and Chemistry of Ice held at Bremerhaven, Germany on 23-28 July 2006), <strong>2007</strong>, 635-639</p><p>Schulson, E. M. & Duval, P. Creep and Fracture of Ice. Cambridge University Press, <strong>2009</strong>, 401</p>

scholarly journals Past Changes of the Antarctic Ice Sheet in Terre Adélie as Deduced from Ice-Core Data and Ice Modelling (Abstract)

1984 ◽  
Vol 5 ◽  
pp. 239-239
Author(s):  
N.W. Young ◽  
D. Raynaud ◽  
M. de Angelis ◽  
J.-R. Petit ◽  
C. Lorius
Keyword(s):  
Ice Core ◽  
Ice Sheet ◽  
Antarctic Ice Sheet ◽  
Core Data ◽  
Terre Adélie ◽  
The Antarctic

scholarly journals Retrieving the paleoclimatic signal from the deeper part of the EPICA Dome C ice core

2015 ◽  
Vol 9 (4) ◽  
pp. 1633-1648 ◽  
Author(s):  
J.-L. Tison ◽  
M. de Angelis ◽  
G. Littot ◽  
E. Wolff ◽  
H. Fischer ◽  
...  
Keyword(s):  
High Resolution ◽  
Large Scale ◽  
Ice Core ◽  
Ice Sheet ◽  
Remote Sensing Data ◽  
Ice Cores ◽  
Air Content ◽  
Confining Effect ◽  
Chemical Profiles ◽  
Subglacial Topography

Abstract. An important share of paleoclimatic information is buried within the lowermost layers of deep ice cores. Because improving our records further back in time is one of the main challenges in the near future, it is essential to judge how deep these records remain unaltered, since the proximity of the bedrock is likely to interfere both with the recorded temporal sequence and the ice properties. In this paper, we present a multiparametric study (δD-δ18Oice, δ18Oatm, total air content, CO2, CH4, N2O, dust, high-resolution chemistry, ice texture) of the bottom 60 m of the EPICA (European Project for Ice Coring in Antarctica) Dome C ice core from central Antarctica. These bottom layers were subdivided into two distinct facies: the lower 12 m showing visible solid inclusions (basal dispersed ice facies) and the upper 48 m, which we will refer to as the "basal clean ice facies". Some of the data are consistent with a pristine paleoclimatic signal, others show clear anomalies. It is demonstrated that neither large-scale bottom refreezing of subglacial water, nor mixing (be it internal or with a local basal end term from a previous/initial ice sheet configuration) can explain the observed bottom-ice properties. We focus on the high-resolution chemical profiles and on the available remote sensing data on the subglacial topography of the site to propose a mechanism by which relative stretching of the bottom-ice sheet layers is made possible, due to the progressively confining effect of subglacial valley sides. This stress field change, combined with bottom-ice temperature close to the pressure melting point, induces accelerated migration recrystallization, which results in spatial chemical sorting of the impurities, depending on their state (dissolved vs. solid) and if they are involved or not in salt formation. This chemical sorting effect is responsible for the progressive build-up of the visible solid aggregates that therefore mainly originate "from within", and not from incorporation processes of debris from the ice sheet's substrate. We further discuss how the proposed mechanism is compatible with the other ice properties described. We conclude that the paleoclimatic signal is only marginally affected in terms of global ice properties at the bottom of EPICA Dome C, but that the timescale was considerably distorted by mechanical stretching of MIS20 due to the increasing influence of the subglacial topography, a process that might have started well above the bottom ice. A clear paleoclimatic signal can therefore not be inferred from the deeper part of the EPICA Dome C ice core. Our work suggests that the existence of a flat monotonic ice–bedrock interface, extending for several times the ice thickness, would be a crucial factor in choosing a future "oldest ice" drilling location in Antarctica.

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