Correction Of Air-content Measurements In Polar Ice For The Effect Of Cut Bubbles At The Surface Of The Sample

AbstractAir content (V) of polar ice has been used as an indicator of the past elevation of the ice sheets. A calculation is presented to correct V measurements performed on ice samples for the effect of cut bubbles at their surface. The results indicate a correction ranging from 1 to 10% for cubic ice samples with about 3 cm length. The correction depends mainly on the size of the bubbles. The theoretical calculation is experimentally verified. The statistical noise linked with the presence of a finite number of bubbles in the ice samples is evaluated. The influence of such a correction on the V profiles measured on polar ice cores is discussed. The method in this paper can also be used for correction of ice-density data obtained by the hydrostatic method.

Download Full-text

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

Annals of Glaciology ◽

10.1017/s0260305500006029 ◽

1985 ◽

Vol 7 ◽

pp. 125-129 ◽

Cited By ~ 9

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.

Download Full-text

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

Annals of Glaciology ◽

10.3189/s0260305500006029 ◽

1985 ◽

Vol 7 ◽

pp. 125-129 ◽

Cited By ~ 2

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.

Download Full-text

Application of AMS 14C Dating to Ice Core Research

Radiocarbon ◽

10.1017/s0033822200031143 ◽

1995 ◽

Vol 37 (2) ◽

pp. 637-641 ◽

Cited By ~ 11

Author(s):

A T. Wilson

Keyword(s):

Ice Core ◽

Ice Sheets ◽

Ice Cores ◽

Unexpected Result ◽

Polar Ice ◽

14C Dating ◽

The Past ◽

Accelerator Mass Spectrometer ◽

Polar Ice Sheets ◽

Ams 14C Dating

I describe here the use of the accelerator mass spectrometer (AMS) sublimation technique to 14C-date polar ice cores. An unexpected result of this work has been to extend the understanding of how polar ice sheets entrap and record the past composition of the Earth's atmosphere. This work has led to the discovery of a new phenomenon in which CO2 and other greenhouse gases can be entrapped in cold (never melted) polar ice sheets.

Download Full-text

Bubbly-ice densification in ice sheets: I. Theory

Journal of Glaciology ◽

10.3189/s0022143000034961 ◽

1997 ◽

Vol 43 (145) ◽

pp. 387-396 ◽

Cited By ~ 1

Author(s):

Andrey N. Salamatin ◽

Vladimir Ya Lipenkov ◽

Paul Duval

Keyword(s):

High Pressures ◽

Similarity Theory ◽

Ice Sheets ◽

Ice Cores ◽

Rheological Parameters ◽

Polar Ice ◽

Load Pressure ◽

Air Content ◽

Bubble Pressure ◽

Asymptotic Phase

AbstractDry snow on the surface of polar ice ice sheets is first densified and metamorphosed to produce firn. Bubbly ice is the next stage of the transformation process which takes place below the depth of pore closure. This stage extends to the transition zone where, due to high pressures and low temperatures. air trapped in bubbles and ice begins to form the mixed air clathrate hydrates, while the gas phase progressively disappears. Here we develop a model of bubbly-ice rheology and ice-sheet dynamics taking into account glacier-ice compressibility. The interaction between hydrostatic compression of air bubbles, deviatoric (uniaxial) compressive deformation of the ice matrix and global deformations of the glacier body is considered. The ice-matrix pressure and the absolute-load pressure are distinguished. Similarity theory and scale analysis are used in examine the resultant mathematical model of bubbly-ice densification. The initial rate of bubble compression in ice sheets appears to be relatively high, so that the pressure (density) relaxation process takes place only 150-200 m in depth (below pore close-off) to reach its asymptotic phase, wherein the minimal drop between bubble and ice pressures is governed by the rate of loading (ice accumulation). This makes it possible to consider densification under stationary (present-day) conditions of ice formation as a special case of primary interest. The computational tests performed with the model indicate that both ice-porosity and bubble-pressure profiles in ice sheets are sensitive to variations of the rheological parameters of pure ice. However, only the bubble-pressure distinguishes between the rheological properties at low and high stresses. The porosity profile at the asymptotic phase is mostly determined by the air content in the ice. In the companion paper (Lipenkov and others, 1997), we apply the model to experimental data from polar ice cores and deduce, through an inverse procedure, the rhelogical properties of pure ice as well as the mean air content in Holocene and glacial ice sediments at vostok Station (Antarctica).

Download Full-text

Bubbly-ice densification in ice sheets: I. Theory

Journal of Glaciology ◽

10.1017/s0022143000034961 ◽

1997 ◽

Vol 43 (145) ◽

pp. 387-396 ◽

Cited By ~ 14

Author(s):

Andrey N. Salamatin ◽

Vladimir Ya Lipenkov ◽

Paul Duval

Keyword(s):

High Pressures ◽

Similarity Theory ◽

Ice Sheets ◽

Ice Cores ◽

Rheological Parameters ◽

Polar Ice ◽

Load Pressure ◽

Air Content ◽

Bubble Pressure ◽

Asymptotic Phase

AbstractDry snow on the surface of polar ice ice sheets is first densified and metamorphosed to produce firn. Bubbly ice is the next stage of the transformation process which takes place below the depth of pore closure. This stage extends to the transition zone where, due to high pressures and low temperatures. air trapped in bubbles and ice begins to form the mixed air clathrate hydrates, while the gas phase progressively disappears. Here we develop a model of bubbly-ice rheology and ice-sheet dynamics taking into account glacier-ice compressibility. The interaction between hydrostatic compression of air bubbles, deviatoric (uniaxial) compressive deformation of the ice matrix and global deformations of the glacier body is considered. The ice-matrix pressure and the absolute-load pressure are distinguished. Similarity theory and scale analysis are used in examine the resultant mathematical model of bubbly-ice densification. The initial rate of bubble compression in ice sheets appears to be relatively high, so that the pressure (density) relaxation process takes place only 150-200 m in depth (below pore close-off) to reach its asymptotic phase, wherein the minimal drop between bubble and ice pressures is governed by the rate of loading (ice accumulation). This makes it possible to consider densification under stationary (present-day) conditions of ice formation as a special case of primary interest. The computational tests performed with the model indicate that both ice-porosity and bubble-pressure profiles in ice sheets are sensitive to variations of the rheological parameters of pure ice. However, only the bubble-pressure distinguishes between the rheological properties at low and high stresses. The porosity profile at the asymptotic phase is mostly determined by the air content in the ice. In the companion paper (Lipenkov and others, 1997), we apply the model to experimental data from polar ice cores and deduce, through an inverse procedure, the rhelogical properties of pure ice as well as the mean air content in Holocene and glacial ice sediments at vostok Station (Antarctica).

Download Full-text

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

Journal of Glaciology ◽

10.1017/s0022143000006547 ◽

1985 ◽

Vol 31 (109) ◽

pp. 229-232 ◽

Cited By ~ 34

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.

Download Full-text

An optimized multi-proxy, multi-site Antarctic ice and gas orbital chronology (AICC2012): 120–800 ka

Climate of the Past ◽

10.5194/cp-9-1715-2013 ◽

2013 ◽

Vol 9 (4) ◽

pp. 1715-1731 ◽

Cited By ~ 216

Author(s):

L. Bazin ◽

A. Landais ◽

B. Lemieux-Dudon ◽

H. Toyé Mahamadou Kele ◽

D. Veres ◽

...

Keyword(s):

Ice Core ◽

Ice Cores ◽

Companion Paper ◽

Polar Ice ◽

Uncertainty Range ◽

Air Content ◽

Dating Method ◽

Long Timescales ◽

Age Constraints ◽

Mis 5

Abstract. An accurate and coherent chronological framework is essential for the interpretation of climatic and environmental records obtained from deep polar ice cores. Until now, one common ice core age scale had been developed based on an inverse dating method (Datice), combining glaciological modelling with absolute and stratigraphic markers between 4 ice cores covering the last 50 ka (thousands of years before present) (Lemieux-Dudon et al., 2010). In this paper, together with the companion paper of Veres et al. (2013), we present an extension of this work back to 800 ka for the NGRIP, TALDICE, EDML, Vostok and EDC ice cores using an improved version of the Datice tool. The AICC2012 (Antarctic Ice Core Chronology 2012) chronology includes numerous new gas and ice stratigraphic links as well as improved evaluation of background and associated variance scenarios. This paper concentrates on the long timescales between 120–800 ka. In this framework, new measurements of δ18Oatm over Marine Isotope Stage (MIS) 11–12 on EDC and a complete δ18Oatm record of the TALDICE ice cores permit us to derive additional orbital gas age constraints. The coherency of the different orbitally deduced ages (from δ18Oatm, δO2/N2 and air content) has been verified before implementation in AICC2012. The new chronology is now independent of other archives and shows only small differences, most of the time within the original uncertainty range calculated by Datice, when compared with the previous ice core reference age scale EDC3, the Dome F chronology, or using a comparison between speleothems and methane. For instance, the largest deviation between AICC2012 and EDC3 (5.4 ka) is obtained around MIS 12. Despite significant modifications of the chronological constraints around MIS 5, now independent of speleothem records in AICC2012, the date of Termination II is very close to the EDC3 one.

Download Full-text

Deformation and recrystallization processes of ice from polar ice sheets

Annals of Glaciology ◽

10.3189/172756400781820688 ◽

2000 ◽

Vol 30 ◽

pp. 83-87 ◽

Cited By ~ 26

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.

Download Full-text

Reconciling the surface temperature–surface mass balance relationship in models and ice cores in Antarctica over the last two centuries

10.5194/tc-2020-36 ◽

2020 ◽

Author(s):

Marie G. P. Cavitte ◽

Quentin Dalaiden ◽

Hugues Goosse ◽

Jan T. M. Lenaerts ◽

Elizabeth R. Thomas

Keyword(s):

Mass Balance ◽

Large Scale ◽

Ice Core ◽

Ice Sheets ◽

Ice Cores ◽

Surface Mass Balance ◽

Weak Correlation ◽

Surface Mass ◽

The Past ◽

Ice Core Records

Abstract. Ice cores are an important record of the past surface mass balance (SMB) of ice sheets, with SMB mitigating the ice sheets’ sea level impact over the recent decades. For the Antarctic Ice Sheet (AIS), SMB is dominated by large-scale atmospheric circulation, which collects warm moist air from further north and releases it in the form of snow as widespread accumulation or focused atmospheric rivers on the continent. This implies that the snow deposited at the surface of the AIS should record strongly coupled SMB and surface air temperature (SAT) variations. Ice cores use δ18O as a proxy for SAT as they do not record SAT directly. Here, using isotope-enabled global climate models and the RACMO2.3 regional climate model, we calculate positive SMB-SAT and δ18O-SMB correlations over ∼90 % of the AIS. The high spatial resolution of the RACMO2.3 model allows us to highlight a number of areas where SMB and SAT are not correlated, and show that wind-driven processes acting locally, such as Foehn and katabatic effects, can overwhelm the large-scale atmospheric input in SMB and SAT responsible for the positive SMB-SAT correlations. We focus in particular on Dronning Maud Land, East Antarctica, where the ice promontories clearly show these wind-induced effects. However, using the PAGES2k ice core compilations of SMB and δ18O of Thomas et al. (2017) and Stenni et al. (2017), we obtain a weak correlation, on the order of 0.1, between SMB and δ18O over the past ~150 years. We obtain an equivalently weak correlation between ice core SMB and the SAT reconstruction of Nicolas and Bromwich (2014) over the past ~50 years, although the ice core sites are not spatially co-located with the areas displaying a low SMB-SAT correlation in the models. To resolve the discrepancy between the measured and modeled signals, we show that averaging the ice core records in close spatial proximity increases their SMB-SAT correlation. This increase shows that the weak measured correlation likely results from random noise present in the ice core records, but is not large enough to match the correlation calculated in the models. Our results indicate thus a positive correlation between SAT and SMB in models and ice core reconstructions but with a weaker value in observations that may be due to missing processes in models or some systematic biases in ice core data that are not removed by a simple average.

Download Full-text