On the gas-ice depth difference (Δdepth) along the EPICA Dome C ice core

Abstract. We compare a variety of methods for estimating the gas/ice depth offset (Δdepth) at EPICA Dome C (EDC, East Antarctica). (1) Purely based on modelling efforts, Δdepth can be estimated combining a firn densification with an ice flow model. (2) The diffusive column height can be estimated from δ15N and converted to Δdepth using an ice flow model and assumptions about past average firn density and thickness of the convective zone. (3) Ice and gas synchronisation of the EDC ice core to the GRIP, EDML and TALDICE ice cores shifts the ice/gas offset problem into higher accumulation ice cores where it can be more accurately evaluated. (4) Finally, the bipolar seesaw hypothesis allows us to synchronise the ice isotopic record with the gas CH4 record, the later being taken as a proxy of Greenland temperature. The general agreement of method 4 with methods 2 and 3 confirms that the bipolar seesaw antiphase happened during the last 140 kyr. Applying method 4 to the deeper section of the EDC core confirms that the ice flow is complex and can help to improve our reconstruction of the thinning function and thus, of the EDC age scale. We confirm that method 1 overestimates the glacial Δdepth at EDC and we suggest that it is due to an overestimation of the glacial lock-in depth (LID) by the firn densification model. In contrast, we find that method 1 very likely underestimates Δdepth during Termination II, due either to an underestimated thinning function or to an underestimated LID. Finally, method 2 gives estimates within a few metres of methods 3 and 4 during the last deglacial warming, suggesting that the convective zone at Dome C cannot have been very large at this time, if it existed at all.

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On the gas-ice depth difference (Δdepth) along the EPICA Dome C ice core

Climate of the Past Discussions ◽

10.5194/cpd-8-1089-2012 ◽

2012 ◽

Vol 8 (2) ◽

pp. 1089-1131 ◽

Cited By ~ 1

Author(s):

F. Parrenin ◽

S. Barker ◽

T. Blunier ◽

J. Chappellaz ◽

J. Jouzel ◽

...

Keyword(s):

Flow Model ◽

Ice Core ◽

Ice Cores ◽

Convective Zone ◽

Column Height ◽

Last Deglaciation ◽

Ice Flow ◽

Depth Difference ◽

The Last Deglaciation ◽

Good Agreement

Abstract. We compare a variety of methods for estimating the gas/ice depth offset (Δdepth) at EPICA Dome C (EDC, East Antarctica). (1) Purely based on modelling efforts, Δdepth can be estimated combining a firn densification with an ice flow model. Observations allow direct and indirect estimate of Δdepth. (2) The diffusive column height can be estimated from δ15N and converted to Δdepth using an ice flow model and assumptions about past average firn density and thickness of the convective zone. (3) Ice and gas synchronisation of the EDC ice core to the GRIP, EDML and TALDICE ice cores shifts the ice/gas offset problem into higher accumulation ice cores where it can be more accurately evaluated. (4) Finally, the bipolar seesaw hypothesis allows us to synchronise the ice isotopic record with the gas CH4 record, the later being taken as a proxy of Greenland temperature. The bipolar seesaw antiphase relationship is generally supported by the ice-gas cross synchronisation between EDC and the GRIP, EDML and TALDICE ice cores, which provide support for method 4. Applying the bipolar seesaw hypothesis to the deeper section of the EDC core confirms that the ice flow is complex and can help improving our reconstruction of the thinning function and thus of the EDC age scale. We confirm that method 1 overestimates the glacial Δdepth at EDC and we suggested that it is due to an overestimation of the glacial Close Off Depth by the firn densification model. In contrast we find that the glaciological models probably underestimate the Δdepth during termination II. Finally, we show that method 2 based on 15N data produces for the last deglaciation a Δdepth estimate which is in good agreement with methods 3 and 4.

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Characterizing the glaciological conditions at Halvfarryggen ice dome, Dronning Maud Land, Antarctica

Journal of Glaciology ◽

10.3189/2013jog12j134 ◽

2013 ◽

Vol 59 (213) ◽

pp. 9-20 ◽

Cited By ~ 27

Author(s):

Reinhard Drews ◽

Carlos Martín ◽

Daniel Steinhage ◽

Olaf Eisen

Keyword(s):

Flow Model ◽

Ice Core ◽

Ice Cores ◽

Radar Data ◽

Ice Thickness ◽

Atmospheric Conditions ◽

Ice Flow ◽

International Partnerships ◽

Drill Site ◽

Dronning Maud Land

AbstractWe present a comprehensive approach (including field data, remote sensing and an anisotropic ice-flow model) to characterize Halvfarryggen ice dome in coastal Dronning Maud Land, Antarctica. This is a potential drill site for the International Partnerships in Ice Core Sciences, which has identified the need for ice cores covering atmospheric conditions during the last few millennia. We derive the surface topography, the ice stratigraphy from radar data, and accumulation rates which vary from 400 to 1670 kg m−2 a−1 due to preferred wind directions and changing surface slope. The stratigraphy shows anticlines and synclines beneath the divides. We transfer Dansgaard–Johnsen age–depth scales from the flanks along isochrones to the divide in the upper 20–50% of the ice thickness and show that they compare well with the results of a full-Stokes, anisotropic ice-flow model which predicts (1) 11 ka BP ice at 90% of the ice thickness, (2) a temporally stable divide for at least 2700–4500 years, (3) basal temperatures below the melting point (−12°C to −5°C) and (4) a highly developed crystal orientation fabric (COF). We suggest drilling into the apices of the deep anticlines, providing a good compromise between record length and temporal resolution and also facilitating studies of the interplay of anisotropic COF and ice flow.

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Change of the ice rheology with climatic transitions – implication on ice flow modelling and dating of the EPICA Dome C core

Climate of the Past Discussions ◽

10.5194/cpd-2-1187-2006 ◽

2006 ◽

Vol 2 (6) ◽

pp. 1187-1219 ◽

Cited By ~ 1

Author(s):

G. Durand ◽

F. Gillet-Chaulet ◽

A. Svensson ◽

O. Gagliardini ◽

S. Kipfstuhl ◽

...

Keyword(s):

Flow Model ◽

Ice Core ◽

Ice Sheets ◽

Ice Cores ◽

Horizontal Shear ◽

Ice Flow ◽

Flow Modelling ◽

The Past ◽

Ice Flows ◽

Crystallographic Orientations

Abstract. The study of the distribution of the crystallographic orientations (the fabric) along ice cores supplies information on the past and current ice flows of ice-sheets. Beside the usually observed formation of a vertical single maximum fabric, the EPICA Dome Concordia ice core (EDC) shows an abrupt and unexpected strenghtening of its fabric during termination II around 1750 m depth. Such strengthenings were already observed for sites located on an ice-sheet. This suggests that horizontal shear could occur along the EDC core. Moreover, the change in the fabric leads to a modification of the viscosity between neighbouring ice layers. Through the use of an anisotropic ice flow model, we quantify the change in viscosity and investigate its implication on ice flow and dating.

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A full Stokes ice-flow model to assist the interpretation of millennial-scale ice cores at the high-Alpine drilling site Colle Gnifetti, Swiss/Italian Alps

Journal of Glaciology ◽

10.1017/jog.2019.82 ◽

2019 ◽

Vol 66 (255) ◽

pp. 35-48 ◽

Cited By ~ 1

Author(s):

Carlo Licciulli ◽

Pascal Bohleber ◽

Josef Lier ◽

Olivier Gagliardini ◽

Martin Hoelzle ◽

...

Keyword(s):

Flow Model ◽

Ice Core ◽

Ice Cores ◽

Italian Alps ◽

Ice Flow ◽

Finite Element Software ◽

Catchment Areas ◽

Drilling Site ◽

Monte Rosa ◽

First Time

AbstractThe high-Alpine ice-core drilling site Colle Gnifetti (CG), Monte Rosa, Swiss/Italian Alps, provides climate records over the last millennium and beyond. However, the full exploitation of the oldest part of the existing ice cores requires complementary knowledge of the intricate glacio-meteorological settings, including glacier dynamics. Here, we present new ice-flow modeling studies of CG, focused on characterizing the flow at two neighboring drill sites in the eastern part of the glacier. The3-D full Stokes ice-flow model is thermo-mechanically coupled and includes firn rheology, firn densification and enthalpy transport, and is implemented using the finite element software Elmer/Ice. Measurements of surface velocities, accumulation, borehole inclination, density and englacial temperatures are used to validate the model output. We calculate backward trajectories and map the catchment areas. This constrains, for the first time at this site, the so-called upstream effects for the stable water isotope time series of the two ice cores drilled in 2005 and 2013. The model also provides a 3-D age field of the glacier and independent ice-core chronologies for five ice-core sites. Model results are a valuable addition to the existing glaciological and ice-core datasets. This especially concerns the quantitative estimate of upstream conditions affecting the interpretation of the deep ice-core layers.

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IceChrono v1: a probabilistic model to compute a common and optimal chronology for several ice cores

Geoscientific Model Development Discussions ◽

10.5194/gmdd-7-6811-2014 ◽

2014 ◽

Vol 7 (5) ◽

pp. 6811-6844

Author(s):

F. Parrenin

Keyword(s):

Probabilistic Model ◽

Accumulation Rate ◽

Ice Core ◽

Ice Cores ◽

Air Bubbles ◽

Ice Flow ◽

Orbital Parameters ◽

Information Depth ◽

Dating Methods ◽

Lock In

Abstract. Polar ice cores provides exceptional archives of past environmental conditions. Dating ice and air bubbles/hydrates in ice cores is complicated since it involves different dating methods: modeling of the sedimentation process (accumulation of snow at surface, densification of snow into ice with air trapping and ice flow), use of dated horizons by comparison to other well dated targets (other dated paleo-archives or calculated variations of Earth's orbital parameters), use of dated depth intervals, use of Δdepth information (depth shift between synchronous events in the ice matrix and its air/hydrate content), use of stratigraphic links in between ice cores (ice-ice, air-air or mix ice-air links). Here I propose IceChrono v1, a new probabilistic model to combine these different kinds of chronological information to obtain a common and optimized chronology for several ice cores, as well as its confidence interval. It is based on the inversion of three quantities: the surface accumulation rate, the Lock-In Depth (LID) of air bubbles and the vertical thinning function. IceChrono is similar in scope to the Datice model, but has differences on the mathematical, numerical and programming point of views. I apply IceChrono on two dating experiments. The first one is similar to the AICC2012 experiment and I find similar results than Datice within a few centuries, which is a confirmation of both IceChrono and Datice codes. The second experiment involves only the Berkner ice core in Antarctica and I produce the first dating of this ice core. IceChrono v1 is freely available under the GPL v3 open source license.

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Change in ice rheology during climate variations – implications for ice flow modelling and dating of the EPICA Dome C core

Climate of the Past ◽

10.5194/cp-3-155-2007 ◽

2007 ◽

Vol 3 (1) ◽

pp. 155-167 ◽

Cited By ~ 51

Author(s):

G. Durand ◽

F. Gillet-Chaulet ◽

A. Svensson ◽

O. Gagliardini ◽

S. Kipfstuhl ◽

...

Keyword(s):

Effective Viscosity ◽

Flow Model ◽

Ice Core ◽

Ice Sheets ◽

Ice Cores ◽

Climate Variations ◽

Horizontal Shear ◽

Ice Flow ◽

Flow Modelling ◽

Crystallographic Orientations

Abstract. The study of the distribution of crystallographic orientations (i.e., the fabric) along ice cores provides information on past and current ice flow in ice-sheets. Besides the usually observed formation of a vertical single maximum fabric, the EPICA Dome C ice core (EDC) shows an abrupt and unexpected strengthening of its fabric during termination II around 1750 m depth. Such strengthening has already been observed for sites located on an ice-sheet flank. This suggests that horizontal shear could occur along the EDC core. Moreover, the change in the fabric leads to a modification of the effective viscosity between neighbouring ice layers. Through the use of an anisotropic ice flow model, we quantify the change in effective viscosity and investigate its implication for ice flow and dating.

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IceChrono1: a probabilistic model to compute a common and optimal chronology for several ice cores

Geoscientific Model Development ◽

10.5194/gmd-8-1473-2015 ◽

2015 ◽

Vol 8 (5) ◽

pp. 1473-1492 ◽

Cited By ~ 9

Author(s):

F. Parrenin ◽

L. Bazin ◽

E. Capron ◽

A. Landais ◽

B. Lemieux-Dudon ◽

...

Keyword(s):

Probabilistic Model ◽

Accumulation Rate ◽

Ice Core ◽

Ice Cores ◽

Complex Problem ◽

Polar Ice ◽

Ice Flow ◽

Marquardt Algorithm ◽

Lock In

Abstract. Polar ice cores provide exceptional archives of past environmental conditions. The dating of ice cores and the estimation of the age-scale uncertainty are essential to interpret the climate and environmental records that they contain. It is, however, a complex problem which involves different methods. Here, we present IceChrono1, a new probabilistic model integrating various sources of chronological information to produce a common and optimized chronology for several ice cores, as well as its uncertainty. IceChrono1 is based on the inversion of three quantities: the surface accumulation rate, the lock-in depth (LID) of air bubbles and the thinning function. The chronological information integrated into the model are models of the sedimentation process (accumulation of snow, densification of snow into ice and air trapping, ice flow), ice- and air-dated horizons, ice and air depth intervals with known durations, Δdepth observations (depth shift between synchronous events recorded in the ice and in the air) and finally air and ice stratigraphic links in between ice cores. The optimization is formulated as a least squares problem, implying that all densities of probabilities are assumed to be Gaussian. It is numerically solved using the Levenberg–Marquardt algorithm and a numerical evaluation of the model's Jacobian. IceChrono follows an approach similar to that of the Datice model which was recently used to produce the AICC2012 (Antarctic ice core chronology) for four Antarctic ice cores and one Greenland ice core. IceChrono1 provides improvements and simplifications with respect to Datice from the mathematical, numerical and programming point of views. The capabilities of IceChrono1 are demonstrated on a case study similar to the AICC2012 dating experiment. We find results similar to those of Datice, within a few centuries, which is a confirmation of both IceChrono1 and Datice codes. We also test new functionalities with respect to the original version of Datice: observations as ice intervals with known durations, correlated observations, observations as air intervals with known durations and observations as mixed ice–air stratigraphic links. IceChrono1 is freely available under the General Public License v3 open source license.

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Recumbent folding in ice sheets: a core-referential study

Journal of Glaciology ◽

10.3189/172756504781830204 ◽

2004 ◽

Vol 50 (168) ◽

pp. 3-16 ◽

Cited By ~ 5

Author(s):

H. Paul Jacobson ◽

Edwin D. Waddington

Keyword(s):

Flow Model ◽

Ice Core ◽

Deformation Gradient ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Ice Cores ◽

Small Cross Section ◽

Ice Flow ◽

Deformation Gradient Tensor ◽

Particle Paths

AbstractTo better understand apparent stratigraphic disturbances in ice cores such as Greenland Ice Sheet Project 2 (GISP2), we examine how ice-sheet flow can transform gentle open folds into order-disturbing recumbent folds. The initial disturbances in the stratigraphy have their roots in transient dynamic processes and local rheological inhomogeneities, but the kinematics of even a simple ice-flow model can deform these disturbances enough to alter paleoclimatic interpretation of an ice core. The local vorticity number suggests which structures can be passively overturned, but analyzing the finite strain along particle paths gives a more complete picture, especially when taken relative to a hypothetical core location. Core-relative isochrones, or “pre-cores”, predict which stratigraphic disturbances will appear as obviously overturned layers in a core. The deformation-gradient tensor along particle paths allows us to calculate the rotation of segments of various reference slopes. These calculations suggest that observed 20° dips in the GISP2 core are rotating on a time-scale of a few hundred years and could result from distortions with much smaller slopes produced upstream. The time during which they can be recognized to be overturning is short because the rotation rate is high. Once overturned they are flattened further and may be hard to recognize, especially in the small cross-section of a core.

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Methanesulphonic acid movement in solid ice cores

Annals of Glaciology ◽

10.3189/172756404781814645 ◽

2004 ◽

Vol 39 ◽

pp. 540-544 ◽

Cited By ~ 13

Author(s):

Barbara T. Smith ◽

Tas D. Van Ommen ◽

Mark A. J. Curran

Keyword(s):

Diffusion Coefficient ◽

Biological Activity ◽

Sea Ice ◽

Diffusion Mechanism ◽

Ice Core ◽

Ice Cores ◽

East Antarctica ◽

The Core ◽

Central Value

AbstractMethanesulphonic acid (MSA) is an important trace-ion constituent in ice cores, with connections to biological activity and sea-ice distribution. Post-depositional movement of MSA has been documented in firn, and this study investigates movement in solid ice by measuring variations in MSA distribution across several horizontal sections from an ice core after 14.5 years storage. The core used is from below the bubble close-off depth at Dome Summit South, Law Dome, East Antarctica. MSA concentration was studied at 3 and 0.5 cm resolution across the core widths. Its distribution was uniform through the core centres, but the outer 3 cm showed gradients in concentrations down to less than half of the central value at the core edge. This effect is consistent with diffusion to the surrounding air during its 14.5 year storage. The diffusion coefficient is calculated to be 2 ×10–13 m2 s–1, and the implications for the diffusion mechanism are discussed.

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Reconstructing Antarctic snow accumulation using nitrogen isotopes of nitrate

10.5194/egusphere-egu21-672 ◽

2021 ◽

Author(s):

Pete D. Akers ◽

Joël Savarino ◽

Nicolas Caillon ◽

Mark Curran ◽

Tas Van Ommen

Keyword(s):

Nitrogen Isotopes ◽

Full Range ◽

Ice Core ◽

Ice Cores ◽

Snow Accumulation ◽

East Antarctica ◽

Accumulation Rates ◽

Sea Levels ◽

Antarctic Snow ◽

Parallel Reconstruction

Precise Antarctic snow accumulation estimates are needed to understand past and future changes in global sea levels, but standard reconstructions using water isotopes suffer from competing isotopic effects external to accumulation. We present here an alternative accumulation proxy based on the post-depositional photolytic fractionation of nitrogen isotopes (d15N) in nitrate. On the high plateau of East Antarctica, sunlight penetrating the uppermost snow layers converts snow-borne nitrate into nitrogen oxide gas that can be lost to the atmosphere. This nitrate loss favors 14NO3- over 15NO3-, and thus the d15N of nitrate remaining in the snow will steadily increase until the nitrate is eventually buried beneath the reach of light. Because the duration of time until burial is dependent upon the rate of net snow accumulation, sites with lower accumulation rates have a longer burial wait and thus higher d15N values. A linear relationship (r2 = 0.86) between d15N and net accumulation-1 is calculated from over 120 samples representing 105 sites spanning East Antarctica. These sites largely encompass the full range of snow accumulation rates observed in East Antarctica, from 25 kg m-2 yr-1 at deep interior sites to >400 kg m-2 yr-1 at near coastal sites. We apply this relationship as a transfer function to an Aurora Basin ice core to produce a 700-year record of accumulation changes. Our nitrate-based estimate compares very well with a parallel reconstruction for Aurora Basin that uses volcanic horizons and ice-penetrating radar. Continued improvements to our database may enable precise independent estimates of millennial-scale accumulation changes using deep ice cores such as EPICA Dome C and Beyond EPICA-Oldest Ice.

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