Ice Flow Along an I.A.G.P. Flow Line and Interpretation of Data From an Ice Core in Terre Adélie, Antarctica

AbstractAn ice core has been obtained to the bedrock about 300 m deep in Terre Adélie, 5 km inland from the coast. Stable isotopes and gas content have been measured over the length of the core. The results have been interpreted in terms of the temperature and elevation of origin of the ice further inland on the ice sheet from the data obtained along an 800 km traverse towards Dome “C”, and from Dome “C”, at an elevation of about 3 200 m. The flow of the ice from Dome “C“ to the coast has been modelled to determine the ages and particle trajectories of the ice for present conditions.It has been found that the upper isotope and gas-content values in the core can be matched with the present regime using a base for ice flow above the present bed which is suggested by moraine in the ice core. The ice in the layer from the 200 m depth, where the age is apparently more than 5 000 years, to the 250 m depth, appears to have originated from conditions which differ substantially from those existing on the present inland ice-sheet surface. The results give an indication of a colder climate and greater ice-sheet thickness in the past.

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Site information and initial results from deep ice drilling on Law Dome, Antarctica

Journal of Glaciology ◽

10.3189/s0022143000002768 ◽

1997 ◽

Vol 43 (143) ◽

pp. 3-10 ◽

Cited By ~ 10

Author(s):

V.I. Morgan ◽

C.W. Wookey ◽

J. Li ◽

T.D. van Ommen ◽

W. Skinner ◽

...

Keyword(s):

Ice Core ◽

Ice Sheet ◽

High Accumulation ◽

Ice Flow ◽

Ice Cap ◽

Basal Ice ◽

Inland Ice ◽

The Last Glacial Maximum ◽

Initial Results ◽

The Last Glacial

AbstractThe aim of deep ice drilling on Law Dome, Antarctica, has been to exploit the special characteristics of Law Dome summit, i.e. low temperature and high accumulation near an ice divide, to obtain a high-resolution ice core for climatic/environmental studies of the Holocene and the Last Glacial Maximum (LGM). Drilling was completed in February 1993, when basal ice containing small fragments of rock was reached at a depth of 1196 m. Accurate ice dating, obtained by counting annual layers revealed by fine-detail δ18О, peroxide and electrical-conductivity measurements, is continuous down to 399 m, corresponding to a date of AD 1304. Sulphate concentration measurements, made around depths where conductivity tracing indicates volcanic fallout, allow confirmation of the dating (for Agung in 1963 and Tambora in 1815) or estimates of the eruption date from the ice dating (for the Kuwae, Vanuatu, eruption ~1457). The lower part of the core is dated by extrapolating the layer-counting using a simple model of the ice flow. At the LGM, ice-fabric measurements show a large decrease (250 to 14 mm2) in crystal size and a narrow maximum in c-axis vertically. The main zone of strong single-pole fabrics however, is located higher up in a broad zone around 900 m. Oxygen-isotope (δ18O) measurements show Holocene ice down to 1113 m, the LGM at 1133 m and warm (δ18O) about the same as Holocene) ice near the base of the ice sheet. The LGM/Holocene δ18O shift of 7.0‰, only ~1‰ larger than for Vostok, indicates that Law Dome remained an independent ice cap and was not overridden by the inland ice sheet in the Glacial.

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Site information and initial results from deep ice drilling on Law Dome, Antarctica

Journal of Glaciology ◽

10.1017/s0022143000002768 ◽

1997 ◽

Vol 43 (143) ◽

pp. 3-10 ◽

Cited By ~ 91

Author(s):

V.I. Morgan ◽

C.W. Wookey ◽

J. Li ◽

T.D. van Ommen ◽

W. Skinner ◽

...

Keyword(s):

Ice Core ◽

Ice Sheet ◽

High Accumulation ◽

Ice Flow ◽

Ice Cap ◽

Basal Ice ◽

Inland Ice ◽

The Last Glacial Maximum ◽

Initial Results ◽

The Last Glacial

Abstract The aim of deep ice drilling on Law Dome, Antarctica, has been to exploit the special characteristics of Law Dome summit, i.e. low temperature and high accumulation near an ice divide, to obtain a high-resolution ice core for climatic/environmental studies of the Holocene and the Last Glacial Maximum (LGM). Drilling was completed in February 1993, when basal ice containing small fragments of rock was reached at a depth of 1196 m. Accurate ice dating, obtained by counting annual layers revealed by fine-detail δ18 О, peroxide and electrical-conductivity measurements, is continuous down to 399 m, corresponding to a date of AD 1304. Sulphate concentration measurements, made around depths where conductivity tracing indicates volcanic fallout, allow confirmation of the dating (for Agung in 1963 and Tambora in 1815) or estimates of the eruption date from the ice dating (for the Kuwae, Vanuatu, eruption ~1457). The lower part of the core is dated by extrapolating the layer-counting using a simple model of the ice flow. At the LGM, ice-fabric measurements show a large decrease (250 to 14 mm2) in crystal size and a narrow maximum in c-axis vertically. The main zone of strong single-pole fabrics however, is located higher up in a broad zone around 900 m. Oxygen-isotope (δ18O) measurements show Holocene ice down to 1113 m, the LGM at 1133 m and warm (δ18O) about the same as Holocene) ice near the base of the ice sheet. The LGM/Holocene δ18O shift of 7.0‰, only ~1‰ larger than for Vostok, indicates that Law Dome remained an independent ice cap and was not overridden by the inland ice sheet in the Glacial.

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Are longitudinal ice-surface structures on the Antarctic Ice Sheet indicators of long-term ice-flow configuration?

Earth Surface Dynamics Discussions ◽

10.5194/esurfd-2-911-2014 ◽

2014 ◽

Vol 2 (2) ◽

pp. 911-933 ◽

Cited By ~ 1

Author(s):

N. F. Glasser ◽

S. J. A. Jennings ◽

M. J. Hambrey ◽

B. Hubbard

Keyword(s):

Flow Line ◽

Ice Sheet ◽

Surface Structures ◽

Surface Velocity ◽

Ice Flow ◽

Antarctic Ice Sheet ◽

Ice Surface ◽

Ice Stream ◽

The Antarctic

Abstract. Continent-wide mapping of longitudinal ice-surface structures on the Antarctic Ice Sheet reveals that they originate in the interior of the ice sheet and are arranged in arborescent networks fed by multiple tributaries. Longitudinal ice-surface structures can be traced continuously down-ice for distances of up to 1200 km. They are co-located with fast-flowing glaciers and ice streams that are dominated by basal sliding rates above tens of m yr-1 and are strongly guided by subglacial topography. Longitudinal ice-surface structures dominate regions of converging flow, where ice flow is subject to non-coaxial strain and simple shear. Associating these structures with the AIS' surface velocity field reveals (i) ice residence times of ~ 2500 to 18 500 years, and (ii) undeformed flow-line sets for all major flow units analysed except the Kamb Ice Stream and the Institute and Möller Ice Stream areas. Although it is unclear how long it takes for these features to form and decay, we infer that the major ice-flow and ice-velocity configuration of the ice sheet may have remained largely unchanged for several thousand years, and possibly even since the end of the last glacial cycle. This conclusion has implications for our understanding of the long-term landscape evolution of Antarctica, including large-scale patterns of glacial erosion and deposition.

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The Debris-Laden Ice at the Bottom of the Greenland Ice Sheet

Journal of Glaciology ◽

10.3189/s002214300002983x ◽

1979 ◽

Vol 23 (89) ◽

pp. 193-207 ◽

Cited By ~ 24

Author(s):

Susan Herron ◽

Hoar ◽

Chester C. Langway

Keyword(s):

Ice Core ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

High Deformation ◽

Fine Grained ◽

Free Zone ◽

The Core ◽

Oxidation Of Methane ◽

Particle Aggregates ◽

Glacier Ice

AbstractThe Camp Century, Greenland, ice core was recovered from a bore hole which extended 1 375 m from the surface of the Greenland ice sheet to the ice/sub-ice interface. The bottom 15.7 m of the core contain over 300 alternating bands of clear and debris-laden ice. The size of the included debris ranges from particles less than 2 μm in diameter to particle aggregates which are a maximum of 3 cm in diameter: the average debris concentration is 0.24ºº by weight. The debris size, concentration, and composition indicate that the debris originates from the till-like material directly below the debris-laden ice. The total gas concentration averages 51 ml/kg ice compared to the average of 101 ml/kg ice for the top 1 340 m. The gas composition of debris-bearing ice has apparently been modified by the oxidation of methane as reflected by traces of methane, high CO2 levels, and low O2 levels with respect to atmospheric air. Argon, which is not affected by the oxidation, shows an enrichment in samples with lower gas concentrations. Both the low gas concentrations in the debris-laden zone and the argon enrichment may be explained by the downward diffusion of gases from bubbly glacier ice into an originally bubble-free zone of refrozen debris-laden ice. Ice texture and ice-fabric analyses reveal extremely fine-grained ice and highly preferred crystal orientation in the lowermost 10 m of the core, indicating a zone of high deformation.

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8. Glaciers of the past

Glaciation: A Very Short Introduction ◽

10.1093/actrade/9780198745853.003.0008 ◽

2018 ◽

pp. 146-152

Author(s):

David J. A. Evans

Keyword(s):

Numerical Models ◽

Ice Core ◽

Three Dimensional ◽

Ice Sheets ◽

Ice Sheet ◽

Aerial Imagery ◽

The Past ◽

Glacial Landforms

To reconstruct the former extent and dynamics of ice sheets and glaciers requires a knowledge of process-form relationships that goes beyond individual landform types. Instead, glacial geomorphologists need to analyse large areas of glaciated terrain in a more holistic way, combining the whole range of glacial landforms and sediments to reconstruct glacier systems of the past, a subject now known as palaeoglaciology. ‘Glaciers of the past’ explains how the combination of aerial imagery and landform analysis is used in palaeoglaciological reconstruction. Increasingly powerful computers are making it possible to compile sophisticated numerical models that use our knowledge of glaciological processes and ice-core-derived palaeoclimate data to create three-dimensional glacier and ice sheet reconstructions.

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Implementing an empirical scalar constitutive relation for ice with flow-induced polycrystalline anisotropy in large-scale ice sheet models

The Cryosphere ◽

10.5194/tc-12-1047-2018 ◽

2018 ◽

Vol 12 (3) ◽

pp. 1047-1067 ◽

Cited By ~ 6

Author(s):

Felicity S. Graham ◽

Mathieu Morlighem ◽

Roland C. Warner ◽

Adam Treverrow

Keyword(s):

Constitutive Relation ◽

Enhancement Factor ◽

Large Scale ◽

Flow Line ◽

Ice Sheet ◽

Computationally Efficient ◽

Ice Shelf ◽

Stress Regime ◽

Ice Flow ◽

Polycrystalline Ice

Abstract. The microstructure of polycrystalline ice evolves under prolonged deformation, leading to anisotropic patterns of crystal orientations. The response of this material to applied stresses is not adequately described by the ice flow relation most commonly used in large-scale ice sheet models – the Glen flow relation. We present a preliminary assessment of the implementation in the Ice Sheet System Model (ISSM) of a computationally efficient, empirical, scalar, constitutive relation which addresses the influence of the dynamically steady-state flow-compatible induced anisotropic crystal orientation patterns that develop when ice is subjected to the same stress regime for a prolonged period – sometimes termed tertiary flow. We call this the ESTAR flow relation. The effect on ice flow dynamics is investigated by comparing idealised simulations using ESTAR and Glen flow relations, where we include in the latter an overall flow enhancement factor. For an idealised embayed ice shelf, the Glen flow relation overestimates velocities by up to 17 % when using an enhancement factor equivalent to the maximum value prescribed in the ESTAR relation. Importantly, no single Glen enhancement factor can accurately capture the spatial variations in flow across the ice shelf generated by the ESTAR flow relation. For flow line studies of idealised grounded flow over varying topography or variable basal friction – both scenarios dominated at depth by bed-parallel shear – the differences between simulated velocities using ESTAR and Glen flow relations depend on the value of the enhancement factor used to calibrate the Glen flow relation. These results demonstrate the importance of describing the deformation of anisotropic ice in a physically realistic manner, and have implications for simulations of ice sheet evolution used to reconstruct paleo-ice sheet extent and predict future ice sheet contributions to sea level.

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

Annals of Glaciology ◽

10.1017/s0260305500006327 ◽

1988 ◽

Vol 11 ◽

pp. 52-59 ◽

Cited By ~ 58

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.

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Debris entrainment at the ice-bedrock interface in sub-freezing temperature conditions (Terre Adélie, Antarctica)

Journal of Glaciology ◽

10.1017/s0022143000015963 ◽

1993 ◽

Vol 39 (132) ◽

pp. 303-315 ◽

Cited By ~ 40

Author(s):

J. -L Tison ◽

J. -R. Petit ◽

J. -M. Barnola ◽

W. C. Mahaney

Keyword(s):

Ice Core ◽

Freezing Temperature ◽

Gas Content ◽

Last Interglacial ◽

Ice Shelf ◽

Compressive Flow ◽

Embedded Particles ◽

Terre Adélie ◽

Pressure Melting ◽

Drilling Site

AbstractThe debris-rich ice from the bottom 6 m of the 82 m deep CAROLINE (Coastal Antarctic Record of Last Interglacial Natural Environment) ice core reaching bedrock, and from five 2 m long surface cores at Moraine Prudhomme in Terre Adélie (Antarctica) is described and compared to debris-laden ice from the core-drilling site DIO. Isotopic, total-gas content, CO2concentration and SEM investigations of embedded particles, together with ice textures and fabrics, rule out “pressure-melting” regelation around bed obstacles or “freezing-on” as possible mechanisms for the debris entrainment at the ice-bedrock interface. It is suggested that the debris entrapment by purely mechanical means (e.g. shearing) is an efficient process in forming basal ice layers (BIL) at sub-freezing temperatures. This process might be dominant at the margin of the Antarctic ice sheet where no ice shelf exists and where a ramp terminus or a buttressing coastal relief induces compressive flow.

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Bottom Topography and Internal Layers in East Dronning Maud Land, East Antarctica, from 179 MHz Radio Echo-Sounding

Annals of Glaciology ◽

10.1017/s0260305500000665 ◽

1987 ◽

Vol 9 ◽

pp. 221-224 ◽

Cited By ~ 6

Author(s):

Minoru Yoshida ◽

Kazunobu Yamashita ◽

Shinji Mae

Keyword(s):

Cross Sections ◽

Flow Line ◽

Bottom Topography ◽

Ice Core ◽

Ice Sheet ◽

Internal Layers ◽

Radio Echo Sounding ◽

Dronning Maud Land ◽

Field Season ◽

Echo Sounding

Extensive echo-sounding was carried out in east Dronning Maud Land during the 1984 field season. A 179 MHz radar with separate transmitting and receiving antennae was used and the echoes were recorded by a digital system to detect minute reflections. The results gave cross-sections of the ice sheet along traverse routes from lat. 69 °S. to 75°S, Detailed observations on the ground at Mizuho station showed that there was elliptical polarization in the internally reflected echoes when two antennae, kept in parallel with each other, were rotated horizontally. The internal echoes were most clearly distinguished when the antenna azimuth was oriented perpendicular to the flow line of the ice sheet. The internal echoes with a high reflection coefficient were detected at depths of 500–700 m and 1000–1500 m at Mizuho station. Since a distinct internal echo at a depth of 500 m coincides with a 5 cm thick volcanic ash-laden ice layer found in the 700 m ice core taken near the observation site, these echoes may correspond to the acidic ice layers formed by past volcanic events in east Dronning Maud Land.

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Modelling Jakobshavn Isbrae from 2009 to 2018

10.5194/egusphere-egu2020-21999 ◽

2020 ◽

Author(s):

Matt Trevers ◽

Tony Payne ◽

Steph Cornford ◽

Anna Hogg

Keyword(s):

Ice Sheet ◽

Ice Flow ◽

The Past ◽

Flow Speeds ◽

Calving Rate

Jakobshavn Isbrae has dramatically accelerated, thinned and retreated since the late 1990s in several stages of retreat and stagnation. Studies have indicated that the loss of buttressing due to retreat of the calving front following the disintegration of its floating ice tongue was the trigger of acceleration and thinning of the terminus, however uncertainty remains over the mechanisms controlling the timing and magnitude of the retreat.The maximum retreat of the calving front was reached between 2013 and 2015 following the peaking of ice flow speeds in excess of 18 km yr-1. Since 2016, ice flow speeds have decelerated from this peak and the terminus has experienced a modest readvance and thickening. We calculated a calving rate for the period 2009 to 2018 which shows that terminus flow speeds and calving are closely related. Until 2009 a transient loosely bonded ice tongue formed but this feature appears not to have formed from 2010 onwards.We aim to demonstrate that the signal of thinning and retreat can be reproduced by driving the glacier with the calculated calving rate. We used the BISICLES ice sheet model to simulate the evolution of Jakobshavn Isbrae over the past decade, with the calving front driven by the calculated 2009 &#8211; 2018 calving rate. The results of these simulations show that the response of the glacier to the applied calving rate is in line with its observed evolution over this period. We also present the results of further experiments designed to examine the mechanisms and controls on the calving retreat.

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