scholarly journals Modelling of anisotropic ice flow in Law Dome, East Antarctica

1999 ◽  
Vol 29 ◽  
pp. 184-190 ◽  
Author(s):  
W. L.Wang ◽  
Roland C. Warner
Keyword(s):  
Shear Strain ◽  
Ice Sheet ◽  
East Antarctica ◽  
Shear Strain Rate ◽  
Ice Flow ◽  
Anisotropic Flow ◽  
Ice Cap ◽  
Model Predictions ◽  
Flow Enhancement ◽  
Good Agreement

AbstractA model for ice flow in a polar ice sheet is presented. It is based on laboratory measurements of ice rheology, and includes the effect of anisotropic-flow enhancement in tertiary creep as the ice progresses through a range of stress regimes as it passes through the ice sheet. This flow model is applied to the transect from the summit of Law Dome, East Antarctica, to Gape Folger. In the upper layers of the ice sheet good agreement is found between the shear strain-rate profiles from the model and borehole-inclination measurements. Modifications of the simple model predictions for high shear strain rates in the lower layers of the ice cap are required in order to match the observed surface velocities. In these lower regions reductions in both the enhancement of shear flow and shear stress appear to be required, and this suggests that more attention needs to be given to the dynaimcs deep within ice sheets.

scholarly journals Ice-flow properties at Dome Summit South, Law Dome, East Antarctica

2002 ◽  
Vol 35 ◽  
pp. 567-573 ◽  
Author(s):  
Weili Wang ◽  
Roland C. Warner ◽  
William F. Budd
Keyword(s):  
Shear Strain ◽  
Ice Core ◽  
Ice Sheet ◽  
East Antarctica ◽  
Shear Strain Rate ◽  
Flow Properties ◽  
Ice Flow ◽  
Antarctic Research ◽  
Flow Enhancement ◽  
Rate Profile

AbstractIce-flow properties within a polar ice sheet are examined using the comprehensive data gathered from ice-core drilling by Australian National Antarctic Research Expeditions (ANARE) at Dome Summit South (DSS), on Law Dome, East Antarctica. Using the shear strain rates derived from borehole inclination measurements we demonstrate the need to modify the ice-flow relations to treat enhanced shear deformation deep within the ice sheet. We show that the relation between enhanced flow and the measured crystallographic properties is generally in accord with expectations, at least in the upper parts of the ice sheet, but it becomes clear that nearer to the bedrock the situation is more complicated. We also compare the observed shear strain-rate profile with results from a model that describes flow enhancement as a function of the applied stresses.

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

1997 ◽  
Vol 43 (143) ◽  
pp. 3-10 ◽  
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.

scholarly journals The symmetry group of the CAFFE model

2008 ◽  
Vol 54 (187) ◽  
pp. 643-645 ◽  
Author(s):  
Sérgio H. Faria
Keyword(s):  
Symmetry Group ◽  
Enhancement Factor ◽  
Flow Model ◽  
Ice Sheet ◽  
Induced Anisotropy ◽  
Isotropic Model ◽  
Sheet Flow ◽  
Anisotropic Flow ◽  
Considerable Controversy ◽  
Flow Enhancement

AbstractA new ice-sheet flow model called CAFFE (Continuum-mechanical Anisotropic Flow model based on an anisotropic Flow Enhancement factor) has recently become a source of considerable controversy within the glaciological community. Its main proponents (Placidi, Greve and Seddik) defend the thesis that this model can describe the effect of induced anisotropy on ice-sheet flow, while others assert that the CAFFE model is merely an isotropic model. Here I resolve this dispute by rigorously deriving the symmetry group of the CAFFE model.

scholarly journals Mass–Balance and Ice–Flow–Law Parameters for East Antarctica

1985 ◽  
Vol 31 (109) ◽  
pp. 334-339 ◽  
Author(s):  
T.C Hamley ◽  
I.N. Smith ◽  
N.W. Young
Keyword(s):  
Power Flow ◽  
Grid Point ◽  
Ice Sheet ◽  
Field Measurements ◽  
East Antarctica ◽  
Surface Velocity ◽  
Shear Strain Rate ◽  
Polar Research Institute ◽  
Flow Law ◽  
Basal Shear

AbstractA comprehensive set of ice-velocity and thickness data from traverses within the IAGP study area (bounded by long. 90°E. and 135°E., and north of lat. 80°S.) is compared with steady-state mass-flux calculations based on Scott Polar Research Institute (SPRI) map compilations.The results of previous regional mass-budget estimates are reviewed and followed by a description of the new field measurements and the basis upon which a computer “grid–point” program is used to calculate balance fluxes.A comparison of measured and balance fluxes indicates that the ice sheet in this region of East Antarctica is unlikely to be significantly out of balance.The ratio of average column to surface velocity is discussed and calculated to be 0.89.An analysis of the mean shear strain-rate (VS/Z), versus down-slope basal shear stress (τb=ρgᾱZ), suggests that power flow-law parameters ofn= 3.21 andk= 0.023 bar−nm−1are appropriate for the effective basal shear zone in this region of the Antarctic ice sheet.

scholarly journals Ice-sheet flow conditions deduced from mechanical tests of ice core

1999 ◽  
Vol 29 ◽  
pp. 179-183 ◽  
Author(s):  
Atsushi Miyamoto ◽  
Hideki Narita ◽  
Takeo Hondoh ◽  
Hitoshi Shoji ◽  
Kunio Kawada ◽  
...  
Keyword(s):  
Uniaxial Compression ◽  
Enhancement Factor ◽  
Flow Behavior ◽  
Ice Core ◽  
Ice Sheet ◽  
Constant Strain Rate ◽  
Uniaxial Compression Test ◽  
Ice Flow ◽  
Schmid Factor ◽  
Flow Enhancement

AbstractUniaxial compression tests were performed on samples of the Greenland Ice Gore Project (GRIP) deep ice core, both in the field and later in a cold-room laboratory, in order to understand the ice-flow behavior of large ice sheets. Experiments were conducted under conditions of constant strain rate (type A) and constant load (type B). Fifty-four uniaxial-compression test specimens from 1327-2922 m were selected. Each test specimen (25 mm x 25 mm x 90 mm) was prepared with its uniaxial stress axis inclined 45° from the core axis in order to examine the flow behavior of strong single-maximum ice-core samples with basal planes parallel to the horizontal plane of the ice sheet. The ice-flow enhancement factors show a gradual increase with depth down to approximately 2000 m. These results can be interpreted in terms of an increase in the fourth-order Schmid factor. Below 2000 m depth, the flow-enhancement factor increases to about 20-30 with a relatively high variability When the Schmid factor was > 0.46, the enhancement factor obtained was higher than expected from the .-axis concentrations measured. The higher values of flow-enhancement factor were obtained from specimens with a cloudy band structure. It was revealed that cloudy bands affect ice-deformation processes, but the details remain unclear.

scholarly journals Implementing an empirical scalar tertiary anisotropic rheology (ESTAR) into large-scale ice sheet models

2017 ◽  
Author(s):  
Felicity S. Graham ◽  
Mathieu Morlighem ◽  
Roland C. Warner ◽  
Adam Treverrow
Keyword(s):  
Enhancement Factor ◽  
Large Scale ◽  
Flow Line ◽  
Ice Sheet ◽  
Computationally Efficient ◽  
Ice Shelf ◽  
Ice Flow ◽  
Maximum Value ◽  
Polycrystalline Ice ◽  
Flow Enhancement

Abstract. The microstructural evolution that occurs in polycrystalline ice during deformation leads to the development of anisotropic rheological properties that are not adequately described by the most common, isotropic, ice flow relation 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, tertiary, anisotropic rheology (ESTAR). The effect of this anisotropic rheology on ice flow dynamics is investigated by comparing idealised simulations using ESTAR with those using the isotropic Glen flow relation, where the latter includes a 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 by ESTAR. Importantly, no single Glen enhancement factor can accurately capture the spatial variations in flow over the ice shelf. For flow-line studies of idealised grounded flow over a bumpy topography or a sticky base – both scenarios dominated at depth by bed-parallel shear – the differences between simulated velocities using ESTAR and the Glen flow relation vary according to the value of the enhancement factor used to calibrate the Glen flow relation. These results demonstrate the importance of describing the anisotropic rheology of 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.

scholarly journals Dynamics of the Law Dome Ice Cap, Antarctica, as Found From Bore-Hole Measurements

1989 ◽  
Vol 12 ◽  
pp. 46-50 ◽  
Author(s):  
D.M. Etheridge
Keyword(s):  
Shear Strain ◽  
Vertical Velocity ◽  
Flow Line ◽  
Velocity Profiles ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Shear Strain Rate ◽  
Orientation Data ◽  
Ice Cap ◽  
The Law

The internal dynamics of the Law Dome ice cap have been investigated by measuring the deformation of three bore holes located on an approximate flow line. Bore holes BHC1 (300 m deep) and BHC2 (344 m) were drilled in the coastal area to within several metres of bedrock and BHQ (418 m) was drilled about half-way towards the dome centre to about 50% of the ice thickness. Detailed measurements of orientation (inclination and azimuth), diameter, and temperature were taken through each bore hole over a 1 year span for BHC1 and BHC2 and a 10 year span for BHQ. The orientation data were reduced to obtain ∂u/∂z, a measure of the shear strain-rate. Changes in the depth of features located by bore-hole diameter measurements were used to obtain vertical velocity profiles. Other measurements discussed are temperatures, oxygen isotopes, crystal structure, surface velocities, and surface and bedrock topography.At the coastal sites, the ∂u/∂z profiles show two maxima in the lower third of the ice sheet. Flow due to the measured deformation accounts for about 55% of the surface velocity, the remainder being due to deformation and sliding in the basal zone. The vertical velocity profiles show mostly firn compression. The deeper ∂u/∂z maximum occurs in ice from the Wisconsin period which appears to deform more rapidly than the Holocene ice immediately above. The upper ∂u/∂z maximum may be related to the stress history of the ice, which can also explain the presence of significant shear strain and crystal-fabric development at only half the ice thickness at the BHQ site.

scholarly journals Strain in the ice sheet deduced from the crystal-orientation fabrics from bare icefields adjacent to the Sør-Rondane Mountains, Dronning Maud Land, East Antarctica

1994 ◽  
Vol 40 (134) ◽  
pp. 135-139 ◽  
Author(s):  
S. Fujita ◽  
S. Mae
Keyword(s):  
Shear Strain ◽  
Crystal Orientation ◽  
Horizontal Plane ◽  
Flow Line ◽  
Ice Sheet ◽  
Vertical Shear ◽  
Surface Cracks ◽  
Ice Flow ◽  
Ice Surface ◽  
Dronning Maud Land

AbstractStructural analyses of ice collected from the bare ice surface in the region of the Sør-Rondane Mountains were carried out. Crystal-orientation fabrics and the disposition of surface cracks were investigated to determine the stress/strain configuration in the ice sheet near the mountains. Single-maximum fabric patterns with the axis of the maximum roughly perpendicular to the flow line on the horizontal plane were observed. It was deduced from the observations that the ice exhibits a fabric pattern indicating that the ice sheet is subjected to vertical shear strain between the ice flow and the nunataks.

scholarly journals A complete map of Greenland ice velocity derived from satellite data collected over 20 years

2017 ◽  
Vol 64 (243) ◽  
pp. 1-11 ◽  
Author(s):  
IAN JOUGHIN ◽  
BEN E. SMITH ◽  
IAN M. HOWAT
Keyword(s):  
Flow Velocity ◽  
Feature Tracking ◽  
Ice Sheet ◽  
Synthetic Aperture ◽  
Landsat 8 ◽  
Ice Flow ◽  
Interferometric Phase ◽  
Ice Velocity ◽  
Slow Moving ◽  
Good Agreement

ABSTRACTWhile numerous maps of Greenland ice flow velocity exist, most have gaps in coverage and/or accuracy is limited. We processed a large volume of synthetic aperture radar and Landsat 8 imagery collected between 1995 and 2015 to produce a nearly complete map of ice flow velocity for Greenland at a far greater accuracy than most prior products. We evaluated the accuracy of this map by comparing it with a variety of measured and estimated velocities. For the slow-moving interior of the ice sheet, where estimates are determined from interferometric phase, the errors are ~2 m a−1 or better. For coastal areas, where estimates are determined entirely from speckle- or feature-tracking methods, errors are 2–3 m a−1, which is in good agreement with the estimated formal errors. Especially for the slow-moving majority of the ice sheet, this map provides an important source of data for numerous types of glaciological studies.

Late Wisconsinan glaciation of Amund and Ellef Ringnes islands, Nunavut: evidence for the configuration, dynamics, and deglacial chronology of the northwest sector of the Innuitian Ice Sheet

2003 ◽  
Vol 40 (3) ◽  
pp. 351-363 ◽  
Author(s):  
Nigel Atkinson
Keyword(s):  
Sea Level ◽  
Ice Sheet ◽  
Marine Fauna ◽  
Ice Flow ◽  
Ice Caps ◽  
Ice Cap ◽  
Sequential Entry ◽  
Data Record ◽  
Late Wisconsinan ◽  
Glacial Landforms

Geomorphic and chronologic evidence from Amund and Ellef Ringnes islands documents the configuration, dynamics, and collapse of the northwest sector of the Innuitian Ice Sheet. These data record the inundation of the Ringnes Islands by northwestward-flowing ice from divides spanning the alpine and lowland sectors of the Innuitian Ice Sheet. Ice-flow indicators and granite dispersal along eastern Amund Ringnes Island suggest Massey Sound was filled by an ice stream discharging coalescent alpine and lowland ice from Norwegian Bay. In contrast, the interior of Amund Ringnes Island was overridden by predominantly non-erosive, granite-free ice from a divide in the lowland sector of the ice sheet. Glacial landforms on Ellef Ringnes Island record coverage by largely non-erosive ice, but it remains uncertain whether these features relate to northward-flowing lowland ice or a cold-based local ice cap. Deglaciation of the Ringnes Islands commenced ~10 000 14C years ago. Deglacial dates between 9.7 and 9.2 ka BP record the sequential entry of marine fauna along Massey and Hassel sounds, concomitant with the southward retreat of trunk ice towards Norwegian Bay. These data suggest marine-based trunk glaciers were vulnerable to calving during pre-Holocene eustatic sea-level rise. However, deglacial dates from inner embayments indicate that residual ice caps persisted on Amund and Ellef Ringnes islands for 800 to 1400 14C years after retreat of trunk ice from the adjacent marine channels. Lateral meltwater channels record the subsequent retreat of these ice caps, which became increasingly confined within upland valleys after 8.6 ka BP.

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