An Analysis of the Relation Between the Surface and Bedrock Profiles of Ice Caps

AbstractResults art, presented of spectral analyses of the surface and bedrock profiles along a flow line of the Wilkes ice cap and the surface along the Greenland E.G.I.G. profile. Although the bedrock appears irregular over all was velengths studied, the ice-cap surface is typically characterized by a smooth curve with small-scale surface undulations superimposed on it. The following relations of Budd (1969, 19701 are confirmed. The “damping factor" or ratio of the bedrock amplitude to the surface amplitude is a minimum for wavelengths λ about 3.3 times the ice thickness. The surface lags the bed in the direction of motion by λ/4. The magnitude of the minimum damping factor φmis typically least near the coast, and increases inland depending on the ice thicknessZ, the velocityV, and the mean ice viscosityη(which is a function of stress and temperature) according towherepis the mean ice density andgis the gravitational acceleration. Thus the determination of the damping factors provides a valuable means of estimating the ice flow parameterη.

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Estimating the ice thickness of the Müller Ice Cap using an inversion of the shallow ice approximation

10.5194/egusphere-egu21-11602 ◽

2021 ◽

Author(s):

Ann-Sofie Priergaard Zinck ◽

Aslak Grinsted

Keyword(s):

Remote Sensing Data ◽

The Arctic ◽

Ice Thickness ◽

Potential Contribution ◽

Mean Squared Errors ◽

Ice Caps ◽

Ice Cap ◽

Regression Parameters ◽

Digital Elevation ◽

Elevation Model

The ice thickness of the M&#252;ller Ice Cap, Arctic Canada, is estimated using regression parameters obtained from an inversion of the shallow ice approximation by the use of a single Operation IceBridge flight line in combination with the glacier outline, surface slope, and elevation. The model is compared with an iterative inverse method of estimating the bedrock topography using PISM as a forward model. In both models the surface elevation is given by the Arctic Digital Elevation Model. The root mean squared errors of the ice thickness on the ice cap is 131 m and 139 m for the shallow ice inversion and the PISM model, respectively. Including the outlet glaciers increases the root mean squared errors to 136 m and 396 m, respectively. The simplicity of the shallow ice inversion model, combined with the good results and the fact that only remote sensing data is needed, means that there is a possibility of applying this model in a global glacier thickness estimate by using the Randolph Glacier Inventory. Most global glacier estimates only provide the volume and not the ice thickness of the glaciers. Hence, global ice thickness models is of great importance in quantifying the potential contribution of sea level rise from the glaciers and ice caps around the globe.

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Global change, Antarctic meteorite traps and the East Antarctic ice sheet

Journal of Glaciology ◽

10.1017/s0022143000016051 ◽

1993 ◽

Vol 39 (132) ◽

pp. 397-408 ◽

Cited By ~ 18

Author(s):

G. Delisle

Keyword(s):

Numerical Models ◽

Accumulation Rate ◽

Theoretical Work ◽

Snow Accumulation ◽

Ice Thickness ◽

Ice Caps ◽

Ice Cap ◽

Field Evidence ◽

Victoria Land ◽

Late Tertiary

AbstractNumerical models to assess the principal response of large ice caps to climatic changes are used as a guide to the interpretation of field evidence of changes in the glaciological regime in the coastal areas of Victoria Land and north Victoria Land, Antarctica. Based on the theoretical work, the following scenario is proposed: areas within about 300 km from the coast of Victoria Land experienced (i) significantly shallower ice slopes and a lesser degree of glaciation during most of the late Tertiary, (ii) steep slopes and thicker ice than today during glacial stages, and (iii) moderate thinning of the ice in intervening interglacial stages.The model predicts, for central regions of Antarctica, a slightly thinner ice cap (lower snow-accumulation rate) during glacial stages, but an estimated 200 m thicker ice cap in warmer Tertiary climates than today. The calculated “Tertiary ice caps” indicate a probable tendency of periodic surges due to basal melting at the outer fringes.Only modest changes of the ice thickness in reasonably good agreement with the model predictions for the current interglacial stage have been observed on four blue-ice fields, all located within 250 km of the coastline. Investigated ice fields include two meteorite traps — the Allan Hills Icefield and the Frontier Mountain meteorite fields. Antarctic meteorite traps are sustained by very specific glaciological conditions — in particular, only moderate changes in ice thickness over time. The sub-ice topography of these fields was determined by radar measurements and reveals a former, very different glaciological regime, which is interpreted as being associated with glacial processes, operative during the late Tertiary.Field evidence for a hypsithermal event during the Holocene is presented.

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The Effects of Wind on δ(18O) and Accumulation Give an Inferred Record of Seasonal δ Amplitude From the Agassiz Ice Cap, Ellesmere Island, Canada

Annals of Glaciology ◽

10.1017/s0260305500004122 ◽

1988 ◽

Vol 10 ◽

pp. 34-37 ◽

Cited By ~ 20

Author(s):

D.A. Fisher ◽

R.M. Koerner

Keyword(s):

Flow Line ◽

Conductivity Measurement ◽

Ellesmere Island ◽

Electrical Conductivity Measurement ◽

Ice Caps ◽

Devon Island ◽

Ice Cap ◽

Annual Layer ◽

Winter Snow ◽

Difference Series

Wind plays an important role in determining accumulation and δ(18O) on some ice caps. Three surface-to-bed cores spaced about 1 km apart have been taken on a flow line of the Agassiz Ice Cap, Ellesmere Island. The A84 core comes from the top of a local dome. The A79 core is 1200 m down the flow line, but very close to the ridge through the local dome. The A77 core is 1100m from A79 and well away from the ridge. The ridge causes wind turbulence, which removes or scours the soft winter snow from the A84 and A79 sites. No snow is scoured from the A77 site. Because of scour the retained accumulation and average δ(l8O) are different. The accumulations are 17.5, 11.5, 9.7 cm/a (ice equivalent) at A77, A79 and A84 respectively and the corresponding surface δs are –30.40, -27.90 and –27.05‰. The core records were dated by annual layer thicknesses and by identification of electrical conductivity measurement (ECM) acid peaks. With the three cores accurately aligned we examine the (δA84-δA77) and (δA84-δA79) time series. Significant variations in these difference series are interpreted as being caused by changes in the seasonal δ amplitude, which is then explained by changes in sea-ice cover. A seasonal δ amplitude series independently obtained from the Devon Island ice cap δ noise record is consistent with that from the Agassiz Ice Cap sites.

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

Annals of Glaciology ◽

10.3189/s0260305500006947 ◽

1989 ◽

Vol 12 ◽

pp. 46-50 ◽

Cited By ~ 3

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.

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Ice Flow Over Bedrock Perturbations

Journal of Glaciology ◽

10.3189/s0022143000026770 ◽

1970 ◽

Vol 9 (55) ◽

pp. 29-48 ◽

Cited By ~ 7

Author(s):

W.F. Budd

Keyword(s):

Surface Shape ◽

Ice Thickness ◽

Damping Factor ◽

Strain Rates ◽

Longitudinal Stress ◽

Surface Slope ◽

Stress Equation ◽

Ice Flow ◽

Small Surface ◽

Ice Caps

AbstractThe use of well known simple periodic solutions of the two-dimensional biharmonic stress equation for studying the flow over undulations of an ice mass of small surface slope is examined. The model considered is one in which most of the shear (deformation or. sliding) takes place near the base and the upper part moves largely as a block, with longitudinal strain-rates varying linearly with the longitudinal stress deviations. For bedrock perturbations of a given wavelength the steady-state surface shape consists of similar waves but out of phase by ½π, such that the steepest slope occurs over the highest bedrock; and the amplitude is reduced by a “damping factor”, depending on the speed, viscosity, ice thickness and wavelength.Minimum damping occurs for λm ≈ 3.3 times the ice thickness, while waves much longer or much shorter than this are almost completely damped out. The energy dissipation and the resistance to the ice flow is also a maximum for an undulation scale of several times the ice thickness, whereas the effects of small basal irregularities die out exponentially with distance into the ice, and only have an effect in so far as the average basal stress is related to the average surface slope. As a result of this a revision of present glacier sliding theories becomes possible.Various predictions of the theory have been confirmed from spectral analysis of surface and bedrock profiles of ice caps.

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Global change, Antarctic meteorite traps and the East Antarctic ice sheet

Journal of Glaciology ◽

10.3189/s0022143000016051 ◽

1993 ◽

Vol 39 (132) ◽

pp. 397-408 ◽

Cited By ~ 2

Author(s):

G. Delisle

Keyword(s):

Numerical Models ◽

Accumulation Rate ◽

Theoretical Work ◽

Snow Accumulation ◽

Ice Thickness ◽

Ice Caps ◽

Ice Cap ◽

Field Evidence ◽

Victoria Land ◽

Late Tertiary

AbstractNumerical models to assess the principal response of large ice caps to climatic changes are used as a guide to the interpretation of field evidence of changes in the glaciological regime in the coastal areas of Victoria Land and north Victoria Land, Antarctica. Based on the theoretical work, the following scenario is proposed: areas within about 300 km from the coast of Victoria Land experienced (i) significantly shallower ice slopes and a lesser degree of glaciation during most of the late Tertiary, (ii) steep slopes and thicker ice than today during glacial stages, and (iii) moderate thinning of the ice in intervening interglacial stages.The model predicts, for central regions of Antarctica, a slightly thinner ice cap (lower snow-accumulation rate) during glacial stages, but an estimated 200 m thicker ice cap in warmer Tertiary climates than today. The calculated “Tertiary ice caps” indicate a probable tendency of periodic surges due to basal melting at the outer fringes.Only modest changes of the ice thickness in reasonably good agreement with the model predictions for the current interglacial stage have been observed on four blue-ice fields, all located within 250 km of the coastline. Investigated ice fields include two meteorite traps — the Allan Hills Icefield and the Frontier Mountain meteorite fields. Antarctic meteorite traps are sustained by very specific glaciological conditions — in particular, only moderate changes in ice thickness over time. The sub-ice topography of these fields was determined by radar measurements and reveals a former, very different glaciological regime, which is interpreted as being associated with glacial processes, operative during the late Tertiary.Field evidence for a hypsithermal event during the Holocene is presented.

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Small-scale horizontal variability of snow, sea-ice thickness and freeboard in the first-year ice region north of Svalbard

Annals of Glaciology ◽

10.3189/2013aog62a157 ◽

2013 ◽

Vol 54 (62) ◽

pp. 261-266 ◽

Cited By ~ 17

Author(s):

Jari Haapala ◽

Mikko Lensu ◽

Marie Dumont ◽

Angelika H.H. Renner ◽

Mats A. Granskog ◽

...

Keyword(s):

Standard Deviation ◽

Sea Ice ◽

Snow Accumulation ◽

Small Scale ◽

Ice Thickness ◽

First Year ◽

Sea Ice Thickness ◽

The Mean ◽

Ridged Ice ◽

Snow Thickness

AbstractVariability of sea-ice and snow conditions on the scale of a few hundred meters is examined using in situ measurements collected in first-year pack ice in the European Arctic north of Svalbard. Snow thickness and surface elevation measurements were performed in the standard manner using a snow stick and a rotating laser. Altogether, 4109 m of measurement lines were surveyed. The snow loading was large, and in many locations the ice freeboard was negative (38.8% of snowline measurements), although the modal ice and snow thickness was 1.8 m. The mean of all the snow thickness measurements was 36 cm, with a standard deviation of 26 cm. The mean freeboard was only 3 cm, with a standard deviation of 23 cm. There were noticeable differences in snow thickness among the measurement sites. Over the undeformed ice areas, the mean snow thickness and freeboard were 23 and 2.4 cm, respectively. Over the ridged ice areas, the mean freeboard was only –0.3 cm due to snow accumulation on the sails of ridges (average thickness 54 cm). These findings imply that retrieval algorithms for converting freeboard to ice thickness should take account of spatial variability of snow cover.

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The pattern of glaciation on the Avalon Peninsula of Newfoundland

Géographie physique et Quaternaire ◽

10.7202/004778ar ◽

2002 ◽

Vol 52 (1) ◽

pp. 23-45 ◽

Cited By ~ 9

Author(s):

Norm R. Catto

Keyword(s):

Sea Level ◽

Ice Thickness ◽

Phase 3 ◽

Ice Caps ◽

Ice Cap ◽

Geomorphic Features ◽

Subsequent Phase ◽

Placentia Bay ◽

Late Wisconsinan ◽

Avalon Peninsula

Abstract The pattern of glaciation on the Avalon Peninsula has been established through study of geomorphic features, striations, and erratic provenance. Three phases in a continuum of glaciation are recognized. The initial phase involved the expansion of ice from several centres. Ice thickness and extent reached a maximum during the subsequent Phase 2 event, correlated with the Late Wisconsinan. Lowered sea level permitted the development of the St. Mary's Bay ice centre. Ice from the Newfoundland mainland coalesced with Avalon Peninsula ice in Placentia Bay, on the Isthmus, and in Trinity Bay. Rising sea level, triggered by the retreat of Laurentide ice in Labrador, resulted in destabilization of the St. Mary's Bay ice cap, marking Phase 3. Final deglaciation of the Avalon Peninsula began before 10,100 ± 250 BP. The Avalon Peninsula ice caps were controlled by regional and hemispheric events, and by the response of the Lauren- tide glaciers.

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Surface undulations of Antarctic ice streams tightly controlled by bedrock topography

The Cryosphere ◽

10.5194/tc-7-407-2013 ◽

2013 ◽

Vol 7 (2) ◽

pp. 407-417 ◽

Cited By ~ 15

Author(s):

J. De Rydt ◽

G. H. Gudmundsson ◽

H. F. J. Corr ◽

P. Christoffersen

Keyword(s):

Flow Line ◽

Spatial Scales ◽

Radar Data ◽

Surface Velocity ◽

Ice Thickness ◽

Ice Streams ◽

Slip Ratio ◽

Bedrock Topography ◽

Ice Stream ◽

The Mean

Abstract. Full Stokes flow-line models predict that fast-flowing ice streams transmit information about their bedrock topography most efficiently to the surface for basal undulations with length scales between 1 and 20 times the mean ice thickness. This typical behaviour is independent of the precise values of the flow law and sliding law exponents, and should be universally observable. However, no experimental evidence for this important theoretical prediction has been obtained so far, hence ignoring an important test for the physical validity of current-day ice flow models. In our work we use recently acquired airborne radar data for the Rutford Ice Stream and Evans Ice Stream, and we show that the surface response of fast-flowing ice is highly sensitive to bedrock irregularities with wavelengths of several ice thicknesses. The sensitivity depends on the slip ratio, i.e. the ratio between mean basal sliding velocity and mean deformational velocity. We find that higher values of the slip ratio generally lead to a more efficient transfer, whereas the transfer is significantly dampened for ice that attains most of its surface velocity by creep. Our findings underline the importance of bedrock topography for ice stream dynamics on spatial scales up to 20 times the mean ice thickness. Our results also suggest that local variations in the flow regime and surface topography at this spatial scale cannot be explained by variations in basal slipperiness.

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