Comparison of 105 Years of Oxygen Isotope and Insoluble Impurity Profiles from the Devon Island and Camp Century Ice Cores

1979 ◽  
Vol 11 (3) ◽  
pp. 299-305 ◽  
Author(s):  
David A. Fisher
Keyword(s):  
Oxygen Isotope ◽  
Flow Line ◽  
Ice Cores ◽  
Devon Island ◽  
Ice Cap ◽  
Particulate Concentration ◽  
The Difference ◽  
Impurity Profiles ◽  
Level Lowering ◽  
Present Site

Oxygen-isotope profiles for the Devon Island ice cap and Camp Century Greenland are affected by a number of variables, some of which must have been the same for both sites. The two δ(18O) records spanning about 120,000 years are brought into relative alignment by comparison of major δ features, and subsequent verification that the insoluble particulate concentration records were also in phase for this alignment. The difference between the δ profiles is shown to be mainly a function of the altitude of the accumulation area for Camp Century. This altitude seems to have been higher than present for the last 100,000 years, suggesting the present flow line through the site has never been shorter. The maximum altitude for the Camp Century accumulation area is 1500 m above the present site and is almost synchronous with the maximum in particulate concentration that occurs at 16,000 yr B.P. The synchronism is likely due to the maximum sea-level lowering that exposed vast areas of continental shelf to wind erosion.

scholarly journals 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

1988 ◽  
Vol 10 ◽  
pp. 34-37 ◽  
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.

scholarly journals Structure and Flow in the Margin of the Law Dome Ice Cap. Antarctica (Abstract)

1988 ◽  
Vol 10 ◽  
pp. 222
Author(s):  
Neal W. Young
Keyword(s):  
Physical Properties ◽  
Crystal Size ◽  
Flow Line ◽  
Ice Core ◽  
Ice Cores ◽  
Crystallographic Structure ◽  
Proxy Records ◽  
Ice Cap ◽  
Radio Echo Sounding ◽  
The Law

The internal structure of the Law Dome ice cap is being investigated by studying ice cores obtained from several sites along the summit-Cape Folger line. Profiles of measured physical properties for four of the ice cores from near the margin of the ice cap are presented. A comparison of the profiles shows a gradual increase and then decrease in crystal size, and the development of strong crystal anisotropy in the upper half of the ice thickness. But in the lower part there is a complex multi-layer crystallographic structure, with an interleaving of ice which has markedly different physical properties. The development of the physical properties in the ice cores is discussed in terms of the deformation in the ice cap in the neighbourhood of the bore holes and the movement of the ice over the rough bedrock. The interdependence of the physical properties and the flow within the ice cap and their effect on other proxy records obtained from the ice cores are also explored. The Law Dome is a small ice cap, about 200 km in diameter, adjoining the main Antarctic ice sheet. It is being studied as a model ice cap, using surface surveys and ice-core drilling. It is large enough to have most of the features of larger ice sheets but small enough to be investigated in considerable detail. The four cores were drilled within 10 km of the coast at Cape Folger and lie approximately along a flow line. Each of the cores covers the Holocene and at least the later part of the Last Glacial Maximum. Two of the cores are within 40 m of bedrock and the remaining two, in thinner ice nearer the coast, are within a few metres of bedrock. Physical properties which were measured include: crystal size, texture and orientation; bubble size, orientation and distribution; and visible stratigraphy. The stratigraphy in the upper layers is related mainly to the occurrence of surface melting during the warmer months of the year. Additional supporting information is available from measurements of the physical properties on shallow cores up-stream of the four bore holes, from radio echo-sounding profiles and from other studies on the ice cores. This data is used in the discussion of the velocity field in the ice cap.

scholarly journals Reports on Current Work Temperatures in the Devon Island Ice Cap, Arctic Canada

1976 ◽  
Vol 16 (74) ◽  
pp. 277
Author(s):  
W.S.B. Paterson
Keyword(s):  
Steady State ◽  
Canadian Arctic ◽  
Canadian Arctic Archipelago ◽  
Climatic Warming ◽  
Devon Island ◽  
The Past ◽  
Ice Cap ◽  
Last Glaciation ◽  
Temperature Ranges ◽  
The Difference

Abstract Temperatures have been measured in a 299 m bore hole that reaches the base of the ice near the divide of the main ice cap on Devon Island in the Canadian Arctic Archipelago. Temperature ranges from — 23.0°C at a depth of 20 m to — 18.4°C at the bottom. The difference between surface and bottom temperatures is about 1.5 deg less than expected for a steady state. Recent climatic warming seems the most likely explanation of the discrepancy. The temperature gradient in the lowest 50 m is approximately linear and corresponds to a geothermal heal flux of 1.5 h.f.u. This value may be invalid, however, because temperatures at and below this depth have probably been perturbed by changes of surface temperature during the past several thousand years, particularly by the warming at the end of the last glaciation. A detailed analysis of the results is in progress.

An oxygen-isotope climatic record from the Devon Island ice cap, arctic Canada

Nature ◽  
1977 ◽  
Vol 266 (5602) ◽  
pp. 508-511 ◽  
Author(s):  
W. S. B. Paterson ◽  
R. M. Koerner ◽  
D. Fisher ◽  
S. J. Johnsen ◽  
H. B. Clausen ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Arctic Canada ◽  
Devon Island ◽  
Ice Cap ◽  
Climatic Record

scholarly journals Application of a Flow Model to the Ice-divide Region of Devon Island Ice Cap, Canada

1988 ◽  
Vol 34 (116) ◽  
pp. 55-63 ◽  
Author(s):  
N. Reeh ◽  
W.S.B. Paterson
Keyword(s):  
Shear Stress ◽  
Steady State ◽  
Vertical Velocity ◽  
Flow Model ◽  
Flow Line ◽  
Surface Strain ◽  
Ice Age ◽  
Depth Profiles ◽  
Devon Island ◽  
Ice Cap

AbstractThe steady-state flow model of Reeh (1988) is applied to a flow line that starts at the highest point of the Devon Island ice cap, follows the surface crest for 7.6 km, and then runs down the slope for a further 3.7 km. The effects of bedrock undulations, divergence of the flow lines, the variation of temperature with depth, and a basal layer of “soft” ice-age ice are taken into account. A flow law withn= 3 and a value ofAclose to that of Paterson (1981) is used. Longitudinal stress variations are neglected so that shear stress is calculated by the usual formula. It is estimated that these calculated values may be in error by at most 30%. Depth profiles of effective shear stress, and of the components of velocity and normal strain-rate, are presented at selected points along the flow line. These illustrate the large variations that occur near an ice divide and over bedrock undulations of amplitude comparable with the mean ice thickness. The model gives good predictions of the surface profile and of longitudinal and transverse surface strain-rates measured at ten points along the flow line. Predicted depth profiles of horizontal and vertical velocity components are compared with those measured in a bore hole. Comparison is limited by the fact that the model works in ice equivalent, whereas about 20% of the ice column consists of firn with different rheological properties from ice. The vertical velocity prediction is good. However, the model does not reproduce well the shape of the horizontal velocity profile, although measured and calculated fluxes differ only slightly. Predicted annual-layer thicknesses are within 15% of the measured ones in the upper half of the ice column, which consists of ice deposited in the last 1000 years. Predicted thicknesses in older ice are too small and the discrepancy increases with depth. This might indicate increased precipitation or, more likely, a thinner ice cap in the climatic optimum. However, it could also result from the fact that the layer of “soft” ice has been thinning continuously since the end of the ice age, so that the ice cap has never been in a steady state.

scholarly journals Development of the Crystal Structure within the Law Dome Ice Cap, Antarctica (Abstract)

1988 ◽  
Vol 11 ◽  
pp. 222-222
Author(s):  
Neal W. Young
Keyword(s):  
Internal Structure ◽  
Crystal Size ◽  
Flow Line ◽  
Layer Structure ◽  
Ice Cores ◽  
Complex Stress ◽  
Crystal Anisotropy ◽  
Ice Cap ◽  
Single Maximum ◽  
The Law

Fourteen shallow and medium-depth cores have been drilled from the Law Dome ice cap, between the summit and the coast near Casey Station. Measurements of their crystal and other physical properties are reviewed briefly. The variations along the cores in crystal size, orientation, fabric type and strength, and bubble dimensions, are used to define the internal structure of the ice cap locally at the bore-hole sites. Surveys of bore-hole deformation and the shape and movement of the ice cap are used to define relations between the structure and the variables: stress, temperature, strain-rate and accumulated strain. The relations and the survey data are incorporated in a numerical model in order to deduce the internal structure of the ice cap along a flow line linking the bore-hole sites. The results of the model in turn depend on the crystal anisotropy of the calculated structure.The main results are provided by the medium-depth bore holes located at the summit, near the margin, and about half-way along the flow line. The major features of the internal structure are determined by the predominant shear deformation in the ice cap. There is horizontal continuity in the properties and structure within the group of bore holes near the margin of the ice cap. There are distinct differences, between the coastal and the inland ice cores, in the changes in properties with depth. Near the margin a strong single-maximum fabric develops within the upper 60% of the ice thickness; crystal size initially increases with depth, then shows a marked decrease at about 50% thickness. For the inland cores, a strong single-maximum fabric also develops, but at a greater total depth and a much shallower fraction of the thickness. A similar decrease in crystal size was not observed.The broad-scale trends of the properties are reproduced by the model. The finer-scale deviations in the properties can be explained by the effects of longitudinal strain and of past changes in surface conditions, such as the effect of surface melting. A complex stress distribution, related to flow over rough bedrock, needs to be invoked to explain the pronounced multi-layer structure in the lower part of the ice cores from near the margin. A series of time lines is modelled, following the flow along the ice-particle trajectories, to produce the stress, temperature and deformation histories of the ice in the cores. These provide the basic data for a reconstruction of past changes in the ice cap.

scholarly journals 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

1988 ◽  
Vol 10 ◽  
pp. 34-37 ◽  
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.

Structure and Flow in the Margin of the Law Dome Ice Cap. Antarctica (Abstract)

1988 ◽  
Vol 10 ◽  
pp. 222-222
Author(s):  
Neal W. Young
Keyword(s):  
Physical Properties ◽  
Crystal Size ◽  
Flow Line ◽  
Ice Core ◽  
Ice Cores ◽  
Crystallographic Structure ◽  
Proxy Records ◽  
Ice Cap ◽  
Radio Echo Sounding ◽  
The Law

The internal structure of the Law Dome ice cap is being investigated by studying ice cores obtained from several sites along the summit-Cape Folger line. Profiles of measured physical properties for four of the ice cores from near the margin of the ice cap are presented. A comparison of the profiles shows a gradual increase and then decrease in crystal size, and the development of strong crystal anisotropy in the upper half of the ice thickness. But in the lower part there is a complex multi-layer crystallographic structure, with an interleaving of ice which has markedly different physical properties. The development of the physical properties in the ice cores is discussed in terms of the deformation in the ice cap in the neighbourhood of the bore holes and the movement of the ice over the rough bedrock. The interdependence of the physical properties and the flow within the ice cap and their effect on other proxy records obtained from the ice cores are also explored.The Law Dome is a small ice cap, about 200 km in diameter, adjoining the main Antarctic ice sheet. It is being studied as a model ice cap, using surface surveys and ice-core drilling. It is large enough to have most of the features of larger ice sheets but small enough to be investigated in considerable detail. The four cores were drilled within 10 km of the coast at Cape Folger and lie approximately along a flow line. Each of the cores covers the Holocene and at least the later part of the Last Glacial Maximum. Two of the cores are within 40 m of bedrock and the remaining two, in thinner ice nearer the coast, are within a few metres of bedrock. Physical properties which were measured include: crystal size, texture and orientation; bubble size, orientation and distribution; and visible stratigraphy. The stratigraphy in the upper layers is related mainly to the occurrence of surface melting during the warmer months of the year. Additional supporting information is available from measurements of the physical properties on shallow cores up-stream of the four bore holes, from radio echo-sounding profiles and from other studies on the ice cores. This data is used in the discussion of the velocity field in the ice cap.

scholarly journals Pollen Analysis and Discussion of Time-Scales in Canadian Ice Cores

1988 ◽  
Vol 10 ◽  
pp. 85-91 ◽  
Author(s):  
R.M. Koerner ◽  
J.C. Bourgeois ◽  
D.A. Fisher
Keyword(s):  
Flow Line ◽  
Ice Cores ◽  
Bulk Sample ◽  
High Arctic ◽  
Interglacial Period ◽  
Drilling Process ◽  
Last Interglacial ◽  
Ice Cap ◽  
Last Interglacial Period ◽  
Pollen Concentrations

Previous pollen analyses of ice cores from Devon and Ellesmere islands have contributed considerably to our knowledge of past climate in the Canadian High Arctic. In this case, in 1979, bulk (35–83 litres) water samples were melted down a hole 139 m deep, drilled to bedrock, 1.2 km from the top of the flow line in Agassiz Ice Cap in northern Ellesmere Island. Analysis of ten of these samples, plus some taken in very dirty ice from the melt tank during drilling 7 years ago, has yielded pollen concentrations that, together with the oygen-isotope (6) signatures, suggest the Agassiz Ice Cap began its growth during the last interglacial period. A discrepancy between melt-tank and bulk-sample pollen concentrations is believed to be due to a loss of pollen from the melt-tank samples during the drilling process.

scholarly journals Application of a Flow Model to the Ice-divide Region of Devon Island Ice Cap, Canada

1988 ◽  
Vol 34 (116) ◽  
pp. 55-63 ◽  
Author(s):  
N. Reeh ◽  
W.S.B. Paterson
Keyword(s):  
Shear Stress ◽  
Steady State ◽  
Vertical Velocity ◽  
Flow Model ◽  
Flow Line ◽  
Surface Strain ◽  
Ice Age ◽  
Depth Profiles ◽  
Devon Island ◽  
Ice Cap

AbstractThe steady-state flow model of Reeh (1988) is applied to a flow line that starts at the highest point of the Devon Island ice cap, follows the surface crest for 7.6 km, and then runs down the slope for a further 3.7 km. The effects of bedrock undulations, divergence of the flow lines, the variation of temperature with depth, and a basal layer of “soft” ice-age ice are taken into account. A flow law with n = 3 and a value of A close to that of Paterson (1981) is used. Longitudinal stress variations are neglected so that shear stress is calculated by the usual formula. It is estimated that these calculated values may be in error by at most 30%. Depth profiles of effective shear stress, and of the components of velocity and normal strain-rate, are presented at selected points along the flow line. These illustrate the large variations that occur near an ice divide and over bedrock undulations of amplitude comparable with the mean ice thickness. The model gives good predictions of the surface profile and of longitudinal and transverse surface strain-rates measured at ten points along the flow line. Predicted depth profiles of horizontal and vertical velocity components are compared with those measured in a bore hole. Comparison is limited by the fact that the model works in ice equivalent, whereas about 20% of the ice column consists of firn with different rheological properties from ice. The vertical velocity prediction is good. However, the model does not reproduce well the shape of the horizontal velocity profile, although measured and calculated fluxes differ only slightly. Predicted annual-layer thicknesses are within 15% of the measured ones in the upper half of the ice column, which consists of ice deposited in the last 1000 years. Predicted thicknesses in older ice are too small and the discrepancy increases with depth. This might indicate increased precipitation or, more likely, a thinner ice cap in the climatic optimum. However, it could also result from the fact that the layer of “soft” ice has been thinning continuously since the end of the ice age, so that the ice cap has never been in a steady state.

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