Devon Island Ice Cap Research Articles

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

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.

On the Special Rheological Properties of Ancient Microparticle-Laden Northern Hemisphere Ice as Derived from Bore-Hole and Core Measurements

AbstractIn the Northern Hemisphere, ice layers which have high microparticle concentrations (in particular late Wisconsin) are “softer” than modern or Holocene ice. Such ice deforms more readily in bore-hole tilt and closure measurements. This enhancement in flow, which is shownnotto be related toc-axis concentration, has a maximum of three for late Wisconsin ice. The closure and tilt of a bore hole in the Agassiz Ice Cap, Ellesmere Island, drilled in 1977, has been followed every year since its drilling and the flow enhancement observed has been compared to the following quantities measured in the cores: concentration, δ(18O), crystal size,c-axis, Ca, Na, conductivity, and density. Flow enhancement of the ice age and bottom ice was found to be unrelated toc-axis concentration and density. Enhancement of flow is best related to microparticle (or Ca) concentration which in turn seems to be inversely related to crystal size. The latter relationship also seems to hold for the Devon Island Ice Cap and Greenland. In future, modellers of northern ice ages should use model ice that is three times softer than modern or Holocene ice.

On the Special Rheological Properties of Ancient Microparticle-Laden Northern Hemisphere Ice as Derived from Bore-Hole and Core Measurements

AbstractIn the Northern Hemisphere, ice layers which have high microparticle concentrations (in particular late Wisconsin) are “softer” than modern or Holocene ice. Such ice deforms more readily in bore-hole tilt and closure measurements. This enhancement in flow, which is shownnotto be related toc-axis concentration, has a maximum of three for late Wisconsin ice. The closure and tilt of a bore hole in the Agassiz Ice Cap, Ellesmere Island, drilled in 1977, has been followed every year since its drilling and the flow enhancement observed has been compared to the following quantities measured in the cores: concentration, δ(18O), crystal size,c-axis, Ca, Na, conductivity, and density. Flow enhancement of the ice age and bottom ice was found to be unrelated toc-axis concentration and density. Enhancement of flow is best related to microparticle (or Ca) concentration which in turn seems to be inversely related to crystal size. The latter relationship also seems to hold for the Devon Island Ice Cap and Greenland. In future, modellers of northern ice ages should use model ice that is three times softer than modern or Holocene ice.

Was the Greenland ice sheet thinner in the late Wisconsinan than now?

Ice of Wisconsinan origin which constitutes the basal layers of the ice caps in arctic Canada and Greenland flows three to four times more readily than the Holocene ice above. A model based on simple ice sheet profile theory is set up for the thickness response of the interior ice sheet regions to the progressive thinning of this soft layer. The model is applied to calculate the thickness response of the Greenland ice sheet at the locations Dye 3 and Crete, and of the Devon Island ice cap in arctic Canada. It is concluded that the mechanism contributes significantly to the thickness change of the Greenland ice sheet, presently at a rate of about 1 cm yr−1 and that this rate of change will persist potentially over thousands of years to come. As regards the Devon Island ice cap, most of the estimated 15% thickness increase has already been accomplished. A further consequence is that in the late Wisconsinan, ice thicknesses of the interior regions of the Greenland ice sheet were likely to have been no greater and possibly even less than at present, in spite of the larger geographical extent of the ice sheet. It is argued that the glacial-interglacial cycles of accumulation rate and ice temperature are likely to enhance this ice thickness variation.

Land/ocean correlations during the last interglacial/glacial transition, Baffin Bay, northwestern North Atlantic: A review

Evidence from terrestrial sections, ice cores, and marine cores are reviewed and used to develop a scenario for environmental change in the area of the extreme northwest North Atlantic during marine isotope stages 5 and 4. The critical physical link between the landbased glacial chronology and marine events in Baffin Bay is the presence of carbonate rich drift along the Baffin Bay coast of Bylot Island and a detrital carbonate facies (Facies B) in Baffin Bay sediments. Cores from Baffin Bay/Labrador Sea can be dated by means of oxygen isotope variations and by peaks in the abundance of volcanic glass shards. One occurrence of Facies B is dated between late stage 5 and stage 4 and we correlate this event with the Eclipse Glaciation of Bylot Island and the Ayr Lake stade of the Foxe Glaciation of Baffin Island (= Kogalu aminozone). In contrast on West Greenland, amino acid racemization evidence suggests that the Greenland Ice Sheet developed throughout stage 4 and reached a maximum in stage 3 (Svartenhuk advance >40 ka). The oxygen isotope record in the Devon Island Ice Cap (northwest Baffin Bay) indicates that Baffin Bay was largely open during marine isotope stage 5. Analyses of shallow water molluscan and foraminiferal assemblages, deep-water foraminifera, pollen from Iand sections and deep-sea cores, and dinoflagellates from marine cores indicate that interglacial conditions prevailed during much of the stage 54 glaciation.

Pollen, Oxygen Isotope Content and Seasonality in an Ice Core from the Penny Ice Cap, Baffin Island

The results of pollen analyses of 12 ice core samples, covering an eight-year period from 1972 through 1979 from the divide of the Penny Ice Cap, Baffin Island, are reported. The pollen spectra are dominated by long distance transported pollen, especially the conifers Picea and Pinus. Alnus pollen is generally rare. In contrast, pollen spectra from both modern polsters and fossil peat sections in the same area are both characterized by local pollen types. Pollen influx values range from 2 to 8 grains/cm²/yr. Where the sampling intervals happened to coincide with established seasonal intervals (as interpreted from later oxygen isotope studies) the pollen spectra showed seasonal characteristics. This occurred in five out of the twelve samples. Comparison of these data is made with data from Devon Island Ice Cap. Such information may be useful in reconstructing paleoclimates.Key words: pollen, ice cap, Baffin, isotope, paleoclimates

Basal Sliding Relations Deduced from Ice-Sheet Data

AbstractThe sliding law is defined as a basal boundary condition for the large-scale bulk ice flow, relating the tangential traction τb, overburden pressure pb, and tangential velocity ub on a smoothed-out mean bed contour. This effective bed is a lower boundary viewed on the scale of the bulk ice flow and is not the physical ice/rock or sediment interface. The sliding relation reflects on the same scale the complex motion taking place in the neighbourhood of the physical interface. The isothermal steady-state ice-sheet analysis of Morland and Johnson (1980, 1982) is applied to known surface profiles from the Greenland ice sheet and Devon Island ice cap, with their corresponding mass-balance distributions, to determine τb, pb, and ub for each case. These basal estimates are used in turn to construct, using least-squares correlation, polynomial representations for an overburden dependence λ(pb) in the adopted form of sliding law τb ═ λ(pb)ub1/m with m ≥ 1.The two different data sets determine functions λ(pb) of very different magnitudes, reflecting very different basal conditions. A universal sliding law must therefore contain more general dependence on basal conditions, but the two relations determined appear to describe the two extremes. Hence use of both relations in turn to determine profiles compatible with given mass-balance distributions can be expected to yield extremes of the possible profiles, and further to show the sensitivity of profile form to variation of the sliding relation. The theory is designed as a basis for reconstruction of former ice sheets and their dynamics which are related to the two fundamental determinants of surface mass balance and basal boundary condition.

Basal Sliding Relations Deduced from Ice-Sheet Data

AbstractThe sliding law is defined as a basal boundary condition for the large-scale bulk ice flow, relating the tangential tractionτb, overburden pressurepb, and tangential velocityubon a smoothed-out mean bed contour. This effective bed is a lower boundary viewed on the scale of the bulk ice flow and is not the physical ice/rock or sediment interface. The sliding relation reflects on the same scale the complex motion taking place in the neighbourhood of the physical interface. The isothermal steady-state ice-sheet analysis of Morland and Johnson (1980, 1982) is applied to known surface profiles from the Greenland ice sheet and Devon Island ice cap, with their corresponding mass-balance distributions, to determineτb,pb, andubfor each case. These basal estimates are used in turn to construct, using least-squares correlation, polynomial representations for an overburden dependenceλ(pb) in the adopted form of sliding lawτb═λ(pb)ub1/mwithm ≥1.The two different data sets determine functionsλ(pb) of very different magnitudes, reflecting very different basal conditions. A universal sliding law must therefore contain more general dependence on basal conditions, but the two relations determined appear to describe the two extremes. Hence use of both relations in turn to determine profiles compatible with given mass-balance distributions can be expected to yield extremes of the possible profiles, and further to show the sensitivity of profile form to variation of the sliding relation. The theory is designed as a basis for reconstruction of former ice sheets and their dynamics which are related to the two fundamental determinants of surface mass balance and basal boundary condition.

Reconstruction of the Glacial Ice Covers of Greenland and the Canadian Arctic Islands by Three-Dimensional, Perfectly Plastic Ice-Sheet Modelling

A three-dimensional perfectly plastic ice-sheet model, developed for determining the surface elevations and the flow pattern of an ice sheet with given bottom topography and ice-margin positions, is applied to the reconstruction of the glacial ice covers of Greenland and the Canadian Arctic islands. In the northern regions, two different reconstructions have been performed with ice margins along the present 600 and 200 m sea-depth contours, respectively. In central Greenland, the ice margin is considered to be at the outermost ice-margin deposits on the coastal shelf to the west, and at the present 200 m sea-depth contour to the east.The main conclusions to be drawn from the reconstructions are: (1). The flow pattern of the glacial ice cover of Greenland shows a great resemblance to the present one, the central ice divide being displaced less than 50 km from its present position and being no more than 200 m higher than today. (2). The main ice divide of the ice sheet covering the Canadian Arctic islands (the Innuitian ice sheet) was located over the highlands of eastern Ellesmere Island with local domes positioned over the present ice caps, indicating that even the deep ice of Wisconsin age in these ice caps is of local origin. This is also the case for the Devon Island ice cap. (3). Even in the not very likely case of a rather extensive glacial ice cover in north-west Greenland, the ice-flow pattern upstream of the Camp Century deep drill site would not have changed radically compared to the present flow pattern. Thus it is concluded that even advanced ice margins in late-Wisconsin time could at most have resulted in an elevation of the deposition site of the late-Wisconsin ice at Camp Century 600 m higher than at present. The consequences of this conclusion are discussed.

Reconstruction of the Glacial Ice Covers of Greenland and the Canadian Arctic Islands by Three-Dimensional, Perfectly Plastic Ice-Sheet Modelling

A three-dimensional perfectly plastic ice-sheet model, developed for determining the surface elevations and the flow pattern of an ice sheet with given bottom topography and ice-margin positions, is applied to the reconstruction of the glacial ice covers of Greenland and the Canadian Arctic islands. In the northern regions, two different reconstructions have been performed with ice margins along the present 600 and 200 m sea-depth contours, respectively. In central Greenland, the ice margin is considered to be at the outermost ice-margin deposits on the coastal shelf to the west, and at the present 200 m sea-depth contour to the east.The main conclusions to be drawn from the reconstructions are: (1). The flow pattern of the glacial ice cover of Greenland shows a great resemblance to the present one, the central ice divide being displaced less than 50 km from its present position and being no more than 200 m higher than today. (2). The main ice divide of the ice sheet covering the Canadian Arctic islands (the Innuitian ice sheet) was located over the highlands of eastern Ellesmere Island with local domes positioned over the present ice caps, indicating that even the deep ice of Wisconsin age in these ice caps is of local origin. This is also the case for the Devon Island ice cap. (3). Even in the not very likely case of a rather extensive glacial ice cover in north-west Greenland, the ice-flow pattern upstream of the Camp Century deep drill site would not have changed radically compared to the present flow pattern. Thus it is concluded that even advanced ice margins in late-Wisconsin time could at most have resulted in an elevation of the deposition site of the late-Wisconsin ice at Camp Century 600 m higher than at present. The consequences of this conclusion are discussed.

Ivory Gull Colonies on the Devon Island Ice Cap, Arctic Canada

Four small Ivory Gull colonies have been found on nunataks on the ice cap of eastern Devon Island. Mainly on the basis of their similarity to known breeding places of the Ivory Gull on Ellesmere Island, all four sites are believed to be those of nesting colonies the first to be reported from Devon Island. Key words: Ivory Gull, Pagophila eburnea , colonies, nunatak nesting sites

Carbon-14 production compared to oxygen isotope records from Camp Century, Greenland and Devon Island, Canada

Carbon-14 production rate variations that are not explainable by geomagnetic changes are thought to be in antiphase with solar activity and as such should be in antiphase with paleotemperature records or proxy temperature histories such as those obtainable from oxygen isotope analyses of ice cores. Oxygen isotope records from Camp Century, Greenland and Devon Island Ice Cap are in phase with each other over thousands of years and in antiphase to the14C production rate residuals.

CANADIAN ARCTIC METEORITE SEARCH: 1981

The recovery of several thousand meteorite fragments from Antarctica has led to speculation that accumulations may occur on the Earth's other major ice caps. Meteorites falling over the past 80,000 years on the Devon Island ice cap in the Canadian Arctic may be exposed at the surface near the ice cap margin. From the terrestrial meteorite flux, ice movement rates, and fragmentation factors it is calculated that 12,560 samples of 150 g mass are potentially concentrated in a 65 km2 zone along the northwest margin. A search of this region on foot and by helicopter in July, 1981, failed to recover any specimens. Although metre‐sized gneissic boulders, plucked from the underlying Precambrian basement, were concentrated in this zone it is postulated that the unseasonal 30 cm snow cover on the ice prohibited the recognition of possible meteorite specimens, which may average only 5 cm in diameter.

Instantaneous glacierization, the rate of albedo change, and feedback effects at the beginning of an ice age

A study of the average annual- and melt-season albedos for the northwest side of the Devon Island Ice Cap shows that there is no step in the average albedo either at the equilibrium or firn line. Similarly, during a period of increasing glacierization there is nowhere any dramatic increase in the average annual- or melt-season albedo with time as the equilibrium line gradually moves downslope. This means that the inception of ice caps and permanent snowfields does not make a significant change to the rate of increasing albedo and its associated feedback effects during the same period of glacierization. The extension of the annual period of snowcover generally is much more important to the feedback process (by increasing albedo) than the specific lowering of the equilibrium line. A decreased variability of summer climate, and hence the disappearance of “anomalously” warm summers, may be an integral part of the glacierizing process.

δ18O variations in snow on the Devon Island ice cap, Northwest Territories, Canada

A study of δ18O variations of snow samples taken on traverses across the Devon Island ice cap in June 1971, 1972, and 1973 has shown a difference between the accumulation conditions on the southeast and northwest sides of the ice cap. On the southeast side there is an increasing depletion of 18O in the snow with increasing elevation. This pattern is attributed to the effect of orographic uplift of air masses moving over the ice cap from the southeast, which promotes condensation and precipitation due to adiabatic cooling. On the northwest side of the ice cap there is no evidence of any further depletion of 18O in snow, neither with increasing distance from the possible moisture source in Baffin Bay to the southeast nor with increasing elevation if the air mass comes from the northwest. In this case condensation is due to isobaric cooling so that precipitation is generally from level cloud bases. The changes inferred for the isotopic composition of the water vapour as it rises up the southeast slope are found to be consistent with its depletion through precipitation under near-equilibrium conditions. It is calculated that approximately 30% of the moisture at sea level on the southeast side of the ice cap and 8% at the top of the ice cap are of local origin. Lower temporal and aerial variabilty of the δ values on the southeast side of the ice cap is attributed to dominance of the Baffin Bay low on that side effecting consistency of storm conditions there.The δ values of ice in the ablation zone on the Sverdrup Glacier show the combined effect of ice movement from the accumulation to the ablation zone and climatic change during the period of movement from cold to warm and back to cold conditions again.

Comparison of 10 5 years of oxygen isotope and insoluble impurity profiles from the Devon Island and Camp Century ice cores

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.

Discontinuous Flow, Ice Texture, and Dirt Content in the Basal Layers of the Devon Island Ice Cap

AbstractSurface-to-bedrock cores obtained with a CRREL thermal drill were taken in 1972 and 1973 from the top of the Devon Island ice cap. There are very pronounced variations in oxygen isotope, micro-particle concentration, and ice texture in the lowermost 5 m of the core. There is a section of isotopically cold, very fine bubbly ice with high micro-particle concentrations between 2.6 and 4.4 m above the bed, considered to represent the Last Ice Age. There is coarse, isotopically warm, clean ice above and below this. For 1.2 m above the bed, the ice is finer again with high micro-particle concentrations but it shows very low bubble concentration and is isotopically the warmest in the core. While the broad variations are common to both cores, in detail there are significant variations despite the fact that the cores were taken only 27 m apart. The variations, when analysed statistically, show that at least 25–30% of the originally continuous profile is missing from each core. Faulting within the near-bedrock ice may be responsible for some of the effect but bubble fabric also gives evidence for irregular non-laminar flow. Because of the strong relationship between crystal size and micro-particle concentrations in the Devon Island cores, it is suggested that the fine-grained nature of dirty layers in the Antarctic and Greenland ice sheets is due to the effect of the dirt inclusions and not of shearing. Steep isotopic gradients in the Devon Island cores are shown to be evidence for possible shearing, which does not effect any change in the crystal texture. Clear ice near the bed is considered a tectonic feature, but the lack of effect on its bed by the ice cap confirms the non-erosional nature of an ice cap frozen to its bed.In terms of paleoclimatic history, it means that, because of bedrock effects, ice caps of intermediate depth (i.e. <400 m) can give continuous information only over the last approximate 5 000 years. Between 5 000 and 10 000 B.P. the time series becomes slightly discontinuous and beyond 10 000 B.P. so discontinuous as to allow only broad climatic inferences to be drawn.

Discontinuous Flow, Ice Texture, and Dirt Content in the Basal Layers of the Devon Island Ice Cap

AbstractSurface-to-bedrock cores obtained with a CRREL thermal drill were taken in 1972 and 1973 from the top of the Devon Island ice cap. There are very pronounced variations in oxygen isotope, micro-particle concentration, and ice texture in the lowermost 5 m of the core. There is a section of isotopically cold, very fine bubbly ice with high micro-particle concentrations between 2.6 and 4.4 m above the bed, considered to represent the Last Ice Age. There is coarse, isotopically warm, clean ice above and below this. For 1.2 m above the bed, the ice is finer again with high micro-particle concentrations but it shows very low bubble concentration and is isotopically the warmest in the core. While the broad variations are common to both cores, in detail there are significant variations despite the fact that the cores were taken only 27 m apart. The variations, when analysed statistically, show that at least 25–30% of the originally continuous profile is missing from each core. Faulting within the near-bedrock ice may be responsible for some of the effect but bubble fabric also gives evidence for irregular non-laminar flow. Because of the strong relationship between crystal size and micro-particle concentrations in the Devon Island cores, it is suggested that the fine-grained nature of dirty layers in the Antarctic and Greenland ice sheets is due to the effect of the dirt inclusions and not of shearing. Steep isotopic gradients in the Devon Island cores are shown to be evidence for possible shearing, which does not effect any change in the crystal texture. Clear ice near the bed is considered a tectonic feature, but the lack of effect on its bed by the ice cap confirms the non-erosional nature of an ice cap frozen to its bed.In terms of paleoclimatic history, it means that, because of bedrock effects, ice caps of intermediate depth (i.e. <400 m) can give continuous information only over the last approximate 5 000 years. Between 5 000 and 10 000 B.P. the time series becomes slightly discontinuous and beyond 10 000 B.P. so discontinuous as to allow only broad climatic inferences to be drawn.

Comparison of theoretical and observed temperature profiles in Devon Island ice cap, Canada

Summary. A non-steady-state theoretical model is used to predict the present variation of temperature with depth in two boreholes in the Devon Island ice cap, Arctic Canada. The boreholes are 300 m apart and one of them reaches bedrock. The heat transfer equation is solved numerically with the record of past temperatures obtained from measurements of the variations of oxygen—isotope ratio with depth in the cores as surface boundary condition. The effects of ice advection, refreezing of meltwater percolating from the surface (the amount of which is recorded in the cores), heating due to firn compaction and ice deformation, and heat flow in the bedrock below the ice sheet are all included in the model. The free parameters are geothermal heat flux, present surface temperature and heat loss at the surface which depends on the depth of meltwater penetration and other factors. Agreement between observed and predicted temperature—depth profiles is very close. Latent heat released by percolating meltwater is the predominating factor in determining the temperature distribution in the upper half of each borehole. The temperature distribution is insensitive to the value of the factor used to convert oxygen—isotope ratio to temperature.

Synoptic Climate Controls of Mass-Balance Variations on Devon Island Ice Cap

Synoptic Climate Controls of Mass-Balance Variations on Devon Island Ice Cap