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

1984 ◽  
Vol 5 ◽  
pp. 115-121 ◽  
Author(s):  
N. Reeh
Keyword(s):  
Flow Pattern ◽  
Bottom Topography ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Canadian Arctic ◽  
Ice Cover ◽  
Glacial Ice ◽  
North West ◽  
Ice Caps ◽  
Perfectly Plastic

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.

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

1984 ◽  
Vol 5 ◽  
pp. 115-121 ◽  
Author(s):  
N. Reeh
Keyword(s):  
Flow Pattern ◽  
Bottom Topography ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Canadian Arctic ◽  
Ice Cover ◽  
Glacial Ice ◽  
North West ◽  
Ice Caps ◽  
Perfectly Plastic

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.

scholarly journals A Plasticity Theory Approach to the Steady-State Shape of a Three-Dimensional Ice Sheet

1982 ◽  
Vol 28 (100) ◽  
pp. 431-455 ◽  
Author(s):  
Niels Reeh
Keyword(s):  
Steady State ◽  
Flow Pattern ◽  
Bottom Topography ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Theory Approach ◽  
Ice Streams ◽  
Perfectly Plastic ◽  
Set Up

AbstractThe differential equation determining the elevations of a perfectly plastic three-dimensional steady-state ice sheet is set up. Analytical solutions of the equation are obtained in two simple case, (1) an ice sheet on a horizontal base with an arbitrary edge curve, and (2) an ice sheet on a plane sloping base with a rectilinear ice margin. The solutions are discussed, particularly with reference to the development of ice divides and ice streams.For arbitrary base and ice-margin geometries, solutions are obtained by means of the method of characteristics, which reduces the problem to solving simultaneously three ordinary first-order differential equations. The integration, which is performed by numerical methods, is generally commenced at the ice margin, where the necessary boundary conditions are known.The method has been applied to model the elevation contours and the flow pattern of the central Greenland ice sheet, using the bottom topography revealed by radio echo soundings and the present ice margin geometry. The result is in surprisingly good agreement with our knowledge of the ice-sheet topography and flow pattern, all significant ice divides and ice streams being reproduced. This suggests, that the method can be applied to model the shape and flow pattern of ice sheets under glacial conditions, using information about former ice-margin positions.

scholarly journals A Plasticity Theory Approach to the Steady-State Shape of a Three-Dimensional Ice Sheet

1982 ◽  
Vol 28 (100) ◽  
pp. 431-455 ◽  
Author(s):  
Niels Reeh
Keyword(s):  
Steady State ◽  
Flow Pattern ◽  
Bottom Topography ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Theory Approach ◽  
Ice Streams ◽  
Perfectly Plastic ◽  
Set Up

AbstractThe differential equation determining the elevations of a perfectly plastic three-dimensional steady-state ice sheet is set up. Analytical solutions of the equation are obtained in two simple case, (1) an ice sheet on a horizontal base with an arbitrary edge curve, and (2) an ice sheet on a plane sloping base with a rectilinear ice margin. The solutions are discussed, particularly with reference to the development of ice divides and ice streams.For arbitrary base and ice-margin geometries, solutions are obtained by means of the method of characteristics, which reduces the problem to solving simultaneously three ordinary first-order differential equations. The integration, which is performed by numerical methods, is generally commenced at the ice margin, where the necessary boundary conditions are known.The method has been applied to model the elevation contours and the flow pattern of the central Greenland ice sheet, using the bottom topography revealed by radio echo soundings and the present ice margin geometry. The result is in surprisingly good agreement with our knowledge of the ice-sheet topography and flow pattern, all significant ice divides and ice streams being reproduced. This suggests, that the method can be applied to model the shape and flow pattern of ice sheets under glacial conditions, using information about former ice-margin positions.

scholarly journals Gas Hydrate Formation and Dissipation Histories in the Northern Margin of Canada: Beaufort-Mackenzie and the Sverdrup Basins

2012 ◽  
Vol 2012 ◽  
pp. 1-17 ◽  
Author(s):  
Jacek Majorowicz ◽  
Kirk Osadetz ◽  
Jan Safanda
Keyword(s):  
Sea Level ◽  
Canadian Arctic ◽  
Beaufort Sea ◽  
Ice Cover ◽  
Pressure Effects ◽  
Ice Age ◽  
Glacial Ice ◽  
The Holocene ◽  
Surface Temperatures ◽  
Gas Hydrate Formation

Gas hydrates (GHs) are a prominent subsurface feature on the Canadian Arctic continental margin. They occur both onshore and offshore, although they formed generally terrestrially, during the last glacial sea level low-stand, both in a region that was persistently glaciated (Queen Elizabeth Islands Group, Canadian Arctic Archipelago (QEIG)), and in a region that was not persistently glaciated (Mackenzie Delta-Beaufort Sea (MD-BS)). Parts of both regions were transgressed in the Holocene. We study the dynamic permafrost and GH history in both regions using a numerical model to illustrate how changes in setting and environment, especially periodic glacial ice cover, affected GH stability. MD-BS models represent the Mallik wellsite and these models successfully match current permafrost and GH bases observed in the well-studied Mallik wells. The MD-BS models show clearly that GHs have persisted through interglacial episodes. Lower surface temperatures in the more northerly QEIG result in an earlier appearance of GH stability that persists through glacial-interglacial intervals, although the base of GH base stability varies up to 0.2 km during the 100 ka cycles. Because of the persistent glacial ice cover QEIG models illustrate pressure effects attributed to regional ice sheet loading on the bases of both permafrost and GHs since 0.9 MYBP. QEIG model permafrost and GH depths are 572 m and 1072 m, respectively, which is like that observed commonly on well logs in the QEIG. In order to match the observed GH bases in the QEIG it is necessary to introduce ice buildup and thaw gradually during the glacials and interglacials. QEIG sea level rose 100–120 m about 10 ka ago following the most recent glaciation. Shorelines have risen subsequently due to isostatic glacial unloading. Detailed recent history modeling in QEIG coastal regions, where surface temperatures have changed from near zero in the offshore to −20°C in the onshore setting results in a model GH stability base, that is, <0.5 km. These coastal model results are significantly shallower than the inferred average GH base about 1 km in wells, Smith and Judge (1993). QEIG interisland channels are generally shallow and much of the previous shoreline inundated by the Holocene transgression was above the glacial sea level low-stand during the last ice age, resulting in a QEIG setting somewhat analogous to the relict terrestrial GH now transgressed by the shallow Beaufort Sea. It is also possible that the marine conditions were present at emergent shorelines for a shorter time or that the pretransgression subsurface temperatures persisted or were influenced by coastal settings, especially where lateral effects may not be well represented by 1D models.

scholarly journals Discovery of a nanodiamond-rich layer in the Greenland ice sheet

2010 ◽  
Vol 56 (199) ◽  
pp. 747-757 ◽  
Author(s):  
Andrei V. Kurbatov ◽  
Paul A. Mayewski ◽  
Jorgen P. Steffensen ◽  
Allen West ◽  
Douglas J. Kennett ◽  
...  
Keyword(s):  
High Explosive ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Impact Indicator ◽  
Glacial Ice ◽  
Ice Caps ◽  
Very High ◽  
Explosive Detonation ◽  
Discrete Layer ◽  
The Last Glacial

AbstractWe report the discovery in the Greenland ice sheet of a discrete layer of free nanodiamonds (NDs) in very high abundances, implying most likely either an unprecedented influx of extraterrestrial (ET) material or a cosmic impact event that occurred after the last glacial episode. From that layer, we extracted n-diamonds and hexagonal diamonds (lonsdaleite), an accepted ET impact indicator, at abundances of up to about 5×106 times background levels in adjacent younger and older ice. The NDs in the concentrated layer are rounded, suggesting they most likely formed during a cosmic impact through some process similar to carbon-vapor deposition or high-explosive detonation. This morphology has not been reported previously in cosmic material, but has been observed in terrestrial impact material. This is the first highly enriched, discrete layer of NDs observed in glacial ice anywhere, and its presence indicates that ice caps are important archives of ET events of varying magnitudes. Using a preliminary ice chronology based on oxygen isotopes and dust stratigraphy, the ND-rich layer appears to be coeval with ND abundance peaks reported at numerous North American sites in a sedimentary layer, the Younger Dryas boundary layer (YDB), dating to 12.9 ± 0.1 ka. However, more investigation is needed to confirm this association.

scholarly journals Brief communication "The aerophotogrammetric map of Greenland ice masses"

2012 ◽  
Vol 6 (5) ◽  
pp. 3891-3902 ◽  
Author(s):  
M. Citterio ◽  
A. P. Ahlstrøm
Keyword(s):  
High Resolution ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Cover ◽  
Data Sources ◽  
Independent Data ◽  
Change Assessment ◽  
Ice Caps ◽  
Resolution Dataset

Abstract. The PROMICE (Programme for Monitoring of the Greenland Ice Sheet) aerophotogrammetric map of Greenland ice masses is the first high resolution dataset documenting the mid-1980's extent of the Greenland Ice Sheet and all the local glaciers and ice caps. The total glacierized area was 1 804 638 km2 ± 2178 km2, of which 88 083 ± 1240 km2 belonged to local glaciers and ice caps (GIC) substantially independent from the Greenland Ice Sheet. This new result of GIC glacierized area is higher than most previous estimates, and is in line with contemporary findings based on independent data sources. Comparison between our map and the recently released GIMP (Greenland Mapping Project) Ice Cover Mask (Howat and Negrete, 2012) show potential for change assessment studies.

scholarly journals Surface Contours and Flow Pattern of a Perfectly Plastic Three-Dimensional Ice Sheet With Arbitrary Bottom and Edge Topography

1979 ◽  
Vol 24 (90) ◽  
pp. 511-512
Author(s):  
Niels Reeh
Keyword(s):  
Differential Equation ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Ice Streams ◽  
Line Segments ◽  
Perfectly Plastic ◽  
Straight Line ◽  
Sloping Bed ◽  
Set Up ◽  
Arbitrary Curve

Abstract The differential equation determining the elevations of a perfectly plastic three-dimensional steady-state ice sheet is set up. Analytical solutions of the equation are obtained in two simple cases, viz. (1) an ice sheet on a horizontal base with an arbitrary curve as edge and (2) an ice sheet ona plane but sloping bed, with an edge composed of straight-line segments. The solutions are discussed in particular with reference to the development of ice divides and ice streams.

scholarly journals Surface Contours and Flow Pattern of a Perfectly Plastic Three-Dimensional Ice Sheet With Arbitrary Bottom and Edge Topography

1979 ◽  
Vol 24 (90) ◽  
pp. 511-512
Author(s):  
Niels Reeh
Keyword(s):  
Differential Equation ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Ice Streams ◽  
Line Segments ◽  
Perfectly Plastic ◽  
Straight Line ◽  
Sloping Bed ◽  
Set Up ◽  
Arbitrary Curve

AbstractThe differential equation determining the elevations of a perfectly plastic three-dimensional steady-state ice sheet is set up. Analytical solutions of the equation are obtained in two simple cases, viz. (1) an ice sheet on a horizontal base with an arbitrary curve as edge and (2) an ice sheet ona plane but sloping bed, with an edge composed of straight-line segments. The solutions are discussed in particular with reference to the development of ice divides and ice streams.

scholarly journals Modelling large-scale ice-sheet–climate interactions following glacial inception

2012 ◽  
Vol 8 (1) ◽  
pp. 169-213 ◽  
Author(s):  
J. M. Gregory ◽  
O. J. H. Browne ◽  
A. J. Payne ◽  
J. K. Ridley ◽  
I. C. Rutt
Keyword(s):  
General Circulation ◽  
Regional Climate ◽  
Computational Cost ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Canadian Arctic ◽  
Circulation Model ◽  
Local Cooling ◽  
North West ◽  
North East

Abstract. We have coupled the FAMOUS global AOGCM (atmosphere–ocean general circulation model) to the Glimmer thermomechanical ice-sheet model in order to study the development of ice-sheets in North-East America (Laurentia) and North-West Europe (Fennoscandia) following glacial inception. This first use of a coupled AOGCM-ice-sheet model for a study of change on long palæoclimate timescales is made possible by the low computational cost of FAMOUS, despite its inclusion of physical parameterisations of a similar complexity to those of higher-resolution AOGCMs. With the orbital forcing of 115 ka BP, FAMOUS-Glimmer produces ice-caps on the Canadian Arctic islands, on the north-west coast of Hudson Bay, and in Southern Scandinavia, which over 50 ka grow to occupy the Keewatin region of the Canadian mainland and all of Fennoscandia. Their growth is eventually halted by increasing coastal ice discharge. The expansion of the ice-sheets influences the regional climate, which becomes cooler, reducing the ablation, while precipitation increases. Ice accumulates in places that initially do not have positive surface mass balance. The results suggest the possibility that the Laurentide glaciation could have begun on the Canadian Arctic islands, producing a regional climate change that caused or enhanced the growth of ice on the mainland. The increase in albedo due to snow and ice cover is the dominant feedback on the area of the ice-sheets, and acts rapidly, whereas the feedback of topography on SMB does not become significant for several centuries, but eventually has a large effect on the thickening of the ice-sheets. These two positive feedbacks are mutually reinforcing. In addition the change in topography perturbs the tropospheric circulation, producing some reduction of cloud and mitigating the local cooling along the margin of the Laurentide ice-sheet. Our experiments demonstrate the importance and complexity of the interactions between ice-sheets and local climate.

scholarly journals An advancing glacier in a recessive ice regime: Berlingske Bræ, North-West Greenland

1969 ◽  
Vol 20 ◽  
pp. 79-82 ◽  
Author(s):  
Peter R. Dawes ◽  
Dirk Van As
Keyword(s):  
Climate Change ◽  
Mass Balance ◽  
Ice Sheet ◽  
West Greenland ◽  
North West ◽  
Ice Caps ◽  
The World ◽  
International Attention ◽  
Ice Regime ◽  
Inland Ice

Greenland is receiving unprecedented international attention, both in scientific and political circles. Characterised by a central ice sheet up to 3.4 km thick (Inland Ice), numerous ice caps and hundreds of outlet glaciers debouching into the surrounding oceans, Greenland supports the second largest ice mass in the world. Analysis of glacier movements, melt rates and ice loss to the sea, provide data with which to assess mass balance changes and thereby predict global sealevel rise. Thus Greenland plays a central role in the current worldwide debate on climate change.

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