scholarly journals Late Wisconsinan and Holocene History of the Laurentide Ice Sheet*

2008 ◽  
Vol 41 (2) ◽  
pp. 237-263 ◽  
Author(s):  
Arthur S. Dyke ◽  
Victor K. Prest
Keyword(s):  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Ice Streams ◽  
The West ◽  
Ice Shelves ◽  
Sea Level Oscillations ◽  
History Of ◽  
Ice Retreat ◽  
Late Wisconsinan ◽  
And Migration

AbstractEleven paleogeographic maps and a summary ice retreat map outline the history of advance, retreat, and readvances of the Laurentide Ice Sheet along with associated changes in proglacial drainage and relative sea level oscillations for Late Wisconsinan and Holocene times. The text outlines pertinent chronological control and discusses the paleoglaciology of the ice sheet, with attention to location and migration of ice divides, their attendant domes and saddles, and to ice streams, ice shelves, and mechanisms of déglaciation. At 18 ka the ice sheet consisted of 3 sectors with an interlocked system of ice divides joined at intersector saddles. A throughgoing superdivide is recognized and named the Trans Laurentide Ice Divide. The ice sheet retreated slowly from 18 to 13 ka, mainly along the west and south margins, but still held a near maximum configuration at 13 ka. A regional change in flow pattern over the Prairies just before 14 ka is thought to represent a large reduction in ice volume, but not in extent, and likely was triggered by a switch from nondeforming to deforming bed conditions. Retreat between 13 and 8 ka was vastly more rapid in the west than in the east, which resulted in eastward migration of the divide system of Keewatin Ice but relatively static divides of Labrador and Foxe Ice. By 10 ka the Trans Laurentide Ice Divide had been fragmented as Hudson Ice became increasingly autonomous. By 8 ka Hudson Ice had disappeared, little ice was left in Keewatin, but Foxe Ice still held its near maximum configuration and Labrador Ice was still larger than Foxe Ice. Repeated surging along aquatic margins and calving back of margins thinned by surging probably was the most important mechanism of deglaciation of Keewatin and Hudson Ice. The core of Foxe Ice disintegrated at 7 ka but retreat and readvance of Foxe Ice remnants continued throughout the Holocene.

scholarly journals Objective Reconstructions of the Late Wisconsinan Laurentide Ice Sheet and the Significance of Deformable Beds

2007 ◽  
Vol 39 (3) ◽  
pp. 229-238 ◽  
Author(s):  
D. A. Fisher ◽  
N. Reeh ◽  
K. Langley
Keyword(s):  
Yield Stress ◽  
Flow Direction ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Hudson Bay ◽  
Ice Streams ◽  
Ice Flow ◽  
Surface Slopes ◽  
Late Wisconsinan

ABSTRACT A three dimensional steady state plastic ice model; the present surface topography (on a 50 km grid); a recent concensus of the Late Wisconsinan maximum margin (PREST, 1984); and a simple map of ice yield stress are used to model the Laurentide Ice Sheet. A multi-domed, asymmetric reconstruction is computed without prior assumptions about flow lines. The effects of possible deforming beds are modelled by using the very low yield stress values suggested by MATHEWS (1974). Because of low yield stress (deforming beds) the model generates thin ice on the Prairies, Great Lakes area and, in one case, over Hudson Bay. Introduction of low yield stress (deformabie) regions also produces low surface slopes and abrupt ice flow direction changes. In certain circumstances large ice streams are generated along the boundaries between normal yield stress (non-deformable beds) and low yield stress ice (deformabie beds). Computer models are discussed in reference to the geologically-based reconstructions of SHILTS (1980) and DYKE ef al. (1982).

A Model for Holocene Retreat of the West Antarctic Ice Sheet

1978 ◽  
Vol 10 (2) ◽  
pp. 150-170 ◽  
Author(s):  
Robert H. Thomas ◽  
Charles R. Bentley
Keyword(s):  
Sea Level ◽  
Ice Sheet ◽  
Ice Shelf ◽  
Ice Streams ◽  
The West ◽  
Antarctic Ice Sheet ◽  
West Antarctic Ice Sheet ◽  
Ice Shelves ◽  
Ross Ice Shelf ◽  
West Antarctic

Marine ice sheets are grounded on land which was below sea level before it became depressed under the ice-sheet load. They are inherently unstable and, because of bedrock topography after depression, the collapse of a marine ice sheet may be very rapid. In this paper equations are derived that can be used to make a quantitative estimate of the maximum size of a marine ice sheet and of when and how rapidly retreat would take place under prescribed conditions. Ice-sheet growth is favored by falling sea level and uplift of the seabed. In most cases the buttressing effect of a partially grounded ice shelf is a prerequisite for maximum growth out to the edge of the continental shelf. Collapse is triggered most easily by eustatic rise in sea level, but it is possible that the ice sheet may self-destruct by depressing the edge of the continental shelf so that sea depth is increased at the equilibrium grounding line.Application of the equations to a hypothetical “Ross Ice Sheet” that 18,000 yr ago may have covered the present-day Ross Ice Shelf indicates that, if the ice sheet existed, it probably extended to a line of sills parallel to the edge of the Ross Sea continental shelf. By allowing world sea level to rise from its late-Wisconsin minimum it was possible to calculate retreat rates for individual ice streams that drained the “Ross Ice Sheet.” For all the models tested, retreat began soon after sea level began to rise (∼15,000 yr B.P.). The first 100 km of retreat took between 1500 and 2500 yr but then retreat rates rapidly accelerated to between 0.5 and 25 km yr−1, depending on whether an ice shelf was present or not, with corresponding ice velocities across the grounding line of 4 to 70 km yr−1. All models indicate that most of the present-day Ross Ice Shelf was free of grounded ice by about 7000 yr B.P. As the ice streams retreated floating ice shelves may have formed between promontories of slowly collapsing stagnant ice left behind by the rapidly retreating ice streams. If ice shelves did not form during retreat then the analysis indicates that most of the West Antarctic Ice Sheet would have collapsed by 9000 yr B.P. Thus, the present-day Ross Ice Shelf (and probably the Ronne Ice Shelf) serves to stabilize the West Antarctic Ice Sheet, which would collapse very rapidly if the ice shelves were removed. This provides support for the suggestion that the 6-m sea-level high during the Sangamon Interglacial was caused by collapse of the West Antarctic Ice Sheet after climatic warming had sufficiently weakened the ice shelves. Since the West Antarctic Ice Sheet still exists it seems likely that ice shelves did form during Holocene retreat. Their effect was to slow and, finally, to halt retreat. The models that best fit available data require a rather low shear stress between the ice shelf and its sides, and this implies that rapid shear in this region encouraged the formation of a band of ice with a preferred crystal fabric, as appears to be happening today in the floating portions of fast bounded glaciers.Rebound of the seabed after the ice sheet had retreated to an equilibrium position would allow the ice sheet to advance once more. This may be taking place today since analysis of data from the Ross Ice Shelf indicates that the southeast corner is probably growing thicker with time, and if this persists then large areas of ice shelf must become grounded. This would restrict drainage from West Antarctic ice streams which would tend to thicken and advance their grounding lines into the ice shelf.

scholarly journals Relict Late Wisconsinan Dune Fields of the Northern Great Plains, Canada*

2006 ◽  
Vol 58 (2-3) ◽  
pp. 323-336 ◽  
Author(s):  
Stephen A. Wolfe ◽  
David J. Huntley ◽  
Jeff Ollerhead
Keyword(s):  
Boreal Forest ◽  
Great Plains ◽  
Sand Dunes ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Northern Great Plains ◽  
The West ◽  
Air Mass ◽  
Late Wisconsinan ◽  
Dune Activity

Abstract Late Wisconsinan dune activity is investigated within the present-day boreal forest and parkland regions of the northern Great Plains, Canada, to extend the understanding of the spatial and temporal eolian record. Optical ages from stabilized sand dunes document the timing of past activity. Eolian activity ranges from about 16 ka in west-central Alberta to 9 ka in northwestern Saskatchewan. Between about 16 and 13 ka, dune activity in central Alberta occurred in an ice-proximal tundra setting along the margins of the Laurentide and Cordilleran ice sheets. Predominant dune-forming winds were from the west and northwest. Dune activity continued in this area between about 13 and 11 ka within parkland and grassland settings as the Laurentide Ice Sheet retreated to the northeast. Winds continued to blow from the west and northwest, and the climate was likely influenced by an increasingly dominant Pacific air mass. Also beginning at about 13 ka, dune-forming winds along the margins of the retreating Laurentide Ice Sheet were influenced by anticyclonic winds from the southeast that were maintained until about 9 ka. As the Laurentide Ice Sheet retreated, these southeasterly anticyclonic winds were successively replaced by winds from the northwest associated with the Pacific air mass. Dune activity across the region terminated in a time-transgressive manner from the southwest, at about 11 ka, to the northeast, at about 9 ka, with the establishment of boreal forest vegetation and reduced wind strength.

scholarly journals First recognition of a Laurentide Ice Stream : Robert Bell on Hudson Strait

2010 ◽  
Vol 61 (2-3) ◽  
pp. 211-215 ◽  
Author(s):  
Ian A. Brookes
Keyword(s):  
Ice Sheet ◽  
Late Glacial ◽  
Laurentide Ice Sheet ◽  
Hudson Bay ◽  
Baffin Island ◽  
Ice Streams ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
Ice Stream ◽  
Late Wisconsinan

Abstract In papers published in 1895 and 1901, and in undated notes for a 1907 paper he did not deliver or publish, Robert Bell of the Geological Survey of Canada interpreted the pattern of glacial striae, stossing of rock knobs, and surficial sediment composition along the margins of Hudson Strait, between Labrador, Ungava Bay and Baffin Island, as evidence of what he called an ice-stream, a long river-like glacier, fed from Hudson Bay and Foxe Basin, that had moved eastward along the Strait during the Late Glacial period. This was the earliest mention of such a glaciological feature within the Laurentide Ice Sheet (LIS). It was not until ice-streams were recognized in the West Antarctic Ice Sheet in the 1970’s that Bell’s concept was revived in the next decade and subsequently, in recognition of several ice-streams within the Late Wisconsinan LIS.

Late Wisconsinan and Holocene history of southwestern Saskatchewan

1994 ◽  
Vol 31 (12) ◽  
pp. 1822-1837 ◽  
Author(s):  
Rudy W. Klassen
Keyword(s):  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Glacial Lakes ◽  
Grassland Vegetation ◽  
Southern Limit ◽  
Northern Margin ◽  
The North ◽  
Proglacial Lakes ◽  
History Of ◽  
Late Wisconsinan

The Late Wisconsinan Laurentide Ice Sheet reached the limit of glaciation along the north-facing slope of the unglaciated part of the Cypress Hills nunatak, but elsewhere around the Cypress Hills and Wood Mountain uplands of southwestern Saskatchewan it did not reach the limit of glaciation. An interval of deglaciation was followed by a readvance of the ice sheet, about 15 ka, to a position near the Late Wisconsinan limit, and was marked by strong flow of Keewatin ice from the north and weaker flow of Hudson ice from the northeast. Final deglaciation resulted in the formation of glacial lakes around the Cypress Hills nunatak. A network of ice-marginal and subglacial trenches, presently occupied by the Frenchman Valley and its tributaries, was formed when these lakes drained along, over, and under ice towards the western part of the Wood Mountain Upland to the east. The main trench joined an ancestral part of Frenchman Valley along the ice-free southern slopes of Wood Mountain Upland. Meltwater from the ice bordering the northern margin of the upland drained southward, excavating trenches across the highest parts of the upland and deepening ancestral valleys across the southern slopes. A succession of proglacial lakes fronted parts of the ice margin as it retreated downslope to the north. The area was deglaciated about 13.5 ka. The southern limit of a north to south forest–grassland transition was established by 13 ka along the regional drainage divide across the study area. Prairie grassland vegetation covered the southern slopes of the uplands and forests of deciduous and coniferous trees covered the highest parts of uplands and drift-mantled parts of the continental glacier to the north. The belt of forest–grassland transition had shifted well to the north of the study area by 9 ka, and a climate that was warmer and drier than at present continued to about 5 ka, when conditions became somewhat cooler.

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