Pleistocene Ice Sheets Research Articles

Subglacial Sediment Dispersal and till Composition

Dispersal of subglacial sediment down-ice from its bedrock source assumes the form of a negative exponential decay curve. Dispersal decay curves can be quantified by their decay constants, half-distances ( = half-lives), and total transport distances. Mapped dispersal decay curves associated with Pleistocene ice sheets in North America and Europe identify several scales of dispersal, ranging from local (kilometers) to continental (100's to 1000's km) scales. Till composition reflects the various scales of dispersal. Local scales (short transport distances) result in tills that reflect underlying bedrock, whereas continental scales (long transport distances) result in tills derived largely from sources far up-ice. A number of parameters proposed as influencing subglacial sediment dispersal and transport distances do not explain the range of scales observed, although they may explain minor variations (kilometers) in transport distances. Topography and basal ice velocity (sliding velocity) are interpreted as primary controls on the observed scales of transport. Topography directs transport paths of basal debris toward topographic lows, resulting in longer transport distances through depressions than across intervening obstructions. Sliding velocities determine rates of entrainment, dilution, and deposition. Relatively high sliding velocities decrease mixing rates by transporting basal debris and result in long transport distances. Relatively low sliding velocities result in short transport distances, as debris is lodged, new debris is entrained, and mixing rates are high.

Remnants of the Pleistocene ice sheets in the permafrost zone as an object for paleoglaciological research

Abstract Glaciogenic ice/sediment complexes which are the remnants of basal layers of the Pleistocene ice sheets and are widespread in the north of Western Siberia are the product of incomplete deglaciation. They are protected from melting by a thin cover mainly composed of till, fluvioglacial sands, solifluction deposits, etc. The main peculiarity of these complexes is the evidence of syngenetic glaciodynamic processes common to both the ice and the sediment components of the complex. They consist primarily of frozen till containing ice cement and lenses of relict glacier ice as well as glaciotectonites, i.e., plucked material from the glacier bed, and dynamorphic ice of non‐glacial origin. The presence of glaciogenic ice/sediment complexes indicates the former existence or regeneration of permafrost beneath the ice sheets. Their structure reflects the nature of ice motion and its impact on the glacier bed and testifies to the great significance of ground ice to glaciodynamic processes. It also indicates...

Melt-Water Drainage Pattern of Composite Glaciers

AbstractMedial moraines and lineations on the surface of composite glaciers enable the detection of structural and hydrological features. A study of the composite glacier Breidamerkurjökull, south Iceland, indicates relationships between subglacial waterways, ice structure in the junction area, and development of the glacier terminus. First, rivers are situated in or near medial moraines because melt water percolates to the bed and moves from there with the subglacial rivers mainly in the direction of ice flow. Secondly, the contact between two feeder glaciers sometimes forms an angle at the glacier terminus. Then the meltwater river escaping from the contact, generally in a radial direction (away from the glacier front), during the retreat will be transferred to the front of the first receding glacier. The drainage of the contact zone then changes from a radial to a tangential direction, destroying the terminal moraines of the recession stages.Similar relations are found in relics of Pleistocene ice sheets, two examples of which are compared. The huge subglacial channel of the Münsterländer Kiessandzug-Esker below the ice sheet of the Saalian glaciation in the Münsterland, north-west Germany, was formed in the ice-flow direction. It therefore gives details of the morphology and of the great ice-dammed lake east of the Teutoburger Wald ridge. At the contact between the Norwegian and Baltic Sea glaciers, the terminus formed an angle during the maximum extent of the Weichselian glaciation in northern Jutland. During retreat, the Norwegian glacier receded first. The large melt-water river escaping from the contact between both glaciers had formed the huge Karup Sandur during the maximum, but now, during the recession, it changed to the front of the Norwegian ice, destroying the recession moraines there.

Melt-Water Drainage Pattern of Composite Glaciers

Abstract Medial moraines and lineations on the surface of composite glaciers enable the detection of structural and hydrological features. A study of the composite glacier Breidamerkurjökull, south Iceland, indicates relationships between subglacial waterways, ice structure in the junction area, and development of the glacier terminus. First, rivers are situated in or near medial moraines because melt water percolates to the bed and moves from there with the subglacial rivers mainly in the direction of ice flow. Secondly, the contact between two feeder glaciers sometimes forms an angle at the glacier terminus. Then the meltwater river escaping from the contact, generally in a radial direction (away from the glacier front), during the retreat will be transferred to the front of the first receding glacier. The drainage of the contact zone then changes from a radial to a tangential direction, destroying the terminal moraines of the recession stages. Similar relations are found in relics of Pleistocene ice sheets, two examples of which are compared. The huge subglacial channel of the Münsterländer Kiessandzug-Esker below the ice sheet of the Saalian glaciation in the Münsterland, north-west Germany, was formed in the ice-flow direction. It therefore gives details of the morphology and of the great ice-dammed lake east of the Teutoburger Wald ridge. At the contact between the Norwegian and Baltic Sea glaciers, the terminus formed an angle during the maximum extent of the Weichselian glaciation in northern Jutland. During retreat, the Norwegian glacier receded first. The large melt-water river escaping from the contact between both glaciers had formed the huge Karup Sandur during the maximum, but now, during the recession, it changed to the front of the Norwegian ice, destroying the recession moraines there.

A glaciofluvial origin for drumlins of the Livingstone Lake area, Saskatchewan

The Livingstone Lake drumlin field of northern Saskatchewan is on the Athabasca Plains. It is draped over high ground underlain by the Precambrian Athabasca Sandstone. The drumlins occur in spindle, parabolic, and transverse asymmetrical forms. A map of individual drumlins shows that features of similar form occur together. The drumlins are related on a regional scale to even larger landforms. There is also an arrangement of drumlins in streams parallel to the assumed flow direction. These patterns illustrate spatial organisation of the drumlin-forming flows. The Livingstone Lake drumlins are closely related to tunnel valleys, large crescentic scours, and eskers. Exposed bedrock reveals widespread scalloping and sichelwannen. An argument is made that drumlins are related to these glaciofluvial forms but were created at different times and by different flows than those forming small-scale flutings and other lodgment features. Sediments within the drumlins are mainly primary water-sorted deposits some of which were resedimented by mass movements. There are also large, striated boulders. Deposition in subglacial cavities is suggested. This explanation is supported by a comparison of patterns and forms of erosional marks produced by wind and water and the implied form of the subglacial cavities. The Livingstone Lake drumlins are considered to represent infillings of cavities developed by meltwater erosion of the underside of glaciers. This conclusion stresses the geomorphic and sedimentologic importance of subglacial meltwater. It has important implications for the behaviour of the large Pleistocene ice sheets and the interpretation of glacigenic sediments. Consequently, it has direct bearing on glacial stratigraphy and chronology.

Recent global changes in sealevel

Tide gauge records indicate that a global rise in sealevel has occurred over the past 80 years at a rate of about 1.5 mm yr−1. Because of the poor geographical distribution of the tide gauges, this rise may be partly a consequence of a redistribution of water in the oceans without there being an increase in volume of the oceans. A principal contribution to this redistribution arises from the ongoing rebound of the crust to the melting of the Pleistocene ice sheets, a contribution that is of global significance even far from the limits of the original ice sheets. Model calculations indicate that this contribution may explain between 30 and 50% of the published estimates of the secular rise in sealevel.

Glaciation of the continental shelves (part I)

Over the past two decades, in no small part due to the author's efforts, considerable evidence has accumulated to indicate that a significant proportion of the total mass of the Pleistocene ice sheets lay on the continental shelves rather than on the continents per se. This fact has extremely far‐reaching implications for the whole area of mass and energy exchange between the atmosphere, the ice sheets and the ocean and for the rate and mechanisms of ice sheet formation and disintegration. The present study represents an overview of the present state of knowledge of these “marine”; ice sheets, sitting on the continental shelves. This first part provides a survey of all such ice sheets during the Wurm glaciation, in which the author examines the available evidence of the extent and thickness of such ice sheets. Particular attention is focused on the Antarctic Ice Sheet since not only were its “marine”; components more extensive during the Wurm, but since the West Antarctic Ice Sheet at the present time pro...

Ice-Sheet Modeling

This paper presents a review of the ice-sheet mechanics behind the modeling work of Pleistocene ice sheets driven by astronomical (Milankovitch) forcing.

Ice-Sheet Modeling

This paper presents a review of the ice-sheet mechanics behind the modeling work of Pleistocene ice sheets driven by astronomical (Milankovitch) forcing.

On the reconstruction of pleistocene ice sheets: A review

Pleistocene ice sheets can be reconstructed through three separate approaches: (1) Evidence based on glacial geological studies, such as erratic trains, till composition, crossing striations and exposures of multiple tills/nonglacial sediments. (2) Reconstructions based on glaciological theory and observations. These can be either two- or three-dimensional models; they can be constrained by ‘known’ ice margins at specific times; or they can be ‘open-ended’ with the history of growth and retreat controlled by parameters resting entirely within the model. (3) Glacial isostatic rebound after deglaciation provides a measure of the distribution of mass (ice) across a region. A ‘best fit’ ice sheet model can be developed that closely approximates a series of relative sea level curves within an area of a former ice sheet; in addition, the model should also provide a reasonable sea level fit to relative sea level curves at sites well removed from glaciation. This paper reviews some of the results of a variety of ice sheet reconstructions and concentrates on the various attempts to reconstruct the ice sheets of the last (Wisconsin, Weischelian, Würm, Devensian) glaciation. Evidence from glacial geology suggests flow patterns at variance with simple, single-domed ice sheets over North America and Europe. In addition, reconstruction of ice sheets from glacial isostatic sea level data suggests that the ice sheets were significantly thinner than estimates based on 18 ka equilibrium ice sheets (cf. Denton and Hughes, 1981). The review indicates it is important to differentiate between ice divides, which control the directions of glacial flow, and areas of maximum ice thickness, which control the glacial isostatic rebound of the crust upon deglaciation. Recent studies from the Laurentide Ice Sheet region indicate that the center of mass was not over Hudson Bay; that a major ice divide lay east of Hudson Bay so that flow across the Hudson Bay and James Bay lowlands was from the northeast; that Hudson Bay was probably open to marine invasions two or three times during the Wisconsin Glaciation; and that the Laurentide Ice Sheet was thinner than an equilibrium reconstruction would suggest.

Studies of the Antarctic and Present-Day Concepts of Global Glaciation

Antarctic researches of the last decades have provided new facts which have made scientists change their ideas. The researches have shown a great difference between the history of the Antarctic and the northern hemisphere glaciation. The former is very old and stable, while the latter was ephemeral. An analogous one to the Antarctic ice sheet in the northern hemisphere is the Greenland inland ice. Both ice sheets are of continental-insular type; the Pleistocene ice sheets were of continental type proper. Icethickness measurements showed the topography of the bed under Antarctic ice and revealed a special type of ice sheet lying partly on the sea-floor: the West Antarctic continental-marine ice sheet. Such ice sheets could exist in the northern hemisphere too. They were especially unstable and their formation and destruction could serve as a triggering mechanism in alternating glacials and interglacials. The main concept is: all the great climatic variations during the Pleistocene were glacioclimatic ones where the feedback mechanism was the most important factor. But there are many details which are uncertain. The Antarctic and Greenland ice sheets are the key regions to research so that problems of glacioclimatology could be solved.

Studies of the Antarctic and Present-Day Concepts of Global Glaciation

Antarctic researches of the last decades have provided new facts which have made scientists change their ideas. The researches have shown a great difference between the history of the Antarctic and the northern hemisphere glaciation. The former is very old and stable, while the latter was ephemeral. An analogous one to the Antarctic ice sheet in the northern hemisphere is the Greenland inland ice. Both ice sheets are of continental-insular type; the Pleistocene ice sheets were of continental type proper. Icethickness measurements showed the topography of the bed under Antarctic ice and revealed a special type of ice sheet lying partly on the sea-floor: the West Antarctic continental-marine ice sheet. Such ice sheets could exist in the northern hemisphere too. They were especially unstable and their formation and destruction could serve as a triggering mechanism in alternating glacials and interglacials. The main concept is: all the great climatic variations during the Pleistocene were glacioclimatic ones where the feedback mechanism was the most important factor. But there are many details which are uncertain. The Antarctic and Greenland ice sheets are the key regions to research so that problems of glacioclimatology could be solved.

Relative sea levels from tide-gauge records

Mean annual sea levels at 247 tide-gauge stations of the world exhibit a general rise of relative sea level of about 3 mm/year during the past 40 years. In contrast, general uplift of the land is typical of high northern latitudes, where unloading of the crust by melt of Pleistocene ice sheets is significant. Erratic movements are typical of belts having crustal overthrusting and active volcanism. Short-term (5- and 10-year) records reveal recent changes in rates, but such short time spans may be so influenced by climatic cycles that identification of new trends is difficult, especially with the existing poor distribution and reporting of tide-gauge data.

Stability of Temperate Ice Caps and Ice Sheets Resting on Beds of Deformable Sediment

AbstractAlthough theories of glacier movement generally assume that glaciers flow over rigid rock beds, there are many places where glaciers rest on beds of deformable sediment, and the great Pleistocene ice sheets which extended from time to time over much of Northern Europe and North America were largely underlain by such beds. Observations show that a large proportion of the forward movement of a glacier lying on such a bed may be contributed by deformation of the bed rather than the glacier. A theory is developed in which the glacier surface profile is related to the hydraulic and strength properties of potentially deformable bed materials. If these have a high hydraulic transmissibility, melt water is readily discharged sub-glacially, the bed is stable, and the profile is a normal parabolic one, governed by the rhcological properties of ice. If bed transmissibility is low, water pressures build up, the bed begins to deform, and a lower equilibrium profile will develop, so that in an extreme case the glacier approximates to a thin flat sheet, similar to an ice shelf. It is suggested that such behaviour may have occurred at the margins of large Pleistocene ice sheets over North America and Europe, and evidence in support of this is drawn from the reconstructed shapes of these ice margins, anomalously small amounts of isostatic rebound, anomalously high retreat-rates, and the presence of glaciotcctonic structures. Reasons are suggested to explain why this behaviour should have been important for Pleistocene glaciers which penetrated into currently temperate latitudes but does not appear to be important in large modern glaciers.

Stability of Temperate Ice Caps and Ice Sheets Resting on Beds of Deformable Sediment

AbstractAlthough theories of glacier movement generally assume that glaciers flow over rigid rock beds, there are many places where glaciers rest on beds of deformable sediment, and the great Pleistocene ice sheets which extended from time to time over much of Northern Europe and North America were largely underlain by such beds. Observations show that a large proportion of the forward movement of a glacier lying on such a bed may be contributed by deformation of the bed rather than the glacier. A theory is developed in which the glacier surface profile is related to the hydraulic and strength properties of potentially deformable bed materials. If these have a high hydraulic transmissibility, melt water is readily discharged sub-glacially, the bed is stable, and the profile is a normal parabolic one, governed by the rhcological properties of ice. If bed transmissibility is low, water pressures build up, the bed begins to deform, and a lower equilibrium profile will develop, so that in an extreme case the glacier approximates to a thin flat sheet, similar to an ice shelf. It is suggested that such behaviour may have occurred at the margins of large Pleistocene ice sheets over North America and Europe, and evidence in support of this is drawn from the reconstructed shapes of these ice margins, anomalously small amounts of isostatic rebound, anomalously high retreat-rates, and the presence of glaciotcctonic structures. Reasons are suggested to explain why this behaviour should have been important for Pleistocene glaciers which penetrated into currently temperate latitudes but does not appear to be important in large modern glaciers.

Oxygen Isotope Composition of Subglacially Precipitated Calcite: Possible Paleoclimatic Implications

Isotopic analyses of subglacially precipitated calcite from near a modern temperate glacier show that the delta(18)O (= (18)O/(16)O relative to standard mean ocean water) of the calcite records the delta(18)O of the ice from that glacier. It may therefore be possible to determine the delta(18)O of Pleistocene ice sheets on the basis of isotopic analyses of calcite formed under that ancient ice. This, in turn, would allow estimation of the delta(18)O of Pleistocene oceans and correction of the paleotemperature scale based on foraminiferal oxygen isotopic analyses.

Basal till fabrics of modern alpine glaciers

Basal-till fabrics from three alpine glaciers ranging in length from 2.5 to 7.5 km were analyzed. Fabric patterns are similar to those reported from basal tills of lowland glaciers: a single mode parallel to ice-flow direction and a preference for up-glacier dips. Eigenvalue analysis, however, showed that the preferred planes of the a axes are weaker than those reported from one Pleistocene ice sheet. Two methods of analysis indicated that there is little relation between clast orientation and clast size or shape.

Volcanic triggering of glaciation

AN instantaneous glaciation model for the formation of the large Pleistocene ice sheets has been proposed by Flohn1 and by Ives et al2. It depends on the sudden buildup of a permanent snow cover over sub-Arctic upland plateaux including Baffin Island, Ungava, Labrador and Keewatin, Melville Peninsula, and the Finnmark Plateau and upland Sweden. The crucial event in this sudden snow buildup is the survival of snow over a large area for a single summer which then results in a series of feedback reactions leading to the establishment of permanent snowfields and, subsequently, icefields. I suggest here that such a survival could have resulted from one or several closely spaced massive volcanic ash eruptions.

Some aspects of late Pleistocene-Holocene drainage of the River Thames in the eastern part of the London Basin

Since 1967 the area of the Thames Estuary has been extensively surveyed using reflexion seismic techniques. The interpretation of these records coupled with the logs and samples from some 140 boreholes has led to the reconstruction of the Late Pleistocene/Early Holocene palaeodrainage pattern of the River Thames. The relationship of this drainage system to the tectonic pattern would indicate that there has been Late Pleistocene re-emphasis of the existing dominant structures. Also a large NW—SE trending monocline would appear to be still a positive area within this subsiding sector of SE England. Some evidence for the existence of a Late Pleistocene ice-sheet is presented. That this might well have dammed the existing drainage systems creating a large lake (Lake Tamesis) is a possibility that requires further investigation.

Sea bed topography off north east Scotland

Abstract From an analysis of recent Admiralty echo‐sounding information two major topographic types are identified in the offshore area between Newburgh and Montrose. They are separated by a major break of slope at about 30 fathoms. Above this break two subzones are found, respectively offshore from modern rocky and sediment‐dominated coasts. The origin and age of the macro‐topography and the individual features are discussed. The slope break is probably related to the junction of crystalline and sedimentary rocks. The ‘deeps’ are superimposed basal glacial meltwater channels formed beneath a Pleistocene ice sheet. Fossil deltas and alluvial fans are found in the large bays. The benches are of Pleistocene marine origin. No well‐defined sediment patterns are found.