scholarly journals ˝Stagnant-Ice˝ Topography and its Relation to Drumlin Genesis, with Reference to South-Central Ulster (Abstract Only)

1981 ◽  
Vol 2 ◽  
pp. 183-184 ◽  
Author(s):  
G. F. Dardis
Keyword(s):  
Thermal Regime ◽  
Thermal State ◽  
Ice Sheet ◽  
Glacial Maximum ◽  
Accumulation Zone ◽  
South Central ◽  
Ice Accumulation ◽  
Melt Water ◽  
Late Weichselian ◽  
High Level

Previous work on drumlin genesis considers the problem at the ice-rock interface and ignores the environmental significance of inter-drumlin sediments and superimposed landform associations. Present work by the author examines two drumlin fields in south-central Ulster, Northern Ireland, and proposes a mechanism of drumlin formation which is time-dependent and results from changes of thermal regime through time.Drumlin exposures in south-central Ulster reveal a particular facies association in drumlin tills showing considerable lithological variation; striae, roches moutonnées, and basal lodgement till beneath drumlins indicate an event early in the last glaciation characterized by a temperate thermal regime. This association is overlain by a basal melt-out till, characterized by striated clasts and containing numerous pockets of stratified sediment. The melt-out till is related to changes in provenance of erratics in the till, associated with a shift in the centre of ice accumulation during the course of glaciation.The stratigraphy suggests that a considerable amount of drift was formed prior to drumlin formation and that a change of thermal state may have characterized the shift in the ice accumulation zone. This change is also suggested by evidence of high-level melt-water transport in the Sperrin Mountains, indicating a sub-polar or sub-temperate thermal regime existing in the early part of the late Weichselian deglaciation.A model based on thermal convection theory of polar ice sheets (Hughes 1976) is proposed in an attempt to relate the juxtaposition of drumlins and glaciofluvial assemblages in southcentral Ulster. In an ice accumulation zone, as characterized this area during the late Weichselian glacial maximum, advection is generally absent and convection is the dominant flow in the ice sheet. In this environment motive ice may develop in the basal zone, resulting from vertical buoyancy stresses acting downward on a column in the ice sheet. This flow environment may coexist within an ice sheet which is "stagnant" and perhaps subject to supraglacial insolation melting, depending on the overall climatic regime. If convection is dominant, it may create areas of basal compression and tension, acting to establish co-existing zones of "hot" and "cold" ice; hot-ice zones are subject to basal erosion, leading to migration of subglacial sediments to points of englacial storage above the density inversion layer. Cold-ice zones act to protect underlying sediments and result in isolation of drift nuclei, protection being afforded by the yield strength of frozen drift being greater than either debris-laden or clean ice.If the model is tenable, it seems likely that drift nucleation in drumlin fields may have been accomplished before the drumlin formation or streamlining event. Vertical migration of subglacial materials also explains the similarity of sediment sources of glacigenic and glaciofluvial assemblages which occur in juxtaposition, and, without reduction in drumlin density. The sequence of events in south-central Ulster may be summarized as follows: (1)Build-up of ice, associated with sub-drumlin erosion forms and basal lodgement till. Change of thermal regime from temperate to sub-temperate.(2)Shift in the ice-accumulation zone from highland to lowland, indicated by erratic dispersals of glaciogenic sediments. Change of thermal regime from sub-polar to polar at the late Weichselian glacial maximum.(3)High-level insolation melting with concomitant basal freezing. Initiation of polygonal array in basal zone. Change of thermal regime from polar to sub-polar or sub-temperate.(4)Down-wastage of ice and nunatak formation. Formation of high-level melt-water phenomena. Deposition of basal melt-out till. Further development of basal polygonal array. Till nuclei established and englacial sediment isolated. Change of thermal regime from sub-polar to sub-temperate.(5)Change of thermal state to temperate. Uncoupling of ice from bedrock. Streamlining of till nuclei and reworking of englacial sediment by melt water.(6)Final disintegration of ice.

scholarly journals Late Weichselian thermal state at the base of the Scandinavian Ice Sheet

2019 ◽  
Author(s):  
Dmitry Y. Demezhko ◽  
Anastasia A. Gornostaeva ◽  
Alexander N. Antipin
Keyword(s):  
Thermal State ◽  
Ice Sheet ◽  
Ground Surface ◽  
Substantial Part ◽  
Temperature Pattern ◽  
Glacial Cycle ◽  
Surface Temperatures ◽  
Scandinavian Ice Sheet ◽  
Late Weichselian ◽  
The Last Glacial

Abstract. Geothermal estimates of the ground surface temperatures for the last glacial cycle in Northern Europe has been analyzed. During the Middle and Late Weichselian (55–12 kyr BP) a substantial part of this area was covered by the Scandinavian Ice Sheet. The analysis of geothermal data has allowed reconstructing limits of the ice sheet extension and its basal thermal state in the Late Weichselian. Ground surface temperatures outside the ice sheet were extremely low (from −8 to −18 °C). Within the ice sheet, there were both thawed and frozen zones. The revealed temperature pattern is generally consistent with the modern one for the ground surface temperatures in Greenland that makes it possible to consider these ice sheets as analogues. The anomalous climatically induced surface heat flux and orbital insolation of the Earth varied consistently outside the glaciation and independently within the limits of the ice sheet.

scholarly journals Radiocarbon Dating Organic Detritus: Implications for Studying Ice Sheet Dynamics

Radiocarbon ◽  
1993 ◽  
Vol 35 (3) ◽  
pp. 449-455 ◽  
Author(s):  
Jaan-Mati Punning ◽  
Raivo Rajamäe
Keyword(s):  
Radiocarbon Dating ◽  
Ice Sheet ◽  
Glacial Maximum ◽  
Organic Detritus ◽  
Organic Debris ◽  
Dating Method ◽  
Ice Sheet Dynamics ◽  
Late Weichselian

We present here a description of the 14C dating method used at the Institute of Geology, Estonian Academy of Science. We discuss results of geochronological studies of several stratigraphic sections, from which we estimate the age of the Late Weichselian (Late Valdaian) glacial maximum. 14C and paleobotanical data indicate that biodetrital materials comprise organic debris from various sources and suggest only a maximum age of investigated strata (16,000 BP).

Degree of rock surface weathering on fjell summits in northern Finland: implications for the thermal regime of the last ice sheet

Boreas ◽  
2008 ◽  
Vol 25 (1) ◽  
pp. 1-7
Author(s):  
DANNY McCARROLL ◽  
JYRKI AUTIO ◽  
OLAVI HEIKKINEN ◽  
LEO KOUTANIEMI
Keyword(s):  
Thermal Regime ◽  
Ice Sheet ◽  
Rock Surface

Dynamics of the Late Weichselian ice sheet on Svalbard inferred from high-resolution sea-floor morphology

Boreas ◽  
2007 ◽  
Vol 36 (3) ◽  
pp. 286-306 ◽  
Author(s):  
DAG OTTESEN ◽  
JULIAN A. DOWDESWELL ◽  
JON Y. LANDVIK ◽  
JUERGEN MIENERT
Keyword(s):  
High Resolution ◽  
Ice Sheet ◽  
Sea Floor ◽  
Late Weichselian

Extent and age of the Last Glacial Maximum in the southeastern sector of the Scandinavian Ice Sheet

2001 ◽  
Vol 31 (1-4) ◽  
pp. 407-425 ◽  
Author(s):  
Juha Pekka Lunkka ◽  
Matti Saarnisto ◽  
Valeri Gey ◽  
Igor Demidov ◽  
Vera Kiselova
Keyword(s):  
Last Glacial Maximum ◽  
Ice Sheet ◽  
Glacial Maximum ◽  
Last Glacial ◽  
Scandinavian Ice Sheet ◽  
The Last Glacial Maximum ◽  
The Last Glacial

On the thickness of the Antarctic ice, and its relations to that of the glacial epoch

2021 ◽  
pp. 1-8
Author(s):  
James CROLL ◽  
David SUGDEN
Keyword(s):  
Thermal Regime ◽  
Freezing Point ◽  
Ice Sheet ◽  
Heat Sources ◽  
Mean Velocity ◽  
Point Estimates ◽  
Glacial Epoch ◽  
Antarctic Continent ◽  
Global Sea Level ◽  
The Antarctic

ABSTRACT At a time when nobody has yet landed on the Antarctic continent (1879), this presentation and accompanying paper predicts the morphology, dynamics and thermal regime of the Antarctic ice sheet. Mathematical modelling of the ice sheet is based on the assumptions that the thickness of tabular icebergs reflects the average thickness of the ice at the margin and that the surface gradients are comparable to those of reconstructed former ice sheets in the Northern Hemisphere. The modelling shows that (a) ice is thickest near the centre at the South Pole and thins towards the margin; (b) the thickness at the pole is independent of the amount of snowfall at that place; and (c) the mean velocity at the margin, assuming a mean annual snowfall of two inches per year, is 400–500 feet per year. The thermal regime of the ice sheet is influenced by three heat sources – namely, the bed, the internal friction of ice flow and the atmosphere. The latter is the most significant and, since ice has a downwards as well as horizontal motion, this carries cold ice down into the ice sheet. Since the temperature at which ice melts is lowered by pressure at a rate of 0.0137 °F for every atmosphere of pressure (something known since 1784), much of the ice sheet and its base must be below the freezing point. Estimates of the thickness of ice at the centre depend closely on the surface gradients assumed and range between 3 and 24 miles. Such uncertainty is of concern since both the volume and gravitational attraction of the ice mass have an effect on global sea level. In order to improve our estimate of the volume of ice, we will have to wait 76 years for John Glen to develop a realistic flow law for ice.

The timing of deglaciation from mountain summits to cirques in Wales: 10Be and 26Al exposure dates from Cadair Idris

2021 ◽  
Author(s):  
Philip Hughes ◽  
Neil Glasser ◽  
David Fink ◽  
Jason Dortch ◽  
Reka Fülöp ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Lake Basin ◽  
Summit Area ◽  
Sheet Surface ◽  
Ice Cap ◽  
Heinrich Event ◽  
Level Ice ◽  
High Level ◽  
Exposure Ages ◽  
Later Phase

<p>Cosmogenic <sup>10</sup>Be and <sup>26</sup>Al exposure ages from 20 erratic samples collected from Cadair Idris (893 m), a mountain in southern Snowdonia, Wales, provide evidence for the timing of deglaciation from summits to cirques at the end of the Late Pleistocene. The summit of the mountain is characterised by intensely modified frost-shattered surfaces that have long been identified as a representing a former nunatak. Numerous glacially-transported quartz boulders on the highest ground indicate that ice overran the summit at some point in the Pleistocene. Two quartz boulders, one with preserved striations, sampled at c. 856 m near the summit of Cadair Idris yielded consistent <sup>10</sup>Be and <sup>26</sup>Al paired exposure ages of 75 ka to 60 ka (using a high-latitude sea level <sup>10</sup>Be spallation production rate of 4.20 at/g/y, scaled by the Lal/Stone scheme). A glacially polished bedrock quartzite outcrop at 735 m gave an age of 17.5 ka. Immediately below this, cirque and down-valley recessional moraine ages, covering an elevation of 480 m to 350 m ranged from 10 to 15 ka respectively.</p><p>These results confirm that Cadair Idris was overridden by the Welsh Ice Cap during marine isotope stage (MIS) 4, when ice was thicker than at the global last glacial maximum (LGM) in MIS 2. This is consistent with findings from northern Snowdonia. The highest Welsh summits, including Cadair Idris, emerged above a thinning Welsh Ice Cap (British Irish Ice Sheet) during the transition from MIS 4 to 3. The summit area above ~800 m then stood as nunataks above the LGM ice sheet surface in MIS 2. The Welsh Ice Cap then rapidly thinned over Cadair Idris at ~20-17 ka based on ages from high-level ice-moulded bedrockThis is supported by more new ages from high-level paired erratics and bedrock samples on several other mountains throughout Snowdonia, leading to a phase of alpine-style deglaciation. Valley glaciers initiated their retreat up-valley from ~17 to 14 ka after Heinrich Event 1. A later phase of glacier stabilisation or still stand formation produced classic cirque moraines near the rim of a present cirque lake basin (480 m elevation) yielding <sup>10</sup>Be ages of 13-10 ka during the Younger Dryas.</p>

The effect of geothermal heat flux on the deglacial evolution of the Greenland ice sheet

2021 ◽  
Author(s):  
Parviz Ajourlou ◽  
François PH Lapointe ◽  
Glenn A Milne ◽  
Yasmina Martos
Keyword(s):  
Boundary Condition ◽  
Heat Flux ◽  
Thermal State ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Sampling Procedure ◽  
Geophysical Research ◽  
Geothermal Heat ◽  
Input Field ◽  
Uncertainty Estimates

<p>Geothermal heat flux (GHF) is known to be an important control on the basal thermal state of an ice sheet which, in turn, is a key factor in governing how the ice sheet will evolve in response to a given climate forcing. In recent years, several studies have estimated GHF beneath the Greenland ice sheet using different approaches (e.g. Rezvanbehbahani et al., Geophysical Research Letters, 2017; Martos et al., Geophysical Research Letters, 2018; Greve, Polar Data Journal, 2019). Comparing these different estimates indicates poor agreement and thus large uncertainty in our knowledge of this important boundary condition for modelling the ice sheet. The primary aim of this study is to quantify the influence of this uncertainty on modelling the past evolution of the ice sheet with a focus on the most recent deglaciation. We build on past work that considered three GHF models (Rogozhina et al., 2011) by considering over 100 different realizations of this input field. We use the uncertainty estimates from Martos et al. (Geophysical Research Letters, 2018) to generate GHF realisations via a statistical sampling procedure. A sensitivity analysis using these realisations and the Parallel Ice Sheet Model (PISM, Bueler and Brown, Journal of Geophysical Research, 2009) indicates that uncertainty in GHF has a dramatic impact on both the volume and spatial distribution of ice since the last glacial maximum, indicating that more precise constraints on this boundary condition are required to improve our understanding of past ice sheet evolution and, consequently, reduce uncertainty in future projections.</p>

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