scholarly journals A case for cold-based continental ice sheets — a transient thermal model

1996 ◽  
Vol 42 (140) ◽  
pp. 37-42 ◽  
Author(s):  
Jan T. Heine ◽  
David F. Mctigue
Keyword(s):  
Heat Flux ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Initial Surface ◽  
Glacial Cycle ◽  
Geothermal Heat ◽  
History Of ◽  
Basal Melting ◽  
Continental Ice Sheets ◽  
Transient Thermal

AbstractA finite-difference numerical model is used to simulate the temperature profile at the center of an ice sheet throughout the course of a glaciation. The ice sheet is gradually built to a thickness of 3000 m over about 10 000 years, starting on permafrost. A geothermal heat flux is applied at large depth. For an initial surface temperature of –12.5°C, our model shows that basal melting occurs 72000 years after the onset of the glaciation. The important parameters determining the basal temperatures are the initial temperature of the ice and substrate, the rate of downward advection of cold ice and, to a lesser extent, the thickness of the ice sheet. The growth history of the ice sheet does not significantly influence the time at which basal melting occurs. Our results show the possibility that the central parts of the continental ice sheets were cold-based for a significant part of their existence. Heating due to the geothermal heat flux cannot account for basal melting during most or all of a glacial cycle. These results may help to explain the existence of preserved land forms under the ice sheets.

scholarly journals A case for cold-based continental ice sheets — a transient thermal model

1996 ◽  
Vol 42 (140) ◽  
pp. 37-42 ◽  
Author(s):  
Jan T. Heine ◽  
David F. Mctigue
Keyword(s):  
Heat Flux ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Initial Surface ◽  
Glacial Cycle ◽  
Geothermal Heat ◽  
History Of ◽  
Basal Melting ◽  
Continental Ice Sheets ◽  
Transient Thermal

AbstractA finite-difference numerical model is used to simulate the temperature profile at the center of an ice sheet throughout the course of a glaciation. The ice sheet is gradually built to a thickness of 3000 m over about 10 000 years, starting on permafrost. A geothermal heat flux is applied at large depth. For an initial surface temperature of –12.5°C, our model shows that basal melting occurs 72000 years after the onset of the glaciation. The important parameters determining the basal temperatures are the initial temperature of the ice and substrate, the rate of downward advection of cold ice and, to a lesser extent, the thickness of the ice sheet. The growth history of the ice sheet does not significantly influence the time at which basal melting occurs. Our results show the possibility that the central parts of the continental ice sheets were cold-based for a significant part of their existence. Heating due to the geothermal heat flux cannot account for basal melting during most or all of a glacial cycle. These results may help to explain the existence of preserved land forms under the ice sheets.

scholarly journals Coupled Northern Hemisphere permafrost–ice-sheet evolution over the last glacial cycle

2015 ◽  
Vol 11 (9) ◽  
pp. 1165-1180 ◽  
Author(s):  
M. Willeit ◽  
A. Ganopolski
Keyword(s):  
Heat Flux ◽  
Northern Hemisphere ◽  
Ice Sheet ◽  
The Arctic ◽  
Sediment Layer ◽  
Glacial Cycle ◽  
Geothermal Heat ◽  
Climate History ◽  
Last Glacial ◽  
The Last Glacial

Abstract. Permafrost influences a number of processes which are relevant for local and global climate. For example, it is well known that permafrost plays an important role in global carbon and methane cycles. Less is known about the interaction between permafrost and ice sheets. In this study a permafrost module is included in the Earth system model CLIMBER-2, and the coupled Northern Hemisphere (NH) permafrost–ice-sheet evolution over the last glacial cycle is explored. The model performs generally well at reproducing present-day permafrost extent and thickness. Modeled permafrost thickness is sensitive to the values of ground porosity, thermal conductivity and geothermal heat flux. Permafrost extent at the Last Glacial Maximum (LGM) agrees well with reconstructions and previous modeling estimates. Present-day permafrost thickness is far from equilibrium over deep permafrost regions. Over central Siberia and the Arctic Archipelago permafrost is presently up to 200–500 m thicker than it would be at equilibrium. In these areas, present-day permafrost depth strongly depends on the past climate history and simulations indicate that deep permafrost has a memory of surface temperature variations going back to at least 800 ka. Over the last glacial cycle permafrost has a relatively modest impact on simulated NH ice sheet volume except at LGM, when including permafrost increases ice volume by about 15 m sea level equivalent in our model. This is explained by a delayed melting of the ice base from below by the geothermal heat flux when the ice sheet sits on a porous sediment layer and permafrost has to be melted first. Permafrost affects ice sheet dynamics only when ice extends over areas covered by thick sediments, which is the case at LGM.

scholarly journals Erosion by Continental Ice Sheets

1979 ◽  
Vol 23 (89) ◽  
pp. 401-402
Author(s):  
I. M. Whillans
Keyword(s):  
Mass Balance ◽  
Short Distance ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Present Theory ◽  
Frictional Heat ◽  
Break Up ◽  
Basal Melting ◽  
Continental Ice Sheets

Abstract Some of the problems with earlier theories for erosion and transport by ice sheets are discussed, and it is noted that those theories cannot simply account for the often-reported finding that most till is derived from bedrock only a few tens of kilometers up-glacier. Considerations of the mass balance of debris in transport lead to the conclusion that ice sheets are capable of transporting most debris only a short distance. The theory that the break-up of bedrock is mostly a preglacial process is developed. The advancing ice sheet collects the debris and then deposits it after a short travel. As the ice sheet first advances over the regolith, debris is frozen onto the base and is carried until basal melting due to geothermal and frictional heat causes lodgment till deposition. Most debris is deposited during the advance of the ice sheet and is carried only a short distance. A generally small amount of debris is carried at higher levels and is deposited during ice standstill and retreat as melt-out and ablation tills. The present theory makes many predictions, among them, that most till units are not traceable over long distances, that thick till sequences represent unstable glacier margins and not necessarily long periods of glacier occupation, and that lodgment tills are to be interpreted in terms of ice advances and ablation tills in terms of ice retreats. This paper is published in full in Journal of Geology, Vol. 86, No. 4, 1978, p. 516–24.

scholarly journals Indication of high basal melting at EastGRIP drill site on the Northeast Greenland Ice Stream

2021 ◽  
Author(s):  
Ole Zeising ◽  
Angelika Humbert
Keyword(s):  
Heat Flux ◽  
Heat Budget ◽  
Ice Sheet ◽  
Water System ◽  
Hydrological Regime ◽  
Ice Streams ◽  
Geothermal Heat ◽  
Ice Stream ◽  
Drill Site ◽  
Basal Melting

Abstract. The accelerated ice flow of ice streams that reach far into the interior of the ice sheet, is associate with lubrication of the ice sheet base by basal melt water. However, the amount of basal melting under the large ice streams – such as the Northeast Greenland Ice Stream (NEGIS) – are largely unknown. In-situ measurements of basal melt rates are important from various perspectives as they indicate the heat budget, the hydrological regime and the role of sliding in glacier motion. The few previous estimates of basal melt rates in the NEGIS region were 0.1 m a−1 and more, based on radiostratigraphy methods. These finding raised the question of the heat source, since even an increased geothermal heat flux could not deliver the necessary amount of heat. Here, we present basal melt rates at the recent deep drill site EastGRIP, located in the center of NEGIS. Within two subsequent years, we found basal melt rates of (0.16–0.22) ± 0.01 m a−1, that are based on analysis of repeated phase-sensitive radar measurements. In order to quantify the contribution of processes that cause a heat flux into the ice, we carried out an assessment of the energy sources and found the subglacial water system to play a key role in facilitating such high melt rates.

scholarly journals High geothermal heat flux measured below the West Antarctic Ice Sheet

2015 ◽  
Vol 1 (6) ◽  
pp. e1500093 ◽  
Author(s):  
Andrew T. Fisher ◽  
Kenneth D. Mankoff ◽  
Slawek M. Tulaczyk ◽  
Scott W. Tyler ◽  
Neil Foley ◽  
...  
Keyword(s):  
Heat Flux ◽  
Ice Sheet ◽  
The West ◽  
Geothermal Heat ◽  
Antarctic Ice Sheet ◽  
West Antarctic Ice Sheet ◽  
Subglacial Lake ◽  
West Antarctic ◽  
Basal Melting ◽  
Subglacial Lake Whillans

The geothermal heat flux is a critical thermal boundary condition that influences the melting, flow, and mass balance of ice sheets, but measurements of this parameter are difficult to make in ice-covered regions. We report the first direct measurement of geothermal heat flux into the base of the West Antarctic Ice Sheet (WAIS), below Subglacial Lake Whillans, determined from the thermal gradient and the thermal conductivity of sediment under the lake. The heat flux at this site is 285 ± 80 mW/m2, significantly higher than the continental and regional averages estimated for this site using regional geophysical and glaciological models. Independent temperature measurements in the ice indicate an upward heat flux through the WAIS of 105 ± 13 mW/m2. The difference between these heat flux values could contribute to basal melting and/or be advected from Subglacial Lake Whillans by flowing water. The high geothermal heat flux may help to explain why ice streams and subglacial lakes are so abundant and dynamic in this region.

scholarly journals Erosion by Continental Ice Sheets

1979 ◽  
Vol 23 (89) ◽  
pp. 401-402
Author(s):  
I. M. Whillans
Keyword(s):  
Mass Balance ◽  
Short Distance ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Present Theory ◽  
Frictional Heat ◽  
Break Up ◽  
Basal Melting ◽  
Continental Ice Sheets

AbstractSome of the problems with earlier theories for erosion and transport by ice sheets are discussed, and it is noted that those theories cannot simply account for the often-reported finding that most till is derived from bedrock only a few tens of kilometers up-glacier. Considerations of the mass balance of debris in transport lead to the conclusion that ice sheets are capable of transporting most debris only a short distance.The theory that the break-up of bedrock is mostly a preglacial process is developed. The advancing ice sheet collects the debris and then deposits it after a short travel. As the ice sheet first advances over the regolith, debris is frozen onto the base and is carried until basal melting due to geothermal and frictional heat causes lodgment till deposition. Most debris is deposited during the advance of the ice sheet and is carried only a short distance. A generally small amount of debris is carried at higher levels and is deposited during ice standstill and retreat as melt-out and ablation tills.The present theory makes many predictions, among them, that most till units are not traceable over long distances, that thick till sequences represent unstable glacier margins and not necessarily long periods of glacier occupation, and that lodgment tills are to be interpreted in terms of ice advances and ablation tills in terms of ice retreats.This paper is published in full in Journal of Geology, Vol. 86, No. 4, 1978, p. 516–24.

scholarly journals Modeling the marine extent of Northern Hemisphere ice sheets during the last glacial cycle

2003 ◽  
Vol 37 ◽  
pp. 173-180 ◽  
Author(s):  
Chris Zweck ◽  
Philippe Huybrechts
Keyword(s):  
Northern Hemisphere ◽  
Water Depth ◽  
Three Dimensional ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Glacial Cycle ◽  
Last Glacial ◽  
History Of ◽  
The Last Glacial Maximum ◽  
The Last Glacial

AbstractMechanisms that determine time-dependent changes of the marine ice margin in dynamic ice-sheet models are important but poorly understood. Here we derive an empirical formulation for changes in the marine extent when modelling the Northern Hemisphere ice sheets over the last glacial cycle in a three-dimensional thermomechanically coupled ice-sheet model. We assume that the strongest control on changes in marine extent is ice calving, and that the variable most crucial to calving is water depth. The empirical marine-extent relationship is tuned so that the major marine-retreat history of the Laurentide and Eurasian ice sheets is modelled accurately in time and space. We find that this empirical treatment relating marine extent to water depth is sufficient to reproduce the observations, and discuss the implications for the physics of marine margin changes and the dynamics of the Northern Hemisphere ice sheets since the Last Glacial Maximum.

scholarly journals Detailed spatially distributed geothermal heat-flow data for modeling of basal temperatures and meltwater production beneath the Fennoscandian ice sheet

2005 ◽  
Vol 40 ◽  
pp. 95-101 ◽  
Author(s):  
Jens-Ove Näslund ◽  
Peter Jansson ◽  
James L. Fastook ◽  
Jesse Johnson ◽  
Leif Andersson
Keyword(s):  
High Resolution ◽  
Heat Flow ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Flow Density ◽  
Glacial Cycle ◽  
Geothermal Heat ◽  
Last Glacial ◽  
Uniform Value ◽  
The Last Glacial

AbstractAccurate modeling of ice sheets requires proper information on boundary conditions, including the geothermal heat flow (or heat-flow density (HFD)). Traditionally, one uniform HFD value is adopted for the entire modeled domain. We have calculated a distributed, high-resolution HFD dataset for an approximate core area (Sweden and Finland) of the Scandinavian ice sheet, and imbedded this within lower-resolution data published for surrounding regions. Within the Last Glacial Maximum ice margin, HFD varies with a factor of as much as 2.8 (HFD values ranging between 30 and 83 mWm–2), with an average of 49 mWm–2. This average value is 17% higher than 42 mWm–2, a common uniform value used in ice-sheet modeling studies of Fennoscandia. Using this new distributed dataset on HFD, instead of a traditional uniform value of 42 mWm–2, yields a 1.4 times larger total basal meltwater production for the last glacial cycle. Furthermore, using the new dataset in high-resolution modeling results in increased spatial thermal gradients at the bed. This enhances and introduces new local and regional effects on basal ice temperatures and melt rates. We observed significant strengthening of local ‘ice streaming’, which in one case correlates to an ice-flow event previously interpreted from geomorphology. Regional to local variations in geothermal heat flow need to be considered for proper identification and treatment of thermal and hydraulic bed conditions, most likely also when studying Laurentide, Greenland and Antarctic ice sheets.

scholarly journals Coupled Northern Hemisphere permafrost-ice sheet evolution over the last glacial cycle

2015 ◽  
Vol 11 (1) ◽  
pp. 555-601 ◽  
Author(s):  
M. Willeit ◽  
A. Ganopolski
Keyword(s):  
Heat Flux ◽  
Northern Hemisphere ◽  
Ice Sheet ◽  
The Arctic ◽  
Sediment Layer ◽  
Glacial Cycle ◽  
Geothermal Heat ◽  
Climate History ◽  
Last Glacial ◽  
The Last Glacial

Abstract. Permafrost influences a number of processes which are relevant for local and global climate. For example, it is well known that permafrost plays an important role in global carbon and methane cycles. Less is known about the interaction between permafrost and ice sheets. In this study a permafrost module is included in the Earth system model CLIMBER-2 and the coupled Northern Hemisphere (NH) permafrost-ice sheet evolution over the last glacial cycle is explored. The model performs generally well at reproducing present-day permafrost extent and thickness. Modelled permafrost thickness is sensitive to the values of ground porosity, thermal conductivity and geothermal heat flux. Permafrost extent at the last glacial maximum (LGM) agrees well with reconstructions and previous modelling estimates. Present-day permafrost thickness is far from equilibrium over deep permafrost regions. Over Central Siberia and the Arctic Archipelago permafrost is presently up to 200–500 m thicker than it would be at equilibrium. In these areas, present-day permafrost depth strongly depends on the past climate history and simulations indicate that deep permafrost has a memory of surface temperature variations going back to at least 800 kya. Over the last glacial cycle permafrost has a relatively modest impact on simulated NH ice sheet volume except at LGM, when including permafrost increases ice volume by about 15 m sea level equivalent. This is explained by a delayed melting of the ice base from below by the geothermal heat flux when the ice sheet sits on a porous sediment layer and permafrost has to be melted first. Permafrost affects ice sheet dynamics only when ice extends over areas covered by thick sediments, which is the case at LGM.

scholarly journals Sensitivity of the Lambert-Amery glacial system to geothermal heat flux

2016 ◽  
Vol 57 (73) ◽  
pp. 56-68 ◽  
Author(s):  
M. L. Pittard ◽  
J. L. Roberts ◽  
B. K. Galton-Fenzi ◽  
C. S. Watson
Keyword(s):  
Heat Flux ◽  
Ice Sheet ◽  
Ice Streams ◽  
Control Solution ◽  
Geothermal Heat ◽  
Local Flow ◽  
Thermal Boundary Conditions ◽  
Grounding Line ◽  
The Difference ◽  
Basal Melting

ABSTRACTGeothermal heat flux (GHF) is one of the key thermal boundary conditions for ice-sheet models. We assess the sensitivity of the Lambert-Amery glacial system in East Antarctica to four different GHF datasets using a regional ice-sheet model. A control solution of the regional model is initialised by minimising the misfit to observations through an optimisation process. The Lambert-Amery glacial system simulation contains temperate ice up to 150 m thick and has an average basal melt of 1.3 mm a−1, with maximum basal melting of 504 mm a−1. The simulations which use a relatively high GHF compared to the control solution increase the volume and area of temperate ice, which causes higher surface velocities at higher elevations, which leads to the advance of the grounding line. The grounding line advance leads to changes in the local flow configuration, which dominates the changes within the glacial system. To investigate the difference in spatial patterns within the geothermal datasets, they were scaled to have the same median value. These scaled GHF simulations showed that the ice flow was most sensitive to the spatial variation in the underlying GHF near the ice divides and on the edges of the ice streams.

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