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 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 Investigating the evolution of major Northern Hemisphere ice sheets during the last glacial-interglacial cycle

2009 ◽  
Vol 5 (3) ◽  
pp. 329-345 ◽  
Author(s):  
S. Bonelli ◽  
S. Charbit ◽  
M. Kageyama ◽  
M.-N. Woillez ◽  
G. Ramstein ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Climate Model ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Co2 Concentration ◽  
Atmospheric Co2 ◽  
Glacial Cycle ◽  
Last Glacial ◽  
Atmospheric Co2 Concentration ◽  
The Last Glacial

Abstract. A 2.5-dimensional climate model of intermediate complexity, CLIMBER-2, fully coupled with the GREMLINS 3-D thermo-mechanical ice sheet model is used to simulate the evolution of major Northern Hemisphere ice sheets during the last glacial-interglacial cycle and to investigate the ice sheets responses to both insolation and atmospheric CO2 concentration. This model reproduces the main phases of advance and retreat of Northern Hemisphere ice sheets during the last glacial cycle, although the amplitude of these variations is less pronounced than those based on sea level reconstructions. At the last glacial maximum, the simulated ice volume is 52.5×1015 m3 and the spatial distribution of both the American and Eurasian ice complexes is in reasonable agreement with observations, with the exception of the marine parts of these former ice sheets. A set of sensitivity studies has also been performed to assess the sensitivity of the Northern Hemisphere ice sheets to both insolation and atmospheric CO2. Our results suggest that the decrease of summer insolation is the main factor responsible for the early build up of the North American ice sheet around 120 kyr BP, in agreement with benthic foraminifera δ18O signals. In contrast, low insolation and low atmospheric CO2 concentration are both necessary to trigger a long-lasting glaciation over Eurasia.

scholarly journals Influence of ablation-related processes in the built-up of simulated Northern Hemisphere ice sheets during the last glacial cycle

2012 ◽  
Vol 6 (6) ◽  
pp. 4897-4938 ◽  
Author(s):  
S. Charbit ◽  
C. Dumas ◽  
M. Kageyama ◽  
D. M. Roche ◽  
C. Ritz
Keyword(s):  
Northern Hemisphere ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Glacial Cycle ◽  
Satisfactory Description ◽  
Last Glacial ◽  
Transient Simulations ◽  
Main Driver ◽  
The Impact ◽  
The Last Glacial

Abstract. Since the original formulation of the positive-degree-day (PDD) method, different PDD calibrations have been proposed in the literature in response to the increasing number of observations. Although these formulations provide a satisfactory description of the present-day Greenland geometry, they have not all been tested for paleo ice sheets. Using the climate-ice sheet model CLIMBER-GRISLI coupled with different PDD models, we evaluate how the parameterization of the ablation may affect the evolution of Northern Hemisphere ice sheets in the transient simulations of the last glacial cycle. Results from fully coupled simulations are compared to time-slice experiments carried out at different key periods of the last glacial period. We find large differences in the simulated ice sheets according to the chosen PDD model. These differences occur as soon as the onset of glaciation, therefore affecting the subsequent evolution of the ice system. To further investigate how the PDD method controls this evolution, special attention is given to the role of each PDD parameter. We show that glacial inception is critically dependent on the representation of the impact of the temperature variability from the daily to the inter-annual time scale, whose effect is modulated by the refreezing scheme. Finally, an additional set of sensitivity experiments has been carried out to assess the relative importance of melt processes with respect to initial ice sheet configuration in the construction and the evolution of past Northern Hemisphere ice sheets. Our analysis reveals that the impacts of the initial ice sheet condition may range from quite negligible to explaining about half of the LGM ice volume depending on the representation of stochastic temperature variations which remain the main driver of the evolution of the ice system.

scholarly journals The sensitivity of Northern Hemisphere ice sheets to atmospheric forcing during the last glacial cycle using PMIP3 models

2019 ◽  
Vol 65 (252) ◽  
pp. 645-661 ◽  
Author(s):  
LU NIU ◽  
GERRIT LOHMANN ◽  
SEBASTIAN HINCK ◽  
EVAN J. GOWAN ◽  
UTA KREBS-KANZOW
Keyword(s):  
Northern Hemisphere ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Climate Forcing ◽  
Phase Iii ◽  
Temperature Pattern ◽  
Glacial Cycle ◽  
Large Variability ◽  
Last Glacial ◽  
The Last Glacial

ABSTRACTThe evolution of Northern Hemisphere ice sheets through the last glacial cycle is simulated with the glacial index method by using the climate forcing from one General Circulation Model, COSMOS. By comparing the simulated results to geological reconstructions, we first show that the modelled climate is capable of capturing the main features of the ice-sheet evolution. However, large deviations exist, likely due to the absence of nonlinear interactions between ice sheet and other climate components. The model uncertainties of the climate forcing are examined using the output from nine climate models from the Paleoclimate Modelling Intercomparison Project Phase III. The results show a large variability in simulated ice sheets between the different models. We find that the ice-sheet extent pattern resembles summer surface air temperature pattern at the Last Glacial Maximum, confirming the dominant role of surface ablation process for high-latitude Northern Hemisphere ice sheets. This study shows the importance of the upper boundary condition for ice-sheet modelling, and implies that careful constraints on climate output is essential for simulating realistic glacial Northern Hemisphere ice sheets.

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 Investigating the evolution of major Northern Hemisphere ice sheets during the last glacial-interglacial cycle

2009 ◽  
Vol 5 (2) ◽  
pp. 1013-1053 ◽  
Author(s):  
S. Bonelli ◽  
S. Charbit ◽  
M. Kageyama ◽  
M.-N. Woillez ◽  
G. Ramstein ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Climate Model ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Co2 Concentration ◽  
Atmospheric Co2 ◽  
Glacial Cycle ◽  
Last Glacial ◽  
Atmospheric Co2 Concentration ◽  
The Last Glacial

Abstract. A 2.5-dimensional climate model of intermediate complexity fully coupled with a 3-dimensional thermo-mechanical ice sheet model is used to simulate the evolution of major Northern Hemisphere ice sheets during the last glacial-interglacial cycle and to investigate the ice sheets responses to both insolation and atmospheric CO2 concentration. This model reproduces the main phases of advance and retreat of Northern Hemisphere ice sheets during the last glacial cycle, although the amplitude of these variations is less pronounced than those based on sea level reconstructions. At the last glacial maximum, the simulated ice volume is 52.5×1015 m3 and the spatial distribution of both the American and Eurasian ice complexes is in reasonable agreement with observations, with the exception of the marine parts of these former ice sheets. A set of sensitivity studies has also been performed to assess the sensitivity of the Northern Hemisphere ice sheets to both insolation and atmospheric CO2. Our results suggest that the decrease of summer insolation is the main factor responsible for the early build up of the North American ice sheet around 120 kyr BP, in agreement with benthic foraminifera δ18O signals. In contrast, low insolation and low atmospheric CO2 concentration are both necessary to trigger a long-lasting glaciation over Eurasia.

scholarly journals Influence of ablation-related processes in the build-up of simulated Northern Hemisphere ice sheets during the last glacial cycle

2013 ◽  
Vol 7 (2) ◽  
pp. 681-698 ◽  
Author(s):  
S. Charbit ◽  
C. Dumas ◽  
M. Kageyama ◽  
D. M. Roche ◽  
C. Ritz
Keyword(s):  
Northern Hemisphere ◽  
Climate Models ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Glacial Cycle ◽  
Satisfactory Description ◽  
Last Glacial ◽  
Transient Simulations ◽  
The Impact ◽  
The Last Glacial

Abstract. Since the original formulation of the positive-degree-day (PDD) method, different PDD calibrations have been proposed in the literature in response to the increasing number of observations. Although these formulations generally provide a satisfactory description of the present-day Greenland geometry, they have not all been tested for paleo ice sheets. Using the climate-ice sheet model CLIMBER-GRISLI coupled with different PDD models, we evaluate how the parameterisation of the ablation may affect the evolution of Northern Hemisphere ice sheets in the transient simulations of the last glacial cycle. Results from fully coupled simulations are compared to time-slice experiments carried out at different key periods of the last glacial period. We find large differences in the simulated ice sheets according to the chosen PDD model. These differences occur as soon as the onset of glaciation, therefore affecting the subsequent evolution of the ice system. To further investigate how the PDD method controls this evolution, special attention is given to the role of each PDD parameter. We show that glacial inception is critically dependent on the representation of the impact of the temperature variability from the daily to the inter-annual time scale, whose effect is modulated by the refreezing scheme. Finally, an additional set of sensitivity experiments has been carried out to assess the relative importance of melt processes with respect to initial ice sheet configuration in the construction and the evolution of past Northern Hemisphere ice sheets. Our analysis reveals that the impacts of the initial ice sheet condition may range from quite negligible to explaining about half of the LGM ice volume depending on the representation of stochastic temperature variations which remain the main driver of the evolution of the ice system. The main findings of this paper underline the need for conducting studies with high resolution climate models coupled to detailed snow models to better constrain the temporal and spatial variations of the PDD parameters. The development of such approaches could improve the calibration of the PDD formulation which is still widely used in climate-ice sheet studies.

A NEW METHOD TO SIMULATE THE ANTARCTIC ICE SHEET OVER THE LAST GLACIAL CYCLE USING A COUPLED 3D GIA – ICE DYNAMIC MODEL

2020 ◽  
Author(s):  
C.J. van Calcar ◽  
◽  
B. de Boer ◽  
B. Blank ◽  
W. van der Wal
Keyword(s):  
Dynamic Model ◽  
Ice Sheet ◽  
New Method ◽  
Glacial Cycle ◽  
Antarctic Ice Sheet ◽  
Last Glacial ◽  
The Antarctic ◽  
The Last Glacial
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