scholarly journals Fennoscandian palaeoglaciology reconstructed using a glacial geological inversion model

1997 ◽  
Vol 43 (144) ◽  
pp. 283-299 ◽  
Author(s):  
Johan Kleman ◽  
Clas Hättestrand ◽  
Ingmar Borgström ◽  
Arjen Stroeven
Keyword(s):  
Flow Pattern ◽  
Numerical Models ◽  
Ice Sheet ◽  
Mountain Range ◽  
Glacial Cycle ◽  
Geological Evidence ◽  
Inversion Model ◽  
Last Glacial ◽  
Late Weichselian ◽  
The Last Glacial

AbstractThe evolution of ice-sheet configuration and flow pattern in Fennoscandia through the last glacial cycle was reconstructed using a glacial geological inversion model, i.e. a theoretical model that formalises the procedure of using the landform record to reconstruct ice sheets. The model uses mapped flow traces and deglacial melt-water landforms, as well as relative chronologies derived from cross-cutting striae and till lineations, as input data. Flow-trace systems were classified into four types: (i) time-transgressive wet-bed deglacial fans, (ii) time-transgressive frozen-bed deglacial fans, (iii) surge fans, and (iv) synchronous non-deglacial (event) fans. Using relative chronologies and aggregation of fans into glaciologically plausible patterns, a series of ice-sheet Configurations at different time slices was erected. A chronology was constructed through correlation with dated stratigraphical records and proxy data reflecting global ice volume. Geological evidence exists for several discrete ice-sheet configurations centred over the Scandinavian mountain range during the early Weichselian. The build-up of the main Weichselian Fennoscandian ice sheet started at approximately 70 Ka, and our results indicate that it was characterised by an ice sheet with a centre of mass located over southern Norway. This configuration had a flow pattern which is poorly reproduced by current numerical models of the Fennoscandian ice sheet. At the Last Glacial Maximum the main ice divide was located overthe Gulf of Bothnia. A major bend in the ice divide was caused by outflow of ice to the northwest over the lowest part of the Scandinavian mountain chain. Widespread areas of preserved pre-late-Weichselian landscapes indicate that the ice sheet had a frozen-bed core area, which was only partly diminished in size by inward-transgressive wet-bed zones during the decay phase.

scholarly journals Fennoscandian palaeoglaciology reconstructed using a glacial geological inversion model

1997 ◽  
Vol 43 (144) ◽  
pp. 283-299 ◽  
Author(s):  
Johan Kleman ◽  
Clas Hättestrand ◽  
Ingmar Borgström ◽  
Arjen Stroeven
Keyword(s):  
Flow Pattern ◽  
Numerical Models ◽  
Ice Sheet ◽  
Mountain Range ◽  
Glacial Cycle ◽  
Geological Evidence ◽  
Inversion Model ◽  
Last Glacial ◽  
Late Weichselian ◽  
The Last Glacial

AbstractThe evolution of ice-sheet configuration and flow pattern in Fennoscandia through the last glacial cycle was reconstructed using a glacial geological inversion model, i.e. a theoretical model that formalises the procedure of using the landform record to reconstruct ice sheets. The model uses mapped flow traces and deglacial melt-water landforms, as well as relative chronologies derived from cross-cutting striae and till lineations, as input data. Flow-trace systems were classified into four types: (i) time-transgressive wet-bed deglacial fans, (ii) time-transgressive frozen-bed deglacial fans, (iii) surge fans, and (iv) synchronous non-deglacial (event) fans. Using relative chronologies and aggregation of fans into glaciologically plausible patterns, a series of ice-sheet Configurations at different time slices was erected. A chronology was constructed through correlation with dated stratigraphical records and proxy data reflecting global ice volume. Geological evidence exists for several discrete ice-sheet configurations centred over the Scandinavian mountain range during the early Weichselian. The build-up of the main Weichselian Fennoscandian ice sheet started at approximately 70 Ka, and our results indicate that it was characterised by an ice sheet with a centre of mass located over southern Norway. This configuration had a flow pattern which is poorly reproduced by current numerical models of the Fennoscandian ice sheet. At the Last Glacial Maximum the main ice divide was located overthe Gulf of Bothnia. A major bend in the ice divide was caused by outflow of ice to the northwest over the lowest part of the Scandinavian mountain chain. Widespread areas of preserved pre-late-Weichselian landscapes indicate that the ice sheet had a frozen-bed core area, which was only partly diminished in size by inward-transgressive wet-bed zones during the decay phase.

scholarly journals Evolution of the large-scale atmospheric circulation in response to changing ice sheets over the last glacial cycle

2014 ◽  
Vol 10 (4) ◽  
pp. 1453-1471 ◽  
Author(s):  
M. Löfverström ◽  
R. Caballero ◽  
J. Nilsson ◽  
J. Kleman
Keyword(s):  
Atmospheric Circulation ◽  
Large Scale ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Glacial Cycle ◽  
Mean Flow ◽  
Geological Evidence ◽  
Last Glacial ◽  
The Last Glacial

Abstract. We present modelling results of the atmospheric circulation at the cold periods of marine isotope stage 5b (MIS 5b), MIS 4 and the Last Glacial Maximum (LGM), as well as the interglacial. The palaeosimulations are forced by ice-sheet reconstructions consistent with geological evidence and by appropriate insolation and greenhouse gas concentrations. The results suggest that the large-scale atmospheric winter circulation remained largely similar to the interglacial for a significant part of the glacial cycle. The proposed explanation is that the ice sheets were located in areas where their interaction with the mean flow is limited. However, the LGM Laurentide Ice Sheet induces a much larger planetary wave that leads to a zonalisation of the Atlantic jet. In summer, the ice-sheet topography dynamically induces warm temperatures in Alaska and central Asia that inhibits the expansion of the ice sheets into these regions. The warm temperatures may also serve as an explanation for westward propagation of the Eurasian Ice Sheet from MIS 4 to the LGM.

Streaming flow in an ice sheet through a glacial cycle

2003 ◽  
Vol 36 ◽  
pp. 117-128 ◽  
Author(s):  
Geoffrey S. Boulton ◽  
Magnus Hagdorn ◽  
Nicholas R.J. Hulton
Keyword(s):  
Three Dimensional ◽  
Ice Sheet ◽  
Glacial Cycle ◽  
Ice Streams ◽  
Geological Evidence ◽  
Last Glacial ◽  
Bed Topography ◽  
Basal Melting ◽  
Realistic Topography ◽  
The Last Glacial

AbstractGeological evidence indicates that the flow of the last European ice sheet was dominated by numerous large ice streams. Although some were ephemeral, most were sustained along well-defined axes at least during the period of retreat after the Last Glacial Maximum. A thermomechanically coupled three-dimensional numerical ice-sheet model has been used to simulate the ice sheet through the whole of the last glacial cycle, but with a spatial resolution that is high enough to capture streaming behaviour. An experiment with a smoothed bed is used to explore the self-organizing behaviour of streams when they are not forced by bed topography. On such a bed, streams typically have a width of 1–10 km, much narrower than the inferred European ice streams. An experiment using a realistic topography suggests that widths of ice streams are strongly influenced by topography, and tend to be of order 100 km. Moreover, even where the topography is muted, it stabilizes the locations of ice streams which, once formed, tend to be sustained along pre-existing axes. The model creates patterns of streaming that are similar to inferred patterns, suggesting strong topographic forcing. In a simulation using a realistic bed in which the ice was very cold and basal melting rarely occurred, streams were again very narrow. Widespread streaming under low driving stresses tends to reduce ice-sheet thicknesses compared with weak streaming or models that do not produce streaming. Consequently, ice thicknesses are smaller and tend to be consistent with the results of sea-level inversions based on geophysical Earth models.

scholarly journals Evolution of the large-scale atmospheric circulation in response to changing ice sheets over the last glacial cycle

2014 ◽  
Vol 10 (2) ◽  
pp. 1381-1420 ◽  
Author(s):  
M. Löfverström ◽  
R. Caballero ◽  
J. Nilsson ◽  
J. Kleman
Keyword(s):  
Atmospheric Circulation ◽  
Large Scale ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Glacial Cycle ◽  
Mean Flow ◽  
Geological Evidence ◽  
Last Glacial ◽  
The Last Glacial

Abstract. We present modelling results of the atmospheric circulation at the cold periods of marine isotope stage 5b (MIS 5b), MIS 4 and the Last Glacial Maximum (LGM), as well as the interglacial. The paleo-simulations are forced by ice sheet reconstructions consistent with geological evidence and by appropriate insolation and greenhouse gas concentrations. The results suggest that the large-scale atmospheric winter circulation remained largely similar to the interglacial for a significant part of the glacial cycle. The proposed explanation is that the ice sheets were located in areas where their interaction with the mean flow is limited. However, the LGM Laurentide Ice Sheet induces a much larger planetary wave that leads to a zonalisation of the Atlantic jet. In summer, the ice sheet topography dynamically induces warm temperatures in Alaska and central Asia that inhibits the expansion of the ice sheets into these regions. The warm temperatures may also serve as an explanation for westward propagation of the Eurasian Ice Sheet from MIS 4 to the 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 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 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.

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