Applying the Community Ice Sheet Model to evaluate PMIP3 LGM climatologies over the North American ice sheets

2019 ◽  
Vol 53 (5-6) ◽  
pp. 2807-2824
Author(s):  
Jay R. Alder ◽  
Steven W. Hostetler
Keyword(s):  
North American ◽  
Ice Sheets ◽  
Ice Sheet ◽  
The North

scholarly journals How might the North American ice sheet influence the northwestern Eurasian climate?

2015 ◽  
Vol 11 (10) ◽  
pp. 1467-1490 ◽  
Author(s):  
P. Beghin ◽  
S. Charbit ◽  
C. Dumas ◽  
M. Kageyama ◽  
C. Ritz
Keyword(s):  
Atmospheric Circulation ◽  
North American ◽  
Gradual Increase ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Total Precipitation ◽  
Surface Mass ◽  
The North ◽  
Albedo Effect ◽  
Eurasian Region

Abstract. It is now widely acknowledged that past Northern Hemisphere ice sheets covering Canada and northern Europe at the Last Glacial Maximum (LGM) exerted a strong influence on climate by causing changes in atmospheric and oceanic circulations. In turn, these changes may have impacted the development of the ice sheets themselves through a combination of different feedback mechanisms. The present study is designed to investigate the potential impact of the North American ice sheet on the surface mass balance (SMB) of the Eurasian ice sheet driven by simulated changes in the past glacial atmospheric circulation. Using the LMDZ5 atmospheric circulation model, we carried out 12 experiments under constant LGM conditions for insolation, greenhouse gases and ocean. In these experiments, the Eurasian ice sheet is removed. The 12 experiments differ in the North American ice-sheet topography, ranging from a white and flat (present-day topography) ice sheet to a full-size LGM ice sheet. This experimental design allows the albedo and the topographic impacts of the North American ice sheet onto the climate to be disentangled. The results are compared to our baseline experiment where both the North American and the Eurasian ice sheets have been removed. In summer, the sole albedo effect of the American ice sheet modifies the pattern of planetary waves with respect to the no-ice-sheet case, resulting in a cooling of the northwestern Eurasian region. By contrast, the atmospheric circulation changes induced by the topography of the North American ice sheet lead to a strong decrease of this cooling. In winter, the Scandinavian and the Barents–Kara regions respond differently to the American ice-sheet albedo effect: in response to atmospheric circulation changes, Scandinavia becomes warmer and total precipitation is more abundant, whereas the Barents–Kara area becomes cooler with a decrease of convective processes, causing a decrease of total precipitation. The gradual increase of the altitude of the American ice sheet leads to less total precipitation and snowfall and to colder temperatures over both the Scandinavian and the Barents and Kara sea sectors. We then compute the resulting annual surface mass balance over the Fennoscandian region from the simulated temperature and precipitation fields used to force an ice-sheet model. It clearly appears that the SMB is dominated by the ablation signal. In response to the summer cooling induced by the American ice-sheet albedo, high positive SMB values are obtained over the Eurasian region, leading thus to the growth of an ice sheet. On the contrary, the gradual increase of the American ice-sheet altitude induces more ablation over the Eurasian sector, hence limiting the growth of Fennoscandia. To test the robustness of our results with respect to the Eurasian ice sheet state, we carried out two additional LMDZ experiments with new boundary conditions involving both the American (flat or full LGM) and high Eurasian ice sheets. The most striking result is that the Eurasian ice sheet is maintained under full-LGM North American ice-sheet conditions, but loses ~ 10 % of its mass compared to the case in which the North American ice sheet is flat. These new findings qualitatively confirm the conclusions from our first series of experiments and suggest that the development of the Eurasian ice sheet may have been slowed down by the growth of the American ice sheet, offering thereby a new understanding of the evolution of Northern Hemisphere ice sheets throughout glacial–interglacial cycles.

scholarly journals The origin of till sequences by subglacial sediment deformation beneath mid-latitude ice sheets

1996 ◽  
Vol 22 ◽  
pp. 75-84 ◽  
Author(s):  
G. S. Boulton
Keyword(s):  
North American ◽  
Large Scale ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Glacial Cycle ◽  
Erosion And Deposition ◽  
The North ◽  
Sediment Deformation ◽  
Source Materials ◽  
The Last Glacial

A theory of erosion and deposition as a consequence of subglacial sediment deformation over beds of unlithified sediment is reviewed and applied to large-scale till sequences formed on the southern flanks of the North American and British and European ice sheets during the last glacial cycle. The distribution of till thickness, till lithology in relation to source materials and intra-till erosion surfaces along a flowline in the Michigan lobe of the North American ice sheet are shown to be compatible with the deformational theory but not with other modes of till genesis. It is then demonstrated, in the case of the British ice sheet, how the assumption of a deformational origin for tills can be used to infer time-dependent patterns of ice-sheet dynamic behaviour. By reference to an example from the Netherlands, it is argued that many till sequences interpreted as melt-out tills are more likely to have formed by subglacial sediment deformation.

scholarly journals The origin of till sequences by subglacial sediment deformation beneath mid-latitude ice sheets

1996 ◽  
Vol 22 ◽  
pp. 75-84 ◽  
Author(s):  
G. S. Boulton
Keyword(s):  
North American ◽  
Large Scale ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Glacial Cycle ◽  
Erosion And Deposition ◽  
The North ◽  
Sediment Deformation ◽  
Source Materials ◽  
The Last Glacial

A theory of erosion and deposition as a consequence of subglacial sediment deformation over beds of unlithified sediment is reviewed and applied to large-scale till sequences formed on the southern flanks of the North American and British and European ice sheets during the last glacial cycle. The distribution of till thickness, till lithology in relation to source materials and intra-till erosion surfaces along a flowline in the Michigan lobe of the North American ice sheet are shown to be compatible with the deformational theory but not with other modes of till genesis. It is then demonstrated, in the case of the British ice sheet, how the assumption of a deformational origin for tills can be used to infer time-dependent patterns of ice-sheet dynamic behaviour. By reference to an example from the Netherlands, it is argued that many till sequences interpreted as melt-out tills are more likely to have formed by subglacial sediment deformation.

scholarly journals The impact of the North American glacial topography on the evolution of the Eurasian ice sheet over the last glacial cycle

2016 ◽  
Vol 12 (5) ◽  
pp. 1225-1241 ◽  
Author(s):  
Johan Liakka ◽  
Marcus Löfverström ◽  
Florence Colleoni
Keyword(s):  
North American ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Stationary Wave ◽  
Ocean Heat Transport ◽  
Glacial Cycle ◽  
Last Glacial ◽  
The North ◽  
The Impact ◽  
The Last Glacial

Abstract. Modeling studies have shown that the continental-scale ice sheets in North America and Eurasia in the last glacial cycle had a large influence on the atmospheric circulation and thus yielded a climate distinctly different from the present. However, to what extent the two ice sheets influenced each others' growth trajectories remains largely unexplored. In this study we investigate how an ice sheet in North America influences the downstream evolution of the Eurasian ice sheet, using a thermomechanical ice-sheet model forced by climate data from atmospheric snapshot experiments of three distinctly different phases of the last glacial cycle: the Marine Isotope Stages 5b, 4, and 2 (Last Glacial Maximum – LGM). Owing to the large uncertainty associated with glacial changes in the Atlantic meridional overturning circulation, each atmospheric snapshot experiment was conducted using two distinctly different ocean heat transport representations. Our results suggest that changes in the North American paleo-topography may have largely controlled the zonal distribution of the Eurasian ice sheet. In the MIS4 and LGM experiments, the Eurasian ice sheet migrates westward towards the Atlantic sector – largely consistent with geological data and contemporary ice-sheet reconstructions – due to a low wave number stationary wave response, which yields a cooling in Europe and a warming in northeastern Siberia. The expansion of the North American ice sheet between MIS4 and the LGM amplifies the Siberian warm anomaly, which limits the glaciation there and may therefore help explain the progressive westward migration of the Eurasian ice sheet in this time period. The ocean heat transport only has a small influence on the stationary wave response to the North American glacial topography; however, because temperature anomalies have a smaller influence on an ice sheet's ablation in a colder climate than in a warmer one, the impact of the North American glacial topography on the Eurasian ice-sheet evolution is reduced for colder surface conditions in the North Atlantic. While the Eurasian ice sheet in the MIS4 and the LGM experiments appears to be in equilibrium with the simulated climate conditions, the MIS5b climate forcing is too warm to grow an ice sheet in Eurasia. First-order sensitivity experiments suggest that the MIS5b ice sheet was established during preceding colder stages.

scholarly journals How might the North American ice sheet influence the Northwestern Eurasian climate?

2015 ◽  
Vol 11 (1) ◽  
pp. 27-61 ◽  
Author(s):  
P. Beghin ◽  
S. Charbit ◽  
M. Kageyama ◽  
C. Dumas ◽  
C. Ritz
Keyword(s):  
Mass Balance ◽  
Atmospheric Circulation ◽  
North American ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Surface Mass Balance ◽  
Surface Mass ◽  
The North ◽  
Albedo Effect ◽  
Circulation Changes

Abstract. During the last glacial period (∼21 000 years ago), two continental-scale ice sheets covered the Canada and northern Europe. It is now widely acknowledged that these past ice sheets exerted a strong influence on climate by causing changes in atmospheric and oceanic circulations. In turn, these changes may have impacted the development of the ice sheets themselves through a combination of different feedback mechanisms. The present study is designed to investigate the potential impact of the North American ice sheet on the surface mass balance (SMB) of the Eurasian ice sheet through simulated changes in the past glacial atmospheric circulation. Using the LMDz5 atmospheric circulation model, we carried out twelve experiments run under constant Last Glacial Maximum (LGM) conditions for insolation, greenhouse gases and ocean. In the all experiments, the Eurasian ice sheet is removed. The twelve experiments differ in the North American ice-sheet topography, ranging from a white and flat (present-day topography) ice sheet to a full-size LGM ice sheet. This experimental design allows to disentangle the albedo and the topographic impacts of the North American ice sheet onto the climate. The results are compared to our baseline experiment where both the North American and the Eurasian ice sheets have been removed. In summer, we show that the only albedo effect of the American ice sheet modifies the pattern of planetary waves with respect to the no-ice sheet case, causing a cooling of the Eurasian region. By contrast, the atmospheric circulation changes induced by the topography of the North American ice sheet imply summer warming in Northwestern Eurasia. In winter, the Scandinavian and the Barents–Kara regions respond differently to the albedo effect: in response to atmospheric circulation changes, Scandinavia is warmed up and precipitation is more abundant whereas Barents–Kara area is cooled down, decreasing convection process and thus leading to less precipitation. The height increase of American ice sheet leads to less precipitation and snowfalls and colder temperatures over both Scandinavian and Barents–Kara sectors. The simulated temperature and precipitation fields have then been used to force an ice-sheet model and to compute the resulting surface mass balance over the Fennoscandian region as a function of the American ice-sheet configuration. It clearly appears that the SMB is dominated by the ablation signal. In response to the summer cooling induced by the American ice-sheet albedo, a highly positive SMB is simulated over the Eurasian ice sheet, leading thus to the growth of the ice sheet. On the contrary, the topography of the American ice sheet leads to more ablation, hence limiting its growth.

scholarly journals The impact of the North American ice sheet on the evolution of the Eurasian ice sheet during the last glacial cycle

2015 ◽  
Vol 11 (6) ◽  
pp. 5203-5241 ◽  
Author(s):  
J. Liakka ◽  
M. Löfverström ◽  
F. Colleoni
Keyword(s):  
North American ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Climate Data ◽  
Glacial Cycle ◽  
Atlantic Sector ◽  
Last Glacial ◽  
The North ◽  
The Impact ◽  
The Last Glacial

Abstract. Modeling studies show that the massive ice sheet expanding over the North American and Eurasian continents in the last glacial cycle has a large impact on the atmospheric stationary waves and thus yielded a glacial climate distinctly different from the present. However, to what extent the two ice sheets influenced each others growth trajectories remains largely unexplored. In this study we investigate how ice sheets in North America influence the downstream evolution of the Eurasian ice sheet, using a thermomechanical ice-sheet model forced by climate data from snapshot simulations of three distinctly different phases of the last glacial cycle: the Marine Isotope Stages 5b, 4 and 2 (LGM). Our results suggest that changes in the North American paleo-topography may have had a large influence on evolution of the Eurasian ice sheet. In the MIS4 and LGM experiments, the Eurasian ice sheet migrates westward towards the Atlantic sector – largely consistent with geological data and contemporary ice-sheet reconstructions – due to a low wavenumber stationary wave response, which yields a cooling in Europe and a warming in northeastern Siberia. The expansion of the North American ice sheet between MIS4 and LGM amplifies the Siberian warm anomaly, which limits the glaciation there and may therefore help to explain the progressive westward migration of the Eurasian ice sheet over this time period. While the Eurasian ice sheet in the MIS4 and LGM experiments appears to be in equilibrium with the simulated climate conditions, the MIS5b climate forcing is too warm to grow an ice sheet. First-order sensitivity experiments suggest that most of the MIS5b ice sheet was established during preceding colder stages.

scholarly journals Application of an ice sheet model to evaluate PMIP3 LGM climatologies over the North American ice sheets

2017 ◽  
Author(s):  
Jay R. Alder ◽  
Steve W. Hostetler
Keyword(s):  
North American ◽  
General Circulation ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Longwave Radiation ◽  
General Circulation Models ◽  
The North ◽  
Temperature And Precipitation ◽  
Simulated Surface

Abstract. We apply the Community Ice Sheet Model (CISM2) to the Palaeoclimate Modelling Intercomparison 3 (PMIP3) Last Glacial Maximum (LGM) simulations to determine if the general circulation models (GCMs) simulated surface temperature and precipitation climatologies would support the large North American ice sheets. We force CISM2 with eight PMIP3 GCMs, and an additional model, GENMOM. The ice sheet simulations indicate seven GCMs produce LGM temperature and precipitation climatologies that support positive mass balances of the Laurentide and Cordilleran ice sheets (LIS, CIS) in areas corresponding to those prescribed in the GCMs, and two GCMs simulate July temperatures that are too warm to support the ice sheets. Four of the nine GCMs support the development of ice sheets in Beringia in the CISM2, in conflict with the driving GCM and reconstructions that indicate the area was ice-free. We test the sensitivity of our results over a range of snow and ice positive degree-day factors, and we evaluate the role of albedo, and shortwave and longwave radiation in the simulations. Areas with perineal snow in the GCM simulations are found to correspond well to the CISM2 simulation of ice presence.

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