Climate and the Initiation of Maritime Ice Sheets

The lower latitude extension of polar water during Quaternary glaciations has two opposing effects on the mass balances of adjacent maritime ice sheets. Cooler air temperatures reduce ablation and increase the fraction of precipitation falling as snow, but also lead to reduced atmospheric moisture content and reduced precipitation. The effects of these contrasting processes on ice-sheet initiation are investigated using a coupled ice-sheet-atmospheric moisture model of the Loch Lomond ice sheet in Scotland (10 000 a B.P.). There is a delicate balance between the degree of cooling required to initiate ice accumulation and that which restricts the flow of moisture over the area. At the regional scale of Scotland, the combined effects of orographic enhancement and the inherent feedback between the rising ice-surface elevation and increasing mass balance are dominant, and ice-sheet growth accelerates. Comparison of the results from models using different wind directions suggests that south-westerly winds were prevalent during the Loch Lomond glaciation in contrast to the dominant westerly winds of the present day. The modelling experiments demonstrate the sensitivity and complexity of the links between ocean surface cooling and ice-sheet growth, particularly at the early stages of a glacial cycle.

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Climate and the Initiation of Maritime Ice Sheets

Annals of Glaciology ◽

10.3189/s026030550000865x ◽

1990 ◽

Vol 14 ◽

pp. 232-237

Author(s):

Antony Payne ◽

David Sugden

Keyword(s):

Regional Scale ◽

Ice Sheets ◽

Ice Sheet ◽

Lower Latitude ◽

Atmospheric Moisture ◽

Glacial Cycle ◽

Surface Cooling ◽

Loch Lomond ◽

Westerly Winds ◽

Comparison Of The Results

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

Climate of the Past ◽

10.5194/cp-5-329-2009 ◽

2009 ◽

Vol 5 (3) ◽

pp. 329-345 ◽

Cited By ~ 62

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.

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Glaciodynamic context of subglacial bedform generation and preservation

Annals of Glaciology ◽

10.3189/172756499781821832 ◽

1999 ◽

Vol 28 ◽

pp. 23-32 ◽

Cited By ~ 80

Author(s):

Chris D. Clark

Keyword(s):

Ice Sheets ◽

Ice Sheet ◽

Shear Stresses ◽

Morphometric Characteristics ◽

Glacial Cycle ◽

Sheet Flow ◽

Ice Flow ◽

Ice Stream ◽

Highly Sensitive ◽

Basal Shear

AbstractSubglacially-produced drift lineations provide spatially extensive evidence of ice flow that can be used to aid reconstructions of the evolution of former ice sheets. Such reconstructions, however, are highly sensitive to assumptions made about the glaciodynamic context of lineament generation; when during the glacial cycle and where within the ice sheet were they produced. A range of glaciodynamic contexts are explored which include: sheet-flow submarginally restricted; sheet-flow pervasive; sheet- flow patch; ice stream; and surge or re-advance. Examples of each are provided. The crux of deciphering the appropriate context is whether lineations were laid down time-trans-gressively or isochronously. It is proposed that spatial and morphometric characteristics of lineations, and their association with other landforms, can be used as objective criteria to help distinguish between these cases.A logically complete ice-sheet reconstruction must also account for the observed patches of older lineations and other relict surfaces and deposits that have survived erasure by subsequent ice flow. A range of potential preservation mechanisms are explored, including: cold- based ice; low basal-shear stresses; shallowing of the deforming layer; and basal uncoupling.

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Does a difference in ice sheets between Marine Isotope Stages 3 and 5a affect the duration of stadials?

10.5194/cp-2021-47 ◽

2021 ◽

Author(s):

Sam Sherriff-Tadano ◽

Ayako Abe-Ouchi ◽

Akira Oka ◽

Takahito Mitsui ◽

Fuyuki Saito

Keyword(s):

Sea Ice ◽

Recovery Time ◽

Ice Sheets ◽

Ice Sheet ◽

Meridional Overturning Circulation ◽

Surface Cooling ◽

Glacial Ice ◽

Formation Region ◽

Background Climate ◽

The Impact

Abstract. Glacial periods undergo frequent climate shifts between warm interstadials and cold stadials on a millennial time-scale. Recent studies have shown that the duration of these climate modes varies with the background climate; a colder background climate and lower CO2 generally results in a shorter interstadial and a longer stadial through its impact on the Atlantic Meridional Overturning Circulation (AMOC). However, the duration of stadials was shorter during the Marine Isotope Stage 3 (MIS3) compared with MIS5, despite the colder climate in MIS3, suggesting potential control from other climate factors on the duration of stadials. In this study, we investigated the role of glacial ice sheets. For this purpose, freshwater hosing experiments were conducted with an atmosphere–ocean general circulation model under MIS5a, MIS3 and MIS3 with MIS5a ice sheet conditions. The impact of ice sheet differences on the duration of the stadials was evaluated by comparing recovery times of the AMOC after freshwater forcing was reduced. Hosing experiments showed a slightly shorter recovery time of the AMOC in MIS3 compared with MIS5a, which was consistent with ice core data. We found that larger glacial ice sheets in MIS3 shortened the recovery time. Sensitivity experiments showed that stronger surface winds over the North Atlantic shortened the recovery time by increasing the surface salinity and decreasing the sea ice amount in the deepwater formation region, which set favourable conditions for oceanic convection. In contrast, we also found that surface cooling by larger ice sheets tended to increase the recovery time of the AMOC by increasing the sea ice thickness over the deepwater formation region. Thus, this study suggests that the larger ice sheet in MIS3 compared with MIS5a could have contributed to the shortening of stadials in MIS3, despite the climate being colder than that of MIS5a, when the effect of surface wind played a larger role.

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

The Cryosphere Discussions ◽

10.5194/tcd-6-4897-2012 ◽

2012 ◽

Vol 6 (6) ◽

pp. 4897-4938 ◽

Cited By ~ 1

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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Impact of mid-glacial ice sheets on deep ocean circulation and global climate: Role of surface cooling on the AMOC

10.5194/cp-2020-75 ◽

2020 ◽

Author(s):

Sam Sherriff-Tadano ◽

Ayako Abe-Ouchi ◽

Akira Oka

Keyword(s):

North Atlantic ◽

General Circulation ◽

Global Climate ◽

Surface Wind ◽

Ice Sheets ◽

Ice Sheet ◽

Meridional Overturning Circulation ◽

Strengthening Effect ◽

Surface Cooling ◽

Glacial Ice

Abstract. This study explores the effect of southward expansion of mid-glacial ice sheets on the global climate and the Atlantic meridional overturning circulation (AMOC), as well as the processes by which the ice sheets modify the AMOC. For this purpose, simulations of Marine Isotope Stage (MIS) 3 and 5a are performed with an atmosphere-ocean general circulation model. In the MIS3 and MIS5a simulations, the global average temperature decreases by 5.0 °C and 2.2 °C, respectively, compared with the preindustrial climate simulation. The AMOC weakens by 3 % in MIS3, whereas it is enhanced by 16 % in MIS5a, both of which are consistent with a reconstruction. Sensitivity experiments extracting the effect of the expansion of glacial ice sheets from MIS5a to MIS3 show a global cooling of 1.1 °C, contributing to about 40 % of the total surface cooling from MIS5a to MIS3. These experiments also demonstrate that the ice sheet expansion leads to a surface cooling of 2 °C over the Southern Ocean as a result of colder North Atlantic deep water. We find that the southward expansion of the mid-glacial ice sheet exerts a small impact on the AMOC. Partially coupled experiments reveal that the global surface cooling by the glacial ice sheet tends to reduce the AMOC by increasing the sea ice at both poles, and hence compensates for the strengthening effect of the enhanced surface wind over the North Atlantic. Our results show that the total effect of glacial ice sheets on the AMOC is determined by the two competing effects, surface wind and surface cooling. The relative strength of surface wind and surface cooling depends on the ice sheet configuration, and the strength of the surface cooling can be comparable to that of surface wind when changes in the extent of ice sheet are prominent.

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Ice-sheet models as tools for palaeoclimatic analysis: the example of the European ice sheet through the last glacial cycle

Annals of Glaciology ◽

10.1017/s0260305500015676 ◽

1995 ◽

Vol 21 ◽

pp. 103-110 ◽

Cited By ~ 10

Author(s):

G. S. Boulton ◽

N. Hulton ◽

M. Vautravers

Keyword(s):

Numerical Model ◽

Ice Sheets ◽

Ice Sheet ◽

Early Holocene ◽

Climate Forcing ◽

Glacial Period ◽

Glacial Cycle ◽

Last Glacial ◽

Sheet Surface ◽

The Last Glacial

A numerical model is used to simulate ice-sheet behaviour in Europe through the last glacial cycle. It is used in two modes: a forward mode, in which the model is driven by a proxy palaeoclimate record and the output compared with a geological reconstruction of ice-sheet fluctuation; and an inverse mode, in which we determine the climate function that would be required to simulate geologically reconstructed ice-sheet fluctuations. From these simulations it is concluded that extra-glacial climates may be poor predictors of ice-sheet surface climates, and that climatic transitions during the glacial period may have been much more rapid and the intensity of warming during the early Holocene much greater than hitherto supposed. Stronger climate forcing is required to drive ice-sheet expansion when sliding occurs at the bed compared with a non-sliding bed. Sliding ice sheets grow more slowly and decay more rapidly than non-sliding ice sheets with the same climate forcing.

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

Journal of Glaciology ◽

10.1017/jog.2019.42 ◽

2019 ◽

Vol 65 (252) ◽

pp. 645-661 ◽

Cited By ~ 1

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.

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

Annals of Glaciology ◽

10.1017/s026030550001524x ◽

1996 ◽

Vol 22 ◽

pp. 75-84 ◽

Cited By ~ 75

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.

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

Climate of the Past ◽

10.5194/cp-10-1453-2014 ◽

2014 ◽

Vol 10 (4) ◽

pp. 1453-1471 ◽

Cited By ~ 57

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.

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