scholarly journals Subglacial floods beneath ice sheets

2006 ◽  
Vol 364 (1844) ◽  
pp. 1769-1794 ◽  
Author(s):  
G.W Evatt ◽  
A.C Fowler ◽  
C.D Clark ◽  
N.R.J Hulton
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Age ◽  
Laurentide Ice Sheet ◽  
Ice Caps ◽  
The Past ◽  
Last Ice Age ◽  
Climatic Disturbances ◽  
Time Periodic ◽  
Do So

Subglacial floods (jökulhlaups) are well documented as occurring beneath present day glaciers and ice caps. In addition, it is known that massive floods have occurred from ice-dammed lakes proximal to the Laurentide ice sheet during the last ice age, and it has been suggested that at least one such flood below the waning ice sheet was responsible for a dramatic cooling event some 8000 years ago. We propose that drainage of lakes from beneath ice sheets will generally occur in a time-periodic fashion, and that such floods can be of severe magnitude. Such hydraulic eruptions are likely to have caused severe climatic disturbances in the past, and may well do so in the future.

Paleoecology and Late Quaternary Environments of the Colorado Rockies

2001 ◽  
Author(s):  
Scott A. Elias
Keyword(s):  
North America ◽  
Late Quaternary ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Rocky Mountain ◽  
Mountain Region ◽  
Ice Age ◽  
Rocky Mountain Region ◽  
Last Ice Age ◽  
Teton Range

Present-day environments cannot be completely understood without knowledge of their history since the last ice age. Paleoecological studies show that the modern ecosystems did not spring full-blown onto the Rocky Mountain region within the last few centuries. Rather, they are the product of a massive reshuffling of species that was brought about by the last ice age and indeed continues to this day. Chronologically, this chapter covers the late Quaternary Period: the last 25,000 years. During this interval, ice sheets advanced southward, covering Canada and much of the northern tier of states in the United States. Glaciers crept down from mountaintops to fill high valleys in the Rockies and Sierras. The late Quaternary interval is important because it bridges the gap between the ice-age world and modern environments and biota. It was a time of great change, in both physical environments and biological communities. The Wisconsin Glaciation is called the Pinedale Glaciation in the Rocky Mountain region (after terminal moraines near the town of Pinedale, Wyoming; see chapter 4). The Pinedale Glaciation began after the last (Sangamon) Interglaciation, perhaps 110,000 radiocarbon years before present (yr BP), and included at least two major ice advances and retreats. These glacial events took different forms in different regions. The Laurentide Ice Sheet covered much of northeastern and north-central North America, and the Cordilleran Ice Sheet covered much of northwestern North America. The two ice sheets covered more than 16 million km2 and contained one third of all the ice in the world’s glaciers during this period. The history of glaciation is not as well resolved for the Colorado Front Range region as it is for regions farther north. For instance, although a chronology of three separate ice advances has been established for the Teton Range during Pinedale times, in northern Colorado we know only that there were earlier and later Pinedale ice advances. We do not know when the earlier advance (or multiple advances) took place. However, based on geologic evidence (Madole and Shroba 1979), the early Pinedale glaciation was more extensive than the late Pinedale was.

scholarly journals The Atmosphere’s Response to the Ice Sheets of the Last Glacial Maximum

1990 ◽  
Vol 14 ◽  
pp. 32-38 ◽  
Author(s):  
Kerry H. Cook
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Age ◽  
Laurentide Ice Sheet ◽  
Stationary Waves ◽  
The North ◽  
The Last Glacial

This paper discusses some modeling results that indicate how the atmospheric response to the topography of the continental ice of the Last Glacial Maximum (LGM) may be related to the cold North Atlantic Ocean of that time. Broccoli and Manabe (1987) used a three-dimensional general circulation model (GCM) of the atmosphere coupled with a fixed-depth, static ocean mixed-layer model with ice-age boundary conditions to investigate the individual influences of the CLIMAP ice sheets, snow-free land albedos, and reduced atmospheric CO2 concentrations. They found that the ice sheets are the most influential of the ice-age boundary conditions in modifying the northern hemisphere climate, and that the presence of continental ice sheets alone leads to cooling over the North Atlantic Ocean. One approach for extending these GCM results is to consider the stationary waves generated by the ice sheets. Cook and Held (1988) showed that a linearized, steady-state, primitive equation model can give a reasonable simulation of the GCM’s stationary waves forced by the Laurentide ice sheet. The linear model analysis suggests that the mechanical effect of the changed slope of the surface, and not changes in the diabatic heating (e.g. the high surface albedos) or time-dependent transports that necessarily accompany the ice sheet in the GCM, is largely responsible for the ice sheet’s influence. To obtain the ice-age stationary-wave simulation, the linear model must be linearized about the zonal mean fields from the GCM’s ice-age climate. This is the case because the proximity of the cold polar air to the region of adiabatic heating on the downslope of the Laurentide ice sheet is an important factor in determining the stationary waves. During the ice age, cold air can be transported southward to balance this downslope heating by small perturbations in the meridional wind, consistent with linear theory. Since the meridional temperature gradient is more closely related to the surface albedo (ice extent) than to the ice volume, this suggests a mechanism by which changes in the stationary waves and, therefore, their cooling influence at low levels over the North Atlantic Ocean, can occur on time scales faster than those associated with large changes in continental ice volume.

scholarly journals A Closer look at the Proposed Late-Wisconsin-Weichselian Arctic Ice Sheet

1979 ◽  
Vol 24 (90) ◽  
pp. 497-500
Author(s):  
J. L. Fastook ◽  
R. Sweet ◽  
T. J. Hughes
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
High Arctic ◽  
Ice Age ◽  
Arctic Seas ◽  
Ice Caps ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
Arctic Ice ◽  
The Tropics

AbstractThe CLIMAP 18000 years b.p. experiment required reconstructing late-Wisconsin-Weichselian ice sheets. In the Northern Hemisphere, the greatest uncertainty in these reconstructions is the area covered by ice sheets. Two schools of thought exist (Hughes and others, in press). The minimum-ice-sheet school holds that ice sheets originated from present ice caps in the High Arctic islands, but the northern seaward margins of these ice sheets retreated as the southern landward margins advanced. This occurred because northern margins became isolated from sources of precipitation as Arctic seas became permanently ice-covered and the advancing southern margin changed atmospheric circulation patterns. In this view, these ice sheets stay about the same size and migrate southward during an ice age. Northern margins rarely reach sea-level during the later stage of the ice age so no marine portions form and ablation is by melting or sublimation. Marine portions formed only when the ice sheets migrated across shallow seas between the High Arctic islands and the mainland. At the end of the ice age, huge amounts of heat had to be transferred from the tropics to the ice sheets in order to account for late-Wisconsin-Weichselian and Holocene retreat-rates by melting along ice-sheet margins.

scholarly journals Isotope Ratios of Large Ice Masses

1985 ◽  
Vol 31 (109) ◽  
pp. 372-374
Author(s):  
A.S. Jones
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Isotope Ratios ◽  
Ice Age ◽  
Last Ice Age

AbstractA model is proposed for determining the relative proportions of 16O and 18O in large ice sheets. Values calculated using this model are in agreement with published values for Antarctica and Greenland. It is intended to use the model for comparisons between the known ocean isotopie records and postulated ice-sheet masses during the last ice age.

scholarly journals The Atmosphere’s Response to the Ice Sheets of the Last Glacial Maximum

1990 ◽  
Vol 14 ◽  
pp. 32-38
Author(s):  
Kerry H. Cook
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Age ◽  
Laurentide Ice Sheet ◽  
Stationary Waves ◽  
The North ◽  
The Last Glacial

This paper discusses some modeling results that indicate how the atmospheric response to the topography of the continental ice of the Last Glacial Maximum (LGM) may be related to the cold North Atlantic Ocean of that time. Broccoli and Manabe (1987) used a three-dimensional general circulation model (GCM) of the atmosphere coupled with a fixed-depth, static ocean mixed-layer model with ice-age boundary conditions to investigate the individual influences of the CLIMAP ice sheets, snow-free land albedos, and reduced atmospheric CO2 concentrations. They found that the ice sheets are the most influential of the ice-age boundary conditions in modifying the northern hemisphere climate, and that the presence of continental ice sheets alone leads to cooling over the North Atlantic Ocean.One approach for extending these GCM results is to consider the stationary waves generated by the ice sheets. Cook and Held (1988) showed that a linearized, steady-state, primitive equation model can give a reasonable simulation of the GCM’s stationary waves forced by the Laurentide ice sheet. The linear model analysis suggests that the mechanical effect of the changed slope of the surface, and not changes in the diabatic heating (e.g. the high surface albedos) or time-dependent transports that necessarily accompany the ice sheet in the GCM, is largely responsible for the ice sheet’s influence. To obtain the ice-age stationary-wave simulation, the linear model must be linearized about the zonal mean fields from the GCM’s ice-age climate. This is the case because the proximity of the cold polar air to the region of adiabatic heating on the downslope of the Laurentide ice sheet is an important factor in determining the stationary waves. During the ice age, cold air can be transported southward to balance this downslope heating by small perturbations in the meridional wind, consistent with linear theory. Since the meridional temperature gradient is more closely related to the surface albedo (ice extent) than to the ice volume, this suggests a mechanism by which changes in the stationary waves and, therefore, their cooling influence at low levels over the North Atlantic Ocean, can occur on time scales faster than those associated with large changes in continental ice volume.

scholarly journals A Closer look at the Proposed Late-Wisconsin-Weichselian Arctic Ice Sheet

1979 ◽  
Vol 24 (90) ◽  
pp. 497-500 ◽  
Author(s):  
J. L. Fastook ◽  
R. Sweet ◽  
T. J. Hughes
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
High Arctic ◽  
Ice Age ◽  
Arctic Seas ◽  
Ice Caps ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
Arctic Ice ◽  
The Tropics

Abstract The CLIMAP 18000 years b.p. experiment required reconstructing late-Wisconsin-Weichselian ice sheets. In the Northern Hemisphere, the greatest uncertainty in these reconstructions is the area covered by ice sheets. Two schools of thought exist (Hughes and others, in press). The minimum-ice-sheet school holds that ice sheets originated from present ice caps in the High Arctic islands, but the northern seaward margins of these ice sheets retreated as the southern landward margins advanced. This occurred because northern margins became isolated from sources of precipitation as Arctic seas became permanently ice-covered and the advancing southern margin changed atmospheric circulation patterns. In this view, these ice sheets stay about the same size and migrate southward during an ice age. Northern margins rarely reach sea-level during the later stage of the ice age so no marine portions form and ablation is by melting or sublimation. Marine portions formed only when the ice sheets migrated across shallow seas between the High Arctic islands and the mainland. At the end of the ice age, huge amounts of heat had to be transferred from the tropics to the ice sheets in order to account for late-Wisconsin-Weichselian and Holocene retreat-rates by melting along ice-sheet margins.

scholarly journals Isotope Ratios of Large Ice Masses

1985 ◽  
Vol 31 (109) ◽  
pp. 372-374
Author(s):  
A.S. Jones
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Isotope Ratios ◽  
Ice Age ◽  
Last Ice Age

AbstractA model is proposed for determining the relative proportions of16O and18O in large ice sheets. Values calculated using this model are in agreement with published values for Antarctica and Greenland. It is intended to use the model for comparisons between the known ocean isotopie records and postulated ice-sheet masses during the last ice age.

8. Glaciers of the past

2018 ◽  
pp. 146-152
Author(s):  
David J. A. Evans
Keyword(s):  
Numerical Models ◽  
Ice Core ◽  
Three Dimensional ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Aerial Imagery ◽  
The Past ◽  
Glacial Landforms

To reconstruct the former extent and dynamics of ice sheets and glaciers requires a knowledge of process-form relationships that goes beyond individual landform types. Instead, glacial geomorphologists need to analyse large areas of glaciated terrain in a more holistic way, combining the whole range of glacial landforms and sediments to reconstruct glacier systems of the past, a subject now known as palaeoglaciology. ‘Glaciers of the past’ explains how the combination of aerial imagery and landform analysis is used in palaeoglaciological reconstruction. Increasingly powerful computers are making it possible to compile sophisticated numerical models that use our knowledge of glaciological processes and ice-core-derived palaeoclimate data to create three-dimensional glacier and ice sheet reconstructions.

scholarly journals The influence of ice sheets on temperature during the past 38 million years inferred from a one-dimensional ice sheet–climate model

2017 ◽  
Vol 13 (9) ◽  
pp. 1243-1257 ◽  
Author(s):  
Lennert B. Stap ◽  
Roderik S. W. van de Wal ◽  
Bas de Boer ◽  
Richard Bintanja ◽  
Lucas J. Lourens
Keyword(s):  
Climate Model ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Atmospheric Temperature ◽  
Temperature Changes ◽  
One Dimensional ◽  
Ice Volume ◽  
The Past ◽  
Polar Amplification ◽  
The Antarctic

Abstract. Since the inception of the Antarctic ice sheet at the Eocene–Oligocene transition (∼ 34 Myr ago), land ice has played a crucial role in Earth's climate. Through feedbacks in the climate system, land ice variability modifies atmospheric temperature changes induced by orbital, topographical, and greenhouse gas variations. Quantification of these feedbacks on long timescales has hitherto scarcely been undertaken. In this study, we use a zonally averaged energy balance climate model bidirectionally coupled to a one-dimensional ice sheet model, capturing the ice–albedo and surface–height–temperature feedbacks. Potentially important transient changes in topographic boundary conditions by tectonics and erosion are not taken into account but are briefly discussed. The relative simplicity of the coupled model allows us to perform integrations over the past 38 Myr in a fully transient fashion using a benthic oxygen isotope record as forcing to inversely simulate CO2. Firstly, we find that the results of the simulations over the past 5 Myr are dependent on whether the model run is started at 5 or 38 Myr ago. This is because the relation between CO2 and temperature is subject to hysteresis. When the climate cools from very high CO2 levels, as in the longer transient 38 Myr run, temperatures in the lower CO2 range of the past 5 Myr are higher than when the climate is initialised at low temperatures. Consequently, the modelled CO2 concentrations depend on the initial state. Taking the realistic warm initialisation into account, we come to a best estimate of CO2, temperature, ice-volume-equivalent sea level, and benthic δ18O over the past 38 Myr. Secondly, we study the influence of ice sheets on the evolution of global temperature and polar amplification by comparing runs with ice sheet–climate interaction switched on and off. By passing only albedo or surface height changes to the climate model, we can distinguish the separate effects of the ice–albedo and surface–height–temperature feedbacks. We find that ice volume variability has a strong enhancing effect on atmospheric temperature changes, particularly in the regions where the ice sheets are located. As a result, polar amplification in the Northern Hemisphere decreases towards warmer climates as there is little land ice left to melt. Conversely, decay of the Antarctic ice sheet increases polar amplification in the Southern Hemisphere in the high-CO2 regime. Our results also show that in cooler climates than the pre-industrial, the ice–albedo feedback predominates the surface–height–temperature feedback, while in warmer climates they are more equal in strength.

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.

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