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In the Arctic, boreal-type forests dominated all the way to the present Arctic Ocean where tundra exists today. This has been verified by finds of fossil wood at a number of sites in northern Greenland and Arctic Canada. Fossil wood logs that have been identified include Larix , Pinus and Picea. Fossil mammalian remains include the extinct rabbit Hypolagus , and fossil insects and marine mollusks from a number of sites around the Arctic confirm with a considerably warmer-than-present environment prior to the onset of Pleistocene cooling and expanding Arctic glaciers. Paleogeographical reconstructions for the Pliocene in the Arctic suggest that summer sea surface temperatures SST in the Arctic Ocean were at least o C higher than today, and sea ice cover was considerably reduced or even absent during long periods of time.

There was considerably more rainfall over the Arctic, originating over the warmer Arctic Ocean, and permafrost was probably restricted to higher terrain. Because there were less ice volumes at high latitudes, global sea level may have been as much as 30m higher than at present during the warmest intervals. The peak phases of warmth during the Pliocene were mostly during the interval Ma the mid-Pliocene , although almost all of the Pliocene was warmer than today's world.

The Pliocene warmth in the Arctic has been enigmatic for our understanding of what controls the Quaternary development of climate and glaciations, since the present continental configuration was largely in place in Pliocene.

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The Arctic then as now experienced a polar night north of the polar circle. The causes of the generally warmer climate of the Pliocene are something of a mystery. The warmth may have been related to changes in ocean and atmospheric circulation patterns, perhaps combined with higher-than-present concentrations of greenhouse gases in the atmosphere. Temperature estimates derived from paleodata reveal that when the global temperature warms, changes at higher latitudes, and in the Polar Regions in particular, are systematically larger than nearer the equator.

In general, climate models do a better job of estimating global temperature changes through time than regional changes. This is because the energy budget of the entire planet is affected. Regional changes reflect the response of the atmosphere and ocean circulation to changes in the total energy budget, and as a result, are more difficult to model and understand. One of the challenges for Pliocene paleogeographical reconstructions in the Arctic is to provide an understanding, in the perspective of the geologic record, of possible environmental responses to a future greenhouse situation.

Deposits from this marine transgression are particularly pronounced along the northern Russian and Siberian coastal lowlands. Regional SST zones also migrated, and sub-tropical warm water was pushed northwards in the North Atlantic. Estimates of SST suggest considerably warmer waters than present in coastal Arctic waters, and even the Arctic Ocean may have been ice-free some summers.

Global eustatic sea level was m higher than today as a result of extensive melting of glaciers on the continents and thermal expansion of ocean water. Negative values mean that the last interglacial ocean was colder than today.

Note that most SST values are similar to present. In northern Russia and western to central Siberia, Eemian marine and estuarine sediments are widely exposed in river sections from the Kola Peninsula in the west to the Taymyr Peninsula in the east. Their fossil content of warm boreal benthic faunas, in areas that today have arctic waters lacking boreal species, easily identifies them.

Finds of fossil marine mammals, such as Narwhales, in marine sediments on the Siberian high arctic islands suggest at least seasonally reduced sea-ice cover compared to the present. The warm Eemian climate in the Eurasian north is also evidenced by more northerly tree line limits than present, with boreal forests spreading all the way to the Arctic Ocean in northern Russia. Summer temperature estimates suggest o C warmer temperatures than present in the Eurasian north, depending on site and proximity to the Arctic Ocean.

Studies of marine and terrestrial deposits of the last interglacial in Beringia suggest that it was warmer than present conditions. At the same time, the treeline was more than km further north in places, displacing the tundra. A compilation of last interglacial localities indicates that boreal forest was much extended beyond its present range in Alaska and Yukon Territory and probably extended to higher elevation sites now occupied by tundra in the interior.

The treeline on Chukotka Peninsula, easternmost Siberia, was more than km further north than today and displacing the tundra all the way to the Arctic Ocean. Summer temperature reconstructions for Beringia vary considerably, from showing values similar to modern to considerably warmer summers. This suggests that summer temperatures were at least o C warmer than present.

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To the contrary, fossil molluscs from proposed Eemian deposits on Svalbard suggest SST similar to modern, but not as warm as during the Holocene climate optimum see below. Most fossil mollusc species are representative of arctic conditions, but few finds of sub-arctic species suggest the marine climate may have been somewhat warmer than present. Figure from Svendsen et al. During the 90 ka BP glaciation an ice sheet centred in the Barents Sea-Kara Sea area expanded far onto the Russian continent and blocked the northbound drainage of rivers towards the Arctic Ocean Fig.

A re-growth of the ice sheet occurred ka BP. The Barents-Kara ice sheet expanded well onto the continent in N Russia and covered the northwestern rim of the Taymyr Peninsula, also leading to blockage of rivers draining to the north and the formation of huge, ice-dammed lakes. Siberia, east of Taymyr Peninsula, was ice-free throughout the last interglacial-glacial cycle, and constituted an enormous steppe environment. The floral composition of the mammoth steppe may have its closest modern analogue with the Central Asian grass steppe, where grasses form the base of the nutritional chain although brushes and trees have occurred in sheltered and wet locations.

In southwestern Alaska glaciers broadly extended beyond the present coast, while further north the glacial expansion was more limited. This was probably due to differences in proximity to moisture sources. A frequently cited illustration of glacial and sea ice cover in the Northern Hemisphere compared to present situation. We now know that Eurasian continental ice volumes and coverage are overe stimated in this reconstruction see Forman et al.

It is generally thought to have occurred around ka BP, but it is, however, acknowledged that the timing, duration and extent of ice cover at LGM differed considerably in different regions of the Arctic. A recent Svendsen et al. Recent interpretations of the northern Eurasian glacial record suggest that most of the mainland of N Russia and Siberia remained ice-free during the LGM.

It probably coalesced with an ice sheet over Novaya Zemlya as well as with the Scandinavian inland ice sheet. The Greenland inland ice expanded considerably, filling many outer shelf basins and extending out on the shelf areas. Major ice-streams probably developed in many Greenland fjords, feeding extensive ice shelves fringing the ice sheet. The LGM ice cover over northern Greenland was thin and probably cold-based except in the fjords where fast moving outlet glaciers and ice streams terminated or fed ice shelves.

In northwestern Greenland, the ice coalesced with the Innuitian ice sheet over Ellesmere Island. West of the Innuitian ice sheet and north of the Laurentide ice sheet, some islands e. Baffin Island was heavily glaciated and partly overrun by ice of the Laurentide ice sheet advancing from the Foxe Basin to the west. The ice drained through ice streams developing in the major fjord systems on southeastern and eastern Baffin Island.

It has been suggested that some coastal nunataks on eastern Baffin Island remained ice-free during the LGM. Climatic conditions in Beringia during the LGM are generally believed to have been cold and dry. Glaciers grew in regional mountain ranges, but reached the lowlands only south of the Alaska Range. The environment was largely a mosaic of steppe-tundra landscapes.

The lowest parts of the Bering Land Bridge were covered with shrub tundra. References and suggested further reading :. Clark, P. Quaternary Science Reviews, 21 , Crowley, T. Paleoclimatology - Oxford Monographs on Geology and Geophysics , Figure 6. Oxford University Press, Inc. New York, NY. Elias, S.

Festschrift in Honour of D. Quaternary Science Reviews , 20 , Forman, S. Quaternary Science Reviews 23 , — Frenzel, B. Manley, W. Svendsen, J. Quaternary Science Reviews , 23 , Thiede, J. Global and Planetary Change , 31 , A general definition of periglacial environments refers to conditions where frost-action and permafrost related processes dominate the physical environment. Common to all periglacial environments are circles of freezing and thawing of the ground and the presence of permafrost, or perennially frozen ground.

Presently these environments primarily occur at high latitudes in the Arctic and Antarctic and at high elevations in mountainous areas at mid-latitudes. Permafrost in the Northern Hemisphere. Illustration credits: www. Certain processes and geological products are unique to the periglacial environment. These include the formation of permafrost and wedge and injection ice, development of thermal contraction cracks, and the formation of thermokarsts due to thawing of permafrost.

Other processes, such as frost heaving, soil creep, solifluction and wind action processes acting on barren soils are also important in the periglacial environment. Recognizing and interpreting fossil periglacial phenomena is an integrated part of reconstructing Quaternary climate development. Fossil periglacial phenomena commonly occur at mid-latitudes in Eurasia and N America; areas that experienced periglacial conditions during cold spells of the Pleistocene but which today have temperate climates. Pleistocene periglacial conditions were not restricted to mid-latitude locations. Extensive areas in the central and eastern Siberian Arctic, as well as parts of the Beringian area and north-western Canadian Arctic remained ice-free through long periods in the Pleistocene and were subject to intensive periglacial activity.

A number of phenomena are indicative of frozen ground and intense frost action, and can be used for paleoclimate reconstructions. These include:. Patterned ground, Thule, Greenland. Frost fissures.

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These are wedge-shaped structures interpreted to be casts of thermal contraction cracks. Since the development of frost fissures only occurs under permafrost conditions and intense cooling o to —20 o C these are first order indicators of periglacial environments. Fossil frost fissures, in the form of frost fissure polygons and ice- and sand wedge casts, have been described from extensive areas in northern and central Europe and N America, and have been mapped for providing evidence on distribution of Pleistocene permafrost.

These indicate frost action and weathering. Extensive accumulations of angular boulders blanketing mountain plateaux and talus scree accumulations along mountain slopes are thought to have formed primarily by frost wedging and cracking of bedrock. In both Europe, N America and Asia, blockfields talus and frost-shattered debris occur on uplands and mountains outside present day distribution of permafrost, and are taken to indicate occurrences of Pleistocene permafrost.

Rock glaciers form in the periglacial zone of mountains, and are unique permafrost landforms. They are often fed by taluses formed upslope by frost shattering of bedrock. Relict inactive rock glaciers, occurring below the periglacial zone or below the treeline, have been reported from many mountainous areas in the world. In the Alps many of those turned inactive by the end of the Pleistocene.

Open system pingo in upper Eskerdalen, 35 km east of Longyearbyen, Svalbard.

Earth's History of Glaciation and Deglaciation

In permafrost areas with frequent freeze-thaw cycles, frost heaving of the surface layers can lead to down-slope movement of the material by frost creep. This is a process that probably was more active at mid-latitudes than high latitudes during the Pleistocene, since mid-latitudes experienced more freeze-thaw cycles than colder arctic environments. Frost-disturbed deposits, or cryoturbated deposits as they also are referred to, very frequently occur in Pleistocene soils at both high and mid-latitude sites. They form by repeated frost heaving and turbation in the active layer, as well as by gravity loading and water-saturation in connection with thermokarst degradation.

Photo: unknown photographer. Hillslope and summit tors commonly occur in both high and mid-latitude uplands and mountain areas. But it has not always been so. During the Pliocene, global temperatures, particularly at high latitudes, are believed to have been significantly warmer than today. Generally, the Pliocene world was warmer than at present. The ancient distribution of warm-climate ocean plankton, and of animal and plant fossils on land, shows that globally the greatest warming relative to the present situation was in the Arctic and cool-temperate latitudes of the Northern Hemisphere.

There, summer and annual mean temperatures were often warm enough to allow species of animals and plants to exist hundreds of kilometers north of the ranges of their nearest present-day relatives. In the Arctic, boreal-type forests dominated all the way to the present Arctic Ocean where tundra exists today. This has been verified by finds of fossil wood at a number of sites in northern Greenland and Arctic Canada. Fossil wood logs that have been identified include Larix , Pinus and Picea.

Fossil mammalian remains include the extinct rabbit Hypolagus , and fossil insects and marine mollusks from a number of sites around the Arctic confirm with a considerably warmer-than-present environment prior to the onset of Pleistocene cooling and expanding Arctic glaciers. Paleogeographical reconstructions for the Pliocene in the Arctic suggest that summer sea surface temperatures SST in the Arctic Ocean were at least o C higher than today, and sea ice cover was considerably reduced or even absent during long periods of time.

There was considerably more rainfall over the Arctic, originating over the warmer Arctic Ocean, and permafrost was probably restricted to higher terrain. Because there were less ice volumes at high latitudes, global sea level may have been as much as 30m higher than at present during the warmest intervals.

The peak phases of warmth during the Pliocene were mostly during the interval Ma the mid-Pliocene , although almost all of the Pliocene was warmer than today's world.


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The Pliocene warmth in the Arctic has been enigmatic for our understanding of what controls the Quaternary development of climate and glaciations, since the present continental configuration was largely in place in Pliocene. The Arctic then as now experienced a polar night north of the polar circle. The causes of the generally warmer climate of the Pliocene are something of a mystery. The warmth may have been related to changes in ocean and atmospheric circulation patterns, perhaps combined with higher-than-present concentrations of greenhouse gases in the atmosphere.

Temperature estimates derived from paleodata reveal that when the global temperature warms, changes at higher latitudes, and in the Polar Regions in particular, are systematically larger than nearer the equator. In general, climate models do a better job of estimating global temperature changes through time than regional changes. This is because the energy budget of the entire planet is affected.

Regional changes reflect the response of the atmosphere and ocean circulation to changes in the total energy budget, and as a result, are more difficult to model and understand. One of the challenges for Pliocene paleogeographical reconstructions in the Arctic is to provide an understanding, in the perspective of the geologic record, of possible environmental responses to a future greenhouse situation. Deposits from this marine transgression are particularly pronounced along the northern Russian and Siberian coastal lowlands. Regional SST zones also migrated, and sub-tropical warm water was pushed northwards in the North Atlantic.

Estimates of SST suggest considerably warmer waters than present in coastal Arctic waters, and even the Arctic Ocean may have been ice-free some summers. Global eustatic sea level was m higher than today as a result of extensive melting of glaciers on the continents and thermal expansion of ocean water. Negative values mean that the last interglacial ocean was colder than today. Note that most SST values are similar to present. In northern Russia and western to central Siberia, Eemian marine and estuarine sediments are widely exposed in river sections from the Kola Peninsula in the west to the Taymyr Peninsula in the east.

Their fossil content of warm boreal benthic faunas, in areas that today have arctic waters lacking boreal species, easily identifies them. Finds of fossil marine mammals, such as Narwhales, in marine sediments on the Siberian high arctic islands suggest at least seasonally reduced sea-ice cover compared to the present. The warm Eemian climate in the Eurasian north is also evidenced by more northerly tree line limits than present, with boreal forests spreading all the way to the Arctic Ocean in northern Russia.

Summer temperature estimates suggest o C warmer temperatures than present in the Eurasian north, depending on site and proximity to the Arctic Ocean. Studies of marine and terrestrial deposits of the last interglacial in Beringia suggest that it was warmer than present conditions. At the same time, the treeline was more than km further north in places, displacing the tundra. A compilation of last interglacial localities indicates that boreal forest was much extended beyond its present range in Alaska and Yukon Territory and probably extended to higher elevation sites now occupied by tundra in the interior.

The treeline on Chukotka Peninsula, easternmost Siberia, was more than km further north than today and displacing the tundra all the way to the Arctic Ocean. Summer temperature reconstructions for Beringia vary considerably, from showing values similar to modern to considerably warmer summers. This suggests that summer temperatures were at least o C warmer than present. To the contrary, fossil molluscs from proposed Eemian deposits on Svalbard suggest SST similar to modern, but not as warm as during the Holocene climate optimum see below. Most fossil mollusc species are representative of arctic conditions, but few finds of sub-arctic species suggest the marine climate may have been somewhat warmer than present.

A Landscape in Motion

Figure from Svendsen et al. During the 90 ka BP glaciation an ice sheet centred in the Barents Sea-Kara Sea area expanded far onto the Russian continent and blocked the northbound drainage of rivers towards the Arctic Ocean Fig. A re-growth of the ice sheet occurred ka BP. The Barents-Kara ice sheet expanded well onto the continent in N Russia and covered the northwestern rim of the Taymyr Peninsula, also leading to blockage of rivers draining to the north and the formation of huge, ice-dammed lakes. Siberia, east of Taymyr Peninsula, was ice-free throughout the last interglacial-glacial cycle, and constituted an enormous steppe environment.

The floral composition of the mammoth steppe may have its closest modern analogue with the Central Asian grass steppe, where grasses form the base of the nutritional chain although brushes and trees have occurred in sheltered and wet locations. In southwestern Alaska glaciers broadly extended beyond the present coast, while further north the glacial expansion was more limited.

This was probably due to differences in proximity to moisture sources. A frequently cited illustration of glacial and sea ice cover in the Northern Hemisphere compared to present situation. We now know that Eurasian continental ice volumes and coverage are overe stimated in this reconstruction see Forman et al. It is generally thought to have occurred around ka BP, but it is, however, acknowledged that the timing, duration and extent of ice cover at LGM differed considerably in different regions of the Arctic. A recent Svendsen et al.

Recent interpretations of the northern Eurasian glacial record suggest that most of the mainland of N Russia and Siberia remained ice-free during the LGM. It probably coalesced with an ice sheet over Novaya Zemlya as well as with the Scandinavian inland ice sheet. The Greenland inland ice expanded considerably, filling many outer shelf basins and extending out on the shelf areas.

Major ice-streams probably developed in many Greenland fjords, feeding extensive ice shelves fringing the ice sheet. The LGM ice cover over northern Greenland was thin and probably cold-based except in the fjords where fast moving outlet glaciers and ice streams terminated or fed ice shelves. In northwestern Greenland, the ice coalesced with the Innuitian ice sheet over Ellesmere Island. West of the Innuitian ice sheet and north of the Laurentide ice sheet, some islands e.

Baffin Island was heavily glaciated and partly overrun by ice of the Laurentide ice sheet advancing from the Foxe Basin to the west. The ice drained through ice streams developing in the major fjord systems on southeastern and eastern Baffin Island. It has been suggested that some coastal nunataks on eastern Baffin Island remained ice-free during the LGM.

Climatic conditions in Beringia during the LGM are generally believed to have been cold and dry. Glaciers grew in regional mountain ranges, but reached the lowlands only south of the Alaska Range. The environment was largely a mosaic of steppe-tundra landscapes. The lowest parts of the Bering Land Bridge were covered with shrub tundra.

References and suggested further reading :. Clark, P. Quaternary Science Reviews, 21 , Crowley, T. Paleoclimatology - Oxford Monographs on Geology and Geophysics , Figure 6. Oxford University Press, Inc. New York, NY. Elias, S. Festschrift in Honour of D. Quaternary Science Reviews , 20 , Forman, S. Quaternary Science Reviews 23 , — Frenzel, B. Manley, W. Svendsen, J. Quaternary Science Reviews , 23 , Thiede, J. Global and Planetary Change , 31 , A general definition of periglacial environments refers to conditions where frost-action and permafrost related processes dominate the physical environment.

Common to all periglacial environments are circles of freezing and thawing of the ground and the presence of permafrost, or perennially frozen ground. Presently these environments primarily occur at high latitudes in the Arctic and Antarctic and at high elevations in mountainous areas at mid-latitudes. Permafrost in the Northern Hemisphere.

Illustration credits: www. Certain processes and geological products are unique to the periglacial environment. These include the formation of permafrost and wedge and injection ice, development of thermal contraction cracks, and the formation of thermokarsts due to thawing of permafrost. Other processes, such as frost heaving, soil creep, solifluction and wind action processes acting on barren soils are also important in the periglacial environment. Recognizing and interpreting fossil periglacial phenomena is an integrated part of reconstructing Quaternary climate development.

Fossil periglacial phenomena commonly occur at mid-latitudes in Eurasia and N America; areas that experienced periglacial conditions during cold spells of the Pleistocene but which today have temperate climates. Pleistocene periglacial conditions were not restricted to mid-latitude locations. Extensive areas in the central and eastern Siberian Arctic, as well as parts of the Beringian area and north-western Canadian Arctic remained ice-free through long periods in the Pleistocene and were subject to intensive periglacial activity.

A number of phenomena are indicative of frozen ground and intense frost action, and can be used for paleoclimate reconstructions. These include:. Patterned ground, Thule, Greenland. Frost fissures.

16.1 Glacial Periods in Earth’s History

These are wedge-shaped structures interpreted to be casts of thermal contraction cracks. Since the development of frost fissures only occurs under permafrost conditions and intense cooling o to —20 o C these are first order indicators of periglacial environments. Fossil frost fissures, in the form of frost fissure polygons and ice- and sand wedge casts, have been described from extensive areas in northern and central Europe and N America, and have been mapped for providing evidence on distribution of Pleistocene permafrost.

These indicate frost action and weathering. Extensive accumulations of angular boulders blanketing mountain plateaux and talus scree accumulations along mountain slopes are thought to have formed primarily by frost wedging and cracking of bedrock. In both Europe, N America and Asia, blockfields talus and frost-shattered debris occur on uplands and mountains outside present day distribution of permafrost, and are taken to indicate occurrences of Pleistocene permafrost.

Rock glaciers form in the periglacial zone of mountains, and are unique permafrost landforms. They are often fed by taluses formed upslope by frost shattering of bedrock. Relict inactive rock glaciers, occurring below the periglacial zone or below the treeline, have been reported from many mountainous areas in the world. In the Alps many of those turned inactive by the end of the Pleistocene. Open system pingo in upper Eskerdalen, 35 km east of Longyearbyen, Svalbard. In permafrost areas with frequent freeze-thaw cycles, frost heaving of the surface layers can lead to down-slope movement of the material by frost creep.