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The Quaternary Period; Quaternary Paleogeography; Fossil Periglacial Phenomena

The Quaternary Period

The Quaternary is the most recent geological period of time in Earth’s history, spanning the last two million years and extending up to the present day. The Quaternary period is subdivided into the Pleistocene  (“Ice Age”) and the Holocene (present warm interval) epochs, with the Pleistocene spanning most of the Quaternary and the Holocene covering the past 10 000 years. The Quaternary period is characterized by a series of large-scale environmental changes that have profoundly affected and shaped both landscapes and life on Earth. One of the most distinctive features of the Quaternary has been the periodic build-up of major continental ice sheets and mountain ice caps in many parts of the world during long lasting glacial stages, divided by warm episodes (interglacials) of shorter duration, when temperatures were similar to or higher than today. During long periods of these climatic cycles, perhaps 8/10th of the time, temperatures were cool or cold. The number of Quaternary interglacial-glacial cycles is probably in the order of 30-50.

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Oxygen isotope record for the past 2,6 million years. Peaks represent warm Earth, troughs a cold Earth

There have been shifts in the frequency of climate oscillations and amplitude of temperatures and glaciations through the Quaternary. At the onset of the Quaternary, many arctic areas were comparatively warm, with trees and bushes growing far north of the present treeline. Prior to about 800 000 years ago each interglacial-glacial cycle lasted for about 40 000 years, but after that the periodicity shifted to a prevailing rhythm of about 100 000 years. Prior to this shift in frequency there was a repeated build-up of relatively small-to-moderate sized ice sheets at high northern latitudes. After c. 800 000 years ago there occurred a major intensification of glaciations, with repeated growth of continental-scale ice sheets reaching mid-latitudes and with ice volumes much larger than during the earlier Quaternary glaciations. There have occurred 8-10 major glaciations during the past 800 000 years. Two of the largest Northern Hemisphere glaciations are the last one (called the Weichselian/Wisconsin glaciation, at its maximum about 20 000 years ago) and the one occurring prior to the last interglacial (called the Saalian/Illinoian glaciation, occurring prior to c. 130 000 years ago). During the peak of both glaciations, ice sheets covered extensive areas north of 40-50oN in both Eurasia and N America. The Saalian glaciation was particularly extensive in the high Eurasian north, covering vast areas of N Russia, coastal Arctic Ocean and Siberia.

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Global view of the Last Glacial Maximum, 18.000 years ago. From http://www.scotese.com/lastice.htm

The effects of the Quaternary climate oscillations were not only repeated expansion of glaciers at mid- and high latitudes, but mid-latitude areas were repeatedly subject to cold climate and permafrost, forcing plant and animal populations to migrate or adapt to changed environmental conditions – or become extinct. At lower latitudes, forested areas, deserts and savannahs shifted through several degrees of latitude as climate zones responded to higher latitude cooling. Global patterns of wind and energy transfer by ocean currents changed, causing large-scale shifts in the pattern of aridity and precipitation around the world. Rates of weathering and erosion changed globally in response to changes in temperature and precipitation, and river regimes fluctuated considerably. During peak glaciations in the Eurasian north, the large rivers of N Russia and Siberia entering the Arctic Ocean were dammed by the huge ice sheets and forced to flow southwards. When huge volumes of water were trapped in ice sheets during peak glaciations, global sea level fell up to 150 m. This caused vast continental shelf areas to become dry land, particularly the shallow shelf areas bordering the Arctic Ocean. Land bridges formed across sounds and between islands, in turn affecting ocean surface currents, shallow-sea life and productivity and opening and closing routes of migration for plants and animals. The Bering land bridge, existing due to lowering of sea level during the last glaciation, made possible the spread of humans from Asia to N America. 


Mammoths and American Lions in the late Pleistocene of Alaska

The frequent and rapid Quaternary environmental changes stimulated rapid evolution and the rise of large mammals, or megafauna. The Pleistocene megafauna included woolly rhinoceros, woolly mammoths and large wolves that were well adapted to cold climates. The major type of ecosystem covering the European, Asian and North American continents south of the ice sheets was a type of grass steppe that has been called the "mammoth steppe". It differed from the modern tundra environment in having higher biomass, much higher productivity and a reduced snow cover in winter. The changing precipitation patterns at the end of the last glaciation probably caused the collapse of the mammoth steppe. Since many animals were dependent on the grass steppe, they became highly vulnerable to extinction when the ecosystem collapsed. This, together with hunting by humans, has probably been the root cause of many of the megafaunal extinctions at the end of the Pleistocene. The last mammoths, lingering on the Siberian islands, became extinct 4000 years ago. Other mammals that evolved during the Pleistocene, like the caribou, the musk ox and the polar bear, continue to be an important part of the arctic fauna. It is also during the Pleistocene that humans evolve and develop the use of technology, language, art and religion. Earliest signs of human occupation in the Russian arctic are 30 000-40 000 years old. Much of the arctic flora and fauna, including native peoples of the arctic, have, however, during the past 10 000-15 000 years migrated from lower latitudes to the arctic latitudes. 


Fluted surface in front of Brúarjökull, Iceland. Photo: Ólafur Ingólfsson 2004.

The repeated Northern Hemisphere Quaternary glaciations have left a complex of landforms, sediments and landscapes that set the frame for mid-high latitude life and human activities. Human societies rely on natural resources that are products of the Pleistocene glaciations, like sands and gravels for construction activities, groundwater magazines in ancient fluvial deltas, fertile glacial till and outwash planes for forestry and agriculture. Large and rapid environmental changes define the Quaternary period – most Quaternary scientists adopt the view that the present (Holocene) interval of relatively warm and stable climate at mid- and high Northern Hemisphere latitudes is, like previous interglacial periods, an exception in the overall cool to cold Quaternary climate – and there is every reason to expect the future to hold major environmental shifts in store.

References and further reading:

Andersen, B.G. & Borns, H.W.Jr., The Ice Age World, Oslo, Scandinavian University Press, 1994.
Dawson, A., Ice Age Earth, London, Routledge, 1992.
Lowe, J. J. and Walker, M.J.C., Reconstructing Quaternary Environments, Harlow, Longman Limited, 1997
Nilsson, T., The Pleistocene, Dordrecht, Reidel, 1983.
Pavlov, P., Svendsen, J.I. and Indrelid, S., 2001, Human presence in the European Arctic nearly 40,000 years ago, Nature, 413, 64-67.

Ward, P., The Call of Distant Mammoths: Why the Ice Age Mammals Disappeared, New York, Springer-Verlag, 1997.
Williams, M., Dunkerley, D., Decker, P., Kershaw, P. and Chappell, J., Quaternary Environments, London, Arnolds, 1998.

Wilson, R.C.L., Drury, S.A. and Chapman, J.L., The Great Ice Age: Climate Change and Life, London, Routledge, 1999.

 

Quaternary paleogeography

Definitions - Paleogeography deals with reconstructing the physical geography of past geological times, where the focus is on physical features such as the shifting locations of shorelines, rivers and drainage systems, tectonics and mountain-building, paleolatitude and continental drift, location in time and space of continental shelf areas and other sedimentary basins. The field of Quaternary paleogeography broadly includes all aspects of paleo-map reconstructions through the Quaternary Period; ice sheet and sea-level fluctuations in time and space; the delineation of past topographic or bathymetric contours; the compilation of biologic, morphologic or lithostratigraphic data that can be presented on time slices, such as paleovegetation maps or distribution of loess basins and fossil permafrost. A Quaternary paleogeographic dataset will cover a number of time intervals, showing e.g. deviations from the present day values of the winter, summer and annual mean temperatures and annual precipitation for the time slices, the values of albedo, sea surface temperatures, sea-ice distribution, zones of permafrost, mountain glaciation and inland ice, geomorphic processes and loess formation, natural vegetation and landscape types for the different time intervals. Paleogeo­graphical maps and reconstructions are used as base information for studies of e.g. past fossil distributions, past climatic changes, evolution of vegetational or oceanographic patterns and for computer modelling studies.


Oceanic Circulation Patterns (Source: Office of Naval Research. Oceanography (http://www.onr.navy.mil/focus/ocean))

Background - The frame for major global environmental changes is set by large-scale tectonics and position and configuration of the continental landmasses. These affect the paths of ocean currents and air masses and in turn decide the global energy distribution. The steady northward drift of Europe, Asia and North America through the Tertiary Period (65-2 Ma (million years) BP (before present)) caused the gradual tectonic closing of the connection between the Pacific Ocean and the Arctic Ocean and reduced the previously efficient ocean heat transport from equatorial regions toward the North Pole. The northern hemisphere thereby experienced increased cooling. The ice sheet in Greenland presumably first formed about 7 Ma BP in response to this cooling. The build-up of huge mountain chains (The Himalayas, The Alps, The Rocky Mountains and The Andes) as well as closing of Equatorial ocean pathways also greatly affected global circulation patterns. The onset of glaciation in Antarctica can be traced back to late Eocene times, 35-40 Ma BP, reflecting the drift of Antarctica over the South Pole and the establishment of the circum-Antarctic pattern of oceanic and atmospheric circulation that inhibits energy transfer to high Southern Hemisphere latitudes. There is strong evidence of large ice sheets in Antarctica during the Miocene, after ca. 24 Ma BP, and since then Antarctica has functioned as a heat sink in the global climate system and strongly influenced the global energy budget and climate.


An example of Paleogeographical reconstruction: The Late Weichselian Barents Sea Ice Sheet (from Forman et al. 2004)

 

Most Quaternary paleogeographic reconstructions focus on time slices through the past ca. 130 ka (kilo-years). That is for the simple reason that there is ample geological and biological evidence preserved in the geological record with resolution high enough to allow for reasonably detailed reconstructions, whereas evidences of earlier large-scale Quaternary environmental changes usually are fragmentary. During the past 130 ka the climate has changed from interglacial to glacial and then back to the present-day interglacial, i.e. fluctuated between end members in the climate-environmental system. It is assumed that environmental changes through the last interglacial-glacial cycle have occurred repeatedly through earlier glacial cycles. The climate-environmental system is an interactive system consisting of five major components: the atmosphere, the hydrosphere, the cryosphere, the land surface and the biosphere, forced or influenced by various external forcing mechanisms, the most important of which is the Sun. There is a general consensus among Quaternary scientists that changes in earth's orbital parameters that influence amount and distribution of energy from the Sun (the tilt of the earth's rotational axis, the eccentricity of the earth's orbit about the sun, and season of perihelion) are very important for explaining the fundamental timing of interglacial and glacial events. However, the phasing and the amplitude of the climate response to orbital changes are non-linear and involve atmosphere, ocean, ice sheet, land and vegetation feedbacks. It is one purpose of paleogeographic reconstructions to highlight spatial and temporal differences in these physical parameters as expressed in the geological archives, for better understanding the underlying processes and dynamics.

 

The following reconstructions will focus on paleoenvironments in Eurasia and Beringia, with brief references to Arctic Canada, Greenland and Svalbard, during the Pliocene and three widely defined time periods through the last 130 ka: (a) The last interglacial, the Eemian/Sangamon/marine oxygen isotope stage (MIS) 5e, 130-115 ka BP; (b) The Early-Middle Weichselian/Wisconsin/MIS 5d-4, ca. 115-50 ka BP; (c) The Last Glacial Maximum (LGM)/MIS 2, 20-18 ka BP. The reconstructions are based on a range of proxy data, from terrestrial macrofossil and pollen data to marine and ice-core data.

 

Paleogeographic reconstruction of the Pliocene (5.4-1.8 Ma) in the Arctic

The Arctic is not a uniform environment today. Different geological histories, large differences in topography and proximity to the Arctic Ocean between regions, as well as varying weather patterns, bring diversity to the present Arctic environment and has done so through time. Climatically, the Arctic today is often defined as the area north of the 10°C July isotherm, i.e. north of a line or region that has a mean July temperature of 10°C. In some areas the treeline roughly coincides with the 10°C July isotherm and defines the southern boundary of the Arctic. The treeline defines a transition zone where continuous forest gives way to tundra with sporadic stands of trees and finally to treeless tundra. The Arctic is thus by definition primarily a treeless area with low summer temperatures. But it has not always been so.

Map of Northern Hemisphere temperature anomaly
During the Pliocene, global temperatures, particularly at high latitudes, are believed to have been significantly warmer than today. (Source: http://www.giss.nasa.gov/research/paleo/pliocene)

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 1-3oC 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 3-4 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. 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.

The Eemian/Sangamon interglacial, 130-115 ka BP - The beginning of the last interglacial is reflected in the marine records by abrupt shift to lighter isotope values. The preceding Saalian/Illinoian glaciation was extremely extensive at both high and middle latitudes, and the onset of the Eemian/Sangamon interglacial is marked at many Arctic locations by marine transgression across isostatically depressed coastal areas. Deposits from this marine transgression are particularly pronounced along the northern Russian and Siberian coastal lowlands. A range of proxy data suggests that the Eemian/Sangamon climate optimum summer temperatures were considerably (2-4oC) warmer than that of the present day, and that vegetation zones on the continents migrated northwards. 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. Glacier extent throughout the Arctic was probably significantly more restricted than present during the Eemian/Sangamon interglacial, with the Greenland Inland Ice considerably reduced. Global eustatic sea level was 4-6 m higher than today as a result of extensive melting of glaciers on the continents and thermal expansion of ocean water.

The figure, pictured above, demonstrates the difference between modern sea surface temperature and estimated February sea surface temperature (in °C) at the last interglaciation, some 120 ka ago. Negative values mean that the last interglacial ocean was colder than today. Note that most SST values are similar to present. Samples with more than one estimate reflect use of more than one proxy source (F = foram, R = radiolaria, C = coccolith). Figure from CLIMAP, 1984.

 

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. Fennoscandia was an island, with water passage between the North Sea and the White Sea across the Baltic Sea and Finland. 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 2-8oC 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. There is evidence for warmer-than-present marine conditions offshore Alaska during the Eemian/Sangamon interglacial, and the winter sea-ice limit in the Bering Strait was at least 800 km further to the north than present. At the same time, the treeline was more than 600 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 600 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. Studies of fossil beetle assemblages estimate that Eemian/Sangamon interglacial July temperatures at certain sites in Beringia may have been about 5oC warmer than modern.

 

Investigations on East Greenland have revealed that during the Eemian/Sangamon interglacial dwarf-shrub heaths with a diverse insect fauna and tree birch and alder growing in sheltered localities dominated the terrestrial environment in areas around 70oN, which today are polar deserts. This suggests that summer temperatures were at least 3-4oC 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). There are numerous collections of fossil shells and some of terrestrial plant materials from arctic NW Canada that are thought to correlate to the Eemian/Sangamon interglacial. 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.

 

The Early-Middle Weichselian/Wisconsin, 115-50 ka BP - In a Northern Hemisphere and global perspective, this time interval represents a transition from interglacial to glacial conditions, with successively falling global sea level as continental ice volumes increased. Recent research has, however, increasingly shown that ice sheets in the high arctic probably reached their maximum extent and volume during the early stages of ice build-up, during the Early-Middle Weichselian/Wisconsin. 


A reconstruction of the Eurasian ice sheet during the Early Weichselian glacial maximum (90-80 ka BP). Figure from Svendsen et al. 2004.

 

In the Eurasian north, west of the Taymyr Peninsula, the limits of the Eurasian ice sheets have been reconstructed for two Early-MiddleWeichselian/Wisconsin glaciations. The Late Quaternary glacial maximum in the Eurasian Arctic occurred around 90 ka BP, in strong contrast to the ice sheets over Scandinavia and North America, which at that time were much smaller than during the LGM. 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. 1). A re-growth of the ice sheet occurred 60-50 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. It has been called “the mammoth steppe” because of the characteristic presence of mammoths in its ecosystem, but supported a diverse herbivorous fauna including mammoths, caribou, musk ox, bison and horses. It differed from the modern tundra environment in having higher biomass, much higher productivity and a reduced snow cover in winter. 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.

 

There is evidence from both Svalbard and East Greenland of two Early-Middle Weichselian/Wisconsin glaciations, with ice extent and volumes similar to or smaller than the LGM glaciation. In Beringia, glacial mapping, soil/loess profiles and chronological data suggest that during Early-Middle Weichselian/Wisconsin Alaskan glaciers were considerably expanded. 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. Early-Middle Weichselian/Wisconsin glaciers in Alaska defined a considerably more extensive glaciation than the following LGM glaciation. The glacial record on Chukotka Peninsula likewise suggests that Early-Middle Weichselian/Wisconsin glaciers were more extensive than during the very limited LGM glaciation there. Because much of Beringia was not glaciated throughout the last glacial cycle, vast areas remained open to active eolian deposition, with resultant loess/yeodoma dune fields and blanketing of the landscape.      

 


A frequently cited illustration of glacial and sea ice cover in the Northern Hemisphere compared to present situation. Figure credits: Mark McCaffrey, NGDC/NOAA. We now
know that Eurasian continental ice volumes and coverage are overe stimated in this reconstruction (see Forman et al. 2004 and Svendsen et al. 2004)

 

The Last Glacial Maximum (LGM), MIS 2, 20-18 ka BP - LGM is defined as the maximum global ice volume as seen in marine oxygen isotope records and coinciding with the maximum extension of middle latitudes Northern Hemisphere ice sheets during the last glacial cycle. It is generally thought to have occurred around 20-18 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. 2004) reconstruction of the extent of the Eurasian ice sheet at the Last Glacial Maximum, 20-18 ka BP.

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. A huge LGM ice sheet built-up in the Barents Sea area and extended over Svalbard and Franz Josef Land. 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. The Innuitian ice sheet probably covered most of the islands in the northeastern Canadian Arctic during LGM. With the exception of a few nunataks on Ellesmere Island, the margin of the Innuitian ice sheet at LGM lay offshore. West of the Innuitian ice sheet and north of the Laurentide ice sheet, some islands (e.g. Banks Island, Prince Patrick Island and Melville Island) experienced limited glaciation or were ice free at LGM. 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. The Bering Land Bridge was flooded by the sea about 11 ka BP, and closed migration routes for plants and animals between N America and Asia. 

 

References and suggested further reading:

Andersen, B.G. & Borns, H.W.Jr., The Ice Age World, Oslo, Scandinavian University Press, 1994.

Clark, P.U. & Mix, A. (eds.), Ice Sheets and Sea Level of the Last Glacial Maximum. Quaternary Science Reviews, 21(1-3), 2002.

CLIMAP 1984: Difference between modern sea surface temperature and estimated February sea surface temperature (in °C) at the last interglaciation 120,000 years ago." Image taken from text. Crowley, T.J. and North, G.R.  Paleoclimatology - Oxford Monographs on Geology and Geophysics, 18. Figure 6.10, p.118. Oxford University Press, Inc. New York, NY. 1991.

Elias, S.A. & Brigham-Grette, J. (eds.), Beringian Paleoenvironments. Festschrift in Honour of D.M. Hopkins. Quaternary Science Reviews, 20(1-3), 2001.

Elverhři, A. (ed.), Glacial and Oceanic History of the Polar North Atlantic Margins, Quaternary Science Reviews, 17(1-3), 1998.

Forman, S.L. et al. 2004: A review of postglacial emergence on Svalbard, Franz Josef Land and Novaya Zemlya, northern Eurasia. Quaternary Science Reviews 23, 1391–1434

Frenzel, B., Pécsi, M. & Velichko, A. A. (eds.), Atlas of paleoclimates and paleoenvironments of the Northern Hemisphere: Late Pleistocene – Holocene. Budapest, Geographical Research Institute, Hungarian Academy of Science, 1992.

Manley, W.F., 2002, Postglacial Flooding of the Bering Land Bridge: A Geospatial Animation: INSTAAR, University of Colorado, v1, http://instaar.colorado.edu/QGISL/bering_land_bridge

Svendsen, J.I. et al. 2004: Late Quaternary ice sheet history of northern Eurasia. Quaternary Science Reviews, 23, 1229-1271.

Thiede, J. & Bauch, H.A. (eds.), The Late Quaternary Stratigraphy and Environments of Northern Eurasia and the Adjaent Arctic Seas – New Contributions from Queen. Global and Planetary Change, 31(1-4), 2001.

 

Fossil periglacial phenomena

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. About 25% of the Earth’s land surface currently experiences periglacial conditions.


Permafrost in the Northern Hemisphere. Illustration credits: www.solcomhouse.com/Permafrost.htm

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. Photo: Ólafur Ingólfsson 1986.

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Frost fissures. 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 (-15o to –20oC) 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.


Rock glacier at Qivitut, Diskofjord, Disko Island, Greenland. Photo: Ole Humlum

 
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Blockfields, screes and rock glaciers. 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. Photo: Hanne Christiansen
 
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Frost-creep and frost-disturbed deposits. 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.


Tors in Öxnadalur, northern Iceland. Photo: unknown photographer.
 
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Tors. Hillslope and summit tors commonly occur in both high and mid-latitude uplands and mountain areas. Tors are frequent in the alpine landscapes of e.g. western Spitsbergen today, occurring on mountain ridges and arętes between glaciated cirques and valleys. Their formation has been attributed to intense frost shattering at non-glaciated sites, although an alternative explanation for some tors suggests they are mainly the result of chemical weathering and thus not indicative of frost action.


Blockfield on Amsterdamöya, Spitsbergen, Svalbard. Photo: Ólafur Ingólfsson 2001.

 
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Fossil permafrost. Much of the thick permafrost in Siberia is in disequilibria with the present climate and is largely a relict of Pleistocene climate conditions. The present occurrence of sub-sea continental shelf permafrost in the Arctic Ocean developed during periods of low global sea levels during the last glacial maximum, illustrates the preservation potential of relict permafrost. The history of permafrost in the Russian Arctic has been traced some 2-1.5 million years back in time and it is presumed that much of it might have started to form in the Middle Pleistocene (>500 thousand years ago).


Massive ground ice along Tuktoyaktuk Coast, Arctic Canada. Photo credits: S.R. Dallimore, Geological Survey of Canada

 
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Massive ground ice. Thick bodies of massive ground ice have been described from northern Alaska, the western Canadian Arctic, China and western Siberia. A favoured genesis is that most bodies of massive ground ice formed through ice segregation and injection processes, where excess pore water froze within the sediments. An alternative explanation is that massive ground ice is buried glacier ice and remnants of Pleistocene ice sheets. Other theories explaining geneses of massive ground ice include buried lake, river or sea ice, and buried snow bank ice. It has been pointed out that massive ground ice in the Arctic primarily occurs within the limits of formerly glaciated areas One explanation for this relationship is that most of these ice bodies might be relict glacier ice.


Duststorm in the highlands of Iceland, north of Vatnajökull. Photo: Ólafur Ingólfsson 2004
 
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Aeolian sediments and ventifacts. It has long been recognized that wind action was particularly intense in the Pleistocene periglacial environment. Huge, non-vegetated outwash plains dried out during late summer and fall, and strong winds generated extensive dust clouds. Sand dunes, cover sands and loess deposits, which occur in belts outside formerly glaciated areas, mainly at mid-latitudes, are the geological products of the periglacial wind action. Pleistocene ventifacts – or stones facetted by dust-laden wind abrasion – are very common in mid-latitude regions of Europe and N America, and have been used to infer prevailing wind directions at the time of their deposition/abrasion.

The interpretation of fossil periglacial phenomena is not always straight forward, and some structures, sediments and forms may develop under non-periglacial conditions as well. As the understanding of the present periglacial environment increases, there will be improved understanding of how fossil periglacial phenomena relate to and provide insight into climates of the past.

References and further reading:

Black, R.F. 1976: Periglacial features indicative of permafrost: ice and soil wedges. Quaternary Research, 6, 3-26.

French, H. M. 1996: The Periglacial Environment. Harlow, Longman, 341 pp.

Guoqing, Q. & Guodong, C. 1995: Permafrost in China, past and present. Permafrost and Periglacial Processes, 6, 3-14.

Ingólfsson, Ó. & Lokrantz, H. 2003: Massive ground ice body of glacial origin at Yugorski Peninsula, arctic Russia. Permafrost and Periglacial Processes 14, 199 - 215

Kondratjeva, K.A., Krutsky, S.F. & Romanovski, N.N. 1993: Changes in the extent of permafrost during the Late Quaternary Period in the territory of the former Soviet Union. Permafrost and Periglacial Processes, 4, 113-119.

Péwé, T.L. The periglacial environment in North America during Wisconsinan time. In Porter, S.C. (ed.), The Late Pleistocene. Late Quaternary environments of the United States, Vol. 1. Minneapolis, University of Minnesota Press, 157-189.

Vandenberghe, J. & Pissart, A. 1993: Permafrost changes in Europe during the last glacial. Permafrost and Periglacial Processes,  4, 121-135.

Washburn, A.L. 1980: Permafrost features as evidence of climatic change. Earth Science Reviews, 15, 327-402.

 

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