Introduction

The present article concerns the reconstruction of thepermafrost history of the Arctic and the creation of acircum-Arctic model of permafrost evolution during theQuaternary. The development of such a model makes itpossible to reveal cause-and effect interrelationshipsbetween permafrost and the environment of the Arcticin their natural dynamics as well as to explain many ofthe patterns observed today in the permafrost zone. Thedevelopment of this model will also form the basis forpredicting permafrost development under the impact ofglobal change.

Methods

The evolution of arctic permafrost was studied byreconstructing its state during extreme climate stages oflate Cenozoic era when the permafrost repeatedly expe-rienced degradation and aggradation. This reconstruc-tion was accomplished by: 1) analysis of modern pat-terns of permafrost distribution; 2) analysis of palaeo-geographic conditions during each stage; 3) calculationof the permafrost temperature and thickness. The distri-bution of three types of permafrost (subaerial, sub-glacial and submarine) during the Quaternary reflectthe influence of several factors: shoreline position, cli-matic continentality, latitudinal and altitudinal zonality.The Arctic reveals a predominance of sectorial diffe-rences over zonal ones and is divided into three largereigions: (1) the European sector, including WestSiberia, which is mainly a platform region with amarine climate and pronounced zonality; (2) the Asiaticsector, which is mainly a mountainous region with apronounced continental climate and altitudinal zonality

but obscured latitudinal zonality; and (3) the NorthAmerican sector, which is mainly an elevated platformregion with a continental climate and pronounced lati-tudinal zonality. The differences between these regionshave been preserved throughout the entire history ofthe development of Arctic permafrost.

Results

Permafrost developed in the Arctic at the end of thePliocene and the beginning of the Pleistocene(Arkhangelov et al., 1989; Burn, 1994). Climatic coolingduring the Pleistocene involved fluctuations whichwere of increasing frequency and amplitude (Velichko,1989). During the cool stage of the Middle Pleistocene,(Riss - Illinois - Dnepr epoch - Oxygen Isotope Stage 6),concurrently with extensive glaciation, a marine trans-gression took place in the Arctic. This transgression wasextensive in the European sector and in north WestSiberia. At this time there was enough moisture forglaciation with the Scandinavian, Laurentide,Cordilleran and Greenland ice covers reaching thegreatest size. Air temperatures were then 5-6¡C coolerthan today (Emiliani, 1970). Subaerial permafrost occu-pied the most space in the Asiatic sector where glacia-tion was of limited extent. Permafrost also formed inice-free areas of Alaska and the Canadian High Arctic.Permafrost was least developed in the European sector,where almost all of the modern land area was coveredby either the sea or glacier ice. The development of sub-glacial permafrost can be estimated by analogy with thecontemporary ice sheet in Greenland: during theMiddle Pleistocene on the surface of Laurentide IceSheet ( 3-4 km thick) the temperature fell as low as -40¡C. The mean vertical thermal gradient in the gla-

Abstract

The history of permafrost in the Arctic is reconstructed based on palaeogeographic and palaeoclimatic scena-rios during two last glacial cycles. Circum-Arctic models of permafrost are created for each stage. The modelsshow the distribution of various types of permafrost (subaerial, subglacial, submarine), and their temperatureand thickness. Palaeopermafrost maps are presented for three stages : 1) Sangamonian - Mikulin ( OxygenIsotope Substage 5e, 125 ka BP), 2) late Wisconsin - late Wurm - late Valday (Oxygen Isotope Stage 2, 20-18 kaBP), 3) Holocene climatic optimum (Oxygen Isotope Stage 1, 9-5 ka BP ). The model of permafrost evolution,which reveals cause-and-effect relations between permafrost and other natural factors, can provide a basis for apredicting the future development of Arctic permafrost.

Rozenbaum G.E., Shpolyanskaya N.A. 973

A MODEL OF QUATERNARY PERMAFROST EVOLUTION IN THE ARCTIC

Rozenbaum G.E., Shpolyanskaya N.A.

Moscow State University, Vorob'evy Gory, Geography faculty, Moscow 119899, Russia e-mail: Rozenbaum@cryoglac.geogr.msu.su

ciers was 2-2.5¡/100m (Balobayev,1991), and at suchtemperatures the zero isotherm must have been at adepth of 1600-2000 m, and the lower part of the glacier,up to 2 km thick, was about 0¡C. Consequently, it ismost likely that under the major ice sheets there was nopermafrost. Subglacial permafrost could only formunder glaciers no more than 1000 m thick or close to1500 m thick in the coldest conditions. Submarine per-mafrost formed under two conditions: 1) in the near-shore shallows where annual freezing of the sea icewith the sea bottom occurred and 2) at depths rangingapproximately from 40 to 100-150 m, where there are nomore seasonal temperature fluctuations and where thetemperature of near-bottom water is less than 0¡C(Shpolyanskaya, 1989).

The interglacial epoch that marked the beginning ofthe Late Pleistocene (Sangamonian - Mikulin - OxygenIsotope Substage 5e), reached its maximum around 125 ka BP. The interglacial was accompanied by aglacioeustatic transgression which was most developedin the European sector. In the American sector, in parti-cular in northern Alaska, the sea level was only 10 mhigher than at present (P�w� et al.,1995). The air tem-perature at the maximum of the interglacial exceededthe contemporary one by 2-3¡C, the smallest changes(2¡C) taking place in the Asiatic sector and the biggestones (3¡C) in the American and European sectors.Nevertheless, the climate in the Arctic remained cold.This is attested to by the mainly Arctic composition ofthe marine fauna and of pollen: forest tundra, which

The 7th International Permafrost Conference974

Figure 1. Permafrost of the Arctic in Sangamonian-Mikulin (Oxygen Isotope Substage 5e,125 ka BP). T (¡C)- ground temperature, H(m)- thickness of permafrost.

replaced tundra, does not preclude a cold climate.Subaerial permafrost degraded in the Arctic as shown byice-wedge pseudomorphs, for example in Alaska(Hopkins,1976). In the European sector, permafrost wasabsent practically everywhere, with the exception of theUral Mountains and Pai-Khoi (Figure 1). In theAmerican sector, permafrost existed north of the ArcticCircle. Ground temperatures ranged from approximate-ly -3¡C near the Arctic Circle to -13 - -14¡C in the HighArctic (Harrison, 1991; Brigham and Miller, 1983).Temperatures in the mountains were lower. Permafrostthickness ranged from 100 to 600 m. In the Asiatic sec-tor, permafrost did not degrade (Figure 1). Subglacialpermafrost was absent throughout Oxygen IsotopeSubstage 5e. Submarine permafrost was widely devel-oped (see Figure 1); today its remains, including thickmassive icy beds, underlie large areas in the north ofWestern Siberia.

Further climate change was characterized by steadilyincreasing cooling and drying, reaching a nadir at 20-18 ka BP (Oxygen Isotope Stage 2), when air tempe-ratures had decreased by 7-8¡C in the Asiatic andAmerican sectors and by 10¡C in the European sector.Climate cooling and drying were aided by the reducedinflow of cyclonic air masses to the Arctic and the isola-tion of the Arctic basin due to a major marine regression(>100 m fall in sea level), which exposed the greaterpart of the Arctic shelf (P�w� et al., 1995). Drying of theclimate brought about a drastic reduction of glaciationin the Asiatic sector and in the American High Arctic(England and Bradley, 1978). At this time there existedhomogenous natural conditions on the vast cooled land(Velichko, 1989). The emergence of Beringia excludedthe warming influence of the Pacific Ocean almost com-pletely. Zonal and sectorial differences were largelysmoothed out. Conditions were suitable for the forma-

Rozenbaum G.E., Shpolyanskaya N.A. 975

Figure 2. Permafrost of the Arctic in Late Wisconsin-Wurm-Valday (Oxygen Isotope Stage 2, 20-18 ka BP).

tion subaerial permafrost (Figure 2) : rock temperatureswere -17 - -20¡C on the plains and as low as - 23¡C inthe mountains while the permafrost thickness fluctuat-ed between 600 and 900 m on the plains and reached2000 m in the mountains. This follows from our calcula-tions and is indicated by Brigham and Miller (1983),Allen et al. (1988), Harrison (1991), and Osterkamp andGosink (1991).

Iceland holds a special position. Its climate, by virtueof Iceland's geographical position, is now marine andrelatively warm, and does not correspond to the

island's northerly position. During Late Wisconsintimes, the island occupied a considerably larger area.As in the European sector, the cooling there was greaterthan in the other regions of the Arctic. This was becausethe region was cut off from the Gulf Stream's warminginfluence and thus the latitudinal factor began to takeeffect there to a larger degree than during interglacials.The temperatures fell by no less than 10¡C below pre-sent values. In such conditions subaerial permafrost exis-ted. Calculations suggest that rock temperatures onIceland were -3 - -4¡C and permafrost thickness was100-200 m. Subglacial permafrost was most likely absent.

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Figure 3. Permafrost of the Arctic in Holocene Climatic Optimum (9-6 ka BP).

Despite the apparent small size of glaciers in Iceland,high temperatures hindered the formation of subglacialpermafrost (see Fig. 2). In the European sector, the tem-perature of subaerial permafrost was from -11, -13¡C to -15, -18¡C and permafrost thickness increased to 700 m.Subglacial permafrost was also widely distributed duringthis epoch because the majority of the glaciers werecomparatively small and thin. Using the calculationscited above, it is likely that permafrost was absentwhere glacier ice exceeded 1500 m in thickness.However, subglacial permafrost probably occuredbeneath ice thinner than 1500 m. Submarine permafrostbeneath those small parts of the shelf still submergedwas represented mainly by near-shore permafrost andperennially cooled sediments .

The Holocene has been marked by a large glacioeusta-tic transgression and considerable climate warming.The warming peaked during the Climatic Optimum,which manifested itself in the various parts of the Arcticdiachronously from 9-8 ka BP to 6-5 ka BP. Air tempera-tures in the Arctic at that time exceeded contemporaryvalues by about 2¡C. Both the warming and the trans-gression affected the permafrost. Both the zonal andsectorial structure of the permafrost zone spatial changewere reestablished. Subaerial permafrost started to thawin southern regions of the Arctic and in the northernregions, thermokarst processes were active. In theAsiatic sector, thermokarst formed alass plains(Arkhangelov et al.,1989). In the American sector, asyn-chroneity in the development of Holocene events mani-fested itself. Maximum thawing of Alaskan permafrostoccurred during the Early Holocene, when numerousthermokarst lakes and depressions formed and borealforest developed (Barnosky et al., 1987; Ritchie, 1984;P�w� et al., 1995). Beneath the greater part of theEuropean sector, frozen ground thawed (Figure 3); only

on the northern islands (Spitsbergen, Franz Josef Land,etc.) did subaerial permafrost remain. In the Asiatic sector,permafrost continued to remain sufficiently severe.Subglacial permafrost was practically absent, except onthe northernmost islands, where glaciers of small sizeand thickness survived, and beneath thin, marginalparts of the Greenland Ice Sheet, where relict subglacialpermafrost could survive. Indications of this are pro-vided by contemporary materials dealing with sub-glacial temperatures of Greenland and adjacent islandsof the Canadian High Arctic (Hansen and Langway,1966). Submarine permafrost, during the HoloceneClimatic Optimum, was present mainly in the form ofnear-shore permafrost and relict submerged subaerialpermafrost (Mackay, 1972) (Figure 3).

Conclusion

Contemporary permafrost of the Arctic was mainlyaffected by its evolution at the end of the Quaternary.At that time, amplitudes of climatic changes reachedtheir maximum; the decrease of air temperatures, rela-tive to the contemporary one, reached 7-10¡C duringcold epochs, while their increase during warm epochsamounted to 2-3¡C. Throughout its entire history thepermafrost was preserved, but repeatedly experienceddegradation and aggradation. It shows a predominanceof sectorial differences over zonal ones.

Acknowledgments

We thank J. Murton and B.L. Berry for helpful com-ments on the manuscript.

Rozenbaum G.E., Shpolyanskaya N.A. 977

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