Th e Int 7th ern Per atio ma Co fro nal nfe st ren ce

Ye llo Jun wk 199 e 23- nife 27 8

PERMAFROST - Seventh International Conference (Proceedings), Yellowknife (Canada), Collection Nordicana No 55, 1998

?

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: [email protected] Abstract The history of permafrost in the Arctic is reconstructed based on palaeogeographic and palaeoclimatic scenarios during two last glacial cycles. Circum-Arctic models of permafrost are created for each stage. The models show the distribution of various types of permafrost (subaerial, subglacial, submarine), and their temperature and thickness. Palaeopermafrost maps are presented for three stages : 1) Sangamonian - Mikulin ( Oxygen Isotope Substage 5e, 125 ka BP), 2) late Wisconsin - late Wurm - late Valday (Oxygen Isotope Stage 2, 20-18 ka BP), 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 a predicting the future development of Arctic permafrost.

Introduction The present article concerns the reconstruction of the permafrost history of the Arctic and the creation of a circum-Arctic model of permafrost evolution during the Quaternary. The development of such a model makes it possible to reveal cause-and effect interrelationships between permafrost and the environment of the Arctic in their natural dynamics as well as to explain many of the patterns observed today in the permafrost zone. The development of this model will also form the basis for predicting permafrost development under the impact of global change.

Methods The evolution of arctic permafrost was studied by reconstructing its state during extreme climate stages of late Cenozoic era when the permafrost repeatedly experienced degradation and aggradation. This reconstruction was accomplished by: 1) analysis of modern patterns of permafrost distribution; 2) analysis of palaeogeographic conditions during each stage; 3) calculation of the permafrost temperature and thickness. The distribution of three types of permafrost (subaerial, subglacial and submarine) during the Quaternary reflect the influence of several factors: shoreline position, climatic continentality, latitudinal and altitudinal zonality. The Arctic reveals a predominance of sectorial differences over zonal ones and is divided into three large reigions: (1) the European sector, including West Siberia, which is mainly a platform region with a marine climate and pronounced zonality; (2) the Asiatic sector, which is mainly a mountainous region with a pronounced continental climate and altitudinal zonality

but obscured latitudinal zonality; and (3) the North American sector, which is mainly an elevated platform region with a continental climate and pronounced latitudinal zonality. The differences between these regions have been preserved throughout the entire history of the development of Arctic permafrost.

Results Permafrost developed in the Arctic at the end of the Pliocene and the beginning of the Pleistocene (Arkhangelov et al., 1989; Burn, 1994). Climatic cooling during the Pleistocene involved fluctuations which were 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 transgression took place in the Arctic. This transgression was extensive in the European sector and in north West Siberia. At this time there was enough moisture for glaciation with the Scandinavian, Laurentide, Cordilleran and Greenland ice covers reaching the greatest size. Air temperatures were then 5-6¡C cooler than today (Emiliani, 1970). Subaerial permafrost occupied the most space in the Asiatic sector where glaciation was of limited extent. Permafrost also formed in ice-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 covered by either the sea or glacier ice. The development of subglacial permafrost can be estimated by analogy with the contemporary ice sheet in Greenland: during the Middle Pleistocene on the surface of Laurentide Ice Sheet ( 3-4 km thick) the temperature fell as low as -40¡C. The mean vertical thermal gradient in the gla-

Rozenbaum G.E., Shpolyanskaya N.A.

973

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.

ciers was 2-2.5¡/100m (Balobayev,1991), and at such temperatures the zero isotherm must have been at a depth of 1600-2000 m, and the lower part of the glacier, up to 2 km thick, was about 0¡C. Consequently, it is most likely that under the major ice sheets there was no permafrost. Subglacial permafrost could only form under glaciers no more than 1000 m thick or close to 1500 m thick in the coldest conditions. Submarine permafrost formed under two conditions: 1) in the nearshore shallows where annual freezing of the sea ice with the sea bottom occurred and 2) at depths ranging approximately from 40 to 100-150 m, where there are no more seasonal temperature fluctuations and where the temperature of near-bottom water is less than 0¡C (Shpolyanskaya, 1989).

974

The interglacial epoch that marked the beginning of the Late Pleistocene (Sangamonian - Mikulin - Oxygen Isotope Substage 5e), reached its maximum around 125 ka BP. The interglacial was accompanied by a glacioeustatic transgression which was most developed in the European sector. In the American sector, in particular in northern Alaska, the sea level was only 10 m higher than at present (PŽwŽ et al.,1995). The air temperature at the maximum of the interglacial exceeded the contemporary one by 2-3¡C, the smallest changes (2¡C) taking place in the Asiatic sector and the biggest ones (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 of the marine fauna and of pollen: forest tundra, which

The 7th International Permafrost Conference

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

replaced tundra, does not preclude a cold climate. Subaerial permafrost degraded in the Arctic as shown by ice-wedge pseudomorphs, for example in Alaska (Hopkins,1976). In the European sector, permafrost was absent practically everywhere, with the exception of the Ural Mountains and Pai-Khoi (Figure 1). In the American sector, permafrost existed north of the Arctic Circle. Ground temperatures ranged from approximately -3¡C near the Arctic Circle to -13 - -14¡C in the High Arctic (Harrison, 1991; Brigham and Miller, 1983). Temperatures in the mountains were lower. Permafrost thickness ranged from 100 to 600 m. In the Asiatic sector, permafrost did not degrade (Figure 1). Subglacial permafrost was absent throughout Oxygen Isotope Substage 5e. Submarine permafrost was widely developed (see Figure 1); today its remains, including thick massive icy beds, underlie large areas in the north of Western Siberia.

Further climate change was characterized by steadily increasing cooling and drying, reaching a nadir at 20-18 ka BP (Oxygen Isotope Stage 2), when air temperatures had decreased by 7-8¡C in the Asiatic and American sectors and by 10¡C in the European sector. Climate cooling and drying were aided by the reduced inflow of cyclonic air masses to the Arctic and the isolation of the Arctic basin due to a major marine regression (>100 m fall in sea level), which exposed the greater part of the Arctic shelf (PŽwŽ et al., 1995). Drying of the climate brought about a drastic reduction of glaciation in the Asiatic sector and in the American High Arctic (England and Bradley, 1978). At this time there existed homogenous natural conditions on the vast cooled land (Velichko, 1989). The emergence of Beringia excluded the warming influence of the Pacific Ocean almost completely. Zonal and sectorial differences were largely smoothed out. Conditions were suitable for the forma-

Rozenbaum G.E., Shpolyanskaya N.A.

975

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

tion subaerial permafrost (Figure 2) : rock temperatures were -17 - -20¡C on the plains and as low as - 23¡C in the mountains while the permafrost thickness fluctuated between 600 and 900 m on the plains and reached 2000 m in the mountains. This follows from our calculations and is indicated by Brigham and Miller (1983), Allen et al. (1988), Harrison (1991), and Osterkamp and Gosink (1991). Iceland holds a special position. Its climate, by virtue of Iceland's geographical position, is now marine and relatively warm, and does not correspond to the

976

island's northerly position. During Late Wisconsin times, the island occupied a considerably larger area. As in the European sector, the cooling there was greater than in the other regions of the Arctic. This was because the region was cut off from the Gulf Stream's warming influence and thus the latitudinal factor began to take effect there to a larger degree than during interglacials. The temperatures fell by no less than 10¡C below present values. In such conditions subaerial permafrost existed. Calculations suggest that rock temperatures on Iceland were -3 - -4¡C and permafrost thickness was 100-200 m. Subglacial permafrost was most likely absent.

The 7th International Permafrost Conference

Despite the apparent small size of glaciers in Iceland, high temperatures hindered the formation of subglacial permafrost (see Fig. 2). In the European sector, the temperature 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 during this epoch because the majority of the glaciers were comparatively small and thin. Using the calculations cited above, it is likely that permafrost was absent where glacier ice exceeded 1500 m in thickness. However, subglacial permafrost probably occured beneath ice thinner than 1500 m. Submarine permafrost beneath those small parts of the shelf still submerged was represented mainly by near-shore permafrost and perennially cooled sediments .

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 on the northernmost islands, where glaciers of small size and thickness survived, and beneath thin, marginal parts of the Greenland Ice Sheet, where relict subglacial permafrost could survive. Indications of this are provided by contemporary materials dealing with subglacial temperatures of Greenland and adjacent islands of the Canadian High Arctic (Hansen and Langway, 1966). Submarine permafrost, during the Holocene Climatic Optimum, was present mainly in the form of near-shore permafrost and relict submerged subaerial permafrost (Mackay, 1972) (Figure 3).

The Holocene has been marked by a large glacioeustatic transgression and considerable climate warming. The warming peaked during the Climatic Optimum, which manifested itself in the various parts of the Arctic diachronously from 9-8 ka BP to 6-5 ka BP. Air temperatures in the Arctic at that time exceeded contemporary values by about 2¡C. Both the warming and the transgression affected the permafrost. Both the zonal and sectorial structure of the permafrost zone spatial change were reestablished. Subaerial permafrost started to thaw in southern regions of the Arctic and in the northern regions, thermokarst processes were active. In the Asiatic sector, thermokarst formed alass plains (Arkhangelov et al.,1989). In the American sector, asynchroneity in the development of Holocene events manifested itself. Maximum thawing of Alaskan permafrost occurred during the Early Holocene, when numerous thermokarst lakes and depressions formed and boreal forest developed (Barnosky et al., 1987; Ritchie, 1984; PŽwŽ et al., 1995). Beneath the greater part of the European sector, frozen ground thawed (Figure 3); only

Conclusion Contemporary permafrost of the Arctic was mainly affected by its evolution at the end of the Quaternary. At that time, amplitudes of climatic changes reached their maximum; the decrease of air temperatures, relative to the contemporary one, reached 7-10¡C during cold epochs, while their increase during warm epochs amounted to 2-3¡C. Throughout its entire history the permafrost was preserved, but repeatedly experienced degradation and aggradation. It shows a predominance of sectorial differences over zonal ones.

Acknowledgments We thank J. Murton and B.L. Berry for helpful comments on the manuscript.

References Allen, D., Michel, F. and Judge, A. (1988). The permafrost regime in the Mackenzie Delta, Beaufort Sea region, N.W.T. and its significance to the reconstruction of the palaeoclimatic history. Journal of Quaternary Science 3, 3 - 13.

Brigham, J. K. and Miller, G. H.(1983). Palaeotemperature estimates of the Alaskan Arctic Coastal Plain during the last 125,000 years. In Proceedings 4th International Conference on Permafrost, Fairbanks, Alaska, National Academy Press, Washington, D.C., pp. 80 - 85.

Arkhangelov, A.A., Konishchev, V.N. and Rozenbaum, G.E. (1989). Coastal-Novosibirsky region. In Regional Cryolithology. Moscow University Press, Moscow, pp.128-151.

Burn, C.R. (1994). Permafrost, tectonics and past and future regional climate change, Yukon and adjacent Northwest Territories. Canadian Journal of Earth Sciences, 31, 182-191.

Balobayev, V.G. (1991). Geothermometry of the frozen zone of the north of Asia's lithosohere. Nauka, Novosibirsk (178 pp). Barnosky, C.W., Anderson, P.M. and Bartlein, P.J. (1987). The northwestern U.S. during deglaciation; vegetational history and palaeoclimatic implications.In The Geology of North America, K-3, North America and Adjacent Oceans during the Last Deglaciation, The Geological Society of America, pp. 289-321.

Emiliani, C. (1970). Pleistocene temperature. Science, 168, 3933. England, J. and Bradley, R.S. (1978). Past Glacial Activity in the Canadian High Arctic. Science, 200, 265-269. Hansen, B.L. and Langway, C.C. (1966). Deep core drilling in ice core analysis at Camp Century, Greenland, 1961 - 1966. Antarctic Journal of the United States, 5, 207 - 208.

Rozenbaum G.E., Shpolyanskaya N.A.

977

Harrison, W.D. (1991). Permafrost responsible to surface temperature change and its implications for the 40 000-year surface temperature history at Prudhoe Bay, Alaska. Journal of Geophysical Research, 96, B1, 683-695. Hopkins, D.M. (1976). The history of the sea level at Beringia during the last 250,000 years. Beringia in Cainozoic era. The Academy of Science of the USSR Press , Habarovsk, pp. 9 32.

PŽwŽ, T.L., Berger, G. W. and Westgate, J.A. (1995). Past major global warming 3 Myr loess Record, Central Alaska, indicated by three buried taiga forest beds: 2 Myr, 125 ka, 10 ka. International Union for Quaternary Research. XIV International Congress, Freie Universitat. Berlin, (217 pp.). Shpolyanskaya, N.A. (1989). On the possibility of freezing of bottom deposits in Arctic seas. Vestnik of Moscow University , Geography, 5, 72-78.

Mackay, J.R. (1972). Offshore permafrost and ground ice, southern Beaufort Sea, Canada. Canadian Journal of Earth Sciences, 9, 1550-1561.

Velichko, A.A. (1989). Palaeoclimates and glaciations in Pleistocene. In Palaeoclimates of Lateglacial and Holocene. Nauka, Moscow , pp 35-43.

Osterkamp, T.E. and Gosink, J.P. (1991). Variations in permafrost thickness in response to changes in paleoclimate. Journal of Geophysical Research, B. 96, 4423-4434.

Velichko, A.A. (1989). Holocene as element of global natural process. In Palaeoclimates of Lateglacial and Holocene. Nauka, Moscow, pp 20-34.

Ritchie, J.C. (1984). Past and Present Vegetation of the Far Northwest of Canada. University of Toronto Press, Toronto, 251 pp.

978

The 7th International Permafrost Conference