Kazakh Steppe Research Articles

The mode of degradation of Pleistocene permafrost in West Siberia

Continuous permafrost 300 to 600 m thick is mapped in West Siberia beyond the Arctic Circle. To the south, it splits into two uneven layers to form a swallow-tail structure in cross-section. The surficial layer, which is about 50 m thick, occurs discontinuously between 66 ° and 64°N (in isolated patches up to the 60th parallel) and is thought to be a product of the Late Holocene cooling. The second, much thicker layer, separated from the surficial permafrost by a 100-200m thick talik, extends to the 60th parallel and must be a Pleistocene relict. Its fossil nature appears in near-zero temperatures and non-gradient curves of the vertical temperature profile (Yershov, 1989). The relict layer is commonly thought to be of the Late Weichselian age when solid permafrost reached the 51st parallel, i.e. shifted by 1500-1600 km south from its present limit (Baulin et al., 1984). Only Zemtsov (1976) related it to the Middle Pleistocene maximum glaciation. The study of fossil glacial ice contained in the thick discontinuous permafrost near the Arctic Circle has shown that relict permafrost must have survived since Early Weicheslian time (Astakhov and Isayeva, 1988). There are different ideas about the process which changed the ubiquitous solid permafrost of the Pleistocene into the present discontinuous swallowtail structure south of the Arctic Circle. The usual reasoning based on temperature profiles, freeze-andthaw structures in sediments and computer simulations does not allow unambiguous conclusions, particularly if geological data are disregarded. Balobayev et al. (1983) have suggested that the abrupt southern boundary of the modern continuous permafrost reflects a shoreline of a Late Weichselian proglacial lake that fringed the ice sheet along the Arctic Circle. Sedimentological research was discovered no traces of large proglacial lakes (Astakhov, 1989, 1992). Most investigators believe that the deep talik over the relict permafrost developed during the Holocene climatic optimum. The popular view, ascribing great mobility to the West Siberian permafrost, suggests that south of the Arctic Circle a permafrost layer approximately 500--600 m thick could form and vanish during the Late Pleistocene-Holocene (Baulin et al., 1981). This apparently contradicts geological data about the conservative nature of Siberian permafrost. The above mentioned lower Weichselian fossil ice and fresh-looking (not decayed) frozen wood of infinite radiocarbon age has survived within the permafrost near the surface (Astakhov and Isayeva, 1988). These facts show that: (i) no deep climatic fluctuations affected the permafrost since the Early Weichselian except the Holocene warming; and (ii) the Holocene thawing of the Arctic permafrost tens of metres deep (Baulin et al., 1981) must have been local. The apparent discrepancy between the data on great inertia of the Pleistocene permafrost in the Arctic and deep taliks registered south of the Arctic Circle must be attributed to heterogeneity of the degradation process in the different geographical zones (Astakhov, 1990). The divergence of geological processes in the Arctic from central West Siberia can be judged from the comparison of the sedimentary records. Facies related to the stable Weichselian permafrost show an arid and very continental climate from the Kara Sea to the Kazakh steppes. They are thick loess sheets (changing laterally into sand dunes), which are frozen with syngenetic ice veins in the Arctic, and thawed with ice wedge casts in the centre and south of West Siberia. The only zonal difference appears in the volume of water-lain facies within this principally aeolian formation. In the Arctic, aqueous sediments are mostly comprised of glaciofluvial sands and glaciolacustrine varves underlying the loess and dunes. Within the uppermost aeolian, mostly sandy formation, waterlain sediments are scarce, especially during 22 to 15 ka BP (Astakhov, 1991). Weichselian sediments in thermokarst sink-holes have not been described, even along the major river valleys. The situation is somewhat different south of the 64th parallel where numerous lenses of sandy, limnic rhythmites with dates from infinite to 22 ka BP are encompassed by loess-like silts with palaeosols and ice-wedge casts. They are especially abundant along the transverse Ob valley and the crest of the Siberian Hills. Such rhythmites, up to 15 m thick ('Kolpashevo sand' by Arkhipov et al., 1980), have nothing to do with large ice-damned lakes, because they:.(i) occur at all hypsometric levels from 40 to 120 m; (ii) contain seams of loess, palaeosols, cryoturbated horizons and ice-wedge casts; (iii) make oval and doughnut-shaped hillocks of thermokarst inversion topography; and (iv) are never traced laterally for more than a few hundred metres (Astakhov, 1989, 1992). These features indicate that in central West Siberia, thermokarst was active in the Middle Weichselian, probably along

Russian Writers Confront the Past: History, Memory, and Literature, 1953-1991

present, one must understand the past.2 A straightforward sentiment perhaps, but under the conditions existing the Soviet Union from Stalin's death until Gorbachev's perestroika it was not easy even to learn about the past, let alone understand it. This was especially true of the Brezhnev era, when the crimes and injustices visited upon the populace were only superficially countenanced by the regime. From the outset, however, writers were the forefront of efforts to rediscover the past, not only to paint an accurate picture of past events but also to examine their consequences several decades on, in order to make sense of the present. Since 1985, when Mikhail Gorbachev came to power, and particular since 1986, when his policy of glasnost' the arts and media was first encouraged, we have seen an unprecedented information explosion the Soviet Union (as it then was). Gorbachev intended that the Communist Party would be the instrument for reform with his program of perestroika from above, and that the freedom to publish criticisms and abuses under glasnost' would only enhance the esteem of the party. However, we can now see that, even before the party's last stand against the people August 1991, its authority and legitimacy to rule had been fatally undermined. The intensive and unprecedented investigation into the blank spots of history those areas previously put out of bounds because of their historical or ideological sensitivity not only did not enhance the party's reputation, but besmirched and destroyed it irredeemably. For some people living the USSR, the Revolution itself was still within living memory, and certainly many, many more could remember the Stalin years. Many thousands of people still had personal and often painful experience of the party's rule from the late 1920s, some of the catastrophic collectivization of agriculture from 1928 to 1930, and the ensuing famine of 1933, others of the Great Purge of the mid-1930s. During the Stalin years, it is estimated, some fifteen to twenty million people died the Gulag.3 A further twenty million casualties were claimed four years of war with Nazi Germany, not all of them the result of enemy action. In the course of the war and afterward, Stalin exiled whole peoples, including some Caucasian peoples, the Volga Germans and the Crimean Tatars, to the inhospitable Kazakh steppes and Central Asia, for alleged collaboration. If we also bear mind the postwar repressions, arrests, and executions (especially the arts and higher education), then it would be no exaggeration to say that no Soviet family was left untouched by the effects of Stalin's rule. In the postStalin period, although political arrests and incarcerations were fewer and the Soviet state