BOLSHEZEMELSKAYA TUNDRA: FLASHBACK

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by Galina RUSSANOVA, Dr. Sc. (Biol.), Biology Institute, Komi Research Center, Ural Branch, Russian Academy of Sciences

 

According to a number of research workers, some episodes of climatic variations in the Late Holocene (the last 2.5 thousand years) can occur again as a result of a predicted global warming. Therefore, it is important to visualize well enough the past stages of modern landscapes development. However, our knowledge of cryogenic territories is still insufficient. Having looked into the "memory" of Bolshezemelskaya tundra soils, we will learn a lot about the bioclimatic conditions which have changed their look and assess more correctly the tendencies of soil landscape formation in future.

 

According to present conceptualization, in the late Atlantic Time (6,000 - 4,600 years ago) the lands of Bolshezemelskaya tundra* up to the Barents Sea coast were covered with taiga forests under the canopy of which there were formed podzolic and gley podzolic soils. Afterwards, they could have been covered by later natural deposits and, thus, it is possible to find them and study. However, very few similar discoveries were described. One of them belongs to Yuri Liverovsky of Russia who found a relict profile under peat and eolian (wind-driven) sands in 1933 during his explorations in the Pechora region. In 1996 on the Barents Sea coast I was lucky to find, including at the micromorphologic level**, the signs of a taiga soil profile under the modern tundra soil.

 

In order to credibly assess the conditions and determine the age of buried holocenic soils within the limits of the main modern landscapes of Bolshezemelskaya tundra, in 2000 - 2005 we carried out research in which the characteristics of macro- and micromorphologic peculiarities, physical and chemical features of soils agree with their age determined by the radiocarbon method. I emphasize: the specifics was in a comparative analysis of buried and daytime (modern) profiles by singling out inherited relict features there. The surveys were made in typical tundra biocenoses and forest islands in

 

 

* Bolshezemelskaya tundra is a hilly morainic plane of 250 m height within the limits of the Nenets Autonomous Area and the Republic of Komi. - Auth.

** By micromorphologic method thin sections of soil of unbroken formation (slides) are examined with a microscope at 40 - 80 fold magnification. - Auth.

 

стр. 12

 

 

 

 

Map of plant zones of Bolshezemelskaya tundra. the basins of the Ortina, Khoseda-Yu, More-Yu and Vorkuta still preserved there.

 

"MEMORY" OF SANDY DEPOSITS

 

Many research workers, namely Ilya Sokolov from the Institute named after V. Dokuchayev, of the Russian Academy of Agricultural Science, and Viktor Targuliyan from the RAS Geography Institute noted that sandy-sab-uluous deposits are not always a reliable keeper of relict features of soil formation-they are very much subject to wind erosion. Moreover, the radiocarbon method does not give an exact idea about the age of organic horizons buried in them due to renewal of humus under the conditions of good aeration. At the same time morphologic manifestations of erstwhile processes are frequent here.

 

These are buried formations in the valley of the river Khoseda-Yu, the tributary of Usa (67°20' N., 59°48' E.), revealed in the steep of river terrace under tundra yernik (brushwood) and lichen vegetation (with domination of dwarf arctic birch). The depth of their bedding varied from 8 to 30 cm depending on the degree of material evacuation from the upper layer of deposits as effected by wind, water and displacements in the processes of cryoturbation*. In the mentioned layer there was formed modern soil of tundra-"podbur" which differs by weak

 

differentiation to horizons. The profile of podzol of sub-Atlantic age under it (2,200 years ago till presently) is partially put on the profile of podzol of average subbore-al interval (4,300 - 3,200 years ago) which was developed earlier with a well expressed illuvial horizon**.

 

Such combination of soils of different ages can be explained by a low rate of precipitation accumulation: a separation layer could not be formed thereby. The very presence of these taiga types in northern latitudes accounts for the propagation of forest formations here 3 - 4 thousand years ago, as a result of climate warming. One can judge about the beginning of cold intervals by profiles deformation, thickness variations and breaks of horizons as a result of cryoturbation.

 

Analysis of the microstructure of modern and relict soils has demonstrated that the intensity of processes in them is not equal. In comparison with podbur, large thickness of clay films in the "grains" of the skeleton*** in the illuvial horizon of buried podzol accounts for development of the latter during a longer period of time under the conditions promoting more intensive movement of fine fractions. The growth of films together with the increase in age of soils was proved in a number of works-first of all, by S. Langly (USA, 1997), who built relevant chronological series.

 

 

* Cryoturbation - the forms of bedding of rocks or soils appearing when they freeze in the state of excessive moistening and further thawing, having the appearance of curls, bends, rings, etc. - Auth.

** Accumulation of substances (iron oxides, organic components, finely dispersed clay minerals) usually results in the formation of illuvial horizon. Usually it is more dense and heavy in texture. - Auth.

*** Soil skeleton-grains of primary minerals and fragments 0.25 - 1 mm in size not displaced in ordinary soil-formation processes. - Auth.

 

стр. 13

 

 

In the modern soil cover of the Vorkuta river basin (67°28' N., 63°43' E.) podburs also prevail. We have found soils with a grassy horizon of 3 - 12 cm competence under them. The signs of removal of organo-ferrein compounds from the upper horizons with further illuvial down the profile were discovered in the latter by micromorphologic and physical and chemical analyses. All of them allow to refer the buried formations to the type of turfy podzols. However, how old are they? According to the data obtained by the radiocarbon method, they developed during an earlier stage of the sub-Atlantic Holocene period (2,200 - 2,000 years ago). However, if renewal of humic substances took place which was more probable in sandy-loan deposits, then the potential of the applied method is limited and, therefore, formation of soils could have begun earlier. One can assume that it began even in the climatic optimum of the Holocene (in the case of Bolshezemelskaya tundra - 6,000 - 4,600 years ago) when the conditions for it were favorable.

 

DISCOVERIES IN RELICT LANDSCAPES

 

As I have mentioned before, we studied the soils of holms of the Siberian fir tree which had remained from the preceding phases of the Holocene, which is confirmed by predominance of boreal types of plants here. In the More-Yu river basin 50 km from the Barents Sea (67°57' N. and 59°50' E.) and the Ortina close to the delta of the Pechora (67°45' N. and 54°05' E.) there is the northern limit of spread of these relicts of once vast taiga. Due to level ground features, the climate to the north from the border of forest with tundra is gradually changed along latitudinal gradient. Thus, forest holms were preserved in terraces of river valleys up to the Barents Sea coast which are protected from wind and well drained. Research of their soils in the Ortina river basin in the northwest of Bolshezemelskaya tundra and similar soils of related tundra associations to be formed in sand deposits have demonstrated an equal set of the formative process-

 

стр. 14

 

 

es. However, the specific character of the soils of forest holms is in the weakening of cryogenic and strengthening of eluvial processes (evacuation of material).

 

In the More-Yu river basin in the modern soil cover of fir tree holms podburs prevail developing on loose sands, being subject to active wind erosion. Relict podburs and podzols are under them. Preservation of subsurface soils is not equal: it depends on the conditions of burial destruction by cryogenic and other processes. According to radiocarbon dating, relict podzol in the basin of the More-Yu's lower reaches was formed in the mid-subboreal period, which confirms the conclusions made by Natalia Bolikhovskaya from the Geographic Department of Moscow Lomonosov State University about climate warming in the north of Bolshezemelskaya tundra at this time. In other words, buried soils can serve as one of the indicators of the sub-Arctic climate change in the Holocene.

 

In the researched area polygonal peaty plateaus destroyed by thermal erosion can also be met. Evidently, these are relict formations as in the late Holocene accumulation of peat of eutrophic origin does not take place. According to the radiocarbon dating suggested by us, the beginning of its growth in More-Yu river basin falls to the Early Atlantic period, while it was formed, mainly, in the Atlantic period of time before formation of tundra landscapes which had begun 3,000 years ago. These results comply with the ones which were obtained earlier by Natalia Bolikhovskaya with relation to the north of Bolshezemelskaya tundra and Pirita Oksan-en from Arctic Center Rovaniemi (Finland) with relation to the Bolshaya Rogovaya river basin (tributary of the Usa river in the north-east of the European Russia).

 

So, though the diagnostics of Late Holocene stages of development of soils is difficult, as a result of their degradation due to erosion and cryogenic processes, we have managed to single out three stages of forming of multilevel profiles on light rocks.

 

стр. 15

 

 

The first one relates to the mid-subboreal period (4,300 - 3,000 years ago). At that time clearly differentiated mature podzols were formed under warmer conditions (compared with modern ones), while cryogenic soils deformations and their burial under eolian deposits took place during cold periods (3,000 - 2,200 years ago) accompanied by the advancement of tundra.

 

The second stage is warm phases of mid-sub-Atlantic period (2,100 - 1,700 years ago and 1,000 years ago). At that time new climate warming and movement of forest formations to the north again promoted development of podzols which were deformed later to the different degree by cryogenic processes.

 

Finally, the third-modern-stage which began 1,000 years ago under the conditions of active accumulation of eolian deposits. Podburs have become its "product".

 

DO LOAMS KEEP INFORMATION BETTER?

 

I would like to say that local climate has a more remarkable effect on morphology of loamy tundra soils compared with the ones that are developed in loamy sands. Due to the property of keeping more moisture, they are more subject to cryoturbation processes in the course of which the mass of fine soil is transferred, while their profile is deformed. It seemed problematic to study relict signs under such conditions: they are obliterated. Indeed, the evidence of the past stages of soil formation on the deposits of heavy granulometric composition of cryogen areas is fragmentary. We were lucky to find an area where the soil that had been formed in the Atlantic time was protected against destruction by deposits of the upper slope superposed as a result of solifluxion* and alluviated in the process of water erosion.

 

We have studied buried soil on loamy deposits in the south-east of Bolshezemelskaya tundra, in the Vorkuta river basin (67°30' N. and 64°01' E.). The profile is clearly divided into layers: the upper is modern and the lower is relict. We have discovered shows of evacuation-accumulation of substances and cryoturbation in the first one of 49 cm thick. However, the most striking features relate to the processes of gleization which are developed under the conditions of overwetting. Day soil is, without doubt, gleyzem. There is a relict formation which is deeper than 50 cm. The fact that it had been created at the Atlantic time was mentioned by Inna Archegova from our Institute, Tatiana Tursina from the Soil Institute named after V. Dokuchaev and others. However, they proceed from single features-no comprehensive characteristics is available yet.

 

We have classified buried soil as meadow and podzolic typical soil. And here are the reasons for it. The peaty horizon changed by erosion, cryogenic and slide processes is defined in it by its nature of aggregation, humus microforms, availability of typical dark spots and roundish biopores described in slides at 70 magnifica-

 

 

* Solifluxion - the slow downhill movement of soils and loose rock as a result of the alternate freezing and thawing of frozen rock. - Auth.

 

стр. 16

 

 

стр. 17

 

 

стр. 18

 

 

tion. The type of humus which had been determined in laboratory and its fractional and group composition allowed us to diagnose the taiga nature of soil formation.

 

The illuvial horizon was also discovered in this soil. The form and heterogeneous clay sinter deposits in slides suggest its formation at the earlier stages of profile development. We see with a microscope clay fillings of pores and channels inside the units of soil mass and films of two layers (pulverescent on clay) and more complex compositions on their surface. Presumably, textural differentiation of buried soil took place at the Later Atlantic time (6,000 - 4,600 years ago) when July temperatures were 3 - 4°C higher than the present ones, the precipitation total - by 100 mm and the northern border of frost-proof broad-leaved types, for example, the elm approached. Soil formation processes were more intensive than today.

 

However, then subboreal period brought a cold snap. Information about the profile degradation at that time is "written" in the texture of soil. At the micromorphologic level we can see rounding of edges of structural joints of soils and plentiful sand-pulverescent films on their surface. The fact of deposits buried by a new formation suggests, as it was mentioned, more intensive deposition. Van Vliet Lanu from the University of Lille (France) made similar conclusions about climatic degradation of soils in Scandinavia in the late Holocene.

 

Thus, today we can single out three stages of soil formation on loamy rocks in Bolshezemelskaya tundra. We must mention that the latter fixed the signs which are more ancient than sandy-loam deposits.

 

The first, late-Atlantic stage (6,000 - 4,600 years ago) was characterized by favorable conditions for formation of humus and processes of evacuation of clay fractions of fine soil. Soddy-podzolic soils were formed then.

 

The second, subboreal stage (4,600 - 4,300 years ago) was marked by a sudden cold snap, degradation and burial of soil as a result of solifluxion freeze-and-thaw processes and deposition under the conditions of tundra landscapes. The initial stage of formation of modern soil, possibly, relates to the phase of warming (4,300 - 3,000 years ago). The signs of accumulation of clays in the lower part of profile suggest it.

 

The third stage of soil formation began at the end of subboreal and sub-Atlantic time (3,000 - 2,200 years ago up to present). Gleization and cryogenic processes resulted in the formation of a loamy and differentiated profile of modern gleyzem.

 

Thus, our research has covered most of Bolshezemelskaya tundra. New credible information was obtained about this area. Though the study of evolution of sandy soils is difficult due to the loss of relict characteristics, however, on the whole, the climatic stages of soil formation on sandy-loam and loamy deposits which we can find out by the methods of paleosoil science, coincide and relate to warm phases of the Holocene. While the maturity of the profiles of buried soils suggests that there was no time enough for their formation, and changes in the environment happened gradually.


Опубликовано 20 октября 2018 года




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© Galina RUSSANOVA • Публикатор (): БЦБ LIBRARY.BY Источник: Science in Russia, №1, 2007, C.12-19

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