S.N.Kirpotin *, N.P. Mironycheva-Tokareva **, E.D.Lapshina ***, W.Bleuten ****
* Tomsk State University, Tomsk, Russia
** Institute of Soil Science and Agrochemistry of the Siberian Branch of
Russian Academy of Science, Novosibirsk, Russia
***Yugorskiy State University,
Khanty-Mansiysk, Russia
**** University of Utrecht, Utrecht, Netherlands
Abstract
Western Siberia is a unique bog region at the World. Siberian peatlands have been a major sink of atmospheric carbon since the last deglaciation. About 104 Mha of Russian peatlands are located in Western Siberia, almost completely consisting of pristine peatland ecosystems. This paper shown, that peatlands, especially palsas in sub-arctic region of Western Siberia, are very sensitive indicator of climatic changes, due to the fact that they are situated in a permafrost zone and consist of frozen pleats, so any changes of a climate towards its warming result in activization of thermokarst process on extensive areas. It is revealed by us, that during last 3-4 years the thermokarst has got a "landslide" and probably irreversible character in the Western-Siberian sub-arctic that is undoubtedly connected to the warming of climate.
United Nations Millennium Declaration intends "to make every effort to ensure the entry into force of the Kyoto Protocol … and to embark on the required reduction in emissions of greenhouse gases". Implementing the Millennium Declaration UN proclaimed the target: reverse the loss of environmental resources and mentioned that carbon dioxide emission is the largest source of greenhouse effect.
Global warming is a major environmental issue and is expected to be greatest at high latitudes. Moreover, arctic and sub-arctic landscapes are particularly sensitive to temperature change because of thawing of permafrost (Callaghan & Jonasson 1995). In addition, linkages between the biosphere and atmosphere affect climate beyond the sub-arctic and arctic region. Some areas of the arctic have already experienced warming of up to 0.75ºC per decade over the last 30 years and these areas include the continental parts of Siberia. Most of the observed warming over the last 50 years is likely the result of increased greenhouse gas concentrations (Dlukokencky et al. 1998, IPCC 2001).
The actual role of pristine peatland in global carbon balance has not been quantified at this time, in particular the sub-arctic peatlands, as extensively present in Western Siberia, are white spaces in knowledge of carbon exchange with the atmosphere. Therefore it is impossible to predict the effects of climate change through changes in summer temperature, permafrost and hydrology on carbon balance of sub-arctic peatlands.
In addition to impacts on carbon sequestration and trace gas emissions, the changes have great implications for biodiversity, and land use for local peoples e.g. forestry and hunting. For instance, some boreal species of animals (e.g. badgers) and plants (e.g. Siberian pine) are now spreading to the North. On the other hand, the West Siberian Plain contains the biggest oil-gas fields in Russia. Their exploitation exerts a great impact on the local environment and can interact with climatic changes, especially in the northern part of the West Siberia Plain. An extensive data base of the nature of the West Siberian region including: vegetation, soils, fauna, climate, hydrology, permafrost processes, dynamics of landscapes has been assembled by consortium of authors of presented paper but is largely unavailable to the Western World. However, at this time, the rates of expansion of bogs in the South and their degradation in the North are unknown and, together with the wider implications of these changes, need urgent investigation.
But sometimes it’s even not necessary to be a professional ecologist to understand the scale of dramatic changes become apparent in the Western-Siberian sub-arctic last time. It becomes clear just from the talks with local people. For instance during our last expedition (August, 2004) on the road New-Urengoy – Pangody one fellow traveler – geophysicist takes a seat in our car and he told about the warming of the local climate, describing that in near past: 10-15 years ago, the winter roads (they functioning only in winter time when the surface of bogs becomes frozen and can stands the pressure of heavy traffic) completely freeze in the late October, and few last years they become frozen only in December or even later. So the gas industry workers face a certain economical problem, because they lost few months of active winter transportation to the distant oil-gas-fields, difficult of access.
The natural dynamics of landscapes is a complex process driven by various factors. Climate, which in many cases determines the general direction of landscape development, plays an important role among them. However, separate components of landscape respond to the influence of climate and its changes in a different degree. Vegetation is one of the most unstable and sensitive components among them.
Since 1989 authors of presented paper repeatedly worked in the sub-arctic region of Western Siberia and thus have a 15-years observation over newest dynamics of landscapes of this area. In 1989-1991 during careful researches of plateaux palsas in Pur-Pe–Tanlova interfluve (64º-65º NL, 75º-76º EL), accompanied by helicopter flights of the investigated area and interpretation of aerial photographs (Scale 1: 10 000 and 1: 25 000), the cyclic succession of development of palsa complex was revealed and described in detail, and it was shown a continuous transformation of one elements of a landscape to others (Kirpotin et al. 1995; Kirpotin et al. 2003).
The idea about endogen cyclic development of palsas was repeatedly expressed by the Scandinavian scientists. Some of them even have detail and long-time observations above palsas and photographed separate stages of this cycle (Matthews et al. 1997; Sollid, Sorbel 1998). However insignificant areas occupied by palsas in Scandinavia and Northern America do not allow to see a time series of their development developed in a space. Only careful long-time observation over formation of separate frozen mounds and interpalsa thawed hollows have allowed for Scandinavian scientists to come to idea of cyclic development of palsas.
Absolutely other situation is typical for Western Siberia: anywhere else this cyclic succession is not shown so brightly, as on extensive spaces occupied by plateaux palsas in West-Siberian sub-arctic. Here all the stages and thinnest nuances of this process are visible in space in a remarkable image, i.e. spatial elements of a landscape extreme precisely reflect the time series of its development (Kirpotin et al. 2003). It is enough just to look at aero-cosmic images of landscapes of West-Siberian palsas to see, that they live, pulse; it’s observed original "spill over" of their elements to each other, making many times repeating cycle.
We are displaying below the description of mentioned succession cycle, to understand on its background the newest tendencies of palsa complex changes. The first stage of this process is small (0.5–3m) saucer-shaped round closed dwarf shrub-sedge-sphagnum thermokarst slumps (Fig. 1). Thermokarst subsidences formed on a surface of flat frozen mounds during incessant rains. On the aerial photographs such palsas have a characteristic "porous" surface, it as though corroded by numerous slumps of round shape.
Fig. 1. The first stage of permafrost melting (thermokarst) on the palsa surface (photographer S. Kirpotin, 1999).
Cracks of lichens cover and underlying peat drying up in the arid period are the basis for formation of some thermokarst subsidences (Fig. 2). The moisture stands in the cracks, and some of them are increased in the sizes especially by the freezing bursting as a result of fast freezing of moisture. In this case subsidences have the extended form, and development of them goes so quickly, that sphagnum mosses have not time to settle. In such subsidences it is usually observed the attenuated wet peat quite often sheeted by a thin layer of Drepanocladus exannulatus or Warnstorphia fluitans sometimes with an open mirror of water. Linear subsidences are a basis for formation of interpalsa hollows and water-currents with cotton-grass-sedge-sphagnum and sedge-sphagnum vegetation. Hollows and water-currents represent a uniform system of drainage of upper-permafrost and permafrost waters from melting turbaries.
Fig. 2. Cracks of lichens cover and underlying peat are the basis for formation of some thermokarst subsidences (photographer S. Kirpotin, 1999, 2004).
Fig. 3. Origin of embryonic thermokarst lake as the third stage of permafrost melting on the palsa surface (photographer S. Kirpotin, 1999).
Fig. 4. Round matured lake as a fourths stage of cyclic succession of permafrost degradation (photographer S. Kirpotin, 1999).
Young thermokarst subsidences irrespective of their origin start to work as catchment’s funnels, intercepting not only the rain waters which are flowing down from melting mounds during the summer (underlying frozen peat plays a role of waterproof rock), but also waters of permafrost origins. Frozen peat of mounds thaws gradually during all summer season and moisture formed as a result of its thawing is flow down to interpalsa hollows, currents and lakes. Therefore thermokarst subsidences increase their area even in the dry period, and if the subsidence is not intercepted by a water-current, it being gradually increased in the sizes, turns into a small thermokarst lake of round shape as a rule (Fig. 3, 4).
Fig. 5. Khasyrei – drained lake, which pours out its water to another reservoir, as a fifth stage of cyclic succession of permafrost degradation (photographer S. Kirpotin, 1999).
Lakes being catchment basins steadily increase the area. They "diffused (dispersed)" on palsa surface in the big abundance and quite often appear in the close neighbourhood. The water-currents conducting to different lakes are overlap, and if lakes occupy different position in a relief, the lake located on lower height intercepts a reservoir of the lake located above. Eventually, the upper lake pours out its waters to the lower one, turning into the drained lake – "khasyrei" (Fig. 5). Active neo-tectonic rising of described area promotes the origin of khasyreis, therefore their abundance is a reliable geomorphological marker of this process.
Thus, shortly characterizing two first stages of describing cyclic succession of the palsa complex it is possible to conclude, that at the first stage flat mound through a series of subsidences and hollows of different degree of watering turns into the thermokarst lake, and the lake, in turn, inevitably turns into the khasyrei.
The outcropping sandy or peat bottom of the lake basin with the rests of water turns into cotton-grass-sedge-sphagnum swamp. As a result of temperature inversion (cold air as a heavier one flows down to the bottom of a lake basin) begins repeated permafrost heaving of the lower bog, resulting to formation of the small-mound microrelief, with small (2-5 m) dome-shaped mounds of regular rounded or the oval form. Lichens and dwarf shrubs, typical for palsas, settle on the surface of these small mounds (Fig. 6). Owing to the proceeding of permafrost heaving isolated small mounds merge in uniform system and gradually turn, depending on capacity of a peat deposit, or in typical palsa plateau, or in dwarf-shrub-lichen tundra of similar view (Fig. 7). But even at this stage boards of the drained lake basin are still looked through on aerial photographs. So, this original succession cycle comes to the end in such a way.
Fig. 6. Mature khasyrei with yang frozen peat mounds (aerial photo, 1989).
Fig. 7. Old khasyrei with restored plateau mounds, as a last stage of cyclic succession of palsa development (aerial photo, 1989).
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Summing up told it is possible to notice, that the enough steady balance of cryogenic processes: a thermal karst and a permafrost heaving was peculiar to Western-Siberian sub-arctic region for a long time. Today there are all reasons to speak that the cyclic succession described by us has got the linear character directed aside strengthening of thermokarst.
Even, studying these processes in the beginning of 90-s, we have seen, that the thermokarst starts to prevail above the permafrost heaving. Though at that time changes in sub-arctic region had no catastrophic character yet, and it was difficult to tell with full confidence: where the cryogenic pendulum will be rocked. Nevertheless, it was expressed the assumption (Kirpotin etc., 2003), that in the near future the reflectance of palsas can sufficiently change owing to the light surface of flat mounds and plateaus covered with lichens steadily reduces the areas, giving up the place for the dark-brown interpalsa hollows. It was possible to admit that there is a certain critical threshold in the ratio of dark and light surfaces after which achievement the processes of their warming up as a result of gradual change of reflectance will be essentially and suddenly changed, and the process of permafrost degradation will go even more swiftly and is irreversible then. Some kind of the mechanism of a trigger hook will work, and the process of permafrost degradation will be as though to stimulate and to urge itself.
Rather recently in August 2004 we had an opportunity once again to return to the North Western Siberia thanks to the INTAS project "The effect of climate change on the pristine peatland ecosystems and (sub)actual carbon balance of the permafrost boundary zone in Subarctic Western Siberia", having passed on the automobile from Khanty-Mansiysk up to New-Urengoy and Pangody carried out the reconnaissance of this vast area with the careful investigation of some key sites.
What we have faced in a reality has appreciably surpassed all our forecasts and expectations; therefore even during preparation of the scientific paper it was rather difficult to be kept from emotional coloring of represented material. If to speak shortly: the "landslide" thermokarst cover landscapes of Western-Siberian sub-arctic region. We simply have not picked up more exact, capacious and expressive term for the general characteristic of what we have seen.
Thermokarst subsidences on the surface of flat mounds develop so swiftly that lichens and dwarf shrubs simply settle down under the water (Fig. 8), and sphagnum mosses in the most cases are not in time to settle in them, or only start to occupy these fresh water-bearing sites (Fig. 9). On the average 5-10 % of the mound’s surface is occupied by similar subsidences.
Fig. 8. Fresh thermokarst subsidence: dwarf shrubs settle down under the water (photographer S. Kirpotin, 2004).
Fig. 9. Sphagnum mosses start to occupy thermokarst subsidence (photographer S. Kirpotin, 2004).
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Besides the area occupied by thermokarst lakes are essentially increased. So, the coastal edge of some big lakes (more than 1 km in a diameter) surveyed by us have moved on the most modest calculations on 50-70 m (Fig. 10). Some of them have been even difficult to identify in a space image of 1999 which we had.
Fig. 10. The coastal edge of big lake (more than 1 km in a diameter) (photographer S. Kirpotin, 2004).
Fig. 11. The coastal edge of small lake (about 100 m in a diameter) (photographer S. Kirpotin, 2004).
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Small and middle-size lakes also appreciably increase their areas (Fig. 11). The strip of fresh-sunken (fresh-submerged) dwarf shrubs (by width 1-3 m): more often Ledum palustre and Betula rotundifolia is clearly looked on the coastal edge of these lakes. By appearance of dwarf shrubs it is possible to make the conclusion that these prompt changes have taken place more recently for last 3-4 years, and in most cases dwarf shrubs were not in time to be perish lost.
On the whole recent changes of palsa landscapes in Scandinavia are not such dramatic as in Western Siberia, because Scandinavia has rather a soft climate: it constantly worming up by Golf-Stream, and western scientist cant to imaging the scales of permafrost melting in the Western-Siberian sub-arctic with its continental type of climate.
It is necessary to note in the conclusion, that materials of the first expedition are not processed yet, and while it is difficult to give quantitative characteristics of the processes revealed by us to estimate their scales, norms and speed. However it is completely clear, that most likely mechanism of the trigger hook, assumed by us, which has started the "landslide" thermokarst in the sub-arctic region of Western Siberia, has worked. Besides the concerned problem for rather a long time hasn’t only scientific character and has passed to the plane of World Politics: global warming of a climate became an environmental problem number one in the World. If the mankind does not want to face serious social and economic losses, it is necessary to take urgent measures, for example, to ratify the Kyoto Protocol. Obviously we have less and less time for it.
This research is financially supported by INTAS 34.35.25
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