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International Journal of EnvironmentalStudiesPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/genv20
Abrupt changes of thermokarst lakesin Western Siberia: impacts of climaticwarming on permafrost meltingS.N. Kirpotin a , Y. Polishchuk b c & N. Bryksina da Tomsk State University , Tomsk, Russiab Ugra State University , Khanty‐Mansiysk, Russiac Institute of Petroleum Chemistry , SB RAS, Tomsk, Russiad Ugra Research Institute of Information Technologies ,Khanty‐Mansiysk, RussiaPublished online: 01 Oct 2009.
To cite this article: S.N. Kirpotin , Y. Polishchuk & N. Bryksina (2009) Abrupt changes ofthermokarst lakes in Western Siberia: impacts of climatic warming on permafrost melting,International Journal of Environmental Studies, 66:4, 423-431, DOI: 10.1080/00207230902758287
To link to this article: http://dx.doi.org/10.1080/00207230902758287
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International Journal of Environmental Studies,Vol. 66, No. 4, August 2009, 423–431
International Journal of Environmental StudiesISSN 0020-7233 print: ISSN 1029-0400 online © 2009 Taylor & Francis
http://www.tandf.co.uk/journalsDOI: 10.1080/00207230902758287
Abrupt changes of thermokarst lakes in Western Siberia: impacts of climatic warming on
permafrost melting
S.N. KIRPOTIN*†, Y. POLISHCHUK‡§ AND N. BRYKSINA¶
†Tomsk State University, Tomsk, Russia; †Ugra State University, Khanty-Mansiysk, Russia; §Institute of Petroleum Chemistry, SB RAS, Tomsk, Russia; ¶Ugra Research Institute of
Information Technologies, Khanty-Mansiysk, RussiaTaylor and FrancisGENV_A_375998.sgm
(Received 30 January 2009)10.1080/00207230902758287International Journal of Environmental Studies0020-7233 (print)/1029-0400 (online)Original Article2009Taylor & [email protected]
Peatlands situated in a permafrost zone and consisting of thin layers of frozen peat, especially palsasin the sub-arctic region of Western Siberia, are a very sensitive indicator of climatic changes, suchthat any changes of climate in the direction of warming lead to increased activity in a thermokarstprocess over extensive areas. Thermokarst lakes as an invariable element of the palsa mire complexare the most convenient object for distant monitoring of the global warming influence on the state ofthe permafrost rocks.
Keywords: Global warming; Methane emission; Permafrost; Remote sensing; Thermokarst lake; West-Siberian palsa bog
Arctic and sub-arctic landscapes are particularly sensitive to temperature change because ofthe thawing of the permafrost [1]. Moreover the Siberian Arctic is warming up much fasterthen other northern areas and according to some estimates it has been heating up more than4°C in the winter period during the last century [2]. Most of the observed warming isprobably the result of increased greenhouse gas concentrations [3,4].
Peatlands situated in a permafrost zone and consisting of frozen peat layers – palsas –cover extensive areas in Western Siberia. In general, palsa mires define the outer limit ofpermafrost, which makes them especially sensitive to climatic fluctuations [5].
Disturbance of endogenous natural cycle of palsa development
Scandinavian scientists have made detailed long-term observations of palsas and have photo-graphed separate stages of this cycle [5,6]. These careful observations cover a long period inthe formation of separate frozen mounds and interpalsa thawed hollows. The Scandinaviansthus developed the concept of the endogenous cyclic development of palsas. But, palsas in
*Corresponding author. Email: [email protected]
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424 S.N. Kirpotin et al.
Scandinavia and indeed in North America occupy only a small area, so that it is not possibleto observe a time series for their development over space.
The situation in Western Siberia is different. Plateaux palsas cover extensive areas in theWest-Siberian sub-arctic. All the stages and the smallest nuances of the endogenous cyclicsuccession process are visible over space in remarkable images. The positions of the edges ofthe landscape precisely reflect the time series of its development. It is enough just to look ataerial images of landscapes of West-Siberian palsas to see that they live and pulse. You cansee the original ‘spill over’ of their elements one to another, making a cycle which is repeatedmany times.Figure 1. Scheme of endogenous cyclic succession of palsa development.In earlier publications we have described the endogenous cyclic succession of palsa devel-opment [7,8] which can be shown by the following scheme (figure 1). In brief: 1) during thefirst stage of the cyclic decay of flat palsa complexes, thermokarst lakes may appear as a resultof the appearance of different sized melted subsidences; 2) these lakes can increase in size dueto shore erosion since lake water acts as a heat source which induces further thawing of perma-frost layers; 3) these thermokarst lakes can also turn into a khasyrei (drained lake without water);4) at the empty lake basin stage, the heaving by renewed permafrost goes on, the isolated smallmounds merge into a uniform system and they turn into typical flat palsa plateaux.
In sum, the thermal karst and the heaving of the permafrost have been peculiar to theWestern-Siberian sub-arctic region for a long time. There has been a steady balance of cryo-genic processes. But today we have observed that the cyclic succession has assumed a linearcharacter directed towards the strengthening of the thermokarst.
When we were studying these processes at the beginning of the 1990s, we saw that thethermokarst was starting to predominate over the heaving of the permafrost. At that time it
Figure 1. Scheme of endogenous cyclic succession of palsa development.
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Abrupt changes of thermokarst lakes in Western Siberia 425
was still difficult to judge with confidence where the cryogenic pendulum would swing.Nevertheless, it was argued [7] that in the near future the reflectance of the land surface ofpalsas could change significantly if the light surface of flat mounds and plateaux coveredwith lichens steadily reduced in area, giving way to dark-brown interpalsa hollows withlower reflectance. It was argued that there was a critical threshold in the ratio of dark andlight surfaces. Once this was reached, the process of warming up as a result of the gradualchange of reflectance would be fundamentally and suddenly changed. The process of perma-frost degradation would then start to accelerate and become irreversible. A trigger mecha-nism would come into play and the process of permafrost degradation would start tostimulate itself and to urge itself onwards.
According to the latest investigations carried out by Russian institutions in the frameworkof the international INTAS project 34.35.25, ‘The effect of climate change on the pristinepeatland ecosystems and (sub) actual carbon balance of the permafrost boundary zone inSubarctic Western Siberia’ in the Novyi-Urengoy-Pangody area near of the Polar Circle inAugust 2004, the degree of thermokarst activity has unusually increased, and for the last fiveto six years has become extremely high. What we found appreciably surpassed our expecta-tions. In brief, the thermokarst has expanded so much that it now covers the landscape of theWest-Siberian sub-arctic region. The trigger process predicted by us was realised so we callthe situation ‘ecological landslide’ [9,10]. This situation demands urgent measures, such asjoint efforts of the scientific community for interdisciplinary study of dynamics of anenvironment in the context of climatic changes.Figure 2. The coastal edge of a small lake (about 100 m in a diameter) (photographer: S. Kirpotin, 2008).Thermokarst subsidences on the surface of flat mounds are developing so swiftly thatlichens and dwarf shrubs simply settle down under the water, and sphagnum mosses in mostcases have not had time to settle in these fresh water-bearing sites, or are only starting tooccupy them. On average, 5–10% of the mounds’ surfaces are occupied by such subsidences.Moreover, the area occupied by thermokarst lakes has increased substantially. The coastaledges of some big lakes (more than 1 km in a diameter) which we surveyed have moved, on
Figure 2. The coastal edge of a small lake (about 100 m in a diameter) (photographer: S. Kirpotin, 2008).
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426 S.N. Kirpotin et al.
the most modest calculations, by 50–70 m. Small and middle-sized lakes have also apprecia-bly increased in area. A strip 1–3 m wide of freshly submerged dwarf shrubs, most oftenLedum palustre and Betula rotundifolia, is clearly visible on the coastal edge of these lakes(figure 2). From the appearance of the dwarf shrubs it is possible to conclude that thesechanges have taken place recently, in the last three to four years. In most cases the dwarfshrubs have not had time to perish and be lost [8].
It is necessary to note that our data also completely correspond to the latest observation ondegradation of Arctic sea ice in the summertime, carried out by researchers of Arctic regionsof the National Snow and Ice Data Center, University of Colorado at Boulder, USA [11].Conducting annual monitoring they have revealed a gradual reduction of the area of polar icesince 1978. They note that the most dramatic thawing began in the last four years. By theirestimations, the critical point beyond which polar ice cannot be restored any more has beenachieved.
Satellite research of thermokarst lake changes
The analysis of remote sensing data in geocryological researches [12] has shown thatthermokarst lakes can be used as the most prospective indicator of cryogenic landscapechanges. Figure 3 shows 10 pilot territories located in different permafrost zones of WestSiberia for carrying out research into cryogenic processes using space images of thermokarstlakes.Figure 3. Pilot territories in different permafrost zones.
Figure 3. Pilot territories in different permafrost zones.
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Abrupt changes of thermokarst lakes in Western Siberia 427
Research into the dynamics of thermokarst lake changes in the test areas was carried out bymeans of measurement of changes of lakes areas using a collection of space images taken atdifferent times in the above 30-year period:
Landsat - 1 (scanner MSS), 10 August 1973Landsat - 5 (scanner MSS), 26 June 1988Resurs - F2 (scanner MK4), 14 June 1993Landsat - 7 (scanner ETM), 3 July 2002Spot - 5 (scanner HRV), 20 July 2005ERS - 2 (scanner SAR), 2005–2008ALOS (AVNIR-2) 2006–2007
Changes of areas of the lakes water surface were measured with use of the softwareERDAS. There were 30–80 thermokarst lakes chosen in each pilot territory. Figure 4 repre-sents fragments of space images taken at different times, showing consequent stages in thedecreasing area of one of the thermokarst lakes in PT-10 during the period 1973–2005. Asshown in figure 10 the studied thermokarst lake decreased significantly in its area of lakewater surface, and became a khasyrei in 2005. Other lakes in different PT increased in area ordid not change in area. So we performed a statistical analysis of the measured data.Figure 4. Consequent stages of decrease of lake number 7 area.Table 1 shows the results of statistical analysis of data. Normalised change of the total areaof lakes (R) is calculated by the formula:
where Sin - total (or summarised) area of studied thermokarst lakes in PT in initial year,Sf - total area of studied lakes in the same PT in final year.As table 1 shows, the values of R for all pilot territories located in the discontinuous perma-
frost zone are negative, but the R value for all pilot territories in the continuous permafrostzone is positive. Therefore the geocryological changes in the discontinuous permafrost zoneon average are accompanied by a decrease in lake area; but the changes in the continuous
R = (S – S ) / Sin f in ,
Figure 4. Consequent stages of decrease of lake number 7 area.
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428 S.N. Kirpotin et al.
permafrost zone, by an increase in lake area. This is an experimental proof of the describedeffect of peat thickness on thermokarst processes in palsa bog under the impact of globalwarming.
Figure 5 represents generalised information on relative values of thermokarst lakesdepending on latitude.Figure 5. Normalised values of thermokarst lake areas changes depending on latitude.
Table 1.
Continuous permafrost zone
Pilot territories PT-1 PT-2 PT-3 PT-4 PT-5
Total area of lakes, ha19731984
6292,7 3421,2 1899,13566,9
3611,85
2006 6965,5 3765,3 2035,0 3998,9 3975,9Volume of samples 80 40 30 40 60Total area decrease of lakes, ha 672,8 344,1 135,9 432,0 364,05R, % 10,7 10 7 12 10
Discontinuous permafrost zone
Pilot territories PT-6 PT-7 PT-8 PT-9 PT-10
Total area of lakes, ha
197319841988 3777,0
3864,2 4370,83673,2
2155,1
20002005 2921,7 2759,6
3453,73234,8 1685,5
Volume of samples 40 40 118 40 40Total area decrease of lakes, ha −855,3 −1104,6 −917,1 −438,4 −469,6R, % −22,6 −29 −21 −12 −22
Figure 5. Normalised values of thermokarst lake areas changes depending on latitude.
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Abrupt changes of thermokarst lakes in Western Siberia 429
Methane threat
One more problem connected to warming of a climate in high latitudes is the possibleactivation of methane emission to the atmosphere caused by thawing of the permafrost.Unfortunately, the functional role and exact parameters of participation of West Siberianbogs in the regional and global circulations of organic carbon and methane remain insuffi-ciently explored. To the greatest degree this is a challenge for peatland researchers in thepermafrost zone. Necessary studies have either not yet been undertaken or have had only anincidental and fragmentary character [13]. According to our observations thermokarst lakesin the north of West Siberia are shallow (1.5–2 m of depth) and they have a peat bottom. Tenyeas ago and earlier, bottoms of thermokarst lake basins usually were completely or partlyfrozen and bottom peat was not decayed. But through climatic change – global warming –peat bottoms of lakes have begun to warm up and melt, producing methane. We establishedthis to be the situation in our last expeditions.
The most widespread and standard techniques of measurement of greenhouse gases arechamber methods of direct measurement of respiration [13]. These permit the exact estimationof greenhouse gases from a surface, and thus the evaluation of diffused methane emissions. Aproblem is that along with diffusion emission of greenhouse gases there are their concentratedemissions or outflow through fractures. In summertime it is practically impossible to revealthe places of gas escape by trying to place the chamber precisely above a fracture. But inSiberian lakes, ice-holes not freezing in winter time despite severe frosts have been discovered[14]. The reason for their occurrence appeared to be intensive emission of methane in theseplaces by bubbling. Such places have been named hot spots of methane emission. We proposeto call the similar type of methane emission concentrated emissions, as in the case of aruptured gas pipeline. This form of methane emission remained unknown to science for a longtime. Thus, it was not taken into account and explored. Nevertheless, West-Siberian huntersover the centuries knew about non-freezing ice-holes in the intra-bog lakes where it is possibleto fall in with ski and sledge even in the middle of winter.
It appears that scientists have conscientiously measured only the diffusion type of methaneemission, ignoring the question of the concentrated emissions in places of outflow. Yet ebul-lition comprises, by estimations of Walter et al. [14], 96% of the total emission of methanefrom the lakes surveyed by them. It is not surprising, therefore, that parameters of methaneemission for thermokarst lakes of the Siberian North have been underestimated. By merelyrough estimates, these should be increased by 58%. Besides it is convincingly shown, that thelandscape process of thermokarst erosion essentially strengthens methane generation and,accordingly, emission of this gas [14].
It is obvious that there must be developed new techniques and methods for direct measure-ment of the greenhouse gases emissions, to include not only diffusion emission from a surface,but also the hot spots for concentrated emissions. Hot spots are expedient for revealing inwinter time on non-freezing ice-holes or methane bubbles, freeze in ice, and in summertimeto establish above these sites special chambers, according to a standard technique. The datacan be extrapolated on a large scale to thermokarst lakes in Siberia.
Conclusions
Thermokarst lakes as an invariable element of the palsa bog complex are the mostconvenient object for distant monitoring of the global warming influence on the state of
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430 S.N. Kirpotin et al.
permafrost rocks. Satellite monitoring (1973–2008) has revealed zonal specifics of geocryo-logicat processes. In the zone of continuous permafrost thermokarst lakes expanded theirareas by about 10–12%, but in the zone of discontinuous permafrost the process of theirdrainage prevails. These features are connected with the thickness of peat layers whichgradually have decreased to the North, and thus have reduced the opportunity for the lakedrainage.
During ground observations we have found that the southern palsas in the discontinuouspermafrost zone are more stable than the northern ones in the continuous permafrost zone.The changes we observed in 2004 in the New Urengoy-Pangody Pilot Territory (near thePolar Circle N 66 E 74°) are much greater than those in the Puritey-Malto Pilot Territory (N64°40–45′, E 75°24–29′) which we observed in 2005. Our explanation of this phenomenon isthat the level of thermokarst activity depends directly on the thickness of the peat layer ofpalsas. The thick layer of frozen peat protected the palsas at the southern site from melting.Farther north the annual growth of mosses becomes progressively less and the peat layer ofpalsas correspondingly becomes thinner. The thin layer of peat melts more easily in thesummer, leading to thermokarst in the more northern areas. Thus, very active thermokarst isapparent in the areas where the peat layer of the frozen bogs is insignificant (about 20–30 cm;50 cm max) and it is almost absent in the southern edge of the permafrost zone where thethickness of frozen peat is about 1.5–2 m.
Acknowledgements
This research was financially supported by EU-INTAS project 34.35.25 and RFBR 08-05-92496.
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