permafrost warming in the tien shan mountains, …permafrost warming in the tien shan mountains,...

e 56 (2007) 311–327www.elsevier.com/locate/gloplacha

Global and Planetary Chang

Permafrost warming in the Tien Shan Mountains, Central Asia

S.S. Marchenko a,⁎, A.P. Gorbunov b, V.E. Romanovsky a

a Geophysical Institute, University of Alaska Fairbanks, AK 99775-7320, USAb Institute of Geography, Almaty, Kazakhstan

Received 11 May 2005; accepted 19 July 2006Available online 5 October 2006

Abstract

The general features of alpine permafrost such as spatial distribution, temperatures, ice content, permafrost and active-layerthickness within the Tien Shan Mountains, Central Asia are described. The modern thermal state of permafrost reflects climaticprocesses during the twentieth century when the average rise in mean annual air temperature was 0.006–0.032 °C/yr for thedifferent parts of the Tien Shan. Geothermal observations during the last 30 yr indicate an increase in permafrost temperatures from0.3 °C up to 0.6 °C. At the same time, the average active-layer thickness increased by 23% in comparison to the early 1970s. Thelong-term records of air temperature and snow cover from the Tien Shan's high-mountain weather stations allow reconstruction ofthe thermal state of permafrost dynamics during the last century. The modeling estimation shows that the altitudinal lowerboundary of permafrost distribution has shifted by about 150–200 m upward during the twentieth century. During the same period,the area of permafrost distribution within two river basins in the Northern Tien Shan decreased approximately by 18%. Bothgeothermal observations and modeling indicate more favorable conditions for permafrost occurrences and preservation in thecoarse blocky material, where the ice-rich permafrost could still be stable even when the mean annual air temperatures exceeds0 °C.© 2006 Elsevier B.V. All rights reserved.

Keywords: climate warming; alpine permafrost; active layer; modeling

1. Introduction

The alpine permafrost zone in the Tien ShanMountains (69–95°E, 40–44°N) belongs to the Asianhigh-mountain permafrost region, the largest in theworld (Fig. 1). The occurrence and evolution of alpinepermafrost in the middle latitudes directly relates to thetectonic history of the Earth. The facts collected recentlyprovide information about the Pre-Quaternary age ofpermafrost in the Tien Shan Mountains. Permafrost firstformed about 1.6 million years ago because of mountain

⁎ Corresponding author. Tel.: +1 907 474 7698; fax: +1 907 4747290.

E-mail address: [email protected] (S.S. Marchenko).

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elevation (Aubekerov and Gorbunov, 1999). Since thenand up to the present day, the alpine permafrost of theTien Shan never disappeared completely. During thistime, the extent of mountain permafrost area in the TienShan changed many times. These changes were causedby the mountain continuously rising and by the un-folding planetary climate events. The glacial andperiglacial features evidently show that during sometime intervals the ancient permafrost occurred at a muchlower elevation than the present day permafrost(Gorbunov, 1985; Aubekerov, 1990; Marchenko andGorbunov, 1997). The maximum glacial expansion inthe Tien Shan Mountains happened during the MiddlePleistocene time (Aubekerov and Gorbunov, 1999).However, the maximum extension of the permafrost

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http://dx.doi.org/10.1016/j.gloplacha.2006.07.023

Fig. 1. Location of the Tien Shan Mountains, Central Asia and alpine permafrost distribution (Brown et al., 1998; Qiu et al., 2002; Marchenko et al.,2005) in the Asian high mountains.

312 S.S. Marchenko et al. / Global and Planetary Change 56 (2007) 311–327

area in the Tien Shan and adjacent foothills and plainsoccurred in the Late Pleistocene when the combinationof low air humidity and cold temperatures created amore favorable condition for permafrost formation andexpansion. At that time, the lower boundary of perma-frost was located at about 900–1000 m a.s.l., which is atleast 1500–1700 m lower than the modern lower alti-tudinal permafrost boundary. This means that during theLate Pleistocene the alpine permafrost of Tien ShanMountains merged with the Siberian permafrost area viaa sporadic permafrost zone that occurred on the foothillplains of Djungar Alatau, Saur-Tarbagatai and Altai.

Ground temperatures in the Tien Shan permafrostarea have been subjected to repeated fluctuations duringthe Holocene brought about by the general planetarychanges in climate. The altitudinal oscillations of themean annual air temperature (MAAT) zero Centigradeisotherm had a range of about 500 m during the Holo-

cene. Early Holocene (approximately between 9000 and7000 yr ago) was the most unfavorable time for theexistence of alpine permafrost in the Tien Shan(Marchenko and Gorbunov, 1997). There was a periodof permafrost degradation in the Tien Shan Mountains.A Middle Holocene cooling was replaced by a shortphase of warming in the Late Holocene, after whichground temperatures again significantly decreased.During the Little Ice Age, there was a downward shiftof the lower boundary of permafrost distribution by200–300 m of altitude. Since the second part of thenineteenth century, permafrost in the Tien Shan Moun-tains is experiencing a warming period, which continuesup to the present. This article considers the recent (lastcentury) permafrost changes in the Tien Shan Moun-tains, which were studied using geothermal measure-ments in boreholes, the analysis of climatic data, andnumerical modeling of permafrost temperature field

313S.S. Marchenko et al. / Global and Planetary Change 56 (2007) 311–327

dynamics. The major aim of this work is to evaluatechanges in Tien Shan's permafrost during the last cen-tury using both observed data and a modeling approach.

2. Results from the previous permafrost research inthe Tien Shan Mountains

2.1. General features of permafrost distribution in theTien Shan

The first information about the presence of perma-frost in the Tien Shan appeared in 1914 (Bezsonov,1914). General features of permafrost distribution in theTien Shan Mountains are resulting from latitudinal andaltitudinal zonality, and from changes in climatic andtopographic factors. The systematic investigations ofmountain permafrost in the Tien Shan began in the mid-1950s (Gorbunov, 1967, 1970). The regional patterns ofpermafrost distribution depend on elevation, slope andaspect, which have a major influence on incoming short-wave radiation to the ground surface. Vegetation andsnow cover, ground texture and moisture content, winterair temperature inversion, surface and groundwaterpresence and movement, and climatic and geothermalconditions are also among the most important para-meters that shape the mountain permafrost distribution.

Traditionally, the alpine permafrost area of the TienShan Mountains is divided into altitudinal sub-zones ofcontinuous, discontinuous and sporadic (sometimescalled islands) permafrost (Gorbunov, 1978, 1988).Table 1 shows the general characteristics of permafrostdistribution and the altitudinal boundaries of continuousand discontinuous permafrost sub-zones in the differentparts of the Tien Shan Mountains. The altitudinalboundaries of these sub-zones move upwards from thenorthern part towards the southern part of the Tien Shan

Table 1The altitudinal zonality of permafrost distribution in the Tien ShanMountains (after Gorbunov et al., 1996)

Part of the Tien ShanMountains

Continuous Discontinuous Sporadic

.Altitudinal sub-zones of permafrost (m a.s.l.)Western (41°30′N) Higher

38003800–3600 3600–

3000Northern and Eastern

(42–43°N)Higher3500

3500–3200 3200–2700

Inner (40°30′–42°N) Higher3600

3600–3300 3300–2800

.Permafrost area (km.2.)Total 41,000 49,000 69,000

159,000

Mountains. This altitudinal shift accounts for about140 m with a decrease in latitude by 1° (Gorbunov et al.,1996). Because of the differences in surface energybalance, the lower limits of permafrost altitudinal zoneson the south-facing slopes are about 400–800 m higherthan on the north-oriented ones (Cheng, 1983; Gorbu-nov, 1988; Map of snow, ice and frozen ground inChina, 1988; Gorbunov et al., 1996). We found isolatedpatches of permafrost beneath coarse debris at an ele-vation of 3250 m a.s.l., which were exposed during roadconstruction in 2000 along the route section betweenKazakhstan and Kyrgyzstan through the Zailiysky andKungei Alatau Mountain Ranges of the Northern TienShan (Fig. 2). This finding indicates the lowest knownboundary of sporadic permafrost for the south-facingslopes in the central Northern Tien Shan.

On the north-facing slopes in the Northern TienShan, sporadic permafrost occurs at elevations above2700 m a.s.l. This elevation approximately coincideswith the tree line and the MAAT isotherm of 0 °C(Gorbunov et al., 1996). However, small isolatedpatches of permafrost can be found much lower than2700 m a.s.l. These patches occur at the feet of north-facing or shaded slopes inside the coarse blocky debrisor beneath a mossy cover even at 1800 m a.s.l. where theMAAT is 3.0–4.0 °C (Gorbunov, 1993).

Coarse blocky debris of various origins is widespreadin the Tien Shan and occupies a large area of high-mountain territory. Convective mass and heat transfer,especially during the cold period, are very typical for theblocky material because of its high porosity (Haeberliet al., 1992; Lieb, 1996; Harris, 1996; Wakonigg, 1996;Humlum, 1997; Harris and Pedersen, 1998; Delaloyeet al., 2003; Goering, 2003; Hertz et al., 2003; Sawadaet al., 2003; Gude et al., 2003; Gorbunov et al., 2004).Our measurements in the Zailiysky Alatau Range (theNorthern Tien Shan) (Fig. 2) during 1974–1987 showthat the temperatures inside the coarse debris aretypically 2.5–4.0 °C colder than the MAAT (Gorbunovet al., 2004). For this reason the altitudinal distributionof rock glaciers are a few hundreds meters lower thanthat of open glaciers.

2.2. Ground ice

Mountain permafrost and associated periglaciallandforms contain large quantities of stored freshwater in the form of ice. The lacustrine and sometimesalluvial sediments, moraines, rock glaciers and othercoarse blocky material have especially high ice content(20–80% by volume). The deeper boreholes weredrilled in 1972–1973 in the vicinity of the Zhusalykezen

Fig. 2. Map of study areas in the Tien Shan Mountains (a) and Bolshaya (BA) and Malaya (MA) Almatinka river basins locations (b). 1—NorthernTien Shan, 2—Inner Tien Shan.


Fig. 3. Ice-supersaturated actively creeping mountain permafrost (rock glaciers) in the upper part of the Bolshaya Almatinka River basin (NorthernTien Shan).


Mountains Pass (the Northern Tien Shan, Fig. 2) in theLate Pleistocene and Holocene moraines. During thedeep excavations (down to 12 m) in the moraines, themassive, syngenetic cryogenic formations with 15–20 cmthick ice lenses were revealed at depths below 4.0–4.5 m.The measured excess ice content in these formationsaccounts for 10% to 40% by volume. These cryogenicformations can be treated as proof that permafrost hasbeen in existence here continuously during the entirepostglacial time.

The rock glaciers are ice-rich cryogenic landforms(ice can occupy up to 80% of the entire volume ofsediment). A rock glacier is a huge accumulation ofcoarse debris cemented together by ice or a glacier thatwas buried under fragments of the mountain's rock.Rock glaciers are present in valleys or on slopes andlook like a glacier, landslide or lava flow (Fig. 3). Thereare 871 active rock glaciers with a total surface area of

90.3 km2 and 183 inactive glaciers with a total surfacearea of 28.68 km2 in the Northern Tien Shan Mountains(Gorbunov and Titkov, 1989). The largest rock glaciersin the Central Asian Mountains are up to 3 km lengthand located in the Zailiysky Alatau Range, NorthernTien Shan (Fig. 2).

The best-studied rock glaciers are situated in thecentral northern part of the Zailiysky Alatau Range(Northern Tien Shan) in the basins of the Bolshaya andMalaya Almatinka Rivers (Fig. 2). The investigations ofrock glaciers in the Northern Tien Shan started in 1923by geodetic observations of the Russian glaciologist N.Palgov near the front of the “Gorodetsky” rock glacier.Based on his geodetic network, the observations wererepeated eleven times. The last observation wasperformed in 2003. Additional data on the temporalvariations of this rock glacier movement have beenobtained recently by the use of aerial photographs taken


during different years (Gorbunov et al., 1992). Most ofthe investigated rock glaciers in the Northern Tien Shandemonstrate an average rate of surface movement ofabout 0.5–2.5 m/yr. The typical length of a rock glacieris several hundred meters. However, some of the rockglaciers can reach several kilometers in length. Theirwidth is typically several hundred meters. A rock glacierends in a frontal lobe, which is usually between 20 and40 m high, but sometimes as high as 50 to 60 m.

Our recent investigations demonstrated the presenceof a significant amount of layered ice in the frontal partof the rock glacier. Several sections of buried ice with atotal thickness up to 8 m were found in the front scarpsof rock glaciers at the elevation of 3100 m a.s.l. Crystalstructure and bubble shapes in the ice are similar to thosefound in glacier ice.

2.3. Active layer and permafrost temperatures

The mean annual temperature at the permafrost tableand the heat flux at the bottom are the main thermalcharacteristics of permafrost. These parameters are veryimportant not only for estimating the distribution andthickness of permafrost, but also for the evaluation ofstability or sensitivity of permafrost to climate changeand to natural or human-induced disturbances. Themean annual ground temperature (MAGT) generallydecreases by about 0.5–0.6 °C per each 100 m ofaltitude and increases by 0.7–1.0 °C per each 1° oflatitude towards the south (Gorbunov, 1986, Graviset al., 2003). The difference in MAGT between south-facing and north-facing slopes at the same altitude variesfrom 1.0 to 6.0 °C depending on topography, groundcomposition, vegetation and snow cover. Geothermalobservations in boreholes in the Tien Shan Mountainsdemonstrate a significant variability of thermal regime(3–6 °C) and thickness of permafrost (100–120 m)within short distances even at the same altitudinal level(Ermolin et al., 1989; Gorbunov et al., 1996).

The first permafrost temperature measurements in theNorthern Tien Shan began in 1973 (Gorbunov andNemov, 1978). One of the permafrost research stationsof the Russian Academy of Sciences was established at2500 m a.s.l. in 1974. The area of original permafroststudies in the Northern Tien Shan is located within thetwo river basins (the Bolshaya and Malaya AlmatinkaRivers) and covers about 670 km2 within the altituderange between 1000 and 4400 m a.s.l. (Fig. 2). There arefive weather stations in operation since 1932 at differentaltitudinal levels within the limits of this territory.During the last 30 yr, permafrost investigations wereconducted by staff members of the Kazakh Alpine

Permafrost Laboratory, which belongs to the YakutskPermafrost Institute. A variety of methods, includingmeasurements of permafrost temperature and the active-layer thermal regime and thickness, spring watertemperatures, and DC resistivity soundings were used(Gorbunov and Nemov, 1978; Zeng et al., 1993;Gorbunov et al., 1996).

The detailed information about cryogenic structureswas made available during deep excavations (down to12 m) in the Late Pleistocene moraines near one of thepermafrost research stations (3336 m a.s.l.). Initialgeothermal observations (1974–1977) in boreholes inthe Northern Tien Shan showed that the permafrosttemperatures within the loose deposits and bedrock at thealtitude of 3300 m a.s.l vary from −0.3 °C to −0.8 °C(Gorbunov and Nemov, 1978). Thickness of permafrostin this area varied from 15 to 90 m and the maximumactive-layer thickness reached 3.5–4.0 m.

Permafrost investigations in the Inner Tien Shan(Fig. 2) were performed between 1985 and 1992. Theresults of these investigations included permafrost tem-perature records, active-layer thickness measurements,descriptions of the cryogenic structures of frozen ground,maps and charts of the distribution of permafrost, groundice, and periglacial landforms. Ground temperaturemeasurements were carried out in 20 boreholes in theAk-Shiyrakmassif (42°N, between 4000 and 4200m a.s.l.), and in more than 25 boreholes in the Kumtor valley(between 3560 and 3790 m a.s.l.). Ground temperaturemeasurements were performed using thermistor sensorsMMT-4 with a sensitivity 0.02 °C and an accuracy notless than 0.05 °C (Ermolin et al., 1989).

In the Ak-Shiyrak Mountain Range (Fig. 2), at theelevations of 4100–4200 m a.s.l., the lowest measuredground temperature was −5 °C in the bedrock (Paleo-zoic schist) and −6.7 °C in the ice-rich Late Pleistocenemoraines. The corresponding thickness of permafrostwas 350–370 and 250–270 m (Ermolin et al., 1989;Gorbunov et al., 1996). Thickness of the active layer onthe western slope of the Ak-Shiyrak massif decreasedfrom 2.5–3.5 to 0.5–0.7 m within 3200–4000 m a.s.l.

In the southwestern part of the Tien Shan (Chatyr-Kol and Aksai depressions, 40°30′N) (Fig. 2), at theelevation of 3500–3600 m, the thickness of permafrostin loose deposits was 60–90 m and its temperatureswere between −1.2 and −1.6 °C. The geothermalgradient in the Tien Shan changes from 0.01 °C/m at themountain ridges and up to 0.02–0.03 °C/m at the bottomof the valleys and within the mountain depressions(Schwarzman, 1985).

Relict Pleistocene permafrost was found in Aksaidepression (40°55′N, 76°25′E) at the elevation of

Fig. 4. Mean annual, summer (JJA), and winter (DJF) air temperaturesat 2500 m a.s.l. (1), 5 yr moving averages (2), and linear regression (3)during 1932–2003 at the BAO meteorological station (Northern TienShan).


3160 m a.s.l. A 400 m deep borehole revealed a two-layered permafrost structure with the lower layer offrozen clay between 214 and 252 m deep (Aubekerovand Gorbunov, 1999). The thickness of the modernupper layer of permafrost is 90–110 m. It is a singlefinding of relic permafrost in the Tien Shan Mountains.

3. Recent changes in climate in the Tien ShanMountains

Many components of the cryosphere, particularlyglaciers and permafrost, are very sensitive to climatechange. Climatic changes and changes in permafrostwere reported recently from many mountain regions. InAsia, analyses of temperature data from 49 stations in

Nepal for the period 1971–1994 revealed warmingtrends after 1977 ranging from 0.06 to 0.12 °C/yr inmost of the Middle Mountain and Himalayan regions(Shrestha et al., 1999). In the western Mongolian sectorof the Altai Mountains, the rise in mean annual airtemperature was 0.03 °C/yr during the last 50 yr(Natsagdorj et al., 2000). Winter warming is stronglypronounced in high mountain areas and in intermoun-tain valleys (0.06 °C/yr) of the Mongolian Altai and lessdetectable in the adjacent plains. Temperature data fromMongolian mountain regions available for the last 30 yrshow a rise in permafrost temperatures by 0.1 °C perdecade in the Khentei andKhangai and 0.2 °C per decadein Hovsgol mountain regions (Sharkhuu, 2003). Latitu-dinal permafrost in northeastern China is less sensitive torecent climatic changes. At the same time, the mountainpermafrost and permafrost on the Qinghai-Tibet Plateauis much more sensitive to climatic warming (Jin et al.,2000a). On the Qinghai-Tibet Plateau during the last15 yr permafrost temperatures at 20 m depth haveincreased 0.2–0.3 °C (Cheng et al., 1993; Jin et al.,2000b). During the 20th century, significant permafrostdegradation has occurred withinmost permafrost regionsin China.

Permafrost and Climate in Europe (PACE) projectconducts permafrost monitoring along a longitudinaltransect through the mountains of Europe from theSierra Nevadas in the south, to Svalbard in the north.Harris and Haeberli (2003) reported 0.4 °C warming ofpermafrost at a depth of 11.6 m in Swiss Alps between1988 and 2003. A Svalbard site shows a near surfacewarming of 1.5±0.5 °C during the 20th century (Isaksenet al., 2000).

A detailed analysis of the recent changes in climateover the entire Tien Shan during 1940–1991 waspublished by Aizen et al. (1997). Above 2000 m a.s.l.,the smallest trend of 0.008 °C/yr was observed in thenorthern part of the Tien Shan, and the greatest(0.012 °C/yr) in the Central Tien Shan. Dikih (1997)has analyzed the longer-term temperature records(1930–1989) from the four weather stations located inthe northern and inner parts of Tien Shan. The followingtrends in mean annual air temperature were found:Alma-Ata (825 m a.s.l.) 0.006 °C/yr, Prjevalsk (1714 ma.s.l.) 0.023 °C/yr, Naryn (2039 m a.s.l.) 0.032 °C/yr,and Tien Shan (3614 m a.s.l.) 0.009 °C/yr. During thelast 70 yr, the average increase in mean annual airtemperature from 0.006 °C/yr to 0.032 °C/yr has beenobserved for the different parts of the Tien Shan (Dikih,1997; Podrezov et al., 2001; Marchenko, 2003).

Mean annual, summer, and winter air temperaturesrecorded at the weather station “Bolshoe Almatinskoe

Fig. 5. Increase in mean seasonal and annual air temperatures in theNorthern Tien Shan during 1932–2000.


Ozero” (BAO) located at 2516 m a.s.l. in the central partof the Zailiysky Alatau Range (frontal mountain rangeof the Northern Tien Shan) (Fig. 2) are shown in Fig. 4.Statistical analysis (Singular Value Decomposition and

Fig. 6. Permafrost temperatures and active-layer thickness variations dur“Cosmostation” permafrost observatory (the location of this observatory is s

Principal Component Analysis) of the monthly meteo-rological data indicates a statistically significant (at .pb0.05 level) increase in mean annual, summer(June–August), and winter (December–February) airtemperatures. Temperature at BAO station has acorrelation between 0.78 and 0.95 with other mountainstations located within the altitudes of 2000–3300 m inthe Zailiysky Alatau (Fig. 2). Generally, a warmingsignal is more pronounced at the higher elevations (Fig.5). However, the statistically significant correlation of0.82 (at a .pb0.05 level) was observed only for the meanwinter temperatures. A similar behavior was reportedfor the minimum air temperatures in the Alps (Benistonand Rebetez, 1996).

During 1940–1991, the maximum snow thicknessand snow cover duration have decreased on an averageof 0.1 m and 9 days, respectively over the entire TienShan (Aizen et al., 1997). In the northern part of the TienShan there was no significant change in cold seasonprecipitation above 2000 m during 1940–1991 (Aizenet al., 1997).

The 1990s have been the warmest decade of the pastcentury. In the Northern Tien Shan the average 10-yr airtemperature for 1991–2000 has increased by 0.4 °C in

ing 1974–1977 and 1990–2004 measured in two boreholes at thehown in Fig. 2).

Table 2Ground thermal properties and moisture/ice content

Depths of the layerboundary(m)

Heat capacity thawed(×106 J/m3 K)

Heat capacity frozen(×106 J/m3 K)

Thermal conductivitythawed(W/m K)

Thermal conductivityfrozen(W/m K)

Moisture/icecontent(Part of unit)

.Site 10–0.1 1.78 1.25 1.8 1.9 0.170.1–2.9 1.48 1.35 2.1 2.2 0.112.9–4.1 1.42 1.22 2.0 2.1 0.084.1–5.0 1.54 1.40 1.6 1.8 0.185.0–30.0 1.65 1.30 1.7 1.9 0.2630.0–50.0 1.95 1.80 1.9 2.0 0.0550.0–100.0 2.50 2.40 2.2 2.3 0.04

.Site 20–0.12 1.8 1.2 1.8 1.9 0.170.12–2.4 1.4 1.3 2.1 2.2 0.122.4–4.2 1.3 1.2 2.0 2.1 0.114.2–5.3 1.8 1.4 1.3 1.7 0.225.3–20.0 1.7 1.2 1.6 1.9 0.1320.0–30.0 2.1 1.4 1.3 1.6 0.1830.0–50.0 1.9 1.75 1.9 2.0 0.0550.0–100.0 2.5 2.3 2.2 2.3 0.04

.Site 30–0.3 1.6 1.3 1.4 1.7 0.240.3–2.9 1.3 1.4 1.8 2.2 0.222.9–4.8 1.4 1.2 1.7 2.1 0.174.8–10.0 1.5 1.4 2.1 2.3 0.1410.0–30.0 1.6 1.2 2.2 2.4 0.1830.0–50.0 2.2 1.8 1.9 2.0 0.0450.0–100.0 2.3 1.9 2.2 2.3 0.03

.Site 40–0.95 1.8 1.4 1.6 2.3 0.210.95–2.9 1.8 1.5 1.3 1.9 0.182.9–6.1 1.9 1.5 1.6 2.0 0.116.1–15.0 1.8 1.6 1.7 2.6 0.5415.0–50.0 2.4 2.2 1.9 2.0 0.0650.0–100.0 2.5 2.1 2.2 2.3 0.04

.Site 50–1.0 1.6 1.5 1.9 2.1 0.03 0.62a

0.0–3.5 1.9 1.8 1.8 1.9 0.05 0.54a

3.5–6.0 1.9 1.6 1.8 2.0 0.18 0.42a

6.0–15.0 1.9 1.65 1.9 2.6 0.52 0.12a

15.0–45.0 2.3 2.1 1.9 2.1 0.05 0a

45.0–100.0 2.5 2.2 2.2 2.3 0.04 0a

a Porosity of coarse debris in which a process of free convection is present.


comparison with 1932–1990 within the altitude range of2000–3000 m a.s.l. The greatest increase for the sameperiod was observed for the mean winter (0.8 °C),maximum winter (0.9 °C) and the minimum summertemperatures (0.5 °C). The warmest years for the lastdecade of the 20th century were 1990, 1997, 1998 and1999, when the MAAT was higher than the long-term(1932–2002) average temperature by 0.76 °C, 1.1 °C,1.49 °C and 0.93 °C, respectively.

4. Permafrost temperature and active-layer changein the Tien Shan Mountains

There are 24 active thermometric boreholes withdepths ranging from 3 m to 300 m in different landscapesettings and at varying altitudes available for measure-ments near the two permafrost stations (“Main Station”and “Cosmostation”) in the Northern Tien Shan (Fig. 2).Ground temperature measurements are carried out by

Fig. 7. Evolution of mean annual air temperature (a) and calculated permafrost dynamics (b) during 1880–2004 at an altitude of 3300 m a.s.l.


using thermistor sensors (MMT-4 and TSM-50) with asensitivity of 0.02 °C and an accuracy not less than0.05 °C. There are three sites equipped with temperaturedata loggers (StowAway Onset Computer Corporation)that have been in operation since 1997. These sites wereestablished as a contribution to the IPA CircumpolarArctic Layer Monitoring (CALM) project. Data fromthese sites are regularly added to the CALM site data-base. A few deep boreholes in the Northern and Inner

Fig. 8. Evolution of mean annual air temperature (a) and calculated perma

Tien Shan belong to the Global Terrestrial Network ofPermafrost (GTNet-P) Program (Burgess et al., 2001).

Our geothermal observations during 1974–1977 and1990–2004 indicate that permafrost has been warmingin the Tien ShanMountains during the last 30 yr (Fig. 6).The increase in permafrost temperatures in the NorthernTien Shan during 1974–2004 varies from 0.3 °C to0.6 °C. In accordance with interpolation of boreholetemperature data, the active-layer thickness showed an

frost dynamics (b) during 1880–2004 at an altitude of 3000 m a.s.l.


increase during the last 30 yr from 3.2 to 3.4 m in the1970s to a maximum of 5.2 m in 1992 and to 5.0 m in2001 and 2004 (Fig. 6). The average active-layer thick-ness for all measured sites increased by 23% in com-parison with the early 1970s. As a result of a deepground thawing, a residual thaw layer (talik) between 5and 8 m in depth at different sites has appeared.

Permafrost is also warming in the Inner Tien Shan(Fig. 2). Permafrost temperatures increased by 0.1 °Cover 1986–1993 both in the valley and on the mountainslopes. Active-layer depth varied between individualyears from 0.5 to 2.5 m depending on the altitude, slope,aspect, the types of surface and lithology.

5. Modeling of permafrost thermal dynamics

The main objectives of the modeling process were toestimate the permafrost thermal regime and assess thearea where permafrost disappeared since the second part

Fig. 9. Evolution of mean annual air temperature (a) and calculated permafro

of the nineteen century. A one-dimensional numericalmodel of heat transfer for a multi-layered medium(Marchenko, 2001; Tipenko and Romanovsky, 2001;Romanovsky et al., 2002) was used for this purpose.The model takes into account the latent heat of waterfreezing/thawing and has the capability for computa-tions of a convective heat transfer in blocky materialsand underlying ground. The blocky materials (coarsedebris, talus) are considered as a porous body, in which aprocess of free convection is present.

The upper boundary conditions were set up as themean monthly air temperatures and snow cover pro-perties (thickness, density and thermal conductivity)observed at the weather stations near the examined siteswithin the Tien Shan Mountains. The vegetation coverwas prescribed accordingly to the site conditions wherethe geothermal observations were made. The longestseries of air temperature and precipitations in the TienShan Mountains are available since 1879. In each case

st dynamics (b, c, d) during 1880–2004 at an altitude of 2500 m a.s.l.


when we did not have such long-term records for theexamined sites (for some sites we have records onlysince 1932) we used the correlation between the shortand long series to fill the existing gaps in the shorterobservations. As a rule, the correlation coefficient be-tween two data sets was not less than 0.95. The lowerboundary for computations was placed at 100 m depth.The geothermal gradient at the lower boundary dependson the site location (hill top or valley bottom) and wasset within the range of 0.01–0.02 °C/m. The groundthermal properties and moisture/ice content (Table 2)were used accordingly with data obtained during thedeep excavations and drilling in the vicinity of theexamined sites in the Tien Shan Mountains. Ananalytical solution of the Fourier heat diffusion problemin a combination with our reconstructions of permafrostthermal state in the Tien Shan Mountains (Gorbunov,1985; Marchenko and Gorbunov, 1997) was used for

Fig. 10. Modeled permafrost extent for 1880 and 2005 within the two river ba

determining the initial conditions for the numericalmodel. For the model calibration the 1991–1995 groundtemperature records obtained from the boreholes wereused. The performance of the calibrated model wastested using 1974–1977 temperature records from thesame boreholes. The comparison between calculatedand measured permafrost temperatures during thatperiod showed a good agreement within 0.3 °C.

For evaluation of ground thermal regime within theTien Shan Mountains we selected three altitudinallevels, 2500, 3000 and 3300 m a.s.l., which could beconsidered as potential altitudinal lower boundaries ofpermafrost distribution during the last 150 yr and for thenext 50–100 yr. Our long-term permafrost and season-ally frozen ground monitoring observations wereperformed at the same altitudinal levels during the last30 yr. The lithological sections and ground thermalproperties were used in accordance with determinations

sins Bolshaya (1) and Malaya (2) Almatinka in the Northern Tien Shan.

Table 3Comparative evaluation of permafrost area decreasing during the last120 yr within two river basins, Northern Tien Shan

Riverbasin

Permafrostarea in1880(km2)

Modernpermafrostarea(km2)

Permafrostarea decrease(km2)

Permafrostarea decrease(%)

BolshayaAlmatinka

146.3 117.6 28.7 19.6

MalayaAlmatinka

55.1 46.9 8.2 14.9

Total 201.4 164.5 36.9 18.3


obtained from the deep pits and boreholes during 1972–1974 in the northern and 1985–1987 in the inner TienShan.

5.1. Site 1

Fig. 7 shows the results of calculated permafrostdynamics for the time interval 1880–2004 at the altitude3300 m a.s.l. Data on the physical properties of the earthmaterial used in our calculations were obtained from theboreholes in the vicinity of the Zhusalykezen Mountainpass (3330 m a.s.l., Northern Tien Shan). Since thebeginning of the second decade of the last century,degradation of permafrost started from the bottom whenthe MAAT has abruptly increased by 1 °C in 1905–1915(Fig. 7A). Thickness of permafrost at that time wasabout 50 m. During the last 70–80 yr, the process ofpermafrost thinning has been continuously progressivewithin the bedrock layer from the bottom up withapproximate rate of 0.4 m/yr. Currently, the permafrostbase is located in ice-rich loose deposits (ice content of20–40% by volume). It is isothermal permafrost nowwith the temperature close to 0 °C within the entirepermafrost layer. During the last 10–15 yr, the near-surface permafrost has experienced significant changes.In individual years, seasonal thawing penetrationreaches 5 m and more in depth. This process leads toa residual thaw layer (talik) formation.

5.2. Site 2

A different scenario of permafrost degradation wasobtained at the altitudes close to 3000 m a.s.l. (Fig. 8).The calculations were carried out for loose deposits witha thickness of 25–30 m and an ice content of 5–20% byvolume within the different layers. At the end of thenineteenth century, the estimated permafrost thicknesswas about 20 m at this site. Atmospheric warming in thebeginning of the twentieth century started permafrost

thawing from its top down. A talik started to form belowthe seasonally frozen layer. It is possible that a fewcooling waves in the air temperature during the lastcentury could produce re-freezing of this talik. Howev-er, the continued warming eventually caused thecomplete disappearance of permafrost around 1960.

The next three examined sites located on the east-facing slope at the elevation of 2500 m a.s.l. Fig. 9shows the MAAT and permafrost evolution during1880–2004 within the three sites with a differentlithology.

5.3. Site 3

The degradation and complete disappearance ofpermafrost took place faster in fine-grained soils at theSite 3 (Fig. 9B). The heat penetration and temperaturefield changes are more dynamic within the fine-grainedsoils because of its rather low heat capacity (1.1–1.5×106 J/m3/K) and low moisture/ice content. Thespecial permafrost and surface energy balance investi-gations during 1980–1981 (Skachkov, 1986) showedthat by the end of the summer season the volumetricmoisture content at this site did not exceed 22–25% inthe fine-grained soils and was basically concentratedwithin a few upper meters. Intensive degradation ofpermafrost at the similar sites probably started sometimebetween 1910 and 1915. Generally, the positive MAATat this time (Fig. 9A) was the major cause of permafrostdegradation. During the next 25–35 yr permafrost infine-grained soils disappeared completely (Fig. 9B).

5.4. Site 4

The different thermal conditions were observed at thesites where the ground was composed by predominantlycoarse debris. In 1955, permafrost was found at thedepth between 15 and 22 m in a 30-m deep pitlocated at the foot of an east-facing slope at the altitude2516 m a.s.l. Grounds were composed of blockymaterial partially filled with loamy soils, sand andloose deposits. According to the geological descriptionof this section, some layers included interstices andcavities filled with ice. The largest ice bodies reached 8–10 cm in thickness. The lithologic section and groundproperties obtained from this pit were used for thepermafrost temperature regime calculations (Fig. 9C).The porous ground structure, ice content up to 35% byvolume within the individual layers and high heatcapacity of icy blocky material made permafrostrelatively more stable in comparison with the previoussite. The fact that the results of our calculations match


the geological description of the permafrost layer thatwas present here in 1955 gives us a reason to assumethat permafrost disappeared at the similar groundconditions and altitudes not earlier than 1970.

5.5. Site 5

A special case of thermal conditions, permafrostoccurrences and preservation relates to coarse blockydebris without a fine-grained filling. Both conductiveand convective heat transfers must be considered whenanalyzing the permafrost conditions and dynamics insuch deposits. The modeling of the thermal regimewithin a blocky material shows the persistence ofpermafrost even after MAAT crossed the 0 °C threshold(Fig. 9D). Since 1910, the MAAT has been generallyabove 0 °C at the altitude 2500 m a.s.l. in the NorthernTien Shan (Fig. 9A). However, permafrost still exists inblocky coarse debris and has a persistence that is due to acooling effect by the winter air convection and also due tothe high energy-consuming latent heat effects in the ice-saturated blocky debris. The data monitoring the thermalregime of collapsed blockymaterials at the same elevationare in general agreement with our modeling results. Thus,our measurements indicate a significant differencebetween the mean annual air temperatures above andinside of the coarse debris. At the altitude 2550 m a.s.l.,where the MAAT is 1.4 °C, the mean annual airtemperatures at depths 3.5, 4.7 and 6.0 m inside thecoarse debris are −1.2 °C, −2.3 °C and −2.7 °Crespectively (Gorbunov et al., 2004).

6. Changes in spatial permafrost distribution

To evaluate the changes in the area of permafrostdistribution during the last 120 yr, two data-rich basinsof the Bolshaya and Malaya Almatinka Rivers (Fig. 2)with different morphological, glaciological and perigla-cial characteristics were selected. A wealth of materialon permafrost conditions (permafrost temperatures,cryogenic structures, and periglacial landforms distri-bution) within the limits of these basins was collectedduring the last 30 yr. Currently, we developed theGeographical Information System (GIS) that is used as abasis for organizing and effectively utilizing some of theclimatic, glaciological, and permafrost data.

The method of permafrost distribution modeling isbased on a numerical computer model and a GIS thatcontains a database of spatially distributed parameters,such as meteorological data, topography, geomorphol-ogy, ground cover (vegetation and snow), ground ther-mal properties (thermal conductivity and heat capacity),

moisture content and geothermal heat fluxes. Thetopographic map of the investigated area (Bolshayaand Malaya Almatinka River basins) was digitized andincorporated in the ArcView GIS as a digital elevationmodel (DEM) of 50 m resolution. Aerial photographs(scale 1:35,000) obtained during August–September1990 were translated into the basic map and applied forcorrections of the geomorphologic and periglacial land-forms layers in GIS. The database contains furtherinformation on the average values of snow-cover thick-ness (for 10 day intervals), snow density and durationfor different-facing slopes and altitudes, and the meanmonthly air temperatures for various altitudes (altitudi-nal step is 100 m). The air temperature vertical gradientfor individual months in the Northern Tien Shan derivedfrom Aizen et al. (1995) was used for calculation. Thedatabase also contains the mean monthly values ofshort-wave radiation with an altitudinal dependency ofapproximately 6.8%/100 m (Perova, 1965; Skachkov,1981), which was observed in the Tien Shan.

The investigated area was overlaid with a grid(250×250 m). The calculation of the ground tempera-ture regime for each grid point was accomplished by anexternal program module, which can be called from theGIS. A result of the calculation is a database file with theground temperatures for each grid point. Because theaim of calculations was to assess the changes in perma-frost extent between 1880 and 2005, the mean annualground temperature (MAGT) at 20 m depth was selectedas an output. This information was transferred back intothe GIS using interpolation methods and producing thegrid with cell size of 100×100 m (Fig. 10). The areawhere permafrost disappeared between 1880 and 2005was derived from the spatial analysis of two grids,which represent the modeled areas of permafrostpresence in 1880 and 2005. As illustrated in Table 3,the total permafrost area decreased by 18.3% within thetwo river basins during the last 125 yr.

7. Conclusions

Both geothermal observations and modeling ofpermafrost thermal state show significant changes inpermafrost temperature and extent during the 20thcentury in the Tien Shan Mountains. Geothermal obser-vations during the last 30 yr indicate an increase inpermafrost temperatures in a range from 0.3 °C up to0.6 °C. The average active-layer thickness increased by23% in comparison with the early 1970s. As a result of adeep thawing penetration of up to 5 m and more, aresidual thaw layer (talik) at different sites above 3000 ma.s.l. has appeared during the last 10–15 yr. The most


significant impacts on permafrost thermal state wereobserved near the lower boundary of alpine permafrost inthe Tien Shan, the region where the frozen ground is verysensitive to changes in the surface energy balance (Harrisand Haeberli, 2003). In the high-mountains regions, thefurther near-surface permafrost degradation will proba-bly accompany a transformation in environmentalconditions and may lead to slope instability andpermafrost-related hazards such as landslides, thermo-karst, and mudflows (Haeberli and Burn, 2002).

The modeling of alpine permafrost dynamics showsthat the altitudinal lower boundary of permafrostdistribution has shifted by about 150–200 m upwardduring the last 125 yr. During the same period, the areaof permafrost distribution within two river basins in theNorthern Tien Shan decreased by approximately 18%.

The geothermal observations and modeling indicatethat in the Northern Tien Shan more favorableconditions of permafrost occurrences and preservationexist in the coarse blocky material where the meanannual temperatures are typically 2.5–4.0 °C colder thanthe MAAT. In such deposits the ice-rich permafrostcould still be stable even when the MAAT exceed 0 °C.This is in agreement with results obtained earlier forother locations (Haeberli et al., 1992; Lieb, 1996; Harris,1996; Wakonigg, 1996; Humlum, 1997; Harris andPedersen, 1998; Delaloye et al., 2003; Goering, 2003;Hertz et al., 2003; Sawada et al., 2003; Gude et al.,2003).

Acknowledgements

This research was been funded by the Polar EarthScience Program, Office of Polar Programs, NationalScience Foundation (OPP-0327664), and by the State ofAlaska. The temperature data used in this study areavailable to other researchers through the GCOS/GTN-Psite: http://www.gtnp.org, CALM site database: http://www.udel.edu/Geography/calm/, and from NSIDC(http://nsidc.org). The authors thank their collaboratorsin Kazakhstan for help in geothermal observations. Wewould like to thank anonymous reviewers for veryhelpful suggestions that were used to improve themanuscript.

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permafrost warming in the tien shan mountains, …permafrost warming in the tien shan mountains,...

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