Permafrost Warming in the Tien Shan Mountains, Central Asia ⁎ S.S

Global and Planetary Change 56 (2007) 311–327 www.elsevier.com/locate/gloplacha

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, USA b Institute of Geography, Almaty, Kazakhstan Received 11 May 2005; accepted 19 July 2006 Available online 5 October 2006

Abstract

The general features of alpine permafrost such as spatial distribution, temperatures, ice content, permafrost and active-layer thickness within the Tien Shan Mountains, Central Asia are described. The modern thermal state of permafrost reflects climatic processes during the twentieth century when the average rise in mean annual air temperature was 0.006–0.032 °C/yr for the different parts of the Tien Shan. Geothermal observations during the last 30 yr indicate an increase in permafrost temperatures from 0.3 °C up to 0.6 °C. At the same time, the average active-layer thickness increased by 23% in comparison to the early 1970s. The long-term records of air temperature and snow cover from the Tien Shan's high-mountain weather stations allow reconstruction of the thermal state of permafrost dynamics during the last century. The modeling estimation shows that the altitudinal lower boundary 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%. Both geothermal observations and modeling indicate more favorable conditions for permafrost occurrences and preservation in the coarse blocky material, where the ice-rich permafrost could still be stable even when the mean annual air temperatures exceeds 0 °C. © 2006 Elsevier B.V. All rights reserved.

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

1. Introduction elevation (Aubekerov and Gorbunov, 1999). Since then and up to the present day, the alpine permafrost of the The alpine permafrost zone in the Tien Shan Tien Shan never disappeared completely. During this Mountains (69–95°E, 40–44°N) belongs to the Asian time, the extent of mountain permafrost area in the Tien high-mountain permafrost region, the largest in the Shan changed many times. These changes were caused world (Fig. 1). The occurrence and evolution of alpine by the mountain continuously rising and by the un- permafrost in the middle latitudes directly relates to the folding planetary climate events. The glacial and tectonic history of the Earth. The facts collected recently periglacial features evidently show that during some provide information about the Pre-Quaternary age of time intervals the ancient permafrost occurred at a much permafrost in the Tien Shan Mountains. Permafrost first lower elevation than the present day permafrost formed about 1.6 million years ago because of mountain (Gorbunov, 1985; Aubekerov, 1990; Marchenko and Gorbunov, 1997). The maximum glacial expansion in ⁎ Corresponding author. Tel.: +1 907 474 7698; fax: +1 907 474 the Tien Shan Mountains happened during the Middle 7290. Pleistocene time (Aubekerov and Gorbunov, 1999). E-mail address: [email protected] (S.S. Marchenko). However, the maximum extension of the permafrost

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. area in the Tien Shan and adjacent foothills and plains cene. Early Holocene (approximately between 9000 and occurred in the Late Pleistocene when the combination 7000 yr ago) was the most unfavorable time for the of low air humidity and cold temperatures created a existence of alpine permafrost in the Tien Shan more favorable condition for permafrost formation and (Marchenko and Gorbunov, 1997). There was a period expansion. At that time, the lower boundary of perma- of permafrost degradation in the Tien Shan Mountains. frost was located at about 900–1000 m a.s.l., which is at A Middle Holocene cooling was replaced by a short least 1500–1700 m lower than the modern lower alti- phase of warming in the Late Holocene, after which tudinal permafrost boundary. This means that during the ground temperatures again significantly decreased. Late Pleistocene the alpine permafrost of Tien Shan During the Little Ice Age, there was a downward shift Mountains merged with the Siberian permafrost area via of the lower boundary of permafrost distribution by a sporadic permafrost zone that occurred on the foothill 200–300 m of altitude. Since the second part of the plains of Djungar Alatau, Saur-Tarbagatai and Altai. nineteenth century, permafrost in the Tien Shan Moun- Ground temperatures in the Tien Shan permafrost tains is experiencing a warming period, which continues area have been subjected to repeated fluctuations during up to the present. This article considers the recent (last the Holocene brought about by the general planetary century) permafrost changes in the Tien Shan Moun- changes in climate. The altitudinal oscillations of the tains, which were studied using geothermal measure- mean annual air temperature (MAAT) zero Centigrade ments in boreholes, the analysis of climatic data, and isotherm had a range of about 500 m during the Holo- numerical modeling of permafrost temperature field S.S. Marchenko et al. / Global and Planetary Change 56 (2007) 311–327 313 dynamics. The major aim of this work is to evaluate Mountains. This altitudinal shift accounts for about changes in Tien Shan's permafrost during the last cen- 140 m with a decrease in latitude by 1° (Gorbunov et al., tury using both observed data and a modeling approach. 1996). Because of the differences in surface energy balance, the lower limits of permafrost altitudinal zones 2. Results from the previous permafrost research in on the south-facing slopes are about 400–800 m higher the Tien Shan Mountains than on the north-oriented ones (Cheng, 1983; Gorbu- nov, 1988; Map of snow, ice and frozen ground in 2.1. General features of permafrost distribution in the China, 1988; Gorbunov et al., 1996). We found isolated Tien Shan patches of permafrost beneath coarse debris at an elevation of 3250 m a.s.l., which were exposed during road The first information about the presence of perma- construction in 2000 along the route section between frost in the Tien Shan appeared in 1914 (Bezsonov, Kazakhstan and Kyrgyzstan through the Zailiysky and 1914). General features of permafrost distribution in the Kungei Alatau Mountain Ranges of the Northern Tien Tien Shan Mountains are resulting from latitudinal and Shan (Fig. 2). This finding indicates the lowest known altitudinal zonality, and from changes in climatic and boundary of sporadic permafrost for the south-facing topographic factors. The systematic investigations of slopes in the central Northern Tien Shan. mountain permafrost in the Tien Shan began in the mid- On the north-facing slopes in the Northern Tien 1950s (Gorbunov, 1967, 1970). The regional patterns of Shan, sporadic permafrost occurs at elevations above permafrost distribution depend on elevation, slope and 2700 m a.s.l. This elevation approximately coincides aspect, which have a major influence on incoming short- with the tree line and the MAAT isotherm of 0 °C wave radiation to the ground surface. Vegetation and (Gorbunov et al., 1996). However, small isolated snow cover, ground texture and moisture content, winter patches of permafrost can be found much lower than air temperature inversion, surface and groundwater 2700 m a.s.l. These patches occur at the feet of north- presence and movement, and climatic and geothermal facing or shaded slopes inside the coarse blocky debris conditions are also among the most important para- or beneath a mossy cover even at 1800 m a.s.l. where the meters that shape the mountain permafrost distribution. MAAT is 3.0–4.0 °C (Gorbunov, 1993). Traditionally, the alpine permafrost area of the Tien Coarse blocky debris of various origins is widespread Shan Mountains is divided into altitudinal sub-zones of in the Tien Shan and occupies a large area of high- continuous, discontinuous and sporadic (sometimes mountain territory. Convective mass and heat transfer, called islands) permafrost (Gorbunov, 1978, 1988). especially during the cold period, are very typical for the Table 1 shows the general characteristics of permafrost blocky material because of its high porosity (Haeberli distribution and the altitudinal boundaries of continuous et al., 1992; Lieb, 1996; Harris, 1996; Wakonigg, 1996; and discontinuous permafrost sub-zones in the different Humlum, 1997; Harris and Pedersen, 1998; Delaloye parts of the Tien Shan Mountains. The altitudinal et al., 2003; Goering, 2003; Hertz et al., 2003; Sawada boundaries of these sub-zones move upwards from the et al., 2003; Gude et al., 2003; Gorbunov et al., 2004). northern part towards the southern part of the Tien Shan Our measurements in the Zailiysky Alatau Range (the Northern Tien Shan) (Fig. 2) during 1974–1987 show that the temperatures inside the coarse debris are Table 1 – The altitudinal zonality of permafrost distribution in the Tien Shan typically 2.5 4.0 °C colder than the MAAT (Gorbunov Mountains (after Gorbunov et al., 1996) et al., 2004). For this reason the altitudinal distribution Part of the Tien Shan Continuous Discontinuous Sporadic of rock glaciers are a few hundreds meters lower than Mountains that of open glaciers. .Altitudinal sub-zones of permafrost (m a.s.l.) Western (41°30′N) Higher 3800–3600 3600– 2.2. Ground ice 3800 3000 Northern and Eastern Higher 3500–3200 3200– Mountain permafrost and associated periglacial – (42 43°N) 3500 2700 landforms contain large quantities of stored fresh Inner (40°30′–42°N) Higher 3600–3300 3300– 3600 2800 water in the form of ice. The lacustrine and sometimes alluvial sediments, moraines, rock glaciers and other .Permafrost area (km.2.) coarse blocky material have especially high ice content Total 41,000 49,000 69,000 (20–80% by volume). The deeper boreholes were 159,000 drilled in 1972–1973 in the vicinity of the Zhusalykezen 314 S.S. Marchenko et al. / Global and Planetary Change 56 (2007) 311–327

Fig. 2. Map of study areas in the Tien Shan Mountains (a) and Bolshaya (BA) and Malaya (MA) Almatinka river basins locations (b). 1—Northern Tien Shan, 2—Inner Tien Shan. S.S. Marchenko et al. / Global and Planetary Change 56 (2007) 311–327 315

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

Mountains Pass (the Northern Tien Shan, Fig. 2) in the 90.3 km2 and 183 inactive glaciers with a total surface Late Pleistocene and Holocene moraines. During the area of 28.68 km2 in the Northern Tien Shan Mountains deep excavations (down to 12 m) in the moraines, the (Gorbunov and Titkov, 1989). The largest rock glaciers massive, syngenetic cryogenic formations with 15–20 cm in the Central Asian Mountains are up to 3 km length thick ice lenses were revealed at depths below 4.0–4.5 m. and located in the Zailiysky Alatau Range, Northern The measured excess ice content in these formations Tien Shan (Fig. 2). accounts for 10% to 40% by volume. These cryogenic The best-studied rock glaciers are situated in the formations can be treated as proof that permafrost has central northern part of the Zailiysky Alatau Range been in existence here continuously during the entire (Northern Tien Shan) in the basins of the Bolshaya and postglacial time. Malaya Almatinka Rivers (Fig. 2). The investigations of The rock glaciers are ice-rich cryogenic landforms rock glaciers in the Northern Tien Shan started in 1923 (ice can occupy up to 80% of the entire volume of by geodetic observations of the Russian glaciologist N. sediment). A rock glacier is a huge accumulation of Palgov near the front of the “Gorodetsky” rock glacier. coarse debris cemented together by ice or a glacier that Based on his geodetic network, the observations were was buried under fragments of the mountain's rock. repeated eleven times. The last observation was Rock glaciers are present in valleys or on slopes and performed in 2003. Additional data on the temporal look like a glacier, landslide or lava flow (Fig. 3). There variations of this rock glacier movement have been are 871 active rock glaciers with a total surface area of obtained recently by the use of aerial photographs taken 316 S.S. Marchenko et al. / Global and Planetary Change 56 (2007) 311–327 during different years (Gorbunov et al., 1992). Most of Permafrost Laboratory, which belongs to the Yakutsk the investigated rock glaciers in the Northern Tien Shan Permafrost Institute. A variety of methods, including demonstrate an average rate of surface movement of measurements of permafrost temperature and the active- about 0.5–2.5 m/yr. The typical length of a rock glacier layer thermal regime and thickness, spring water is several hundred meters. However, some of the rock temperatures, and DC resistivity soundings were used glaciers can reach several kilometers in length. Their (Gorbunov and Nemov, 1978; Zeng et al., 1993; width is typically several hundred meters. A rock glacier Gorbunov et al., 1996). ends in a frontal lobe, which is usually between 20 and The detailed information about cryogenic structures 40 m high, but sometimes as high as 50 to 60 m. was made available during deep excavations (down to Our recent investigations demonstrated the presence 12 m) in the Late Pleistocene moraines near one of the of a significant amount of layered ice in the frontal part permafrost research stations (3336 m a.s.l.). Initial of the rock glacier. Several sections of buried ice with a geothermal observations (1974–1977) in boreholes in total thickness up to 8 m were found in the front scarps the Northern Tien Shan showed that the permafrost of rock glaciers at the elevation of 3100 m a.s.l. Crystal temperatures within the loose deposits and bedrock at the structure and bubble shapes in the ice are similar to those altitude of 3300 m a.s.l vary from −0.3 °C to −0.8 °C found in glacier ice. (Gorbunov and Nemov, 1978). Thickness of permafrost in this area varied from 15 to 90 m and the maximum 2.3. Active layer and permafrost temperatures active-layer thickness reached 3.5–4.0 m. Permafrost investigations in the Inner Tien Shan The mean annual temperature at the permafrost table (Fig. 2) were performed between 1985 and 1992. The and the heat flux at the bottom are the main thermal results of these investigations included permafrost tem- characteristics of permafrost. These parameters are very perature records, active-layer thickness measurements, important not only for estimating the distribution and descriptions of the cryogenic structures of frozen ground, thickness of permafrost, but also for the evaluation of maps and charts of the distribution of permafrost, ground stability or sensitivity of permafrost to climate change ice, and periglacial landforms. Ground temperature and to natural or human-induced disturbances. The measurements were carried out in 20 boreholes in the mean annual ground temperature (MAGT) generally Ak-Shiyrak massif (42°N, between 4000 and 4200 m a.s. decreases by about 0.5–0.6 °C per each 100 m of l.), and in more than 25 boreholes in the Kumtor valley altitude and increases by 0.7–1.0 °C per each 1° of (between 3560 and 3790 m a.s.l.). Ground temperature latitude towards the south (Gorbunov, 1986, Gravis measurements were performed using thermistor sensors et al., 2003). The difference in MAGT between south- MMT-4 with a sensitivity 0.02 °C and an accuracy not facing and north-facing slopes at the same altitude varies less than 0.05 °C (Ermolin et al., 1989). from 1.0 to 6.0 °C depending on topography, ground In the Ak-Shiyrak Mountain Range (Fig. 2), at the composition, vegetation and snow cover. Geothermal elevations of 4100–4200 m a.s.l., the lowest measured observations in boreholes in the Tien Shan Mountains ground temperature was −5 °C in the bedrock (Paleo- demonstrate a significant variability of thermal regime zoic schist) and −6.7 °C in the ice-rich Late Pleistocene (3–6 °C) and thickness of permafrost (100–120 m) moraines. The corresponding thickness of permafrost within short distances even at the same altitudinal level was 350–370 and 250–270 m (Ermolin et al., 1989; (Ermolin et al., 1989; Gorbunov et al., 1996). Gorbunov et al., 1996). Thickness of the active layer on The first permafrost temperature measurements in the the western slope of the Ak-Shiyrak massif decreased Northern Tien Shan began in 1973 (Gorbunov and from 2.5–3.5 to 0.5–0.7 m within 3200–4000 m a.s.l. Nemov, 1978). One of the permafrost research stations In the southwestern part of the Tien Shan (Chatyr- of the Russian Academy of Sciences was established at Kol and Aksai depressions, 40°30′N) (Fig. 2), at the 2500 m a.s.l. in 1974. The area of original permafrost elevation of 3500–3600 m, the thickness of permafrost studies in the Northern Tien Shan is located within the in loose deposits was 60–90 m and its temperatures two river basins (the Bolshaya and Malaya Almatinka were between −1.2 and −1.6 °C. The geothermal Rivers) and covers about 670 km2 within the altitude gradient in the Tien Shan changes from 0.01 °C/m at the range between 1000 and 4400 m a.s.l. (Fig. 2). There are mountain ridges and up to 0.02–0.03 °C/m at the bottom five weather stations in operation since 1932 at different of the valleys and within the mountain depressions altitudinal levels within the limits of this territory. (Schwarzman, 1985). During the last 30 yr, permafrost investigations were Relict Pleistocene permafrost was found in Aksai conducted by staff members of the Kazakh Alpine depression (40°55′N, 76°25′E) at the elevation of S.S. Marchenko et al. / Global and Planetary Change 56 (2007) 311–327 317

Nepal for the period 1971–1994 revealed warming trends after 1977 ranging from 0.06 to 0.12 °C/yr in most of the Middle Mountain and Himalayan regions (Shrestha et al., 1999). In the western Mongolian sector of the Altai Mountains, the rise in mean annual air temperature was 0.03 °C/yr during the last 50 yr (Natsagdorj et al., 2000). Winter warming is strongly pronounced in high mountain areas and in intermoun- tain valleys (0.06 °C/yr) of the Mongolian Altai and less detectable in the adjacent plains. Temperature data from Mongolian mountain regions available for the last 30 yr show a rise in permafrost temperatures by 0.1 °C per decade in the Khentei and Khangai and 0.2 °C per decade in Hovsgol mountain regions (Sharkhuu, 2003). Latitu- dinal permafrost in northeastern China is less sensitive to recent climatic changes. At the same time, the mountain permafrost and permafrost on the Qinghai-Tibet Plateau is much more sensitive to climatic warming (Jin et al., 2000a). On the Qinghai-Tibet Plateau during the last 15 yr permafrost temperatures at 20 m depth have increased 0.2–0.3 °C (Cheng et al., 1993; Jin et al., 2000b). During the 20th century, significant permafrost degradation has occurred within most permafrost regions in China. Permafrost and Climate in Europe (PACE) project conducts permafrost monitoring along a longitudinal transect through the mountains of Europe from the Sierra Nevadas in the south, to Svalbard in the north. Harris and Haeberli (2003) reported 0.4 °C warming of permafrost at a depth of 11.6 m in Swiss Alps between 1988 and 2003. A Svalbard site shows a near surface warming of 1.5±0.5 °C during the 20th century (Isaksen et al., 2000). Fig. 4. Mean annual, summer (JJA), and winter (DJF) air temperatures A detailed analysis of the recent changes in climate at 2500 m a.s.l. (1), 5 yr moving averages (2), and linear regression (3) over the entire Tien Shan during 1940–1991 was during 1932–2003 at the BAO meteorological station (Northern Tien published by Aizen et al. (1997). Above 2000 m a.s.l., Shan). the smallest trend of 0.008 °C/yr was observed in the 3160 m a.s.l. A 400 m deep borehole revealed a two- northern part of the Tien Shan, and the greatest layered permafrost structure with the lower layer of (0.012 °C/yr) in the Central Tien Shan. Dikih (1997) frozen clay between 214 and 252 m deep (Aubekerov has analyzed the longer-term temperature records and Gorbunov, 1999). The thickness of the modern (1930–1989) from the four weather stations located in upper layer of permafrost is 90–110 m. It is a single the northern and inner parts of Tien Shan. The following finding of relic permafrost in the Tien Shan Mountains. trends in mean annual air temperature were found: Alma-Ata (825 m a.s.l.) 0.006 °C/yr, Prjevalsk (1714 m 3. Recent changes in climate in the Tien Shan a.s.l.) 0.023 °C/yr, Naryn (2039 m a.s.l.) 0.032 °C/yr, Mountains and Tien Shan (3614 m a.s.l.) 0.009 °C/yr. During the last 70 yr, the average increase in mean annual air Many components of the cryosphere, particularly temperature from 0.006 °C/yr to 0.032 °C/yr has been glaciers and permafrost, are very sensitive to climate observed for the different parts of the Tien Shan (Dikih, change. Climatic changes and changes in permafrost 1997; Podrezov et al., 2001; Marchenko, 2003). were reported recently from many mountain regions. In Mean annual, summer, and winter air temperatures Asia, analyses of temperature data from 49 stations in recorded at the weather station “Bolshoe Almatinskoe 318 S.S. Marchenko et al. / Global and Planetary Change 56 (2007) 311–327

Principal Component Analysis) of the monthly meteorological data indicates a statistically significant (at . p b0.05 level) increase in mean annual, summer (June–August), and winter (December–February) air temperatures. Temperature at BAO station has a correlation between 0.78 and 0.95 with other mountain stations located within the altitudes of 2000–3300 m in the Zailiysky Alatau (Fig. 2). Generally, a warming signal is more pronounced at the higher elevations (Fig. 5). However, the statistically significant correlation of 0.82 (at a.pb0.05 level) was observed only for the mean winter temperatures. A similar behavior was reported for the minimum air temperatures in the Alps (Beniston and Rebetez, 1996). During 1940–1991, the maximum snow thickness and snow cover duration have decreased on an average of 0.1 m and 9 days, respectively over the entire Tien Fig. 5. Increase in mean seasonal and annual air temperatures in the Shan (Aizen et al., 1997). In the northern part of the Tien Northern Tien Shan during 1932–2000. Shan there was no significant change in cold season precipitation above 2000 m during 1940–1991 (Aizen Ozero” (BAO) located at 2516 m a.s.l. in the central part et al., 1997). of the Zailiysky Alatau Range (frontal mountain range The 1990s have been the warmest decade of the past of the Northern Tien Shan) (Fig. 2) are shown in Fig. 4. century. In the Northern Tien Shan the average 10-yr air Statistical analysis (Singular Value Decomposition and temperature for 1991–2000 has increased by 0.4 °C in

Fig. 6. Permafrost temperatures and active-layer thickness variations during 1974–1977 and 1990–2004 measured in two boreholes at the “Cosmostation” permafrost observatory (the location of this observatory is shown in Fig. 2). S.S. Marchenko et al. / Global and Planetary Change 56 (2007) 311–327 319

Table 2 Ground thermal properties and moisture/ice content Depths of the layer Heat capacity thawed Heat capacity frozen Thermal conductivity Thermal conductivity Moisture/ice boundary (×106 J/m3 K) (×106 J/m3 K) thawed frozen content (m) (W/m K) (W/m K) (Part of unit) .Site 1 0–0.1 1.78 1.25 1.8 1.9 0.17 0.1–2.9 1.48 1.35 2.1 2.2 0.11 2.9–4.1 1.42 1.22 2.0 2.1 0.08 4.1–5.0 1.54 1.40 1.6 1.8 0.18 5.0–30.0 1.65 1.30 1.7 1.9 0.26 30.0–50.0 1.95 1.80 1.9 2.0 0.05 50.0–100.0 2.50 2.40 2.2 2.3 0.04

.Site 2 0–0.12 1.8 1.2 1.8 1.9 0.17 0.12–2.4 1.4 1.3 2.1 2.2 0.12 2.4–4.2 1.3 1.2 2.0 2.1 0.11 4.2–5.3 1.8 1.4 1.3 1.7 0.22 5.3–20.0 1.7 1.2 1.6 1.9 0.13 20.0–30.0 2.1 1.4 1.3 1.6 0.18 30.0–50.0 1.9 1.75 1.9 2.0 0.05 50.0–100.0 2.5 2.3 2.2 2.3 0.04

.Site 3 0–0.3 1.6 1.3 1.4 1.7 0.24 0.3–2.9 1.3 1.4 1.8 2.2 0.22 2.9–4.8 1.4 1.2 1.7 2.1 0.17 4.8–10.0 1.5 1.4 2.1 2.3 0.14 10.0–30.0 1.6 1.2 2.2 2.4 0.18 30.0–50.0 2.2 1.8 1.9 2.0 0.04 50.0–100.0 2.3 1.9 2.2 2.3 0.03

.Site 4 0–0.95 1.8 1.4 1.6 2.3 0.21 0.95–2.9 1.8 1.5 1.3 1.9 0.18 2.9–6.1 1.9 1.5 1.6 2.0 0.11 6.1–15.0 1.8 1.6 1.7 2.6 0.54 15.0–50.0 2.4 2.2 1.9 2.0 0.06 50.0–100.0 2.5 2.1 2.2 2.3 0.04

.Site 5 0–1.0 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 of 4. Permafrost temperature and active-layer change 2000–3000 m a.s.l. The greatest increase for the same in the Tien Shan Mountains period was observed for the mean winter (0.8 °C), maximum winter (0.9 °C) and the minimum summer There are 24 active thermometric boreholes with temperatures (0.5 °C). The warmest years for the last depths ranging from 3 m to 300 m in different landscape decade of the 20th century were 1990, 1997, 1998 and settings and at varying altitudes available for measure- 1999, when the MAAT was higher than the long-term ments near the two permafrost stations (“Main Station” (1932–2002) average temperature by 0.76 °C, 1.1 °C, and “Cosmostation”) in the Northern Tien Shan (Fig. 2). 1.49 °C and 0.93 °C, respectively. Ground temperature measurements are carried out by 320 S.S. Marchenko et al. / Global and Planetary Change 56 (2007) 311–327

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 a Tien Shan belong to the Global Terrestrial Network of sensitivity of 0.02 °C and an accuracy not less than Permafrost (GTNet-P) Program (Burgess et al., 2001). 0.05 °C. There are three sites equipped with temperature Our geothermal observations during 1974–1977 and data loggers (StowAway Onset Computer Corporation) 1990–2004 indicate that permafrost has been warming that have been in operation since 1997. These sites were in the Tien Shan Mountains during the last 30 yr (Fig. 6). established as a contribution to the IPA Circumpolar The increase in permafrost temperatures in the Northern Arctic Layer Monitoring (CALM) project. Data from Tien Shan during 1974–2004 varies from 0.3 °C to these sites are regularly added to the CALM site data- 0.6 °C. In accordance with interpolation of borehole base. A few deep boreholes in the Northern and Inner temperature data, the active-layer thickness showed an

Fig. 8. Evolution of mean annual air temperature (a) and calculated permafrost dynamics (b) during 1880–2004 at an altitude of 3000 m a.s.l. S.S. Marchenko et al. / Global and Planetary Change 56 (2007) 311–327 321 increase during the last 30 yr from 3.2 to 3.4 m in the of the nineteen century. A one-dimensional numerical 1970s to a maximum of 5.2 m in 1992 and to 5.0 m in model of heat transfer for a multi-layered medium 2001 and 2004 (Fig. 6). The average active-layer thick- (Marchenko, 2001; Tipenko and Romanovsky, 2001; ness for all measured sites increased by 23% in com- Romanovsky et al., 2002) was used for this purpose. parison with the early 1970s. As a result of a deep The model takes into account the latent heat of water ground thawing, a residual thaw layer (talik) between 5 freezing/thawing and has the capability for computa- and 8 m in depth at different sites has appeared. tions of a convective heat transfer in blocky materials Permafrost is also warming in the Inner Tien Shan and underlying ground. The blocky materials (coarse (Fig. 2). Permafrost temperatures increased by 0.1 °C debris, talus) are considered as a porous body, in which a over 1986–1993 both in the valley and on the mountain process of free convection is present. slopes. Active-layer depth varied between individual The upper boundary conditions were set up as the years from 0.5 to 2.5 m depending on the altitude, slope, mean monthly air temperatures and snow cover pro- aspect, the types of surface and lithology. perties (thickness, density and thermal conductivity) observed at the weather stations near the examined sites 5. Modeling of permafrost thermal dynamics within the Tien Shan Mountains. The vegetation cover was prescribed accordingly to the site conditions where The main objectives of the modeling process were to the geothermal observations were made. The longest estimate the permafrost thermal regime and assess the series of air temperature and precipitations in the Tien area where permafrost disappeared since the second part Shan Mountains are available since 1879. In each case

Fig. 9. Evolution of mean annual air temperature (a) and calculated permafrost dynamics (b, c, d) during 1880–2004 at an altitude of 2500 m a.s.l. 322 S.S. Marchenko et al. / Global and Planetary Change 56 (2007) 311–327 when we did not have such long-term records for the determining the initial conditions for the numerical examined sites (for some sites we have records only model. For the model calibration the 1991–1995 ground since 1932) we used the correlation between the short temperature records obtained from the boreholes were and long series to fill the existing gaps in the shorter used. The performance of the calibrated model was observations. As a rule, the correlation coefficient be- tested using 1974–1977 temperature records from the tween two data sets was not less than 0.95. The lower same boreholes. The comparison between calculated boundary for computations was placed at 100 m depth. and measured permafrost temperatures during that The geothermal gradient at the lower boundary depends period showed a good agreement within 0.3 °C. on the site location (hill top or valley bottom) and was For evaluation of ground thermal regime within the set within the range of 0.01–0.02 °C/m. The ground Tien Shan Mountains we selected three altitudinal thermal properties and moisture/ice content (Table 2) levels, 2500, 3000 and 3300 m a.s.l., which could be were used accordingly with data obtained during the considered as potential altitudinal lower boundaries of deep excavations and drilling in the vicinity of the permafrost distribution during the last 150 yr and for the examined sites in the Tien Shan Mountains. An next 50–100 yr. Our long-term permafrost and season- analytical solution of the Fourier heat diffusion problem ally frozen ground monitoring observations were in a combination with our reconstructions of permafrost performed at the same altitudinal levels during the last thermal state in the Tien Shan Mountains (Gorbunov, 30 yr. The lithological sections and ground thermal 1985; Marchenko and Gorbunov, 1997) was used for properties were used in accordance with determinations

Fig. 10. Modeled permafrost extent for 1880 and 2005 within the two river basins Bolshaya (1) and Malaya (2) Almatinka in the Northern Tien Shan. S.S. Marchenko et al. / Global and Planetary Change 56 (2007) 311–327 323

Table 3 thawing from its top down. A talik started to form below Comparative evaluation of permafrost area decreasing during the last the seasonally frozen layer. It is possible that a few 120 yr within two river basins, Northern Tien Shan cooling waves in the air temperature during the last River Permafrost Modern Permafrost Permafrost century could produce re-freezing of this talik. Howev- basin area in permafrost area decrease area decrease 2 er, the continued warming eventually caused the 1880 area (km ) (%) (km2) (km2) complete disappearance of permafrost around 1960. The next three examined sites located on the east- Bolshaya 146.3 117.6 28.7 19.6 Almatinka facing slope at the elevation of 2500 m a.s.l. Fig. 9 Malaya 55.1 46.9 8.2 14.9 shows the MAAT and permafrost evolution during Almatinka 1880–2004 within the three sites with a different Total 201.4 164.5 36.9 18.3 lithology.

5.3. Site 3 obtained from the deep pits and boreholes during 1972– 1974 in the northern and 1985–1987 in the inner Tien The degradation and complete disappearance of Shan. permafrost took place faster in fine-grained soils at the Site 3 (Fig. 9B). The heat penetration and temperature 5.1. Site 1 field changes are more dynamic within the fine-grained soils because of its rather low heat capacity (1.1– Fig. 7 shows the results of calculated permafrost 1.5×106 J/m3/K) and low moisture/ice content. The dynamics for the time interval 1880–2004 at the altitude special permafrost and surface energy balance investi- 3300 m a.s.l. Data on the physical properties of the earth gations during 1980–1981 (Skachkov, 1986) showed material used in our calculations were obtained from the that by the end of the summer season the volumetric boreholes in the vicinity of the Zhusalykezen Mountain moisture content at this site did not exceed 22–25% in pass (3330 m a.s.l., Northern Tien Shan). Since the the fine-grained soils and was basically concentrated beginning of the second decade of the last century, within a few upper meters. Intensive degradation of degradation of permafrost started from the bottom when permafrost at the similar sites probably started sometime the MAAT has abruptly increased by 1 °C in 1905–1915 between 1910 and 1915. Generally, the positive MAAT (Fig. 7A). Thickness of permafrost at that time was at this time (Fig. 9A) was the major cause of permafrost about 50 m. During the last 70–80 yr, the process of degradation. During the next 25–35 yr permafrost in permafrost thinning has been continuously progressive fine-grained soils disappeared completely (Fig. 9B). within the bedrock layer from the bottom up with approximate rate of 0.4 m/yr. Currently, the permafrost 5.4. Site 4 base is located in ice-rich loose deposits (ice content of 20–40% by volume). It is isothermal permafrost now The different thermal conditions were observed at the with the temperature close to 0 °C within the entire sites where the ground was composed by predominantly permafrost layer. During the last 10–15 yr, the near- coarse debris. In 1955, permafrost was found at the surface permafrost has experienced significant changes. depth between 15 and 22 m in a 30-m deep pit In individual years, seasonal thawing penetration located at the foot of an east-facing slope at the altitude reaches 5 m and more in depth. This process leads to 2516 m a.s.l. Grounds were composed of blocky a residual thaw layer (talik) formation. material partially filled with loamy soils, sand and loose deposits. According to the geological description 5.2. Site 2 of this section, some layers included interstices and cavities filled with ice. The largest ice bodies reached 8– A different scenario of permafrost degradation was 10 cm in thickness. The lithologic section and ground obtained at the altitudes close to 3000 m a.s.l. (Fig. 8). properties obtained from this pit were used for the The calculations were carried out for loose deposits with permafrost temperature regime calculations (Fig. 9C). a thickness of 25–30 m and an ice content of 5–20% by The porous ground structure, ice content up to 35% by volume within the different layers. At the end of the volume within the individual layers and high heat nineteenth century, the estimated permafrost thickness capacity of icy blocky material made permafrost was about 20 m at this site. Atmospheric warming in the relatively more stable in comparison with the previous beginning of the twentieth century started permafrost site. The fact that the results of our calculations match 324 S.S. Marchenko et al. / Global and Planetary Change 56 (2007) 311–327 the geological description of the permafrost layer that moisture content and geothermal heat fluxes. The was present here in 1955 gives us a reason to assume topographic map of the investigated area (Bolshaya that permafrost disappeared at the similar ground and Malaya Almatinka River basins) was digitized and conditions and altitudes not earlier than 1970. incorporated in the ArcView GIS as a digital elevation model (DEM) of 50 m resolution. Aerial photographs 5.5. Site 5 (scale 1:35,000) obtained during August–September 1990 were translated into the basic map and applied for A special case of thermal conditions, permafrost corrections of the geomorphologic and periglacial land- occurrences and preservation relates to coarse blocky forms layers in GIS. The database contains further debris without a fine-grained filling. Both conductive information on the average values of snow-cover thick- and convective heat transfers must be considered when ness (for 10 day intervals), snow density and duration analyzing the permafrost conditions and dynamics in for different-facing slopes and altitudes, and the mean such deposits. The modeling of the thermal regime monthly air temperatures for various altitudes (altitudi- within a blocky material shows the persistence of nal step is 100 m). The air temperature vertical gradient permafrost even after MAAT crossed the 0 °C threshold for individual months in the Northern Tien Shan derived (Fig. 9D). Since 1910, the MAAT has been generally from Aizen et al. (1995) was used for calculation. The above 0 °C at the altitude 2500 m a.s.l. in the Northern database also contains the mean monthly values of Tien Shan (Fig. 9A). However, permafrost still exists in short-wave radiation with an altitudinal dependency of blocky coarse debris and has a persistence that is due to a approximately 6.8%/100 m (Perova, 1965; Skachkov, cooling effect by the winter air convection and also due to 1981), which was observed in the Tien Shan. the high energy-consuming latent heat effects in the ice- The investigated area was overlaid with a grid saturated blocky debris. The data monitoring the thermal (250×250 m). The calculation of the ground tempera- regime of collapsed blocky materials at the same elevation ture regime for each grid point was accomplished by an are in general agreement with our modeling results. Thus, external program module, which can be called from the our measurements indicate a significant difference GIS. A result of the calculation is a database file with the between the mean annual air temperatures above and ground temperatures for each grid point. Because the inside of the coarse debris. At the altitude 2550 m a.s.l., aim of calculations was to assess the changes in perma- where the MAAT is 1.4 °C, the mean annual air frost extent between 1880 and 2005, the mean annual temperatures at depths 3.5, 4.7 and 6.0 m inside the ground temperature (MAGT) at 20 m depth was selected coarse debris are −1.2 °C, −2.3 °C and −2.7 °C as an output. This information was transferred back into respectively (Gorbunov et al., 2004). the GIS using interpolation methods and producing the grid with cell size of 100×100 m (Fig. 10). The area 6. Changes in spatial permafrost distribution where permafrost disappeared between 1880 and 2005 was derived from the spatial analysis of two grids, To evaluate the changes in the area of permafrost which represent the modeled areas of permafrost distribution during the last 120 yr, two data-rich basins presence in 1880 and 2005. As illustrated in Table 3, of the Bolshaya and Malaya Almatinka Rivers (Fig. 2) the total permafrost area decreased by 18.3% within the with different morphological, glaciological and perigla- two river basins during the last 125 yr. cial characteristics were selected. A wealth of material on permafrost conditions (permafrost temperatures, 7. Conclusions cryogenic structures, and periglacial landforms distribution) within the limits of these basins was collected Both geothermal observations and modeling of during the last 30 yr. Currently, we developed the permafrost thermal state show significant changes in Geographical Information System (GIS) that is used as a permafrost temperature and extent during the 20th basis for organizing and effectively utilizing some of the century in the Tien Shan Mountains. Geothermal obser- climatic, glaciological, and permafrost data. vations during the last 30 yr indicate an increase in The method of permafrost distribution modeling is permafrost temperatures in a range from 0.3 °C up to based on a numerical computer model and a GIS that 0.6 °C. The average active-layer thickness increased by contains a database of spatially distributed parameters, 23% in comparison with the early 1970s. As a result of a such as meteorological data, topography, geomorphol- deep thawing penetration of up to 5 m and more, a ogy, ground cover (vegetation and snow), ground ther- residual thaw layer (talik) at different sites above 3000 m mal properties (thermal conductivity and heat capacity), a.s.l. has appeared during the last 10–15 yr. The most S.S. Marchenko et al. / Global and Planetary Change 56 (2007) 311–327 325 significant impacts on permafrost thermal state were Aubekerov, B., 1990. Pleistocenovye kriogennye struktury Kazakh- observed near the lower boundary of alpine permafrost in stanskoi kriolotozony (in Russian). (Pleistocene cryogenic structures of Kazakhstan's cryolithozone). Proceedings of Academy of the Tien Shan, the region where the frozen ground is very Science of USSR, Almaty, Geography, pp. 102–110. sensitive to changes in the surface energy balance (Harris Aubekerov, B., Gorbunov, A.P., 1999. Quaternary permafrost and and Haeberli, 2003). In the high-mountains regions, the mountain glaciation in Kazakhstan. Permafrost and Periglacial further near-surface permafrost degradation will proba- Processes 10, 65–80. blyaccompanyatransformationinenvironmental Beniston, M., Rebetez, M., 1996. Regional behavior of minimum temperatures in Switzerland for the period 1979–1993. Theoretical conditions and may lead to slope instability and and Applied Climatology 53, 231–243. permafrost-related hazards such as landslides, thermo- Bezsonov, A.I., 1914. Predvaritelnyi otchet ob organizatcii i ispolnenii karst, and mudflows (Haeberli and Burn, 2002). rabot po issledovaniu pochv Aziatskoi Rossii v 1913 godu (in The modeling of alpine permafrost dynamics shows Russian). (Preliminary report on organizing and performance of that the altitudinal lower boundary of permafrost the soil investigation in the Asian Russia in 1913. St. Petersburg, – 245–260. distribution has shifted by about 150 200 m upward Brown, J., Ferrians Jr., O.J., Heginbottom, J.A., Melnikov, E.S., 1998. during the last 125 yr. During the same period, the area Circum-Arctic Map of Permafrost and Ground Ice Conditions. of permafrost distribution within two river basins in the National Snow and Ice Data Center/World Data Center Northern Tien Shan decreased by approximately 18%. for Glaciology, Boulder, CO. revised February 2001, Digital The geothermal observations and modeling indicate media. Burgess, M., Smith, S., Brown, J. Romanovsky, V., 2001. The Global that in the Northern Tien Shan more favorable Terrestrial Network for Permafrost (GTN-P), Status Report, March conditions of permafrost occurrences and preservation 25, 2001. Submitted to the IPA Executive Committee Meeting, exist in the coarse blocky material where the mean Rome. Available at www.gtnp.org. annual temperatures are typically 2.5–4.0 °C colder than Cheng, G., 1983. Vertical and horizontal zonation of high-altitude the MAAT. In such deposits the ice-rich permafrost permafrost. Forth International Conference on Permafrost, Washington, pp. 131–136. could still be stable even when the MAAT exceed 0 °C. Cheng, G.D., Huang, X.M., Kang, X.C., 1993. Recent permafrost This is in agreement with results obtained earlier for degradation along the Qinghai-Tibet Highway. Proc. 6th Int. other locations (Haeberli et al., 1992; Lieb, 1996; Harris, Conf. Perm., vol. 2. South China University of Technology Press, 1996; Wakonigg, 1996; Humlum, 1997; Harris and pp. 1010–1013. Pedersen, 1998; Delaloye et al., 2003; Goering, 2003; Delaloye, R., Reynard, E., Lambiel, C., Marescot, L., Monnet, R., 2003. Thermal anomaly in a cold scree slope, Creux du Van, Switzerland. Hertz et al., 2003; Sawada et al., 2003; Gude et al., Proc. 8th Int. Conf. Perm., Zurich, vol. 2003, pp. 175–180. 2003). Dikih, A.N., 1997. Globalnoe poteplenie klimata, ego proyavlenie na Tyan-Shane i reaktcia lednikov. (Global climate warming event in Acknowledgements the Tien Shan and glaciers reaction). Data of Glac. Studies. Moscow, vol. 83, pp. 135–139 (in Russian). Ermolin, E.D., Nemov, A.E., Popov, M.V., 1989. Geotermicheskaya This research was been funded by the Polar Earth harakteristika mestorojdeniya Kumtore. (Geothermal characteristic Science Program, Office of Polar Programs, National of the Kumtor gold mine). Geocryological Investigations in the Science Foundation (OPP-0327664), and by the State of Mountains of USSR, Yakutsk, pp. 31–40 (in Russian). Alaska. The temperature data used in this study are Goering, D.J., 2003. Thermal response of air convection embankments available to other researchers through the GCOS/GTN-P to ambient temperature fluctuations. Proc. 8th Int. Conf. Perm., vol. 1. Balkema, Lisse, pp. 291–296. site: http://www.gtnp.org, CALM site database: http:// Gorbunov, A.P., 1967. Vechnaya Merzlota Tyan-Shanya (Permafrost www.udel.edu/Geography/calm/, and from NSIDC of the Tien Shan). Ilim, Frunze (in Russian). (http://nsidc.org). The authors thank their collaborators Gorbunov, A.P., 1970. Kriogennye yavleniya Tyan-Shanya (Cryogenic in Kazakhstan for help in geothermal observations. We phenomena of the Tien Shan). Gidrometeoizdat, Moscow (in would like to thank anonymous reviewers for very Russian). Gorbunov, A.P., 1978. Permafrost investigations in high-mountain helpful suggestions that were used to improve the regions. Arctic and Alpine Research 10, 283–294. manuscript. Gorbunov, A.P., 1985. 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