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Abstract: In this paper, the authors present the main results on long-term monitoring of permafrost in Mongolia. In Mongolia, permafrost under the influence of climate change is ubiquitously degrading at different rates. Average trends of the increases in active layer thickness and mean annual ground temperature are 5-20 cm and 0.1-0.3 °C per decade, respectively. In general, the trends are higher during the last 15-20 years than during the previous 15-20 years. Furthermore, the degradation of permafrost in Hovsgol mountainous region was more intense than in the Hentei and Hangai mountainous regions. The recent degradation of permafrost leads to significant change in ecosystem, especially in soil thermal state and moisture content.
Keywords: Permafrost, active layer, monitoring, temperature, climate
The IPCC report documented recent changes in permafrost and seasonally frozen ground due to climate change in all over northern latitude with few exceptions . The recent degradation of permafrost under the influence of climate warming has a direct impact on ecosystems of permafrost affected regions. Assessing, predicting the effects of permafrost degradation without knowing its trend is difficult, and thus permafrost monitoring is of considerable scientific and practical significant. Since early 1990s, countries with underlying permafrost have started to conduct long-term monitoring of permafrost within the framework of international and national programs (Brown et al., 2000; Burgess et al., 2000; e.g., Jorgenson et al., 2001; Nelson., 2004). In Mongolia, the effect of the climate warming on permafrost has been monitored within the framework of several international projects in recent years. The long-term (10-38 years) monitoring of permafrost in Mongolia has been conducted by Sharkhuu and Anarmaa within the framework of CALM (Circum-arctic Active Layer Monitoring) and GTN-P (Global Terrestrial Network for Permafrost) programs since 1996 (Sharkhuu.N 1998; 2003; Sharkhuu.N et al 2008). In addition, the monitoring of permafrost in six valleys along the north-eastern shore of Hovsgol Lake was carried out by Anarmaa and Sharkhuu within the framework of the Hovsgol Global Environment Facility/World Bank Project in the period of 2002 to 2007 (Goulden et al 2005; Etzelmuller et al 2006; Sharkhuu.A et al 2006; 2007). Since 2008 new experimental observations of this monitoring are continued by Anarmaa within the framework of PIRE (Partnerships for International Research and Education) - Ecological and Evolutionary Effects of Climate Change and Anthropogenic Influences in Mongolia project, implemented by University of Pennsylvania and Mongolian State University, sponsored by NSF of USA (Sharkhuu A et al 2009). Moreover, the long-term monitoring of ground temperature regime in the Nalayh depression and Terelj valley near Ulaanbaatar has been conducted by joint Japanese and Mongolian permafrost researchers within the framework of IORGC (Institute of observational research for global change) project since 2002 (Ishikawa et al 2005; Jambaljav et al 2008). In order to extend permafrost monitoring, the Institute of Geography, MAS, has drilled and instrumented several 10 m deep boreholes in 2009, and started monitoring in Mongolia. The objective of this article is to summarize initial data on long-term monitoring of permafrost under the influence of climate warming in Mongolia, obtained by the authors.
2. Climate warming
According to Gavrilova's (2003) estimate, the increase of mean annual air temperature in Central and eastern Yakutia (Russia) is 1.5 times as much as in the eastern Siberia and 3 times as much as in Mongolia. According to the climate change studies (Natsagdorj et al. 2000), the mean annual air temperature in Mongolia increased by 1.56 °C during the last 60 years. While winter temperature increased by 3.61 °C, spring-autumn temperature increased by 1.4-1.5 °C. The mean annual air temperatures increased by 1.8°C in Western Mongolia, 1.4°C in Central Mongolia and 0.3°C in Southern and Eastern Mongolia in the period of 1940 to 1990. The most of monitoring sites for the permafrost monitoring in Mongolia are around Hatgal (near Hovsgol lake) and Buyant ukhaa (near Ulaanbaatar) weather stations. Therefore, the linear trends of increase in mean winter (MWT), summer (MST) and annual (MAT) air temperatures at these weather stations are presented in Figure 1, as an example. The trends of increase in mean annual air temperatures at Hatgal and Buyant ukhaa weather stations are 0.35 °C and 0.30 °C per decades, respectively. Nevertheless, the rate of increase in the mean annual temperature was not constant; the mean annual air temperature in Hatgal increased by 0.61 °C in a period of 1963 1989, and by 0.84 °C in a period of 1990 2003.
Figure 1. Mean winter (MWT), summer (MST) and annual (MAT) air temperatures in Hatgal and Buyant ukhaa weather stations
3. Permafrost conditions
Territory underlain by permafrost occupies almost two thirds of Mongolia, predominantly in the Hentei, Hovsgol, Hangai and Altai Mountains and surrounding areas, and it is located on the southern fringe of the Siberian continuous permafrost zone (See Figure 2). The territory is characterized by mountain and arid-land permafrost, sporadic to continuous in its extent. The temperature of permafrost is close to 0 °C in the most areas, thus thermally unstable under the influence of climate change and human activities. In continuous and discontinuous permafrost zones, talics are found on steep south-facing slopes, under large river channels and deep lake bottoms, and along tectonic fractures with hydrothermal activity. In sporadic and isolated permafrost zones, frozen ground is found only on north-facing slopes and in fine-grained and moist deposits. The lower limit of continuous permafrost zone is found on south-facing slopes, at an elevation of 1400 to 2200 m in the Hovsgol and Hentei mountains, and of between 2200 and 3200 m in the Altai and Hangai mountains. The lowest limit of sporadic permafrost is found at an altitude between 600 and 700 m asl. The average thickness and mean annual temperature of permafrost in continuous and discontinuous zones are 50-100 m and -1 to -2 °C in valleys and depressions, and 100-250 m and -1 to -3 °C in mountains, respectively. Permafrost in Mongolia has low to moderate ice content in unconsolidated sediments. Ice-rich (content is more than 20% by weight) permafrost is characteristic of lacustrine and alluvial sediments in valleys and depressions. In addition, ice wedges are found in Darhad depression. The thickness of the active layer is 1-3 m in fine-grained soils and 4-6 m in course material. Cryogenic features such as frost heaves, cracks, icings, thermokarst terrain, solifluction lobes and sorted polygons are abundant in Mongolia (Gravis et al. 1974; Sharkhuu N. 2000; 2003).
Figure 2 Permafrost map and monitoring sites of Mongolia: 1. Permafrost monitoring sites,
2. Continuous and discontinuous permafrost, 3. Islands of permafrost, 4. Sporadic permafrost
4. Monitoring of permafrost
The monitoring of permafrost in Mongolia, based on the studies of TSP (Thermal State of Permafrost) program, within the framework of GTN-P and CALM programs, has been conducted since 1996 and extended from year to year. At present, there are 16 monitoring sites, consisting of 46 boreholes of GTN-P and CALM in Mongolia (See Figure 2); according to TSP borehole depth classification 19 of them are classified as surface (SU) boreholes with 5-9 m depth, 17 of them as shallow (SH) boreholes with 10-25 m depth, 6 of them as intermediate (ID) boreholes with 25-125 m depth and 4 of them as deep (DB) boreholes with 130-200 m depth. In the last 5-15 years, additional boreholes with the average depth of 10-15 m were drilled in locations where temperature measurements were made 15-40 years ago in the old boreholes. The most DB and ID geological boreholes are located at Buren-khan and Ardag monitoring sites. Except for seven DB and ID boreholes, all boreholes were prepared by dry drilling. Currently, all boreholes are situated in natural conditions without thermal disturbance.
4.1. Methodology of permafrost monitoring
The primary parameters being monitored are active layer thickness and mean annual permafrost temperature at the (10-15 m deep) level of the zero annual amplitude, as well as temperature gradient of permafrost (See Figure 3a). Temperature measurements in all boreholes have been made using identical thermistors at corresponding depths, and have been carried out on approximately the same dates of each year. We use moveable thermistors strings, prepared at the Geothermal Laboratory of the Melnikov Permafrost Institute, Siberian branch, Russian Academy of Sciences. The accuracy of temperature measurements by a calibrated Russian thermistor (MMT-4 model) is 0.02 °C. Thermistor resistance has been measured by a multimeter (MB-400 model). In all boreholes, the active layer thickness is determined by the interpolation of ground temperature profiles, obtained by temperature measurements in boreholes usually in the late September. In addition, four-channel temperature data loggers (HOBO U12) are installed in 25 monitoring boreholes, and seven boreholes are equipped with Stow-Away or UTL-1 miniature data loggers. The accuracies of ground temperature measurements by HOBO U12 and miniature data loggers were 0.03 °C and 0.25 °C, respectively. The interval time of temperature recordings by data loggers is 90 minutes. Besides, six boreholes have permanent thermistor strings. Ground temperature measurements in the boreholes with permanent thermistors, located near Ulaanbaatar, are made monthly. The monitoring of frost heaving, thermokarst and icing is based on a leveling measurement with Russian leveling equipment of model type HB-1.
Figure 3. Methodology of permafrost monitoring: (a) parameters of permafrost monitoring and (b) borehole instrumentation
Each borehole is designed to prevent air convection and to protect against damage by passing people. All re-drilled boreholes are cased by parallel steel and plastic pipes of 3-5 cm diameter with the mouth of the pipe at depth of about 15-20 cm and covered by soil (See Figure 3b). The gap outside of casing pipes in all the boreholes is filled by sands.
4.2. Selected monitoring boreholes
We selected six typical boreholes as an example of the initial results of permafrost monitoring. The characteristics of the boreholes are presented in Table 1.
Table 1 Characteristics of the selected boreholes
Landform and terrain
Dry steppe plain in the depression
Dry steppe valley bottom
Flood plain of wide valley
10 m high pingo top
Flood plain of wide valley
Northern slope of mountain grassland.
Predominant soil profile
Sandstones covered by 3 m sands.
0-6 m loam, 6-12 m clay
0-45 m sand, 45-90 m clay
0-5 m silt, 5-32 m ice,
>32 m sand
sand,12-56 m loam
Limestones covered by 1 m thick debris
Thickness of permafrost, m
5. Results: Recent degradation of permafrost under the influence of climate warming
5.1. Active layer
Active layer thickness (ALT) in Mongolia varies over a wide range of 1-1.5 to 5-8 m, depending on ground texture and its temperature-moisture regime. The predominant ALT is 2.5-4.0 m. The thickest active layer has been observed in January-February in the boreholes such as M1a and M3, located at sites of which permafrost is characterized by high MAGT and low-medium ice content, or at sites with bedrock. The full refreezing of such thick active layer continues until February-April. Relatively shallow active layer is characteristic of the boreholes such as M6a, M7a and M8, located at sites of which permafrost is characterized by relatively low MAGT or ice-rich fine sediments. The shallow active layer thoroughly refreezes in November-December. ALT in all CALM boreholes of Mongolia increases at different rates, depending on a change in mean annual air temperature, an environmental and ground conditions of region, and human activity, especially grazing regime (See Figure 4 and Table 2). Estimating the rates of ALT increase in boreholes is difficult and obviously depends on soil properties and moisture content at the sites. Normally, ALT varies about 10% between consecutive yearly measurements (eg., Williams and Smith, 1989). The ALT measured in the Chuluut, Terkh and Sharga boreholes were very similar, and no substantial changes happened. In contrast, the active layer depth in the Burenkhan and Argalant increased at rates of 25-40 cm per decade, and appeared to be characteristic of areas with deep active layer. The low rate of change in ALT in the Chuluut, Terkh and Sharga boreholes is probably due to ice-rich and fine-grained sediments. However, it should be noted that we have no long-term monitoring data to estimate a real trend of increase in active layer thickness in Mongolia. The ALT at Hatgal monitoring site, composed of sandy gravel with relatively low ice content, was 3.6 m in 1969, 4.0 m in 1983, and 4.7 m in 2004 by the ground temperature interpolation. This shows also relatively intense degradation of permafrost during the last 15-20 years. The estimated average increase in ALT varies over the range of 0.2-1.5 cm yr-1 in Hangai and Hentei regions, and 0.3-2.4 cm yr-1 in the Hovsgol region (Sharkhuu A et al 2006). In general, the active layer thickness in the Hovsgol region varies tremendously from year to year due to deep seasonal freezing and thawing of the ground. For example, ALT in most boreholes in 2009 was less than in previous two years. We cannot conclude that ALT in the all monitoring boreholes is increasing significantly in recent years. Likewise, no significant trend of increase in the active layer thickness was observed in Alaska and Siberia (Brown et al, 2000; Romanovsky et al, 2003).
Figure 4 Trends of increase in the active layer thickness in the selected boreholes
Table 2 Changes in ALT, MAGT and TG in the selected boreholes
Borehole name and number
MAGT at 10-15 m depth, oC
TG at 15-50 m depth, oC/m
5.2. Mean annual ground temperatures
The mean annual ground or permafrost temperatures (MAGT) in Mongolia vary from 0 - -0.5 °C in sporadic permafrost zones to -1 - -3 °C in continuous permafrost zones. As an example, the ground temperature regime down to a depth of yearly zero amplitude in the Terkh borehole M6a is presented in Table 3. The mean annual ground temperatures gradually increased with depth. The mean winter (average December, January and February) ground temperatures increased down to 4-5 m depth and then decreased at depths between 6 and 14 m. The mean summer (average June, July and August) ground temperatures decreased down to 6 m depth and then increased with depth (deeper 6 m). The yearly amplitude of soil surface temperatures decreased with depth. The depth of yearly zero amplitude temperature is about 14-15 m. There is a time lag as to when a certain temperature is achieved at increasing soil depth. For example, the time lags for achieving same temperatures like the mean summer soil surface temperatures at 1, 4 and 10 m depths are 1, 5 and 7 months, respectively. Meanwhile, the time lag for achieving same temperatures like the mean winter soil surface temperatures at 1, 4 and 10 m depths are 1, 3 and 5 months, respectively. Relatively short time lag for achieving winter temperature at deeper depth is caused by high thermal conductivity of frozen state of the active layer.
Table 3. Mean winter, summer, annual and yearly amplitude ground temperatures -T (oC)
at different depths of Terkh borehole M6a (September 2009-2010)
Borehole depth, m
Mean winter T
Mean summer T
Mean annual T
Yearly amplitude T
Max/Min T month
During the last 10-40 years, the MAGT in all boreholes increased at different rates. Increase in MAGT is the direct indicator of warming and degradation of permafrost (See Figure 5 and Table 2). The rate of increase in the MAGT depends on texture or the thermal conductivity of sediment. Data show that this rate in bedrock and sandy sediments was more than loose and ice-rich fine sediments, respectively. The rate of increase in mean annual permafrost temperatures varies from 0.01 to 0.04 °C yr-1, depending on a local landscape and ground conditions such as thermal conductivity. The highest rates are observed in Ardag and Burenkhan boreholes on mountain watersheds and slopes, composed of bedrock with high thermal conductivity. Compared to Tsagaan nuur borehole (measured since 1989), the relatively low rate of increase of temperature in the Sharga borehole (measured since 1968) shows that permafrost is degrading more intensively during the last 15 years than during the previous 15-20 years (1970-1980s). Moreover, the MAGT in the Burenkhan mountain area increased by 0.27 °C per decade on the south-facing slope, 0.19 °C on the north-facing slope, 0.23 °C in the upper watershed and 0.11 °C in the valley bottom (Sharkhuu N 1998). These changes show that the rate of increase in mean annual temperature in bedrock with high thermal conductivity is higher than that in unconsolidated sediments with low thermal conductivity, and the rate on a south-facing slope is higher than that on a north-facing slope. Mean while, the average trend of increase in MAGT at 10-15 m depth in the Hovsgol Mountain region reaches 0.02 °C -0.03 °C/year, but in the Hangai and Hentei Mountain regions it does not exceed 0.01 °C-0.02 °C/year.
Figure 5 Trends of increase in mean annual permafrost temperatures in the selected boreholes
The average increases in MAGT of permafrost in Mongolia are similar to these in central Asia and European mountain territories, (Harris et al 2003; Zhao et al 2008a and 2008b). However, comparing with eastern Siberia and Alaska, the average increases in MAGT are lower (Osterkamp et al 1999, Gavrilova 2003; Pavlov et al 2006). The comparison of increases in permafrost temperatures in Alaska and Siberian regions shows almost the same trend. The trends over the interval of the late 1970s to the middle 1990s are 0.05-0.08 °C yr-1 in Siberia (Pavlov et al 2006). The trends of increase in permafrost table temperatures between 1987 and 2001 are 0.14 °C yr-1 at the West Dock and Franklin Bluffs sites and 0.21 °Cyr-1 at the Deadhorse site, in northern Alaska (Romanovsky et al., 2003). This comparison shows that permafrost in the high latitudinal continuous permafrost zones (in Siberia and Alaska) is degrading more rapidly than that on the southern fringe of continuous permafrost zone (in Mongolia).
5.3 Ground temperature gradients
The increasing permafrost temperature gradient with depth can be addressed as an indicator of the recent and former degradation of permafrost (Harris et al 2003). The temperature gradients of permafrost at its upper part decreased in almost all monitoring boreholes of Mongolia. The permafrost or ground temperature gradients (TG) at 15-50 m depth of the selected boreholes decreased by 0.01-0.02 °C/m during the last 40 years (See Table 2). Based on the analyses and calculation of ground temperature gradients, Sharkhuu et al. (2007) made the temperature reconstruction of permafrost in the Burenkhan and Darhad deep boreholes. According to this reconstruction, the estimated surface temperature change of 0.67 °C in Darhad and 0.81 °C in Burehkhan can be reached 15 - 30 years, and 20 - 40 years after the start of the warming pulse in the Darhad and Burenkhan boreholes, respectively. The Darhad depression would then represent a warming trend during the early 1980s, while the Burenkhan site would respond to warming trends during the early 1960s (Sharkhuu A et al 2007). The difference in the periods of warming trends is caused by climate change in the regions and thermal conductivity of sediments in the boreholes. The deeper penetration of temperature change in the surface is observed in bedrock with high thermal conductivity. For example, we present a change in TG of permafrost in each 200 m deep boreholes M5b and M5c at Ardag mountain watershed site composed of dolomite and limestone. Thickness of permafrost in the boreholes M5b and M5c is 210 m and 160 m, respectively. Data from the borehole temperature measurements shows that GT of permafrost at depth of 20 to 80 m in the borehole M5b was 0.009 °C/m in 1987 and 0.002 °C/m in 2008. Then, in a period of 1987 to 2008, TG at depth of 80 to 200 m in the borehole was 0.007 °C/m. Almost the same change in GT of permafrost is observed in the borehole M5c. In particular, GT of permafrost at depths of 20-60 m and 60-200 m in the borehole M5c were 0.003 °C/m and 0.009 °C/m, respectively in 2008. Therefore, decrease in GT at the upper part of permafrost is a direct indicator of recent degradation of permafrost under the influence of climate warming.
5.4 Some cryogenic processes and phenomena
Some intensely ongoing thermokarst and thermo-erosion processes in the Hovsgol, Hangai and Hentei mountain regions are direct indicators of degradation of ice-rich permafrost under the influence of recent climate warming. Here, are presented thermokarst and thermo-erosion processes in Darhad depression (Hovsgol region, Figure 6), Chuluut valley (Hangai region, Figure 7) and Nalayh depression (Hentei region, Figure 8), as an example.
The vertical extent of some thermokarst depressions and thermoerosional riverbanks at Sharga ganga in the Darhad depression reaches 15-25 m, although the average is 3-7 m. Small subsidence cavities on the permafrost table are formed as a result of melting ice wedges. We have observed ice wedge polygons on the land surface and ice wedge bodies in steep exposures (outcrops) of thermoerosional river banks. Large animals (yaks and horses) have fallen into deep (3 m) surface cavities and died of exposure to?. This is evidence of subsurface cavities formed as a result of melting ice wedges or degradation of permafrost under climate warming (Sharkhuu A 2007). At the present day, active thermokarst processes are observed everywhere in the Darhad depression. Landforms or phenomena of the active thermokarst processes are characterized by a thermokarst lake and a deep hollow with steep shore of 1-5 m in height. Sometimes fresh cracks are formed along the shore as a result of thaw settlement of ice-rich sediments. However, due to lack of data on thermokarst age, we are unable to document when the permafrost started to degrade (See Figures 6a and 6b).
As shown on a river bank exposure and 36 m deep borehole profile, the Chuluut River valley bottom is composed of ice-rich lacustrine sediments consisting of clays with mostly 5-20 cm, maximum 50-80 cm thick ice layers and nets (See Figure 7a). Volumetric ice content of the lacustrine clays is about 20-50%. Permafrost thickness in the valley is 15-30 m. Data from measurements in a period of 1969 to 1987 show that a rate of thermo-erosion collapsing of 6-8 m high Chuluut River banks was estimated to be in the range of 15 to 30 cm per year (Sharkhuu N 1998). There are numerous pingos and thermokarst lakes of different sizes and evolutional stages in the valley bottom. The uneven distribution of ground ice leads to highly uneven thaw settlement and surface subsidence of active thermokarst both in spatial and temporal dimensions (See Figure 7b). The data of leveling measurement at one of active thermokarst sites in the Chuluut valley is presented in Table 4. According to communication with local people, thermokarst processes at this site have started in the late 1980s and leads to maximum subsidence in the mid and late 1990s. The data from measurements in a period of 1999 to 2009 showed that the maximum subsidence of up to 25 - 40 cm per year was observed during the formation of incipient thermokarst lake in a period of 1996 to 1998. The rate of the thermokarst subsidence is decreased from 15-25 cm/year in 1999-2001 to 0-8 cm/year in 2005-2009. Its average rate in a period of 1999 to 2009 was 10-15 cm/year. Water discharge in a channel from the thermokarst pond was 1.2 liter/s in 1999 and 0.9 liter/s in 2002. Besides, water discharge in a new spring channel from newly subsiding ravine was 0.3 liter/s in 2002.
Table 4 Value of Chuluut thermokarst settlement in a period of 1999 to 2009, cm
Bank of ravine slope
Top of rest-mound
Dry hollow bottom
Level of water pond
A small thermokarst lake basin in the Nalayh depression is composed of ice-rich lacustrine sediment consisting of silt and clay with mostly 5-10 cm thick ice layers (Figure 8). The estimated value of volumetric ice content in the sediment is about 20-40%. The permafrost thickness is 30-40 m, and the active layer thickness is 1.3 m. The water level in the lake is decreasing; the water depth was 3 m in 1999 and 1.8 m in 2009. 4-5 m high pingo is located in the middle of the lake. Until 2002, the pingo was surrounded by lake waters (See Figure 8a). In late August 2004, thaw slumping of 1.3 m thick active layer on permafrost (pingo ice core) table is suddenly occurred on the south-eastern slope of this degrading pingo due to recent climate warming and the decrease in the water level of the lake (See Figure 8b). According to data of leveling measurements, south-eastern part of the pingo top was subsided by 50 cm in 2005, 40 cm in 2006 and also 45 cm between 2007 and 2009. This subsidence was caused by melting of pingo ice core from its table.
Recent climate warming leads not only to increase in ALT and MAGT, but also to a significant decrease in soil moisture content which is the main factor effecting ecosystem in permafrost zone. Mean while, the increasing ALT and MAGT are due to the decrease in soil moisture content.
As a result of permafrost degradation during last 40 years, the southern boundary of permafrost zone in Mongolia can be retreated by 80-120 km, and altitudinal belt of permafrost distribution is increased by 150-200 m. This estimate is based on data of altitudinal and latitudinal changes in MAGT in the territory of Mongolia (Sharkhuu N 2000).
Active layer thickness, mean annual ground temperature, permafrost temperature gradient and some cryogenic processes such as thermokarst and thermo-erosion are main parameters for permafrost monitoring. Permafrost under the influence of recent climate warming is degrading with trends of increase in average active layer thickness by 0.5-2.0 cm per year and mean annual ground temperature is increased by 0.1-0.3oC per decade. The permafrost in the Hovsgol Mountain region is degrading more intensely than in the Hangai and Hentei Mountain regions. Meanwhile, permafrost degradation under the influence of climate warming was more intense during the last 15-20 years than during previous 15-20 years (1970-1980). A rate of permafrost degradation in bedrock is more than in unconsolidated sediments, in ice-poor substrates more than ice-rich ones, on south-facing more than on north-facing slopes. Recent degradation of permafrost is one of main factors affecting ecosystem in permafrost zone.