Evolution of the thermal state of permafrost under climate warming in Central Yakutia

Abstract

The relevance of the problem under review is explained by the need to study the thermal response of permafrost to the modern climate change. Evolution of the thermal state of grounds has been studied with a view to evaluate the effects of modern climate warming on permafrost in Central Yakutia. The leading method to study this problem is the arrangement and performance of long-term monitoring observations of the permafrost thermal state that enable quantitative evaluation of the thermal response of upper permafrost layers to climatic fluctuations of recent decades. The analysis of long-term records from weather stations in the region has clearly revealed one of the highest increasing trends in the mean annual air temperature in northern Russia. Quantitative relationships in the long-term variability of ground thermal parameters, such as ground temperature at the bottom of the active layer, at the bottom of the annual heat exchange layer, and active thaw depth, have been established. The thermal state dynamics of the annual heat exchange layer under climate warming indicates that both warm and cold permafrost are thermally stable. Short-term variability of the snow accumulation regime is the main factor controlling the thermal state of the ground in permafrost landscapes. The active-layer thickness is characterized by low interannual variability and exhibits little response to climate warming, with no statistically meaningful increasing or decreasing trend. The results of ground thermal monitoring can be extended to similar landscapes in the region, providing a reliable basis for predicting heat transfer in natural landscapes.

Keywords

active-layer thickness climate warming ground temperature monitoring permafrost response

Introduction

Recent decades have seen an increased interest in the study of the problems of permafrost response to predictable climate warming. This interest has been caused by advances in studies of modern climate change in many countries. The studies encompass a broad range of tasks, including the evolution of the thermal state of upper permafrost layers. This has become one of the top-priority focus areas of permafrost studies that are important both in terms of science and practice.

Data from weather and permafrost stations, monitoring ranges, and regional and engineering permafrost operations are used as sources of information for studies of the thermal state of upper permafrost layers and prediction estimates of its changes under expected climate warming.

In the face of major climate changes in the recent decades in Central Yakutia (Skachkov, 2012), the most densely populated and promising region in terms of agricultural and industrial development, having information on the permafrost response to the modern warming is critical.

In Central Yakutia, the first regular temperature measurements in wells up to 10–15 m deep were conducted since 1935 at a permafrost station of the Northern Sea Route Headquarters. Studies revealed peculiarities in temperature variations and ground thawing depth under the influence of the vegetation and snow cover, ‘crop layer’, and geologic-geomorphological conditions (Melnikov, 1950; Solov’ev, 1959). The 1940s saw the arrangement of all-year experimental observations of changes in temperature conditions of grounds under insulation coatings with snow and grass cover removed and in natural conditions at experimental sites of Yakut research permafrost station (Efimov, 1952; Gerasimov, 1950; Shimanovskii, 1942). The 1950s and 1960s saw arrangement of more detailed and comprehensive thermophysical observations of the establishment of rock thermal conditions in line with the improved method at the experimental site of the Permafrost Institute under the guidance of N S Ivanov (1963).

In Central Yakutia, local and regional regularities of the establishment of ground thermal conditions have been revealed in the greatest detail thanks to the wide use of stationary survey methods (Are, 1973; Gavrilova, 1978). In the 1960–1980s, all-year thermal balance studies were conducted following a significantly expanded program at Yakutsk, Syrdakh, Zelenyj Lug, and Chabyda stations (Pavlov, 1975, 1979; Skryabin et al., 1998; Varlamov et al., 2002). These studies encompassed both natural and man-made landscapes. Daily, seasonal, and annual cycles of surface heat exchange with the atmosphere were studied in detail, and a number of new mathematical models of ground freeze–thaw action were elaborated. Studies of hydrothermal conditions of cryogenic soils during agricultural development and engineering were conducted in the 1960–1980s at Khatassy, Khorobut, and Amga seasonal stations (Gavriliev et al., 1984; Ugarov and Mandarov, 2000).

Presently, monitoring studies of the ground thermic regime are conducted at Chabyda, and Tuimaada stations and in the ranges at the northern section of the Tommot-Yakutsk railway route, Yukechi, Umaibyt, Kerdyugen, and so on.

In the 1990s, ‘GEMEX-GAME’, ‘CREST’, and ‘JST’ international programs as a part of the joint Russian-Japanese and Russian-Dutch research projects launched experimental studies at Spasskaya Pad and Neleger stations. The studies were focused on long-term temperature changes in soils and upper permafrost layers, soil humidity conditions, seasonal thawing depth, water-and-thermal balance, and carbonic flows (Fedorov et al., 2006).

A V Pavlov (2008) summarized the results of the studies of evolution of the thermal state of upper permafrost layers over the period from International Geophysical Year III (1957/1959) to International Polar Year IV (2007/2008) in the territory of Russia. At the same time, V E Romanovsky et al. (2010) evaluated the thermal state of the Russian permafrost for the past 20–30 years. S P Varlamov et al. studied the permafrost of Central Yakutia (Varlamov et al., 2012).

Since early 1990, the unified system of observations of the geologic environment condition in the territory of perennial and seasonal freezing of the crust of the earth, assessment, monitoring, and forecast of its changes under the influence of natural, climatic and man-triggered factors has come to be defined as permafrost monitoring. Permafrost monitoring may be recognized as a method that enables the determination of prospective trends of the modern permafrost evolution amidst climate changes and technogenesis (Pavlov, 1996, 2008).

The main thermal parameters that may be used as indicators of the thermal evolution of upper permafrost layers in the context of modern climate warming are seasonal thawing depth (ξ), mean annual temperatures at the bottom of the seasonal thawing (Т_ξ), and annual heat exchange (Т_o) layers.

Materials and methods

For the purposes of monitoring observations of the thermal state of upper permafrost layers, the Permafrost Institute of the Siberian branch of the Russian Academy of Sciences arranged monitoring thermometrical wells in 1981 in the territory of Chabyda and Tuimaada (in 1987) stations and monitoring ranges at the right bank of Lena River.

In Central Yakutia, long-term 22–36-year continuous series of observations of the thermal state of grounds in the annual heat exchange layer in natural conditions continue in six physiographic regions on the right and left banks of Lena River at the latitude of Yakutsk (Figure 1). This has enabled identification of long-term changes in the temperature field in a broad range of natural conditions. The depth of the seasonal thawing layer, depending on the ground composition, nature of the vegetation and ground covers, and their moisture content, varies greatly – from 0.4 to 4.2 m; the mean annual ground temperature at a depth of 10 m varies from + 0.9 to −6.4°C (Varlamov et al., 2002).

Figure 1.

Map of the study area. (a) 1 – stations; 2 – ranges; 3 – boundary of physiographic regions. Subregions (b): 1 – Prilensky valley-forest-steppe; 2 – Bestyakhsky sand-ridge; 3 – Tyungyulyunsky alas-kettle; 4 – Leno-Amginsky alas-valley; 5 – Leno-Amginsky sandstone (subregions: a – sandstone, b – borderline polygenetic plain); 6 – Prilensky left-bank small valley-alas; 7 – Prilensky left-bank sandstone; 8 – Kenkeme-Lensky small valley-alas.

The monitoring study results are provided in dozens of publications (Varlamov et al., 2012, 2016, 2017) and in the documents published under the authority of the Federal Service for Hydrometeorology and Monitoring of the Environment (Second, 2014; Sixth, 2014). As of now, a significant volume of long-term observations series that have no parallel in Central Yakutia has been accumulated. The information obtained from stations and ranges allows us to evaluate the response of the upper permafrost layers to the climatic fluctuations of the recent decades.

Studies are conducted in line with landscape thermophysics method requirements under long-term field studies. Data of weather stations, geothermal studies in permafrost stations, and monitoring range wells are used as a source of information on the thermal state of upper permafrost layers.

The study areas feature complicated permafrost conditions: prevalence of ground ice, and the presence of water-bearing taliks and hazardous cryogenic processes.

The monitoring network for comprehensive studies in natural landscapes is arranged in nine terrains: bottomland, low-terrace, sand-ridge, swale-lowland, small-valley, alas, inter-alas, slope, and upland (Table 1). The study targets are annual heat exchange layer rocks to a depth of 10–15 m. The generally accepted indicators of changes in the thermic regime of upper permafrost layers are seasonal thawing depth and mean annual ground temperature at a depth of 10 m. MMT-4 solid-state heat-variable resistors with a measurement accuracy of ± 0.1^oC are used as ground temperature sensors. Ground temperatures were measured in wells with thermistor sets at a depth of 1, 2, 3, 4, 6, 8, and 10 m. In monitoring wells, thermistor sets were installed on site, that is, their shafts were filled in with earlier excavated material.

Table 1.

Landscape conditions of monitoring ranges in various terrains.

No. of wells (B) and sites (S)	Abs. elev., (m)	Vegetation	Ground composition
Upland terrain
B-8/95	375	Vaccinium larch forest	Sand clay, sand
B-11/95	431	Ledum-vaccinium birch forest	Sand clay, loam
Inter-alas terrain
B-5/95	305	Blueberry-vaccinium larch forest	Loam
B-2/95	265	Moss-blueberry-vaccinium larch forest	Loam
B-57/87	192	Blueberry-vaccinium larch forest	Sand clay, sand
B-210/90	228	Vaccinium-pine larch forest	Sand, clay sand
B-61/87	215	Blueberry-vaccinium larch forest	Loam
B-162	215	Poaceous forb meadow	Sand clay, loam
B-10/93	167	Vaccinium larch forest	Loam
Alas terrain
B-192/89	209	Grass birch forest	Turf, sand
Sand-ridge terrain
B-3/87	142	Litter-bearberry pine forest	Sand
B-59/87	191	Litter-bearberry pine forest	Sand
B-22/87	145	Vaccinium-pine larch forest	Sand
Swale-lowland terrain
B-1/87	127	Moss-ledum larch forest with a mix of pine and birch	Sand
B-5/87	133	Sphagnous-ledum-bushy dish	Sand
B-39/87	134	Sphagnous-ledum-vaccinium larch light forest	Turf, sand
Small-valley terrain
B-11/87	102	Sedge-sphagnum dwarf birch thicket	Turf, loam, sand
B-12/87	103	Blueberry-vaccinium larch forest	Sand
B-174/89	102	Grass spruce-larch forest	Sand
S-3a	197	Sphagnous-ledum dwarf birch thicket	Turf, sand
S-8	201	Moss-ledum-vaccinium larch forest	Sand
Low-terrace terrain
B-165/89	128	Ledum-vaccinium spruce-larch forest	Sand
S-Meadow	105	Grass meadow	Sand clay, sand
S-Forest	105	Grass pine forest	Sand clay, sand
Bottomland terrain
B-168/89	92	Grass meadow	Sand
Slope terrain
S-5	205	Litter-bearberry pine forest	Sand
S-9	240	Vaccinium larch forest at water parting	Loam, sand

Mean annual Т_o values reflect the averaged monthly data in the territory of stations and four measurements in the cold and warm season at the ranges of the right bank of Lena River. The error of these observations is within 0–0.1^oC, which makes this method quite feasible to measure the ground temperature at a depth of 10 m. The ground seasonal thawing depth is determined at the end of the warm season (mid-September) with a metal probe and a hand drill.

Monitoring studies imply repeated landscape survey, observations of the factors that determine the ground thermic regime (snow depth and density, thawing and ground temperature, ground cover heat conductivity ground cover, and cryogenic processes). Systematic comprehensive observations of different durations are conducted monthly at stations and four times in a year (March, June, September, and December) at the ranges.

Results and discussion

Modern climate changes

The variability of the main climate elements (air temperature and precipitation) over the study period at Chabyda station can be tracked down by the data from Yakutsk weather station, the nearest one to the study area (Figures 2 and 3). We should mention the high correlation between Yakutsk and other weather stations in Central Yakutia (Skachkov, 2012). The standard (average for 1961–1990) mean annual air temperature in Yakutsk is −10.0^oC and the standard mean annual precipitation total is 235 mm.

Figure 2.

Long-term variability (1981–2016) of the mean annual air temperature in Yakutsk (^oC). Linear trend is shown by the dotted line.

Figure 3.

Long-term variability (1981–2016) of the annual precipitation total in Yakutsk (mm). Linear trend is shown by the dotted line.

As follows from Figure 2, the trend of mean annual air temperature increase is significant and it exhibits stable growth. This increase was mainly conditioned by growing temperatures in winter (October–April). In summer (May–September), warming was less expressed.

Data shown in Figure 3 indicate that the recent decades have seen major year-to-year variations of annual precipitation totals, but they have not increased in Yakutsk on the whole. The precipitation total by months and for a whole year observed during the past 35 years is close to normal. Yet, it should be mentioned that some years (1989, 1993, 2005–2007, 2013) saw abnormal precipitation totals.

Data from weather stations measuring ground temperatures (to a depth of 3.2 m) set up in the USSR as early as the 1930s–1950s are also used to evaluate permafrost thermal changes. By the early 1990s, 1/4 of weather stations (some 1000 of them) conducted ground temperature monitoring. The main benefit of the information obtained is the availability of long-term observation series. By the early 1990s, 100–110 weather stations monitored ground temperatures in northern Russia. They included 45–50 weather stations that operated in the continuous permafrost zone and 55–60 in the intermittent permafrost zone. The largest ground temperature monitoring in the continuous permafrost zone was conducted in Yakutia (45 points) and northeast of Russia, and in the intermittent permafrost zone – in the central part of Western Siberia, Transbaikalia, and Amur River region (Pavlov, 2008).

Regular weather observations of the temperature of the upper permafrost layer using pull-out thermometers (0.2, 0.4, 0.8, 1.6, 2.4, 3.2 m) have been conducted for a century in some instances, which is an apparent benefit. However, ground temperature measuring errors at weather stations are sometimes significant and the measuring depth is not sufficient for permafrost survey purposes (Pavlov, 2008). Thus, ground temperature data obtained from weather stations require very cautious interpretation because of changes in the station location and natural conditions affected by technogenesis.

This may be exemplified by the data from Yakutsk weather station; in 1964, the instrument platform was moved to another location with different frozen ground conditions. Next, starting from the 1980s, temperature data from pull-out thermometers became unacceptable because of formation and elevation of the groundwater level in the weather station area and its influence on instruments. The absence of temperature fluctuations at this depth over 3 years in the mid-1990s (Figure 4) means that these data are not representational and are affected by technogenesis.

Figure 4.

The long-term course of variability of mean monthly ground temperatures at a depth of 3.2 m at the Yakutsk meteorological station (according to A N Fedorov).

Analysis of long-term variability of ground temperature

Observation posts (wells and platforms) were set up at the monitoring ranges that cover more than 100 elementary landscape complexes with varying lithogenous foundations.

At the right bank of Lena River, the study area is geomorphologically represented by Prilenskoye table and terrace complexes of Lena River at different levels. The left bank is represented by outwash plain areas near the watershed and high terraces. Terrace complexes belong to Central Yakutian lowland. Monitoring observations of the ground thermic regime in six physiographic regions covered nine terrain types: upland, slope, inter-alas, alas, sand-ridge, swale-lowland, small-valley, low-terrace, and bottomland (see Figure 1).

The Leno-Amginsky sandstone region is represented by Prilenskoye table made up of Cambrian limestone and dolomite, sand, sandstone, bench gravel, silty rocks, and mudstone, Lower Jurassic conglomerates capped by the quaternary deposit coat. Ground ice is found at lower levels in the quaternary loamy deposit coat. These areas belong to the inter-alas terrain. Compared with Central Yakutian lowland, the Prilenskoye table features higher terrain absolute elevations (up to 430 m), deeper snow cover (0.6 m), and high-temperature frozen grounds (−0.8 to −2.0°C). The region’s landscape structure is represented by upland, small-valley, slope and, in spots, inter-alas terrains.

The Leno-Amginsky alas-valley region comprises the territory of Lena River ancient terraces with absolute elevations of 200–290 m that represent Abalakhskaya erosion-depositional plain made up of mantle ice deposits with a depth of 25–60 m. The top part is made up of loam and clay sand. Rocks contain wedge ice. The modern plain surface is heavily pitted with thermokarst and erosion processes, which resulted in the formation of a typical alas and alas-valley terrain. The depth of incision of thaw lakes and valleys reaches 10–20 m. The region features relatively uniform permafrost conditions. Its main peculiarity is the solid distribution of permafrost rocks in plan and continuous distribution vertically as well as the prevalence of wedge ice. Exceptions are the largest thaw lakes, beneath which very deep or continuous permafrost may exist (Skryabin et al., 1992). The region’s landscape structure is represented by inter-alas, alas, and small-valley terrains.

In the Tyungyulyunsky alas-kettle region, long-term studies of the ground thermic regime have been conducted in two key areas. The first key area is represented in the south by Tyungyulyunsky terrace selvedge at its juncture with Abalakhskaya, Bestyakhskaya, and Kerdemskaya terraces with absolute elevations of up to 190 m. Covering deposits here are made up of sand clay and loam seams and are capped with Dyolkuminskaya suite eolian sand. The latter defines permafrost-landscape and hydrogeological conditions here. Supra- and intra-permafrost water-bearing taliks are common. Grounds are of high temperatures (−1.5 to +0.5°C); STL and SFL depth varies from 1.5 to 3.0–4.0 m, accordingly. The area has virtually the same appearance as the adjacent Bestyakhsky sand-ridge region and its relief is a combination of sand ridges and swale features and, thus, it is represented by sand-ridge and swale-lowland terrains.

The second area is a typical alas-kettle region with well-developed ice complex deposits with wedge ice. A peculiarity of the area is heavy thaw breakdown of its surface. The ice complex depth reaches 20 m. Deposits are represented by the sandy-loam material. The region’s landscape structure is represented by alas and inter-alas terrains.

The Bestyakhsky sand-ridge region covers the territory of the same-name and is the fourth terrace above the floodplain of Lena River with absolute elevations of 140–163 m. Deposits of this geomorphological level feature complex structures and are of various age and origin. The top part of Bestyakhskaya terrace and the first area of the previous region is made up of Upper Quaternary deposits of Dyolkuminskaya suite that resulted from eolian sand processing under the embedded Mavrinskaya suite and is made up of sand. The predominance of sand in alluvial and eolian deposits and drainage conditions of terrace surfaces conditioned a peculiar morphologic appearance of the landscapes and their specific permafrost conditions. Supra- and intra-permafrost water-bearing taliks are found. Cryogenic layers are of high temperatures. Sand-ridge and swale-lowland terrains prevail in the landscapes. Overall, in the sand-ridge terrain, spatial variability of the seasonal thawing layer depth is from 1.3 to 4.2 m, while the ground temperature at a depth of 10 m varies from −0.2 to −2.5°C. In the swale-lowland terrain, these values are, accordingly, 0.4–2.9 m and −3.4to −0.1°C.

The Prilensky valley-forest-steppe region combines landscapes within the modern bottomland and three low terraces above the floodplain of Lena River with alluvial deposits with absolute elevations of 88–113 m. In the area of the bottomland, first and second terraces above the floodplain, meadow, and steppe complexes prevail, while forested complexes prevail in the third terrace above the floodplain. The region is represented by bottomland and low-terrace terrains.

Bottomland terrain deposits are the youngest natural complexes. They are represented by sand, bench gravel, clay sand, and loam with turf seams. Taliks of different depths may be found by inter-low ridge bottomland depressions and under bayou lakes. STL has the maximum depth (3–4 m) in sandy channel banks. In inter-low ridge depressions with a well-developed ground cover, the STL depth is only 1.2–1.8 m. In channel bars, sand ridges, and graded low banks there is a seasonal frozen layer with a depth of up to 3.5–5.0 m under formation. The island rock temperature is close to zero; if not affected by the water flow, it goes down to −2°C. On the second bottom, in icy deposits of inter-low ridge depressions, the temperature reaches −3 to 4°C.

Terraces I–III above the floodplain of Lena River belong to the low-terrace terrain. The first terrace above the floodplain occupies the levels that are 8–12 m high. Its deposits are represented by alluvium with a depth of 17–25 m. The terrace section is made up of bench gravel, sand, clay sand with clay, and turf seams. The top of the first terrace is mainly made up of loamy-sabulous deposits and its bottom is sand, sometimes with cobble. The second terrace above the floodplain is 18–22 m high and is traced down as small islands along the left bank of the Lena River valley. Alluvium is 30–35 m deep. Channel facies deposits are found throughout the section in the third terrace above the floodplain 108–115 m high. These deposits are made up of cross-bedded anisomerous sands with gravel and small cobble seams in the section bottom. Overall, spatial variability of the seasonal thawing layer depth in this terrain is from 1.2 to 2.4 m, while the ground temperature at a depth of 10 m varies from −0.1 to −3.8°C.

The Prilensky left-bank sandstone region covers watershed areas, and high-terrace complexes of the outwash plain in the interfluve area of Lena and Kenkeme Rivers. Outwash plain areas near the watershed with absolute elevations of 250–270 m feature flattened relief, poor drainage conditions, waterlogged dishes, and drain cloughs. High-terrace complexes with absolute elevations of 200–250 m are scoured along with elongated small valleys and erosional creek valleys. Slopes of these terraces are scoured with shallows. The dissection depth increases west-to-east and reaches 100 m at the bedrock coast of the Lena River. Four terrains are well developed within this area: upland, slope, inter-alas, and small-valley.

Experimental data of the region’s permafrost monitoring have been used to evaluate changes in the ground thermal state in the annual heat exchange layers in predominant terrains.

Long-term observations of ground thermal conditions have shown that year-to-year variations in the ground mean annual temperature at a depth of 10 m range from −1.5 to −0.8°C (Figure 5), and temperature increase trend in ledum-vaccinium birch forest (B-11/95) over 1995–2017 and in vaccinium larch forest (B-8/95) over 1995–2009 amounted to 0.11 and 0.33°C/10 years, accordingly. The limits of year-to-year variations of the STL depth in loamy soils in ledum-vaccinium birch forest vary from 1.25 to 2.0. Its increase trend over 1995–2017 amounted to 28 cm/10 years (Table 2). Snow depth and ground covers are the main natural factors that determine changes in the ground thermal state.

Figure 5.

Long-term changes in the ground mean annual temperature at a depth of 10 m in lowland (B-8/95, B-11/95) and slope (S-5, S-9) terrains.

Table 2.

Extreme and mean long-term values of STL depth (ξ), ground temperature at a depth of 10 m (T₁₀) and their trends by terrains on the right bank of Lena River.

No. of wells, sites	Observation period	Interannual variability (extrema, in parenthesis – long-term average)		Trends of STL depth (αξ) and ground temperature (αT₁₀)
No. of wells, sites	Observation period	ξ, m	T₁₀, ⁰C	αξ, m/10 years	αT₁₀, ⁰ C/10 years
1	2	3	4	6	8
Upland terrain
B-8/95	1994/1995–2008/2009	–	−1.5 to −0.8 (−1.2)	–	0.33
B-11/95	1994/1995–2016/2017	1.25–2.00 (1.60)	−1.3 to −0.9 (−1.0)	0.28	0.11
Inter-alas terrain
B-5/95	1994/1995–2007/2008	1.15–1.81 (1.44)	−2.0 to −1.3 (−1.6)	0.21	0.29
B-2/95	1994/1995–2016/2017	1.20–1.55 (1.34)	−2.0 to −1.1 (−1.3)	0.01	0.29
B-57/87	1986/1987–2016/2017	1.33–1.92 (1.42)	−2.2 to −0.7 (−1.4)	–0.05	0.39
B-210/90	1989/1990–2016/2017	1.60–1.83 (1.66)	−2.4 to −0.9 (−1.6)	0.00	0.16
B-61/87	1986/1987–2016/2017	1.00–1.38 (1.15)	−2.6 to −1.6 (−1.9)	0.00	0.31
B-162	1987/1988–2016/2017	1.80–2.20 (1.95)	−0.9 to −0.5 (−0.7)	–0.03	0.07
B-10/93	1992/1993–2016/2017	1.20–1.86 (1.45)	−2.9 to −2.0 (−2.4)	0.14	0.26
Alas terrain
B-192/89	1988/1989–2016/2017	–	−0.4 to −0.1 (−0.2)	–	−0.11
Sand-ridge terrain
B-3/87	1986/1987–2016/2017	3.50–4.40 (3.93)	−0.6 to −0.2 (−0.3)	0.19	0.06
B-59/87	1986/1987–2016/2017	–	0.9 to 0.2 (0.6)	–	0.05
B-22/87	1986/1987–2016/2017	1.81–2.15 (1.97)	−2.6 to −0.8 (−1.8)	0.00	−0.04
Swale-lowland terrain
B-1/87	1986/1987–2016/2017	1.08–1.40 (1.22)	−1.7 to −0.2 (−1.0)	−0.03	0.16
B-5/87	1986/1987–2016/2017	0.54–1.25 (0.95)	−3.4 to −1.6 (−2.4)	−0.16	0.11
B-39/87	1986/1987–2016/2017	0.61–1.05 (0.84)	−3.4 to −1.7 (−2.5)	–	0.10
Small-valley terrain
B-11/87	1986/1987–2016/2017	0.40–1.50 (0.64)	−6.8 to −2.7 (−5.5)	0.09	0.23
B-12/87	1986/1987–2005/2006	0.80–1.30 (1.07)	−4.6 to −2.9 (−3.7)	0.02	−0.10
B-174/89	1988/1989–2010/2011	2.00–2.80 (2.27)	−1.4 to −0.5 (−1.0)	0.26	0.12
S-3a	1986/1987–2016/2017	0.37–0.53 (0.47)	−5.0 to −2.8 (−4.0)	0.02	0.11
S-8	1982/1983–2016/2017	0.86–1.37 (1.18)	−3.3 to −1.9 (−2.8)	0.02	−0.08
Low-terrace terrain
B-165/89	1988/1989–2016/2017	0.97–1.39 (1.21)	−2.5 to −1.7 (−2.0)	–0.06	−0.02
S-Meadow	1995/1996–2016/2017	1.82–1.90 (1.86)	−2.3 to −1.4 (−1.9)	0.02	0.40
S-Forest	1995/1996–2016/2017	1.70–1.98 (1.84)	−3.8 to −3.0 (−3.4)	0.04	0.23
Bottomland terrain
B-168/89	1988/1989–2016/2017	1.4–2.20 (1.79)	−3.5 to −1.1 (−2.1)	−0.18	−0.38
Slope terrain
S-5	1981/1982–2016/2017	3.26–3.86 (3.45)	−0.6 to −0.3 (−0.4)	−0.07	0.01
S-9	1985/1986–2016/2017	1.31–1.72 (1.48)	−2.6to −1.8 (−2.2)	−0.04	−0.04

Dash means that indicator values are not representational because of discontinuity of observations.

In the slope terrain, the ground temperature conditions were studied in litter-bearberry pine forest of a smooth sand slope (S-5) and in vaccinium larch forest of a loamy-sand slope near the watershed (S-9). The thawing depth on the smooth sand slope over 1982–2017 and on the loamy-sand slope near the watershed over 1986–2017 ranges, accordingly, from 3.26 to 3.86 and from 1.31 to 1.72 m with negative trends of, accordingly, 7 and 4 cm/10 years. Year-to-year variations in the ground temperature on the smooth slope (S-5) and the slope near the watershed (S-9) are, accordingly, from −0.6 to −0.3 and from −2.6 to −1.8 °C (see Figure 5). Smooth slope has a trend of ground temperature increase (0.01°C/10 years), and the slope near the watershed has a negative trend of −0.04°C/10 years.

Inter-alas terrain is very common in high Abalakhskaya (B-57/87, B-61/87, B-162, B-210/90) and medium Tyungyulyunskaya (B-10/93) terraces; it is also rarely found at low levels of the Prilenskoye table (B-2/95, B-5/95). Within the limits of Abalakhskaya terrace, depending on the composition of deposits and ground cover type, the ground thawing depth varies greatly – from 1.00 to 2.20 m with mean long-term values of 1.15–1.95 m. Over 1987–2017, it showed a negative trend equal to 3–5 cm/10 years. The ground mean annual temperature based on conditions of heat exchange with the atmosphere in various survey marks varied from −0.5 to −2.6 °C. Its year-to-year variations were 0.4−1.5°C (Figure 6). Over the observation period, the trend of ground temperature increase at a depth of 10 m varies from 0.07 to 0.39°C/10 years. Over 1993–2017, the ground thawing depth within the limits of Tyungyulyunskaya terrace varied from 1.20 to 1.86 m and a positive trend of 14 cm/10 years was observed. The ground mean annual temperature was −2.9 to −2.0°C; the ground temperature increase trend is 0.26°C/10 years. Within the limits of the Prilenskoye table, year-to-year variations of the ground thawing depth in this terrain over 1995–2017 were 1.20–1.81 m with a positive trend of 1–21 cm/10 years. The grounds are of high temperature (−2.0 to −1.1°C) and show an increasing trend of 0.29°C/10 years (see Table 2).

Figure 6.

Long-term changes in the ground mean annual temperature at a depth of 10 m in inter-alas (B-57/87, B-162, B-10/93, BC-210/90) and alas (B-192/89) terrains.

Alas terrain is a typical landscape common in Abalakhskaya terrace. The thawing depth of sandy-loam and sandy grounds here varies from 1.2 to 2 m and Т_o in various survey marks ranges from 0.1 to −0.3°C (see Figure 6). Ground temperature conditions are mainly because of meadow vegetation and grassy turf. Over the observation period, year-to-year variations of Т_o did no exceed 0.3°C. A ground temperature decrease trend of -0.11°C/10 years (see Table 2) is typical here.

The sand-ridge terrain is characterized by shallow intra- and suprapermafrost waters. Over 1987–2017, the ground thawing depth varied from 1.81 to 4.40 m. The maximum values are typical of litter-bearberry pine forest (B-3/87) with a thawing depth increase trend of 19 cm/10 years and the minimum values are typical of vaccinium-pine larch forest (B-22/87) with no trend observed. The mean annual values of Т_o in the former case ranged from −0.6 to −0.2°C with a temperature increase trend of only 0.06°C/10 years and in the latter case – from −2.6 to −0.8°C with a negative trend of 0.04°C/10 years (see Table 2 and see Figure 7). The ground temperature conditions are affected by the moisture content of the seasonal thawing layer and intra-permafrost water-bearing formation.

Figure 7.

Long-term changes in the ground mean annual temperature at a depth of 10 m in sand-ridge (B-3/87, B-22/87, B-59/87) and swale-lowland (B-1/87, B-5/87) terrains.

In the Tyungyulyunsky alas-kettle region, in the first key area of the sand-ridge terrain, water-bearing taliks with close supra-permafrost water and ‘dry’ taliks with deep supra-permafrost water (B-59/87) are common. In the areas dominated by supra-permafrost taliks, the seasonal frozen layer depth varies from 2.5 m on water-bearing taliks to 4–5 m on ‘dry’ ones. Sandy grounds are of high temperatures. The ground temperature at the bottom of the annual heat exchange layer in the areas dominated by taliks varies from 0 to + 0.5°C. Outside of a talik, it ranges from −0.1 to −1.3°C. Over 1987–2017, in the B-59/87 area, the ground mean annual temperature at a depth of 10 m was 0.2–0.9°C, with a ground temperature increase trend of 0.05°C/10 years (see Table 2 and see Figure 7).

The swale-lowland terrain is made up of sandy deposits. It features common shallow organic deposits and close supra-permafrost waters of the seasonal thawing layer. The sandy ground thawing depth varies greatly depending on the ground moisture content and ground cover – from 0.54 to 1.40 m. Over 1987–2017, it showed a negative trend (3–16 cm/10 years). The ground mean annual temperature varies from −3.4 to −0.2°C (see Figure 7); the temperature increase trend is 0.10–0.16°C/10 years (see Table 2). Ground temperature conditions are affected by the ground cover and moisture content. Year-to-year variations of Т_o of waterlogged sands are bigger compared with dry sands.

The small-valley terrain is represented by a small river and brook valley bottoms. It is found in all the physiographic regions under study from the top to the mouth sections. In this paper, the ground thermal state in this terrain is exemplified by two regions: Bestyakhsky sand-ridge (B-11/87, B-12/87 and B-174/89) and Prilensky left-bank sandstone (S-3a and S-8). Ground temperature conditions in the small-valley terrain feature the highest space-time variability (Figure 8). Over 1987–2017, the thawing depth of organic deposits with sphagnous-ledum-bushy dish (S-3a) varied from 0.37 to 0.53 m with a positive trend of 2 cm/10 years. The ground mean annual temperature varies from −5.0 to −2.8°C (see Figure 8); the temperature increase trend is 0.11°C/10 years (see Table 2).

Figure 8.

Long-term changes in the ground mean annual temperature at a depth of 10 m in the small-valley terrain (S-3a, S-8, B-11/87, B-12/87 and B-174/89).

In the sedge-sphagnum dwarf birch thicket of turf-loamy-sand deposits (B-11/87), the thawing depth is 0.40–1.50 m with a positive trend of 9 cm/10 years. Year-to-year variations in the ground mean annual temperature are the highest (−6.8 to −2.7°C); the ground temperature increase trend is 0.23°C/10 years (see Table 2 and see Figure 8). Over 1987–2017, the thawing depth of sandy deposits under larch forests with well-developed ground covers (C-B/87, S-8) varied from 0.80 to 1.37 m with a slight positive trend (2 cm/10 years). The ground mean annual temperature varies from −4.6 to −1.9°C (see Figure 8); the temperature decrease trend is 0.08–0.10°C/10 years (see Table 2). Over 1989–2011, the biggest thawing depth of sandy deposits was observed under grass spruce-larch forest (B-174/89); it varies from 2.00 to 2.80 m. A major positive trend is observed (26 cm/10 years). The grounds are of a high temperature that varied from −1.4 to −0.5°C with a positive trend of 0.12°C/10 years (see Table 2 and see Figure 8).

Terraces I–III above the floodplain of Lena River belong to the low-terrace terrain. The top of terraces I and II is mainly made up of loamy deposits, and its bottom is sand, sometimes with turf and cobble seams. The alluvium depth of the first terrace is 17–25 m, and of the second terrace it is 30–35 m. The surface of terraces above the floodplain shows the highest snow depth (0.18–0.31 m) and density (170–340 kg/m³) variability because of the prevalence of steppe-heath and meadowy areas that contribute to snow repurification and compaction under the influence of the wind. Deposits of the third terrace above the floodplain are made up of sand and its surface is mainly occupied by forest vegetation. In the Tuimaada station territory, year-to-year variations of the ground thawing depth in poaceous forb meadow (S-Meadow) and grass pine forest (S-Forest) on the second terrace above the floodplain over 1995–2017 were insignificant and amounted to, accordingly, 1.82–1.90 and 1.70–1.98 m with an increasing trend of 2 and 4 cm/10 years. The ground mean annual temperature in the meadow and forest varies, accordingly, from −2.3 to −1.4 and from −3.8 to −3.0°C (Figure 9) with a temperature increasing trend of 0.40 and 0.23°C/10 years (see Table 2). Over 1989–2017, in the third terrace under ledum-vaccinium spruce-larch forest (B-165/89), the ground thawing depth varied from 0.97 to 1.39 m with a negative trend (6 cm/10 years). The ground mean annual temperature varies from −2.5 to −1.7°C with a negative trend observed (0.2°C/10 years (see Table 2).

Figure 9.

Long-term changes in the ground mean annual temperature at a depth of 10 m in the low-terrace (S-5/86, S-Meadow, S-Forest, B-43/87) and bottomland (B-168/89) terrains.

Over 1989–2017, in the bottomland terrain, in poaceous forb meadow (B-168/89), the thawing depth of sandy-loam-grounds varied from 1.4 to 2.2 m with a negative trend of 18 cm/10 years observed. The ground mean annual temperature varies from −3.5 to −1.1°C (see Figure 9) with a negative trend observed (0.2°C/10 years (see Table 2). Bottomland conditions of Lena River play a key role in the establishment of ground temperature conditions and their year-to-year variations. Since 2009, a visible decrease in the ground mean annual temperature by 1.7−2.0°C was observed (see Figure 9).

Monitoring observations allow us to conclude that changes in Т_o are not well defined and a certain decrease in the ground temperature in individual landscapes is indicative of their stability. The studies have shown that from 1987 to 2004, snowy and dry winters alternated in a uniform manner with a decrease in the snow depth. Heat-protective properties of the snow cover are the main factors that determine changes in the ground temperature conditions. Winters in 2005–2007 were abnormally snowy with early formation of a stable snow cover, which resulted in dramatic increase in Т_o, especially in low-temperature complexes. Winters in 2009 and 2010 were abnormally dry with late formation of a stable snow cover, which is why the ground temperature dropped to have almost reached the level of 2002/2003 (see Figures 5 –9).

The lowest and abnormally high ground temperatures over the entire observation period were recorded, accordingly, in the 2002/2003 and 2006/2007 water years. The winter period of 2002/2003 was abnormally dry with abnormally late formation of the snow cover. This was the main reason for a ground temperature drop despite abnormally warm winter and summer periods. As we noted above, the subsequent years had snowy winters, visible spring floods, and heavy precipitation in fall. Overall, from 2002/2003 to 2006/2007, the ground temperature at the bottom of the annual heat exchange layer in various landscapes increased by 0.3–3.5^oC. Increased temperature and permafrost thawing depth triggered different cryogenic processes (thermokarst, thermal erosion, etc.). Waterlogging and flooding were observed in low-lying landscape areas. These factors resulted in an increased water surface level of lakes, water fillup of previously dry lake beds, and an increase in the level of supra-permafrost water of the seasonal thawing layer.

Analysis of long-term field data shows that there is a meaningful dependence between trends in the ground temperature at a depth of 10 m and mean annual air temperature in the small-valley and swale-lowland terrains, while dependence is weak in the inter-alas terrain (Figure 10). An inverse relationship is observed in the sand-ridge terrain. In lowland, alas, and low-terrace terrains, a short series of observations makes it impossible to correctly establish dependencies between trends of the ground temperature at a depth of 10 m and mean annual air temperature. In landscape complexes of small-valley, low-terrace, and bottomland terrains, there are concurrent trends of ground temperature increase and decrease amidst modern climate warming.

Figure 10.

Dependence of the trend of the ground temperature at a depth of 10 m (αT₁₀, °C/year) on the trend of the mean summer air temperature (αT_air, °C/year) in (a) inter-alas, (b) sand-ridge, (c) swale-lowland, and (d) small-valley terrains.

No empirical dependence has been established between trends of the seasonal thawing layer depth and mean annual air temperature in sand-ridge and certain complexes of the inter-alas terrain. Weak dependence is observed in landscape complexes of inter-alas and swale-lowland terrains. Meaningful dependence of the sedge-sphagnum dwarf birch thicket of the marginal seam of the terrace above the floodplain in the small-valley terrain is observed (Figure 11).

Figure 11.

Dependence of the trend of the seasonal thawing layer depth (αξ, m/year) on the trend of the mean summer air temperature (αT_as, °C/year) in (a) inter-alas, (b) sand-ridge, (c) swale-lowland and (d) small-valley terrains.

Dimensionless factor К_α = αТ₁₀/αТ_air proposed by A V Pavlov (2008) was accepted as one of the criteria of stability of permafrost rocks and their sensitivity to climate changes. With К_α ⩽ 0.50, frozen ground features thermal stability, with 0.5 < К_α ⩽ 0.75 – medium stability and with К_α > 0.75 – low stability. In Central Yakutia, К_α in the lowland terrain varies from 0.15 to 0.55, in inter-alas – from 0.11 to 0.53, in sand-ridge – 0.07–0.08, in swale-lowland – 0.14–0.22, in small-valley – 0.31–0.32. In landscape complexes of alas, bottomland, low-terrace, and, to some extent, in certain natural complexes of sand-ridge and small-valley terrains, grounds get cool with К_α having negative values. Overall, the lithogenous foundation of the region’s natural complexes amidst modern climate warming mainly shows the high thermal stability of frozen ground. In local areas of lowland and inter-alas terrains, grounds feature medium stability.

In terms of response to climatic fluctuations (warming), terrains may be divided into three groups – high-, medium- and low-sensitive, making up the following landscape series: small-valley, bottomland – inter-alas, sand-ridge, swale-lowland – upland, slope, alas, low-terrace. Year-to-year variations in the ground temperature at the bottom of the annual heat exchange layer have the following range by groups, accordingly: 0.9–4.1; 0.4–1.8; 0.3–0.9ºC. Year-to-year variations of the active layer depth depend on its long-term mean values and have the following range by groups, accordingly: 34–172, 14–75% and 4–47%.

Conclusion

The main conclusions were made based on the results of permafrost monitoring data analysis.

The results of studies of the thermal state of permafrost landscapes in Central Yakutia for 1982(1987)–2017 were provided. The response of the thermal state of the upper permafrost layers to modern climate warming is affected by an increase in the air temperature and in the main parameters of permafrost landscapes (vegetation, ground and snow covers, deposit composition, moisture, and ice content).

Despite significant modern climate warming in Central Yakutia, changes in the thermal state of the annual heat exchange layer in natural landscapes are not pronounced. Overall, the modern period is characterized by fair thermal stability of the ground. Short-term ground temperature fluctuations in the recent years are mainly caused by abnormally snowy and abnormally dry winters. Due to more frequent abnormal winter seasons, ranges of ground temperatures in the active layer have significantly increased, which has to be considered when solving theoretical and practical problems.

The active layer depth in natural landscapes is quite stable and it shows low year-to-year variations. The seasonal thawing depth increase trend is not statistically significant.

The criteria of stability for various permafrost landscapes and their sensitivity to climate changes were elaborated for the region. Overall, the lithogenous foundation of the region’s natural complexes amidst modern climate warming mainly shows high thermal stability, although, in local areas of lowland and inter-alas terrains, grounds feature medium stability.

The next step of monitoring studies implies arrangement of new ranges in complicated permafrost conditions, the continuation of series of long-term observations, permafrost forecasting, and elaboration of measures to control changes in parameters of ground temperature conditions.

Footnotes

Acknowledgements

Long-term monitoring observations of the thermal state of upper permafrost layers have been backed up by research scientific works as a part of priority focus areas and fundamental research programs of the Siberian branch of the Russian Academy of Sciences.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Stepan P Varlamov

References

Are

(1973) Ground temperature regime beneath a draining thaw lake in Central Yakutia. In: Are

(ed.) Issues of the Geography of Yakutia. Leningrad: Gidrometeoizdat, pp. 70–75 (in Russian).

Efimov

(1952) Selected results of 3-year ground temperature observations in the Yakutsk area. In: Efimov

(ed.) Permafrost Investigations in the Yakut Republic, vol. 3. Moscow: USSR Academy of Science Press, pp. 8–19 (in Russian).

Fedorov

Maximov

TKh

Gavriliev

, et al. (2006) Spasskaya Pad: Integrated Investigations of the Permafrost Landscapes. Yakutsk: Permafrost Institute Press (in Russian).

Gavriliev

Mandarov

Ugarov

(1984) Hydrothermal Reclamation of Agricultural Lands in Yakutia. Novosibirsk: Nauka (in Russian).

Gavrilova

(1978) Climate and Perennial Freezing of Soils and Rocks. Novosibirsk: Nauka (in Russian).

Gerasimov

(1950) Annual ground temperature variations in the Yakutsk area. In: Gerasimov

(ed.) Permafrost Investigations in the Yakut Republic. Yakutsk: Academy of Sciences of the USSR Publ., pp. 179–191 (in Russian).

Ivanov

(1963) On the thermal regime of the upper earth crust in the Yakutsk area. In: Ivanov

(ed.) Heat and Mass Exchange in Frozen Layers of the Earth Crust. Moscow: USSR Academy of Science Press, pp. 9–55 (in Russian).

Melnikov

(1950) Permafrost in the Yakutsk area. In: Melnikov

(ed.) Permafrost Investigations in Yassr, vol. 2. Moscow; Leningrad: USSR Academy of Science Press, pp. 52–70 (in Russian).

Pavlov

(1975) Heat Exchange between Soil and Atmosphere in Northern and Temperate Latitudes of the USSR. Yakutsk: Yakut Publishing House (in Russian).

10.

Pavlov

(1979) Thermal Physics of Landscapes. Novosibirsk: Nauka (in Russian).

11.

Pavlov

(1996) Current state of the monitoring of the permafrost of Russia development challenges. In: Proceedings of the 1st conference of geocryologists of Russia, book 3, Moscow, 3–5 June, pp. 327–336. Moscow: MGU Publishing House.

12.

Pavlov

(2008) Permafrost Monitoring. Novosibirsk: Academic Publishing House “Geo, (in Russian).

13.

Romanovsky

Drozdov

Oberman

, et al. (2010) Thermal state of permafrost in Russia. Permafrost and Periglacial Processes 21: 136–155.

14.

Second assessment report of Rosgodromet of Russia on climate changes and their consequences the territory of the Russian Federation Electronic resource access code (2014), http://downloads.igce.ru/publications/OD_2_2014/v2014/htm/1.ht

15.

Shimanovskii

(1942) Effect of pavements on the ground thermal regime. In: Shimanovskii

(ed.) Permafrost Investigations in the Yakut Republic, vol. 1. Yakutsk: Yakut Publishing House, pp. 44–55 (in Russian).

16.

6th National Communication of the Russian Federation (2014) Electronic resource, access code, http://downloads.igce.ru/publications/nac_soobs/nc_2014.pdf

17.

Skachkov

(2012) Climate change trends in Central Yakutia at the turn of XX-XXI centuries. In: Proceedings of the international scientific conference, vol. 1, Irkutsk, 17-21 September, pp. 236–238. Irkutsk: Publishing House of the В.Б. Sochava Institute of Geography SB RAS.

18.

Skryabin

Skachkov

Varlamov

(1992) Pattern for the formation of temperature conditions in bottom deposits of shallow lakes in Central Yakutia. In: Geography Natural Resources, vol. 2. Novosibirsk: Science pp. 164–168.

19.

Skryabin

Varlamov

Skachkov

(1998) Interannual Variability of the Ground Thermal Regime in the Yakutsk Area. Novosibirsk: SB RAS Press (in Russian).

20.

Solov’ev

(1959) Permafrost in the Northern Part of the Lena-amga Watershed. Moscow: USSR Academy of Science Press (in Russian).

21.

Ugarov

Mandarov

(2000) Overhead Irrigation of Fodder Crops in Central Yakutia. Yakutsk: Permafrost Institute Press (in Russian).

22.

Varlamov

Skachkov

Skryabin

(2002) Ground Temperature Regime in Permafrost Landscapes of Central Yakutia. Yakutsk: Permafrost Institute Press (in Russian).

23.

Varlamov

Skachkov

Skryabin

(2016) Monitoring of the thermal state of soils of Tuimaada valley. In: Climate and permafrost ecosystems: Proceedings of the IX international symposium C/H2O/energy balance and climate over the Boreal and Arctic regions with special emphasis on Eastern Eurasia (The symposium is dedicated to the 25th anniversary of the joint Russian-Japanese research on climate change in the permafrost), Yakutsk, 1–4 November, pp. 248–251. Nagoya, Japan: Publishing House of the Nagoya University.

24.

Varlamov

Skachkov

Skryabin

(2017) Results of 35 years of permafrost monitoring at the Chabyda station, Central Yakutia. Nauka i obrazovaniye 86(2): 34–40.

25.

Varlamov

Skachkov

Skryabin

, et al. (2012) Thermal state of the upper horizons of the permafrost in Central Yakutia. In: Proceedings of the tenth international conference on permafrost, vol. 2, Salekhard, 25–29 June, pp. 481–486. [The Northern Publisher]