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Thermal properties are important for featuring the water-heat transfer capacity of soil. They are also key to many processes in earth sciences, such as the land surface processes and ecological and geoenvironmental dynamics and their changes in permafrost regions. With loose and porous structures, the organic matter layer in soil strata substantially influences soil thermal conductivity. So far, thermal conductivity of mineral soils has been explored extensively and in depth, but there are only limited studies on that of organic soils. In this study, influences of soil temperature, soil moisture saturation (SMS), and soil organic matter (SOM) content on soil thermal conductivity were analyzed on the basis of laboratory experiments on the silt-organic soil mixtures of varied mixing ratios. Results show that soil thermal conductivity declines slowly with the lowering temperatures from 10 to 0°C; however, it increases and finally stabilizes when temperature further lowers from 0 to -10°C. It is important to note that thermal conductivity peaks in the temperature range of -2~0°C (silty and organic-poor soil) and -5~0°C (organic-rich soil), possibly due to phase changes of ice/water in warm permafrost. Under both thawed and frozen states, soil thermal conductivity is positively related with SMS. However, with rising SOM content, the growth rate of soil thermal conductivity with SMS slows gradually. Given the same SMS, soil thermal conductivity declines exponentially with increasing SOM content. Based on the experimental and theoretical analyses, a new empirical computational formula of soil thermal conductivity is established by taking into account of the SOM content, SMS, and soil temperature. The results may help better parameterize in simulating and predicting land surface processes and for optimizing frozen soil engineering designs and provide theoretical bases for exploring the dynamic mechanisms of environmental changes in cold regions under a changing climate.

During the last 50 ka, cryogenic wedges on the Ordos Plateau formed during three major periods: (i) early local Last Glaciation, ca. 50 ka BP; (iii) local Last Permafrost Maximum(local LPM), 25–19 ka BP; and (v) post-local LPM, 16–9 ka BP. Cryoturbations mainly formed in the following periods: (ii) pre-local LPM, 45–30 ka BP and (iv) ~ 20 ka BP. The coldest periods with well-developed permafrost (i and iii) were most conducive for forming cryogenic wedges. The following periods of warming climate and degrading permafrost favored the formation of cryoturbations. During the local LPM, sand wedges and polygons were well developed and widely distributed on the Ordos Plateau when mean annual air temperatures (MAATs) were approximately 12°C lower than that at present. At ~30 ka BP, MAAT was 6–7°C lower than that at present. Paleoclimate conditions on the Ordos Plateau were reconstructed since 50 ka BP as follows: cold (ca. 50 ka BP) → cool (45–30 ka BP) → very cold (25–19 ka BP) → cool (19–9 ka BP) → intermittent warming until the present day. The amount of precipitation fluctuated, but with a general trend of drying since 50 ka BP. Under the next generally warming climate (after 9 ka BP), permafrost gradually degraded and eventually disappeared from the Ordos Plateau.

The framework of Quaternary permafrost in China was reconstructed for the first time on the basis of available periglacial, glacial, and other proxies. During the Early Pleistocene (2.68–0.80 Ma BP), permafrost advanced southwards to 47–50◦ N in northern China and possibly occurred in alpine regions in western China. During the Middle Pleistocene (800–130 ka BP), permafrost occurred extensively on the Qinghai-Tibet Plateau (QTP) and in alpine or mountainous regions of northern, western, central, and northeastern China. The Great Interglacial occurred afterward and before the Last Glaciation, but the evidence of permafrost for this period has been seldom found. Permafrost evolution of the Last Glaciation (72–19 ka BP) in China is divided into: Expansion (72~50 ka BP), degradation (50–26 ka BP), and intensive expansion during the Last Permafrost Maximum (LPMax, 26–19 ka BP) with a permafrost extent of 5.3 × 106~5.4 × 106 km2, and when major features of present permafrost took shape. Permafrost fluctuated during the Younger Dryas (12.9–11.7 ka BP). Since the Holocene, permafrost in China expanded and retreated to lesser extents, forming the current permafrost environment. The Holocene evolution of permafrost was divided into: Unstable climate but stable permafrost during the early Holocene (11.7~8.5–7.0 ka BP); permafrost degradation during the Last Permafrost Minimum (LPMin, or the Holocene Megathermal; 8.5–7.0~4.0–3.0 ka BP) and the Medieval Warm Period (MWP; 1.0~0.5 ka BP); permafrost expansion during the Neoglaciation (4.0–3.0~1.0 ka BP) and the Little Ice Age (LIA; 0.5~0.1 ka BP); and recent permafrost degradation (20th century to the present). However, this review paper only provides the framework of Quaternary permafrost in China and some preliminary discussions. Many key questions await further investigations.

Data scarcity is a major obstacle for high-resolution mapping of permafrost on the Tibetan Plateau (TP). This study produces a new permafrost stability distribution map for the 2010s (2005–2015) derived from the predicted mean annual ground temperature (MAGT) at a depth of zero annual amplitude (10–25 m) by integrating remotely sensed freezing degree-days and thawing degree-days, snow cover days, leaf area index, soil bulk density, high-accuracy soil moisture data, and in situ MAGT measurements from 237 boreholes on the TP by using an ensemble learning method that employs a support vector regression model based on distance-blocked resampled training data with 200 repetitions. Validation of the new permafrost map indicates that it is probably the most accurate of all currently available maps. This map shows that the total area of permafrost on the TP, excluding glaciers and lakes, is approximately 115.02 (105.47–129.59) ´ 104 km2. The areas corresponding to the very stable, stable, semi-stable, transitional, and unstable types are 0.86 ´ 104, 9.62 ´ 104, 38.45 ´ 104, 42.29 ´ 104, and 23.80 ´ 104 km2, respectively. This new map is of fundamental importance for engineering planning and design, ecosystem management, and evaluation of the permafrost change in the future on the TP as a baseline.

The large variety of the semi-automated methods in mapping the surface water bodies and the frequent omission of ponds (< 10,000 m2) from permafrost regions inventories motivates this work. Based o...

Changes in the frequency and extent of wildfires are expected to lead to substantial and irreversible alterations to permafrost landscapes under a warming climate. Here we review recent publications (2010–2019) that advance our understanding of the effects of wildfire on surface and ground temperatures, on active layer thickness and, where permafrost is ice‐rich, on ground subsidence and the development of thermokarst features. These thermal and geomorphic changes are initiated immediately following wildfire and alter the hydrology and biogeochemistry of permafrost landscapes, including the release of previously frozen carbon. In many locations, permafrost has been resilient, with key characteristics such as active layer thickness returning to pre‐fire conditions after several decades. However, permafrost near its southern limit is losing this resiliency as a result of ongoing climate warming and increasingly common vegetation state changes. Shifts in fire return intervals, severity and extent are expected to alter the trajectories of wildfire impacts on permafrost, and to enlarge spatial impacts to more regularly include the burning of tundra areas. Modeling indicates some lowland boreal forest and tundra environments will remain resilient while uplands and areas with thin organic layers and dry soils will experience rapid and irreversible permafrost degradation. More work is needed to relate modeling to empirical studies, particularly incorporating dynamic variables such as soil moisture, snow and thermokarst development, and to identify post‐fire permafrost responses for different landscape types and regions. Future progress requires further collaboration among geocryologists, ecologists, hydrologists, biogeochemists, modelers and remote sensing specialists.

Cast-in-place pile foundations are widely employed to support basic infrastructures on the Qinghai-Tibet Plateau (QTP). However, concrete hydration heat substantially affects the thermal stabilization of pile foundations in permafrost regions. In this paper, the thermal characteristics of a cast-in-place pile foundation in a warm (>−1 °C) permafrost region on the interior QTP were studied via field observations and numerical simulations. The temperature field observations showed that the peak temperature of the pile foundation occurred two days after the concrete was poured, and that positive temperatures of the pile foundation lasted 21 days. The temperatures at different depths of the pile foundation dropped below 0 °C 93 days after the concrete was poured. However, even 224 days after the concrete was poured, the temperatures in the pile foundation were still higher than that of the natural ground. Based on the observational data, three-dimensional numerical models were established to analyze the thermal disturbances and the freezing process. The results showed that the thickness of the thermal disturbance annulus around the pile foundation was 1.6 m, namely, twice the pile diameter. It would take approximately 420 days for the temperatures in the pile foundation to recover to approximately that of the natural ground. When the mean annual ground temperature (MAGT) decreased, the thickness of the thermal disturbance annulus around the pile foundation increased, and the freezeback time of the pile foundation decreased.

This paper presents new field observations that assist in further defining the extent of Last Permafrost Maximum (LPM) permafrost and frozen ground in north China. In that respect, this region is specific by its arid environment and continental position. Bedrock exposures and sand and gravel pits were examined along a south-north transect from southern Ordos as far as the vicinity of Dongsheng District, Ordos City on the Ordos Plateau (North China). Attention focussed upon the recognition of sand-wedge remains and possible cryoturbations. Two types of wedge structures were recognized: type A wedges extend to depths in excess of 3.0 m and are thought to have formed under conditions of continuous permafrost. Type B wedges are restricted to the upper 1.5 m and are thought to reflect discontinuous permafrost and/or deep seasonal frost. OSL dating of wedge infills indicates that type A wedges formed between 23–19 ka and younger type B wedges formed until the early Holocene. It is now possible to delineate a more exact position of the boundary between continuous permafrost and discontinuous permafrost and/or deep seasonal frost on the Ordos Plateau during the LPM. This boundaries occur between Dongsheng and Jinbian at 37°-39°N.

Hydrogeologic processes and shallow subsurface flows control runoff generation, groundwater dynamics, and permafrost distribution at high latitudes and elevations. Electrical resistivity tomography (ERT) can effectively delineate the frozen and thawed zones in the cold environment and can be applied in permafrost hydrogeology by measuring the differences in subsurface electrical potential. A combined approach of ERT and borehole measurements is implemented to map the flow paths of the supra-permafrost and sub-permafrost waters around the Wanlong Worma Lake (WWL) basin in the headwaters of the Yellow River (northeastern Qinghai-Tibet Plateau, China). The ERT sounding results are further validated using drilling records and measured data on ground temperatures and groundwater level. Then, basic features for permafrost hydrogeology are outlined according to the ERT sounding, vegetation distribution, and geological data in the WWL basin. The results show the presence of permafrost at depths up to 15 m, in which electrical resistivity is >250 Ωm. Below the permafrost (at depth 15–80 m), electrical resistivity is generally

Thermokarst lakes are widespread and developing on the Qinghai‐Tibet Plateau (QTP), and they have modified hydrological processes and water balance in the region. Despite increasing attention, our understanding of the hydrological behaviors of thermokarst lakes under permafrost degradation remains limited on the QTP. In this study, water stable isotope tracers were used to characterize the spatial and seasonal hydrological changes of thermokarst lakes on the central QTP. Significant seasonal variations and factors influencing the isotopic hydrology of lakes were revealed through the ice‐free season. Substantial differences in lake‐specific input water isotope compositions (δI) among the lakes indicate two lake‐recharge regimes: rain‐dominated, and snowmelt/permafrost thaw‐dominated. We suggest that precipitation and active‐layer hydrology controlled these hydrological changes in the ice‐free season. However, under ice cover, melting of the surrounding permafrost (including ground ice) dominated the hydrology of thermokarst lakes. Importantly, a conceptual model delineates the hydrological evolution of thermokarst lakes under permafrost degradation. This study serves as a baseline for future investigations of hydrological processes and water balance relating to thawing permafrost on the QTP.

The thermal regime of permafrost in the rugged topography on parts of the Qinghai-Tibet Plateau (QTP) remains ambiguous, due to general inaccessibility and inconvenient investigations with geophysical prospecting. While the relatively easy implementations of monitoring ground surface temperature (GST) may facilitate the investigations of permafrost thermal state. Here, surface freezing and thawing and the relationship between GST and permafrost temperature are investigated in the Bayan Har Mountains, NE QTP on the basis of 22 monitoring sites. Results demonstrate that, unlike the air temperature (Ta) mainly controlled by elevation, the GST is complicately influenced by elevation and the surface characteristics, such as vegetation, local soil textures, as well as the exposure to solar radiation. Mean annual GST (MAGST) ranges from 1.1 °C to −3.1 °C and is averaged at −0.8 °C. MAGST generally decreases at a lapse rate of 1.1 °C/100 m in relation to elevation. Surface freezing and thawing processes depend on topography and local surface characteristics. The onset of unstable thawing, stable thawing, unstable freezing, and stable freezing are averaged at 6 April 2015, 15 May 2015, 14 October 2015, and 21 October 2015. Based on the relationship between MAGST and the ground temperature at the depth of zero annual amplitude, GST likely serves as a reliable indicator of the thermal state of permafrost. For the 22 sites, it is estimated that the lowest TZAA of permafrost is −3.4 °C and the thickest permafrost is 106.2 m. However, detailed investigations of subsurface characteristics are indispensable for the accurate inference of permafrost.

Multiple proxy records have been used for the understanding of environmental and climate changes during the Holocene. For the first time, we here measure meteoric 10Be isotope of sediments from a drill core collected at the Kunlun Pass (KP) on the northeastern Qinghai-Tibet Plateau (NETP) to investigate mositure and atmospheric circulation changes during the Holocene. The 10Be flux suggests relative low levels in the Early Holocene, followed by a sharp increase to high values at around 4 ka BP (4 ka BP = 4000 years before present). Afterwards, the 10Be flux remains on a high level during the Late Holocene, but decreases slightly towards today. These 10Be deposition patterns are compared to moisture changes in regions dominated by the Indian Summer Monsoon (ISM), East Asian Summer Monsoon (EASM), and the Westerlies. Different from the gradual changes in monsoon patterns, the 10Be data reveal low levels during the Early Holocene until ~4 ka BP when an obvious increase was indicated and a relative high level continues to this day, which is relatively more in agreement with patterns of the Westerlies. This finding provides a new evidence for a shift in the dominant pattern of atmospheric circulation at the KP region from a more monsoonal one to one dominated by the Westerlies. Our results improve the understanding of non-stationary interactions and spatial relevance of the EASM, the ISM and the Westerlies on the Qinghai-Tibet Plateau.

Various proxy records have been used for the understanding of environmental and climate variations during the Holocene. Here, for the first time, we use meteoric 10Be isotope measurements performed on sediments from a drill core collected at the Kunlun Pass (KP) on the northeastern Qinghai-Tibet Plateau (NETP) to investigate hydroclimate changes during the Holocene. The 10Be flux suggests relative low levels in the Early Holocene, followed by a sharp increase to high values at around 4 ka BP (4 ka BP = 4000 years before present). Afterwards, the 10Be flux remains on a high level during the Late Holocene, but decreases slightly towards today. These 10Be deposition patterns are compared to moisture changes in regions dominated by the Indian Summer Monsoon (ISM), East Asian Summer Monsoon (EASM), and the Westerlies. Different from the gradual changes in monsoon patterns, the 10Be data reveal low levels during the Early Holocene until ~4 ka BP when an obvious increase is indicated and a relative high level continues to this day, which is relatively more in agreement with patterns of the Westerlies. This finding provides a new evidence for a shift in the dominant pattern of atmospheric circulation at the KP region from a more monsoonal one to one dominated by the Westerlies. Our results improve the understanding of non-stationary interactions and spatial relevance of the EASM, the ISM and the Westerlies on the Qinghai-Tibet Plateau.

Reconstructions of the Holocene (especially the mid-Holocene) climatic and environmental changes may serve as an analogue for future scenarios. About 7 ka of Holocene climatic variability in the north of Bayan Har Mountains on the northeastern Tibetan Plateau is reconstructed, using grain size, magnetic susceptibility, geochemical parameters, and accelerator mass spectrometry 14C chronology from peat bog sediments. The peat’s source is found to be aeolian sediments. Climatic variability from the peat bog sediments during the last 7.3 ka can be divided into four stages: warm and wet from 7.3 to 5.7 cal ka BP; cool and dry (semi-wet) from 5.7 to 2.5 cal ka BP; relatively cool and wet from 2.5 to 1.1 cal ka BP; and cold and dry from 1.1 cal ka BP to present. Mid-late Holocene climate in the north of Bayan Har Mountains was significantly unstable during the last 7.3 ka and characterized by five centennial-scale oscillations: 6.2‒6.0, 4.3‒3.9, 2.5‒2.1, 1.7‒1.4, and 0.7‒0.2 cal ka BP. This mid-late Holocene climate recorded by peat bog deposits is consistent with most lacustrine sediment records in the north of Bayan Har Mountains and its adjacent areas. These lacustrine sediments indicated that the climate on the northeastern Tibetan Plateau was warm and humid in the early Holocene, cold and dry after the mid-Holocene (ca. 7.5‒6.0 cal ka BP), and relatively cool and wet in the late Holocene.

Permafrost degradation on the Qinghai-Tibet Plateau (QTP) will substantially alter the surface runoff discharge and generation, which changes the recharge processes and influences the hydrological cycle on the QTP. Hydrological connections between different water bodies and the influence of thawing permafrost (ground ice) are not well understood on the QTP. This study applied water stable isotopic method to investigate the permafrost hydrological variabilities in Beiluhe Basin (BLB) on Central QTP. Isotopic variations of precipitation, river flow, thermokarst lake, and near-surface ground ice were identified to figure out the moisture source of them, and to elaborate the hydrological connections in permafrost region. Results suggested that isotopic seasonalities in precipitation is evident, it is showing more positive values in summer seasons, and negative values in winter seasons. Stable isotopes of river flow are mainly distributed in the range of precipitation which is indicative of important replenishment from precipitation. δ 18 O, δD of thermokarst lakes are more positive than precipitation, indicating of basin-scale evaporation of lake water. Comparison of δ I values in different water bodies shows that hydrology of thermokarst lakes was related to thawing of permafrost (ground ice) and precipitation. Near-surface ground ice in BLB exhibits different isotopic characteristics, and generates a special δD-δ 18 O relationship (freezing line): δD = 5.81δ 18 O–23.02, which reflects typical freezing of liquid water. From isotopic analysis, it is inferred that near-surface ground ice was mainly recharged by precipitation and active layer water. Stable isotopic and conceptual model is suggestive of striking hydrological connections between precipitation, river flow, thermokarst lake, and ground ice under degrading permafrost. This research provides fundamental comprehensions into the hydrological processes in permafrost regions on QTP, which should be considered in investigating the influence of thawing permafrost on the hydrological cycle on QTP.

The electrical resistivity tomography and vegetation surveys were conducted for investigating the distribution of frozen ground and other engineering geological characteristics at four representative sites (BHP, XFB, WLG, and XAZ) along the China-Russia Crude Oil Pipelines (CRCOPs) I and II. The comprehensive analysis shows that CRCOPs play an important role in forming and connecting supra-permafrost subaerial taliks and in facilitating thermokarst landforms, further accelerating permafrost degradation. The survey results indicate that on 15–29 August 2019, the permafrost base under the CRCOP at the XFB site was 21.5 m in depth, that of WLG site was 21.5 m (32.8 m at the undisturbed sites), and that of XAZ site, 37.3 m; the permafrost table of XFB site was 6.72 m (4.97 m on 20 m away from the pipeline), that of WLG site was 8.64 m (1.94 m at the undisturbed sites), and that of XAZ site was 6.72 and 3.38 m on the southern and northern slopes; the hydrothermal influences of CRCOPs extended horizontally to about 60 m away from the pipelines, but the vertical hydrothermal impacts were largely limited to about 10–15 m in depth at the BHP site in the zone of deep (>1.5 m) seasonal frost. The extent of engineering influences from the pipelines and associated engineering activities in patchy and island permafrost are evidently larger than those in seasonal frost. The sites with substantial changes are found in pipeline foundation soils underlain by warm (> − 1 °C; thermally unstable) and ice-rich permafrost. This study can timely help decision makers mitigate frost hazards in a proactive manner.

Timely and proper backfilling of open-pits in strip coal-mines has been an effective measurement for the recovery of the hydrothermal regimes and ecological environment in permafrost regions. In this study, numerical simulations and statistical regressions were applied for analyzing the recovery processes of the backfill and its major influencing factors for the thermal equilibrium in recently backfilled open pits at the Gulian strip coalmine in Mo'he, Northeast China. Results show that the thermal recovery time of backfilled areas is positively correlated to the backfill depth (BD) of the soils, the backfilled soil temperature (BST), and the mean annual ground surface temperature (MAGST); meanwhile, climate warming can impact on thermal regimes of the backfill area. The impact of climate warming on ground temperature of the backfill will show up significantly in about 50 years after backfilling (BD at 10.0 and 20.0 m, BST at 20.0°C) under the climate warming scenario (CWS) of 0.025°C·year−1. Grey-relation analyses show that the sensitivity of the backfill recovery time declines in the order of the BD, BST and MAGST. On the basis of the abovementioned studies, the layer-by-layer backfilling in cold seasons is advised for more effective and more rapid recovery of thermal regimes of the backfilled open-pits in cold regions.

Study of climatic evolution in the source area of the Yellow River (SAYR) and its mechanisms is of significance for understanding and predicting the climate and environmental changes and permafrost evolution on the northeastern Tibetan Plateau (TP). This study reconstructed the Asian monsoon and climatic evolution in SAYR since 6.1 cal (cal = the calendar year, as below) ka BP in the mid-late Holocene using geochemical parameters (i.e., SiO2/[RO+R2O], SiO2/Al2O3, SiO2/TiO2, SiO2/[Al2O3 + Fe2O3], chemical index of alteration (Al2O3/[Al2O3 + CaO* + Na2O + K2O]), chemical index of weathering (Al2O3/[Al2O3 + CaO* + Na2O]), [CaO + K2O + Na2O]/Al2O3 and K/Na ratios) of peat deposits and AMS 14C chronology. The climate was warm and humid between 6.1 and 5.4 cal ka BP, with weak winter monsoon intensity and strong summer monsoon intensity, and accompanied by strong chemical weathering and leaching. From 5.4 to 1.5 cal ka BP, the climate was relatively cold and dry with enhanced winter monsoon and weakened summer monsoon intensities. During 1.5 and 0.8 cal ka BP, with the winter and summer monsoon changing rapidly, lower winter monsoon intensity, higher summer monsoon intensity, and higher chemical weathering and leaching since 6.1 cal ka BP indicated a warm and humid regional climate. It has been relatively cold and dry as a whole, with a trend of being warm and wet, since 0.8 cal ka BP, accompanied by gradually weakened winter monsoon intensity, gradually enhanced summer monsoon intensity, and gradually enhanced chemical weathering and leaching. The Asian monsoon and climatic evolution process in SAYR is highly unstable and has undergone centennial–millennial scale oscillations since 6.1 cal ka BP. Also, six phases at 6.1–5.9, 4.5–4.2, 2.7–2.4, 1.9–1.7, 1.5–1.4, and 0.6–0.4 cal ka BP correspond with cold events recorded by peat and lacustrine deposits and ice cores on the northeastern and eastern TP and with deep-sea sediments in high-latitude regions in the Northern Hemisphere. The results show that climate change in SAYR on the northeastern TP has been consistent with global climate change since the mid-late Holocene.

Observation data of the hydrothermal processes in the active layer are vital for the verification of permafrost formation and evolution, eco-hydrology, ground-atmosphere interactions, and climate models at various time and spatial scales. Based on measurements of ground temperatures in boreholes, of temperatures and moisture contents of soils in the active layer, and of the mean annual air temperatures at the Qilian, Yeniugou and Tuole meteorological stations in the upper Heihe River Basin (UHRB) and the adjacent areas, a series of observations were made concerning changes in the lower limit of permafrost (LLP) and the related hydrothermal dynamics of soils in the active layer. Because of the thermal diode effect of peat soils, the LLP (at 3600 m) was lower on the northern slope of the Eboling Mountains at the eastern branch of the UHRB than that (at 3650–3700 m) on the alluvial plain at the western branch of the UHRB. The mean temperature of soils at depths of 5 to 77 cm in the active layer on peatlands was higher during periods with subzero temperatures and lower during periods with above-zero temperatures in the vicinity of the LLP on the northern slope of the Eboling Mountains than those at the LLP at the western branch of the UHRB. The thawing and downward freezing rates of soils in the active layer near the LLP on the northern slope of the Eboling Mountains were 0.2 and 1.6 times those found at the LLP at the western branch of the UHRB. From early May to late August, the soil water contents at the depths of 20 to 60 cm in the active layer near the LLP on the northern slope of the Eboling Mountains were significantly lower than those found at the LLP at the western branch of the UHRB. The annual ranges of soil temperatures (ARSTs), mean annual soil temperatures (MASTs) in the active layer on peatlands, and the mean annual ground temperature (MAGT) at a depth of 14 m of the underlying permafrost were all significantly lower near the LLP on the northern slope of the Eboling Mountains. Moreover, the thermophysical properties of peat soils and high moisture contents in the active layer on peatlands resulted in the lower soil temperatures in the active layer close to the LLP on the northern slope of the Eboling Mountains than those found at the LLP at the western branch of the UHRB in the warm season, especially at the deeper depths (20–77 cm). They also resulted in the smaller freezing index (FI) and thawing index (TI) and larger FI/TI ratios of soils at the depths of 5 to 77 cm in the active layer near the LLP on the northern slope of the Eboling Mountains. In short, peatlands have unique thermophysical properties for reducing heat absorption in the warm season and for limiting heat release in the cold season as well. However, the permafrost zone has shrunk by 10–20 km along the major highways at the western branch of the UHRB since 1985, and a medium-scale retrogressive slump has occurred on the peatlands on the northern slope of the Eboling Mountains in recent decades. The results can provide basic data for further studies of the hydrological functions of different landscapes in alpine permafrost regions. Such studies can also enable evaluations and forecasts the hydrological impacts of changing frozen ground in the UHRB and of other alpine mountain regions in West China.

Observational data collection on permafrost and active layer freeze–thaw cycle is extremely limited in the upper reaches of the Heihe River (URHHR) in the Qilian Mountains of the north-eastern Qinghai-Tibet Plateau. It acts as a bottleneck, restricting the hydrological effects of the changes in the permafrost and active layer in the Heihe River Basin. Using soil temperature, moisture and air temperature data collected from the four active layer observation sites (AL1, AL3, AL4 and AL7) established in the alpine permafrost regions in the URHHR, from 2013 to 2014, the region's active layer freeze–thaw cycle and the soil hydrothermal dynamics were comparatively analysed. As the elevation increased from 3700 m a.s.l. to 4132 m a.s.l., the mean annual ground temperatures (MAGTs) of the active layer and the active layer thicknesses (ALTs) decreased, the onset date of soil freeze of the active layer occurred earlier and the soil freeze rate increased. However, the onset date of soil thaw and the thaw rate did not exhibit significant trends. Compared to the thaw process, the duration of the active layer freeze process was significantly shortened and its rate was significantly higher. The soil freeze from bottom to top did not occur earlier than that from top to bottom. Furthermore, as elevation increased, the proportion of the bottom-up freeze layer thickness increased. The soil moisture in the thaw layer continuously moved to the freeze front during the active layer's two-way freeze process, causing the thaw layer to be dewatered. The seasonal thaw process resulted in significant reduction of the soil water content in the thaw layer, accounting for the high ice content in the vicinity of the permafrost table. Controlled by elevation, the active layer's seasonal freeze–thaw cycle was also affected by local factors, such as vegetation, slope, water (marsh water and super-permafrost water), lithology and water (ice) content. This study provides quantitative data that identify, simulate and predict the hydrological effects of the changes in the permafrost and active layer of the Heihe River Basin.

The Headwater Region of the Yellow River (HRYR) is the catchment upstream of Duoshi Gorge, covering an area of 29,588 km2. The HRYR is located in the northeastern Tibet Plateau with an altitude higher than 4000 m above sea level, and is especially sensitive to climate change. Since the late 19th century, the mean annual temperature in Tibet Plateau has increased sharply. As a result of increasing air temperature, a significant number of environmental problems have occurred during the past decades, including aeolian desertification. In recent decades, aeolian desertification has become a severe environmental problem in the Tibet Plateau due to permafrost degradation, because permafrost plays an important role in maintaining the grassland vegetation. With the increase in ground temperature, the aeolian activity in the HRYR is likely to become more serious. However, the history of aeolian activity in the HRYR remains unknown due to a lack of chronological studies. In this study, 15 Optical Stimulated Luminescence (OSL) ages from three typical sections were used to reveal the history of aeolian activities in the HRYR during the Holocene. All of the OSL ages were late Holocene, and the oldest age is 2.13 ± 0.16 ka BP. The relative young OSL ages and deep aeolian sediment indicated very high sedimentation rates in the late Holocene, especially after around 1 ka BP. The intensive aeolian activity and low TOC content indicate a drier climate in the late Holocene. The well-sorted sediments and similar grain size distributions of the three sections imply their similar wind regimes. Based on the evolution history of the Yellow River's headward erosion, it is inferred that little aeolian activity occurred in this region during the early and mid-Holocene.

In cold regions, the occurrence of frozen ground has a fundamental control over the character of the water cycle. To investigate the impact of changing ground temperature conditions on hydrological processes in the context of climate change, a distributed hydrological model with an explicit frozen ground module was applied to an alpine watershed in the upstream area of the Hei'he River in the Qilian Mountains, northwest China. After evaluating the base model, we considered scenarios of frost-free ground and climate change. Results showed that the base model with a frozen ground module successfully captured the water balance and thermal regimes in the basin. When the frozen ground module was turned off, the simulated groundwater recharge and base flow increased by a factor of two to three because surface runoff caused by exceeding infiltration capacities at high elevations, which occurred in the base model, was eliminated. Consequently, the river hydrograph became smoother and flatter, with summer flood peaks delayed and reduced in volume. The annual mean depth where subsurface runoff was generated, was about 2.4 m compared to 1.1 m in the base model. For a warming climate, a combination of increasing evapotranspiration and reducing permafrost area results in smoother and flatter hydrographs, and a reduction in total river discharge. Although our analysis using numerical models has its limitations, it still provides new quantitative understanding of the influences of frozen ground and climate change on hydrological processes in an alpine watershed. Copyright © 2016 John Wiley & Sons, Ltd.

On-site monitoring is very important for understanding formation mechanisms of frost hazards frequently occurring in pipeline foundation soils and for designing and deploying according mitigative measures in permafrost regions. Significant thaw subsidence of ground surfaces along the China-Russia Crude Oil Pipeline (CRCOP) from Mo'he to Daqing, Heilongjiang Province, Northeast China have been observed at some segments underlain by ice-rich, warm (>1.0°C) permafrost since the official operation in January 2011. Recent monitoring results of the thermal states of foundation soils at the kilometer post (KP) 304 site along the CRCOP are presented in this paper. The results indicate that during the period from 2012 to 2014, shallow soils (at the depths from 0.8 to 4.0 m from ground surface) has warmed by approximately 1.0°C in the lateral range of 1.2 to 2.1 m away from the pipeline axis, and deeper permafrost (such as at the depth of 15 m, or the depth of zero annual amplitude of ground temperatures) by 0.08°C per year 4 m away from the pipe axis, and 0.07°C per year 5 m away from the pipeline axis. The results indicate an all-season talik has developed around and along the CRCOP. The thaw bulb, with a faster lateral expansion (compared with the vertical growth), enlarges in summer and shrinks in winter. This research will provide important references and bases for evaluating thermal influences of warm pipeline on permafrost and for design, construction, operation and maintenance of pipelines in permafrost regions.

Observational data on permafrost and active layer soil hydrothermal processes are extremely limited in the upper reaches of the Heihe River (URHHR) in Qilian Mountains. This lack acts as a bottleneck, restricting the research on the hydrological functions of different landscapes and the hydrological effects of the changes in the permafrost and active layer in the alpine permafrost regions of the Heihe River Basin. The active layer seasonal freeze-thaw processes and the soil hydrothermal dynamics and influencing factors were analyzed using soil temperature and water content observation data of the active layer established on the north slope of Ebo Mountains (NSEBM) in the east branch and in the alluvial plain in the west branch in alpine permafrost regions in the URHHR from 2013 to 2014. The results showed that climatic conditions in the alpine permafrost regions and local factors, such as topography, geomorphology, vegetation, lithology, and soil water content, evidently affected the active layer seasonal freeze-thaw processes and soil hydrothermal dynamics, and the main influence factors also contained snow, water, and winter temperature inversion. The annual surface temperature range (ASTR), mean annual ground temperatures (MAGTs) of the active layer, ground temperature at the bottom of the active layer (TTOP), and MAGT at the depth of zero annual amplitude were lower by 8.8, 0.6 to 1.7 (at depths of 5–77 cm), 0.7, and 0.7°C, respectively, on the NSEBM than at the same elevation in the west branch. Compared with the active layer at the same elevation in the west branch, the active layer onset date of soil thaw on the NSEBM occurred earlier. Moreover, the date reaching the maximum thaw depth occurred later, the duration of the seasonal thaw process was significantly longer, and the rate of the seasonal thaw process was lower. With the later active layer onset date of soil freeze from the ground surface downward, the duration and the rate of the seasonal freeze process on the NSEBM was longer and lower, respectively. Furthermore, the duration of the completely frozen stage on the NSEBM was longer. The active layer onset date of the thaw-rising stage, the relative completely thaw stage, the freeze-fall stage, and the completely frozen stage on the NSEBM lagged significantly from top to bottom, whereas that of the last three stages were evident at the same elevation in the west branch. The rate of change in the active layer soil water content at depths of 20–60 cm at the thaw-rising stage and the freeze-fall stage was both significantly higher on the NSEBM. In addition, the active layer soil water content at the depths of 20–60 cm from the mid- to late completely frozen stage in the beginning of the year to the early thaw-rising stage was lower on the NSEBM. These results were mainly due to the effects of local factors, such as the soil particle composition, dry density, ice content, and organic matter content on the active layer soil water dynamics. This study provides basic data that identify, simulate, and predict the hydrological functions of different landscapes and the hydrological effects of the changes in the permafrost and active layer of the Heihe River Basin. Our study can also provide a reference for the study of seasonal freeze-thaw processes and influencing factors in permafrost regions with different climate types, such as other alpine areas in Western China, the north-eastern Qinghai-Tibet Plateau, Northeast China, and even in the Arctic or sub-Arctic.

The China–Russia Crude Oil Pipeline (CRCOP) was built to transport Siberian crude oil across 1030 km of frozen ground. The Chinese portion of the CRCOP crosses 441 km of discontinuous permafrost zones along the eastern flanks of the Da Xing'anling (Hinggan) Mountains. Significant thaw settlement of some of the pipeline foundation soils has occurred since the pipeline began operating in January 2011. The differential thaw settlement around the pipeline at the transitions between the thaw-settling and thaw-stable zones may lead to displacement or even buckling of the pipeline. To evaluate the engineering safety and long-term stability of pipeline foundations, ground-penetrating radar (GPR) was used to detect the freeze–thaw states of pipeline foundation soils in the permafrost zones. From April 2012 to November 2013, a total of 2780 m of GPR profiles and 62 cross-sections (perpendicular to the CRCOP route) were obtained at eight GPR study sites on various terrains and vegetative coverage, with different thermal insulation configurations around the pipe, and with and without thermosyphons installed. The GPR profiles were interpreted and cross-checked with data from drilling, hand-dug pit or trench excavations, and ground temperature measurements. The results showed that the foundation soils around the pipeline were thawing, with maximum thaw depths under the pipeline of about 1.1 m to 4.5 m from the pipe bottom and increased maximum thaw depths of 0.5 m to 3.7 m during the period of this study. However, GPR profiles from the areas with dense vegetative coverage, and with pipe insulation of 80-mm-thick extruded polystyrene (XPS), and also with vertical thermosyphons installed, showed that permafrost foundation soils were thermally better protected, with only minor thaw settlement. The thermal states of pipeline foundation soils and the underlying permafrost varied markedly with different terrains. The drainage patterns and engineering activities, especially the heating from operating oil flows at an average annual oil temperature of 7.7 °C (with a range of 0.7 °C to 20.4 °C) along the pipeline route may have been responsible for the extensive and substantial thaw subsidence in the ice-rich permafrost zones. Additionally, there was positive feedback between the thaw subsidence of ground surface in the vicinity of the pipeline route and the thaw settlement of the pipeline foundation soils. The greater the earth surface subsidence, the more surface water ponding and soil disturbances, and even more progressive thawing. Therefore, some measures are recommended for stabilizing the pipeline foundation soils. The research results also indicate that the GPR method is effective, nondestructive, and convenient for evaluating the spatiotemporal extent and development processes of the freeze–thaw states of pipeline foundation soils and the underlying permafrost.

Considering the widespread distribution of thermokarst lakes and their significant influence on the hydrological cycle in permafrost regions on the Qinghai–Tibet Plateau (QTP), it is necessary to study their hydrological regimes, which are responding to ongoing climate-induced permafrost thaw. In this paper, water isotopic tracers were used to assess the temporal and interannual hydrological variations and the hydrological processes of two thermokarst lakes (TL-A and TL-B) associated with thawing permafrost in Beiluhe Basin on the QTP. The isotopic results revealed significant differences between the two thermokarst lakes: the TL-A showed more positive isotopic values and small fluctuations than TL-B did. This can be attributed to the hydrological discrepancies between them. Based on the water isotopic mass balance (IMB) model and estimated evaporation, the contributions of permafrost melt water and precipitation to the thermokarst lakes were determined. In both 2011 and 2012, the contributions of thawing permafrost water to thermokarst lakes were of significance, as high as 61.3%. The modeled isotopic composition of input water ( δ I ), and the relationships between climatic factors and lake water isotopes were evaluated. Results suggested that the two lakes originated from multiple sources and confirmed the modeling process well. It also indicated that thawing of permafrost significantly affected the development and hydrological regime of thermokarst lakes on the QTP. It is necessary to emphasize the significant impact of thawing permafrost on the thermokarst lakes on the QTP. Findings demonstrate that ongoing permafrost thaw may have major implications for thermokarst landscapes as climate change continues.

This paper examines the relationship between the extent of permafrost during the Last Permafrost Maximum (LPM, largely between 22 and 17 ka BP) and the altitudinal and latitudinal temperature gradients that controlled its extent. The region chosen, namely, the Qinghai-Tibet Plateau and the transition to the northern adjacent plains in the North China Plain, is of relatively limited extent in order to avoid regional effects. This area extends over 15 degrees of latitude while altitudes vary from 1000 to 1500 m above sealevel (asl) in the northern plains to more than 4000 m asl in the central-to-south part of the Qinghai-Tibet Plateau. The respective lowest southernmost permafrost occurrences at a northern and a southern position are used for reconstruction of the latitudinal and altitudinal gradients. As a first approximation, we conclude that the elevation compensation during the LPM for a 1° latitude change was between 309 m and 385 m. This is considerably higher than the value calculated for existing permafrost in the region that uses thermal data at a depth of zero amplitude change (139–198 m altitudinal compensation for 1° latitude).

A comprehensive observing system was established at the Da Xing'anling (Hinggan) Mountains Station (Gen'he) of China Forest Ecological Research Network (CFERN) in Northeast China in 2009 and gradually improved since in order to evaluate the influences of boreal forest vegetation with complex structures and various components on the thermal regimes of active layer and shallow permafrost soils. At three selected typical forest sites with similar micro-reliefs, soils, and drainage conditions, the soil temperatures on the ground surface and at various depths ranging from 0.05 to 5.0 m were measured with thermistor cables permanently installed in boreholes. The temperature data were compared and contrasted for various vegetative features. In a control experiment, trees and shrubs were removed to better understand the hydrothermal effects of vegetation removal. Results show that: (1) The vegetative layer provides an evident effect of thermal insulation on the ground. The ground temperature at the same ...

Inactive ice wedges are still present today at Yituli'he in the middle Da Xing'anling (Greater Hinggan) Mountains in northeastern China, which is the southernmost known site (50°37′N) with ice wedges in the Northern Hemisphere. However, it is uncertain whether the ice-wedge isotope composition, characterized by low δ18O, δD and low deuterium excess values, is representative of the isotope signature of a broader region. In this paper, the ice-wedge isotope compositions were examined in the context of the stable isotopes of precipitation from the nearby Global Network of Isotopes in Precipitation (GNIP) stations. In addition, the pollen spectra from the host sediments were analysed to provide additional information on local vegetation in order to better understand the climate conditions favouring ice-wedge formation. The pollen spectra suggest that the Yituli'he ice wedges developed during the colder and wetter period after 6000 cal. a BP. The isotopes in the Yituli'he ice wedges are consistent with the isotope background recorded in atmospheric precipitation collected at the nearby GNIP stations. When the snow-melt froze into ice veinlets, the isotope signals did not change substantially because of the strong, cold, continental anticyclones in winter as well as a strong temperature inversion that prevail in the Da Xing'anling Mountains. As the climate pattern did not change substantially, the neoglacial cold period is unlikely to have allowed for strong secondary fractionation of isotope records during ice-wedge formation. Thus, the annual isotope signature can be interpreted as a valid archive of climate data.

This paper accompanies a map that shows the extent of permafrost in the Northern Hemisphere between 25 and 17 thousand years ago. The map is based upon existing archival data, common throughout the Northern Hemisphere, that include ice-wedge pseudomorphs, sand wedges and large cryoturbations. Where possible, a distinction is made between areas with continuous permafrost and areas where permafrost is either spatially discontinuous or sporadic. The associated mean annual palaeo-temperatures that are inferred on the basis of present-day analogues increase understanding of the possible changes in permafrost extent that might accompany current global warming trends. Areas with relict permafrost and areas that were formerly exposed due to lower sea level (submarine permafrost) are also mapped. Mapping is mostly limited to lowland regions (areas approximately

Recent investigations into relict periglacial phenomena in northern and western China and on the Qinghai-Tibet Plateau provide information for delineating the extent of permafrost in China during the Late Pleistocene. Polygonal and wedge-shaped structures indicate that, during the local Last Glacial Maximum (LLGM, between approximate to 35 and 10.5ka BP), the southern limit of latitudinal permafrost in northern China advanced southward at least to approximate to 38-40 degrees N in the east and to approximate to 37-39 degrees N in the west. This represents an advance of about 5-10 degrees of latitude beyond present-day permafrost limits. The lower limits of elevationally controlled permafrost on the Qinghai-Tibet Plateau and its peripheries were about 1000m lower: this permafrost was largely continuous during the LLGM. This suggests a cooling of between 4 and 10 degrees C, or more. This paper discusses the extent of permafrost during the LLGM and presents maps that have been constructed on the basis of extensive and integrative analysis of all reliable and pertinent data. The results indicate that the extent of LLGM permafrost in China was between approximate to 3.8 and 4.3x106km2. This is 80 to 100% more than that of approximate to 2.15x106km2 in the 1970s, and 120 to approximate to 150% more than that of approximate to 1.75x106km2 today.

The source region of the Yellow River, located in the northeastern portion of the Qinghai–Tibet Plateau, plays a critical role in water conservation, biodiversity protection, and wetland conservation. Aeolian desertification of this area is an important concern. Remote sensing and GIS technology were employed to assess the trends in aeolian desertification from 1975 to 2005. The monitoring results showed that, aeolian desert land increased from 15,112 to 17,214 km2 during 1975–2005. In addition, it was found that the area of aeolian desertification increased rapidly from 1975 to 1990, was stable from 1990 to 2000, and slightly decreased from 2000 to 2005. Increasing temperature, overgrazing, and drainage of wetlands have been key driving factors of aeolian desertification. Thus, to control the expansion of aeolian desert lands in the source region of the Yellow River and to rehabilitate existing desert areas, the priority should be given to altering human behavior in these areas.

To better understand the ecological and hydrological responses to climatic and cryospheric changes, the spatiotemporal variations in the active layer thickness (ALT) need to be scrupulously studied. Based on more than 230 sites from the circumpolar active layer monitoring network, the spatiotemporal characteristics of the ALT across the northern hemisphere during 1990–2015 were investigated. Results indicate that the ALT exhibits substantial spatial variations across the northern hemisphere, ranging from approximately 30 cm in the arctic and subarctic regions to greater than 10 m in the mountainous permafrost regions at mid-latitudes. Regional averages of ALT are 48 cm in Alaska, 93 cm in Canada, 164 cm in the Nordic countries (including Greenland and Svalbard) and Switzerland, 330 cm in Mongolia, 476 cm in Kazakhstan, and 230 cm on the Qinghai-Tibetan Plateau (QTP), respectively. In Russia, the regional averages of ALT in European North, West Siberia, Central Siberia, Northeast Siberia, Chukotka, and Kamchatka are 110, 92, 69, 61, 53 and 60 cm, respectively. Increasing trends of ALT were not uniformly present in the observational records. Significant changes in the ALT were observed at 73 sites, approximately 43.2 % of the investigated 169 sites that are available for statistical analysis. Less than 25 % Alaskan sites and approximately 33 % Canadian sites showed significant increase in the ALT. On the QTP, almost all the sites showed significant ALT increases. Insignificant increase and even decrease in the ALT were observed in some parts of the northern hemisphere, e.g., Mongolia, parts of Alaska and Canada. The air and ground temperatures, vegetation, substrate, microreliefs, and soil moisture in particular, play decisive roles in the spatiotemporal variations in the ALT, but the relationships among each other are complicated and await further studies.

Many permafrost maps in China have been compiled since the early 1960s. The scales of these maps range from the local (1:600 000) to the regional scale (1:10 000 000). The permafrost classification systems differ among these maps. The indices for permafrost classification used in these mapping projects include spatial continuity (areal extent) and thickness of the permafrost, air and ground temperatures and ground -ice content. All of those data have been retrieved, digitised and published in the Environmental and Ecological Science Data Center for West China. These maps represent the best understanding at the time regarding the distribution of permafrost in China and its changes over the past century. An updated map of permafrost in China, including frozen ground area, is also provided. The total area of permafrost in China is estimated at ~ 1.59 × 106 km2 (glaciers and lakes excluded), and the area of seasonally frozen ground (excluding instantaneous frozen ground) is ~ 5.36 × 106 km2. The total area of high-altitude (plateau and mountain) permafrost in China is ~ 1.35 × 106 km2, the area of mountain permafrost is ~ 0.30 × 106 km2 and the area of plateau permafrost is ~ 1.05 × 106 km2. The latitudinal permafrost is located in the northern part of northeastern China, and its area is ~ 0.24 × 106 km2. Additionally, some suggestions are proposed for future mapping of permafrost in China. Copyright © 2012 John Wiley & Sons, Ltd.

The significant changes of cryosphere on the Tibetan Plateau (TP) are an important cause of concern for the huge population in Asia which depends on the glacier-permafrost feed rivers. Up to now, little is known about the response of runoff to the cryospheric changes under a warming climate. Taking an example of a typical alpine river (hereafter named KLR River) in Kunlun Mountains Pass on the TP to investigate the hydrological processes and quantify the potential recharge sources using stable isotopes and electrical conductivities. The results showed significantly temporal variations in isotopes of precipitation and river water. Deviations in the precipitation isotopes indicated that precipitation in Kunlun Mountains Pass during summer months mainly originated from local recycled moisture and slightly influenced by monsoon. The KLR river was separated into three hydrological components which include precipitation, meltwater of glacier and meltwater of subsurface ground ice. On average, the meltwater of glacier accounted for 56.64 % of total flow, whereas the meltwater of subsurface ground ice contributed 37.44 % and only 5.92 % was supplied by precipitation. Evidently, the contributions of glacier and thawing permafrost are up to as high as 94 %. The cryosphere played a crucial role on the hydrological cycle on the TP which would be important to understand the water resource distribution in permafrost regions on the TP under the global warming.

The design and building of a pipeline in permafrost regions challenge engineers and scientists in many regards, and the geohazards resulting from the (differential) frost heaving and thaw settlement of the pipeline foundation soils present one of the most daunting tasks. The China–Russia Crude Oil Pipeline, a spur line from the Siberia–Pacific Pipeline System, presented unique scientific and engineering problems because of: 1) extensive presence of the more ice-rich permafrost in boreal forests and swamps; 2) an insistence on a buried construction mode because of concerns about the potential for frequent forest fires and other safety issues; 3) great uncertainties in the temperatures of oil being transported although the given estimated oil temperature of − 6.4 to + 3.6 °C entering the Mo'he Pump Station, and the estimated oil temperatures could vary from about − 6 to + 10 °C along the southward pipeline route; 4) the limited lead time for detailed surveys on engineering geology along the pipeline routes and for engineering design; 5) very much limited investment and a limited number of engineers experienced in designing and building a major pipeline in an area where about one-half of its length would be impacted by generally warm (− 3 to 0 °C) permafrost. Nevertheless, the pipeline engineers and permafrost scientists strived to economically build and satisfactorily operate the first major crude oil pipeline in the boreal ecosystem in China. The major results on the formation mechanisms and mitigative measures for the (differential) frost heave and thaw settlement were presented in the eight papers in this special issue on permafrost pipeline, and one additional paper on the Golmud–Lhasa Oil Products Pipeline on the Qinghai–Tibet Plateau was also included. They may provide insights to the understanding of pipeline–permafrost interactions and benefit the future design and construction of pipelines in similar northern environments.

The China–Russia Crude Oil Pipeline (CRCOP), 813 mm in diameter, is designed to transport 603,000 barrels of Siberian crude oil per day across 1030 km of frozen-ground. About 500 boreholes, with depths of 5 to 20 m, were drilled and cored for analyses, and the frozen-ground conditions were evaluated. After detailed surveys and analyses of the permafrost conditions along the pipeline route, a conventional burial construction mode at a nominal depth of 1.5 m was adopted. This paper discusses the principles and criteria for the zonation and assessment of the frozen-ground environments and conditions of engineering geology for the design, construction, and operation of the pipeline system based on an extensive and in-depth summary and analysis of the survey and exploration data. The characteristics of pipelining crude oil at ambient temperatures in the permafrost regions and the interactive processes between the pipeline and foundation soils were taken into account. Two zones of frozen-ground environment and conditions of engineering geology, i.e., seasonally-frozen-ground and permafrost, were defined on the basis of the regional distribution and differentiations in frozen-ground environments and conditions. Then, four subzones of the permafrost zone were classified according to the areal extent, taking into consideration the temperatures and thicknesses of permafrost, as well as changes in vegetation coverage. In the four subzones, 151 sections of engineering geology were categorized according to the ice/moisture contents of the permafrost, as well as the classes of frost-heaving and thaw-settlement potentials. These 151 sections are comprehensively summarized into four types for engineering construction and operation: good, fair, poor, and very poor, for overall conditions of engineering geology. The zonation, assessment principles and criteria have been applied in the design of the pipeline. They have also been used as the scientific bases for the construction, environmental management, operation and maintenance/contingency plans.

The 1076-km-long Golmud–Lhasa oil product pipeline is located closely parallel to the highway constructed 20 years earlier within the relatively narrow north–south engineering corridor crossing the treeless central area of the Qinghai–Tibet Plateau. Much of the corridor is at elevations exceeding 4500 m and high-elevation, generally warm permafrost is encountered in more than one-half of the length. The pipeline, transporting mostly diesel, motor and aviation fuels at ambient temperatures, is 159 mm in diameter, has a wall thickness of 6 mm and was buried in a trench at a nominal depth of between 1.2 and 1.4 m. The soils encountered, mostly periglacial sands, silts and gravels, often have elevated saline contents and are subject to severe wind erosion and occasional monsoon flash flooding conditions. During its first quarter century of operation, the pipeline suffered at least 30 significant leaks and four pipeline ruptures. About 337 km of the pipeline was extensively rehabilitated, including relocations or replacements in major problem areas and, where feasible for an existing pipeline, improvements in pipeline protection during 2001–2004. It was supposed to safely operate for another 30 years with proper checks and needed repairs. This paper provides a review on the history of the permafrost and cold regions environmental problems of the pipeline, and their major rehabilitation, repairs and problems in the future, which might have useful implications for similar oil product pipeline at high elevations or permafrost regions.

Using the finite element method, thermal effects of the Chinese–Russian crude oil pipeline in permafrost regions were estimated under two construction modes (conventional burial and aboveground embankment), two thermal control techniques (bare and insulated pipe), and three climate conditions along the route (marked under the natural mean ground surface temperatures of − 0.5, − 1.0, − 1.5 °C, respectively). The results show that with the silt embankment on gravel berm and the insulated pipe, the thaw of permafrost under the pipeline could be prevented during its service life. However, thawing of the permafrost under the conventionally buried pipeline cannot be prevented regardless of climate conditions or thermal insulation around the pipe. So it is strongly recommended that over-excavation and/or thermosyphons be applied for the conventional burial construction mode, especially in the warm and ice-rich permafrost sections to mitigate frost heave and thaw settlement in the subsoil.

Basin morphology and depositional stratigraphy of Lake Donggi Cona on the north-eastern Tibetan Plateau has been studied with echo depth sounding and shallow seismic sub-bottom profiling. The basin is a pull-apart structure situated at the highly active Kunlun fault. It is characterised by a 92 m deep graben structure in the western part of the lake basin, and a shallow eastern lake part, the latter filled up with fluvial sediments from a large alluvial plain. Three prominent morphological levels were identified at 24 m, 39 m and 57 m below present lake level. They were partly created by basin subsidence, while the deposition of prograding delta sediments primarily formed the morphological steps. The inherited tectonic structures control on-going neotectonic activity, which seems to have only minor influence on present basin morphology. The basin is filled by sediments of at least 30 m thickness in the depocentre. Three major depositional units can be distinguished. In comparison with lithological changes in a sediment core, they give evidence of pronounced lake-level fluctuations and dramatic changes in lake volume. A numerical age datum of w19 cal ka BP at the base of the sediment core allows a tentative reconstruction of Late Glacial to Holocene lake development. A very low base level preceded a time of delta formation during higher lake level, i.e. w26 m lower than present during Last Glacial Maximum, creating a lake of only 18% of its present size. At the transition to Holocene the lake-level rose very quickly changing to a deep lake environment. Thus, transgression may have promoted maximum lake stands.

A calibration data set of 51 surface sediment samples from Lake Donggi Cona on the northeastern Tibetan Plateau was investigated to study the relationship between sub-fossil ostracod assemblages and water depth. Samples were collected over a depth range from 0.6 to 80 m. A total of 16 ostracod species was identified from the lake with about half of the species restricted to the Tibetan Plateau and its adjacent mountain ranges and poorly known in terms of ecological preferences, and the other half displaying a mainly Holarctic distribution. Living macrophytes and macroalgae were recorded in Lake Donggi Cona down to a depth of about 30 m, and bivalve (Pisidium cf. zugmayeri) and gastropod (Gyraulus, Radix) shells were found down to depths of 43 and 48 m, respectively. The ostracod-water-depth relationship was assessed by multivariate statistical analysis and ostracod-based transfer functions for water depth were constructed. Weighted averaging partial least squares (WA-PLS) regression provided the best model with a coefficient of determination r 2 of 0.91 between measured and ostracod-inferred water depth, a root mean square error of prediction of 8% and a maximum bias of 10.6% of the gradient length, as assessed by leave-one-out cross-validation. Our results show the potential of ostracods as palaeo-depth indicators in appropriate settings. However, transfer-function applications using fossil ostracod assemblages for palaeo-depth estimations require a thorough understanding of the palaeolimnological conditions of lakes and therefore detailed multi-proxy analysis to avoid misinterpretation of ostracod-based inferences.