In permafrost terrains, the frozen-unfrozen boundary, located at the base of the active layer, is a prominent ground-penetrating radar (GPR) target and is typically used to retrieve active layer thickness. Less attention has been given to the capability of the GPR in detecting structures within the active layer. In this paper, using 500 MHz GPR data from a thermokarst site in the Arctic Coastal Plain, we demonstrate that GPR can retrieve, when present, the internal stratigraphy of the thawed layer. We recognized two types of thermokarst-related microtopographic units: dry-and-uniform peaty hummocks with a thin (∼30 cm) active layer and inter-hummock depressions with a thicker (∼60 cm) active layer characterized by two different layers—a surface peat layer on top of silt confirmed by test pits. Radar wave velocity analysis, done with a common-midpoint survey, suggests a contrast in volumetric water content (87% and 45% for the upper and lower layers, respectively). The subsurface radar wave velocity suggests that the porous peat layer contains more water (87% by volume) than the underlying silt layer (45% by volume), resulting in a strong dielectric contrast and a strong radar reflection. This study demonstrates the usefulness of GPR to measure the thickness and properties of the surface organic layer in permafrost regions.

The sensitivity of soil carbon and nitrogen to warming is a major uncertainty in projections of climate. However, previous studies about soil organic carbon (SOC) stocks and potential emission predominantly concentrated on the shallow soil layer in high latitude ecosystems. In this study, we analyzed the SOC, total nitrogen (TN) and soil inorganic carbon (SIC) stocks, C/N ratios, and stable carbon isotope (δ¹³C) in the active layer and permafrost layer on the Eboling Mountain in the upper reach of Heihe River basin, northwestern China. Our results showed that the average stocks of SOC, TN, and SIC in permafrost layer above soil parent materials (71.7 kg m^-2, 8.0 kg m^-2, 34.7 kg m^-2) were much higher than those in the active layer (44.3 kg m^-2, 5.3 kg m^-2, 12.2 kg m^-2). The δ¹³C pattern in the soil profiles indicated that historical drainage conditions and pedogenesis were important factors in determining soil organic matter (SOM) stocks in this permafrost region. The δ¹³C and C/N ratios of the transient layer and some layers of permafrost implied that the degradation of SOM was different. These results highlight that carbon and nitrogen in permafrost regions with Alpine Kobresia meadow could make significant contribution to China's terrestrial carbon cycle.

This paper aims to provide a long time-series data set documenting the surface soil freeze-thaw cycles in China over a period of more than 30 years. The remote sensing data are from the daily brightness temperatures recorded by the Scanning Multichannel Microwave Radiometer (SMMR, 1978–1987) and Special Sensor Microwave Imager (SSM/I, 1987–2008), which have a 25 km spatial resolution. The classification method used to identify the surface soil freeze-thaw states is a dual-indices algorithm based on the 37 GHz vertical polarization brightness temperature and spectral gradient between the 37 GHz and 18/19 GHz brightness temperatures. This algorithm has been recalibrated for SMMR and SSM/I using the in situ daily minimal ground surface temperatures observed at 77 meteorological stations covering the dominant land surface types of China. The daily classifications of surface soil freeze-thaw states were validated by observations from an additional 273 meteorological stations. The classification accuracy of the frozen and thawed soils as well as the total accuracy exceed 80%. Based on this data set, we analyzed the seasonal and interannual variations across the areal extent and timing of surface soil freezing, trend of the onset date of surface soil freezing and thawing, and duration of surface soil thawing in China. The results showed that the maximum frozen extent during 1978–1987 was 6.93 × 10⁶ km² or 72.8% of the area, and it generally occurred in late December and January. The minimum frozen extent was 0.26 × 10⁶ km² or 3.0% of the area, and it occurred in late July and August. The first day of soil freezing occurred between September and November, whereas the first day of soil thawing occurred between March and May. The trend analysis demonstrated that from 1978 to 2008, the onset date of surface freezing was postponed by 19.6 ± 14.6 days, whereas the onset of surface thawing was advanced by -19.0 ± 9.4 days, and the thawing period was prolonged by 34.3 ± 16.5 days. These trends revealed a pattern of earlier thawing, later freezing, and longer growing seasons because of climate warming, especially in the seasonally frozen ground and permafrost regions with high ground temperatures.

Investigation of the changes in soil thermal regimes is essential to the understanding of ecohydrological processes, resource development, and climate change. We use soil temperatures from 12 meteorological stations of the China Meteorological Administration in the Heihe River Basin to estimate soil seasonal freeze depth, the onset and end dates of soil freeze, and the duration of soil freeze. Based on the characteristics of the soil temperature in the seasonal freezing layer, the freeze/thaw processes of this layer were divided into four stages: the winter freezing stage, spring thawing stage, summer warming stage, and autumn cooling stage. Spring, summer, autumn, and winter ground surface temperatures in the basin exhibit significant increasing trends in 1972–2006, of 0.65 °C decade^-1, 0.73 °C decade^-1, 0.48 °C decade^-1, and 0.44 °C decade^-1, respectively. Mean annual soil temperature at 0.0–0.20 m depths reveals an increasing trend of 0.58–0.63 °C decade^-1 in 1972–2006. The onset date of soil freeze, the end date of soil freeze, and the duration of soil freeze in 1972–2006 exhibit a statistically significant trend of 2 days decade^-1, -4 days decade^-1, and -6 days decade^-1, respectively. The maximum thickness of the seasonally frozen ground for 1960–2007 reveals a statistically significant trend of -4.0 cm decade^-1 and a net change of -19.2 cm for the 48-year period. These are all related to the increase in spring, summer, autumn, and winter air temperature and the mean annual air temperature in the basin, a possible result of global warming.

In this paper the climate characteristics of the first date of ≤0 °C temperature are analyzed; furthermore, the farming responses to climate warming are discussed using a climate diagnosis analysis and the least squares methods, which are based on the daily minimum temperature data in East China from 1961 to 2009. It was found that over the past 50 years there has been a trend of the first date of ≤0 °C temperature being delayed at a rate of 1.6 days per 10 years; however, between 1961 and 1990 the first date of ≤0 °C temperature arrived early at a rate of 1.8 days per 10 years, and then was delayed at a rate of 3.3 days per 10 years. Furthermore, the average first date of ≤0 °C temperature is 30 October in northern regions, and the frequency of the first date of ≤0 °C temperature is greater in October and November than in other months; however, the boundary of the first date of ≤0 °C temperature shifts from south to north during September to December, and this has been especially evident since the 1990s. It was also found that in some southern stations, ≤0 °C temperature never occurs. The first date of ≤0 °C temperature occurs earlier in the north than in the south, and the interannual variation of the first date of ≤0 °C temperature is large in low latitudes and small in high latitudes. Additionally, the sustained period of ≤0 °C temperature, from beginning to end, decreased at a rate of 5 days per 10 years, which leads to a reduction in the length of the frost periods and causes a structural adjustment to the type of crops that can be planted. Therefore, the study reveals the significant effects that the first date of ≤0 °C temperature can have on the length of frost periods and farming and provides useful findings with regard to the prevention of frost damage and agricultural management.

The use of satellite-infrared sensors to map permafrost distribution is a new research topic. Two important permafrost indices, the mean annual surface temperature (MAST) and the surface frost number (SFN), are estimated using MODIS Aqua/Terra LST products based on a pragmatic scheme proposed in this study. The advantage of this approach is that it allows the full use of every value at any time and at any pixel of MODIS LST products. This scheme is simple, easy to implement, and independent of other observations. The accuracy of the method depends only on the accuracy of the MODIS LST products. Eight years of data sets from 2003 to 2010 were generated using this scheme to reflect the spatial distribution of permafrost and the surface thermal state. A comparison between the southern/lower limit of permafrost and results from the 8-year average MAST and SFN show that the 0 °C MAST isotherm and 0.5 contour of SFN agree well with the identified southern/lower limits of permafrost in China.

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 depth was lower at a stand with denser vegetation when other conditions are held the same. (2) The ground warms up when the vegetation degrades, and the ground temperature rises from the vegetation degradation could reach much deeper in winter than in summer. (3) In cases of extensive vegetation degradation, the resultant ground warming persists for a long time, resulting in a deepening active layer.

Albedo, which impacts the surface heat budget of a glacier, is a dominant factor governing snow and ice melt variability. We analyzed variations in albedo on the Dongkemadi Glacier (92°4.94′E, 33°05.88′N) using MODIS daily snow albedo products. The results show that the summer albedo over the accumulation zone and the ablation zone all presented a decreasing trend from 2002 to 2012, and both precipitation and summer temperature were critical factors that impacted variations in the albedo of the glacier. We linked the albedo variation with the measured mass balance of the glacier and found that 2006 and 2010 were high-melt years at the Dongkemadi Glacier, with lower albedo and a more negative mass balance. The area around the equilibrium line altitude (ELA) on the glacier was very sensitive to albedo feedback. The albedo change rate reached approximately -34% when the summer average temperature increased about 1 °C and the summer precipitation declined 94.5 mm. We built a linear model between the annual lowest albedo and the annual mass balance of the Xiao Dongkemadi Glacier, one branch of the Dongkemadi Glacier. This model was used to evaluate the annual mass balance of another branch of the Dongkemadi Glacier, the Da Dongkemadi Glacier. The mass balance of the Da Dongkemadi Glacier was significantly negative in 2006 (-768.7 mm w.e.) and 2010 (-696.9 mm w.e.). This work indicates that the glacier surface annual lowest albedo may be a reasonable proxy for evaluating the inter-annual variability of the mass balance of the glacier.

Firn line altitude is an indicator of equilibrium line altitude (ELA) and plays an important role in predicting climate behavior and global change. Landsat 30-m resolution data from clear sky at the end of 21 summer melt seasons (July and August, 1990–2011) were used to obtain the firn lines and extract the glacier boundary at Qiyi Glacier in the Qilian Mountains of China. High-resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer 30-m resolution Global Digital Elevation Model (ASTER GDEM) was employed to obtain the firn line altitudes. The firn line altitudes on the Qiyi Glacier increased from 4540 m a.s.l. to 5000 m a.s.l. during the study period, a rise of 460 m. Changes in firn line altitudes had good positive correlations with air temperature data and were in good agreement with measured and simulated ELA changes. The calculated firn zone area decreased (increased) with the increase (decrease) of firn line altitude. Linear regression was used to fit the variational trend, indicating that the firn zone area decreased by ∼1.19 km², with a change rate 0.057 km² a^-1, during the study period. The firn zone area ratio decreased from 76.2% to 18.1% during the same time.

Heterogeneous mass wastage has been found across the northwestern Tibet Plateau, and both slight positive and negative average mass budgets were observed using different data sets during the past decades. The north bank of the Bangong Co Basin partly covers the Western Kunlun Mountains and Karakoram Mountains. The assessment of glacier mass budget in this region over a long period is of particular interest to understanding the regional diversity of the mass changes of glaciers. Changes in glacier mass in the area of concern were assessed by differentiation of digital elevation models (DEMs) from the earliest available topographic maps, the Shuttle Radar Terrain Mission (SRTM), and the Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) stereo images. Results show that glaciers in this basin have in general experienced a decelerated mass loss but with regional differences. Glaciers were found to have lost a volume of 4.45 ± 0.63 km³ from 1968 to 2007, corresponding to -0.18 ± 0.03 m a^-1 water equivalent (w.e.) in the north bank of the Bangong Co Basin. Loss of glacier mass in this region from 1999 to 2007 was 0.11 ± 0.12 m w.e. a^-1, which was approximately half the loss that occurred from 1968 to 1999 (-0.20 ± 0.01 m w.e. a^-1). From 1968 to 1999, higher mass losses were found in the north with smaller losses in the south, while from 1999 to 2007 there was more loss of mass in the southeast and a somewhat balanced mass budget in the northeast.

The spatial distribution of the snow water equivalent (SWE) of ground snow cover is one of the most important variables for understanding and simulating cold-region hydrological processes in high mountain areas. In this paper, the characteristics of C-band synthetic aperture radar (SAR) data in an area of shallow dry snow cover were analyzed based on microwave backscattering models and field snow cover measurements. The analysis revealed that the backscattering of shallow dry snow cover was dominated by the scattering of the snow-ground interface, and the dielectric constant and roughness parameters of the underlying frozen soil were the primary factors that affected the total scattering. The dielectric constant of the soil depended on the amount of liquid water present in the soil, and the amount of liquid water was primarily determined by the soil temperature. Furthermore, the insulation properties (thermal resistance) of the snow cover affected the underlying soil temperature. Consequently, the snow cover characteristics affected the backscattering signal recorded by the SAR sensors. Based on an investigation involving ENVISAT-ASAR data and simultaneous ground-based snow observations conducted on 14 March 2008, we found that the snow temperature decreased with increasing snow depth when the snow depth was less than 20 cm, and the temperature increased with decreasing snow depth when the snow depth exceeded 20 cm. Additionally, the amount of liquid water in the underlying frozen soil rapidly increased with increasing temperature. To estimate the SWE, we used a small number of field measurements data and SAR ratio images to develop two equations. The first equation defined the relationship between the snow's thermal resistance and backscattering ratio, and the second equation yielded the SWE from the estimated thermal resistance of the snow-covered area. The root mean square and relative errors of the estimated SWE were approximately 7.41 mm and 6.17%, respectively. The derived SWE also indicated that blowing snow and sun radiation were two primary factors that determined the spatial distribution of snow cover in mountainous areas.

Electrical conductivity (EC) in aerosols, snow, and meltwater were evaluated at the headwater of the Urumqi River during the ablation seasons of 2003–2008. The results show that EC in meltwater can indicate the intensity of glacier ablation, which negatively correlated with air temperature and discharge. During the early ablation period, EC presents a fluctuation trend and runoff may be primarily from snow, frozen soil, and groundwater. EC decreases to the lowest level during the peak-flow period and runoff flows rapidly through a hydrological system predominantly in ice-walled conduits. EC increases to the highest level during the late ablation period, and runoff transports slowly through a distributed hydrological system at the ice-rock interface. EC in meltwater is far greater than in aerosols, surface snow, and precipitation, which are closely related to atmospheric circulation and dust loading. EC in snow pits denote the spatial variation of snow melting, the enrichment and loss of dissolved ions, and are affected by air temperature. The key ions to determine EC in meltwater are HCO₃^-, Ca² and SO₄^2-, and its dominant control might be biogeochemical pyrite oxidation coupled with calcite and/or dolomite dissolution.

The Lancang River Basin (LRB) crosses from the higher inland Tibet Plateau to lower south Asia. Glaciers in upper reaches of the basin are significant reservoirs of freshwater and are considered to contribute substantially to the runoff of the Lancang River. In this study, we present the results of glacier inventories of the LRB and demonstrate its changes during the past 40 years, based on investigations conducted during two periods: the first (1968–1975) and the second (2005–2010) glacier inventory of China. Total area of the 423 measured glaciers in the LRB decreased by 98.50 ± 26.61 km² from 328.16 ± 20.29 km² in 1968–1975 to 229.66 ± 16.48 km² in 2005–2010, indicating a loss in total glacier area of about 30% ± 8% during the past 40 years (at a mean area loss rate of 0.75% ± 0.2% a^-1), which is comparable to glacier changes in other regions of high Asia. Southern glaciers in the LRB have experienced greater area loss than the northern inland Tibet regions, indicating more sensitivity of temperate glaciers to climate warming. The general warming trend but with less significant precipitation changes during the past 50 years (1960–2010), which has been confirmed by the observation of several meteorological stations across from the south to the north of the basin, could be one of the main causes accounting for the overall glacier recessions in the LRB.

The plant and insect communities of many summer pastures in the Swiss Alps are changing as they become encroached by woody plants. To understand the implications for overall biodiversity, we need to determine how different taxonomic groups respond to shrub encroachment. We investigated effects of encroachment upon species diversity of vascular plants, butterflies, and grasshoppers on two subalpine pastures (Mesocco and Guarda). On each site, we recognized a sequence of vegetation types representing a gradient of increasing shrub cover. The number of rare plant species was strongly affected by the degree of encroachment, with areas dominated by either dwarf shrubs or Alnus viridis having fewer species than areas of open grassland. In the Mesocco site, we also found differences in other measures of plant species richness (total species richness, number of herbaceous species) and in the number of grasshopper species. While plant richness was highest in grassland-dominated vegetation types, the species richness of grasshoppers was highest in types with a low to intermediate cover of dwarf shrubs. We found no effect of shrub cover upon butterfly species richness at either site. Biotic factors (shrub cover, grazing intensity, and also vegetation-related variables for the insect groups) explained a larger proportion of the variance in species composition of both plants and insects than did large-scale abiotic factors (altitude, aspect, and slope). Our results demonstrate that shrub encroachment is a threat to the biodiversity of subalpine grassland ecosystems. We recommend conservation actions that prevent extensive shrub encroachment but promote a mosaic of small areas at different successional stages.

Soil water content (SWC) regulation on the responses of soil respiration (R_s), autotrophic respiration (R_a), and heterotrophic respiration (R_h) to warming are rarely investigated in alpine meadow ecosystem in the Qinghai-Tibet Plateau (QTP). We conducted a warming experiment to investigate how SWC regulates the responses of R_s and its components (R_a and R_h) to warming. Infrared heaters were used to simulate climatic warming. Soil respiration was measured inside surface collars (2–3 cm deep) and R_h was measured inside deep collars (50 cm deep), which excludes root respiration. Autotrophic respiration was calculated by subtracting R_h from R_s. Warming increased the average R_s and R_h by 9.9% and 12.7% but had no significant effect on R_a. Interaction between warming and SWC had significant effect on R_s and its components. Soil respiration and R_a decreased by 5.8% and 36.3% in dry conditions, but they increased by 23.5% and 47.7% in wet conditions. Growing season above-ground biomass was enhanced by 0.1 kg m^-2 in wet conditions but reduced by 0.10 kg m^-2 in dry conditions under warming manipulation. The estimated net ecosystem carbon (C) balance was 0.65 and -0.16 kg m^-2 in wet and dry conditions, respectively, which indicates a net C emission of alpine meadow in wet but a net C sequestration in dry conditions. Our results emphasize the importance of incorporating SWC in simulation of ecosystem carbon balance under a warming climate.

Diatoms were found in late Holocene age ice-core samples recovered from the Quelccaya Summit Dome in the tropical Andes of Peru and were imaged by environmental scanning electron microscopy and identified. Freshwater diatoms in the genera Hantzschia, Pinnularia, and Aulacoseira were the most common taxa in the samples and indicate a freshwater source for the material, which also is suggested by the presence of the freshwater alga Volvox. The overall species composition of the diatoms suggests that the majority of taxa originated from a high-elevation lake or wetland in the cordillera surrounding the ice cap. The abundant diatom valves, up to 70 µm in size, likely were transported to the ice via wind.

Records of high resolution climate variability in the past are essential to understanding the climate change observed today. This is particularly true for Arctic regions, which are rapidly warming. Prior to instrumental data, proxy records can be extracted from high-latitude climate archives to provide critical records of past Arctic climate variability. Here, we investigate the feasibility of extracting records of climate and environmental variability from the skeleton of the crustose coralline alga Leptophytum foecundum from offshore the Sagavanirktok River in the Beaufort Sea. Although this alga forms an annually banded skeleton, age chronologies were established with difficulty due to the large uncalcified reproductive structures relative to low annual growth rates. Average measurements of skeletal Mg content, δ¹⁸O_alga values, and δ¹³C_alga values were consistent among the analyzed specimens, but time series of these parameters only significantly correlated between two of the collected specimens for δ¹⁸O_alga. No clear trends in environmental variability explained the patterns in the skeletal geochemistry over time. This suggests that ambient seawater combined with freshwater from the Sagavanirktok River drives the geochemistry of L. foecundum at this site. Thus, coralline algal specimens located near variable sources of low-salinity waters are not ideal organisms to use as proxy archives.

To estimate the impact of atmospheric deposition on alpine ecosystems, we evaluated the interactions between atmospheric deposition and the Pinus pumila canopy close to the summit of Mount Tateyama, central Japan. We analyzed the chemical characteristics of rain, fog, and throughfall under the canopy in the summertime for 5 years. The concentrations of inorganic nitrogen and sulfate in precipitation at the summit (2839 m a.s.l.) were lower than at the base (13 m a.s.l.), but the total amounts deposited tended to be larger, because the precipitation was greater at the summit and highly concentrated fog water was deposited on the pine canopy. Large fluctuations in the quality and quantity of deposition were due to interannual variations in the meteorological conditions. About 80% of NO₃^--N and NH₄ -N (0.40 and 0.47 kg ha^-1 month^-1) from rain and fog were retained in the P. pumila canopy, and contributions from fog were twice those from rain. Considerable amounts of K , Mg² , and Ca² ions (0.97, 0.13, and 0.13 kg ha^-1 month^-1) were leached out from the canopy to the soil as throughfall. The leaching did not increase with rainfall, but increased as the duration of the fog and dew increased.

When the review was originally published in November 2014, the price listed was incorrect. The editors regret the error.