The cryosphere plays an important role in the earth system and has experienced a dramatic and rapid decline due to climate change. Most cryospheric research focuses on changes in individual ...components, but there is no single metric that quantifies the cryosphere as a whole. We initially investigate 17 parameters representing various cryospheric components, and ultimately use principal component analysis on 13 of these variables to define an integrated index that quantifies cryospheric changes. Based on its strong negative correlation with air temperatures, we reconstruct the cryospheric index back to 1850, and also project it to 2100 using different climate model scenarios. An overall decrease is found in the cryospheric index, with interdecadal variability: an increase during 1940–1970, a subsequent strong decrease during the recent 50 years, and a projected fast decline in the future. We assess the associations between the cryospheric index and vegetation, greenhouse gases, and sea level rise. This cryospheric index represents an important new indicator of cryospheric and climatic change, that will be useful to compare against changes in other environmental variables.
•17 variables are identified to assess the 1984–2016 Northern Hemisphere cryosphere.•Principal component analysis combines 13 of the variables into a cryospheric index.•The index is reconstructed to 1850 and projected to 2100 based on air temperature.•Interdecadal variability dominates the index, with a strong decline starting ∼1970.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
Permafrost collapse can rapidly change regional soil-thermal and hydrological conditions, potentially stimulating production of climate-warming gases. Here, we report on rate and extent of ...permafrost collapse on the extensive Tibetan Plateau, also known as the Asian Water Tower and the Third Pole. Combined data from
in situ
measurements, unmanned aerial vehicles (UAV), manned aerial photographs, and satellite images suggest that permafrost collapse was accelerating across the Eastern Tibetan Plateau. From 1969 to 2017, the area of collapsed permafrost has increased by approximately a factor of 40, with 70% of the collapsed area forming since 2004. These widespread perturbations to the Tibetan Plateau permafrost could trigger changes in local ecosystem state and amplify large-scale permafrost climate feedbacks.
Given the current confirmed permafrost degradation and its considerable impacts on ecosystems, water resources, infrastructure and climate, there is great interest in understanding the causes of ...permafrost degradation. Using the surface frost index (SFI) model and multimodel data from the fifth phase of the Coupled Model Intercomparison Project (CMIP5), this study, for the first time, investigates external anthropogenic and natural forcing impacts on historical (1921-2005) near-surface permafrost change in the Northern Hemisphere. The results show that anthropogenic greenhouse gas (GHG) forcing produces a significant decrease in the area of near-surface permafrost distribution at a rate of 0.46 × 106 km2 decade−1, similar to observations and the historical simulation (ALL). Anthropogenic aerosol (AA) forcing yields an increase in near-surface permafrost distribution area at a rate of 0.25 × 106 km2 decade−1. Under natural (NAT) forcing, there is a weak trend and distinct decadal variability in near-surface permafrost area. The effects of ALL and GHG forcings are detectable in the observed change in historical near-surface permafrost area, but the effects of NAT and AA forcings are not detected using the optimal fingerprint methods. This indicates that the observed near-surface permafrost degradation can be largely attributed to GHG-induced warming, which has decreased the near-surface permafrost area in the Northern Hemisphere by approximately 0. 21 × 106 km2 decade−1 on average over the study period, according to the attribution analysis.
The response of seasonal soil freeze depth to climate change has repercussions for the surface energy and water balance, ecosystems, the carbon cycle, and soil nutrient exchange. Despite its ...importance, the response of soil freeze depth to climate change is largely unknown. This study employs the Stefan solution and observations from 845 meteorological stations to investigate the response of variations in soil freeze depth to climate change across China. Observations include daily air temperatures, daily soil temperatures at various depths, mean monthly gridded air temperatures, and the normalized difference vegetation index. Results show that soil freeze depth decreased significantly at a rate of −0.18 ± 0.03 cm yr−1, resulting in a net decrease of 8.05 ± 1.5 cm over 1967–2012 across China. On the regional scale, soil freeze depth decreases varied between 0.0 and 0.4 cm yr−1 in most parts of China during 1950–2009. By investigating potential climatic and environmental driving factors of soil freeze depth variability, we find that mean annual air temperature and ground surface temperature, air thawing index, ground surface thawing index, and vegetation growth are all negatively associated with soil freeze depth. Changes in snow depth are not correlated with soil freeze depth. Air and ground surface freezing indices are positively correlated with soil freeze depth. Comparing these potential driving factors of soil freeze depth, we find that freezing index and vegetation growth are more strongly correlated with soil freeze depth, while snow depth is not significant. We conclude that air temperature increases are responsible for the decrease in seasonal freeze depth. These results are important for understanding the soil freeze–thaw dynamics and the impacts of soil freeze depth on ecosystem and hydrological process.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
•We measured the organic carbon associated with iron in slump deformation landscapes.•Slump deformation changed soil variables and decreased organic carbon and nitrogen.•Changes of the carbon ...associated with iron varied among vegetation types.•Organic carbon stabilization processes can be affected by slump deformation features.
Soil organic carbon (SOC) associated with iron (Fe-OC) can be recognized as an important component of the stabilized carbon pool. In permafrost regions, slump deformation can expose soil organic carbon and alter moisture conditions, which change the Fe-OC distribution. We measured the top 30 cm of soils in five slump deformation landscapes under three vegetation types on the middle and eastern Qinghai-Tibetan Plateau. Three stages of slump deformation were defined according to their microtopography. In the slump deformation areas, the SOC and total nitrogen (TN) contents in the surface 30 cm of soils were all lower than the soils without slump deformation in wet meadow (22% and 26%), meadow (16% and 29%), and steppe (14% and 20%) areas. The contents of Fe-OC in wet meadow were 4.1% and 12.5% in the soils without and with slump deformation, respectively, whereas these contents in the meadow and steppe soils were 25.6% and 17.2%, respectively. Slump deformation greatly changed the physiochemical soil variables and affected the Fe-OC% based on different vegetation types. Fe-OC was correlated with factors such as soil moisture, pH and C/Fe ratio. The study shows that slump deformation greatly affected the SOC and TN distribution and SOC stabilization processes in areas with slump deformation features.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The near‐surface soil freeze/thaw (F/T) cycle affects the surface energy balance, hydrological processes, and soil greenhouse gas release. Passive microwave remote sensing data are the most widely ...used method for determining the near‐surface soil F/T status. While many algorithms have been developed for this purpose, their performance has never been compared using same and large in situ data set. Here, we evaluate and inter‐compare the classification results of the four most widely used algorithms using a large ground truth data set covering China. Based on the ground observations, our evaluation shows a wide range of near‐surface soil F/T detection performance, with Cohen's kappa coefficient ranging from 0.42 to 0.72 and an overall accuracy between 73.8% and 86.2%. We suggest performing parameter calibration for the decision tree algorithm and the discriminant function algorithm before applying them to areas outside of the training sites. All these four algorithms exhibited remarkable uncertainty in the detection of the onset and offset of near‐surface soil freezing with root mean squared errors of more than 27 days. These results suggest that careful cautions should be taken when outputs of these algorithms are used for investigations of long‐term changes.
Key Points
The algorithms showed a wide range of performance with Cohen's kappa coefficient of 0.42–0.72 and an overall accuracy between 73.8% and 86.2%
All the four algorithms show a reduced ability to capture the near‐surface soil freeze status in F/T transition seasons
The algorithms were found not suitable in investigating the long‐term changes, and the RMSE could be more than 27 days
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
•Higher levels of most heavy metals were discovered in AL relative to PL.•Metal resistant or DNA repair genes were more abundant in AL relative to PL.•Four heavy metal-resistant phyla were more ...abundant in AL relative to PL.•C, N, and S cycling genes were less in abundance in AL relative to PL.•Bacteria in AL have evolved an integrated approach to heavy metal tolerance.
The relationship between heavy metals and the expression of heavy metal resistance genes (HMRGs) in the active layer (AL) and the permafrost layer (PL) are not well understood, despite being closely linked to the impact of human activity on heavy metal levels and bacterial response to heavy metal stress. Herein, we conducted a metagenomics sequencing analysis to understand how bacteria adapt to such heavy metal stress. We detected higher levels of heavy metals in the AL relative to the PL. Consistent with this, analyses of AL samples revealed the presence of more genes associated with DNA damage repair, DNA recombination, and heavy metal resistance relative to PL samples. Heavy metal-resistant bacterial phyla including Actinobacteria, Acidobacteria, Bacteroidetes, and Cyanobacteria were more abundant in the AL than the PL. At the genera level, we found that bacteria responsible for nitrification, sulfur reduction, and methane oxidation and reduction were less prevalent in the AL relative to the PL. In summary, bacteria in the AL have evolved such that they are able to resist prolonged heavy metal pollution.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Climate warming increases thermokarst landscapes and thus leads to land degradation in the Circum-Arctic regions. Thermokarst landscapes were estimated to cover ~ 20% of the northern permafrost ...region, and their development is related to ground ice content and topographic conditions. However, changes in thaw slump distribution and development in mid- to low-latitude permafrost areas largely remain unknown. Here, we selected the Qilian Mountains of the northern Qinghai-Tibetan Plateau (QTP) as the study area. Combined with field investigation to measure the boundary of thaw slump using Real Time Kinematic (RTK), we analyzed historical changes in thaw slumps using 1969 and 1997 aerial photographs, 2009 and 2015 satellite imagery, and 2017 unmanned aerial vehicle (UAV) aerial images. The results showed that there are 15 thaw slumps covering an area of 0.03 km
2
, which were mainly distributed in terrain with a slope of 2–8° and elevation of 3552–3611 m. For the time periods of 1997–2009, 2009–2015, and 2015–2017, the average increase rates of thaw slump areas were approximately 61.8, 60.0, and 156.8 m
2
/y, and annual headwall retreat rates were approximately 1.3, 1.6 and 2.0 m/y. Based on the slopes, aspects, and altitudes from the Digital Elevation Model generated by UAV imagery, it suggested that geomorphic factors have no significant effect on the growth rates of thaw slump due to high heterogeneities of alpine environments. Our results showed that thaw slumps with polycyclic and active characteristics covered at least 0.9% of northern QTP permafrost regions and are expected to rapidly accelerate with climate warming.
Permafrost thaw subsidence, a key indicator of permafrost degradation, remains poorly quantified or understood. It is particularly challenging to detect and measure surface subsidence due to the loss ...of subsurface ice over a large area because it usually develops gradually, over several years or decades. Here we utilize the persistent scatterer interferometric synthetic aperture radar (PSI) approach to remotely measure gradual surface subsidence on Eboling Mountain in the northeastern region of the Qinghai‐Tibet Plateau, where thermal erosion gullies are well developed. Most of the previous multitemporal interferometric synthetic aperture radar studies on permafrost used the small baseline subset method. By contrast, the PSI approach benefits from the full spatial resolution and is less affected by temporal or geometric decorrelation. In the PSI analysis, we incorporate a piecewise elevation change model that includes periodic subsidence/uplift because of its seasonally varying components as well as its linear subsidence trends. Applying this permafrost‐designated PSI algorithm to 17‐L band ALOS‐1 PALSAR images taken between 2006 and 2011, we find that both the thermal erosion gullies and the surrounding regions (within about 300 m) subside gradually. The subsidence trends range from 0.3 to 3 cm/yr. This suggests that permafrost areas near the gullies are more vulnerable to gradual thawing and degradation. This study demonstrates the potential of using PSI to study permafrost thaw processes and of assessing its impacts over vast areas on the Qinghai‐Tibet Plateau and in the Arctic.
Key Points
Persistent scatterer interferometry is used to map gradual permafrost thaw subsidence with the full spatial resolution by exploiting all the repeat SAR acquisitions
A piecewise elevation change model is introduced to capture the dynamic processes of the active layer and the underlying permafrost
Ground surface subsidence, ranging from 0.3 to 3 cm/yr, occurred both inside the visible thermal erosion gullies and their surroundings
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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