Increase In Active Layer Thickness Research Articles

Amount and timing of permafrost carbon release in response to climate warming

The thawand release of carbon currently frozen in permafrost will increase atmospheric CO2 concentrations and amplify surface warming to initiate a positive permafrost carbon feedback (PCF) on climate.We use surface weather from three global climate models based on the moderate warming, A1B Intergovernmental Panel on Climate Change emissions scenario and the SiBCASA land surface model to estimate the strength and timing of the PCF and associated uncertainty. By 2200, we predict a 29-59% decrease in permafrost area and a 53-97 cm increase in active layer thickness. By 2200, the PCF strength in terms of cumulative permafrost carbon flux to the atmosphere is 190 ± 64 Gt C. This estimate may be low because it does not account for amplified surface warming due to the PCF itself and excludes some discontinuous permafrost regions where SiBCASA did not simulate permafrost. We predict that the PCF will change the arctic from a carbon sink to a source after the mid-2020s and is strong enough to cancel 42-88% of the total global land sink. The thaw and decay of permafrost carbon is irreversible and accounting for the PCF will require larger reductions in fossil fuel emissions to reach a target atmospheric CO2 concentration.

Changes in active layer thickness over the Qinghai‐Tibetan Plateau from 1995 to 2007

The active layer over permafrost plays a significant role in surface energy balance, hydrologic cycle, carbon fluxes, ecosystem, and landscape processes and on the human infrastructure in cold regions. Over a period from 1995 to 2007, a systematic soil temperature measurement network of 10 sites was established along the Qinghai‐Tibetan Highway. Soil temperatures up to 12 m depth were continuously measured semimonthly. In this study, we investigate spatial variations of active layer thickness (ALT) and its change over the period of record. We found that ALT can be estimated with confidence using semimonthly soil temperature profiles compared to those determined from available daily soil temperature profiles over the Qinghai‐Tibetan Plateau. The primary results demonstrate that long‐term and spatially averaged ALT is ∼2.41 m with a range of 1.32–4.57 m along the Qinghai‐Tibetan Highway. All monitoring sites show an increase in ALT over the period of their records. The mean increasing rate of ALT is ∼7.5 cm/yr. ALT shows a closely positive correlation with the thawing index of air temperature on the plateau. We estimated ALT using the thawing index over a period from 1956 to 2005 near the Wudaoliang Meteorological Station in the northern plateau. ALT had no or very limited change from 1956 to 1983 and a sharp increase of ∼39 cm from 1983 to 2005. The magnitude of ALT increase is greater in the warm permafrost region than in the cold permafrost region. The primary control of increase in ALT is caused by an increase in summer air temperature, whereas changes in the winter air temperature and snow cover condition play no or a very limited role.

Ecosystem responses to increased precipitation and permafrost decay in subarctic Sweden inferred from peat and lake sediments

AbstractRecent accelerated decay of discontinuous permafrost at the Stordalen Mire in northern Sweden has been attributed to increased temperature and snow depth, and has caused expansion of wet minerotrophic areas leading to significant changes in carbon cycling in the mire. In order to track these changes through time and evaluate potential forcing mechanisms, this paper analyses a peat succession and a lake sediment sequence from within the mire, providing a record for the last 100 years, and compares these with monitored climate and active layer thickness data. The peat core was analysed for testate amoebae to reconstruct changes in peatland surface moisture conditions and water table fluctuations. The lake sediment core was analysed by near infrared spectroscopy to infer changes in the total organic carbon (TOC) concentration of the lake‐water, and changes in δ13C and C, N and δ15N to track changes in the dissolved inorganic carbon (DIC) pool and the influence of diagenetic effects on sediment organic matter, respectively. Results showed that major shifts towards increased peat surface moisture and TOC concentration of the lake‐water occurred around 1980, one to two decades earlier than a temperature driven increase in active layer thickness. Comparison with monitored temperature and precipitation from a nearby climate station indicates that this change in peat surface moisture is related to June–September (JJAS) precipitation and that the increase in lake‐water TOC concentration reflects an increase in total annual precipitation. A significant depletion in 13C of sediment organic matter in the early 1980s probably reflects the effect of a single or a few consecutive years with anomalously high summer precipitation, resulting in elevated DIC content of the lake water, predominantly originating from increased export and subsequent respiration of organic carbon from the mire. Based on these results, it was not possible to link proxy data obtained on peat and lake‐sediment records directly to permafrost decay. Instead our data indicate that increased precipitation and anomalously high rainfall during summers had a significant impact on the mire and the adjacent lake ecosystem. We therefore propose that effects of increased precipitation should be considered when evaluating potential forcing mechanisms of recent changes in carbon cycling in the subarctic.

Influence of optical interference and carrier lifetime on the short circuit current density of organic bulk heterojunction solar cells

Based on simple analytical equations, short circuit current density (JSC) of the organic bulk heterojunction solar cells has been calculated. It is found that the optical interference effect plays a very important role in the determination of JSC; and obvious oscillatory behaviour of JSC was observed as a function of thickness. At the same time, the influence of the carrier lifetime on JSC also cannot be neglected. When the carrier lifetime is relatively short, JSC only increases at the initial stage and then decreases rapidly with the increase of active layer thickness. However, for a relatively long carrier lifetime, the exciton dissociation probability must be considered, and JSC behaves wave-like with the increase of active layer thickness. The validity of this model is confirmed by the experimental results.

The effect of active-layer thickness on the characteristic of nanocrystalline silicon thin film transistor

AbstractWe fabricated nc-Si TFTs in order to investigate the effect of the active-layer thickness on the characteristic of the nc-Si TFT. Bottom gate nc-Si TFTs were fabricated at 350°C using ICP-CVD. The thicknesses of the nc-Si layer were remained to 700, 1200 and 1700 Å. As the active-layer thickness increases, the mobility and the on-current level were not altered. However, the off-current level increased considerably and on/off ratio decreased. It may be attributed to highly doped characteristic of thick nc-Si film. As the nc-Si film thicker, the conductivity increases considerably and the Fermi level approaches to the conduction band minimum, which indicates the increases of doping level. The oxygen concentration shows high level of unintentional doping. Also, columnar growth of nc-Si film makes that the crystallinity of top region is much higher than that of bottom region. So, the conductivity of thick nc-Si film becomes high compared to that of thin nc-Si film. The structure of the nc-Si TFT with thick nc-Si film can be similar to the serial connection of N+, N- and N+ resistance, so that it suffers difficulty to suppress the off current and to secure high on/off ratio. Therefore, the off current can be suppressed by thinning of the high conducting active nc-Si layer and nc-Si TFT with channel thickness of 700 Å shows good on/off characteristic. It is deduced that bottom gate nc-Si TFT is necessary to have intrinsic channel layer as well as thin channel layer to reduce the leakage current.

Spatio-temporal simulation of permafrost geothermal response to climate change scenarios in a building environment

Significant climate warming, as observed over the past decades and projected by global climate models, would inevitably cause permafrost degradation in the Arctic regions. Several studies have been conducted to assess geothermal response to climate change in natural conditions; no study, however, has been observed yet to examine the potential response of the permafrost geothermal regime in a building environment. This paper presents a methodology and the results of a case study in the community of Inuvik, Canada of the spatio-temporal dynamics simulation of the geothermal regime under climate change scenarios in a building environment. A process-based, surface-coupled, 3-dimensional geothermal model was used for the simulation. The results suggest that the permafrost under the study would deteriorate under all the three climate change scenarios assessed, and the rate of the deterioration would depend on geotechnical properties of subsurface materials and climate change scenarios. Two patterns of the geothermal dynamics were revealed from the simulation results: spatially, there are significant differences in the rate of increase in active layer thickness underneath vs. around a building; and temporally, there is an abrupt rise in the active layer thickness around the middle of this century.

Comment on “A projection of severe near‐surface permafrost degradation during the 21st century” by David M. Lawrence and Andrew G. Slater

Comment on “A projection of severe near‐surface permafrost degradation during the 21st century” by David M. Lawrence and Andrew G. Slater

Interactions between climate, vegetation and the active layer in soils at two Maritime Antarctic sites

In the summer 2000–01, thermal monitoring of the permafrost active layer within various terrestrial sites covered by lichen, moss or grasses was undertaken at Jubany (King George Island) and Signy Island in the Maritime Antarctic. The results demonstrated the buffering effect of vegetation on ground surface temperature (GST) and the relationship between vegetation and active layer thickness. Vegetation type and coverage influenced the GST in both locations with highest variations and values in the Deschampsia and Usnea sites and the lowest variations and values in the Jubany moss site. Active layer thickness ranged from 57 cm (Jubany moss site) to 227 cm (Signy Deschampsia site). Active layer thickness data from Signy were compared with data collected at the same location four decades earlier. Using a regression equation for air temperature versus ground surface temperatures the patterns of changing air temperature over time suggest that the active layer thickness increased c. 30 cm between 1963 and 1990 and then decreased 30 cm between 1990 and 2000. The documented increased rate of warming (2°C ± 1) since 1950 for air temperatures recorded in the South Orkney Islands suggests that the overall trend of active layer thickness increase will be around 1 cm year−1.

Circumpolar‐Active‐Layer‐Monitoring (CALM) sites in the Mackenzie Valley, northwestern Canada

AbstractActive‐layer studies have been maintained for more than a decade throughout the 1200 km length of the Mackenzie Valley. An important goal of these programmes is to monitor processes linking climate, permafrost and the active layer. Thirteen sites have been selected from these studies for the Circumpolar Active Layer Monitoring programme of the International Permafrost Association. Annual maximum thaw penetration and ground surface movements are measured relative to thaw tubes and soil temperature probes anchored in the permafrost. Active layer thickness, calculated from thaw penetration and surface movement or measured directly, varies more with local soil properties, vegetation and microclimate than with regional atmospheric climate. While depth of thaw penetration has increased at most sites for much of the record, this increase is not always reflected by a proportional increase in active layer thickness because of variable thaw settlement. Air thawing degree‐days (DDT) in the Subarctic and Boreal regions are more than double those in the Arctic regions. These increases in DDT are not reflected in active‐layer depths, suggesting the insulating effect of the surface organic layer, vegetation and snow cover on active‐layer development. Copyright © 2004 John Wiley & Sons, Ltd.

Analytic representation of the active layer thickness field, Kuparuk River Basin, Alaska

The initial response of permafrost to global warming could be an increase in active-layer thickness. Given that such changes could have severe consequences for human infrastructure and ecosystem stability, it is important to obtain information about spatial variations of the active layer corresponding to current climatic conditions, and to determine the magnitude of possible near-surface permafrost degradation associated with climatic change. Simple analytical solutions for frost and thaw penetration depth have long been available, but were used primarily for practical applications at point locations in cold-region engineering. One of these methods, developed at Moscow State University by Kudryavtsev and co-workers, was used to develop a spatially distributed analytic model that estimates the maximum annual depth of thaw. Kudryavtsev’s procedures account for the effects of snow cover, vegetation, soil moisture, thermal properties, and regional climate, and provide estimates of surface temperature and active-layer thickness. GIS techniques were used to incorporate climate records, digital cartographic products, and field data into a spatially distributed estimate of active-layer thickness. Procedures were applied over a rectangular 22 300 km 2 area in north-central Alaska containing complex patterns of topography, vegetation, and soils. Validation procedures indicate that the Kudrayavtsev solution, adapted for spatial applications, yields accuracy and spatial resolution comparable to an existing semi-empirical method. The simplicity and low data requirements of the Kudryavtsev solution make it readily adaptable to different geographic scales and areas. The method has potential applications in climate-change studies.

Microbial life in permafrost: A historical review

AbstractThis paper reviews the literature on cold‐adapted micro‐organisms which might exist in ice and permafrost. Properly identified, microbial markers in the cryolithozone could be used in palaeoenvironmental reconstructions, in distinguishing between epigenetic and syngenetic depositional sequences, and in the recognition of secondary thaw unconformities. Cryobiological problems include (1) whether the bacteria are dead, dormant or in the active state, and (2) what factors determine the preservation of cell structures. A possible consequence of permafrost thawing, based upon predicted global warming scenarios, is that there may be an increase in microbial activity and an increase in active layer thickness.

A model of environmental craze growth in polymers

AbstractA model of environmental craze growth has been developed based on the customary meniscus (or Rayleigh‐Taylor) instability model of craze propagation but allowing for the possibility that environmental plasticization may cause the active layer of material adjacent to the craze to be of significant thickness with respect to the fibril spacing. Initially, as the active layer thickness increases, the fibril growth rate increases at constant fibril spacing, but eventually the fibril spacing comes to be controlled only by the active layer thickness and not by the surface tension and stress. This model of craze growth has been coupled to a model of stress‐enhanced case II diffusion that is itself based on the Thomas‐Windle model. Two main regimes of craze thickness growth are distinguished. In one the craze growth rate is controlled by the velocity of the diffusion front, the meniscus instability growth rate is assumed to be relatively slow, so that a significant plasticized active layer exists whose thickness assures that the meniscus instability front travels at the same speed as the diffusion front. In the other regime the propagation of the craze front is sufficiently fast that it also forms the diffusion front, so the growth rate is controlled by a combination of the two processes: diffusion and meniscus instability.