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Multi-channel ground-penetrating radar to explore spatial variations in thaw depth and moisture content in the active layer of a permafrost site  [PDF]
U. Wollschl?ger,H. Gerhards,Q. Yu,K. Roth
The Cryosphere Discussions , 2009,
Abstract: Multi-channel ground-penetrating radar was applied at a permafrost site on the Tibetan Plateau to investigate the influence of surface properties and soil texture on the late-summer thaw depth and average soil moisture content of the active layer. Measurements were conducted on an approximately 85×60 m2 sized area with surface and soil textural properties that ranged from medium to coarse textured bare soil to finer textured, vegetated areas covered with fine, wind blown sand, and it included the bed of a gravel road. The survey allowed a clear differentiation of the various units. It showed (i) a shallow thaw depth and low average soil moisture content below the sand-covered, vegetated area, (ii) an intermediate thaw depth and high average soil moisture content along the gravel road, and (iii) an intermediate to deep thaw depth and low to intermediate average soil moisture content in the bare soil terrain. From our measurements, we found plausible hypotheses for the permafrost processes at this site leading to the observed late-summer thaw depth and soil moisture conditions. The study clearly indicates the complicated interactions between surface and subsurface state variables and processes in this environment. In addition, the survey demonstrates the potential of multi-channel ground-penetrating radar to efficiently map thaw depth and soil moisture content of the active layer with high spatial resolution at scales from a few meters to a few kilometers.
Multi-channel ground-penetrating radar to explore spatial variations in thaw depth and moisture content in the active layer of a permafrost site  [PDF]
U. Wollschl?ger,H. Gerhards,Q. Yu,K. Roth
The Cryosphere , 2010, DOI: 10.5194/tc-4-269-2010
Abstract: Multi-channel ground-penetrating radar (GPR) was applied at a permafrost site on the Tibetan Plateau to investigate the influence of surface properties and soil texture on the late-summer thaw depth and average soil moisture content of the active layer. Measurements were conducted on an approximately 85 × 60 m2 sized area with surface and soil textural properties that ranged from medium to coarse textured bare soil to finer textured, sparsely vegetated areas covered with fine, wind blown sand, and it included the bed of a gravel road. The survey allowed a clear differentiation of the various units. It showed (i) a shallow thaw depth and low average soil moisture content below the sand-covered, vegetated area, (ii) an intermediate thaw depth and high average soil moisture content along the gravel road, and (iii) an intermediate to deep thaw depth and low to intermediate average soil moisture content in the bare soil terrain. From our measurements, we found hypotheses for the permafrost processes at this site leading to the observed late-summer thaw depth and soil moisture conditions. The study clearly indicates the complicated interactions between surface and subsurface state variables and processes in this environment. Multi-channel GPR is an operational technology to efficiently study such a system at scales varying from a few meters to a few kilometers.
Seasonal methane emission from a boreal peatland in continuous permafrost zone of Northeast China: effects of active layer depth and vegetation  [PDF]
Y. Miao,C. Song,L. Sun,X. Wang
Biogeosciences Discussions , 2012, DOI: 10.5194/bgd-9-6751-2012
Abstract: Boreal peatlands are significant natural sources of methane and especially vulnerable to abrupt climate change. However, the controlling factors of CH4 emission in boreal peatlands are still unclear. In this study, we investigated CH4 fluxes and abiotic factors (temperature, water table depth, active layer depth, and dissolved CH4 concentrations in pore water) during the growing seasons in 2010 and 2011 both in shrub-sphagnum- and sedge-dominated plant communities in continuous permafrost zone of Northeast China. The objective of our study was to examine the effects of vegetation types and abiotic factors on CH4 fluxes from a boreal peatland. In Eriophorum-dominated community, mean CH4 emissions were 1.015 and 0.801 mg m 2 h 1 in 2010 and 2011, respectively. CH4 fluxes (0.384 mg m 2 h 1) released from the shrub-mosses-dominated community were lower than that from Eriophorum-dominated community. Moreover, in Eriophorum-dominated community, CH4 fluxes showed a significant temporal pattern with a peak value in late August both in 2010 and 2011. However, no distinct seasonal variation was observed in the CH4 flux in the shrub-mosses-dominated community. Interestingly, both in Eriophorum- and shrub-sphagnum-dominated communities, CH4 fluxes did not show close correlation with air or soil temperature and water table depth, whereas CH4 emissions correlated well to active layer depth and CH4 concentration in soil pore water, especially in Eriophorum-dominated community. Our results suggest that CH4 released from the thawed CH4-rich permafrost layer may be a key factor controlling CH4 emissions in boreal peatlands, and highlight that CH4 fluxes vary with vegetation type in boreal peatlands.
Highway Roadway Stability Influenced by Warm Permafrost and Seasonal Frost Action: A Case Study from Glennallen, Alaska, USA

Huijun Jin,Max C Brewer,

寒旱区科学 , 2008,
Abstract: Ground temperatures from four of the seven extensively studied highway cross-sections near Gulkana/Glennallen, Alaska during 1954~1962, were chosen to better understand the impacts of highway construction on warm permafrost. Both the thawing of permafrost and seasonal frost action impacted on road surface stability for about 6 years until the maximum summer thaw reached about 3 m in depth. Seasonal frost action caused most of the ensuing stability problems. Unusually warm summers and the lengths of time required to re-freeze the active layer were far more important than the average annual air temperatures in determining the temperatures of the underlying shallow permafrost, or the development of taliks. The hypothesized climate warming would slightly and gradually deepen the active layer and the developed underlying talik, but its effect would be obscured by unusually warm summers, by warmer than usual winters, and by the variable lengths of time of the zero curtains. At least one period of climate mini-cooling in the deeper permafrost during the early 20th century was noted.
Estimating the permafrost-carbon feedback on global warming  [PDF]
T. Schneider von Deimling,M. Meinshausen,A. Levermann,V. Huber
Biogeosciences Discussions , 2011, DOI: 10.5194/bgd-8-4727-2011
Abstract: Thawing of permafrost and the associated release of carbon constitutes a positive feedback in the climate system, elevating the effect of anthropogenic GHG emissions on global-mean temperatures. Multiple factors have hindered the quantification of this feedback, which was not included in the CMIP3 and C4MIP generation of AOGCMs and carbon cycle models. There are considerable uncertainties in the rate and extent of permafrost thaw, the hydrological and vegetation response to permafrost thaw, the decomposition timescales of freshly thawed organic material, the proportion of soil carbon that might be emitted as carbon dioxide via aerobic decomposition or as methane via anaerobic decomposition, and in the magnitude of the high latitude amplification of global warming that will drive permafrost degradation. Additionally, there are extensive and poorly characterized regional heterogeneities in soil properties, carbon content, and hydrology. Here, we couple a new permafrost module to a reduced complexity carbon-cycle climate model, which allows us to perform a large ensemble of simulations. The ensemble is designed to span the uncertainties listed above and thereby the results provide an estimate of the potential strength of the permafrost-carbon feedback. For the high CO2 concentration scenario (RCP8.5), 12–52 PgC, or an extra 3–11 % above projected net CO2 emissions from land carbon cycle feedbacks, are released by 2100 (68 % uncertainty range). This leads to an additional warming of 0.02–0.11 °C. Though projected 21st century emissions are relatively modest, ongoing permafrost thaw and slow but steady soil carbon decomposition means that, by 2300, more than half of the potentially vulnerable permafrost carbon stock in the upper 3m of soil layer (600–1000 PgC) could be released as CO2, with an extra 1–3 % being released as methane. Our results also suggest that mitigation action in line with the lower scenario RCP3-PD could contain Arctic temperature increase sufficiently that thawing of the permafrost area is limited to 15–30 % and the permafrost-carbon induced temperature increase does not exceed 0.01–0.07 °C by 2300.
Comparison of algorithms and parameterisations for infiltration into organic-covered permafrost soils
Y. Zhang, S. K. Carey, W. L. Quinton, J. R. Janowicz, J. W. Pomeroy,G. N. Flerchinger
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2010,
Abstract: Infiltration into frozen and unfrozen soils is critical in hydrology, controlling active layer soil water dynamics and influencing runoff. Few Land Surface Models (LSMs) and Hydrological Models (HMs) have been developed, adapted or tested for frozen conditions and permafrost soils. Considering the vast geographical area influenced by freeze/thaw processes and permafrost, and the rapid environmental change observed worldwide in these regions, a need exists to improve models to better represent their hydrology. In this study, various infiltration algorithms and parameterisation methods, which are commonly employed in current LSMs and HMs were tested against detailed measurements at three sites in Canada's discontinuous permafrost region with organic soil depths ranging from 0.02 to 3 m. Field data from two consecutive years were used to calibrate and evaluate the infiltration algorithms and parameterisations. Important conclusions include: (1) the single most important factor that controls the infiltration at permafrost sites is ground thaw depth, (2) differences among the simulated infiltration by different algorithms and parameterisations were only found when the ground was frozen or during the initial fast thawing stages, but not after ground thaw reaches a critical depth of 15 to 30 cm, (3) despite similarities in simulated total infiltration after ground thaw reaches the critical depth, the choice of algorithm influenced the distribution of water among the soil layers, and (4) the ice impedance factor for hydraulic conductivity, which is commonly used in LSMs and HMs, may not be necessary once the water potential driven frozen soil parameterisation is employed. Results from this work provide guidelines that can be directly implemented in LSMs and HMs to improve their application in organic covered permafrost soils.
Comparison of algorithms and parameterisations for infiltration into organic-covered permafrost soils
Y. Zhang,S. K. Carey,W. L. Quinton,J. R. Janowicz
Hydrology and Earth System Sciences Discussions , 2009,
Abstract: Infiltration into frozen and unfrozen soils is critical in hydrology, controlling active layer soil water dynamics and influencing runoff. Few Land Surface Models (LSMs) and Hydrological Models (HMs) have been developed, adapted or tested for frozen conditions and permafrost soils. Considering the vast geographical area influenced by freeze/thaw processes and permafrost, and the rapid environmental change observed worldwide in these regions, a need exists to improve models to better represent their hydrology. In this study, various infiltration algorithms and parameterisation methods, which are commonly employed in current LSMs and HMs were tested against detailed measurements at three sites in Canada's discontinuous permafrost region with organic soil depths ranging from 0.02 to 3 m. Field data from two consecutive years were used to calibrate and evaluate the infiltration algorithms and parameterisations. Important conclusions include: (1) the single most important factor that controls the infiltration at permafrost sites is ground thaw depth, (2) differences among the simulated infiltration by different algorithms and parameterisations were only found when the ground was frozen or during the initial fast thawing stages, but not after ground thaw reaches a critical depth of 15–30 cm, (3) despite similarities in simulated total infiltration after ground thaw reaches the critical depth, the choice of algorithm influenced the distribution of water among the soil layers, and (4) the ice impedance factor for hydraulic conductivity, which is commonly used in LSMs and HMs, may not be necessary once the water potential driven frozen soil parameterisation is employed. Results from this work provide guidelines and can be directly implemented in LSMs and HMs to improve their application in organic covered permafrost soils.
Characteristics of abrupt changes of snow cover and seasonal freeze-thaw layer in the Tibetan Plateau and their impacts on summer precipitation in China

Rong Gao,HaiLing Zhong,WenJie Dong,ZhiGang Wei,

寒旱区科学 , 2011,
Abstract: In this paper, a variation series of snow cover and seasonal freeze-thaw layer from 1965 to 2004 on the Tibetan Plateau has been established by using the observation data from meteorological stations. The sliding T-test, M-K test and B-G algorithm are used to verify abrupt changes of snow cover and seasonal freeze-thaw layer in the Tibetan plateau. The results show that the snow cover has not undergone an abrupt change, but the seasonal freeze-thaw layer obviously witnessed a rapid degradation in 1987, with the frozen soil depth being reduced by about 15 cm. It is also found that when there is less snow in the plateau region, precipitation in South China and Southwest China increases. But when the frozen soil is deep, precipitation in most of China apparently decreases. Both snow cover and seasonal freeze-thaw layer on the plateau can be used to predict the summer precipitation in China. However, if the impacts of snow cover and seasonal freeze-thaw layer are used at the same time, the predictability of summer precipitation can be significantly improved. The significant correlation zone of snow is located in middle reaches of the Yangtze River covering the Hexi Corridor and northeastern Inner Mongolia, and the seasonal freeze-thaw layer exists in Mt. Nanling, northern Shannxi and northwestern part of North China. The significant correlation zone of simultaneous impacts of snow cover and seasonal freeze-thaw layer is larger than that of either snow cover or seasonal freeze-thaw layer. There are three significant correlation zones extending from north to south: the north zone spreads from Mt. Daxinganling to the Hexi Corridor, crossing northern Mt. Taihang and northern Shannxi; the central zone covers middle and lower reaches of the Yangtze River; and the south zone extends from Mt. Wuyi to Yunnan and Guizhou Plateau through Mt. Nanling.
Exploring the sensitivity of soil carbon dynamics to climate change, fire disturbance and permafrost thaw in a black spruce ecosystem  [PDF]
J. A. O'Donnell,J. W. Harden,A. D. McGuire,V. E. Romanovsky
Biogeosciences Discussions , 2010, DOI: 10.5194/bgd-7-8853-2010
Abstract: In the boreal region, soil organic carbon (OC) dynamics are strongly governed by the interaction between wildfire and permafrost. Using a combination of field measurements, numerical modeling of soil thermal dynamics, and process-based modeling of OC dynamics, we tested the sensitivity of soil OC storage to a suite of individual climate factors (air temperature, soil moisture, and snow depth) and fire severity. We also conducted sensitivity analyses to explore the combined effects of fire-moisture interactions and snow seasonality on OC storage. OC losses were calculated as the difference in OC stocks after three fire cycles (~450 years) following a prescribed step-change in climate and/or fire. Across single-factor scenarios, our findings indicate that warmer air temperatures resulted in the largest soil OC losses (5.3 kg C m 2), whereas dry soil conditions alone (in the absence of wildfire) resulted in the smallest carbon losses (0.1 kg C m 2). Increased fire severity resulted in carbon loss of 3.3 kg C m 2, whereas changes in snow depth resulted in smaller OC losses (2.1–2.2 kg C m 2). Across multiple climate factors, we observed larger OC losses than for single-factor scenarios. For instance, high fire severity regime associated with warmer and drier conditions resulted in OC losses of 6.1 kg C m 2, whereas a low fire severity regime associated with warmer and wetter conditions resulted in OC losses of 5.6 kg C m 2. A longer snow-free season associated with future warming resulted in OC losses of 5.4 kg C m 2. Soil climate was the dominant control on soil OC loss, governing the sensitivity of microbial decomposers to fluctuations in temperature and soil moisture; this control, in turn, is governed by interannual changes in active layer depth. Transitional responses of the active layer depth to fire regimes also contributed to OC losses, primarily by determining the proportion of OC into frozen and unfrozen soil layers. Carbon cycle feedbacks from the boreal region to the climate system will clearly depend upon these interactions among climate drivers, fire regime characteristics, and permafrost dynamics.
Exploring the sensitivity of soil carbon dynamics to climate change, fire disturbance and permafrost thaw in a black spruce ecosystem
J. A. O'Donnell, J. W. Harden, A. D. McGuire,V. E. Romanovsky
Biogeosciences (BG) & Discussions (BGD) , 2011,
Abstract: In the boreal region, soil organic carbon (OC) dynamics are strongly governed by the interaction between wildfire and permafrost. Using a combination of field measurements, numerical modeling of soil thermal dynamics, and mass-balance modeling of OC dynamics, we tested the sensitivity of soil OC storage to a suite of individual climate factors (air temperature, soil moisture, and snow depth) and fire severity. We also conducted sensitivity analyses to explore the combined effects of fire-soil moisture interactions and snow seasonality on OC storage. OC losses were calculated as the difference in OC stocks after three fire cycles (~500 yr) following a prescribed step-change in climate and/or fire. Across single-factor scenarios, our findings indicate that warmer air temperatures resulted in the largest relative soil OC losses (~5.3 kg C m 2), whereas dry soil conditions alone (in the absence of wildfire) resulted in the smallest carbon losses (~0.1 kg C m 2). Increased fire severity resulted in carbon loss of ~3.3 kg C m 2, whereas changes in snow depth resulted in smaller OC losses (2.1–2.2 kg C m 2). Across multiple climate factors, we observed larger OC losses than for single-factor scenarios. For instance, high fire severity regime associated with warmer and drier conditions resulted in OC losses of ~6.1 kg C m 2, whereas a low fire severity regime associated with warmer and wetter conditions resulted in OC losses of ~5.6 kg C m 2. A longer snow-free season associated with future warming resulted in OC losses of ~5.4 kg C m 2. Soil climate was the dominant control on soil OC loss, governing the sensitivity of microbial decomposers to fluctuations in temperature and soil moisture; this control, in turn, is governed by interannual changes in active layer depth. Transitional responses of the active layer depth to fire regimes also contributed to OC losses, primarily by determining the proportion of OC into frozen and unfrozen soil layers.
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