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Arctic lowlands are characterized by large numbers of small waterbodies, which are known to affect surface energy budgets and the global carbon cycle. Statistical analysis of their size distributions has been hindered by the shortage of observations at sufficiently high spatial resolutions. This situation has now changed with the high-resolution (

One of the most conspicuous signals of climate change in high‐latitude tundra is the expansion of ice wedge thermokarst pools. These small but abundant water features form rapidly in depressions caused by the melting of ice wedges (i.e., meter‐scale bodies of ice embedded within the top of the permafrost). Pool expansion impacts subsequent thaw rates through a series of complex positive and negative feedbacks which play out over timescales of decades and may accelerate carbon release from the underlying sediments. Although many local observations of ice wedge thermokarst pool expansion have been documented, analyses at continental to pan‐Arctic scales have been rare, hindering efforts to project how strongly this process may impact the global carbon cycle. Here we present one of the most geographically extensive and temporally dense records yet compiled of recent pool expansion, in which changes to pool area from 2008 to 2020 were quantified through satellite‐image analysis at 27 survey areas (measuring 10–35 km2 each, or 400 km2 in total) dispersed throughout the circumpolar tundra. The results revealed instances of rapid expansion at 44% (± $\pm $15%) of survey areas. Considered alone, the extent of departures from historical mean air temperatures did not account for between site variation in rates of change to pool area. Pool growth was most clearly associated with upland (i.e., hilly) terrain and elevated silt content at soil depths greater than one meter. These findings suggest that, at short time scales, pedologic and geomorphologic conditions may exert greater control on pool dynamics in the warming Arctic than spatial variability in the rate of air temperature increases. Plain Language Summary: Ice wedge thermokarst pools are meter‐scale water features with a distinctive shape that form on the tundra in response to permafrost thaw. They occupy pits in the ground surface caused by the melting of ice wedges, or subsurface ice bodies which form an interconnected network that manifests at the surface as polygonal ground. Ice wedge thermokarst pool growth not only signals permafrost thaw, but also creates feedbacks on subsequent thaw by altering the surface energy balance, which may accelerate carbon release from permafrost‐affected soils. There are many prior observations of pool growth, but they have typically been locally or regionally focused, and circumpolar analyses are rare. We analyzed recent (2008–2020) time series of sub‐meter resolution satellite imagery at 27 survey areas throughout the Arctic to create one of the largest observational records yet of ice wedge thermokarst pool extent. We then analyzed which environmental and meteorological factors have been most strongly associated with recent trends in pool area at the circumpolar scale. Overall, we found evidence for recent pool growth at 44% (± $\pm $15%) of the survey areas. There was no difference in the recent rate of air temperature increase between sites with and without expanding pools. However, sites with ice wedge thermokarst pool expansion were hillier and had more silt‐rich soils than sites with stable or shrinking pools. Key Points: Decadal‐scale thermokarst pool expansion was observed at 12 (plus or minus 4) of 27 landscapes monitored throughout the ArcticExpanding thermokarst pools were most likely to be found in topographically convex positions within hilly landscapesTrends in air temperature alone were a poor predictor of recent thermokarst pool expansion [ABSTRACT FROM AUTHOR]

Ponds and lakes are abundant in Arctic permafrost lowlands. They play an important role in Arctic wetland ecosystems by regulating carbon, water, and energy fluxes and providing freshwater habitats. However, ponds, i.e., waterbodies with surface areas smaller than 1. 0 × 104ĝ€m2, have not been inventoried on global and regional scales. The Permafrost Region Pond and Lake (PeRL) database presents the results of a circum-Arctic effort to map ponds and lakes from modern (2002-2013) high-resolution aerial and satellite imagery with a resolution of 5ĝ€m or better. The database also includes historical imagery from 1948 to 1965 with a resolution of 6ĝ€m or better. PeRL includes 69 maps covering a wide range of environmental conditions from tundra to boreal regions and from continuous to discontinuous permafrost zones. Waterbody maps are linked to regional permafrost landscape maps which provide information on permafrost extent, ground ice volume, geology, and lithology. This paper describes waterbody classification and accuracy, and presents statistics of waterbody distribution for each site. Maps of permafrost landscapes in Alaska, Canada, and Russia are used to extrapolate waterbody statistics from the site level to regional landscape units. PeRL presents pond and lake estimates for a total area of 1. 4 × 106ĝ€km2 across the Arctic, about 17ĝ€% of the Arctic lowland ( < ĝ€300ĝ€mĝ€a.s.l.) land surface area. PeRL waterbodies with sizes of 1. 0 × 106ĝ€m2 down to 1. 0 × 102ĝ€m2 contributed up to 21ĝ€% to the total water fraction. Waterbody density ranged from 1. 0 × 10 to 9. 4 × 101ĝ€kmĝ'2. Ponds are the dominant waterbody type by number in all landscapes representing 45-99ĝ€% of the total waterbody number. The implementation of PeRL size distributions in land surface models will greatly improve the investigation and projection of surface inundation and carbon fluxes in permafrost lowlands. Waterbody maps, study area boundaries, and maps of regional permafrost landscapes including detailed metadata are available at https://doi.pangaea.de/10.1594/PANGAEA.868349.

CO2 release from thawing permafrost is both a consequence of, and a driver for, global warming, making accurate information on the Arctic carbon cycle essential for climate predictions. Eddy covariance data obtained from Bayelva (Svalbard) in 2015, using well‐established processing and quality control techniques, indicate that most of the annual net CO2 uptake is due to high CO2 flux events in winter that are associated with strong winds and probably relate to technical limitations of the gas analyzer. Emission events may relate to either (unidentified) instrumental limitations or to physical processes such as CO2 advection. Excluding the high winter uptake events yields an annual CO2 budget close to zero; whether or not these events are included can, therefore, have a considerable effect on carbon budget calculations. Further investigation will be crucial to pinpoint the factors causing these high CO2 flux events and to derive scientifically substantiated flux processing standards. Plain Language Summary: Global warming is making Arctic soils thaw, with formerly frozen organic material decomposing and producing the greenhouse gas CO2. This CO2 release further amplifies the rise in temperature. In order to predict how our climate will develop in the future, we, therefore, need to investigate how much CO2 is released into the atmosphere and how much is taken up by plants. Strong CO2 release or uptake signals are not expected during the Arctic winter due to the reduced microbial and plant activity but have nevertheless been observed at Arctic sites. We have investigated CO2 exchanges during the winter of 2015 at the Bayelva site, Svalbard, using the eddy covariance technique. We found that high levels of CO2 emission and uptake occurred during periods with high wind speed and have a significant impact on the calculated net annual CO2 exchange. The apparent CO2 uptake is likely to be an artefact resulting from technical limitations of the instruments, while the high levels of CO2 emission are probably a result of physical processes. However, known physical mechanisms alone, such as episodic outbursts of CO2 stored within the snow, cannot adequately explain our observations. Additional measurements will be required to identify the processes at play. Key Points: High levels of CO2 exchange during the Arctic winter, associated with high wind speeds, have a marked effect on the annual carbon budgetConventional flux measurement and calculation techniques are subject to large uncertainties under Arctic low‐flux conditionsLocal abiotic processes cannot explain the high‐flux events, suggesting advective flux contributions or unidentified instrumental limitations [ABSTRACT FROM AUTHOR]

In high‐latitude and mountain regions, local processes such as redistribution by wind, snow metamorphism, and percolation of water produce a complex spatial distribution of snow depths and snow densities. With its strong control on the ground thermal regime, this snow distribution has pronounced effects on ground temperatures at small spatial scales which are typically not resolved by land surface models (LSMs). This limits our ability to simulate the local impacts of climate change on, for example, vegetation and permafrost. Here, we present a tiling approach combining the CryoGrid permafrost model with snow microphysics parametrizations from the CROCUS snow scheme to account for subgrid lateral exchange of snow and water in a process‐based way. We demonstrate that a simple setup with three coupled tiles, each representing a different snow accumulation class with a specific topographic setting, can reproduce the observed spread of winter‐time ground surface temperatures (GST) and end‐of‐season snow distribution for a high‐Arctic site on Svalbard. For the 3‐year study period, the three‐tile simulations showed substantial improvement compared to traditional single‐tile simulations which naturally cannot account for subgrid variability. Among others, the representation of the warmest and coldest 5% of the observed GST distribution was improved by 1–2°C, while still capturing the average of the distribution. The simulations also reveal positive mean annual GSTs at the locations receiving the greatest snow cover. This could be an indication for the onset of localized permafrost degradation which would be obscured in single‐tile simulations. Key Points: In high‐Arctic areas, wind redistribution of snow leads to a strong variability in snow depths and hence ground surface temperaturesA parametrization for lateral transport of snow between three model tiles is implemented in the CryoGrid 3 permafrost modelThe three‐tile setup reproduces the observed spatial variability of snow depths and ground surface temperatures in a process‐based fashion [ABSTRACT FROM AUTHOR]

Thaw slumps in ice‐rich permafrost can retreat tens of metres per summer, driven by the melt of subaerially exposed ground ice. However, some slumps retain an ice‐veneering debris cover as they retreat. A quantitative understanding of the thermal regime and geomorphic evolution of debris‐covered slumps in a warming climate is largely lacking. To characterize the thermal regime, we instrumented four debris‐covered slumps in the Canadian Low Arctic and developed a numerical conduction‐based model. The observed surface temperatures >20° C and steep thermal gradients indicate that debris insulates the ice by shifting the energy balance towards radiative and turbulent losses. After the model was calibrated and validated with field observations, it predicted sub‐debris ice melt to decrease four‐fold from 1.9 to 0.5 mas the thickness of the fine‐grained debris quadruples from 0.1 to 0.4 m. With warming temperatures, melt is predicted to increase most rapidly, in relative terms, for thick (∼0.5–1.0 m) debris covers. The morphology and evolution of the debris‐covered slumps were characterized using field and remote sensing observations, which revealed differences in association with morphology and debris composition. Two low‐angle slumps retreated continually despite their persistent fine‐grained debris covers. The observed elevation losses decreased from ∼1.0 m/yr where debris thickness ∼0.2 mto 0.1 m/yr where thickness ∼1.0 m. Conversely, a steep slump with a coarse‐grained debris veneer underwent short‐lived bursts of retreat, hinting at a complex interplay of positive and negative feedback processes. The insulative protection and behaviour of debris vary significantly with factors such as thickness, grain size and climate: debris thus exerts a fundamental, spatially variable influence on slump trajectories in a warming climate. © 2020 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Knowledge of soil moisture conditions is important for modeling soil temperatures, as soil moisture influences the thermal dynamics in multiple ways. However, in permafrost regions, soil moisture is highly heterogeneous and difficult to model. Satellite soil moisture data may fill this gap, but the degree to which they can improve permafrost modeling is unknown. To explore their added value for modeling soil temperatures, we assimilate fine‐scale satellite surface soil moisture into the CryoGrid‐3 permafrost model, which accounts for the soil moisture's influence on the soil thermal properties and the surface energy balance. At our study site in the Canadian Arctic, the assimilation improves the estimates of deeper (>10 cm) soil temperatures during summer but not consistently those of the near‐surface temperatures. The improvements in the deeper temperatures are strongly contingent on soil type: They are largest for porous organic soils (30%), smaller for thin organic soil covers (20%), and they essentially vanish for mineral soils (only synthetic data available). That the improvements are greatest over organic soils reflects the strong coupling between soil moisture and deeper temperatures. The coupling arises largely from the diminishing soil thermal conductivity with increasing desiccation thanks to which the deeper soil is kept cool. It is this association of dry organic soils being cool at depth that lets the assimilation revise the simulated soil temperatures toward the actually measured ones. In the future, the increasing availability of satellite soil moisture data holds promise for the operational monitoring of soil temperatures, hydrology, and biogeochemistry. Plain Language Summary: We explore whether soil moisture data improve the accuracy with which we can predict the soil temperature profile in cold regions. Knowledge of the temperature conditions is important for monitoring the stability of the terrain, for understanding the response of vegetation and microorganisms, and many other applications. Soil moisture data may be useful in this context because soil moisture influences the thermal dynamics of the soil, but so far, such data have been in short supply. Using novel satellite soil moisture data, we show that soil moisture information does indeed help to improve the estimates of deeper temperatures, at least in organic soils. In the future, the increasing availability of satellite soil moisture data holds promise for the operational monitoring of soil temperatures, hydrology, and biogeochemistry. Key Points: Satellite soil moisture was assimilated into a permafrost model to constrain temperature profilesTemperature estimates improved most for porous organic soils, mediated by the strong moisture control on thermal conductivityImprovements were larger for deeper temperatures than for surface temperatures [ABSTRACT FROM AUTHOR]

Abstract: We conducted eddy covariance measurements from April to August 2014 on a Siberian thermokarst lake. The study site is located in the Lena River Delta and characterized as a floating ice lake. Heat fluxes differed in magnitudes, directions and temporal patterns depending on the lake surface conditions (“frozen” ice cover, ice cover melt, and open water). Significant heat release during frozen ice cover conditions highlighted the importance of lakes for the landscape heat budget and water balance. The energy balance was nearly closed during the open water period and highlighted the impact of melting energy on its closure during the ice cover period. Sensible and latent heat dynamics were driven by temperature and water vapor gradients scaled by wind speed, respectively. We calculated bulk aerodynamics transfer coefficients and evaluated the performance of the derived in situ and three independent heat flux parameterization schemes. We found that bulk transfer models perform moderately to poorly for the different lake surface conditions. During the open water period small‐scale temporal variability could not be represented by the models, particularly in case of latent heat flux. The model results were less sensitive to the specific model type than to the accuracy of the surface water temperature measurement, which is dependent on a well‐thought‐out measurement design. Our study stresses considerations that are crucial for similar campaigns in the future, in order to face the measurement challenges encountered on arctic lakes especially during the ice cover period. [ABSTRACT FROM AUTHOR]

Thawing of permafrost in a warming climate is governed by a complex interplay of different processes of which only conductive heat transfer is taken into account in most model studies. However, observations in many permafrost landscapes demonstrate that lateral and vertical movement of water can have a pronounced influence on the thaw trajectories, creating distinct landforms, such as thermokarst ponds and lakes, even in areas where permafrost is otherwise thermally stable. Novel process parameterizations are required to include such phenomena in future projections of permafrost thaw and subsequent climatictriggered feedbacks. In this study, we present a new landsurface scheme designed for permafrost applications, Cryo-Grid 3, which constitutes a flexible platform to explore new parameterizations for a range of permafrost processes. We document the model physics and employed parameterizations for the basis module CryoGrid 3, and compare model results with in situ observations of surface energy balance, surface temperatures, and ground thermal regime from the Samoylov permafrost observatory in NE Siberia. The comparison suggests that CryoGrid 3 can not only model the evolution of the ground thermal regime in the last decade, but also consistently reproduce the chain of energy transfer processes from the atmosphere to the ground. In addition, we demonstrate a simple 1-D parameterization for thaw processes in permafrost areas rich in ground ice, which can phenomenologically reproduce both formation of thermokarst ponds and subsidence of the ground following thawing of ice-rich subsurface layers. Long-term simulation from 1901 to 2100 driven by reanalysis data and climate model output demonstrate that the hydrological regime can both accelerate and delay permafrost thawing. If meltwater from thawed ice-rich layers can drain, the ground subsides, as well as the formation of a talik, are delayed. If the meltwater pools at the surface, a pond is formed that enhances heat transfer in the ground and leads to the formation of a talik. The model results suggest that the trajectories of future permafrost thaw are strongly influenced by the cryostratigraphy, as determined by the late Quaternary history of a site. [ABSTRACT FROM AUTHOR]

It is important to correctly simulate permafrost in global climate models, since the stored carbon represents the source of a potentially important climate feedback. This carbon feedback depends on the physical state of the permafrost. We have therefore included improved physical permafrost processes in JULES (Joint UK Land Environment Simulator), which is the land-surface scheme used in the Hadley Centre climate models. The thermal and hydraulic properties of the soil were modified to account for the presence of organic matter, and the insulating effects of a surface layer of moss were added, allowing for fractional moss cover. These processes are particularly relevant in permafrost zones. We also simulate a higherresolution soil column and deeper soil, and include an additional thermal column at the base of the soil to represent bedrock. In addition, the snow scheme was improved to allow it to run with arbitrarily thin layers. Point-site simulations at Samoylov Island, Siberia, show that the model is now able to simulate soil temperatures and thaw depth much closer to the observations. The root mean square error for the near-surface soil temperatures reduces by approximately 30 %, and the active layer thickness is reduced from being over 1m too deep to within 0.1m of the observed active layer thickness. All of the model improvements contribute to improving the simulations, with organic matter having the single greatest impact. A new method is used to estimate active layer depth more accurately using the fraction of unfrozen water. Soil hydrology and snow are investigated further by holding the soil moisture fixed and adjusting the parameters to make the soil moisture and snow density match better with observations. The root mean square error in near-surface soil temperatures is reduced by a further 20% as a result. [ABSTRACT FROM AUTHOR]

Thermokarst lakes are typical features of the northern permafrost ecosystems, and play an important role in the thermal exchange between atmosphere and subsurface. The objective of this study is to describe the main thermal processes of the lakes and to quantify the heat exchange with the underlying sediments. The thermal regimes of five lakes located within the continuous permafrost zone of northern Siberia (Lena River Delta) were investigated using hourly water temperature and water level records covering a 3-year period (2009-2012), together with bathymetric survey data. The lakes included thermokarst lakes located on Holocene river terraces that may be connected to Lena River water during spring flooding, and a thermokarst lake located on deposits of the Pleistocene Ice Complex. Lakes were covered by ice up to 2m thick that persisted for more than 7 months of the year, from October until about mid-June. Lake-bottom temperatures increased at the start of the ice-covered period due to upward-directed heat flux from the underlying thawed sediment. Prior to ice break-up, solar radiation effectively warmed the water beneath the ice cover and induced convective mixing. Ice break-up started at the beginning of June and lasted until the middle or end of June. Mixing occurred within the entire water column from the start of ice breakup and continued during the ice-free periods, as confirmed by the Wedderburn numbers, a quantitative measure of the balance between wind mixing and stratification that is important for describing the biogeochemical cycles of lakes. The lake thermal regime was modeled numerically using the FLake model. The model demonstrated good agreement with observations with regard to the mean lake temperature, with a good reproduction of the summer stratification during the ice-free period, but poor agreement during the ice-covered period. Modeled sensitivity to lake depth demonstrated that lakes in this climatic zone with mean depths > 5m develop continuous stratification in summer for at least 1 month. The modeled vertical heat flux across the bottom sediment tends towards an annual mean of zero, with maximum downward fluxes of about 5Wm-2 in summer and with heat released back into the water column at a rate of less than 1Wm-2 during the ice-covered period. The lakes are shown to be efficient heat absorbers and effectively distribute the heat through mixing. Monthly bottom water temperatures during the ice-free period range up to 15 °C and are therefore higher than the associated monthly air or ground temperatures in the surrounding frozen permafrost landscape. The investigated lakes remain unfrozen at depth, with mean annual lake-bottom temperatures of between 2.7 and 4 °C. [ABSTRACT FROM AUTHOR]

The thermal regimes of five lakes located within the continuous permafrost zone of northern Siberia (Lena River Delta) have been investigated using hourly water temperature and water level records covering a three year period (2009-2012), together with bathymetric survey data. The lakes included thermokarst lakes located on Holocene river terraces that may be connected to Lena River water during spring flooding, and a thermokarst lake located on deposits of the Pleistocene Ice Complex. The data were used for numerical modeling with FLake software, and also to determine the physical indices of the lakes. The lakes vary in area, depths and volumes. The winter thermal regime is characterized by an ice cover up to 2 m thick that survives for more than 7 months of the year, from October until about mid-June. Lake-bottom temperatures increase at the start of the ice-covered period due to upward-directed heat flux from the underlying thawed sediment. The effects of solar radiation return prior to ice break-up, effectively warming the water beneath the ice cover and inducing convective mixing. Ice break-up starts the beginning of June and takes until the middle or end of June for completion. Mixing occurs within the entire water column from the start of ice break-up and continues during the ice-free periods, as confirmed by the Wedderburn numbers. Some of the lakes located closest to the Lena River are subjected to varying levels of spring flooding with river water, on an annual basis. Numerical modeling using FLake software indicates that the vertical heat flux across the bottom sediment tends towards an annual mean of zero, with maximum downward fluxes of about 5 W m-2 in summer and with heat released back into the water column at a~rate of less than 1 W m-2 during the ice-covered period. The lakes are shown to be efficient heat absorbers and effectively distribute the heat through mixing. Monthly bottom water temperatures during the ice-free period range up to 15 °C and are therefore higher than the associated monthly air or ground temperatures in the surrounding frozen permafrost landscape. The investigated lakes remain unfrozen at depth, with mean annual lake-bottom temperatures of between 2.7 and 4 °C. [ABSTRACT FROM AUTHOR]

There is a large amount of organic carbon stored in permafrost in the northern high latitudes, which may become vulnerable to microbial decomposition under future climate warming. In order to estimate this potential carbon-climate feedback it is necessary to correctly simulate the physical dynamics of permafrost within global Earth system models (ESMs) and to determine the rate at which it will thaw. Additional new processes within JULES, the land-surface scheme of the UK ESM (UKESM), include a representation of organic soils, moss and bedrock and a modification to the snow scheme; the sensitivity of permafrost to these new developments is investigated in this study. The impact of a higher vertical soil resolution and deeper soil column is also considered. Evaluation against a large group of sites shows the annual cycle of soil temperatures is approximately 25% too large in the standard JULES version, but this error is corrected by the model improvements, in particular by deeper soil, organic soils, moss and the modified snow scheme. A comparison with active layer monitoring sites shows that the active layer is on average just over 1m too deep in the standard model version, and this bias is reduced by 70 cm in the improved version. Increasing the soil vertical resolution allows the full range of active layer depths to be simulated; by contrast, with a poorly resolved soil at least 50% of the permafrost area has a maximum thaw depth at the centre of the bottom soil layer. Thus all the model modifications are seen to improve the permafrost simulations. Historical permafrost area corresponds fairly well to observations in all simulations, covering an area between 14 and 19 millionkm2. Simulations under two future climate scenarios show a reduced sensitivity of permafrost degradation to temperature, with the near-surface permafrost loss per degree of warming reduced from 1.5 millionkm2 °C-1 in the standard version of JULES to between 1.1 and 1.2 millionkm2 °C-1 in the new model version. However, the near-surface permafrost area is still projected to approximately half by the end of the 21st century under the RCP8.5 scenario. [ABSTRACT FROM AUTHOR]

Modeling soil thermal dynamics at high latitudes and altitudes requires representations of physical processes such as snow insulation, soil freezing and thawing and subsurface conditions like soil water/ice content and soil texture. We have compared six different land models: JSBACH, ORCHIDEE, JULES, COUP, HYBRID8 and LPJ-GUESS, at four different sites with distinct cold region landscape types, to identify the importance of physical processes in capturing observed temperature dynamics in soils. The sites include alpine, high Arctic, wet polygonal tundra and non-permafrost Arctic, thus showing how a range of models can represent distinct soil temperature regimes. For all sites, snow insulation is of major importance for estimating topsoil conditions. However, soil physics is essential for the subsoil temperature dynamics and thus the active layer thicknesses. This analysis shows that land models need more realistic surface processes, such as detailed snow dynamics and moss cover with changing thickness and wetness, along with better representations of subsoil thermal dynamics. [ABSTRACT FROM AUTHOR]

High-latitude soils store vast amounts of perennially frozen and therefore inert organic matter. With rising global temperatures and consequent permafrost degradation, a part of this carbon stock will become available for microbial decay and eventual release to the atmosphere. We have developed a simplified, two-dimensional multi-pool model to estimate the strength and timing of future carbon dioxide (CO2) and methane (CH4) fluxes from newly thawed permafrost carbon (i.e. carbon thawed when temperatures rise above pre-industrial levels). We have especially simulated carbon release from deep deposits in Yedoma regions by describing abrupt thaw under newly formed thermokarst lakes. The computational efficiency of our model allowed us to run large, multi-centennial ensembles under various scenarios of future warming to express uncertainty inherent to simulations of the permafrost carbon feedback. Under moderate warming of the representative concentration pathway (RCP) 2.6 scenario, cumulated CO2 fluxes from newly thawed permafrost carbon amount to 20 to 58 peta-grams of carbon (Pg-C) (68 % range) by the year 2100 and reach 40 to 98 Pg-C in 2300. The much larger permafrost degradation under strong warming (RCP8.5) results in cumulated CO2 release of 42 to 141 Pg-C and 157 to 313 Pg-C (68% ranges) in the years 2100 and 2300, respectively. Our estimates only consider fluxes from newly thawed permafrost, not from soils already part of the seasonally thawed active layer under pre-industrial climate. Our simulated CH4 fluxes contribute a few percent to total permafrost carbon release yet they can cause up to 40 % of total permafrost-affected radiative forcing in the 21st century (upper 68% range). We infer largest CH4 emission rates of about 50 Tg-CH4 per year around the middle of the 21st century when simulated thermokarst lake extent is at its maximum and when abrupt thaw under thermokarst lakes is taken into account. CH4 release from newly thawed carbon in wetland-affected deposits is only discernible in the 22nd and 23rd century because of the absence of abrupt thaw processes. We further show that release from organic matter stored in deep deposits of Yedoma regions crucially affects our simulated circumpolar CH4 fluxes. The additional warming through the release from newly thawed permafrost carbon proved only slightly dependent on the pathway of anthropogenic emission and amounts to about 0.03-0.14 °C (68 % ranges) by end of the century. The warming increased further in the 22nd and 23rd century and was most pronounced under the RCP6.0 scenario, adding 0.16 to 0.39 °C (68% range) to simulated global mean surface air temperatures in the year 2300. [ABSTRACT FROM AUTHOR]

Lakes and ponds play a key role in the carbon cycle of permafrost ecosystems, where they are considered to be hotspots of carbon dioxide CO2 and methane CH4 emission. The strength of these emissions is, however, controlled by a variety of physical and biogeochemical processes whose responses to a warming climate are complex and only poorly understood. Small waterbodies have been attracting an increasing amount of attention since recent studies demonstrated that ponds can make a significant contribution to the CO2 and CH4 emissions of tundra ecosystems. Waterbodies also have a marked effect on the thermal state of the surrounding permafrost; during the freezing period they prolong the period of time during which thawed soil material is available for microbial decomposition. This study presents net CH4 production rates during the freezing period from ponds within a typical lowland tundra landscape in northern Siberia. Rate estimations were based on CH4 concentrations measured in surface lake ice from a variety of waterbody types. Vertical profiles along ice blocks showed an exponential increase in CH4 concentration with depth. These CH4 profiles were reproduced by a 1-D mass balance model and the net CH4 production rates were then inferred through inverse modeling. Results revealed marked differences in early winter net CH4 production among various ponds. Ponds situated within intact polygonal ground structures yielded low net production rates, of the order of 10-11 to 10-10 molm-2 s-1 (0:01 to 0:14mg>CH4 m-2 day-1). In contrast, ponds exhibiting clear signs of erosion yielded net CH4 production rates of the order of 10-7 molm-2 s-1 (140mgCH4 m-2 day-1). Our results therefore indicate that once a particular threshold in thermal erosion has been crossed, ponds can develop into major CH4 sources. This implies that any future warming of the climate may result in nonlinear CH4 emission behavior in tundra ecosystems. [ABSTRACT FROM AUTHOR]

High-latitude soils store vast amounts of perennially frozen and therefore inert organic matter. With rising global temperatures and consequent permafrost degradation, a part of this carbon store will become available for microbial decay and eventual release to the atmosphere. We have developed a simplified, two-dimensional multi-pool model to estimate the strength and timing of future carbon dioxide (CO2) and methane (CH4) fluxes from newly thawed permafrost carbon (i.e. carbon thawed when temperatures rise above pre-industrial levels). We have especially simulated carbon release from deep deposits in Yedoma regions by describing abrupt thaw under thermokarst lakes. The computational efficiency of our model allowed us to run large, multi-centennial ensembles under various scenarios of future warming to express uncertainty inherent to simulations of the permafrost-carbon feedback. Under moderate warming of the representative concentration pathway (RCP) 2.6 scenario, cumulated CO2 fluxes from newly thawed permafrost carbon amount to 20 to 58 petagrammes of carbon (Pg-C) (68% range) by the year 2100 and reach 40 to 98 Pg-C in 2300. The much larger permafrost degradation under strong warming (RCP8.5) results in cumulated CO2 release of 42-141 and 157-313 Pg-C (68% ranges) in the years 2100 and 2300, respectively. Our estimates do only consider fluxes from newly thawed permafrost but not from soils already part of the seasonally thawed active layer under preindustrial climate. Our simulated methane fluxes contribute a few percent to total permafrost carbon release yet they can cause up to 40 % of total permafrost-affected radiative forcing in the 21st century (upper 68% range). We infer largest methane emission rates of about 50Tg-CH4year-1 around the mid of the 21st century when simulated thermokarst lake extent is at its maximum and when abrupt thaw under thermokarst lakes is accounted for. CH4 release from newly thawed carbon in wetland-affected deposits is only discernible in the 22nd and 23rd century because of the absence of abrupt thaw processes. We further show that release from organic matter stored in deep deposits of Yedoma regions does crucially affect our simulated circumpolar methane fluxes. The additional warming through the release from newly thawed permafrost carbon proved only slightly dependent on the pathway of anthropogenic emission and amounts about 0.03-0.14°C (68% ranges) by end of the century. The warming increased further in the 22nd and 23rd century and was most pronounced under the RCP6.0 scenario with adding 0.16-0.39°C (68% range) to simulated global mean surface air temperatures in the year 2300. [ABSTRACT FROM AUTHOR]

Subgrid processes occur in various ecosystems and landscapes but, because of their small scale, they are not represented or poorly parameterized in climate models. These local heterogeneities are often important or even fundamental for energy and carbon balances. This is especially true for northern peatlands and in particular for the polygonal tundra, where methane emissions are strongly influenced by spatial soil heterogeneities. We present a stochastic model for the surface topography of polygonal tundra using Poisson-Voronoi diagrams and we compare the results with available recent field studies. We analyze seasonal dynamics of water table variations and the landscape response under different scenarios of precipitation income. We upscale methane fluxes by using a simple idealized model for methane emission. Hydraulic interconnectivities and large-scale drainage may also be investigated through percolation properties and thresholds in the Voronoi graph. The model captures the main statistical characteristics of the landscape topography, such as polygon area and surface properties as well as the water balance. This approach enables us to statistically relate large-scale properties of the system to the main small-scale processes within the single polygons. [ABSTRACT FROM AUTHOR]

Freeze/thaw (F/T) processes can be quite different under the various land surface types found in the heterogeneous polygonal tundra of the Arctic. Proper simulation of these different processes is essential for accurate prediction of the release of greenhouse gases under a warming climate scenario. In this study we have modified the dynamic organic soil version of the Terrestrial Ecosystem Model (DOS-TEM) to simulate F/T processes beneath the polygon rims, polygon centers (with and without water), and lakes that are common features in Arctic lowland regions. We first verified the F/T algorithm in the DOS-TEM against analytical solutions, and then compared the results with in situ measurements from Samoylov Island, Siberia. In the final stage, we examined the different responses of the F/T processes for different water levels at the various land surface types. The simulations revealed that (1) the DOS-TEM was very efficient and its results compared very well with analytical solutions for idealized cases, (2) the simulations compared reasonably well with in situ measurements although there were a number of model limitations and uncertainties, (3) the DOS-TEM was able to successfully simulate the differences in F/T dynamics under different land surface types, and (4) permafrost beneath water bodies was found to respond highly sensitive to changes in water depths between 1 and 2 m. Our results indicate that water is very important in the thermal processes simulated by the DOS-TEM; the heterogeneous nature of the landscape and different water depths therefore need to be taken into account when simulating methane emission responses to a warming climate. [ABSTRACT FROM AUTHOR]

Samoylov Island is centrally located within the Lena River Delta at 72° N, 126° E and lies within the Siberian zone of continuous permafrost. The landscape on Samoylov Island consists mainly of late Holocene river terraces with polygonal tundra, ponds and lakes, and an active floodplain. The island has been the focus of numerous multidisciplinary studies since 1993, which have focused on climate, land cover, ecology, hydrology, permafrost and limnology. This paper aims to provide a framework for future studies by describing the characteristics of the island's meteorological parameters (temperature, radiation and snow cover), soil temperature, and soil moisture. The land surface characteristics have been described using high resolution aerial images in combination with data from ground-based observations. Of note is that deeper permafrost temperatures have increased between 0.3 to 1.3 °C over the last five years. However, no clear warming of air and active layer temperatures is detected since 1998, though winter air temperatures during recent years have not been as cold as in earlier years. [ABSTRACT FROM AUTHOR]

Samoylov Island is centrally located within the Lena River Delta at 72° N, 126° E and lies within the Siberian zone of continuous permafrost. The landscape on Samoylov Island consists mainly of late Holocene river terraces with polygonal tundra, ponds and lakes, and an active floodplain. The island has been the focus of numerous multidisciplinary studies since 1993, which have focused on climate, land cover, ecology, hydrology, permafrost, and limnology. This paper aims to provide a framework for future studies by describing the characteristics of the island's meteorological parameters (temperature, radiation, and snow cover), soil temperature, and soil moisture. The land surface characteristics have been described using high resolution aerial images in combination with data from ground-based observations. Of note is that deeper permafrost temperatures have increased between 0.5 to 1 °C over the last five years. However, no clear warming of air and active layer temperatures is detected since 1998, though winter air temperatures during recent years have not been as cold as in earlier years. [ABSTRACT FROM AUTHOR]

Information on soil surface state is valuable for many applications such as climate studies and monitoring of permafrost regions. C-band scatterometer data indicate good potential to deliver information on surface freeze/thaw. Variation in state or amount of water contained in the soil causes significant alteration of dielectric properties of the soil which is markedly observable in scatterometer backscattered signal. A threshold-analysis method is developed to derive a set of parameters to be used in evaluating the normalized backscatter measurements through decision trees and anomaly detection modules for determination of freeze/thaw conditions. The model parameters are extracted from two years (2007-2008) backscatter data from ASCAT scatterometer onboard Metop satellite collocated with ECMWF ReAnalysis (ERA-Interim) soil temperature. Backscatter measurements are flagged as indicator of frozen/unfrozen surface, and snowmelt or existing water on the surface. The output product, so-called surface state flag (SSF), compares well with two modeled soil temperature data sets as well as the air temperature measurements from synoptic meteorological stations across the northern hemisphere. The SSF time series are also validated with soil temperature data available at four in situ observation sites in Siberian and Alaska regions showing the overall accuracy of about 80% to 90%. [ABSTRACT FROM AUTHOR]

Although ponds make up roughly half of the total area of surface water in permafrost landscapes, their relevance to carbon dioxide emissions on a landscape scale has, to date, remained largely unknown. We have therefore investigated the inflows and outflows of dissolved organic and inorganic carbon from lakes, ponds, and outlets on Samoylov Island, in the Lena Delta of northeastern Siberia in September 2008, together with their carbon dioxide emissions. Outgassing of carbon dioxide (CO2) from these ponds and lakes, which cover 25% of Samoylov Island, was found to account for between 74 and 81% of the calculated net landscape-scale CO2 emissions of 0.2-1.1 g C m-2 d-1 during September 2008, of which 28-43% was from ponds and 27-46% from lakes. The lateral export of dissolved carbon was negligible compared to the gaseous emissions due to the small volumes of runoff. The concentrations of dissolved inorganic carbon in the ponds were found to triple during freezeback, highlighting their importance for temporary carbon storage between the time of carbon production and its emission as CO2. If ponds are ignored the total summer emissions of CO2-C from water bodies of the islands within the entire Lena Delta (0.7-1.3 Tg) are underestimated by between 35 and 62%. [ABSTRACT FROM AUTHOR]

The article presents a study on the use stochastic model based on Poisson-Voronoi Diagrams to analyze polygonal tundra. The study analyzes the landscape response and seasonal dynamics of water table variations under different precipitation income scenarios and the geometric characteristics of polygonal tundra and physical vapor deposition (PVD). Result shows that the model can show the statistical qualities of landscape topography like polygon area, water balance, and surface properties.

Ignoring small-scale heterogeneities in Arctic land cover may bias estimates of water, heat and carbon fluxes in large-scale climate and ecosystem models. We investigated subpixel-scale heterogeneity in CHRIS/PROBA and Landsat-7 ETM + satellite imagery over ice-wedge polygonal tundra in the Lena Delta of Siberia, and the associated implications for evapotranspiration (ET) estimation. Field measurements were combined with aerial and satellite data to link fine-scale (0.3m resolution) with coarse-scale (upto 30m resolution) land cover data. A large portion of the total wet tundra (80%) and water body area (30%) appeared in the form of patches less than 0.1 ha in size, which could not be resolved with satellite data. Wet tundra and small water bodies represented about half of the total ET in summer. Their contribution was reduced to 20% in fall, during which ET rates from dry tundra were highest instead. Inclusion of subpixel-scale water bodies increased the total water surface area of the Lena Delta from 13% to 20%. The actual land/water proportions within each composite satellite pixel was best captured with Landsat data using a statistical downscaling approach, which is recommended for reliable large-scale modelling of water, heat and carbon exchange from permafrost landscapes. [ABSTRACT FROM AUTHOR]

The article presents a study on the impact of wintertime rain events on the thermal regime of permafrost in Svalbard, Norway. It mentions field measurements and numerical process modeling from the western part of the archipelago which show effect of the events on the ground surface temperature underneath the snow. It also notes the percolation of rain water under the snow pack where it freezes and releases potential heat.

The article presents a study which examines the thermal dynamics of the active layers at permafrost sites in Svalbard, Norway and in the Tibetan Plateau. The study uses a thermal and hydraulic numerical model with parameters such as heat conduction, heat convection and liquid water flow to analyze the applicability of the model and to quantify the process dominating the sites. It is found out that both sites are dominated by the process of heat conduction.

The article discusses a study on winter time surface energy balance at a polygonal tundra site in northern Siberia, Russia. It mentions that the study was based on independent measurements of net radiation as well as sensible and ground heat fluxes from different winter seasons. It notes radiative losses which are balanced to 60% by the heat fluxes. It also points out the major controlling factors of surface energy budget such as the snow cover, cloudiness and soil temperature gradient.

The article presents a study on the surface energy balance of a polygonal tundra landscape in Siberia, Russia. It discusses the surface energy balance which is obtained from independent measurements of net radiation, heat fluxes and ground heat flux and added that its controlling factors for partitioning are snow cover, cloud cover and temperature gradient in the soil. It concludes that energy balance is the key to a more complete understanding of the couple permafrost-snow-atmosphere system.

The article assesses the active layer dynamics at the high-arctic continuous permafrost site in Svalbard, Norway. It tackles the thaw depths inferred from non-invasive multi-channel ground-penetrating radar (GPR). It also evaluates the average volumetric soil water content and presents the estimation of the sensible heat content of the soil.

An abstract of the article "Page21: A Large-Scale International and Integrated Project to Measure the Impact of Permafrost Degradation on the Climate System," by Hans-Wolfgang Hubberten is presented.

Field campaigns were undertaken in May and June of 1992 and 1997 in order to study spectral reflectance characteristics of snow during melt-off. The investigations were performed on snow-covered tundra at Ny-Alesund, Svalbard (79 deg. N). Spectral measurements were acquired with spectroradiometers covering wavelengths from 350 to 2500 nm. Supporting measurements such as snow thickness, density, content of liquid water, grain size and shape, stratification of snowpack, as well as cloud observations and air temperature, were monitored throughout the field campaigns. Spectral measurements demonstrate that the near-infrared albedo is most affected by the ongoing snow metamorphism while the albedo in the visible wavelength range is more strongly affected by surface pollution. Comparisons of spectral measurements and spectrally integrated measurements emphasize the need for narrow-band to broad-band conversion when applying satellite-derived albedo to surface energy-balance calculations. As an example, Landsat TM Band 4 albedo is shown to produce slightly high albedo values compared to the spectrally integrated albedo (285-2800 nm). Daily albedo measurements from 1981-1997 show that the albedo normally drops from 80% to bare ground levels (10%) within two to four weeks and the date when the tundra becomes snow-free varies from early June to early July. Thus, the changing spectral characteristics of snow during melt-off combined with a general rapid decrease in albedo call for cautious use of satellite-derived albedo, especially when used as absolute numbers. Our data also illustrate the effect of cloud cover on surface albedo for an event in which the integrated albedo increased by 7% under cloudy conditions compared to clear skies without changes of surface properties. Finally, the reflectance of snow increases relative to nadir for measurements facing the sun and at azimuths 90 deg. and 180 deg. by 8, 15, 19, and 26% for viewing angles 15 deg. , 30 deg. , 45 deg. , an [ABSTRACT FROM AUTHOR]

Abstract: Thermokarst lakes and basins are major components of ice-rich permafrost landscapes in East Siberian coastal lowlands and are regarded as indicators of regional climatic changes. We investigate the temporal and spatial dynamics of a 7.5km2, partly drained thermokarst basin (alas) using field investigations, remote sensing, Geographic Information Systems (GIS), and sediment analyses. The evolution of the thermokarst basin proceeded in two phases. The first phase started at the Pleistocene/Holocene transition (13 to 12ka BP) with the initiation of a primary thermokarst lake on the Ice Complex surface. The lake expanded and persisted throughout the early Holocene before it drained abruptly about 5.7ka BP, thereby creating a >20m deep alas with residual lakes. The second phase (5.7ka BP to present) is characterized by alternating stages of lower and higher thermokarst intensity within the alas that were mainly controlled by local hydrological and relief conditions and accompanied by permafrost aggradation and degradation. It included diverse concurrent processes like lake expansion and stepwise drainage, polygonal ice-wedge growth, and the formation of drainage channels and a pingo, which occurred in different parts of the alas. This more dynamic thermokarst evolution resulted in a complex modern thermokarst landscape. However, on the regional scale, the changes during the second evolutionary phase after drainage of the initial thermokarst lakes were less intense than the early Holocene extensive thermokarst development in East Siberian coastal lowlands as a result of a significant regional change to warmer and wetter climate conditions. [Copyright &y& Elsevier]

Arctic soil microbial communities may shift with increasing temperatures and water availability from climate change. We examined temperature and volumetric liquid water content (VWC) in the upper 80 cm of permafrost-affected soil over 2 years (2018-2019) at the Bayelva monitoring station, Ny Ålesund, Svalbard. We show VWC increases with depth, whereas in situ temperature is more stable vertically, ranging from -5°C to 5 °C seasonally. Prokaryotic metagenome-assembled genomes (MAGs) were obtained at 2-4 cm vertical resolution collected while frozen in April 2018 and at 10 cm vertical resolution collected while thawed in September 2019. The most abundant MAGs were Acidobacteriota, Actinomycetota, and Chloroflexota. Actinomycetota and Chloroflexota increase with depth, while Acidobacteriota classes Thermoanaerobaculia Gp7-AA8, Blastocatellia UBA7656, and Vicinamibacteria Vicinamibacterales are found above 6 cm, below 6 cm, and below 20 cm, respectively. All MAGs have diverse carbon-degrading genes, and Actinomycetota and Chloroflexota have autotrophic genes. Genes encoding β -glucosidase, N-acetyl-β-D-glucosaminidase, and xylosidase increase with depth, indicating a greater potential for organic matter degradation with higher VWC. Acidobacteriota dominate the top 6 cm with their classes segregating by depth, whereas Actinomycetota and Chloroflexota dominate below ∼6 cm. This suggests that Acidobacteriota classes adapt to lower VWC at the surface, while Actinomycetota and Chloroflexota persist below 6 cm with higher VWC. This indicates that VWC may be as important as temperature in microbial climate change responses in Arctic mineral soils. Here we describe MAG-based Seqcode type species in the Acidobacteriota, Onstottus arcticum, Onstottus frigus, and Gilichinskyi gelida and in the Actinobacteriota, Mayfieldus profundus., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier GmbH.)

Purpose: This study aimed to present the institutional experience and algorithm for performing biliary interventions in liver transplant patients using the modified Hutson loop access (MHLA) and the impact of percutaneous endoscopy via the MHLA on these procedures., Methods: Over 13 years, 201 MHLA procedures were attempted on 52 patients (45 liver transplants; 24 living and 21 deceased donors) for diagnostic (e.g., cholangiography) and therapeutic (e.g., stent/drain insertion and cholangioplasty) purposes. The most common indications for MHLA were biliary strictures (60%) and bile leaks (23%). Percutaneous endoscopy was used to directly visualize the biliary-enteric anastomosis, diagnose pathology (e.g., ischemic cholangiopathy), and help in biliary hygiene (removing debris/casts/stones/stents) in 138/201 (69%) procedures. Technical success was defined as cannulating the biliary-enteric anastomosis and performing diagnostic/therapeutic procedure via the MHLA., Results: The technical success rate was 95% (190/201). The failure rate among procedures performed with and without endoscopy was 2% (3/138) versus 13% (8/63) (P = 0.0024), and the need for new transhepatic access (to aid the procedure) was 12% (16/138) versus 30% (19/63) (P = 0.001). Despite endoscopy, failure in 2% of the cases resulted from inflamed/friable anastomosis (1/3) and high-grade stricture (2/3) obstructing retrograde cannulation of biliary-enteric anastomosis. Major adverse events (bowel perforation and injury) occurred in 1% of the procedures, with no procedure-related mortality., Conclusions: MHLA-based percutaneous biliary intervention is a safe and effective alternative to managing complications after liver transplant. Percutaneous endoscopy via the MHLA improves success rates and may reduce the need for new transhepatic access. Level of Evidence Level 4., (© 2024. Springer Science+Business Media, LLC, part of Springer Nature and the Cardiovascular and Interventional Radiological Society of Europe (CIRSE).)