The Arctic climate is changing. Permafrost is warming, hydrological processes are changing and biological and social systems are also evolving in response to these changing conditions. Knowing how the structure and function of arctic terrestrial ecosystems are responding to recent and persistent climate change is paramount to understanding the future state of the Earth system and how humans will need to adapt. Our holistic review presents a broad array of evidence that illustrates convincingly; the Arctic is undergoing a system-wide response to an altered climatic state. New extreme and seasonal surface climatic conditions are being experienced, a range of biophysical states and processes influenced by the threshold and phase change of freezing point are being altered, hydrological and biogeochemical cycles are shifting, and more regularly human sub-systems are being affected. Importantly, the patterns, magnitude and mechanisms of change have sometimes been unpredictable or difficult to isolate due to compounding factors. In almost every discipline represented, we show Climatic Change (2005) 72: 251-298 how the biocomplexity of the Arctic system has highlighted and challenged a paucity of integrated scientific knowledge, the lack of sustained observational and experimental time series, and the technical and logistic constraints of researching the Arctic environment. This study supports ongoing efforts to strengthen the interdisciplinarity of arctic system science and improve the coupling of large scale experimental manipulation with sustained time series observations by incorporating and integrating novel technologies, remote sensing and modeling.

Permafrost warming has the potential to amplify global climate change, because when frozen sediments thaw it unlocks soil organic carbon. Yet to date, no globally consistent assessment of permafrost temperature change has been compiled. Here we use a global data set of permafrost temperature time series from the Global Terrestrial Network for Permafrost to evaluate temperature change across permafrost regions for the period since the International Polar Year (2007–2009). During the reference decade between 2007 and 2016, ground temperature near the depth of zero annual amplitude in the continuous permafrost zone increased by 0.39 ± 0.15 °C. Over the same period, discontinuous permafrost warmed by 0.20 ± 0.10 °C. Permafrost in mountains warmed by 0.19 ± 0.05 °C and in Antarctica by 0.37 ± 0.10 °C. Globally, permafrost temperature increased by 0.29 ± 0.12 °C. The observed trend follows the Arctic amplification of air temperature increase in the Northern Hemisphere. In the discontinuous zone, however, ground warming occurred due to increased snow thickness while air temperature remained statistically unchanged.

The purpose of this study was to characterize the geomorphological processes controlling the dynamics of ponds and to identify and characterize groundwater infiltration and surface water dynamics for a tundra terrain located in discontinuous permafrost near Council, Alaska. Thermokarst processes and permafrost degradation were studied, focusing upon the interaction between surface and groundwater systems via an open talik. Synthetic aperture radar (SAR) data were used for classification of terrain units and surface water properties, while historical aerial photographs and satellite images (IKONOS) were used for assessment of pond shrinking and recent thermokarst progression. Geophysical surveys (ground penetrating radar and DC resistivity) were conducted to detect permafrost thickness and talik formations. Temperature boreholes and hydrological observation wells were monitored throughout the year and provided ground truth for validation of remotely-sensed data and geophysical surveys. Field and laboratory analyses enabled quantitative determination of subsurface hydrologic and thermal properties. We found many areas where alluvium deposits and ice-wedge polygonal terrain had developed thermokarst features within the last 20 years. Thermokarst ponds located over ice-wedge terrain have decreased in surface area since at least the early 20th Century. Small thermokarst features initially developed into tundra ponds perched over permafrost in response to some local disturbance to the surface. These thermokarst ponds grew larger and initiated large taliks that completely penetrated the permafrost. These taliks allowed internal drainage throughout the year causing the ponds to shrink under recent climatic conditions. Shrinking pond surface areas may become a common feature in the discontinuous permafrost regions as a consequence of warming climate and thawing permafrost.

No abstract

[1] The impact to the permafrost during and after wildfire was studied using 11 boreal forest fire sites including two controlled burns. Heat transfer by conduction to the permafrost was not significant during fire. Immediately following fire, ground thermal conductivity may increase 10-fold and the surface albedo can decrease by 50% depending on the extent of burning of the surficial organic soil. The thickness of the remaining organic layer strongly affects permafrost degradation and aggradation. If the organic layer thickness was not reduced during the burn, then the active layer (the layer of soil above permafrost that annually freezes and thaws) did not change after the burn in spite of the surface albedo decrease. Any significant disturbance to the surface organic layer will increase heat flow through the active layer into the permafrost. Approximately 3-5 years after severe disturbance and depending on site conditions, the active layer will increase to a thickness that does not completely refreeze the following winter. This results in formation of a talik (an unfrozen layer below the seasonally frozen soil and above the permafrost). A thawed layer (4.15 m thick) was observed at the 1983 burned site. Model studies suggest that if an organic layer of more than 7-12 cm remains following a wildfire then the thermal impact to the permafrost will be minimal in the boreal forests of Interior Alaska.