We studied processes of ice-wedge degradation and stabilization at three sites adjacent to road i... more We studied processes of ice-wedge degradation and stabilization at three sites adjacent to road infrastructure in the Prudhoe Bay Oilfield, Alaska, USA. We examined climatic, environmental, and subsurface conditions and evaluated vulnerability of ice wedges to thermokarst in undisturbed and road-affected areas. Vulnerability of ice wedges strongly depends on the structure and thickness of soil layers above ice wedges, including the active, transient, and intermediate layers. In comparison with the undisturbed area, sites adjacent to the roads had smaller average thicknesses of the protective intermediate layer (4 cm vs. 9 cm), and this layer was absent above almost 60% of ice wedges (vs. ∼45% in undisturbed areas). Despite the strong influence of infrastructure, ice-wedge degradation is a reversible process. Deepening of troughs during ice-wedge degradation leads to a substantial increase in mean annual ground temperatures but not in thaw depths. Thus, stabilization of ice wedges in...
The overarching goal was to refine the understanding of the hydrological, thermal, and biogeochem... more The overarching goal was to refine the understanding of the hydrological, thermal, and biogeochemical processes that control methane emissions from thermokarst (thaw) lakes in discontinuous permafrost regions by assessing the coupled hydrology-permafrost-methane system at lake to watershed-scales. The effort included assessing the role of sub-permafrost methane as a source in lake methane emission. The study area was the Goldstream Creek watershed, Fairbanks, Interior Alaska, with field measurements during the period 2015-2018. A combination of methods were used, including numerical modeling, field measurements (meteorology, hydrology, permafrost, geochemistry), ground-based and airborne geophysics for 3D watershed-scale permafrost mapping, and laboratory incubations of permafrost, sediments, and groundwater. The temporal frequency of data ranges from three years of continuous hourly measurements to one-time samplings. The new data and findings can help to reduce uncertainties in fe...
Vegetation properties of arctic tundra vary dramatically across its full latitudinal extent, yet ... more Vegetation properties of arctic tundra vary dramatically across its full latitudinal extent, yet few studies have quantified tundra ecosystem properties across latitudinal gradients with field-based observations that can be related to remotely sensed proxies. Here we present data from field sampling of six locations along the Eurasia Arctic Transect in northwestern Siberia. We collected data on the aboveground vegetation biomass, the normalized difference vegetation index (NDVI), and the leaf area index (LAI) for both sandy and loamy soil types, and analyzed their spatial patterns. Aboveground biomass, NDVI, and LAI all increased with increasing summer warmth index (SWI—sum of monthly mean temperatures > 0 °C), although functions differed, as did sandy vs. loamy sites. Shrub biomass increased non-linearly with SWI, although shrub type biomass diverged with soil texture in the southernmost locations, with greater evergreen shrub biomass on sandy sites, and greater deciduous shrub ...
Very high spatial resolution commercial satellite imagery can inform observation, mapping, and do... more Very high spatial resolution commercial satellite imagery can inform observation, mapping, and documentation of micro-topographic transitions across large tundra regions. The bridging of fine-scale field studies with pan-Arctic system assessments has until now been constrained by a lack of overlap in spatial resolution and geographical coverage. This likely introduced biases in climate impacts on, and feedback from the Arctic region to the global climate system. The central objective of this exploratory study is to develop an object-based image analysis workflow to automatically extract ice-wedge polygon troughs from very high spatial resolution commercial satellite imagery. We employed a systematic experiment to understand the degree of interoperability of knowledge-based workflows across distinct tundra vegetation units—sedge tundra and tussock tundra—focusing on the same semantic class. In our multi-scale trough modelling workflow, we coupled mathematical morphological filtering ...
Climate warming is expected to alter the arctic tundra ecosystem that is currently dominated by a... more Climate warming is expected to alter the arctic tundra ecosystem that is currently dominated by an abundance of naturally perturbed, patterned-ground features called non-sorted circles. These non-sorted circles are the result of an intricate equilibrium relationship between the hydrology, vegetation and soil processes. An increase in the annual energy budget would increase the active layer depth and the available unfrozen water, change annual water and energy cycles, change biogeochemistry and soil processes and change the vegetation, which in turn would change the characteristics of non-sorted circles, thus impacting the existing equilibrium. The effect of climate warming on these features and how such changes would feed back into the ecosystem are areas of active contemporary research. The objective of the study is to model the development of the non-sorted circle ecosystem through processes governing the liquid water movement in the active layer during the freezing process, which...
Non-sorted circle ecosystems are naturally stable and abundant ecosystems throughout the Arctic t... more Non-sorted circle ecosystems are naturally stable and abundant ecosystems throughout the Arctic tundra. These are formed by processes of differential frost heave and are an important component of the water cycle in tundra regions. Even though the soil surface is basically bare, these systems are very stable. The stability of the system equilibrium and associated water and energy fluxes is, however, poorly understood. Water and ice are critical to non-sorted circle formation and interact in complex ways with the surrounding vegetation, soils, atmosphere and hydrological systems. Climate warming is expected to significantly affect such complex interaction in these ecosystems. It is also not clear how these systems will react to a larger shift in the perturbation of the soil surface. The objective of this study is to develop a laboratory scale model using soil from a non-sorted circle ecosystem to understand the effects of differential freezing on water and energy fluxes across its bou...
A warming climate has been identified as unequivocal by the Intergovernmental Panel on Climate Ch... more A warming climate has been identified as unequivocal by the Intergovernmental Panel on Climate Change with greater and faster temperature increase demonstrated at northern latitudes, and with an overall increase in precipitation. Analysis of field data collected throughout the arctic and subarctic corroborates with these findings, demonstrating an overall warming of permafrost temperatures. As indicated by thermal modeling, the stability of permafrost below roadway embankments is greatly affected by surface temperatures; thus, as climate warms, permafrost degradation represents a major issue for the design and maintenance of embankments. While the thermal stability of embankments in a warming climate has been investigated, the impact of groundwater and the effect of advective heat transfer on permafrost degradation below embankments has been overlooked. Recent studies indicate that groundwater flow along the permafrost table will cause permafrost degradation to occur one to several ...
A continuous time series of air temperatures and snow depths were constructed by combining inform... more A continuous time series of air temperatures and snow depths were constructed by combining information from four different climate stations in the Ilulissat area. Snow depths were estimated based on precipitation, air temperature and an estimated linear snow density function over the course of the winter period. This time series was used to perform a reanalysis of the ground temperature field and unfrozen water content from 1969 to 2009. This analysis indicate the development of a tallik in the deeper part of the sedimentary sequence due to the presense of residual salinity in the fine grained glacio-marine sediments. This effect was confirmed by geophysical measurements in the surrounding areas. By using the output of the high resolution regional climate model HIRHAM (provided through the Greenland Climate Change data archive, see http://klimagroenland.dmi.dk) as climatic forcing, we have produced a projection for the permafrost temperature dynamics and active layer thickness varia...
ABSTRACT Observations and model studies indicate warming of frozen ground in northern regions. We... more ABSTRACT Observations and model studies indicate warming of frozen ground in northern regions. We address these processes by using high-resolution versions (25 km and 5 km) of a regional climate model to create boundary conditions for an advanced permafrost model, which allows for simulation at very high resolutions. Since ensembles of different model combinations do not exist at such high resolutions, we estimate the bias of our approach with a quantile-quantile ranking of an ensemble of existing coarser simulations. We compare time-slice integrations for present-day climate and two future periods for most of Greenland. Permafrost is projected to degrade in most ice-free regions south of 76°N toward the end of the century, faster in the 5 km simulation than at the 25 km scale. We discuss a permafrost thaw potential based on modeled active layer thickness increase to assess the risk of permafrost degradation depending on surface properties and ice content.
ABSTRACT Wetlands and ice wedge polygon mires occupy a significant portion of Arctic terrestrial ... more ABSTRACT Wetlands and ice wedge polygon mires occupy a significant portion of Arctic terrestrial landscapes, a region that is important to the global climate system. The different types of ice wedge polygon networks, i.e. low- and high-centered, with and without well-developed troughs, can have major effects on the hydrologic cycle, which ultimately impacts the regional exchange of energy and carbon. Here we present multiple locations of ice wedge degradation observed in the continuous permafrost zones of North America and Eurasia. The subsequent ground subsidence has resulted in major surface water alterations across decadal time periods, some presenting much more rapid permafrost degradation than the typical pan-arctic models predict. Informed by analyses of high-resolution imagery, our model experiments explore the hydrologic impacts of the different stages of landscape-scale hydrologic connectivity. The observed degradation of ice wedges has major effects on watershed hydrology that typical variations in climate forcing alone are unable to produce. Not accounting for the ground subsidence at sub-meter spatial scales undermines the effectiveness of any regional scale projections of water, energy and carbon.
We studied processes of ice-wedge degradation and stabilization at three sites adjacent to road i... more We studied processes of ice-wedge degradation and stabilization at three sites adjacent to road infrastructure in the Prudhoe Bay Oilfield, Alaska, USA. We examined climatic, environmental, and subsurface conditions and evaluated vulnerability of ice wedges to thermokarst in undisturbed and road-affected areas. Vulnerability of ice wedges strongly depends on the structure and thickness of soil layers above ice wedges, including the active, transient, and intermediate layers. In comparison with the undisturbed area, sites adjacent to the roads had smaller average thicknesses of the protective intermediate layer (4 cm vs. 9 cm), and this layer was absent above almost 60% of ice wedges (vs. ∼45% in undisturbed areas). Despite the strong influence of infrastructure, ice-wedge degradation is a reversible process. Deepening of troughs during ice-wedge degradation leads to a substantial increase in mean annual ground temperatures but not in thaw depths. Thus, stabilization of ice wedges in...
The overarching goal was to refine the understanding of the hydrological, thermal, and biogeochem... more The overarching goal was to refine the understanding of the hydrological, thermal, and biogeochemical processes that control methane emissions from thermokarst (thaw) lakes in discontinuous permafrost regions by assessing the coupled hydrology-permafrost-methane system at lake to watershed-scales. The effort included assessing the role of sub-permafrost methane as a source in lake methane emission. The study area was the Goldstream Creek watershed, Fairbanks, Interior Alaska, with field measurements during the period 2015-2018. A combination of methods were used, including numerical modeling, field measurements (meteorology, hydrology, permafrost, geochemistry), ground-based and airborne geophysics for 3D watershed-scale permafrost mapping, and laboratory incubations of permafrost, sediments, and groundwater. The temporal frequency of data ranges from three years of continuous hourly measurements to one-time samplings. The new data and findings can help to reduce uncertainties in fe...
Vegetation properties of arctic tundra vary dramatically across its full latitudinal extent, yet ... more Vegetation properties of arctic tundra vary dramatically across its full latitudinal extent, yet few studies have quantified tundra ecosystem properties across latitudinal gradients with field-based observations that can be related to remotely sensed proxies. Here we present data from field sampling of six locations along the Eurasia Arctic Transect in northwestern Siberia. We collected data on the aboveground vegetation biomass, the normalized difference vegetation index (NDVI), and the leaf area index (LAI) for both sandy and loamy soil types, and analyzed their spatial patterns. Aboveground biomass, NDVI, and LAI all increased with increasing summer warmth index (SWI—sum of monthly mean temperatures > 0 °C), although functions differed, as did sandy vs. loamy sites. Shrub biomass increased non-linearly with SWI, although shrub type biomass diverged with soil texture in the southernmost locations, with greater evergreen shrub biomass on sandy sites, and greater deciduous shrub ...
Very high spatial resolution commercial satellite imagery can inform observation, mapping, and do... more Very high spatial resolution commercial satellite imagery can inform observation, mapping, and documentation of micro-topographic transitions across large tundra regions. The bridging of fine-scale field studies with pan-Arctic system assessments has until now been constrained by a lack of overlap in spatial resolution and geographical coverage. This likely introduced biases in climate impacts on, and feedback from the Arctic region to the global climate system. The central objective of this exploratory study is to develop an object-based image analysis workflow to automatically extract ice-wedge polygon troughs from very high spatial resolution commercial satellite imagery. We employed a systematic experiment to understand the degree of interoperability of knowledge-based workflows across distinct tundra vegetation units—sedge tundra and tussock tundra—focusing on the same semantic class. In our multi-scale trough modelling workflow, we coupled mathematical morphological filtering ...
Climate warming is expected to alter the arctic tundra ecosystem that is currently dominated by a... more Climate warming is expected to alter the arctic tundra ecosystem that is currently dominated by an abundance of naturally perturbed, patterned-ground features called non-sorted circles. These non-sorted circles are the result of an intricate equilibrium relationship between the hydrology, vegetation and soil processes. An increase in the annual energy budget would increase the active layer depth and the available unfrozen water, change annual water and energy cycles, change biogeochemistry and soil processes and change the vegetation, which in turn would change the characteristics of non-sorted circles, thus impacting the existing equilibrium. The effect of climate warming on these features and how such changes would feed back into the ecosystem are areas of active contemporary research. The objective of the study is to model the development of the non-sorted circle ecosystem through processes governing the liquid water movement in the active layer during the freezing process, which...
Non-sorted circle ecosystems are naturally stable and abundant ecosystems throughout the Arctic t... more Non-sorted circle ecosystems are naturally stable and abundant ecosystems throughout the Arctic tundra. These are formed by processes of differential frost heave and are an important component of the water cycle in tundra regions. Even though the soil surface is basically bare, these systems are very stable. The stability of the system equilibrium and associated water and energy fluxes is, however, poorly understood. Water and ice are critical to non-sorted circle formation and interact in complex ways with the surrounding vegetation, soils, atmosphere and hydrological systems. Climate warming is expected to significantly affect such complex interaction in these ecosystems. It is also not clear how these systems will react to a larger shift in the perturbation of the soil surface. The objective of this study is to develop a laboratory scale model using soil from a non-sorted circle ecosystem to understand the effects of differential freezing on water and energy fluxes across its bou...
A warming climate has been identified as unequivocal by the Intergovernmental Panel on Climate Ch... more A warming climate has been identified as unequivocal by the Intergovernmental Panel on Climate Change with greater and faster temperature increase demonstrated at northern latitudes, and with an overall increase in precipitation. Analysis of field data collected throughout the arctic and subarctic corroborates with these findings, demonstrating an overall warming of permafrost temperatures. As indicated by thermal modeling, the stability of permafrost below roadway embankments is greatly affected by surface temperatures; thus, as climate warms, permafrost degradation represents a major issue for the design and maintenance of embankments. While the thermal stability of embankments in a warming climate has been investigated, the impact of groundwater and the effect of advective heat transfer on permafrost degradation below embankments has been overlooked. Recent studies indicate that groundwater flow along the permafrost table will cause permafrost degradation to occur one to several ...
A continuous time series of air temperatures and snow depths were constructed by combining inform... more A continuous time series of air temperatures and snow depths were constructed by combining information from four different climate stations in the Ilulissat area. Snow depths were estimated based on precipitation, air temperature and an estimated linear snow density function over the course of the winter period. This time series was used to perform a reanalysis of the ground temperature field and unfrozen water content from 1969 to 2009. This analysis indicate the development of a tallik in the deeper part of the sedimentary sequence due to the presense of residual salinity in the fine grained glacio-marine sediments. This effect was confirmed by geophysical measurements in the surrounding areas. By using the output of the high resolution regional climate model HIRHAM (provided through the Greenland Climate Change data archive, see http://klimagroenland.dmi.dk) as climatic forcing, we have produced a projection for the permafrost temperature dynamics and active layer thickness varia...
ABSTRACT Observations and model studies indicate warming of frozen ground in northern regions. We... more ABSTRACT Observations and model studies indicate warming of frozen ground in northern regions. We address these processes by using high-resolution versions (25 km and 5 km) of a regional climate model to create boundary conditions for an advanced permafrost model, which allows for simulation at very high resolutions. Since ensembles of different model combinations do not exist at such high resolutions, we estimate the bias of our approach with a quantile-quantile ranking of an ensemble of existing coarser simulations. We compare time-slice integrations for present-day climate and two future periods for most of Greenland. Permafrost is projected to degrade in most ice-free regions south of 76°N toward the end of the century, faster in the 5 km simulation than at the 25 km scale. We discuss a permafrost thaw potential based on modeled active layer thickness increase to assess the risk of permafrost degradation depending on surface properties and ice content.
ABSTRACT Wetlands and ice wedge polygon mires occupy a significant portion of Arctic terrestrial ... more ABSTRACT Wetlands and ice wedge polygon mires occupy a significant portion of Arctic terrestrial landscapes, a region that is important to the global climate system. The different types of ice wedge polygon networks, i.e. low- and high-centered, with and without well-developed troughs, can have major effects on the hydrologic cycle, which ultimately impacts the regional exchange of energy and carbon. Here we present multiple locations of ice wedge degradation observed in the continuous permafrost zones of North America and Eurasia. The subsequent ground subsidence has resulted in major surface water alterations across decadal time periods, some presenting much more rapid permafrost degradation than the typical pan-arctic models predict. Informed by analyses of high-resolution imagery, our model experiments explore the hydrologic impacts of the different stages of landscape-scale hydrologic connectivity. The observed degradation of ice wedges has major effects on watershed hydrology that typical variations in climate forcing alone are unable to produce. Not accounting for the ground subsidence at sub-meter spatial scales undermines the effectiveness of any regional scale projections of water, energy and carbon.
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