Beschreibung: Thawing of permafrost triggers a wide range of morphodynamic processes which magnitude and pace direly relate to the ground ice content. Already induced or completed degradation processes are visible as intriguing geomorphological features of permafrost landscapes such as thermokarst lakes, thermo erosion gullies, thaw slumps, and degraded ice wedged polygons. The formation of these features is, on the one hand, strongly controlled by the topographical and hydrological landscape properties. On the other hand, these landscape properties are explicitly modified by permafrost thaw and the accompanying morphodynamics. Consequently, a wide range of positive and negative feedback mechanisms can lead to either accelerated permafrost degradation (due to e.g. ponding water) or permafrost preservation (due to e.g. enhanced drainage and insulation). Based on different modeling exercises using the permafrost – land surface model CryoGrid, we demonstrate the high sensitivity of permafrost landscapes to small morphodynamic landscape changes on the one side and permafrost stability on the other side. Therefore, we present simulations of ice wedged polygons, thaw slumps, and thermokarst lakes and follow their different trajectories of degradation under a warming climate. Our preliminary results indicate that already minor changes in the lateral flow rates of water and/or matter can result in different pathways of permafrost degradation leading to different landscape morphologies. This finding may have strong implications for biogeochemical processes such as the decomposition of organic soil components.

Beschreibung: Ice-rich permafrost is estimated to underlie 20% of the Northern hemisphere’s permafrost region. It is particularly vulnerable to thawing processes referred to as “thermokarst”, which manifest in emerging characteristic landforms and rapidly changing landscapes. Prominent examples for theses processes are ground subsidence, thaw slumps, thermo-erosional valleys or the degradation of ice-wedge polygonal tundra. Altogether thermokarst poses risks to intact infrastructure and ecosystems in the Arctic, particularly in conjunction with a warming climate. To assess theses risks efficient prediction tools are demanded which are able to simulate the landscape changes due to thawing of ice-rich permafrost. We present a simple modeling approach based on the permafrost model CryoGrid3 which is able to simulate physical dynamics of thermokarst landforms. The landscape is partitioned into a set of distinct “tiles” which represent functionally different parts of it. Between adjacent tiles the lateral exchange of water, snow and heat is possible. We demonstrate the capability of our approach with showcasing the degradation of an ice-wedge polygonal tundra landscape. This landscape change involves a transition from an intact to an degraded permafrost landscape which can be considered as a regime shift between different stationary states. We further quantify the implications of this transition for cycling of water and energy in the landscape. We discuss the applicability of our model approach to other ice-rich permafrost landforms and its potential to a pan-Arctic risk assessment for infrastructure an ecosystems.

Beschreibung: Due to permafrost degradation, triggered by climate warming and human activities, infrastructure in the Arctic is at particularly high risk. Linear infrastructure such as roads or railway lines can influence the evolution of polygonal tundra and enhance degradation due to changes in the hydrological conditions. In this study, the CryoGrid 3 land surface model is used to simulate the impact of different hydrological conditions triggered by a gravel road. In addition, a sensitivity analysis is performed to better understand the influence of different snow properties on the simulations. The results show that a reduced water runoff leads to a higher soil subsidence due to melting ice wedges, whereas the timing of the degradation is strongly controlled by the snow density. A more accurate determination of soil temperatures and better knowledge of stratigraphy and snow conditions could increase the accuracy of future simulations. Furthermore,factors such as snowdrifts and road dust are not taken into account yet, but might be important to consider in future studies. This will help to better understand the complex underlying processes that affect the evolution of polygonal tundra under the influence of infrastructure and changing climate conditions.

Beschreibung: Thawing of permafrost potentially affects the global climate system through the mobilization of greenhouse gases, and poses a risk to human infrastructure in the Arctic. The response of ice-rich permafrost landscapes to a changing climate is particularly uncertain, and challenging to be addressed with numerical models. A main reason for this is the rapidly changing surface topography resulting from melting of ground ice, which is referred to as thermokarst. It is expressed in characteristic landforms which alter the hydrology, the surface energy balance, and the redistribution of snow of the entire landscapes. Polygonal patterned tundra which is underlain by massive ice-wedges, is a prototype of a sensitive permafrost system which is increasingly subjected to thermokarst activity throughout the Arctic. In this talk I will present a scalable modeling approach, based on the CryoGrid land surface model, to investigate the degradation of ice-wedges. The numerical model takes into account lateral fluxes of heat, water, and snow between different topographic units of polygonal tundra and simulates topographic changes resulting from melting of excess ground ice (i.e., thermokarst), and from lateral erosion of sediment. We applied the model to investigate the influence of hydrological conditions on the development of different types of ice-wedge polygons in a study area in northern Siberia. We further used projections of future climatic conditions to confine the evolution of ice-wedge polygons in a changing climate, and assessed the amount of organic matter which could thaw under different scenarios. In a related study for a study site in northern Alaska, we demonstrated that the model setup can be used to study the effect of infrastructure on the degradation of ice-wedges. Altogether, our modeling approach can be seen as a blueprint to investigate complexly inter-related processes in ice-rich permafrost landscapes, and marks a step forward towards an improved representation of these landscapes in large-scale land surface models.

Beschreibung: Industrial contaminants accumulated in Arctic permafrost regions have been largely neglected in existing climate impact analyses. Here we identify about 4500 industrial sites where potentially hazardous substances are actively handled or stored in the permafrost-dominated regions of the Arctic. Furthermore, we estimate that between 13,000 and 20,000 contaminated sites are related to these industrial sites. Ongoing climate warming will increase the risk of contamination and mobilization of toxic substances since about 1100 industrial sites and 3500 to 5200 contaminated sites located in regions of stable permafrost will start to thaw before the end of this century. This poses a serious environmental threat, which is exacerbated by climate change in the near future. To avoid future environmental hazards, reliable long-term planning strategies for industrial and contaminated sites are needed that take into account the impacts of cimate change.

Beschreibung: Boreal forests cover over half of the global permafrost area and protect underlying permafrost. Boreal forest development, therefore, has an impact on permafrost evolution, especially under a warming climate. Forest disturbances and changing climate conditions cause vegetation shifts and potentially destabilize the carbon stored within the vegetation and permafrost. Disturbed permafrost-forest ecosystems can develop into a dry or swampy bush- or grasslands, shift toward broadleaf- or evergreen needleleaf-dominated forests, or recover to the pre-disturbance state. An increase in the number and intensity of fires, as well as intensified logging activities, could lead to a partial or complete ecosystem and permafrost degradation. We study the impact of forest disturbances (logging, surface, and canopy fires) on the thermal and hydrological permafrost conditions and ecosystem resilience. We use a dynamic multilayer canopy-permafrost model to simulate different scenarios at a study site in eastern Siberia. We implement expected mortality, defoliation, and ground surface changes and analyze the interplay between forest recovery and permafrost. We find that forest loss induces soil drying of up to 44%, leading to lower active layer thicknesses and abrupt or steady decline of a larch forest, depending on disturbance intensity. Only after surface fires, the most common disturbances, inducing low mortality rates, forests can recover and overpass pre-disturbance leaf area index values. We find that the trajectory of larch forests after surface fires is dependent on the precipitation conditions in the years after the disturbance. Dryer years can drastically change the direction of the larch forest development within the studied period.

Beschreibung: Soil surface temperatures were collected with help of iButtons along different transects and clusters in the region of Lena-Viluy (Russia). The interval was set to 4 hours resp. 4.25 hours. Different models of iButtons were used (with a resolution of 0.0625 °C and 0.5°C resp.), see Comment.

Beschreibung: Soil surface temperatures were collected with help of iButtons along different transects and clusters in the North Slope of Alaska. The interval was set to 4 hours resp. 4.25 hours. Different models of iButtons were used (with a resolution of 0.0625 °C and 0.5°C resp.), see Comment.

Beschreibung: Soil surface temperatures were collected with help of iButtons along different transects and clusters in the North Slope of Alaska. The interval was set to 4 hours resp. 4.25 hours. Different models of iButtons were used (with a resolution of 0.0625 °C and 0.5°C resp.), see Comment.

Beschreibung: Soil surface temperatures were collected with help of iButtons along different transects and clusters in the North Slope of Alaska. The interval was set to 4 hours resp. 4.25 hours. Different models of iButtons were used (with a resolution of 0.0625 °C and 0.5°C resp.), see Comment.