Stability Conditions of Peat Plateaus and Palsas in Northern Norway

Abstract. Palsas and peat plateaus are permafrost landforms occurring in subarctic mires which constitute sensitive ecosystems with strong significance for vegetation, wildlife, hydrology and carbon cycle. We have systematically mapped the occurrence of palsas and peat plateaus in the northernmost county of Norway (Finnmark, ~ 50 000 km2) by manual interpretation of aerial images from 2005–2014 at a spatial resolution of 250 m2. At this resolution, mires and wetlands with palsas or peat plateaus occur in about 850 km2 of Finnmark, with the actual palsas and peat plateaus underlain by permafrost covering a surface area of approximately 110 km2. Secondly, we have quantified the lateral changes of the extent of palsas and peat plateaus for four study areas located along a NW–SE transect through Finnmark by utilizing repeat aerial imagery from the 1950s to the 2010s. The results of the lateral changes reveal a total decrease of 33–71 % in the areal extent of palsas and peat plateaus during the study period, with the largest lateral change rates observed in the last decade. However, the results indicate that degradation of palsas and peat plateaus in northern Norway has been a consistent process during the second half of the 20th century and possibly even earlier. Significant rates of degradation are observed in all investigated time periods since the 1950s, and thermokarst landforms observed on aerial images from the 1950s suggest that lateral degradation was already an ongoing process at this time. The results of this study show that lateral erosion of palsas and peat plateaus is an important pathway for permafrost degradation in the sporadic permafrost zone in northern Scandinavia. While the environmental factors governing the rate of erosion are not yet fully understood, we note a moderate increase in both air temperature and precipitation during the last few decades in the region.

Download Full-text

Measuring and modelling thermal erosion patterns of peat plateaus in northern Norway

10.5194/egusphere-egu2020-10183 ◽

2020 ◽

Author(s):

Sebastian Westermann ◽

Leo Martin ◽

Jan Nitzbon ◽

Kjetil Aas ◽

Johanna Scheer ◽

...

Keyword(s):

Land Surface ◽

Surface Subsidence ◽

Surface Fluxes ◽

Heat Fluxes ◽

Major Type ◽

Surface Model ◽

Climatic Data ◽

Climate Signal ◽

Northern Norway ◽

Peat Plateaus

Peat plateaus are a major type of permafrost landscape in Arctic and Siberian lowlands. They represent a substantial pool of several hundreds of petagrams of organic carbon that has the potential to contribute to the Permafrost Carbon Feedback. The thermal response of these soils to the climate signal is complex and implies the interaction of various surface and subsurface processes operating at a very small spatial scale involving water, snow and heat fluxes and surface subsidence. As these processes have the ability to generate feedbacks between each other and trigger non-linear evolutions of the landscape, they challenge our abilities to measure and model them.Peat plateaus in Northern Norway have been actively degrading over at least the last 60 years. They thus offer a precious opportunity to measure and model the degradation patterns they exhibit. We present new topographical observations derived from drone-based photogrammetry that we acquired for one site in Northern Norway. Over a period of 3 years, these Digital Elevation Models allows quantifying precisely the surface subsidence and resulting lateral degradation of the peat plateaus. In a second time, we use the land surface model CryoGrid to model the observed patterns. The model is able to (i) simulate the snow fluxes and the water and heat sub-surface fluxes within the plateau and between the plateau and the surrounding wet mire and to (ii) represent the soil surface subsidence due to excess ice melt in the soil. We implement a set up that discretize the interface between the peat plateaus and the wet mire and force the Surface Energy Balance module of the model with climatic data derived from regional atmospheric modelling.Our simulations manage to reproduce the degradation speed we observe in our topographical data. We also present a sensitivity analysis of the degradation speed to snow cover and to the geometry of the peat plateaus and show how the feedbacks between the dynamical topography and the lateral fluxes of snow and water can trigger rapid permafrost thawing and fast degradation of permafrost landscapes.

Download Full-text

Thermal erosion patterns of permafrost peat plateaus in northern Norway

10.5194/tc-2020-338 ◽

2020 ◽

Author(s):

Léo C. P. Martin ◽

Jan Nitzbon ◽

Johanna Scheer ◽

Kjetil S. Aas ◽

Trond Eiken ◽

...

Keyword(s):

Thermal Regime ◽

Snow Depth ◽

Subsurface Water ◽

Small Scale ◽

Surface Model ◽

Permafrost Degradation ◽

Modeling Framework ◽

Northern Norway ◽

Thermal Erosion ◽

Peat Plateaus

Abstract. Subarctic peatlands underlain by permafrost contain significant amounts of organic carbon and our ability to quantify the evolution of such permafrost landscapes in numerical models is critical to provide robust predictions of the environmental and climatic changes to come. Yet, the accuracy of large-scale predictions is so far hampered by small-scale physical processes that create a high spatial variability of surface ground thermal regime and thus of permafrost degradation patterns. In this regard, a better understanding of the small-scale interplay between microtopography and lateral fluxes of heat, water and snow can be achieved by field monitoring and process-based numerical modeling. Here, we quantify the topographic changes of the Šuoššjávri peat plateau (Northern Norway) over a three-years period using repeated drone-based high-resolution photogrammetry. Our results show that edge degradation is the main process through which thermal erosion occurs and represents about 80 % of measured subsidence, while most of the inner plateau surface exhibits no detectable subsidence. Based on detailed investigation of eight zones of the plateau edge, we show that this edge degradation corresponds to a volumetric loss of 0.13 ± 0.07 m3 yr−1 m−1 (cubic meter per year and per meter of plateau circumference). Using the CryoGrid land surface model, we show that these degradation patterns can be reproduced in a modeling framework that implements lateral redistribution of snow, subsurface water and heat, as well as ground subsidence due to melting of excess ice. We reproduce prolonged climate-driven edge degradation that is consistent with field observations and present a sensitivity test of the plateau degradation on snow depth over the plateau. Small snow depth variations (from 0 to 30 cm) result in highly different degradation behavior, from stability to fast degradation. These results represent a new step in the modeling of climate-driven landscape development and permafrost degradation in highly heterogeneous landscapes such as peat plateaus. Our approach provides a physically based quantification of permafrost thaw with a new level of realism, notably, regarding feedback mechanisms between the dynamical topography and the lateral fluxes through which a small modification of the snow depth result in dramatic modifications of the permafrost degradation intensity. In this regard, these results also highlight the major control of snow pack characteristics on the ground thermal regime and the potential improvement that accurate snow representation and prediction could bring to projections of permafrost degradation.

Download Full-text

Strong degradation of palsas and peat plateaus in northern Norway during the past 60 years

10.5194/tc-2016-12-rc2 ◽

2016 ◽

Author(s):

Anonymous

Keyword(s):

Northern Norway ◽

The Past ◽

Peat Plateaus

Download Full-text

Carbon degradation in Subarctic organic permafrost (peat plateaus) after thawing – what constraints CO2 and CH4 production?

10.5194/egusphere-egu21-11121 ◽

2021 ◽

Author(s):

Sigrid Trier Kjær ◽

Nora Nedkvitne ◽

Sebastian Westermann ◽

Inge Althuizen ◽

Peter Dörsch

Keyword(s):

Organic Matter ◽

Active Layer ◽

Degradation Kinetics ◽

Soil Depth ◽

The Arctic ◽

Permafrost Degradation ◽

Northern Norway ◽

Degradation Rates ◽

Peat Plateaus ◽

Carbon Degradation

Rapid warming in Subarctic areas releases large amounts of frozen carbon which can potentially result in large CO2 and CH4 emissions to the atmosphere. In Northern Norway vast amount of carbon are stored in peat plateaus, but these landscape elements have been found to decrease laterally since at least the 1950s. Peat plateaus are very sensitive to climate change as the permafrost is relatively warm compared to permafrost found in the arctic. So far, only limited information is available about potential degradation kinetics of organic carbon in these ecosystems. We sampled organic matter from depth profiles along a well-documented chronosequence of permafrost degradation in Northern Norway. After thawing over-night, we incubated permafrost and active layer for up to 3 months at 10&#176;C. To determine factors constraining degradation, we measured gas kinetics (O2, CO2, CH4) under different conditions (oxic/anoxic, loosely packed/stirred suspensions in water, with altered DOC content and nutrient amendments) and related them to pH, DOC, element (C, N, P, S) and &#948;13C and &#948;15N signatures of the peat. Organic matter degradation was strongly inhibited in the absence of oxygen. By contrast, CH4 production or release seemed to be related to soil depth rather than incubation conditions and was found to be highest in samples from the transition zone between active layer and permafrost. Degradation rates and their dependencies on peat characteristics will be compared with permafrost characteristics along the chronosequence and additional experiments exploring the role of O2, DOC and other nutrients for carbon degradation will be discussed.

Download Full-text

Strong degradation of palsas and peat plateaus in northern Norway during the last 60 years

The Cryosphere ◽

10.5194/tc-11-1-2017 ◽

2017 ◽

Vol 11 (1) ◽

pp. 1-16 ◽

Cited By ~ 23

Author(s):

Amund F. Borge ◽

Sebastian Westermann ◽

Ingvild Solheim ◽

Bernd Etzelmüller

Keyword(s):

Snow Depth ◽

Aerial Imagery ◽

Aerial Images ◽

Moderate Increase ◽

Permafrost Degradation ◽

Northern Norway ◽

Important Pathway ◽

The 1950S ◽

Lateral Erosion ◽

Peat Plateaus

Abstract. Palsas and peat plateaus are permafrost landforms occurring in subarctic mires which constitute sensitive ecosystems with strong significance for vegetation, wildlife, hydrology and carbon cycle. Firstly, we have systematically mapped the occurrence of palsas and peat plateaus in the northernmost county of Norway (Finnmark, ∼ 50 000 km2) by manual interpretation of aerial images from 2005 to 2014 at a spatial resolution of 250 m. At this resolution, mires and wetlands with palsas or peat plateaus occur in about 850 km2 of Finnmark, with the actual palsas and peat plateaus underlain by permafrost covering a surface area of approximately 110 km2. Secondly, we have quantified the lateral changes of the extent of palsas and peat plateaus for four study areas located along a NW–SE transect through Finnmark by utilizing repeat aerial imagery from the 1950s to the 2010s. The results of the lateral changes reveal a total decrease of 33–71 % in the areal extent of palsas and peat plateaus during the study period, with the largest lateral change rates observed in the last decade. However, the results indicate that degradation of palsas and peat plateaus in northern Norway has been a consistent process during the second half of the 20th century and possibly even earlier. Significant rates of areal change are observed in all investigated time periods since the 1950s, and thermokarst landforms observed on aerial images from the 1950s suggest that lateral degradation was already an ongoing process at this time. The results of this study show that lateral erosion of palsas and peat plateaus is an important pathway for permafrost degradation in the sporadic permafrost zone in northern Scandinavia. While the environmental factors governing the rate of erosion are not yet fully understood, we note a moderate increase in air temperature, precipitation and snow depth during the last few decades in the region.

Download Full-text

Lateral thermokarst patterns in permafrost peat plateaus in northern Norway

The Cryosphere ◽

10.5194/tc-15-3423-2021 ◽

2021 ◽

Vol 15 (7) ◽

pp. 3423-3442

Author(s):

Léo C. P. Martin ◽

Jan Nitzbon ◽

Johanna Scheer ◽

Kjetil S. Aas ◽

Trond Eiken ◽

...

Keyword(s):

Numerical Models ◽

Ground Subsidence ◽

Subsurface Water ◽

Small Scale ◽

Surface Model ◽

Permafrost Degradation ◽

Modeling Framework ◽

Northern Norway ◽

Annual Volume ◽

Peat Plateaus

Abstract. Subarctic peatlands underlain by permafrost contain significant amounts of organic carbon. Our ability to quantify the evolution of such permafrost landscapes in numerical models is critical for providing robust predictions of the environmental and climatic changes to come. Yet, the accuracy of large-scale predictions has so far been hampered by small-scale physical processes that create a high spatial variability of thermal surface conditions, affecting the ground thermal regime and thus permafrost degradation patterns. In this regard, a better understanding of the small-scale interplay between microtopography and lateral fluxes of heat, water and snow can be achieved by field monitoring and process-based numerical modeling. Here, we quantify the topographic changes of the Šuoššjávri peat plateau (northern Norway) over a three-year period using drone-based repeat high-resolution photogrammetry. Our results show thermokarst degradation is concentrated on the edges of the plateau, representing 77 % of observed subsidence, while most of the inner plateau surface exhibits no detectable subsidence. Based on detailed investigation of eight zones of the plateau edge, we show that this edge degradation corresponds to an annual volume change of 0.13±0.07 m3 yr−1 per meter of retreating edge (orthogonal to the retreat direction). Using the CryoGrid3 land surface model, we show that these degradation patterns can be reproduced in a modeling framework that implements lateral redistribution of snow, subsurface water and heat, as well as ground subsidence due to melting of excess ice. By performing a sensitivity test for snow depths on the plateau under steady-state climate forcing, we obtain a threshold behavior for the start of edge degradation. Small snow depth variations (from 0 to 30 cm) result in highly different degradation behavior, from stability to fast degradation. For plateau snow depths in the range of field measurements, the simulated annual volume changes are broadly in agreement with the results of the drone survey. As snow depths are clearly correlated with ground surface temperatures, our results indicate that the approach can potentially be used to simulate climate-driven dynamics of edge degradation observed at our study site and other peat plateaus worldwide. Thus, the model approach represents a first step towards simulating climate-driven landscape development through thermokarst in permafrost peatlands.

Download Full-text