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

Abstract

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.

Degradation potentials of dissolved organic carbon (DOC) from thawed permafrost peat

“…Our palsa study site which is located in the discontinuous permafrost zone32, will most likely be affected by global warming due to the weakening of thermal boundaries43 and result in extensive thawing and palsa collapse as reported in Northern Scandinavia44. Permafrost zones in northern latitudes are rich in surface waters454647 and in the discontinuous permafrost zone the areal extent of surface waters is larger than either in the continuous or isolated permafrost zones24.…”

Holocene development and permafrost history in sub‐arctic peatlands in Tavvavuoma, northern Sweden

“…Warmer conditions during recent decades have resulted in extensive permafrost degradation in Fennoscandian palsas and peat plateaus (Sollid & Sørbel ; Zuidhoff & Kolstrup ; Luoto & Seppälä ; Sannel & Kuhry ; Borge et al . ). At present the permafrost is close to thawing with mean annual ground temperatures just below 0 °C (Christiansen et al .…”

Ecosystem carbon response of an Arctic peatland to simulated permafrost thaw

“…The intact plant‐soil systems (mesocosms) used in this study were collected in a palsa mire (“Peera Palsa”, 68.88°N, 21.05°E) in the discontinuous/sporadic permafrost zone of Finnish Lapland. Peat plateaus and palsas, permafrost peatlands uplifted above the surrounding mires by frost heave, are a common feature in the Subarctic (Borge et al, ; Kuhry, ; Seppälä, ). As a result of permafrost uplift, the water table in these permafrost peatlands is low (Estop‐Aragonés, Cooper et al, ; Nykänen, Heikkinen, Pirinen, Tiilikainen, & Martikainen, ; Turetsky, Wieder, & Vitt, ).…”

“…Subarctic regions, where permafrost temperatures are already close to zero, are particularly vulnerable to near‐term C losses with permafrost thaw (Koven et al, ). These areas, underlain by discontinuous and sporadic permafrost, currently experience extensive permafrost degradation (Sweden: Åkerman & Johansson, , Norway: Borge, Westermann, Solheim, & Etzelmüller, , Canada: Helbig, Chasmer, Desai et al, , Alaska: Lara et al, , Russia: Romanovsky et al, ). The Subarctic is also the region where highly sensitive, warm permafrost coincides with the occurrence of vast peatlands (Gorham, ).…”

“…About half of these C stocks (147 Pg) occur in organic soils underlain by permafrost (histels; Hugelius et al, ). Due to their location in the rapidly warming southern Arctic, and their large ice content in the porous peat material, permafrost peatlands are vulnerable to thaw and thermokarst formation (Hugelius, Routh, Kuhry, & Crill, ; Sannel & Kuhry, ), and degradation of permafrost peatlands is observed in the entire subarctic region (Baltzer, Veness, Chasmer, Sniderhan, & Quinton, ; Borge et al, ; Helbig, Chasmer, Desai et al, ; Malmer, Johansson, Olsrud, & Christensen, ).…”