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. Firstly, we have systematically mapped the occurrence of palsas and peat plateaus in the northernmost county of Norway (Finnmark, ∼ 50 000 km 2 ) 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 km 2 of Finnmark, with the actual palsas and peat plateaus underlain by permafrost covering a surface area of approximately 110 km 2 . 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.

Characteristics and fate of isolated permafrost patches in coastal Labrador, Canada

“…Vorren, 2017) for delimiting the upper climatic boundary for palsas is too low for Labrador, and that our results resemble those from a recent survey in Finnmark which found permafrost patches at MAATs as high as +1°C (Borge et al, 2017).…”

“…A detailed inventory of current palsas and peat plateaux, however, would require high resolution aerial photography or sub-meter 30 resolution satellite imagery to identify the very small mounds found in many areas (Borge et al, 2017) thick surface peat (Henningsmoen, 1977), and given the similar geographic setting and climate in northernmost parts of Newfoundland to sites at the southern end of our transect, there is no reason a priori that palsas could not exist there.…”

“…Peat plateaux form due to similar processes operating where extensive areas of peatlands are well-drained, allowing for larger areas of frost heave, windscouring in the winter and less heat penetration in the summer (Zoltai, 1972;Zoltai and Tarnocai, 1975). 20 Peatland permafrost bodies have partially or completely thawed at many locations within the Circumpolar North over the past few decades, including Scandinavia (Borge et al, 2017), eastern Canada (Thibault and Payette, 2009) and western Canada (e.g. Halsey et al, 1995;Quinton et al, 2011).…”

Increased nitrous oxide emissions from Arctic peatlands after permafrost thaw

“…In the dry mesocosms, peak emissions after permafrost thaw were preceded by an immediate accumulation of N 2 Tables S7 and S8), where moisture conditions (water-filled pore space >90%; SI Appendix, Table S2) were favorable for N 2 O production via denitrification (SI Appendix, Fig. S14).…”

“…Arctic soils | nitrogen | greenhouse gases | climate change | tundra A rctic land areas are predicted to warm up to 5.6-12.4°C by the end of this century (1), likely leading to widespread permafrost degradation (2)(3)(4)(5) and substantial changes in ecosystem functioning (6). With thawing, a vast pool of immobile C stored in permafrost (7) becomes available for decomposition and remobilization, triggering greenhouse gas emissions of carbon dioxide (CO 2 ) and methane (CH 4 ).…”