Holocene development of subarctic permafrost peatlands in Finnmark, northern Norway

Abstract

Subarctic permafrost peatlands are important soil organic carbon pools, and improved knowledge about peat properties and peatland sensitivity to past climate change is essential when predicting future response to a warmer climate and associated feedback mechanisms. In this study, Holocene peatland development and permafrost dynamics of four subarctic peat plateaus in Finnmark, northern Norway have been investigated through detailed analyses of plant macrofossils and geochemical properties. Peatland inception occurred around 9800 cal. yr BP and 9200 cal. yr BP at the two continental sites Suossjavri and Iskoras. Younger basal peat ages were found at the two coastal locations Lakselv and Karlebotn, at least partly caused by the time lag between deglaciation and emergence of land by isostatic uplift. Here peatland development started around 6150 cal. yr BP and 5150 cal. yr BP respectively. All four peatlands developed as wet fens throughout most of the Holocene. Permafrost aggradation, causing frost heave and a shift in the vegetation assemblage from wet fen to dry bog species, probably did not occur until during the last millennium, ca. 950 cal. yr BP in Karlebotn and ca. 800 cal. yr BP in Iskoras, and before ca. 150 cal. yr BP in Lakselv and ca. 100 cal. yr BP in Suossjavri. In Karlebotn there are indications of a possible earlier permafrost phase around 2200 cal. yr BP due to climatic cooling at the late Subboreal to early Subatlantic transition. The mean longterm Holocene carbon accumulation rate at all four sites was 12.3±4.1 gC m-2 yr-1 (±SD) and the mean soil organic carbon storage was 97±46 kgC m-2 .

Stability Conditions of Peat Plateaus and Palsas in Northern Norway

“…In September 2015, we collected one surficial and one 50‐cm‐deep sample in peat soils as well as one in mineral soil at a 45–50‐cm depth. We measured the volumetric content of organic and mineral material in these samples to derive a synthetic profile for the modeling experiments which is consistent with coring observations of Kjellman et al () at the two sites. It consists of a 3‐m‐thick peat soil layer with 5% of mineral and 15% of organic material in total volumetric content (and thus a 80% porosity), underlain by a 7‐m saturated mineral silt layer with 50% porosity, above a mineral bedrock layer (3% porosity, as in Westermann et al ()).…”

“…Evolution of the vegetal macrofossil assemblages shows dry surface conditions associated with permafrost peat plateau aggradation around 950–100 cal year B.P. likely caused by the Little Ice Age cooling (Kjellman et al, ).…”

Permafrost Thaw Increases Methylmercury Formation in Subarctic Fennoscandia

“… 27 To core the permafrost at all sites, steel pipes were hammered into the peat plateau. 27 , 28 The sample material was carefully extruded, subdivided into 2.5 cm increments, and bagged in the field. All active layer and permafrost samples were kept frozen following the return from the field.…”

Transitional rock glaciers at sea-level in Northern Norway

“…Both current climate information and permafrost models suggest that these coast-near areas are permafrost-free. However, landforms such as palsas and peat plateaus are found in mires developed close to sea-level, especially in glacio-fluvial delta deposits, all along the northern coasts of Finnmark (Sollid and Sørbel, 1998;Borge et al, 2017;Meier, 1987;Kjellman et al, 2018), which clearly demonstrate sporadic permafrost in these locations. Both the peat cover associated with organic material and the blocky talus material normally depress and delay warming of ground temperatures, and thus both palsas and rock glaciers can be found below the regional lower limit of mountain permafrost, such as in high latitude mountain areas in e.g.…”