Permafrost Peat Plateau on Sosnovets Island: Formation and Long-Term Stability (the White Sea,NW Russia)

Frozen peatlands in the Northern Hemisphere are vulnerable to climate change and, according to recent scenarios, may degrade within the current century. However, the variability of regional factors and features of the development history can distort forecasts of their dynamics. To highlight this, we investigate the unique frozen peat plateau of Sosnovets Island (White Sea, NW Russia) on the edge of the sporadic permafrost zone. We show the developmental stages of the island peatland, identify patterns of peat accumulation and examine the permafrost in peat. The studied peatland formed when the top of the Sosnovets Island emerged from the sea ca. 7000 cal BP. In the mid-Holocene, its rate of isostatic uplift was 1.8 mm/year. In the late Holocene, it decreased to 1 mm/year, and now it has entered a subsidence phase. Although the age of permafrost formation is estimated ca. 2400 cal BP, peat accumulation after that did not stop and is now ongoing at a rate of 0.1–0.2 mm/year. Since occurrence, permafrost has been present without interruption on the island, and despite positive mean annual temperatures, is characterized by sufficient stability. Exogenous factors for the stability of the plateau are severe winters, strong winds, and low amounts of precipitation. The endogenous factors are large thickness of the peat deposit, dry conditions because of drainage, and undulating terrain that does not promote a large accumulation of snow. As a result, this combination provides good thermal insulation properties of peat, prevents lateral thermal effects, and reduces the wind erosion. Overall, the frozen peat plateau of Sosnovets Island is an important site of the permafrost monitoring network in Northern Fennoscandia, as it would take significant climate shifts to cause its irreversible degradation.