Arctic coasts that are composed of frozen deposits are extremely sensitive to climate change and human impact. They retreat with average rates of 1–2 m per year, depending on climatic and permafrost conditions. In recent decades, retreat rates have shown a tendency to increase. In this paper, we studied the coastal dynamics of two key sites (Ural and Yamal coasts) of Baydaratskaya Bay, Kara Sea, where a gas pipeline had been constructed. Based on multi-temporal aerial and satellite imagery, we identified coastal erosion rates at several time lapses, in natural conditions and under human impact, and discussed their temporal variability. In addition to planimetric (m/yr), we calculated volumetric (m3/m/yr) retreat rates of erosional coasts using ArcticDEM. We also estimated the influence of geomorphology, lithology, and permafrost structure of the coasts on spatial variations of their dynamics. Erosional coasts of the Ural key site retreat with higher mean rates (1.2 m/yr and 8.7 m3/m/yr) as compared to the Yamal key site (0.3 m/yr and 3.7 m3/m/yr) due to their exposure to higher open sea waves, more complex lithology, higher ice content and lower coastal bluffs. Since the 1960s, coastal retreat rates have been growing on both coasts of Baydaratskaya Bay; we relate this effect with Arctic climate warming. From the 1960s to 2005, such growth was moderate, while in 2005–2016 it became rapid, which may be explained by the enhanced wave and thermal action or by the onset of industrial development. The adjacent coastal segments, originally accumulative, remained relatively stable from the 1960s to 2005. After 2005, a considerable part of them began to retreat as a result of changing weather conditions and/or increasing human impact.

Recent years of increasing air temperature in the Arctic have led to a significant increase in the rate of retreat of permafrost coast, which has threatened livelihoods and infrastructure in these areas. The Kara Sea hosts more than 25% of the total Arctic coastline. However, little is known about how coastal erosion in the Kara Sea may have changed through time, and the climatic and environmental drivers remain unclear. Here we study coastal dynamics along a 4-km stretch of permafrost and sea-ice-affected coastline in south-west Baydaratskaya Bay of the Kara Sea, western Siberia, between 2005 and 2016, by using handheld differential GPS mapping and satellite imagery.We identified temporal and spatial variations in the retreat rates, ranging between 1.0 (+0.1/−0.6) and 1.9 (+0.7/−1.3) m/yr over the studied coastline during 2005-2016. We also made ground temperature measurements, subsurface resistivity measurements and estimates of wave energy flux of wind-driven ocean waves, to investigate the dominant climatic factors influencing the observed retreat rates through time. We found that wind-driven wave activity during sea-ice-free days influences the magnitude of coastal retreat in the study area, while recent temperature rise has contributed less to enhancing coastal retreat during the study period. This suggests that the amount of eroded sediment and the associated release of nutrient to the nearshore zone are controlled by the magnitude of wave activity, which may influence infrastructure along the permafrost coast and marine ecosystems in the proximal ocean.

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The paper considers laboratory results of the composition, structure and properties for frozen and thawed soils at west coast of Baydara Bay. Experimental data of unfrozen water content and thermal properties are discussed and summarized for different soils. The roles of soil salinity and organic matter content on these data were estimated for frozen and thawed soils.

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