Study areasWe used two contrasting coastal environments in the European Arctic to calibrate and validate the procedure for extracting shoreline displacement time series. First, the procedure was iteratively calibrated, tested and validated in the Tanafjorden area, at the Barents Sea coast of Norway (Figure S1). Second, the final procedure was validated in the Ny-Ålesund area at the Greenland Sea coast of the Svalbard archipelago (Figure S1).The first study area in Tanafjorden (Deanuvuotna in northern Sámi language, Tenovuono in Finnish; c. 70.5° N, 28.5° E; Figure S1), is located in the Fennoscandian Barents Sea coasts of northern Finnmark, Norway. The study area included south-western parts of the Nordkinn Peninsula (Nordkinnhalvøya), the Tana River delta, and north-western parts of the Varanger Peninsula (Varangerhalvøya). The area was selected since it was relatively easy to access during the COVID pandemic and provided varying landscape, including a major delta. We used sea level data from the nearest tide gauge, located in Honningsvåg c. 100 km from the study area and operated by the Norwegian Mapping Authority. The study area is characterised by steep fjord landscapes, the highly dynamic delta, lack of glaciers and sea ice, and mesotidal conditions.The Tanafjorden coast is in most parts dominated by steep cliffs. Where rivers enter the fjords, the topography is generally flatter and regular water level fluctuations create tidal flats and salt marshes. The largest river in the area is Tana River (Deatnu in northern Sámi language, Tenojoki in Finnish). It is the border river between Norway and Finland and one of the largest rivers in Norway. While there are some snowbeds in the mountains (patches of snow that melt late in the summer), there is no sea ice (data by National Snow and Ice Data Center), no glaciers (Andreassen et al., 2012), and no coastal permafrost in the area (Gisnås et al., 2017). Rivers entering the Barents Sea and their brackish deltas have an ice cover from mid-October to mid-May.The Tanafjorden study area has a humid subarctic climate. The annual mean temperature in Tanafjorden is around 1 °C and the mean annual precipitation around 500 mm (Norwegian Centre for Climate Services). The coast has a seasonal snow cover and is mainly free of snow from mid-June to mid-October. The area is characterized by a semidiurnal lunar tide with a period of 12 hours and 25 minutes and mean tidal range of 2.3 meters during spring tide (Norwegian Mapping Authority).