Impact of increasing storminess and decreasing sea ice cover on high-latitude beach erosion (Hornsund, Svalbard)

Observed and further predicted decreasing sea ice extent and increasing storminess over the North Atlantic are deemed to intensify coastal erosion along the shores of Western Svalbard. We investigate these relationships in Isbjornhamna, a bay with ~3 km shoreline located in north-western Hornsund fjord. The bay is delimited by Wilczekodden and Baranowskiodden headlands with 1.5 km opening to the main basin of the fjord where the depth is ~20-25 m. Mean significant wave height is 0.26 m and its 99^th percentile is 1.5 m with highest values in autumn (mean of 0.4 m and 99^th percentile of 1.91 m). A minor protrusion divides the bay into two basins. In the eastern part (Hansvika) a thick layer of glacier till deposits overlays metamorphic bedrock, while the western part (Krossvika) is cut in shists and paragneisses. Coastal cliffs are present at the outer parts of the bay, while gravel beach occupies its central 2 km section. There is an alongshore variability in beach morphology (width, slope) and grain size distribution. Glacier ice from calving Hansbreen often accumulates at the shore in summer and autumn months, while in winter/spring sea ice and ice foot are present. Polish Polar Station infrastructure is located on the shore which makes it directly exposed to storm waves.

We used repetitive Uncrewed Aerial Vehicle surveys combined with Structure-from-Motion photogrammetry to detect beach change over 5 years. In total 13 surveys were performed between July 2018 and August 2023 which allowed a separation of shorter- and longer-term changes in beach morphology. We observed processes such as formation and destruction of beach cusps, creation and disappearance of holes from melting growlers, shoreline retreat and across- and alongshore sediment transport. We calculated mean erosion rates, and analysed its spatial and temporal variability. Finally, the short-term measurements were compared to the decadal-scale erosion rates derived from orthophotographs. Relationships between beach erosion, wind wave conditions, and sea ice coverage were inspected to understand the role of changing climate on the rates of coastal change.